Bladder Cancer

Cancer that forms in tissues of the bladder (the organ that stores urine). Most bladder cancers are transitional cell carcinomas (cancer that begins in cells that normally make up the inner lining of the bladder). Other types include squamous cell carcinoma (cancer that begins in thin, flat cells) and adenocarcinoma (cancer that begins in cells that make and release mucus and other fluids). The cells that form squamous cell carcinoma and adenocarcinoma develop in the inner lining of the bladder as a result of chronic irritation and inflammation.

Signs and symptoms

Bladder cancer characteristically causes blood in the urine; this may be visible to the naked eye (frank hematuria) or detectable only by microscope (microscopic hematuria). Other possible symptoms include pain during urination, frequent urination (Polyuria) or feeling the need to urinate without results. These signs and symptoms are not specific to bladder cancer, and are also caused by non-cancerous conditions, including prostate infections and cystitis. Kidney cancer also can cause hematuria.

Causes

Tobacco smoking is the main known cause of urinary bladder cancer: in most populations, smoking causes over half of bladder cancer cases in men and a sizeable proportion in women. There is a linear relationship between smoking and risk, and quitting smoking reduces the risk.  In a 10-year study involving almost 48,000 men, researchers found that men who drank 1.5L of water a day had a significantly reduced incidence of bladder cancer when compared with men who drank less than 240mL (around 1 cup) per day. The authors proposed that bladder cancer might partly be caused by the bladder directly contacting carcinogens that are excreted in urine. Thirty percent of bladder tumors probably result from occupational exposure in the workplace to carcinogens such as benzidine. 2-Naphthylamine, which is found in cigarette smoke, has also been shown to increase bladder cancer risk. Occupations at risk are metal industry workers, rubber industry workers, workers in the textile industry, and people who work in printing. Some studies also suggest that auto mechanics have an elevated risk of bladder cancer due to their frequent exposure to hydrocarbons and petroleum-based chemicals. Hairdressers are thought to be at risk as well because of their frequent exposure to permanent hair dyes.

Hydronephrosis

Hydronephrosis is distention (dilation) of the kidney with urine, caused by backward pressure on the kidney when the flow of urine is obstructed.

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  Kidney stones are common causes of urinary tract obstruction.
  
  
  
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  When hydronephrosis occurs quickly, people may have excruciating pain, most often in the flank (the area between the ribs and the hips).
  
  
  
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  When hydronephrosis occurs more gradually, people may have no symptoms or experience attacks of dull, aching discomfort in the flank.
  
  
  
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  Doctors initially use bladder catheterization (or ultrasonography) to detect hydronephrosis, and they may use ultrasonography or another imaging test to determine the site of the blockage.
  
  
  
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  Treatment depends on the cause of the obstruction.
  
  
  

Normally, urine flows out of the kidneys at extremely low pressure. If the flow of urine is obstructed, urine backs up behind the point of blockage, eventually reaching the small tubes of the kidney and its collecting area (renal pelvis), distending the kidney and increasing the pressure on its internal structures. The elevated pressure from obstruction may ultimately damage the kidney and can result in loss of its function. When the flow of urine is obstructed, urinary tract infections are fairly common and stones are more likely to form. If both kidneys are obstructed, kidney failure may result.

Long-standing distention of the renal pelvis and ureter can also inhibit the rhythmic muscular contractions that normally move urine down the ureter from the kidney to the bladder (peristalsis). Scar tissue may then replace the normal muscular tissue in the walls of the ureter, resulting in permanent damage.

What is hemodialysis?

The blood circulates outside the body of the patient - it goes through a machine that has special filters. The blood comes out of the patient through a catheter (a flexible tube) that is inserted into the vein. The filters do what the kidney's do; they filter out the waste products from the blood. The filtered blood then returns to the patient via another catheter. The patient is, in effect, connected to a kind of artificial kidney.

Patients need to be prepared for hemodialysis. A blood vessel, usually in the arm, needs to be enlarged. Surgery is required for this. The enlarged vein makes the insertion of the catheters possible. US researchers have developed a new way of growing blood vessels using patients' own skin cells to seed the growth of tissue and have tested it in dialysis patients with end stage kidney disease.

Hemodialysis usually lasts about 3 to 4 hours each week. The duration of each session depends on how well the patient's kidneys work, and how much fluid weight the patient has gained between treatments.

In the UK hemodialysis is either done in a special dialysis center in a hospital, or at home. When it is carried out at home it is important that the patient, and/or his/her caregiver knows what to do. A study revealed that kidney disease patients who are educated about dialysis are more likely to undergo a standard but under-utilized dialysis-related procedure than less knowledgeable patients The following people may have hemodialysis done at home:

• People who can and want to learn how to do it at home.
• People who are willing to carry on doing it at home.
• People whose condition has been stable while on dialysis.
• People who do not suffer from other diseases which would make home hemodialysis unsafe.
• People who have suitable blood vessels for the insertion of the catheters.
• People who have a caregiver, and that caregiver is willing to help with hemodialysis. People whose homes can be adapted for hemodialysis equipment.

In the UK, the National Institutes of Health and Clinical Excellence (NICE) recommends that every patient deemed suitable for home dialysis should have both home dialysis and hospital offered.

What Is Dialysis?

What Is Dialysis? Understanding Kidney Treatment and Its Importance

Dialysis is a medical treatment that helps people whose kidneys are not functioning properly. The kidneys play a vital role in filtering waste products, excess fluids, and toxins from the blood. When the kidneys fail or lose their ability to function effectively, harmful substances can build up in the body, which can be life-threatening. Dialysis performs the essential role of cleansing the blood, maintaining proper chemical balance, and keeping the body healthy.

How Dialysis Works

Dialysis works by artificially removing waste products and excess fluids from the blood. There are two main types of dialysis:

1. Hemodialysis

In hemodialysis, a machine called a dialyzer or artificial kidney filters the blood. The patient’s blood is pumped through tubes into the machine, where it passes through a special filter. This filter removes waste, extra salt, and fluid before returning the cleaned blood to the body. Hemodialysis is usually done in a hospital or dialysis center three times a week, with each session lasting about 3–5 hours.

2. Peritoneal Dialysis

Peritoneal dialysis uses the lining of the abdomen (peritoneum) as a natural filter. A special fluid called dialysate is introduced into the abdominal cavity through a catheter. Waste products and excess fluids from the blood pass into this fluid, which is then drained and replaced with fresh fluid. Peritoneal dialysis can be performed at home, often multiple times a day, or overnight using a machine called a cycler.

Who Needs Dialysis?

Dialysis is usually required for people with severe kidney damage, often caused by conditions such as:

• Chronic kidney disease (CKD)

• High blood pressure (hypertension)

• Diabetes

• Kidney infections or obstructions

• Acute kidney failure due to sudden injury or illness

Doctors usually recommend dialysis when kidney function drops to about 10–15% of normal.

Importance of Dialysis

Dialysis is not a cure for kidney failure but a life-saving procedure that can help patients live longer and healthier lives. It removes harmful substances from the blood, controls blood pressure, balances electrolytes, and prevents complications such as fluid overload and heart problems. For many patients, dialysis is also a bridge to kidney transplantation.

Living With Dialysis

While dialysis allows patients to survive, it requires lifestyle adjustments. Patients need to follow dietary restrictions, monitor fluid intake, and maintain regular treatment schedules. Emotional support from family and counseling can also be very helpful.

Conclusion

Dialysis is a crucial medical treatment for people with kidney failure. Whether through hemodialysis or peritoneal dialysis, it performs the essential function of cleansing the blood and keeping the body in balance. Early detection of kidney problems and timely dialysis can greatly improve the quality of life and longevity of patients. If you or a loved one experiences kidney issues, consulting a nephrologist (kidney specialist) is the first step toward proper care and treatment.

Kidney transplantation

Kidney transplantation or renal transplantation is the organ transplant of a kidney in a patient with end-stage renal disease. Kidney transplantation is typically classified as deceased-donor (formerly known as cadaveric) or living-donor transplantation depending on the source of the donor organ. Living-donor renal transplants are further characterized as genetically related (living-related) or non-related (living-unrelated) transplants, depending on whether a biological relationship exists between the donor and recipient.

History

The first documented kidney transplant in the United States was performed June 17, 1950, on Ruth Tucker, a 44-year-old woman with polycystic kidney disease, at Little Company of Mary Hospital in Evergreen Park, Illinois. Although the donated kidney was rejected because no immunosuppressive therapy was available at the time—the development of effective antirejection drugs was years away—Tucker's remaining diseased kidney began working again and she lived another five years before dying of an unrelated illness.[citation needed] Thereafter, successful kidney transplantations were undertaken in 1954 in Boston and Paris. The Boston transplantation was done between identical twins to eliminate any problems of an immune reaction. The first kidney transplant in the United Kingdom did not occur until 1960, when Michael Woodruff performed one between identical twins in Edinburgh. Until the routine use of medications to prevent and treat acute rejection, introduced in 1964, deceased donor transplantation was not performed. The kidney was the easiest organ to transplant: tissue typing was simple, the organ was relatively easy to remove and implant, live donors could be used without difficulty, and in the event of failure, kidney dialysis was available from the 1940s. Tissue typing was essential to the success: early attempts in the 1950s on sufferers from Bright's disease had been very unsuccessful. In 1954, at Brigham Hospital Dr. Joseph E. Murray and Dr. J. Hartwell Harrison performed the world's first successful renal transplant between genetically identical patients, for which Dr. Murray received the Nobel Prize for Medicine in 1990. The donor is still alive as of 2005; the recipient died eight years after the transplantation.

The major barrier to organ transplantation between genetically non-identical patients lay in the recipient's immune system, which would treat a transplanted kidney as a "non-self" and immediately or chronically, reject it. Thus, having medications to suppress the immune system was essential. However, suppressing an individual's immune system places that individual at greater risk of infection and cancer (particularly skin cancer and lymphoma), in addition to the side effects of the medications.

The basis for most immunosuppressive regimens is prednisolone, a corticosteroid. Prednisolone suppresses the immune system, but its long-term use at high doses causes a multitude of side effects, including glucose intolerance and diabetes, weight gain, osteoporosis, muscle weakness, hypercholesterolemia, and cataract formation. Prednisolone alone is usually inadequate to prevent rejection of a transplanted kidney. Thus other, non-steroid immunosuppressive agents are needed, which also allow lower doses of prednisolone.

General information about kidney

Normally, all of us have two kidneys which are located in the flank or the mid back area of our body. They are protected by the lower ribs and the thick musculature in this region. The kidneys are bean-shaped organs which are about the same size as a man's fist.

The kidneys play an important role in a number of bodily functions. These include:

• Excreting (taking out] the waste products from blood

The kidneys clean our blood. Every two minutes, every drop of blood in our body passes through our kidneys.

Blood enters kidneys although ARTERY from the Heart

Inside our kidneys are millions of tiny filters that take out waste products from the blood. These waste products are taken away from kidney by two tubes and leave the body as urine. Once waste products are removed, the blood is clean and can then be sent to other parts of the body.

• Keeping the right amount of fluid in the body

The kidneys help the body keep the right amount of fluid. If there is too the kidneys will excrete the excess water in the form of urine. If there is less amount of fluid in the body the kidneys will try to conserve water and less amount will be excreted in the urine.

• Regulating your blood pressure

Keeping good fluid levels helps keep the blood pressure at normal levels, too. If blood pressure is too high, the heart has to work harder to pump blood all over the body.

The kidneys also work to keep the right amounts of important things like sodium (salt), potassium and protein.

• Regulating red blood cell production

Proper production of red blood cells depends upon erythropoietin levels, adequate intake and proper assimilation of folic acid, vitamin B12, iron and protein.

Erythropoietin is a hormone produced primarily by the kidneys. Normally, the kidneys are able to sense the reduced amount of oxygen present in the blood. The kidneys respond by secreting a hormone called erythropoietin which stimulates the bone marrow to produce more red blood cells, thus increasing the capacity of the blood to carry more oxygen.

• Activating vitamin D

The kidneys also change vitamin D into an active form. This helps body use more of the calcium it takes in from food and medicines. This is important because the bones will not be strong Without calcium.

Skin Function. What is it?

The skin is the largest organ of our body and one of the 7 channels of elimination containing about 70% water, 25% protein and 2% lipids, the skin helps the main organs of elimination (liver, kidneys, intestines) get rid of waste buildup.

The uppermost layer of the skin is called epidermis. The deeper layer is called the dermis, which contains collagen and elastin ( keep the skin flexible and firm). The dermis also contains sebaceous glands, sweat glands, lymph vessels, hair follicles and nerves. Beneath the dermis lies a tissue of fat cells. Infection can occur when the exfoliation process ( the renewal of cells when they shed to make room for new ones) slows down and your skin pores get blocked.

The Skin has five main functions :

 

1.It acts as a mechanical barrier to infections. It ultimately prevents microorganisms and other substances from entering the body. Langerhans cells (a type of macrophage) are found within the dermis, they engulf invaders foreign to the body and debris. Keratin layers in the epidermis together with sebum produced by sebaceous glands act as a waterproof barrier. Melanocytes protect the body from ultraviolet light.Finger and toenails protect the extremities of fingers and toes from damage. Fingertips are important for dexterity and the sense of touch; they have ridged areas to assist in picking things up.Hair follicles offer some extra protection to certain parts of the body such as eyes and head.

2. Skin provides the sense of touch or sensation we need to know more about our outside environment through recognizing heat, cold, pain and other sensations. Nerve endings of the skin provide the body with a great deal of information about the outside environment.

3. It regulates body temperature. Considerable heat is lost through the skin. Even under extreme conditions of high temperature and exercise, our skin tends to make body temperature normal. The production (evaporation) of sweat in the skin cools us down when exposed to too much heat.

The core body temperature needs to be kept constant for normal physiological activity to take place (370c). It needs to maintain a core temperature for homeostasis.

4. Skin excretes waste product and excess salt from the body. Sweat includes waste products in solution. Water is lost continuously through the skin as insensible sweating. More pronounced water loss through sweating occurs as part of temperature regulation.

5. Skin synthesizes the use of Vitamin D in the presence of sunlight and ultra violet radiation needed for the absorption of calcium and phosphate.

M U S C U L A R S Y S T E M

C O N T E N T S :

The human body contains more than 650 individual muscles which are attached to the skeleton, which provides the pulling power for us to move around. The main job of the muscular system is to provide movement for the body. The muscular system consist of three different types of muscle tissues : skeletal, cardiac, smooth. Each of these different tissues has the ability to contract, which then allows body movements and functions. There are two types of muscles in the system and they are the involuntary muscles, and the voluntary muscles. The muscle in which we are allow to control by ourselves are called the voluntary muscles and the ones we can? control are the involuntary muscles. The heart, or the cardiac muscle, is an example of involuntary muscle.

Front muscles

CARDIAC MUSCLE:

The cardiac muscles is the muscle of the brain itself. The cardiac muscle is the tissue that makes up the wall of the heart called the mydocardium. Also like the skeletal muscles, the cardiac muscle is striated and contracts through the sliding filament method. However it is different from other types of muscles because it forms branching fibers. Unlike the skeletal muscles, the cardiac muscle is attached together instead of been attach to a bone.

SKELETAL MUSCLE:

The skeletal muscle makes up about 40 % of an adults body weight. It has stripe-like markings, or striations. The skeletal muscles is composed of long muscle fibers. Each of these muscles fiber is a cell which contains several nuclei. The nervous system controls the contraction of the muscle. Many of the skeletal muscle contractions are automatic. However we still can control the action of the skeletal muscle. And it is because of this reason that the skeletal muscle is also called voluntary muscle.

SMOOTH MUSCLE:

Much of our internal organs is made up of smooth muscles. They are found in the urinary bladder, gallbladder, arteries, and veins. Also the digestive tract is made up of smooth muscle as well. The smooth muscles are controlled by the nervous system and hormones. We cannot consciously control the smooth muscle that is why they are often called involuntary muscles.

Back muscles

Skeletal muscle

Skeletal muscle

Skeletal muscle fibres are multinucleated cells, with the nuclei situated immediately beneath the sarcolemma (cell membrane). An individual fibre may be up to 35cm long. A mature skeletal muscle fibre is composed of a large number parallel running myofibrils. The myofibrils in turns consist of overlapping parallel-arranged thin actin filaments and thick myosin filaments. The filaments are anchored to specific accessory proteins. The functional unit of the fibril is the sarcomere, which is situated between two Z-lines.

A thin layer of connective tissue, the endomysium, surrounds each muscle fibre. Several muscle fibres are bundled together as a fasciculus (Pl fasciculi). The connective tissue layer surrounding the fasciculi is known as the perimysium. An individual muscle is a number of fasciculi enclosed by the epimysium, a thick dense connective tissue capsule. The connective tissue framework is continuous with that of the tendons and muscle attachments to direct the muscle forces to the bone, skin, etc.

Muscles are highly vascular with the blood vessels running in the various connective tissue layers. The different fibre types may histologically visualized by the use of histochemical techniques.  Skeletal muscle contraction is regulated by intracellular calcium stored in the T-tubule system.

Muscle

Muscle (from Latin musculus, diminutive of mus "mouse") is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause either locomotion of the organism itself or movement of internal organs. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Examples are the contraction of the heart and peristalsis which pushes food through the digestive system. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh. There are two broad types of voluntary muscle fibers: slow twitch and fast twitch. Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly.

Muscular tissue

Wat is muscle?

Specialised cells whose primary function is contraction characterize muscular tissue. These cells, called muscle fibres, are elongated and arranged in parallel arrays. Their coordinated contraction results in movement. Muscular tissue may be classified based on appearance and location. Striated muscle exhibits cross-striations visible under the microscope, while smooth muscle does not. Striated muscle may be further divided into skeletal muscle and cardiac muscle. Skeletal muscle is, for obvious reasons, under voluntary nervous control and is often referred to as voluntary muscle. Smooth muscle is under autonomic nervous control and is largely restricted to the viscera and blood vessels.

Introduction to pregnancy symptoms

Introduction to pregnancy symptoms

Most women equate a missed menstrual period with the possibility of being pregnant, but other symptoms and signs are experienced by most women in the early stages of pregnancy. It's important to remember that not all women will experience all of these symptoms or have the symptoms to the same degree. Even the same woman can have different types of symptoms in a subsequent pregnancy than she had in previous pregnancies. The following are the most common pregnancy symptoms in the first trimester.

Missed period

A missed menstrual period is most often the first sign of pregnancy. Sometimes a woman who is pregnant may still experience some bleeding or spotting around the time of the expected period. This small amount of bleeding that occurs at the time of the expected menstrual period happens when the fertilized egg attaches to the uterine wall and is referred to as implantation bleeding.

Any bleeding during pregnancy is typically lighter than that observed during the regular menstrual period. However, if a woman does not have regular menstrual cycles, she may notice some of the other symptoms of early pregnancy before it is apparent that the menstrual period has been missed. A missed menstrual period also does not confirm that a woman is pregnant even if she has regular cycles, since both emotional and physical conditions may cause absent or delayed periods.

Breast swelling, tenderness, and pain

Feelings of breast swelling, tenderness, or pain are also commonly associated with early pregnancy. These symptoms are sometimes similar to the sensations in the breasts in the days before an expected menstrual period. Women may also describe a feeling of heaviness or fullness in the breasts. These symptoms can begin in some women as early as one to two weeks after conception. Women may also notice a deepening of the color of the area surrounding the nipple (called the areola) and/or a dark line going down from the middle of the central abdomen area to the pubic area (known as the linea nigra). Some degree of darkening of the areola persists after pregnancy in many women, but the linea nigra typically disappears in the months following delivery of the baby.

Nausea and vomiting

Nausea and vomiting are also common in early pregnancy. Traditionally referred to as "morning sickness," the nausea and vomiting associated with early pregnancy can occur at any time of the day or night. Its typical onset is anywhere between the 2nd and 8th weeks of pregnancy. Most women who have morning sickness develop nausea and vomiting about one month after conception, but it may develop sooner in some women.

Elevations in estrogen that occur early in pregnancy are thought to slow the emptying of the stomach and may be related to the development of nausea. Accompanying the characteristic "morning sickness" may be cravings for, or aversions to, specific foods or even smells. It is not unusual for a pregnant woman to change her dietary preferences, often having no desire to eat previous "favorite" foods. In most women, nausea and vomiting begin to subside by the second trimester of pregnancy.

Fatigue and tiredness

Fatigue and tiredness are symptoms experienced by many women in the early stages of pregnancy. The cause of this fatigue has not been fully determined, but it is believed to be related to rising levels of the hormone progesterone. Fatigue is another symptom that may be experienced early, in the first weeks after conception.

Abdominal bloating

Some women may experience feelings of abdominal enlargement or bloating, but there is usually only a small amount of weight gain in the first trimester of pregnancy. In this early stage of pregnancy a weight gain of about one pound per month is typical. Sometimes women also experience mild abdominal cramping during the early weeks of pregnancy, which may be similar to the cramping that occurs prior to or during the menstrual period.

Frequent urination

A woman in the early stages of pregnancy may feel she has to urinate frequently, especially at nighttime, and she may leak urine with a cough, sneeze, or laugh. The increased desire to urinate may have both physical and hormonal causes. Once the embryo has implanted in the uterus, it begins to produce the hormone known as human chorionic gonadotrophin (hCG), which is believed to stimulate frequent urination. Another cause of frequent urination that develops later is the pressure exerted by the growing uterus on the bladder.

Elevated basal body temperature

A persistently elevated basal body temperature (the oral temperature measured first thing in the morning, before arising from bed) is another characteristic sign of early pregnancy. An elevation in the basal body temperature occurs shortly after ovulation and persists until the next menstrual period occurs. Persistence of the elevated basal body temperature beyond the time of the expected menstrual period is another sign of early pregnancy.

Melasma (darkening of the skin)

Some women may develop a so-called "mask of pregnancy" in the first trimester, referring to a darkening of the skin on the forehead, bridge of the nose, upper lip, or cheekbones. The darkened skin is typically present on both sides of the face. Doctors refer to this condition as melasma or chloasma, and it is more common in darker-skinned women than those with lighter skin. Melasma can also occur in some conditions other than pregnancy. Women who have a family history of melasma are at greater risk of developing this sign of pregnancy.

Mood swings and stress

Mood swings and stress are common symptoms reported by many women in the early stages of pregnancy. Many women in the early stages of pregnancy describe feelings of heightened emotions or even crying spells. The rapid changes in hormone levels are believed to cause these changes in mood. Pregnant women may also notice more rapid and drastic changes in their moods.

What causes problems in the urinary system?

What causes problems in the urinary system?

Problems in the urinary system can be caused by aging, illness, or injury. As you get older, changes in the kidneys’ structure cause them to lose some of their ability to remove wastes from the blood. Also, the muscles in your ureters, bladder, and urethra tend to lose some of their strength. You may have more urinary infections because the bladder muscles do not tighten enough to empty your bladder completely. A decrease in strength of muscles of the sphincters and the pelvis can also cause incontinence, the unwanted leakage of urine. Illness or injury can also prevent the kidneys from filtering the blood completely or block the passage of urine.

How are problems in the urinary system detected?

Urinalysis is a test that studies the content of urine for abnormal substances such as protein or signs of infection. This test involves urinating into a special container and leaving the sample to be studied.

Urodynamic tests evaluate the storage of urine in the bladder and the flow of urine from the bladder through the urethra. Your doctor may want to do a urodynamic test if you are having symptoms that suggest problems with the muscles or nerves of your lower urinary system and pelvis—ureters, bladder, urethra, and sphincter muscles.

Urodynamic tests measure the contraction of the bladder muscle as it fills and empties. The test is done by inserting a small tube called a catheter through your urethra into your bladder to fill it either with water or a gas. Another small tube is inserted into your rectum or vagina to measure the pressure put on your bladder when you strain or cough. Other bladder tests use x-ray dye instead of water so that x-ray pictures can be taken when the bladder fills and empties to detect any abnormalities in the shape and function of the bladder. These tests take about an hour.

 

How does the urinary system work?

How does the urinary system work?

The organs, tubes, muscles, and nerves that work together to create, store, and carry urine are the urinary system. The urinary system includes two kidneys, two ureters, the bladder, two sphincter muscles, and the urethra.

Front view of urinary tract.

Your body takes nutrients from food and uses them to maintain all bodily functions including energy and self-repair. After your body has taken what it needs from the food, waste products are left behind in the blood and in the bowel. The urinary system works with the lungs, skin, and intestines—all of which also excrete wastes—to keep the chemicals and water in your body balanced. Adults eliminate about a quart and a half of urine each day. The amount depends on many factors, especially the amounts of fluid and food a person consumes and how much fluid is lost through sweat and breathing. Certain types of medications can also affect the amount of urine eliminated.

The urinary system removes a type of waste called urea from your blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

The kidneys are bean-shaped organs about the size of your fists. They are near the middle of the back, just below the rib cage. The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

From the kidneys, urine travels down two thin tubes called ureters to the bladder. The ureters are about 8 to 10 inches long. Muscles in the ureter walls constantly tighten and relax to force urine downward away from the kidneys. If urine is allowed to stand still, or back up, a kidney infection can develop. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.

The bladder is a hollow muscular organ shaped like a balloon. It sits in your pelvis and is held in place by ligaments attached to other organs and the pelvic bones. The bladder stores urine until you are ready to go to the bathroom to empty it. It swells into a round shape when it is full and gets smaller when empty. If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours.

Circular muscles called sphincters help keep urine from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body.

Nerves in the bladder tell you when it is time to urinate, or empty your bladder. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The sensation to urinate becomes stronger as the bladder continues to fill and reaches its limit. At that point, nerves from the bladder send a message to the brain that the bladder is full, and your urge to empty your bladder intensifies.

When you urinate, the brain signals the bladder muscles to tighten, squeezing urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax. As these muscles relax, urine exits the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.

Urinary system

The urinary system (also called excretory system or the genitourinary system) is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder, the urethra, and the penis in males. The analogous organ in invertebrates is the nephridium.

Kidney

The kidneys are bean-shaped organs, which lie in the abdomen, retroperitoneal to the organs of digestion, around or just below the ribcage and close to the lumbar spine. The organ is about the size of a human fist and is surrounded by what is called Peri-nephric fat, and situated on the superior pole of each kidney is an adrenal gland. The kidneys receive their blood supply of 1.25 L/min (25% of the cardiac output) from the renal arteries which are fed by the abdominal aorta. This is important because the kidneys' main role is to filter water soluble waste products from the blood. The other attachment of the kidneys are at their functional endpoints the ureters, which lies more medial and runs down to the trigone of urinary bladder.

The kidneys perform a number of tasks, such as: concentrating urine, regulating electrolytes, and maintaining acid-base homeostasis. The kidney excretes and re-absorbs electrolytes (e.g. sodium, potassium and calcium) under the influence of local and systemic hormones. pH balance is regulated by the excretion of bound acids and ammonium ions. In addition, they remove urea, a nitrogenous waste product from the metabolism of amino acids. The end point is a hyperosmolar solution carrying waste for storage in the bladder prior to urination.

Humans produce about 2.9 liters of urine over 24 hours, although this amount may vary according to circumstances. Because the rate of filtration at the kidney is proportional to the glomerular filtration rate, which is in turn related to the blood flow through the kidney, changes in body fluid status can affect kidney function. Hormones exogenous and endogenous to the kidney alter the amount of blood flowing through the glomerulus. Some medications interfere directly or indirectly with urine production. Diuretics achieve this by altering the amount of absorbed or excreted electrolytes or osmalites, which causes a diuresis.

Breast Infection Symptoms

Breast Infection Symptoms

•Infection: Breast infections may cause pain, redness, and warmth of the breast along with the following symptoms:

◦Tenderness and swelling

◦Body aches

◦Fatigue

◦Breast engorgement

◦Fever and chills

◦Rigor or shaking

•Abscess: Sometimes a breast abscess can complicate mastitis. Harmless, noncancerous masses such as abscesses are more often tender and frequently feel mobile beneath the skin. The edge of the mass is usually regular and well defined. Indications that this more serious infection has occurred include the following:

◦Tender lump in the breast that does not get smaller after breastfeeding a newborn (If the abscess is deep in the breast, you may not be able to feel it). The mass may be moveable and/or compressible.

◦Pus draining from the nipple

◦Persistent fever and no improvement of symptoms within 48-72 hours of treatment

Breast Infection Causes

Breast Infection Causes

Mastitis (inflammation of breast tissue) is a common benign cause of a breast mass. It is commonly seen in women after childbirth while breastfeeding. These masses are often quite painful. Women who are not breastfeeding can also develop mastitis. In healthy women, mastitis is rare. However, women with diabetes, chronic illness, AIDS, or an impaired immune system may be more susceptible to the development of mastitis.

•Bacteria normally found in a baby's mouth or on the nipple can enter the milk ducts through small cracks in the skin of the nipple and can multiply rapidly in the breast milk. This can lead to a superficial small area of inflammation (frequently from streptococcal bacteria) or a deeper walled-off infection or abscess (frequently from staphylococcal bacteria).

•Mild temperature elevations (previously termed milk fever) accompanied by some breast or nipple soreness is usually secondary to engorgement and dehydration immediately (24-72 hours) after delivery and is treated by improved breastfeeding technique. The body temperature should not be above 39°C (102.2°F), nor should the fever persist for longer than about 4-16 hours. This condition may also occur in women who are not breastfeeding and have not completely suppressed lactation yet.

•About one to three percent of breastfeeding mothers develop mastitis, usually within the first few weeks after delivery. Most breast infections occur within the first or second month after delivery or at the time of weaning. Typically, the infection is only in one breast. Engorgement and incomplete breast emptying can contribute to the problem and make the symptoms worse.

•Chronic mastitis occurs in women who are not breastfeeding. In postmenopausal women, breast infections may be associated with chronic inflammation of the ducts below the nipple. Hormonal changes in the body can cause the milk ducts to become clogged with dead skin cells and debris. These clogged ducts make the breast more prone to bacterial infection. This type of infection tends to come back after treatment with antibiotics.

Breast Infection Overview

Mastitis is an infection of the tissue of the breast that occurs most frequently during the time of breastfeeding. This infection causes pain, swelling, redness, and increased temperature of the breast. It can occur when bacteria, often from the baby's mouth, enter a milk duct through a crack in the nipple. This causes an infection and painful inflammation of the breast.

Breast infections most commonly occur one to three months after the delivery of a baby, but they can occur in women who have not recently delivered as well as in women after menopause. Other causes of infection include chronic mastitis and a rare form of cancer called inflammatory carcinoma.

•The breast is composed of several glands and ducts that lead to the nipple and the surrounding colored area called the areola. The milk-carrying ducts extend from the nipple into the underlying breast tissue like the spokes of a wheel. Under the areola are lactiferous ducts. These fill with milk during lactation after a woman has a baby. When a girl reaches puberty, changing hormones cause the ducts to grow and cause fat deposits in the breast tissue to increase. The glands that produce milk (mammary glands) that are connected to the surface of the breast by the lactiferous ducts may extend to the armpit area (axilla).

•A breast infection that leads to an abscess (a localized pocket or collection of pus) is a more serious type of infection. If mastitis is left untreated, an abscess can develop in the breast tissue. This type of infection may require surgical drainage.

Diseases Caused by Virus To Human

Diseases Caused by Virus To Human

Disease	Causal Agent	Organs Affected	Transmission / Vector
Influenza	RNA	Respiratory Tract	Droplets
Adenovirus Infections	DNA	Lungs, Eyes	Droplets, Contact Droplets
Respiratory Syncytial Disease	RNA	Respiratory Tract	Droplets
Rhinovirus Infections	RNA	Upper Respiratory Tract	Droplets,Contact
Herpes Simplex	DNA	Skin,Pharynx, Genital organs	Contact
Chicken pox ( Varicella)	DNA	Skin, Nervous System	Droplets, Contact
Measles (Rubeola)	RNA	Respiratory Tract, Skin	Droplets, Contact
German Measles ( Rubella)	RNA	Skin	Droplets, Contact
Mumps (Epidemic Parotitis)	RNA	Salivary Glands, Blood	Droplets
Small Pox (Variola)	DNA	Skin, Blood	Contact, Droplets
Warts Kawasaki Disease	DNA	Skin	?
Yellow Fever	RNA	Liver, Blood	Mosquito ( Aedes Aegypti)
Dengue Fever	RNA	Blood, Muscles	Mosquito ( Aedes Aegypti )
Hepatitis A	RNA	Liver	Food, Water, Contact
Hepatitis B	DNA	Liver	Contact with body Fluids
NANB Hepatitis	RNA	Liver	Contact with body Fluids
Viral Gastroenteritis	Many RNA Viruses	Intestine	Food, Water
Viral Fevers	Many RNA Viruses	Blood	Contact,arthropods
Cytomegalovirus Disease	DNA	Blood, Lungs	Contact, Congenital transfer
AIDS	Retrovirus ( RNA)	T-lymphocytes	Contact with body Fluids
Rabies	RNA	Brain, Spinal cord	Conact with body Fluids
Polio	RNA	Intestine,Brain, Spinal Cord	Food, Water, Contact
Slow Virus Disease	Prions	Brain	?
Arboviral Enephalitis	Many RNA viruses	Brain	Anthropods

Factors Affecting Microorganisms Growth and Growth Rates

Factors Affecting Growth

Microorganisms, like other living organisms, are dependent on their environment to provide for their basic needs. Adverse conditions can alter their growth rate or kill them. Growth of microorganisms can be manipulated by controlling:

1. Nutrients available 
2.  Oxygen
3. Water
4. Temperature Acidity and pH
5. Light
6. Chemicals

1. Nutrients

Nutrients such as carbohydrates, fats, proteins, vitamins, minerals and water, required by, man are also needed by microorganisms to grow. Microbes differ in their abilities to use substrates as nutrient sources. Their enzyme systems are made available according to their genetic code. They vary in ability to use nitrogen sources to produce amino acids and, therefore, proteins. Some require amino acids to be supplied by the substrate. When organisms need special materials provided by their environment, we refer to them as fastidious. Difference in the utilization of nutrients and the waste products they produce are important in differentiating between organisms.

2. Oxygen

Microbes also differ in their needs for free oxygen. Aerobic organisms must grow in the presence of free oxygen and anaerobic organisms must grow in the absence of free oxygen. Facultative organisms can grow with or without oxygen, while microaerophilic organisms grow in the presence of small quantities of oxygen.

3. Water

Water is necessary for microbes to grow, but microbes cannot grow in pure water. Some water is not available. A measurement of the availability of water is aw or water activity. The aw of pure water is 1.0 while that of a saturated salt solution is 0.75. Most spoilage bacteria require a minimum aw of 0.90. Some bacteria can tolerate an aw above 0.75 as can some yeasts and most molds. Most yeasts require 0.87 water activity. An aw of 0.85 or less suppresses the growth of organisms of public health significance.

4. Temperature

Microorganisms can grow in a wide range of temperatures. Since they depend on water as a solvent for nutrients, frozen water or boiling water inhibits their growth. General terms are applied to organisms based on their growth at different temperatures. Most organisms grow best at or near room and body temperature. These are mesophiles. Those growing above 400C (1050F) are called thermophiles while those growing below 250C(750F) are called psychrotrophs.

5. Acidity

The nature of a solution based on its acidity or alkalinity is described as pH. The pH scale ranges from 0, strongly acidic, to 14, strongly basic. Neutral solutions are pH 7, the pH of pure water. Most bacteria require near neutral conditions for optimal growth with minimums and maximums between 4 and 9. Many organisms change the pH of their substrate by producing by-products during growth. They can change conditions such that the environment can no longer support their growth. Yeasts and molds are more tolerant of lower pH than the bacteria and may outgrow them under those conditions.

6. Light & Chemicals

Ultraviolet light and the presence of chemical inhibitors may also affect the growth of organisms. Many treatments such as hydrogen peroxide and chlorine can kill or injure microbes. Under certain conditions those given a sublethal treatment are injured, but can recover.

Helminthes

In earlier times, the term Worm was loosely used to describe any small animal having a long slender body without appendages. It was used to include not only worms but caterpillars and other insect larvae, and even creatures as unrelated as rotifers and centipedes, all lumped together in the now obsolete category Vermes.

In modern classifications, worms are still recognized as a highly diverse group, and there are a number of systems in use for classifying them. Depending on the particular system, there are around ten worm phyla. Most worms are marine, and many live their lives in tubes which they construct in the sand of the ocean floor. Others live as internal parasites of marine animals including whales and fish, molluscs and octopus.

Many of the parasitic worms of terrestrial animals have larval stages in fresh water, and these can be encountered in water samples collected from lakes and ponds. The three worm phyla of most interest to freshwater biologists are presented below. Additionally, the category "Parasitic" is included, which acknowledges the immense impact of worm parasites upon human and other animal communities.

Helminthes is One of the grand divisions or branches of the animal kingdom. It is a large group including a vast number of species, most of which are parasitic. Called also Enthelminthes, Enthelmintha.

Protozoa

Protozoa or Cornelius protozoans (from Greek πρῶτον proton "first" and ζῷα zoa "animals"; singular protozoon; the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular eukaryotes. basicly its a small thing that you carnt see and it can make you very sick.

While there is no exact definition of the term "protozoan", most scientists use the word to refer to a unicellular heterotrophic protist, such as an amoeba or a ciliate. The term algae is used for microorganisms that photosynthesize. However, the distinction between protozoa and algae is often vague. For example, the alga Dinobryon has chloroplasts for photosynthesis, but it can also feed on organic matter and is motile.

Protozoa are paraphyletic. Though they have sometimes been described as a subkingdom or phylum, they do not constitute a formal taxon in modern classification systems.

Fungus

A fungus (pronounced /ˈfʌŋɡəs/) is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. The Fungi (pronounced /ˈfʌndʒaɪ/ or /ˈfʌŋɡaɪ/) are classified as a kingdom that is separate from plants and animals. One major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants, which contain cellulose. These and other differences show that the fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (a monophyletic group). This fungal group is distinct from the structurally similar slime molds (myxomycetes) and water molds (oomycetes). The discipline of biology devoted to the study of fungi is known as mycology, which is often regarded as a branch of botany, even though genetic studies have shown that fungi are more closely related to animals than to plants.

Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil, on dead matter, and as symbionts of plants, animals, or other fungi. They may become noticeable when fruiting, either as mushrooms or molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange. They have long been used as a direct source of food, such as mushrooms and truffles, as a leavening agent for bread, and in fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. Fungi are also used as biological agents to control weeds and pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g. rice blast disease) or food spoilage can have a large impact on human food supplies and local economies.

The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, and morphologies ranging from single-celled aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of Kingdom Fungi, which has been estimated at around 1.5 million species, with about 5% of these having been formally classified. Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, and Elias Magnus Fries, fungi have been classified according to their morphology (e.g., characteristics such as spore color or microscopic features) or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits. Phylogenetic studies published in the last decade have helped reshape the classification of Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla.

Bacteria

The bacteria ( [bækˈtɪərɪə] (help·info); singular: bacterium)[α] are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on Earth,  forming much of the world's biomass. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. However, most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, bacteria are important in sewage treatment, the production of cheese and yoghurt through fermentation, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.

Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea

Virus

A virus (from the Latin virus meaning toxin or poison) is a microscopic infectious agent that can reproduce only inside a host cell. Viruses infect all types of organisms: from animals and plants, to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, more than 5,000 types of virus have been described in detail, although most types of virus remain undiscovered. Viruses are ubiquitous, as they are found in almost every ecosystem on Earth, and are the most abundant type of biological entity on the planet. The study of viruses is known as virology, and is a branch of microbiology.

Viruses consist of two or three parts: all viruses have genes made from either DNA or RNA, long molecules that carry genetic information; all have a protein coat that protects these genes; and some have an envelope of fat that surrounds them when they are outside a cell. Viruses vary in shape from simple helical and icosahedral shapes, to more complex structures. They are about 1/100th the size of bacteria. The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.

Viruses spread in many ways; plant viruses are often transmitted from plant to plant by insects that feed on sap, such as aphids, while animal viruses can be carried by blood-sucking insects. These disease-bearing organisms are known as vectors. Influenza viruses are spread by coughing and sneezing, and others such as norovirus, are transmitted by the faecal-oral route, when they contaminate hands, food, or water. Rotaviruses are often spread by direct contact with infected children. HIV is one of several viruses that are transmitted through sexual contact.

Not all viruses cause disease, as many viruses reproduce without causing any obvious harm to the infected organism. Viruses such as hepatitis B can cause life-long or chronic infections, and the viruses continue to replicate in the body despite the hosts' defence mechanisms. In some cases, these chronic infections might be beneficial as they might increase the immune system's response against infection by other pathogens. However, in most cases viral infections in animals cause an immune response that eliminates the infecting virus. These immune responses can also be produced by vaccines that give immunity to a viral infection. Microorganisms such as bacteria also have defences against viral infection, such as restriction modification systems. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat both life-threatening and more minor infections.

Microorganism

A microorganism (from the Greek: μικρός, mikrós, "small" and ὀργανισμός, organismós, "organism"; also spelled micro organism or micro-organism) or microbe is an organism that is microscopic (usually too small to be seen by the naked human eye). The study of microorganisms is called microbiology, a subject that began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design.

Microorganisms are very diverse; they include bacteria, fungi, archaea, and protists; microscopic plants (called green algae); and animals such as plankton and the planarian. Some microbiologists also include viruses, but others consider these as non-living. Most microorganisms are unicellular (single-celled), but this is not universal, since some multicellular organisms are microscopic, while some unicellular protists and bacteria, like Thiomargarita namibiensis, are macroscopic and visible to the naked eye.

                                                                      Fig -Bacteria

Microorganisms live in all parts of the biosphere where there is liquid water, including soil, hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth's crust. Microorganisms are critical to nutrient recycling in ecosystems as they act as decomposers. As some microorganisms can fix nitrogen, they are a vital part of the nitrogen cycle, and recent studies indicate that airborne microbes may play a role in precipitation and weather.

Microbes are also exploited by people in biotechnology, both in traditional food and beverage preparation, and in modern technologies based on genetic engineering. However, pathogenic microbes are harmful, since they invade and grow within other organisms, causing diseases that kill millions of people, other animals, and plants.

                                                                           Fig- Fungi

                                                                        Fig - Protozoa

Meiosis

Meiosis

Mitosis provides a method for the asexual reproduction of singular cellular organism and a means of growth and cell replacement in multicellular organisms. An alternative to asexual reproduction, where the offspring are identical to the parent, is sexual reproduction where the genetic material from reproductive partners combines to produce offspring. Clearly such combination cannot involve all the genetic material of the parents, otherwise, with each successive generation we would see a doubling of the genetic material within each cell. To accommodate this the parents produce sex cells (eggs/sperm) called gametes that each contain half the parental genetic material, these fuse to produce offspring.

The gamete cells, then, are unusual in that they contain half the number of chromosomes of 'normal' cells and, as such, are termed haploid (normal cells, containing two sets of chromosomes, are termed diploid).

The normal number of chromosomes in human cells is 46 (in 23 pairs). These pairs originate from parental gamete cells containing 23 single chromosomes, 23 in the mother's egg and 23 form the father's sperm. These two sets of chromosomes are called homologues in that they carry genetic code for the same function, that is a particular chromosome from the mother may carry the genetic coding for hair colour, this is the partner chromosome for the paternal chromosome carrying the same genetic information. Each of the 23 chromosomes can be distinguished by its size, the position of its centromere and the pattern of dark bands. The process of identifying specific chromosomes is called karyotyping and you will undertake a karyotyping exercise in class - external visitors to this page can find the karyotyping exercise on the links page. You can learn more about karyotyping from the set.

The process of meiosis can be considered in two stages; Meiosis I and Meiosis II.

Meiosis I

As with mitosis, meiosis I is preceded by an interphase stage. During this stage chromosomal replication takes place resulting in two identical chromatids, attached by centromeres. Centrosomes are also replicated during this stage.

Interphase is followed by Prophase (I). Homologous pairs of chromosomes pair up and the chromatids of these (of which there are four) cross over one another (see diagram, set book page 140). This coming together of chromatids is important in understanding genetic inheritance. The alignment of chromatids seems random and during this cross over phase there is an exchange of genetic material from one chromatid to the other. In other words, segments of genetic code are exchanged - see Figure 8.18b, page 145 in the set book. This grouping of four chromatids is termed a tetrad. This exchange of genetic material results in chromatids that are uniquely different from that of the parent and ensures genetic variation from one generation to the next.

As this exchange of genetic material takes place, the rest of the cell prepares for division. The centrosomes, with their spindle mictrotubules, separate and the nuclear membrane dissolves. The chromosomes now move to the metaphase plate, as in mitosis, except now they arrive as pairs. Spindle fibres from one pole of the cell (cf mitosis where fibres from both poles) attach to one chromosome of each pair.

Anaphase I

As in mitosis, anaphase I sees the movement of chromosomes to opposite poles of the cell. Paired chromatids are attached by their centromere and so move together towards the poles, in effect the homologous pairs of chromosomes are separated and we have two individual sets of chromosomes at either end of the cell. This process of reducing the amount of genetic material to be passed onto the daughter cells is called reduction division.

Following Anaphase I are the stages of Teleophase I and Cytokinesis. Cell division begins with the formation of a cleavage furrow (in animals) or cell wall (in plants) and the two sets of chromosomes are separated into daughter cells. This is similar to mitosis but, unlike mitosis, there is no further duplication genetic material during the subsequent interphase.

Meiosis II

Meiosis II can follow meiosis 1 immediately or can be delayed by a period of interphase during which time the chromosomes decondense and the nucleus reforms. As in meiosis I, interphase is followed by stages called prophase, metaphase, anaphase, telophase and cytokinesis.

Prophase II

The chromosomes (containing two chromatids) condense, the spindle apparatus forms and the chromosomes move to the metaphase II plate.

Metaphase II

The chromosomes position themselves along the metaphase plate ready for separation.

Anaphase II

The sister chromids separate into individual chromosomes and move in opposite directions to the poles of the cell.

Teleophase II

The chromosomes decondense and nuclei of the (now four) cell(s) reforms. The new cells separate during cytokinesis.

Interphase II

Normal cellular activity continues but there is no further DNA replication and the gamete awaits fertilization.

Advantages of meiosis

The advantage of meiosis (sexual reproduction) lies in the shuffling and combination of genetic material. We have seen that homologous chromosomes code for certain characteristics - by exchanging DNA and combining different sources of genetic material we create a new set of genetic code. It is this generation of new code that results in variation within a population (such as eye colour etc.). This variation enables a population to evolve. Genetic diversity also enables populations to adapt and overcome threatening circumstances.