Artificial kidneys consists of a number of tubes with semi-permeable lining (selective permeable membrane). These tubes are suspended in a tank filled with dialysing fluid. The dialysing fluid has the same osmotic pressure as blood. This fluid does not contain nitrogenous wastes.
Working: The blood of the patient is passed through dialysing tubes. As blood passes through tubes, the waste products (e.g., urea) from the blood pass into dialysing fluid by diffusion. The purified blood is pumped back into the patient artificial kidney does filtration but no reabsorption, like kidney.
Fig. Dialysis
Lymph: Lymph is a circulatory fluid which also helps in transportation. This is also called tissue fluid. It is formed when some amount of plasma, proteins, inorganic salts and white blood cells pass through the pores present in the walls of capillaries into intercellular spaces in the tissues. The lymph similar to plasma except that tissue fluid is colourless and contains very less proteins.
From intercellular spaces, lymph goes into lymphatic capillaries. Lymphatic capillaries join to form large lymph vessels which finally open into larger veins. Lymph flows only in one direction, that is from tissues to heart through veins.
Arterial capillaries → Lymph in the intercellular spaces → Lymph capillaries → Lymph vessels → Larger veins → Heart
[Note: Lymphatic system consists of lymph capillaries, lymph vessels, lymph nodes and lymph glands (such as tonsils].
Functions of lymph
(i) Lymph carries digested and absorbed fats from small intestine to different tissues of the body.
(ii) It drains excess fluid from extra cellular space back into the blood.
(iii) Lymph protects tissues/cells from infection.
(iv) It also removes waste products from the body cells to drain into blood.
The urinary system of man is concerned with the excretion of nitrogenous wastes. It consists of:
(a) a pair of kidneys (b) ureters (c) urinary bladder and urethera.
Kidneys are bean shaped and are located in the abdominal region on either sides of vertebral column. From each kidney a tubular structure emerges which is called ureter. The
Fig. Excretory system in human beings
ureter travels downwards and open, the sac like structure in the urinary bladder, which stores urine. Besides the two openings of ureters in this bladder it has another opening which opens in the urethera. Urethera forms the passage of urine outside.
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