Question

(a)Ascending limb of Henle’s loop is …………. to water whereas the descending limb is ………… to it.
(b)Reabsorption of water from distal parts of the tubules is facilitated by hormone ………….
(c)Dialysis fluid contains all the constituents as in plasma except …………..
(d)A healthy adult human excretes (on an average) ………………. gm of urea/day.

Answer 1

Hint: The structural and functional unit of kidneys is the nephron which is further divided into many parts such as the proximal convoluted tubule, Loop of Henle, distal convoluted tubule, etc. There are many hormones such as aldosterone which regulate the functioning of the tubules of the nephron.

Complete Answer:
Let us look at the statements individually.
(a)Ascending limb of Henle’s loop is impermeable to water whereas the descending limb is permeable to it.
The loop of Henle’s consists of an ascending limb, descending limb, and a hairpin. The descending limb of the loop of Henle is permeable to water but impermeable to electrolytes and this concentrates the filtrate as water moves out from the limb as the filtrate moves down. Whereas the ascending limb is impermeable to water but permeable to electrolytes, this dilutes the filtrate as it moves upward.
(b)Reabsorption of water from distal parts of the tubules is facilitated by hormone vasopressin or antidiuretic hormone (ADH).
Vasopressin is a hormone produced by the hypothalamus and released by the posterior pituitary. The process of urine formation is known as diuresis and vasopressin reduces the loss of water through urine by increasing water absorption from later parts of the tubules, hence it is preventing the formation of urine. Thus, it is also known as the antidiuretic hormone.
(c)Dialysis fluid contains all the constituents as in plasma except nitrogenous wastes.
Haemodialysis is the process of purification of blood by using an artificial kidney as the real kidney is no longer able to perform properly. The blood is pumped into a dialyzing unit which has a fluid containing all the constituents as in plasma except nitrogenous wastes, thus the nitrogenous wastes flow from the blood into the dialyzing fluid according to the concentration gradient.
(d)A healthy adult human excretes (on an average) 25-30 gm of urea/day.
On average 1-1.5 liters of urine is excreted by an adult human in one day. And through this urine 25-30 grams of urea is released out.

Note:
-Improper secretion of ADH leads to the diminished ability of the kidney to reabsorb water back resulting in water loss and dehydration. Such a condition is known as DIabetes insipidus.
-The process of release of urine is known as micturition and it is controlled by neural mechanisms known as the micturition reflex.
-The presence of glucose in the urine is known as glycosuria whereas the presence of ketone bodies is known as ketonuria and it can be indicative of diabetes mellitus.