Question 1

Describe the structure and functioning of nephrons.


Nephron is a unit of structure and function in a kidney. Nephron is composed of two parts renal cortex and renal medulla. Renal cortex is composed of Bowman’s capsule, Proximal convoluted tubule and Distal convoluted tubule and on the other hand, renal medulla is composed of Loop of Henle. 

Structure of a nephron:

Nephron is a long tubule length varying from 35-55 mm and having four regions with their different anatomical and physiological features.

  1. Bowman’s capsule:- is a large, having double walled cup present at the starting of the nephron structure and lies in the renal cortex. Capsule encloses a cluster a blood vessels known as glomerulus. The Bowman’s capsule and the glomerulus (group of almost 50 capillaries) together forms the Renal corpuscle or also known as Malpighian body. The inner wall of the Bowman’s capsule has wide gaps called slit pores. So, the basement membrane of the capillary walls is present in between the blood in the glomerulus capillaries, which helps in the ultrafilteration.

  2. Proximal convoluted tubule (PCT):- it is twisted part extends from the Bowman’s capsule and lies in the renal cortex. It wall or membrane consists of single layer of columnar cells having microvilli on the free surface, lies on the basement membrane.

  3. Loop of Henle:- it is U-shaped lies in the renal medulla that is the lower part of the nephron. It is consist of thick and thin descending limb extended from the proximal convoluted tubule and an ascending limb which joins the Distal convoluted tubule.

  4. Distal convoluted tubule:- it is greatly twisted and lies in the renal cortex. It extends from the loop of Henle and straight goes and opens up into the collecting tubule. Distal convoluted tubule have special sensitive region formed by the cellular modifications and the afferent arteriole occurs at their contact site. This mechanism plays the important role in the glomerulus filtration rate.

  5. Collecting ducts:- they are the large tubes, receives the collecting tubule of several nephrons. They pass into the renal medulla and join each other and forms the large Duct of Bellini. They run across the medullary pyramids and opens up into the calyces and extends to the pelvis part.

Functions of the nephron:-

  1. Nephron helps in the removal of the nitrogenous wastes (urea and the uric acid) from the blood.

  2. Nephron regulates the fluid balance or the water balance by eliminating the excess water from the blood by converting them into the urine. So, balancing of fluid regulates the blood pressure.

  3. It also removes the pigments, drugs, poison, extra salt and vitamins from the blood. Ionic balance should be constant for the normal functioning of the nerves and the muscles.

  4. It helps in the ultrafiltration process performed by the Bowman’s capsule which filters out the acidic substances from the blood to maintain the basic hydrogen ion concentration, i.e, 7.4.

  5. The blood around the nephron travels back into the body organs through the renal vessels which are non- toxic and the the waste that is collected by the ultrafiltration technique travels down by crossing the collecting duct to the bladder and get released through the urethra. 

By eliminating the acidic substances, excess water, minerals and salts and the nitrogenous waste from the blood; this maintain the volume, composition, pH and the osmotic pressure of the body fluids known as fluid homeostasis.

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