Question

Identify the following structures and explain their significance in renal physiology?

1. Juxtaglomerular apparatus
2. Podocytes
3. Sphincters in the bladder

Answer 1

1) Juxtaglomerular apparatus: It is a specialized tissue in the afferent arteriole of the nephron that consists of macula densa and granular cells.

1. Action: The macula densa cells sense distal tubular flow and aspect afferent arteriole diameter.
2. Actions of Glandular cells: When there is a fall in glomerular blood flow it can activate Juxta glomerulus cells to release renin from the liver which converts angiotensinogen to angiotensin I.
3. Angiotensin converting enzyme converts angiotensin I to angiotensin II.
4. It stimulates Na+ reabsorption in the proximal convoluted tubule by vasoconstriction of the blood vessel and increases the glomerular blood pressure.

2) Podocytes:

1. The visceral layer of Bowman’s capsule is made of epithelial cells called podocytes.
2. The podocytes and the foot processes and the basement membrane of the glomerulus act as a filtering membrane.
3. Podocytes act in glomerulus filtration.

3) Sphincters in the bladder:

1. The sphincters of the bladder regulate urination.
2. When the bladder is full the stretching of the urinary bladder stimulates the CNS through the sensory neurons of the parasympathetic nervous system and brings about contraction of the bladder.
3. Somatic motor neurons induce the sphincters to close.
4. Smooth muscles contract results in the opening of the internal sphincters and relaxing the external sphincter.
5. The sphincter opens and the urine is expelled out.