Explain the mechanism of formation of concentrated urine in mammals.
The Henle’s loop and vasa recta play a significant role in producing a concentrated urine in mammals. A counter current is formed by the movement of the filtrate in the two limbs of Henle’s loop in opposite directions. The flow of blood through the two limbs of vasa recta is also in a counter current’ pattern. An increased osmolarity towards the inner medullary interstitium is maintained by the proximity between the Henle’s loop and vasa recta, as well as the counter current in them i.e., from 300 m Osmol L -1 in the cortex to about 1200 m Osmol L -1 in the inner medulla. This gradient is mainly caused by NaCl and urea. NaCl is transported by the ascending limb of Henle’s loop which is exchanged with the descending limb of vasa recta. NaCl is returned to the interstitium by the ascending limb of vasa recta. Similarly, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule. This special arrangement of Henle’s loop and vasa recta that facilitates the transport of substances is called counter current mechanism. This mechanism helps to maintain a concentration gradient in the medullary interstitium. Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine).
Fill in the blanks appropriately.
Organ Excretory wastes
(a) Kidneys ______________
(b) Lungs ______________
(c) Liver ______________
(d) Skin ______________
Match the items of column I with those of column II.
Column I Column II
(a) Ammonotelism (i)Birds
(b) Bowman’s capsule (ii)Water reabsorption
(c) Micturition (iii)Bony fish
(d) Uricotelism (iv)Urinary bladder
(e) ADH (v)Renal tubule
Mention the substances that exit from the tubules in order to maintain a concentration gradient in the medullary interstitium.
Fill in the gaps.
(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.
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 the proximal convoluted tubule.
Sort the following into actively or passively transported substances during reabsorption of GFR. glucose, aminoacids, nitrogenous wastes, Na+, water
The glomerular filtrate in the loop of Henle gets concentrated in the descending limb and then gets diluted in the ascending limb. Explain.
How does tubular secretion help in maintaining ionic and acid-base balance in body fluids?
The following abbreviations are used in the context of excretory functions, what do they stand for?
(a) ANF (b) ADH
(c) GFR (d) DCT
Name the following.
(a) A chordate animal having flame cells as excretory structures.
(b) Cortical portions projecting between the medullary pyramids in the human kidney.
(c) A loop of capillary running parallel to the Henle’s loop.
Complete the following:
(a) Urinary excretion = Tubular reabsorption +Tubular secretion ________
(b) Dialysis fluid = Plasma ________
What is the procedure advised for the correction of extreme renal failure? Give a brief account of it.
Aquatic animals generally are ammonotelic in nature whereas terrestrial forms are not. Comment.
Draw a labelled diagram showing reabsorption and secretion of major substances at different partsof the nephron.