Chapter 6 life process class 10th

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            Excretion

The process of elimination of waste products mainly the nitrogenous wastes from the body is known as  excretion.
The removal of wastes it is necessary to maintain the water and salt percentage of the blood by osmoregulation which is defined as the process of maintaining the right amount of water, salt and proper ionic balance in the body. 
Both excretion and osmoregulation go side by side and the organs responsible for these processes form the urinary system or excretory system.

Need for excretion

The excretory processes play an important role in maintaining:
• The internal environment of the body constant, i.e., homeostasis.
• Osmotic relationship between blood, lymph and tissue fluids.
• Acid base balance in the body.

Excretion in Human Beings

All body organs which help the animal in excretion of soluble nitrogenous waste product, excess of salts, excess of water and other metabolic wastes collectively constitute excretory system.
The excretory system of human beings consists of two bean- shaped kidneys located in the abdomen two excretory tubes or ureters, a urinary bladder and a urethra.

1. Kidneys  
     The kidneys of human beings are two in number. They are reddish brown, bean-shaped organs present just below the stomach protected by last two ribs. They are present at different levels. 
Each kidney is about 10cm long, 5cm wide and 3cm thick. 
Its outer margin is convex and inner margin is concave. In the middle of inner concavity is present a notch called hilus or hilum.
The blood in our body is constantly passing through our kidneys. 
The function of kidneys is to remove the poisonous substances like urea, other waste products and excess of water from the blood and excrete them in the form of urine.


2. Ureters
      These are slender, whitish tubes, one emerging from hilus of each kidney. Each ureter is about 30 cm long and 4 mm in diameter.
The ureters carry urine from kidney to urinary bladder.

3. Urinary bladder
   It is a pear shaped muscular sac situated in the lower region of abdominal cavity. Its size depend on the amount of urine present in it. The lower part of urinary bladder is guarded by two sphincters which normally remains contracted but relax to pass out urine from the bladder. 

4. Urethra
     The urethra starts from lower part of urinary bladder. It opens to the outside by urinary opening. The urine collected in the urinary bladder passes through urethra from where it is thrown out of the body through urinary opening.

Functional unit of kidney-- Nephron

Each kidney contains about one million highly
 Coiled very minute structures called uriniferous tubules or nephrons. All nephrons are held together by connective tissue in which there are present a large number of vessels, lymph Vessels and nerve fibres.
The nephron has a cup -shaped bag at its upper end which is called Bowman's capsule.
The lower end of Bowman's capsule is like a tube and is called tubule.
 One end of the tubule is connected to urine collecting duct of the kidney. Bowman's capsule contains a clump of thin blood capillaries known as glomerulus. 
The function of glomerulus is to filter the blood passing through it while that of nephron tubules is to allow the selective reabsorption of the useful substances like glucose, amino acids, salts and water into the blood capillaries.


Kidney failure and technology for survival
Sometimes the kidneys of a person may stop working. It may be due to some Infection in kidneys or restricted blood supply to the kidneys.
Complete failure of the kidneys allow the urea and other waste products to build up in the blood.
The best long term solution for kidney failure is the kidney Transplant.
The damaged kidney is removed and a matching kidney is transplanted in its place by surgery. If a kidney transplant is not possible due to some reasons, then the patient with kidney failure is treated periodically on a kidney machine. This kidney machine is also known as Artificial kidney.
Artificial kidney:  Artificial kidney is a device to filter the blood of patients whose both of the kidneys are completely damaged. In case of kidney failure the various mineral salts and toxic substances goes on accumulating in the blood which can even lead to the death of patient. 
Artificial kidney is also called as dialysis machine.
The artifical kidney consists of a cellophane tube, suspended in a circulating path and fluid having the same composition as normal blood except that no nitrogenous wastes are present. Blood of the patient is pumped from one of the arteries into the cellophane tube which is attached with the vein on the other end. Substances present in the blood and bath fluid diffuse through the pores in the cellophane tube, according to their concentration gradient. 
Thus the artificial kidney works like a kidney expect that there is no reabsorption involved in it.



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