Question

Describe the structure of the renal tubule with neatly labelled diagrams.

Answer 1

Hint: Renal tubules consist of a cup and the long tubular parts. It does not include the tuft of capillaries. The function of the renal tubule is absorption of water, glucose and sodium back to blood.

Complete Answer:
Nephron or Uriniferous tubules is the structural and functional unit of the kidneys. Each nephron has two parts. Glomerulus and Renal tubule.

A) Glomerulus: It is the tuft of capillaries formed by branches of afferent arterioles which is a branch of renal artery and then joins to form efferent arterioles.

B) Renal tubules: It begins with Bowman’s capsule which encloses glomerulus. The capsule further forms PCT (Proximal convoluted tubule), Henle’s loop and DCT (Distal convoluted tubule).
(i) Bowman’s capsule : It is a blind sac. It has a double membrane. Outer is parietal and inner is visceral. Both are made up of squamous epithelium. There is Bowman’s space between the two layers. The visceral layer has specialised cells known as podocytes. A podocyte has a number of interdigitated evaginations known as feet or pedicles. These act as filtration slits. It contains the Glomerulus.
(ii) Proximal Convoluted tubule : Lower part of Bowman’s capsule continues as PCT. It is lined by cuboidal epithelium and has microvilli to increase the surface area of absorption. Thus the cells are also very active. Hence it contains abundant mitochondria and food reserves for providing energy to perform work (Proximal-beginning). Vasa recta runs parallel to it.
(iii) Henle’s loop : It is a hair pin loop. It consists of two limbs. Descending limb that is continuation of PCT and ascending limb that continues as DCT. The two limbs are attached by U bend.
(iv) Distal Convoluted tubule : It is highly coiled and has less microvilli compared to PCT (Distal means end).

Functions of each part of Renal tubule:
1. Bowman’s capsule : This helps in Ultrafiltration
2. PCT : Nearly all the essential nutrients, 70-80 % of electrolytes and water are reabsorbed by this segment. PCT also maintains the pH and ionic balance of the body fluids by selective secretion of Hydrogen ions and ammonia into the filtrate and by absorption of bicarbonate ions into it.
3. Henle’s loop : The descending limb is permeable to water and the ascending limb is permeable to electrolytes.Thus the filtrate when entering the descending limb from PCT becomes more concentrated and then it becomes dilute in the ascending limb.
4. DCT : Conditioned absorption of sodium and water takes place in DCT. It also is responsible for reabsorption of bicarbonate ions.

Note: Bowman’s capsule and Glomerulus together is known as Malphigian Corpuscle. The Glomerulus is a tuft of capillaries. It is unique as it is formed from an arteriole (afferent) and continues as an arteriole (efferent).