Question

Describe the structure of the nephron in the kidney. How does it function?

Hint:

- The nephron is essential for regulating blood pressure, electrolyte balance, and waste removal. - The process of urine formation in the nephron is highly efficient, ensuring the body retains vital nutrients and removes toxins.

Answer 1

Structure and Function of the Nephron

The nephron is the
structural and functional unit of the kidney responsible for filtering blood, removing waste products, and regulating water and electrolyte balance. Each kidney contains approximately
one million nephrons.

Structure of the Nephron

1. 
   Bowman’s Capsule:
   A cup-shaped structure surrounding the
   glomerulus (a network of capillaries). It collects the filtrate from the blood. The process of
   glomerular filtration occurs here — water, salts, glucose, and waste products are filtered into the Bowman’s capsule.
2. 
   Proximal Convoluted Tubule (PCT):
   Reabsorbs most essential substances like glucose, amino acids, and salts back into the blood. About
   65 of filtered sodium and water are reabsorbed here.
3. 
   Loop of Henle:
   A U-shaped tube with descending and ascending limbs. - Descending limb: Permeable to water, not salts. 
   - Ascending limb: Impermeable to water, actively transports salts out. It helps create a
   concentration gradient in the medulla for water reabsorption.
4. 
   Distal Convoluted Tubule (DCT):
   Regulates sodium, potassium, and calcium levels, and helps maintain pH balance. Further reabsorption occurs here under the influence of
   aldosterone.
5. 
   Collecting Duct:
   Collects urine from multiple nephrons and carries it to the renal pelvis. It reabsorbs water under the control of
   antidiuretic hormone (ADH) to form concentrated urine.

Functions of the Nephron

1. 
   Filtration:
   Blood enters through the
   afferent arteriole into the glomerulus. Small molecules (water, salts, glucose, urea) pass into Bowman’s capsule, while larger molecules like proteins and blood cells remain in the bloodstream.
2. 
   Reabsorption:
   Occurs mainly in the PCT, Loop of Henle, and DCT. Useful substances such as glucose, amino acids, and most water are reabsorbed into the blood.
3. 
   Secretion:
   Certain ions (H⁺, K⁺) and drugs are secreted into the filtrate from the blood in DCT and collecting duct.
4. 
   Excretion:
   The final filtrate becomes urine and passes through the collecting duct → renal pelvis → ureter → urinary bladder → outside the body.

Diagram