Parts of Human Excretory system MCQ - Practice Questions with Answers

• As urine is formed, it drains into the calyces of the kidney, which merge to form the funnel-shaped renal pelvis in the hilum of each kidney. 
• The renal pelvis narrows to become the ureter of each kidney.
• The ureters are approximately 30 cm long. 
• These are composed of transitional epithelium. 
• These are retroperitoneal and run along with the wall of the abdominal cavity.
   

• It is situated in the pelvic cavity and is lined with the transitional epithelium.
• The bladder is partially retroperitoneal (outside the peritoneal cavity) with its peritoneal-covered “dome” projecting into the abdomen when the bladder is distended with urine.
• The muscular layer of the urinary bladder is called the detrusor muscle.
• The detrusor muscle is made up of three layers of smooth muscles as inner and outer layers of longitudinal fibres and middle layer of circular fibres.
• The area where the bladder and urethra join contains internal sphincter formed by the modification of the circular muscles. 
• It allows urine into the bladder but prevents reflux of urine from the bladder back into the ureter.
• Internally, the bladder has a triangular area called the trigone formed by three openings - two openings through which the ureters open into the bladder and one opening through which the urethra leaves the bladder.

• It is a canal-like structure which extends from the neck of the bladder and leads to the exterior.
• It is shorter in females and carries only urine. It opens by the urethral aperture in front of the genital aperture.
• In males, it is longer and opens at the tip of external genitalia by the urinogenital aperture. It carries both urine and sperm.
• In males, the urethra is 15-20 cm long while in females the urethra is about 4 cm long
   

Proximal Convoluted Tubule (PCT): 

• PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption.
• Nearly all of the essential nutrients and 70-80 percent of electrolytes and water are reabsorbed by this segment. 
• PCT also helps to maintain the pH and ionic balance of the body fluids by selective secretion of hydrogen ions, ammonia and potassium ions into the filtrate and by absorption of HCO3– from it.

Henle’s Loop:

• Reabsorption is minimum in its ascending limb. However, this region plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid.
• The descending limb of the loop of Henle is permeable to water but impermeable to electrolytes. 
• This concentrates the filtrate as it moves down. 
• The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. 
• Therefore, as the concentrated filtrate passes upward, it gets diluted due to the passage of electrolytes to the medullary fluid.

Distal Convoluted Tubule (DCT):

• Conditional reabsorption of Na+ and water takes place in this segment. 
• DCT is also capable of reabsorption of HCO3– and selective secretion of hydrogen and potassium ions and NH3+ to maintain the pH and sodium-potassium balance in the blood.

Collecting Duct: 

• This long duct extends from the cortex of the kidney to the inner parts of the medulla.
• Large amounts of water could be reabsorbed from this region to produce concentrated urine. 
• This segment allows passage of small amounts of urea into the medullary interstitium to keep up the osmolarity. 
• It also plays a role in the maintenance of pH and ionic balance of blood by the selective secretion of H+ and K+ ions.