Structure and function of a nephron

  

     STRUCTURE AND FUNCTION OF A NEPHRON

 Nephrons are excretory or functional units of the kidneys. Each nephron is formed of two parts . 

 1 Bowman's capsule.

 2 nephric tubule. 

                                   

 

                  

                                             1  BOWMAN'S CAPSULE

                                           /

                NEPHRON {. 

                                           \   2 NEPHRIC TUBULE 

                                                            |

                                                         P C T

                                                             |

                                             LOOP OF. HENLE

                                                             | 

                                                          D C T 

1 Bowman's capsule 

                                           It  is a double - walled cup present in the renal cortex . It is lined by a thin and semipermeable epithelium of flat cells. In the cavity of bowman's capsule, there is a group of blood capillaries, called glomeerulus, formed by the division of afferent arteriole ( a branch of renal artery). Bowman's capsule and glomerulus are collectively called Malpighian body or renal corpuscle. Glomerulus act as an ultrafilter and is the site of fertilization under pressure called ultrafiltration . In this, larg amount of water along with certain useful compounds and certain harmful wastes are filtered out into bowman's capsule. The filtrate so formed is called glomerular or nephric filtrate. 

2 . Nephric tubule. 

                                   It is long and coiled and is formed of three parts: 

  a) proximal convoluted tubule (P C T) . 

           It is the convoluted part of the nephron, and lies in the renal cortex. It is the main site of selective reabsorption of sodium, calcium, glucose, amino acids. etc, from the nephric filtrate. 

  b) loop of Henle . 

            It is a U - shaped tubular structure present in the renal medulla. It is formed of two limbs: thin walled descending limb and thick - walled ascending limb. Descending limb is permeable to water but impermeable to minerals like sodium chloride, but ascending limb is impermeable to water but permeable to sodium chloride. It concentrates the urine. 

  C) Distal convoluted tubule (D C T) 

          It is  a convoluted part and lies in the renal cortex. It opens in the collecting tubule. Most of water from the nephric filtrate is reabsorbed through the wall of DCT  and collecting tubule. 

        OSMOREGULATION

1 Definition  .

                       OSMOREGULATION is the process of regulating the concentration and osmotic pressure of blood by regulating the water contents of blood plasma . 

 2 during reduced water amount in the body fluid 

             Reduced osmotic pressure of blood

    

                                             ↓

Detected by osmoreceptors present in hypothalamus of brain.

                                           ↓

              Pituitary gland inhibition

                                            ↓

         ADH secration reduced (anti - diuretic hormone) 

                                            ↓

 

         Water permeability of DCT and collecting

         Tubules decreased. 

                                           ↓

        Dilute ( hypotonia) urine , more volume 

                                          ↓ 

         Osmotic pressure rises to normal  reverse 

Occurs when there is increase of osmotic pressure of blood.

       Haemodialysis ( Artificial kidney) 

1 need of haemodialysis 

                        Kidneys are excretory and osmoregulatory in function and expel the nitrogenous wastes , excess of water, pigments, etc, so as to maintain homeostasis inside the body . A number of causes decrease the activity of the kidneys called renal insufficiency or renal failure, eg. Certain pathogenic infections, injury or obstructed blood flow . Renal insufficiency usually results in accumulation of toxic nitrogenous wastes such as urea , leading to uraemia which is generally fatal . So there is need of an artifical kidney to remove such toxic compounds from such patients .

2 Defination. 

                Haemodialysis is the process of removing unwanted and toxic substances from blood while adding desirable substances into the blood through a semipermeble membrane of a dialysing membrane . 

3. Mechanism 

                       Blood from an artery of the patient is passed through a dialysing cellophane memberne of a dialysing machine, called artificial kidney , after cooling it to 0 °c and mixing with an anticoagulant ( heparin) . Dialysing membrane has pores equal to those of glomerular capillaries and acts as a superfine strainer . The dialysing tube is immeesed in a solution, called dialysate , which is isotonic to blood plasma but is devoid of nitrogenous wastes. So the wastes like urea , uric acid creatinine, excess of H +, etc diffuse across the dialysing membrane in the dialysing dolution . Blood from dialysing machine is returned to the body through a vein after warming it to body temperature and mixing with an antiheparin. Artifical kidney differs from the functioning of normal kidney in the fact that no reabsorption occurs during haemodialysis. 

                                   

    4. Advantages

           1. Patient can lead more or less normal life. 

            2. It provides time for recovery from reversible kidney damage . 

            3 . No equipment is fitted inside the body. 

            4 . Bacteria and viruses cannot pass through it.