Question

Indicate whether the following statements are true or false.
(a) Micturition is carried out by a reflex.
(b) ADH helps in water elimination, making the urine hypotonic.
(c) Protein- free fluid is filtered from blood plasma into the Bowman's capsule.
(d) Henle's loop plays an important role in concentrating the urine.
(e) Glucose is actively reabsorbed in proximal convoluted tubules.

Answer 1

Hint:-The major function of kidneys is to rid the body of waste materials that are either ingested or produced by metabolism. It also controls the volume and electrolyte composition of body fluids. Each kidney in a human contains about one million minute tubular structures called nephrons. Each nephron is capable of forming urine. A nephron is made up of a bowman's capsule, glomerulus, proximal and distal convoluted tubules, and a loop of Henle.

Complete Answer:-
Micturition is the process by which the urinary bladder empties when it becomes filled. When there is no urine in the bladder, the intravesical pressure is about zero, but by the time some urine has collected, the pressure rises. As the bladder fills, many micturition contractions begin to appear. These are the result of a stretch reflex initiated by sensory stretch receptors in the bladder wall. This is called a micturition reflex. Thus, statement (a) is true.
ADH is the hormone that is responsible for the absorption of water from the nephrons. Thus, ADH increases the volume of water in the blood which leads to the excretion of concentrated (hypertonic) urine. Thus, statement (b) is false.
As urine formation begins with the filtration process, blood plasma is filtered into Bowman's capsule. Blood proteins, being negatively-charged molecules, do not filter out from the blood into the Bowman's capsule. Thus, statement (c) is true.
Urine is concentrated by the mechanism called the countercurrent mechanism. It takes place in Henle's loop. In this mechanism, water and salt concentrations are altered to produce concentrated urine. Thus, statement (d) is true.
The proximal convoluted tubule is the part of the nephron which is responsible for maximum reabsorption of the substances. Essential substances like glucose and some amino acids are actively reabsorbed from PCT. Thus, statement (e) is true.

Note:- Urine formation occurs in three major steps- ultrafiltration, tubular reabsorption, and tubular secretion. The blood plasma is filtered through the filtration membrane into the Bowman's capsule. This filtrate then travels through a proximal convoluted tubule. Here, maximum essential substances are reabsorbed into the blood. Then this filtrate enters Henle's loop. Here it gets concentrated and finally, it reaches the distal tubule in which some excretory substances are secreted back to the filtrate from the blood. Finally, the urine formed is released by the micturition reflex.