Excretory+System

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=**__Excretion__**:= The elimination by an organism of waste products that result from metabolic processes. In plants, waste is minimal and is eliminated primarily by diffusion to the outside environment. Animals have specific organs of excretion. In vertebrates, the kidney filters blood, conserving water and producing urea and other waste products in the form of urine. The urine is then passed through the ureters to the bladder and discharged through the urethra. The skin and lungs, which eliminate carbon dioxide, are also excretory organs.
 * Excretory System **

=**__Major functions of__** **__the kidney:__**= Kidneys perform several homeostatic functions:
 * 1) Maintain volume of extracellular fluid
 * 2) Maintain ionic balance in extracellular fluid
 * 3) Maintain pH and osmotic concentration of the extracellular fluid.
 * 4) Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.

=__**Major Parts of the Kidney**__:= The **urinary system** is composed of the **kidneys**, **ureters**, **bladder** and **urethra**. Blood from the heart travels down the **aorta** where it enters the kidney via the **renal arteries**. The kidney acts as a filter and regulator, removing waste products (urea) and balancing glucose, electrolytes (salt, potassium and other minerals) and water levels in the blood. Urine from the kidney flows through the **ureter** to the **bladder**, where is leaves the body via the **urethra**.



=**__The Nephron:__**=


 * Nephron** is the basic structural and functional unit of the kidney . Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine . A nephron eliminates wastes from the body, regulates blood volume and blood pressure , controls levels of electrolytes and metabolites , and regulates blood pH . Its functions are vital to life and are regulated by the endocrine system by hormones such as anti-diuretic hormone , aldosterone , and parathyroid hormone . In humans, a normal kidney contains 800,000 to 1.5 million nephrons.

=**__Formation of the Urine:__**=

**__Filtration:__**


As blood courses through the glomeruli, much of its fluid, containing both useful chemicals and dissolved waste materials, soaks out of the blood through the membranes (by osmosis and diffusion) where it is filtered and then flows into the Bowman's capsule. These substances, which include amino acids, glucose, and about 99 per cent of the water, then rejoin the blood in the capillaries.The capillaries return the blood to the heart by way of the renal vein. Substances not absorbed in the tubule are wastes that the body cannot use. These various substances, which include ammonia, urea, uric acid, and excess water, make up urine. The urine passes from the convoluted tubules into larger collecting tubules and then into the pelvis layer of the kidney. A tube called the ureter carries urine from each kidney into the urinary bladder. Urine collects in the bladder until it passes out of the body through another tube, the urethra. Healthy kidneys produce from 1 to 2 litres of urine daily.This process is called glomerular filtration.


 * __Re-absorption:__**

Large amounts of water - more than 178 liters per day - are reabsorbed back into the bloodstream from the proximal tubules because the physical forces acting on the water in these tubules actually push most of the water back into the blood capillaries. In other words, about 99% of the 180 liters of water that leave the blood each day by glomerular filtration returns to the blood from the proximal tubule through the process of **passive re-absorption**. Sodium ions (Na+) and other ions are only partially reabsorbed from the renal tubules back into the blood. For the most part, however, sodium ions are **actively transported** back into blood from the tubular fluid. The amount of sodium reabsorbed varies from time to time; it depends largely on how much salt we take in from the foods that we eat. (As stated earlier, sodium is a major component of table salt, known chemically as sodium chloride.) As a person increases the amount of salt taken into the body, that person's kidneys decrease the amount of sodium reabsorption back into the blood. That is, more sodium is retained in the tubules. Therefore, the amount of salt excreted in the urine increases. The process works the other way as well. The less the salt intake, the greater the amount of sodium reabsorbed back into the blood, and the amount of salt excreted in the urine decreases.
 * Re-absorption**, by definition, is the movement of substances out of the renal tubules back into the blood capillaries located around the tubules. Substances reabsorbed are water, glucose and other nutrients, and sodium (Na+) and other ions. Re-absorption begins in the proximal convoluted tubules and continues in the loop of Henle, distal convoluted tubules, and collecting tubules Let's discuss for a moment the three main substances that are reabsorbed back into the bloodstream.



**What is the difference between Filtration and Reabsorption?**

 * Filtration takes place initially and then the reabsorption.
 * Filtration occurs in the renal capsule whereas reabsorption takes place in the other parts of the nephrons.
 * After filtration, a diluted filtrate is produced, and after reabsorption, it gets concentrated.
 * Reabsorption occurs selectively whereas, in the filtration, most of the molecules are filtered (not very selective).

 Read more: [|http://www.differencebetween.com/difference-between-filtration-and-vs-reabsorption/#ixzz1w7LS54zc]

__ Blood pressure regulation: __


Osmoregulation is the process which regulates the concentration and osmotic pressure of blood by regulating the water contents of blood plasma. It is an important process as excessive loss of water may cause dehydration whereas excess of water intake may dilute the body fluids. Our bodies need to constantly replenish the water in our bodies that is lost by perspiration, urine, and breathing. An excessive level of water will call osmosis, causing cells to burst. Hypothalamus maintains a steady level of water in the body. If there is too little water in your blood, the hypothalamus signals the pituitary gland to produce ADH (Anti-Diuretic Hormone), which stops the removal of water from the blood in the kidneys. Your blood water level returns to normal.




 * __Kidney working with other Organ Systems:__**

**Parathyroid Hormone**
Elevated levels of phosphorus in kidney patients indirectly cause the skeletal system to become weakened. Impaired kidneys lose the ability to remove phosphorus from the blood which causes serum phosphorus levels to increase. Since phosphorus is involved in the regulation of calcium, high blood levels of phosphorus cause calcium to drop. If calcium levels drop, the parathyroid glands in the neck secrete parathyroid hormone which pulls calcium from the bones to compensate. This gradually and silently weakens the bones.

**Circulatory, Nervous and Digestive Systems**
There are some things in our body that can't be used and may even be dangerous to your body. They need to be rid of. The job of the excretory system is to get rid of that waste. The Excretory System interacts with your Digestive System as they both work with the Nervous System in both conscious and unconscious ways. While digestion goes on without your thoughts, eating, urinating, and defecating is under your control. The undigested food remains are expelled outside the body. The large intestine & anus are the last two organs related to the Digestive System. Solid waste is filtered out by the digestive system. It also works with the Circulatory System as it carries blood around the body to function. All of our blood runs through our kidneys every day. There is an artery and a vein that runs into and out of each kidney to take the blood there and back. Without the excretory system, the other parts of the body would eventually be poisoned by waste.

**The Endocrine System**
The endocrine system controls the hypothalamus that contains cells that are sensitive to the amount of water in your blood stream. The pituitary gland is then signaled to release a hormone called the anti-diuretic hormone. ADH molecules are also told by the hypothalamus and go to the kidneys which then slow down the removal of water.

**__Diseases related to the kidneys:__**

Chronic kidney disease (CKD) means that your kidneys are damaged and can't filter blood as they should. This damage can cause wastes to build up in your body. It can also cause other problems that can harm your health. Diabetes and high blood pressure are the most common causes of CKD. Treatment may include medicines to lower blood pressure, control blood glucose, and lower blood cholesterol. CKD can get worse over time. CKD may lead to kidney failure. The only treatment options for kidney failure are dialysis or a kidney transplantation. You can take steps to keep your kidneys healthier longer:
 * Chronic kidney disease**
 * Choose foods with less salt (sodium)
 * Keep your blood pressure below 130/80
 * Keep your blood glucose in the target range, if you have diabetes

Over time, diabetes can damage the filtering units and blood vessels within the kidneys. In some cases, kidney failure may occur. Diabetic kidney disease can take many years to develop, and often the person does not know his/her kidneys are failing. Other forms of kidney problems, such as infections, nephritis, or kidney stones, can be more serious in the diabetic person.
 * Diabetes**
 * What is diabetic kidney disease?**

Take care of urinary tract/kidney infections quickly. Symptoms for these may include: • Frequent need to urinate • Burning during urination • Severe pain in abdomen or lower back • Blood in the urine • Headache, fever and chills
 * I am diabetic. What can I do to lower my risk of developing kidney disease?**

Treatment is available for people whose diabetes causes total kidney failure. There are three treatment options available:
 * What treatment options exist for kidney failure?**


 * Hemodialysis.** This is the circulation of the patient's blood through an artificial kidney, which then removes waste and excel water from the body.
 * Peritoneal dialysis.** A plastic tube is surgically placed through the patient's abdominal wall. Sterile fluid is run through this tube into the abdominal cavity. Waste and excess fluids pass from the blood vessels lining the cavity into the fluid. The fluid is then removed and replaced with new sterile fluid.
 * Transplantation.** This involves transplanting a kidney from a close relative of the patient. Or the patient can receive a kidney and/or pancreas from someone who has died. Transplantation has several advantages, including increased independence and fewer kidney-related diet restrictions

The success of treatment for diabetic kidney failure through dialysis and transplantation can vary. Diabetes will continue to affect the eyes, heart, and other areas of the body. This may affect how you respond to treatment. Therefore, your overall health will have a significant effect on the outcome of treatment. Often, once you are stabilized, you can continue to enjoy many of the same things you did before your diagnosis.
 * What are the results of treatment for kidney failure?**

<span style="background-color: #ffffff; color: #000000; display: block; text-align: left; text-decoration: none;">**__Facts:__**
 * 1. The kidneys have a higher blood flow than even the brain, liver or heart.
 * 2. The kidneys reabsorb and redistribute 99% of the blood volume and only 0.1% of the blood filtered becomes urine.
 * 3. Kidney stones are an accumulation of mineral salts and mostly combined with calcium which can lodge anywhere along the course of the urinary tract.
 * 4. Refined carbohydrates and sugar help the body make kidney stones.
 * 5. Sugar will stimulate the pancreas to release insulin. This causes extra calcium to be excreted in the urine. . . alas, kidney stones.
 * 6. An excess of milk or antacids may cause kidney stones.
 * 7. Each kidney is about 4 ½ inches long.
 * 8. Each kidney weighs approximately 4 to 6 ounces.
 * 9. The kidneys of a newborn baby are about 3X larger in proportion to body weight as in the adult.
 * 10. The volume of urine excreted daily varies from 1000 to 2000 ml (averaging 1500 ml). 1000 ml (milliliters) = 1 liter.

__**Vocabulary**__:

 * =====**Excretion:** The process of eliminating or expelling waste matter.=====
 * **Kidney:** Each of a pair of organs in the abdominal cavity of mammals, birds, and reptiles, excreting urine
 * **Nephron:**Each of the functional units in the kidney, consisting of a glomerulus and its associated tubule
 * **Bowman's capsule:**A double-walled, cup-shaped structure around the glomerulus of each nephron of the vertebrate kidney. It serves as a filter to remove organic wastes, excess inorganic salts, and water.
 * **Glomerulus:**A tuft of capillaries situated within a Bowman's capsule at the end of a renal tubule in the vertebrate kidney that filters waste products from the blood and thus initiates urine formation.
 * **Efferent arterioles:**Directed away from a central organ or section.
 * **Proximal tubule:** Any small tubular structure esp one in an animal as in the kidney
 * **Distal tubule:** A portion of kidney nephron between the loop of Henle and the collecting duct system.
 * **Collecting duct:**The collecting duct system collects the urine from the nephron and send it to the ureter.
 * **Filtration:**The renal process whereby fluid in the blood is filtered across the capillaries of the glomerulus and into the urinary space of Bowman's capsule.
 * **Re-absorption:** The process by which the nutrients are being absorbed into the blood
 * **Secretion:** The process of releasing a substance, especially one that is not a waste, from the blood or cells
 * **Anti-diuretic hormone:** A hormone secreted by the pituitary gland that raises blood pressure, and reduces excretion of urine.
 * **Aldosterene:** A hormone that stimulates absorption of sodium by the kidneys and so regulates water and salt balance.
 * **Liver:** A large, reddish-brown, glandular vertebrate organ located in the upper right portion of the abdominal cavity that secretes bile and is active in the formation of certain blood proteins and in the metabolism of carbohydrates, fats, and proteins.
 * **loop of Henle:**The segment of the nephron of a vertebrate kidney that is situated between the proximal and distal convoluted tubules. It plays a role in the transport of ions and water and the concentrating of urine
 * **Ureter:** One of the two tubes that carry urine from the kidneys to the bladder.
 * **Urethra:**The duct by which urine is conveyed out of the body from the bladder, and which in male vertebrates also conveys semen.
 * **Urine:** The waste product secreted by the kidneys that in mammals is a yellow to amber-colored, slightly acid fluid discharged from the body through the urethra.
 * **Bladder:** A membranous sac in humans and other animals, in which urine is collected for excretion.
 * **Renal artery:** An artery originating from the abdominal aorta and supplying the kidneys and adrenal glands and ureters.
 * **Renal vein:** A vein which returns blood from the kidney to the vena cava.
 * **Adrenal gland:** A small endocrine gland located on top of the kidney
 * **Metabolic wastes:**Metabolic wastes or excretes are substances left over from excretory processes, which cannot be used by the organism

__**References**__

 * http://www.stockmedicalart.com/medicalartlibrary/urinary-system-diagram.html
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 * http://library.thinkquest.org/28807/data/excr11.htm
 * http://www.differencebetween.com/difference-between-filtration-and-vs-reabsorption/
 * http://answers.yahoo.com/question/index?qid=20080121111010AAeTZGD
 * http://www.tutorvista.com/content/biology/biology-iv/excretion/role-kidney-osmoregulation.php
 * <span style="background-color: #ffffff; color: #000000; display: block; text-align: left; text-decoration: none;">http://www.livestrong.com/article/177937-what-body-systems-do-the-kidneys-work-with/
 * http://wiki.answers.com/Q/How_does_the_Excretory_system_work_with_other_body_systems
 * http://wiki.answers.com/Q/How_does_the_kidneys_work_with_the_endocrine_system#ixzz1w7U9I58a
 * http://www.nlm.nih.gov/medlineplus/chronickidneydisease.html
 * http://www.healthinsite.gov.au/content/internal/page.cfm?ObjID=00012984-0340-1D2D-81CF83032BFA006D
 * http://www.nwkidney.org/kidneyInformation/kidneyDiseases/diabetes.html
 * http://www.drstandley.com/facts_kidneys.shtml