14. Why do birds and reptiles have salt glands, but mammals don’t? 15. What are
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Question
14. Why do birds and reptiles have salt glands, but mammals don’t?
15. What are some adaptations seen in desert rodents that enable them to live without ever drinking water?
16. What are the three main processes in urine formation?
17. How does counter current exchange in the two limbs of the Loop of Henle assist in urine formation?
18. How is the vasa recta another example of counter current exchange?
19. How is urine production regulated by the nervous and endocrine systems?
ps: please kindly answer all these questions
Explanation / Answer
Please find the answers below:
14. Why do birds and reptiles have salt glands, but mammals don’t?
Answer: Salt glands are the organs of secretion of excessive hypertonic concentrated salt solution from the body of bird/reptile. Since these organisms are devoid of a highly functional kidney system to expell out excess salts and retain sufficient amount of ions, they have developed these surface organs/glands to secrete out excessive salts. The salt glands are membranous structures found near the eye, nostril or mouth cavity of these animals. By the mechanism of active transport by Na/K-Cl co-transporters, excessive salts are eliminated out of the body. This also helps these organisms to consume high-salt containing diets such as sea-weeds, small sea-animals etc.
On the contrary, mammals are not evolved with any such organs because they have a highly advanced and functional renal system which excretes out excessive salts, ions and liquid waste out of the body in order to maintain ionic balance in the body. Hence, mammals do not require any salt gland in their body and are devoid of them.
15. What are some adaptations seen in desert rodents that enable them to live without ever drinking water?
Answer: There are some discrete renal adaptations seen in desert rodents which enables them to live without ever drinking water in high temperature environments. These renal adaptations are discussed as below:
16. What are the three main processes in urine formation?
Answer: Urine formation is the process by which essential fluid (water), ions and minerals are reabsobed in the kidney cells and the left-over liquid is excreted out of the body. It is comprised of three major processes:
1) Glomerular filtration: Glomerular filtration is defined as the siveing process in which the non-filterable components are left outside and the filterable components are filtered from the blood. The afferent artery brings the circulating blood towards the glomerulus. The glomerulus membrane functions lika a molecular sieve of very high surface area. The sieve of the glomerular membrnae filter out non-filterable parts like cells, components of cells and other large molecules and those which can be filtered such as water, ions etc enter the glomerular vessels and is called glomerular filtrate. The non-filterable part is taken away from the glomerulus by efferent arteriole.
2) Tubular reabsorption: The tubular reabsorption of water and essential ions takes place in the ascending and descending parts of loop of Henle of the nephron. Owing to its differential permeability to water and ions, the ascending and descending parts of loop of Henle are involved in differential absorption of water and ions. This finally maintains the fluid and ionic balance by regulating osmolarity of the filtrate with respect to the matrix fluid.
3) Tubular secretion: This is the final step in which all the tubular filtrate is collected and excreted out of the body by means of voluntary and involuntary muscular control via ureter and the urethra. The concentrated filtrate removed out of this channel is finally called urine.
17. How does counter current exchange in the two limbs of the Loop of Henle assist in urine formation?
Answer: The loop of Henle display counter current multiplier mechanism for generation of urine and reabsorption of water and salts. According to this mechanism, if two partially permeable tubes are flowing side by side, then the difference in their osmolarity drives the extraction of fluid/salts from each other across the osmotic gradinet so that an osmotic balance could be maintained.
The process of formation of urine is highly dependent upon differential permeability of ascending and descending loops of Henle in the nephron and their counter current filtration. The descending loop of Henle is slightly permeable to ions and urea whereas it is highly permeable to water. As a result, a very large amount of water is reabsorbed in the descending loop of Henle thus making the filtrate highly concentrated in nature. This makes this part of loop of Henle "concentrating" in nature.
On the other hand, the thin and thick parts of ascending loop of Henle are highly permeable to ions and urea whereas they are very less permeable to water i.e. water cannot move out of the tubule. This makes reabsorption of ions and urea from the urine so that an appropriate osmolarity of the blood could be maintained. Ions such as sodium, potassium, chloride, calcium, magnesium etc are reabsorbed from the filtrate at this part. This makes this part of loop of Henle "diluting" in nature.
Thus, the counter-current mechanism of ascending and descending loops of Henle play a critical role in maintaining urine formation.
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