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Here is a term paper on the excretory system.
Term Paper on Excretory System
Term Paper # 1. Excretory System in Human Beings:
The urinary system maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine. Other function includes regulating the concentration of various electrolytes in the body fluids and maintaining normal pH of the blood. Several body organs carry out excretion, but the kidneys are the most important excretory organ.
The primary function of the kidneys is to maintain a stable internal environment (homeostasis) for optimal cell and tissue metabolism. They do this by separating urea, mineral salts, toxins, and other waste products from the blood and conserving water, salts, and electrolytes that are essential for body functions.
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The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
I. Kidney:
The kidneys are a pair of bean-shaped, brown organs about the size of the human fist with the concave side having an entry for renal artery and exit for renal vein and convex shape on the outer side. They are covered by the renal capsule, which is a tough fibrous connective tissue.
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There are three major regions of the kidney are:
i. Renal cortex,
ii. Renal medulla and
iii. The renal pelvis.
The renal medulla contains pyramid shaped tissue called the renal pyramids, separated by renal columns. The ureters are continuous with the renal pelvis and are the very center of the kidney.
II. Ureters:
The ureters are two tubes that drain urine from the kidneys to the bladder. Muscles in the walls of the ureters send urine in small spurts into the bladder, (a balloon sac that allows temporary storage of urine). After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine.
The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allows the release of the urine that enters the urethra.
III. Urinary Bladder:
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It is a hollow, distensible, muscular and elastic organ which can hold upto 500- 530 ml of urine. When urine accumulates in the bladder, the stretch receptor sends signal to the brain and nerve impulse is sent back to the sphincter (at neck of the bladder), indicating it to relax the muscles and allow the urine to flow into urethra.
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IV. Urethra:
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The urethra is a muscular tube that connects the bladder with the outside of the body. The function of the urethra is to remove urine from the body.
V. Nephrons:
A nephron is the basic structural and functional unit of the kidney. The name nephron comes from the Greek word “nephros” meaning kidney. Its chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine.
Each nephron has its own supply of blood from two capillary regions from the renal artery. Each nephron is composed of an initial filtering component (the renal corpuscle) and a tubule specialized for reabsorption and secretion (the renal tubule). Glomerulus, Bowman’s capsule, Distal Convoluted tubule (DCT), Proximal convoluted tubule (PCT), Loop of Henley and collecting duct are its parts.
Urine Formation:
The kidney contains numerous filtering units called nephrons in the renal cortex region. The blood enters the kidney and is filtered through the Glomerulus and Bowman’s capsule. Then it passes through PCT, Loop of Henley and DCT where reabsorption and removal of elements occur.
Then the concentrated filtrate containing water, sodium chloride, potassium, bicarbonate, creatinine and urea enters into ureters that open into the urinary bladder. The urinary bladder excretes the urine through the urethra when urged by the pressure build up in the bladder.
Artificial Kidney:
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The artificial kidney is used when the kidney stops working due to injury, infection or less blood supply. The artificial kidney contains a dialysis tank with a fluid that is similar to the blood and has same osmotic pressure but no nitrogenous waste.
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The blood of the patient passes through the numerous tubes of the artificial kidney. The tubes are semi-permeable in nature and allow the diffusion of nitrogenous waste from the blood into the fluid in the tank. The purified blood is then pumped back using a pump.
The process of removing the nitrogenous waste from the blood using artificial kidney is called as dialysis. If the nitrogenous waste accumulated in the body is not excreted, it turns poisonous and may even lead to death. In a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, due to reabsorption by kidneys actual fluid urinated is only a liter or two a day.
Term Paper # 2. Excretory System in Plants and Animals:
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Excretory System in Plants:
The process of excretion in plants is different, and the wastes that are to be excreted are also of different types. Oxygen (day) and Carbon dioxide (night) are waste generated during photosynthesis are eliminated through leaves.
Excess of water is released by transpiration through stomata in leaves. The other waste such as dead cells are stored in vacuoles and are lost as dried leaves or excreted as gums and resins from Xylem tissue.
Illustration:
What artificial measures are adopted for removing the accumulated waste products from the blood in patients suffering from renal failure or nephritis?
Solution:
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The process is called Haemodialysis and the apparatus used in this process is artificial kidney. In Haemodialysis, the blood of the patient is taken out from the main artery and cooked to 100°C. Then an anticoagulant (heparin) is mixed with it and pumped into the apparatus.
Inside the kidney, the blood flows through tubes bounded by cellophane membrane, which is permeable to only small molecules like urea, uric acid, creatinine and mineral ions. The dialyzing fluid used in the apparatus is a salt solution isotonic to blood plasma.
Thus, the blood flowing through the channels or tubules containing wastes like urea, uric acid, creatinine, etc. diffuses out in the dialyzing fluid across the cellophane membrane. This process is called dialysis.
Finally, the blood coming out of artificial kidney is warmed to body temperature and mixed with anti-heparin to restore its normal coagulability and then pumped into the body of the patient through a vein.
Excretory System in Animals:
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.
