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2008-02-21T03:18:00.000-08:00

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WHY MOSQUITOES CANNOT TRANSMIT AIDS...

2007-12-20T04:30:00.000-08:00

There are three theoretical mechanisms which would allow blood-sucking insects such as mosquitoes to transmit HIV.

1. In the first mechanism, a mosquito would initiate the cycle by feeding on an HIV positive carrier and ingest virus particles with the blood meal. For the virus to be passed on, it would have to survive inside the mosquito, preferably increase in numbers, and then migrate to the mosquito's salivary glands. The infected mosquito would then seek its second blood meal from an uninfected host and transfer the HIV from its salivary glands during the course of the bite. This is the mechanism used by most mosquito-borne parasites, including malaria, yellow fever, dengue, and the encephalitis viruses.

2. In the second mechanism, a mosquito would initiate the cycle by beginning to feed on an HIV carrier and be interrupted after it had successfully drawn blood. Instead of resuming the partial blood meal on its original host, the mosquito would select an AIDS-free person to complete the meal. As it penetrated the skin of the new host, the mosquito would transfer virus particles that were adhering to the mouthparts from the previous meal. This mechanism is not common in mosquito-borne infections, but equine infectious anemia is transmitted to horses by biting flies in this manner.

3. The third theoretical mechanism also involves a mosquito that is interrupted while feeding on an HIV carrier and resumes the partial blood meal on a different individual. In this scenario, however, the AIDS-free host squashes the mosquito as it attempts to feed and smears HIV contaminated blood into the wound. In theory, any of the mosquito-borne viruses could be transmitted in this manner providing the host circulated sufficient virus particles to initiate re-infection by contamination.

Each of these mechanisms has been investigated with a variety of blood sucking insects and the results clearly show that mosquitoes cannot transmit AIDS. News reports on the findings, however, have been confusing, and media interpretation of the results has not been clear. The average person is still not convinced that mosquitoes are not involved in the transmission of a disease that appears in the blood, is passed from person to person and can be contracted by persons that share hypodermic needles. Here are just some of the reasons why the studies showed that mosquitoes cannot transmit AIDS

Mosquitoes Digest the Virus that Causes AIDS

When a mosquito transmits a disease agent from one person to another, the infectious agent must remain alive inside the mosquito until transfer is completed. If the mosquito digests the parasite, the transmission cycle is terminated and the parasite cannot be passed on to the next host. Successful mosquito-borne parasites have a number of interesting ways to avoid being treated as food. Some are refractory to the digestive enzymes inside the mosquito's stomach; most bore their way out of the stomach as quickly as possible to avoid the powerful digestive enzymes that would quickly eliminate their existence. Malaria parasites survive inside mosquitoes for 9-12 days and actually go through a series of necessary life stages during that period. Encephalitis virus particles survive for 10-25 days inside a mosquito and replicate enormously during the incubation period. Studies with HIV clearly show that the virus responsible for the AIDS infection is regarded as food to the mosquito and is digested along with the blood meal. As a result, mosquitoes that ingest HIV-infected blood digest that blood within 1-2 days and completely destroy any virus particles that could potentially produce a new infection. Since the virus does not survive to reproduce and invade the salivary glands, the mechanism that most mosquito-borne parasites use to get from one host to the next is not possible with HIV.

Mosquitoes Do Not Ingest Enough HIV Particles to Transmit AIDS by Contamination

Insect-borne disease agents that have the ability to be transferred from one individual to the next via contaminated mouthparts must circulate at very high levels in the bloodstream of their host. Transfer by mouthpart contamination requires sufficient infectious particles to initiate a new infection. The exact number of infectious particles varies from one disease to the next. HIV circulates at very low levels in the blood--well below the levels of any of the known mosquito-borne diseases. Infected individuals rarely circulate more that 10 units of HIV, and 70 to 80% of HIV-infected persons have undetectable levels of virus particles in their blood. Calculations with mosquitoes and HIV show that a mosquito that is interrupted while feeding on an HIV carrier circulating 1000 units of HIV has a 1:10 million probability of injecting a single unit of HIV to an AIDS-free recipient. In laymen's terms, an AIDS-free individual would have to be bitten by 10 million mosquitoes that had begun feeding on an AIDS carrier to receive a single unit of HIV from contaminated mosquito mouthparts. Using the same calculations, crushing a fully engorged mosquito containing AIDS positive blood would still not begin to approach the levels needed to initiate infection. In short, mechanical transmission of AIDS by HIV-contaminated mosquitoes appears to be well beyond the limits of probability. Therefore, none of the theoretical mechanisms cited earlier appear to be possible for mosquito transmission of HIV.

Mosquitoes Are Not Flying Hypodermic Needles

Many people think of mosquitoes as tiny, flying hypodermic syringes, and if hypodermic needles can successfully transmit HIV from one individual to another then mosquitoes ought to be able to do the same. We have already seen that HIV-infected individuals do not circulate enough virus particles to result in infection by contamination. However, even if HIV-positive individuals did circulate high levels of virus, mosquitoes could not transmit the virus by the methods that are employed in used syringes. Most people have heard that mosquitoes regurgitate saliva before they feed, but are unaware that the food canal and salivary canal are separate passageways in the mosquito. The mosquito's feeding apparatus is an extremely complicated structure that is totally unlike the crude single-bore syringe. Unlike a syringe, the mosquito delivers salivary fluid through one passage and draws blood up another. As a result, the food canal is not flushed out like a used needle, and blood flow is always unidirectional. The mechanics involved in mosquito feeding are totally unlike the mechanisms employed by the drug user's needles. In short, mosquitoes are not flying hypodermic needles and a mosquito that disgorges saliva into your body is not flushing out the remnants of its last blood meal.

KIDNEY...

2007-12-15T00:04:00.000-08:00

The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. The medical field that studies the kidneys and diseases of the kidney is called nephrology. The prefix nephro- meaning kidney is from the Ancient Greek word nephros (νεφρός); the adjective renal meaning related to the kidney is from Latin rēnēs, meaning kidneys.

In humans, the kidneys are located in the posterior part of the abdomen. There is one on each side of the spine; the right kidney sits just below the liver, the left below the diaphragm and adjacent to the spleen. Above each kidney is an adrenal gland (also called the suprarenal gland). The asymmetry within the abdominal cavity caused by the liver results in the right kidney being slightly lower than the left one while the left kidney is located slightly more medial.The kidneys are retroperitoneal. They are approximately at the vertebral level T12 to L3. The upper parts of the kidneys are partially protected by the eleventh and twelfth ribs, and each whole kidney is surrounded by two layers of fat (the perirenal and pararenal fat) which help to cushion it. Congenital absence of one or both kidneys, known as unilateral or bilateral renal agenesis, can occur.

Organization

In a normal human adult, each kidney is about 10 cm long, 5.5 cm in width and about 3 cm thick, weighing 150 grams.^[2] Together, kidneys weigh about 0.5% of a person's total body weight^{[citation needed]}. The kidneys are "bean-shaped" organs, and have a concave side facing inwards (medially). On this medial aspect of each kidney is an opening, called the hilum, which admits the renal artery, the renal vein, nerves, and the ureter.

The outer portion of the kidney is called the renal cortex, which sits directly beneath the kidney's loose connective tissue/fibrous capsule. Deep to the cortex lies the renal medulla, which is divided into 10-20 renal pyramids in humans. Each pyramid together with the associated overlying cortex forms a renal lobe. The tip of each pyramid (called a papilla) empties into a calyx, and the calices empty into the renal p elvis. The pelvis transmits urine to the urinary bladder via the ureter.

Blood supply

Each kidney receives its blood supply from the renal artery, two of which branch from the abdominal aorta. Upon entering the hilum o f the kidney, the renal artery divides into smaller interlobar arteries situated between the renal papillae. At the outer medulla, the interlobar arteries branch into arcuate arteries, which course along the border between the renal medulla and cortex, giving off still smaller branches, the cortical radial arteries (sometimes called inte rlobular arteries). Branching off these cortical arteries are the afferent arterioles supplying the glomerular capillaries, which drain into efferent arterioles. Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the renal vein. Efferent arterioles of glomeruli closest to the medulla (those that belong to juxtamedullary nephrons) send branches into the medulla, forming the vasa recta. Blood supply is intimately linked to blood pressure.

Nephron

The basic functional unit of the kidney is the n ephron, of which there are more than a million within the cortex and medulla of each normal adult human kidney. Nephrons regulate water and solute within the cortex and medulla of each normal adult human kidney. Nephrons regulate water and soluble matter (especially electrolytes) in the body by first filtering the blood under pressure, and then reabsorbing some necessary fluid and molecules back into the blood while secreting other, unneeded molecules. Reabsorption and secretion are accomplished with both cotransport and countertransport mechanisms established in the nephrons and associated collecting ducts.

Collecting duct system

The fluid flows from the nephron into the collecting duct system. This segment of the nephron is crucial to the process of water conservation by the organism. In the presence of antidiuretic hormone (ADH; also called vasopressin), these ducts become permeable to water and facilitate its reabsorption, thus concentrating the urine and reducing its volume. Conversely, when the organism must eliminate excess water, such as after excess fluid drinking, the production of ADH is decreased and the collecting tubule becomes less permeable to water, rendering urine dilute and abundant. Failure of the organism to decrease ADH production appropriately, a condition known as syndrome of inappropriate ADH (SIADH), may lead to water retention and dangerous dilution of body fluids, which in turn may cause severe neurological damage. Failure to produce ADH (or inability of the collecting ducts to respond to it) may cause excessive urination, called diabetes insipidus (DI).A second major function of the collecting duct system is the maintenance of acid-base homeostasis.After being processed along the collecting tubules and ducts, the fluid, now called urine, is drained into the bladder via the ureter, to be finally excluded from the organism

Functions

Excretion of waste products

The kidneys excrete a variety of waste products produced by metabolism, including the nitrogenous wastes: urea (from protein catabolism) and uric acid (from nucleic acid metabolism) and water.

Homeostasis

The kidney is one of the major organs involved in whole-body homeostasis. Among its homeostatic functions are acid-base balance, regulation of electrolyte concentrations, control of blood volume, and regulation of blood pressure. The kidneys accomplish these homeostatic functions independently and through coordination with other organs, particularly those of the endocrine system. The kidney communicates with these organs through hormones secreted into the bloodstream.

Acid-base balance

The kidneys regulate the pH, by eliminating H ions concentration called augmentation mineral ion concentration, and water composition of the blood.By exchanging hydronium ions and hydroxyl i ons, the blood plasma is maintained by the kidney at a slightly alkaline pH of 7.4. Urine, on the other hand, is acidic at pH 5 or alkaline at pH 8.

The pH is maintained through four main protein transporters: NHE3 (a sodium-hydrogen exchanger), V-type H-ATPase (an isoform of the hydrogen ATPase), NBC1 (a sodium-bicarbonate cotransporter) and AE1 (an anion exchanger which exchanges chloride for bicarbonate). Due to the polar alignment of cells in the renal epithelia NHE3 and the H-ATPase are exposed to the lumen (which is essentially outside the body), on the apical side of the cells, and are responsible for excreting hydrogen ions (or protons). Conversely, NBC1 and AE1 are on the basolateral side of the cells, and allow bicarbonate ions to move back into the extracellular fluid and thus are returned to the blood plasma.

Blood pressure

Sodium ions are controlled in a homeostatic process involving aldosterone which increases sodium ion reabsorption in the distal convoluted tubules.When blood pressure becomes low, a proteolytic enzyme called Renin is secreted by cells of the juxtaglomerular apparatus (part of the distal convoluted tubule) which are sensitive to pressure. Renin acts on a blood protein, angiotensinogen, converting it to angiotensin I (10 amino acids). Angiotensin I is then converted by the Angiotensin-converting enzyme (ACE) in the lung capillaries to Angiotensin II (8 amino acids), which stimulates the secretion of Aldosterone by the adrenal cortex, which then affects the renal tubules.

Aldosterone stimulates an increase in the reabsorption of sodium ions from the kidney tubules which causes an increase in the volume of water that is reabsorbed from the tubule. This increase in water reabsorption increases the volume of blood which ultimately raises the blood pressure.

Plasma volume

Any significant rise or drop in plasma osmolality is detected by the hypothalamus, which communicates directly with the posterior pituitary gland. A rise in osmolality causes the gland to secrete antidiuretic hormone, resulting in water reabsorption by the kidney and an increase in urine concentration. The two factors work together to return the plasma osmolality to its normal levels.

Hormone secretion

The kidneys secrete a variety of hormones, including erythropoietin, urodilatin, renin and vitamin D.

Embryology

The mammalian kidney develops from intermediate mesoderm. Kidney development, also called nephrogenesis, proceeds through a series of three successive phases, each marked by the development of a more advanced pair of kidneys: the pronephros, mesonephros, and metanephros. (The plural forms of these terms end in -oi.)

Pronephros

During approximately day 22 of human gestation, the paired pronephroi appear towards the cranial end of the intermediate mesoderm. In this region, epithelial cells arrange themselves in a series of tubules called nephrotomes andjoin laterally with the pronephric duct, which does not reach the outside of the embryo. Thus the pronephros is considered nonfunctional in mammals because it cannot excrete waste from the embryo.

Mesonephros

Each pronephric duct grows towards the tail of the embryo, and in doing so induces intermediate mesoderm in the thoracolumbar area to become epithelial tubules called mesonephric tubules. Each mesonephric tubule receives a blood supply from a branch of the aorta, ending in a capillary tuft analogous to the glomerulus of the definitive nephron. The mesonephric tubule forms a capsule around the capillary tuft, allowing for filtration of blood. This filtrate flows through the mesonephric tubule and is drained into the continuation of the pronephric duct, now called the mesonephric duct or Wolffian duct. The nephrotomes of the pronephros degenerate while the mesonephric duct extends towards the most caudal end of the embryo, ultimately attaching to the cloaca. The mammalianmesonephros is similar to the kidneys of aquatic amphibians and fishes.

Metanephros

During the fifth week of gestation, the mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca. This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo. The elongated stalk of the ureteric bud, the metanephric duct, later forms the ureter. As the cranial end of the bud extends into the intermediate mesoderm, it undergoes a series of branchings to form the collecting duct system of the kidney. It also forms the major and minor calyces and the renal pelvis.

The portion of undifferentiated intermediate mesoderm in contact with the tips of the branching ureteric bud is known as the metanephrogenic blastema. Signals released from the ureteric bud induce the differentiation of the metanephrogenic blastema into the renal tubules. As the renal tubules grow, they come into contact and join with connecting tubules of the collecting duct system, forming a continuous passage for flow from the renal tubule to the collecting duct. Simultaneously, precursors of vascular endothelial cells begin to take their position at the tips of the renal tubules. These cells differentiate into the cells of the definitive glomerulus.

TERMS

renal capsule: The membranous covering of the kidney.
cortex: The outer layer over the internal medulla. It contains blood vessels, glomeruli (which are the kidneys' "filters") and urine tubes and is supported by a fibrous matrix.
hilus: The opening in the middle of the concave medial border for nerves and blood vessels to pass into the renal sinus.
renal column: The structures which support the cortex. They consist of lines of blood vessels and urinary tubes and a fibrous material.
renal sinus: The cavity which houses the renal pyramids.
calyces: The recesses in the int ernal medulla which hold the pyramids. They are used to subdivide the sections of the kidney. (singular - calyx)
papillae: The small conical projections along the wall of the renal sinus. They have openings through which urine passes into the calyces. (singular - papilla)
renal pyramids: The conical segments within the internal medulla. They contain the secreting apparatus and tubules and are also called malpighian pyramids.
renal artery: Two renal arteries com e from the aorta, each connecting to a kidney. The artery divides into five branches, each of which leads to a ball of capillaries. The arteries supply (unfiltered) blood to the kidneys. The left kidney receives about 60% of the renal bloodflow.
renal vein: The filtered blood returns to circulation through the renal veins which join into the inferior vena cava.
renal pelvis: Basically just a funnel, the renal pelvis accepts the urine and channels it out of the hilus into the ureter.
ureter: A narrow tube 40 cm long and 4 mm in diameter. Passing from the renal pelvis out of the hilus and down to the bladder. The ureter carries urine from the kidneys to the bladder by means of peristalsis.
renal lobe: Each pyramid together with the associated overlying cor tex forms a renal lobe

SOURCE: WIKIPEDIA

2007-12-12T03:18:00.001-08:00

MICHAEL JOSEPH JACKSON

DOUBLE CIRCULATION OF BLOOD IN HEART

2007-12-12T01:21:00.001-08:00

ANIMATION OF THE CIRCULATION OF THE BLOOD

Double Circulation of the Blood refers to the passage of the blood firstly through the lungs (the pulmonary circulation - where it picks up oxygen and releases carbon dioxide) and then through the body (the systemic circulation) where it delivers its cargo of oxygen and picks up carbon dioxide. These two circuits are powered by different sides of the heart. The right side of the heart pushes the blood at relatively low pressure through the lungs. The left side of the heart pushes the blood at relatively high pressure through the whole body.

The circulation has been unravelled and the two sides of the heart have been separated. This makes it clear that there is really only one circulation but that it happens in two stages (in series). The right side of the heart (at left of graphic) pushes the blood through the lungs (at top of graphic). The passage of carbon dioxide is illustrated as a flow of blue particles from the body and out through the lungs. The intake of oxygen through the lungs and to the body is illustrated as a flow of yellow particles. The vascular system (blood vessels) is illustrated as a tube connecting the right heart to the lungs, the lungs to the left heart, the left heart to the body and the body back to the right heart. The red blood cells can be glimpsed moving within this tube.

The system of vessels and the heart is known as the cardiovascular system. The heart is really a highly specialised segment of vessel that is muscular and supplied with valves (heart valves) to create the one way flow of blood. In the heart, the two sides are joined and the complex plumbing of vessels makes the flow rather difficult to understand.

BLOOD FLOW THROUGH THE HEART

1. Deoxygenated blood returning from the body enters the heart through the superior vena cava and inferior vena cava.

2. Blood passes into the right atrium and right ventricle

3. Right ventricle pushes the blood through the pulmonary arteries

4. Blood passes through the lungs where it loses carbon dioxide and picks up oxgen

5. This oxygenated blood returns to the heart via the pulmonary veins

6. Blood enters the left atrium and left ventricle

7. The left ventricle pushes the blood out through the main artery, the aorta

8. Blood travels to all parts of the body where it delivers oxygen and picks up carbon dioxide

THE CORONARY ARTERIES branch from the aorta as soon as it emerges from the heart (please see diagram of the heart at left). They deliver oxygenated blood the the heart muscle. Coronary artery disease (or coronary heart disease) involves the build up of deposits in these crucial vessels. This reduces and sometimes completely blocks the flow of blood resulting in a heart attack.

ARTERIES: are vessels that take blood away from the heart
VEINS: are vessels that bring blood towards the heart
ATRIUM: smaller chamber of the heart through which blood enters the heart
VENTRICLE: larger chamber of the heart which pushes blood away from the heart
AORTA: major artery carrying blood away from the left ventricle
VENA CAVA: main vein returning blood to the right atrium
CORONARY ARTERIES: the first vessels to branch from the aorta; they supply blood to the heart muscle

SOURCE: www.rkm.com

LYMPHATIC SYSTEM

2007-12-12T00:56:00.000-08:00

ENTIRE LYMPHATIC SYSTEM

The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. The lymphatic system is a major part of the immune system.

The lymphatic system has three interrelated functions: (1) removal of excess fluids from body tissues, (2) absorption of fatty acids and subsequent transport of fat, as chyle, to the circulatory system and, (3) production of immune cells such as lymphocytes (e.g. antibody producing plasma cells) and monocytes.

Lymphatic circulation

Unlike the blood system, the lymphatic system is not closed and has no central pump. Lymph movement occurs slowly with low pressure due to peristalsis, valves, and the milking action of skeletal muscles. Like veins, lymph travels through vessels in one way only, due to semilunar valves. This depends mainly on the movement of skeletal muscles to squeeze fluid through them, especially near the joints. Rhythmic contraction of the vessel walls through movements may also help draw fluid into the smallest lymphatic vessels, capillaries. Tight clothing can restrict this, thus reducing the removal of wastes and allowing them to accumulate. If tissue fluid builds up the tissue will swell; this is called edema. As the circular path through the body's system continues, the fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); both ducts drain into the circulatory system at the right and left subclavian veins. The system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a secondary circulatory system.

Development of Lymphatic Tissues

Lymphatic tissues begin to develop by the end of the fifth week of embryonic life. Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesoderm.

The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck and head. Some of the plexuses enlarge and form lymphatic vessels in their respective regions. Each jugular lymph sac retains at least one connection with its jugular vein, the left one developing into the superior portion of the thoracic duct.

The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine. It develops from the primitive vena cava and mesonephric veins. Capillary plexuses and lymphatic vessels spread form the retroperitoneal lymph sac to the abdominal viscera and diaphragm. The sac establishes connections with the cisterna chyli but loses its connections with neighboring veins.

The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins. The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs. The posterior lymph sacs join the cisterna chyli and lose their connections with adjacent veins.

With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes.

The spleen develops from mesenchymal cells between layers of the dorsal mesentery of the stomach. The thymus arises as an outgrowth of the third pharyngeal pouch.

SOURCE: WIKIPEDIA

ATHEROSCLEROSIS

2007-12-11T21:10:00.000-08:00

Severe atherosclerosis of the aorta. Autopsy specimen.

Atherosclerosis is a disease affecting arterial blood vessels. It is a chronic inflammatory response in the walls of arteries, in large part due to the deposition of lipoproteins (plasma proteins that carry cholesterol and triglycerides). It is commonly referred to as a "hardening" or "furring" of the arteries. It is caused by the formation of multiple plaques within the arteries.

The atheromatous plaque is divided into three distinct components:

1. The atheroma ("lump of porridge", from Athera, porridge in Greek,), which is the nodular accumulation of a soft, flaky, yellowish material at the center of large plaques, composed of macrophages nearest the lumen of the artery

2. Underlying areas of cholesterol crystals

3. Calcification at the outer base of older/more advanced lesions.

The following terms are similar, yet distinct, in both spelling and meaning, and can be easily confused: arteriosclerosis, arteriolosclerosis, and atherosclerosis. Arteriosclerosis is a general term describing any hardening (and loss of elasticity) of medium or large arteries (from the Greek Arterio, meaning artery, and sclerosis, meaning hardening), arteriolosclerosis is any hardening (and loss of elasticity) of arterioles (small arteries), atherosclerosis is a hardening of an artery specifically due to an atheromatous plaque. Therefore, atherosclerosis is a form of arteriosclerosis.

Atherosclerosis causes two main problems. First, the atheromatous plaques, though long compensated for by artery enlargement, see IMT, eventually lead to plaque ruptures and stenosis (narrowing) of the artery and, therefore, an insufficient blood supply to the organ it feeds. If the compensating artery enlargement process is excessive, then a net aneurysm results.

These complications are chronic, slowly progressing and cumulative. Most commonly, soft plaque suddenly ruptures (see vulnerable plaque), causing the formation of a thrombus that will rapidly slow or stop blood flow, that is, within 5 minutes, leading to death of the tissues fed by the artery. This catastrophic event is called an infarction. One of the most common recognized scenarios is called coronary thrombosis of a coronary artery, causing myocardial infarction (a heart attack). Another common scenario in very advanced disease is claudication from insufficient blood supply to the legs, typically due to a combination of both stenosis and aneurysmal segments narrowed with clots. Since atherosclerosis is a body-wide process, similar events occur also in the arteries to the brain, intestines, kidneys, legs, etc.

SOURCE : WIKIPEDIA

SICKLE CELL ANAEMIA

2007-12-10T04:09:00.000-08:00

Normal and Sickled Red Blood Cells in Blood Vessels

What Is Sickle Cell Anemia?

Sickle cell anemia is a serious condition in which the red blood cells can become sickle-shaped (that is, shaped like a “C”).

Normal red blood cells are smooth and round like a doughnut without a hole. They move easily through blood vessels to carry oxygen to all parts of the body. Sickle-shaped cells don’t move easily through blood. They’re stiff and sticky and tend to form clumps and get stuck in blood vessels.

The clumps of sickle cells block blood flow in the blood vessels that lead to the limbs and organs. Blocked blood vessels can cause pain, serious infections, and organ damage.

Figure A shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin. Figure B shows abnormal, sickled red blood cells clumping and blocking the blood flow in a blood vessel. The inset image shows a cross-section of a sickled red blood cell with abnormal strands of hemoglobin.

Sickle cell anemia is an inherited, lifelong condition. People who have sickle cell anemia are born with it. They inherit two copies of the sickle cell gene, one from each parent. People who inherit a sickle cell gene from one parent and a normal gene from the other parent have a condition called sickle cell trait.

Sickle cell trait is different from sickle cell anemia. People with sickle cell trait don’t have the condition, but they have one of the genes that cause the condition. Like people with sickle cell anemia, people with sickle cell trait can pass the gene on when they have children. To learn more about sickle cell trait, see the section on causes of sickle cell anemia.

Anemia

Anemia (uh-NEE-me-uh) is a condition in which a person’s blood has a lower than normal number of red blood cells, or the red blood cells don’t have enough hemoglobin (HEE-muh-glow-bin). Hemoglobin is an iron-rich protein that gives blood its red color and carries oxygen from the lungs to the rest of the body.

Red blood cells are made in the spongy marrow inside the large bones of the body. Bone marrow constantly makes new red blood cells to replace old ones. Normal red blood cells last about 120 days in the bloodstream and then die. Their main role is to carry oxygen, but they also remove carbon dioxide (a waste product) from cells and carry it to the lungs to be exhaled.

In sickle cell anemia, a lower-than-normal number of red blood cells occurs because sickle cells don’t last very long. Sickle cells die faster than normal red blood cells, usually after only about 10 to 20 days. The bone marrow can’t make new red blood cells fast enough to replace the dying ones. The result is anemia.

Outlook

Sickle cell anemia affects millions of people worldwide. There are excellent treatments for the symptoms and complications of the condition, but in most cases there’s no cure. (Some researchers believe that bone marrow transplants may offer a cure in a small number of cases.)

Over the past 30 years, doctors have learned a great deal about the condition. They know what causes it, how it affects the body, and how to treat many of the complications. Today, with good health care, many people with the condition live close to normal lives and are in fairly good health much of the time. These people can live into their forties or fifties, or longer.

SOURCE: NATIONAL HEALTH DEPARTMENT, INDIA

DADA'S COMEBACK......

2007-12-10T04:03:00.000-08:00

Maharaj Sourav Ganguly’s double ton at the third Test match against Pakistan in Bangalore on Sunday thrilled Kolkata, a city that has stood steadfast in its belief that the former captain would make an emphatic comeback in Test cricket, though age might have slowed him down in the faster version of the game.

Overjoyed fans came out on the streets, waving posters of their ‘dada’, chanting his name. After all, Ganguly’s score of 239 is his highest in Test cricket.

But what better way to celebrate any achievement if not through food. On Sunday, Ganguly’s restaurant Sourav’s The Food Pavilion, served free gulabjamun, the cricketer’s favourite sweet. There were also special discounts on every bill, the eatery’s senior floor manager Arun Kumar Daga said. The restaurant was choc-a-bloc today and the management would have decorated it if Ganguly had hit the double hundred a little faster.

The gossip on every table was about Ganguly’s two splendid partnerships in India’s first innings, one with Yuvraj Singh on Saturday where the duo put up 300 for the fifth wicket; and the other partnership on Sunday with Irfan Pathan in which the two scored 182.

However, the big celebration is yet to come. This is Ganguly’s 99th Test match. His hundredth will be later this month in Australia. Kolkata is ready to honour Ganguly’s century of Tests. Cricket Association of Bengal Joint Secretary Samar Paul said Ganguly had asked them not to arrange for any felicitation yet.

Paul said, “He wants to concentrate on his 100th Test match in Australia. Once he returns, we shall arrange something huge. We shall invite celebrities from all walks of life to this event.”

SOURCE: express india

OFF THE RAILS........

2007-10-22T05:51:00.000-07:00

Off The Rails

Navigate your handcar safely.

Play this free game now!!

BIOGRAPHY OF SHAHRUKH

2007-10-04T03:54:00.000-07:00

First Name: Shah Rukh

Last Name: Khan

Called: The King Khan, Baadshah of Bollywood
Day of Birth: 2nd of November, 1965

Place of Birth: Talwar Nursing Home (Rajinder Nagar) New Delhi-India

Shah Rukh was born with the umbilical cord entangled around his neck. A nurse said that it was by the blessings of Hanuman and that he would be a very lucky child.

Mother: Fatima Begum (a social worker and a first class magistrate,

who died of complications from diabetes in 1991)

Father: Mir Taj Mohammed(a lawyer and a freedom fighter, who

died of cancer in 1981)

Siblings: One sister named Shehnaz fondly called Lala Rukh

Zodiac Sign: Scorpio
Religion: Moslem
Height: 5'9'' (around 1,75 m)Weight:around 75 kg
Eyes: Magic brownHair

Color: Shiney black

Education:-

High School: St. Columbia High School In New Delhi.

College: Graduated from Hansraj College, & then Masters in

Mass Communication from Jamiya Miliya Islamiya, New Delhi

Qualifications and Achievements:

Masters: A Brilliant Student
Sword of Honour to the most outstanding student
The Ravi Subramaniam award
The Sujit Memorial award
He captained all teams in football, hockey, and cricket
He was also good in dramatics
He was a king in Hindi, Electronics, Biology

Occupation: Actor, producer

If not an Actor: In the arm force or a school teacher.

Start his Career: In a TV serial called "Fauji"

Film Debut: Deewana (2002)
Hobbies &

Interests: His family, his work, playing computer games
Martial Status: Married, since October 25, 1991 with Gauri Chibber / Khan

(born 8th of October 1970)

Children: Son Aryan (born on the 13th of November, 1997) daughter Suhana

(born on 22nd of May 2000)

HUMAN CLONING

2007-09-24T23:32:00.000-07:00

HUMAN CLONING

Although genes are recognized as influencing behavior and cognition, "genetically identical" does not mean altogether identical; identical twins, despite being natural human clones with identical DNA, are separate people, with separate experiences and not altogether overlapping personalities. The relationship between an "original" and a clone is rather like that between identical twins raised apart; they share all the same DNA, but little of the same environment. A lively scientific debate on this topic occurred in the journal Nature in 1997.Ultimately, the question of how similar an original and a clone would be boils down to how much of personality is determined by genetics, an area still under active scientific investigation.

TECHNIQUES

The most successful common cloning technique in non-human mammals is the process which produced Dolly the sheep. It is also the technique used by Advanced Cell Technology, the first company to successfully clone a human embryo (see research section below). The process is as follows: an egg cell taken from a donor has its nucleus removed. Another cell with the genetic material to be cloned is fused with the original egg cell. In theory, this process, known as somatic cell nuclear transfer, could be applied to human beings.

In principle, another way of cloning would be by parthenogenesis, where an unfertilized egg cell is induced to divide and grow as if it were fertilized. Even if it were practical with mammals, this technique could work only with females. Discussion of human cloning generally assumes the use of somatic cell nuclear transfer, rather than parthenogenesis.

Claims of success in human cloning beyond the embryo stage

In 1978 David Rorvik claimed in his book In His Image: The Cloning of a Man that he had personal knowledge of the creation of a human clone. A court case followed. He failed to produce corroborating evidence to back up his claims; now regarded as a hoax.

Severino Antinori made claims in November, 2002 that a project to clone human beings had succeeded, with the first human clone due to be born [in January 2003.] His claims were received with skepticism from many observers.

In December 2002, Clonaid, the medical arm of a religion called Raëlism, who believe that aliens introduced human life on Earth, claimed to have successfully cloned a human being. They claim that aliens taught them how to perform cloning, even though the company has no record of having successfully cloned any previous animal. A spokesperson said an independent agency would prove that the baby, named Evá, is in fact an exact copy of her mother. Shortly thereafter, the testing was cancelled, with the spokesperson claiming the decision would ultimately be left up to Evá's parents.

In December 2004 Dr. Brigitte Boisselier, claimed in a letter to the UN that Clonaid has successfully cloned 13 children, however their identities cannot be revealed to the public in order to protect them.

On October 9, 2003, newspaper Le journal de Montréal published an article accusing Clonaid and the Raelian religion of maintaining an outright hoax in its claims regarding cloning a human baby.

In 2004 a group of scientists led by Hwang Woo-Suk of Seoul National University in South Korea claimed to have grown 30 cloned human embryos to the one-week stage, and then successfully harvested stem cells from them. The results of their experiment were published in the peer-reviewed journal Science.

On May 30, 2005, Hwang's team announced the creation of 11 lines of human stem cells, using a different technique (Hwang et al. 2005). The journal Science later retracted Hwang's publications when investigations into the matter revealed that the claims were fraudulent.

Possible advantages

Human cloning might produce many benefits. Human therapeutic cloning could provide genetically identical cells for regenerative medicine, and tissues and organs for transplantation.Such cells, tissues, and organs would neither trigger an immune response nor require the use of immunosuppressive drugs.[citation needed] Both basic research and therapeutic development for serious diseases such as cancer, heart disease, and diabetes, as well as improvements in burn treatment and reconstructive and cosmetic surgery, are areas that might benefit from such new technology.

Human reproductive cloning also might produce benefits. Antinori and Zavos hope to create a fertility treatment that allows parents who are both infertile to have children with at least some of their DNA in their offspring.

Some scientists, including Dr. Richard Seed, suggest that human cloning might obviate the human aging processHow this might work is not entirely clear since the brain or identity would have to be transferred to a cloned body. Dr. Preston Estep has suggested the terms "replacement cloning" to describe the generation of a clone of a previously living person, and "persistence cloning" to describe the production of a cloned body for the purpose of obviating aging, although he maintains that such procedures currently should be considered science fiction

The current law on human cloning

U.N.

On December 12, 2001 the United Nations General Assembly began elaborating an international convention against the reproductive cloning of human beings. Lawrence S. B. Goldstein, college professor of cellular and molecular medicine at the University of California at San Diego, claims that the United States, unable to pass a national law, forced Costa Rica to start this debate in the UN over the international cloning ban. Unable to reach a consensus on a binding convention, in February 2005 a vaguely worded and non-binding United Nations Declaration on Human Cloning was finally adopted

U.K.

The British government introduced legislation in order to allow licensed therapeutic cloning in a debate in January 2001 after an amendment to the Human Fertilisation & Embryology Act 1990. However on November 15, 2001 a prolife group won a High Court legal challenge that effectively left cloning unregulated in the UK. Their hope was that Parliament would fill this gap by passing prohibitive legislation. The government was quick to pass legislation prohibiting reproductive cloning Human Reproductive Cloning Act 2001. The remaining gap with regard to therapeutic cloning was closed when the appeals courts reversed the previous decision of the High Court. Currently therapeutic cloning is allowed under license from the Human Fertilisation and Embryology Authority. The first licence was granted on August 11, 2004 to researchers at the University of Newcastle to allow them to investigate treatments for diabetes, Parkinson's disease and Alzheimer's disease.

SOURCE: WIKIPEDIA

SPACE SUIT

2007-09-24T23:04:00.000-07:00

SPACE SUIT

A space suit is a complex system of garments, equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space. This applies to extra-vehicular activity (EVA) outside spacecraft orbiting Earth and has applied to walking, and riding the Lunar Rover, on the Moon.

Some of these requirements also apply to pressure suits worn for other specialized tasks, such as high-altitude reconnaissance flight. Above Armstrong's Line (~63,000 ft/~19,000 m), pressurized suits are needed in the sparse atmosphere. Hazmat suits that resemble space suits are also used when dealing with certain types of biological hazard

SPACE SUIT REQUIREMENTS

Several things are needed for the space suit to function properly in space. It must provide:

A stable internal pressure. This can be less than earth's atmosphere, as there is usually no need for the spacesuit to carry nitrogen.

Lower pressure allows for greater mobility, but introduces the requirement of pre-breathing to avoid decompression sickness.

Movement is typically opposed by the pressure of the suit; mobility is achieved by careful joint design.

Breathable oxygen. Circulation of cooled and purified oxygen is controlled by the Primary Life Support System.

Temperature regulation. Heat can only be lost in space by thermal radiation, or conduction with objects in physical contact with the space suit. Since heat is lost very slowly by radiation, temperature is regulated by a Liquid Cooling Garment and heavy insulation on the hands and possibly feet.

Shielding against harmful electromagnetic radiation

Shielding against particle radiation

Protection against micrometeoroids, provided by a Thermal Micrometeoroid Garment, which is the outermost layer of the suit

A communication system

Means to recharge and discharge gases and liquids

Means to maneuver, dock, release, and/or tether onto space craft

Means of collecting and containing solid and liquid waste

OPERATING PRESSURE

Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about 4.7 psi, equal to the 3 psi partial pressure of oxygen in the Earth's atmosphere at sea level, plus 40 torr CO2 and 47 torr water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation.The latter two figures add to 87 torr (mm Hg) which is about 1.7 psi, which is why many modern spacesuits don't use 3 psi, but 4.7 psi (this is a slight overcorrection, as alveolar partial pressures at sea level are not a full 3 psi = 155 torr, but a bit less). In spacesuits that use 3 psi, the astronaut gets only 3 - 1.7 = 1.3 psi of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of 6,100 ft. (1860 m) above sea level. This is about 78% of normal sea level pressure, about the same as pressure in a commercial passenger jet aircraft, and is the realistic lower limit for safe ordinary space suit pressurization which allows reasonable work capacity

REPRESENTATION OF SPACE SUIT WIT IT'S VARIOUS PARTS

COURTESY: WIKIPEDIA

GPRS

2007-09-24T22:41:00.000-07:00

General Packet Radio Service(GPRS)

General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. GPRS data transfer is typically charged per megabyte of transferred data, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user has actually transferred data or has been in an idle state. GPRS can be used for services such as Wireless Application Protocol (WAP) access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access.

2G cellular systems combined with GPRS is often described as "2.5G", that is, a technology between the second (2G) and third (3G) generations of mobile telephony. It provides moderate speed data transfer, by using unused Time division multiple access (TDMA) channels in for example the GSM system. Originally there was some thought to extend GPRS to cover other standards, but instead those networks are being converted to use the GSM standard, so that GSM is the only kind of network where GPRS is in use. GPRS is integrated into GSM Release 97 and newer releases. It was originally standardized by European Telecommunications Standards Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP).

Basics

GPRS is packet-switched, which means that multiple users share the same transmission channel, only transmitting when they have data to send. Thus the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher use where users only send or receive data intermittently. Web browsing, receiving e-mails as they arrive and instant messaging are examples of uses that require intermittent data transfers, which benefit from sharing the available bandwidth. By contrast, in the older Circuit Switched Data (CSD) standard included in GSM standards, a connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection.

Usually, GPRS data are billed per kilobyte of information transceived, while circuit-switched data connections are billed per second. The latter is because even when no data are being transferred, the bandwidth is unavailable to other potential users.

The multiple access methods used in GSM with GPRS are based on frequency division duplex (FDD) and FDMA. During a session, a user is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain statistical multiplexing, i.e. packet mode communication, which makes it possible for several users to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. The down-link uses first-come first-served packet scheduling, while the up-link uses a scheme very similar to reservation ALOHA. This means that slotted Aloha (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using dynamic TDMA with first-come first-served scheduling.

GPRS originally supported (in theory) Internet Protocol (IP), Point-to-Point Protocol (PPP) and X.25 connections. The last has been typically used for applications like wireless payment terminals, although it has been removed from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a router to perform encapsulation or intelligence built in to the end-device/terminal e.g. UE(User Equipment). In practice, when the mobile built-in browser is used, IPv4 is being utilized. In this mode PPP is often not supported by the mobile phone operator, while IPv6 is not yet popular. But if the mobile is used as a modem to the connected computer, PPP is used to tunnel IP to the phone. This allows DHCP to assign an IP Address and then the use of IPv4 since IP addresses used by mobile equipment tend to be dynamic.

DNA RETROVIRUS

2007-09-24T03:05:00.000-07:00

The 3D retrovirus is unique to other viruses in that it carries its genomic information in RNA, not the standard DNA that most do. The retrovirus is somewhat of an oddity in the world of molecular biology. It's name is indicative of why this molecule stands out from other viruses. Most viruses take over their host cells by injecting them with their own viral DNA, which then follows the central dogma of molecular biology to transcribe RNA and translate proteins. What the retrovirus does, however, is inject its own viral RNA into the cell which then encodes the viral DNA to be produced within the host cell. This goes retroactively to the traditional order of DNA to RNA to proteins, hence the name, retrovirus. The retrovirus itself stores its genome on two strands of RNA that eventually injected into the cytosol of the host cell along with enzymes such as reverse transcriptase that initiate the reversed transcription of DNA from the viral RNA. This newly formed DNA is integrated into the genome of the host cell, and is now referred to as a provirus. This reversed transcription lacks "proof-reading" mechanisms otherwise had, and consequently mutations occur frequently in a typical retrovirus. It is for this reason, vaccines against retroviruses-such as HIV-are so difficult to obtain. Not all retroviruses are bad as it may seem. Some insert into human DNA and are passed on to succeeding generations, becoming endogenous retroviruses. These endgenous retrovirus play an important role in protecting the genome against some infections of other harmful retroviruses and even assisting in development during gestation.

COURTESY: 3Dscience.com

2007-09-24T02:37:00.000-07:00

A THREE DIMENSIONAL VIEW OF THE HUMAN HEART

COURTESY: 3Dscience.com

HUMAN EYE

2007-09-23T23:46:00.000-07:00

EYE

Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors. The visual fields of some such complex eyes largely overlap, to allow better depth perception (binocular vision), as in humans; and others are placed so as to minimize the overlap, such as in rabbits and chameleons.

ANATOMY OF MAMMALIAN EYE

The structure of the mammalian eye can be divided into three main layers or tunics whose names reflect their basic functions: the fibrous tunic, the vascular tunic, and the nervous tunic
The fibrous tunic, also known as the tunica fibrosa oculi, is the outer layer of the eyeball consisting of the cornea and sclera. The sclera gives the eye most of its white color. It consists of dense connective tissue filled with the protein collagen to both protect the inner components of the eye and maintain its shape.

The vascular tunic, also known as the tunica vasculosa oculi, is the middle vascularized layer which includes the iris, ciliary body, and choroid.The choroid contains blood vessels that supply the retinal cells with necessary oxygen and remove the waste products of respiration. The choroid gives the inner eye a dark color, which prevents disruptive reflections within the eye.

The nervous tunic, also known as the tunica nervosa oculi, is the inner sensory which includes the retina. The retina contains the photosensitive rod and cone cells and associated neurons. To maximise vision and light absorption, the retina is a relatively smooth (but curved) layer. It does have two points at which it is different; the fovea and optic disc. The fovea is a dip in the retina directly opposite the lens, which is densely packed with cone cells. It is largely responsible for color vision in humans, and enables high acuity, such as is necessary in reading. The optic disc, sometimes referred to as the anatomical blind spot, is a point on the retina where the optic nerve pierces the retina to connect to the nerve cells on its inside. No photosensitive cells whatsoever exist at this point, it is thus "blind". Squids and Octupi don't have this blind spot, however.

ANTERIOR SEGMENT

The anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens. Within the anterior segment are two fluid-filled spaces: the anterior chamber and the posterior chamber. The anterior chamber is the space between the posterior surface of the cornea (i.e. the corneal endothelium) and the iris, whereas the posterior chamber is between the iris and the front face of the vitreous.

The cornea and lens help to converge light rays to focus onto the retina. The lens, behind the iris, is a convex, springy disk which focuses light, through the second humour, onto the retina. It is attached to the ciliary body via a ring of suspensory ligaments known as the Zonule of Zinn. To clearly see an object far away, the ciliary muscle is relaxed, which stretches the fibers connecting it with the lens, flattening the lens. When the ciliary muscle contracts, the tension of the fibers decrease (imagine that the distance between the tip of a triangle to its base, is less than the tip of the triangle to the other two tips.) which lets the lens bounce back a more convex and round shape. Humans gradually lose this flexibility with age, resulting in the inability to focus on nearby objects, which is known as presbyopia. There are other refraction errors arising from the shape of the cornea and lens, and from the length of the eyeball. These include myopia, hyperopia, and astigmatism. The iris, between the lens and the first humour, is a pigmented ring of fibrovascular tissue and muscle fibres. Light must first pass though the centre of the iris, the pupil. The size of the pupil is actively adjusted by the circular and radial muscles to maintain a relatively constant level of light entering the eye. Too much light being let in could damage the retina; too little light makes sight difficult.

All of the individual components through which light travels within the eye before reaching the retina are transparent, minimising dimming of the light. Light enters the eye from an external medium such as air or water, passes through the cornea, and into the first of two humours, the aqueous humour. Most of the light refraction occurs at the cornea which has a fixed curvature. The first humour is a clear mass which connects the cornea with the lens of the eye, helps maintain the convex shape of the cornea (necessary to the convergence of light at the lens) and provides the corneal endothelium with nutrients.

POSTERIOR SEGMENT

The posterior segment is the back two-thirds of the eye that includes the anterior hyaloid membrane and all structures behind it: the vitreous humor, retina, choroid, and optic nerve.[18] On the other side of the lens is the second humour, the vitreous humour, which is bounded on all sides: by the lens, ciliary body, suspensory ligaments and by the retina. It lets light through without refraction, helps maintain the shape of the eye and suspends the delicate lens. In some animals, the retina contains a reflective layer (the tapetum lucidum) which increases the amount of light each photosensitive cell perceives, allowing the animal to see better under low light conditions.

CYTOLOGY

The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain.

The retina contains two forms of photosensitive cells important to vision—rods and cones. Though structurally and metabolically similar, their function is quite different. Rod cells are highly sensitive to light allowing them to respond in dim light and dark conditions, however, they cannot detect color. These are the cells which allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). This is why the darker conditions become, the less color objects seem to have. Cone cells, conversely, need high light intensities to respond and have high visual acuity. Different cone cells respond to different wavelengths of light, which allows an organism to see color.

The differences are useful; apart from enabling sight in both dim and light conditions, humans have given them further application. The fovea, directly behind the lens, consists of mostly densely-packed cone cells. This gives humans a highly detailed central vision, allowing reading, bird watching, or any other task which primarily requires looking at things. Its requirement for high intensity light does cause problems for astronomers, as they cannot see dim stars, or other objects, using central vision because the light from these is not enough to stimulate cone cells. Because cone cells are all that exist directly in the fovea, astronomers have to look at stars through the "corner of their eyes" (averted vision) where rods also exist, and where the light is sufficient to stimulate cells, allowing the individual to observe distant stars.

Rods and cones are both photosensitive, but respond differently to different frequencies of light. They both contain different pigmented photoreceptor proteins. Rod cells contain the protein rhodopsin and cone cells contain different proteins for each color-range. The process through which these proteins go is quite similar—upon being subjected to electromagnetic radiation of a particular wavelength and intensity, the protein breaks down into two constituent products. Rhodopsin, of rods, breaks down into opsin and retinal; iodopsin of cones breaks down into photopsin and retinal. The opsin in both opens ion channels on the cell membrane which leads to hyperpolarization, this hyperpolarization of the cell leads to a release of transmitter molecules at the synapse.

This is the reason why cones and rods enable organisms to see in dark and light conditions—each of the photoreceptor proteins requires a different light intensity to break down into the constituent products. Further, synaptic convergence means that several rod cells are connected to a single bipolar cell, which then connects to a single ganglion cell by which information is relayed to the visual cortex. This is in direct contrast to the situation with cones, where each cone cell is connected to a single bipolar cell. This results in the high visual acuity, or the high ability to distinguish between detail, of cone cells and not rods. If a ray of light were to reach just one rod cell this may not be enough to hyperpolarize the connected bipolar cell. But because several "converge" onto a bipolar cell, enough transmitter molecules reach the synapse of the bipolar cell to hyperpolarize it.

Furthermore, color is distinguishable due to the different iodopsins of cone cells; there three different kinds, in normal human vision, which is why we need three different primary colors to make a color space.

DISEASE'S,DISORDERS AND AGE RELATED CHANGES

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures.
As the eye ages certain changes occur that can be attributed solely to the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates also decreases with age. Because of the smaller pupil size, older eyes receive much less light at the retina. In comparison to younger people, it is as though older persons wear medium-density sunglasses in bright light and extremely dark glasses in dim light. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older persons require extra lighting. Certain ocular diseases can come from sexually transmitted diseases such as herpes and genital warts. If contact between eye and area of infection occurs, the STD will be transmitted to the eye.
With aging a prominent white ring develops in the periphery of the cornea- called arcus senilis. Aging causes laxity and downward shift of eyelid tissues and atrophy of the orbital fat. These changes contribute to the etiology of several eyelid disorders such as ectropion, entropion, dermatochalasis, and ptosis. The vitreous gel undergoes liquefaction (posterior vitreous detachment or PVD) and its opacities—visible as floaters—gradually increase in number.
Various eye care professionals, including ophthalmologists, optometrists, and opticians, are involved in the treatment and management of ocular and vision disorders. A Snellen chart is one type of eye chart used to measure visual acuity. At the conclusion of an eye examination, an eye doctor may provide the patient with an eyeglass prescription for corrective lenses

SOURCE: WIKIPEDIA

2007-09-23T07:46:00.000-07:00

DNA

Deoxyribonucleic acid, or DNA, is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA is a long polymer of simple units called nucleotides, with a backbone made of sugars and phosphate groups joined by ester bonds. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription. Most of these RNA molecules are used to synthesize proteins, but others are used directly in structures such as ribosomes and spliceosomes.

Within cells, DNA is organized into structures called chromosomes and the set of chromosomes within a cell make up a genome. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms such as animals, plants, and fungi store their DNA inside the cell nucleus, while in prokaryotes such as bacteria it is found in the cell's cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA, which helps control its interactions with other proteins and thereby control which genes are transcribed.

PHYSICAL AND CHEMICAL PROPERTIES

DNA is a long polymer made from repeating units called nucleotides. The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Ångstroms (0.33 nanometres) long.[3] Although each individual repeating unit is very small, DNA polymers can be enormous molecules containing millions of nucleotides. For instance, the largest human chromosome, chromosome number 1, is 220 million base pairs long.

In living organisms, DNA does not usually exist as a single molecule, but instead as a tightly-associated pair of molecules.[5][6] These two long strands entwine like vines, in the shape of a double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix. In general, a base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide. If multiple nucleotides are linked together, as in DNA, this polymer is referred to as a polynucleotide.

The backbone of the DNA strand is made from alternating phosphate and sugar residues. The sugar in DNA is 2-deoxyribose, which is a pentose (five carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand. This arrangement of DNA strands is called antiparallel. The asymmetric ends of DNA strands are referred to as the 5′ (five prime) and 3′ (three prime) ends. One of the major differences between DNA and RNA is the sugar, with 2-deoxyribose being replaced by the alternative pentose sugar ribose in RNA.

The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are shown below and are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate.

These bases are classified into two types; adenine and guanine are fused five- and six-membered heterocyclic compounds called purines, while cytosine and thymine are six-membered rings called pyrimidines.[6] A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring. Uracil is not usually found in DNA, occurring only as a breakdown product of cytosine, but a very rare exception to this rule is a bacterial virus called PBS1 that contains uracil in its DNA.[9] In contrast, following synthesis of certain RNA molecules, a significant number of the uracils are converted to thymines by the enzymatic addition of the missing methyl group. This occurs mostly on structural and enzymatic RNAs like transfer RNAs and ribosomal RNA.

Base pairing

Each type of base on one strand forms a bond with just one type of base on the other strand. This is called complementary base pairing. Here, purines form hydrogen bonds to pyrimidines, with A bonding only to T, and C bonding only to G. This arrangement of two nucleotides binding together across the double helix is called a base pair. In a double helix, the two strands are also held together via forces generated by the hydrophobic effect and pi stacking, which are not influenced by the sequence of the DNA. As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can therefore be pulled apart like a zipper, either by a mechanical force or high temperature.[15] As a result of this complementarity, all the information in the double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. Indeed, this reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in living organisms.

The two types of base pairs form different numbers of hydrogen bonds, AT forming two hydrogen bonds, and GC forming three hydrogen bonds (see figures, left). The GC base pair is therefore stronger than the AT base pair. As a result, it is both the percentage of GC base pairs and the overall length of a DNA double helix that determine the strength of the association between the two strands of DNA. Long DNA helices with a high GC content have stronger-interacting strands, while short helices with high AT content have weaker-interacting strands.[16] Parts of the DNA double helix that need to separate easily, such as the TATAAT Pribnow box in bacterial promoters, tend to have sequences with a high AT content, making the strands easier to pull apart.[17] In the laboratory, the strength of this interaction can be measured by finding the temperature required to break the hydrogen bonds, their melting temperature (also called Tm value). When all the base pairs in a DNA double helix melt, the strands separate and exist in solution as two entirely independent molecules. These single-stranded DNA molecules have no single common shape, but some conformations are more stable than others

DNA damage

DNA can be damaged by many different sorts of mutagens. These include oxidizing agents, alkylating agents and also high-energy electromagnetic radiation such as ultraviolet light and x-rays. The type of DNA damage produced depends on the type of mutagen. For example, UV light mostly damages DNA by producing thymine dimers, which are cross-links between adjacent pyrimidine bases in a DNA strand. On the other hand, oxidants such as free radicals or hydrogen peroxide produce multiple forms of damage, including base modifications, particularly of guanosine, as well as double-strand breaks. It has been estimated that in each human cell, about 500 bases suffer oxidative damage per day. Of these oxidative lesions, the most dangerous are double-strand breaks, as these lesions are difficult to repair and can produce point mutations, insertions and deletions from the DNA sequence, as well as chromosomal translocations.

Many mutagens intercalate into the space between two adjacent base pairs. Intercalators are mostly aromatic and planar molecules, and include ethidium, daunomycin, doxorubicin and thalidomide. In order for an intercalator to fit between base pairs, the bases must separate, distorting the DNA strands by unwinding of the double helix. These structural changes inhibit both transcription and DNA replication, causing toxicity and mutations. As a result, DNA intercalators are often carcinogens, with benzopyrene diol epoxide, acridines, aflatoxin and ethidium bromide being well-known examples.Nevertheless, due to their properties of inhibiting DNA transcription and replication, they are also used in chemotherapy to inhibit rapidly-growing cancer cells

Replication

Cell division is essential for an organism to grow, but when a cell divides it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication. Here, the two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase. This enzyme makes the complementary strand by finding the correct base through complementary base pairing, and bonding it onto the original strand. As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix.[71] In this way, the base on the old strand dictates which base appears on the new strand, and the cell ends up with a perfect copy of its DNA

History

DNA was first isolated by the Swiss physician Friedrich Miescher who, in 1869, discovered a microscopic substance in the pus of discarded surgical bandages. As it resided in the nuclei of cells, he called it "nuclein". In 1919 this discovery was followed by Phoebus Levene's identification of the base, sugar and phosphate nucleotide unit. Levene suggested that DNA consisted of a string of nucleotide units linked together through the phosphate groups. However, Levene thought the chain was short and the bases repeated in a fixed order. In 1937 William Astbury produced the first X-ray diffraction patterns that showed that DNA had a regular structure.

In 1943, Oswald Theodore Avery discovered that traits of the "smooth" form of the Pneumococcus could be transferred to the "rough" form of the same bacteria by mixing killed "smooth" bacteria with the live "rough" form. Avery, along with coworkers Colin MacLeod and Maclyn McCarty, identified DNA as this transforming principle. DNA's role in heredity was confirmed in 1953, when Alfred Hershey and Martha Chase in the Hershey-Chase experiment showed that DNA is the genetic material of the T2 phage.

In 1953, based on X-ray diffraction images taken by Rosalind Franklin and the information that the bases were paired, James D. Watson and Francis Crick suggested what is now accepted as the first accurate model of DNA structure in the journal Nature.Experimental evidence for Watson and Crick's model were published in a series of five articles in the same issue of Nature. Of these, Franklin and Raymond Gosling's paper was the first publication of X-ray diffraction data that supported the Watson and Crick model, this issue also contained an article on DNA structure by Maurice Wilkins and his colleagues. In 1962, after Franklin's death, Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine. However, speculation continues on who should have received credit for the discovery, as it was based on Franklin's data.

In an influential presentation in 1957, Crick laid out the "Central Dogma" of molecular biology, which foretold the relationship between DNA, RNA, and proteins, and articulated the "adaptor hypothesis". Final confirmation of the replication mechanism that was implied by the double-helical structure followed in 1958 through the Meselson-Stahl experiment. Further work by Crick and coworkers showed that the genetic code was based on non-overlapping triplets of bases, called codons, allowing Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg to decipher the genetic code. These findings represent the birth of molecular biology.

SIR FRANCIS CRICK(RIGHT) WITH JAMES WATSON (LEFT.)

Pioneer James Watson in 1957 with a molecular model of DNA.

SOURCE: WIKIPEDIA

MALE REPRODUCTIVE SYSTEM

2007-09-23T06:36:00.000-07:00

This article is about human male reproductive system.

The human male reproductive system is a series of organs located outside of the body and around the pelvic region of a male that contribute towards the reproductive process.
The male contributes to reproduction by producing spermatozoa. The spermatozoa then fertilize the egg in the female body and the fertilized egg (zygote) gradually develops into a fetus, which is later born as a child.

Testes
Main article: Testicle
The testes lie outside the abdominal cavity of the male within the scrotum. They begin their development in the abdominal cavity but descend into the scrotal sacs during the last 2 months of fetal development. This is required for the production of sperm because internal body temperatures are too high to produce viable sperm.
In the body of an average male, there are two testicles located in a sac called the scrotum. On top of these organs is the epididymis, the "housing area" for sperm that has been produced.

Penis
Main article: Penis
The penis has a long shaft and enlarged tip called the glans penis. The penis is the copulatory organ of the males. When the male is sexually aroused, the penis becomes erect and ready for intercourse. Erection is achieved because blood sinuses within the erectile tissue of the penis become filled with blood. The arteries of the penis are dilated while the veins are passively compressed so that blood flows into the erectile tissue under pressure.

Sperm & seminal fluid

Main article: Spermatozoon

A mature sperm, or spermatozoan, has 3 distinct parts: a head, a mid-piece, and a tail. The tail is made up of microtubules that form cilia and flagella, and the mid-piece contains energy-producing mitochondria. The head contains 23 chromosomes within a nucleus. The tip of the nucleus is covered by a cap called the acrosome, which is believed to contain enzymes needed to breach the egg for fertilization. A normal human male usually produces several hundred million sperm per day. Sperm are continually produced throughout a male's reproductive life, though production decreases with age.
During ejaculation, sperm leaves the penis in a fluid called seminal fluid. This fluid is produced by 3 types of glands, the seminal vesicles, the prostate gland, and Cowper's glands. Each component of a seminal fluid has a particular function. Sperm are more viable in a basic solution, so seminal fluid has a slightly basic pH. Seminal fluid also acts as an energy source for the sperm, and contains chemicals that cause the uterus to contract.

FRIENDSHIP SHAYARI'S

2007-09-23T06:26:00.000-07:00

Friendship is not about finding similarities, it is about respecting differences. You are not my friend coz you are like me, but because i accept you and respect you the way you are.

Thank you for touching my life in ways you may never know. My riches do not lie in material wealth, but in having friend like you - a precious gift from God.

Good FRIENDS CaRE for each Other.. CLoSE Friends UNDERSTaND each Other... and TRUE Friends STaY forever beyond words, beyond time...**

FRiEND in different lanaguages... Iranian - DOST German - FREUND Herbew - CHAVER French - AMi Pinoy - KAiBiGAN Dutch - VREND Mexican - AMiGO For me.. just simply "YOU"

Stars has 5 ends Square has 4 ends Trinagle has 3 ends Line has 2 ends but Circle of our friendship has no end...

A daily thought... A silent tear... A Constant wish that u r near... Words are few but thoughts r deep... Memories of our frenship i'll always keep!!

We met it was Luck! We talked it was CHANCE! We became friends it was DESTINY! We are still friends it is FAITH! We will always be friends its a PROMISE!

When does a friend become a best friend? When his dialouge, "I care for you" converts into "I will kill you if you don't care for me

Dont write your name on sand, waves will wash it. Dont write your name on sky, wind may blow it. Write your name on hearts of your friends, thats where it will stay.

The one who likes you most, sometimes hurts you, but again he is the only one who feels your pain.

For me U r as... Chees 4 pizza.. passport 4 visa... butter 4 bread.. ice 4 freezer.. cream 4 cake... water 4 lake.. leaf 4 tree.. a FRIEND like u is 4 ever 4 me..!!

Friends are like shoes, some loose some tight, some fit just right, they help u as u walk through life. thanks for being my size!

F: FIELD of LOVE!..R: ROOT ofJOy!.. I: ISLAND of GOD!.. E: END of SoRROW!.. N: NAME of HOPE!.. D: DOOR of UNDERSTANDING! dats YOU my FRIEND..

Science has proved that sugar melts in water,so plz don`t walk in the rain, otherwise I may lose a sweet friend like u!!!

A deep friend is like rainbow, when the perfect amount of happiness and tears r mixed, the result is a colorful bridge between 2 hearts.

LYRICS OF THE MOVIE DARLING

2007-09-23T06:19:00.000-07:00

SAATHIYA

saathiya saathiya.........
(ishq bedardi mujhko pata hai
isaki chaahat mein milati saja hai) - 2
bekaraari mein mar hi na jaau
na samajh ko main kaise samajhaau
(dil hai ki maanata nahi hai
bechaini jaanata nahi hai
main karuun kya bata jaraasa ??yaar) - 2
saathiya saathiya.........
(narm khwaabon ki baahon mein jaagengi aankhein
garm yaadon ke saaye mein bitengi raatein) - 2
yaad toh aayegi, bekhudi chhayegi
dard de jaayegi, tanhaayi tadpaayegi
(dil hai ki maanata nahi hai
bechaini jaanata nahi hai
main karuun kya bata jaraasa ??yaar) - 2
saathiya saathiya.........
(saare aalam pe aahon ka chhaayega jaadu
apane hi jajbon pe toh hoga na kaabu) - 2
jakhm yeh ??jigar ho gaye sau asar
na rahegi khabar bechida hoga safar
(dil hai ki maanata nahi hai
bechaini jaanata nahi hai
main karuun kya bata jaraasa ??yaar) - 2
saathiya saathiya.........