Describe the structure and functioning of nephrons?

Nephrons are the functional units of the kidneys responsible for the filtration of blood and the formation of urine. Each kidney contains approximately one million nephrons, which consist of two main parts: the renal corpuscle and the renal tubule.

Renal Corpuscle

 

a. The renal corpuscle consists of two main structures: the glomerulus and the Bowman's capsule.
b. The glomerulus is a network of capillaries where blood filtration occurs. It is surrounded by the Bowman's capsule, a double-walled capsule that collects the filtrate.
c. Blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole. The high pressure in the glomerulus forces water, ions, and small molecules to pass through the capillary walls into the Bowman's capsule, forming the filtrate.

Renal Tubule

 

a. The filtrate collected in the Bowman's capsule enters the renal tubule, which is divided into several segments: the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct.
b. The proximal convoluted tubule reabsorbs most of the filtered water, ions, and nutrients back into the bloodstream through active transport and passive diffusion.
c. The loop of Henle consists of a descending limb and an ascending limb. It plays a crucial role in maintaining the concentration gradient of the interstitial fluid in the kidney.
d. The distal convoluted tubule regulates the concentration of ions such as sodium, potassium, and calcium through active transport and secretion.
e. The collecting duct receives filtrate from multiple nephrons and is responsible for adjusting the final composition of urine based on the body's hydration status and electrolyte balance.

Functioning of Nephrons

 

a. Filtration: Blood enters the glomerulus under high pressure, and small molecules are filtered through the capillary walls into the Bowman's capsule, forming the filtrate.
b. Reabsorption: The filtrate passes through the renal tubule, where most of the water, ions, and nutrients are reabsorbed back into the bloodstream to maintain body homeostasis.
c. Secretion: Some substances, such as drugs and metabolic waste products, are actively secreted from the bloodstream into the renal tubule for excretion in urine.
d. Concentration of Urine: The concentration of urine is regulated by the hormonal control of water reabsorption in the collecting duct, primarily through the action of antidiuretic hormone (ADH).

In summary, nephrons function to filter blood, reabsorb essential substances, secrete waste products, and regulate the concentration of urine, thereby maintaining overall fluid and electrolyte balance in the body.