Question

Human kidneys can produce urine nearly four times more concentrated than the initial filtrate formed .Explain the mechanism of production of hyper-tonic urine ?

Answer 1

Answer:

Human kidneys can produce urine nearly 4 times concentrated than the initial filtrate formed.Â

Osmoreceptors in the body are activated by changes in blood volume, body fluid volume and ionic concentration. ... While aldosterone acts mainly at the renal tubules and stimulates the reabsorption of Na+ and water and excretion of K+ and phosphate ions. This, in turn, helps in the production of hypertonic urine.

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Answer 2

$\fbox{ What is Excretion ?\ }$

$\star$ Excretion is a biological process, which plays a vital role by eliminating toxins and other waste products from the body. In plants and animals, including humans, as part of metabolism, a lot of waste products are produced. Plants usually excrete through the process of transpiration and animals excrete the wastes in different forms such as by urine, sweat, faeces and tears. Among all these, the usual and the main form of excretion is urine

$\fbox{Urine Formation}$

$\star$ Waste is excreted from the human body, mainly in the form of urine. Our kidneys play a major role in the process of excretion. Constituents of normal human urine include 95 percent water and 5 percent solid wastes. It is produced in the nephron, which is the structural and functional unit of the kidney. Urine formation in our body is mainly carried out in three phases namely

1.    Glomerular filtration
2.    Reabsorption
3.    Secretion

$\fbox{Mechanism of Urine Formation}$

Glomerular Filteration

$\rightarrow$ Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers.

Blood is filtered in such a way that all the constituents of the plasma reach the Bowman’s capsule, except proteins. Therefore, this process is known as ultrafiltration.

reabsorption

$\rightarrow$ Around 99 percent of the filtrate obtained is reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport.

secretion

$\rightarrow$ The next step in urine formation is the tubular secretion. Here, tubular cells secrete substances like hydrogen ion, potassium ion, etc into the filtrate. By this process, the ionic, acid-base and the balance of other body fluids are maintained. The secreted ions combine with the filtrate and form urine. The urine passes out of the nephron tubule into a collecting duct.

Urine

The urine produced is 95% water and 5% nitrogenous wastes. Wastes such as urea, ammonia, creatinine are excreted in the urine. Apart from these, the potassium, sodium and calcium ions are also excreted.

osmoregulation

$\rightarrow$  Osmoregulation is the process of regulating body fluids and its compositions. It maintains the osmotic pressure of the blood and helps in the homeostasis. This is why it is recommended to consume more water about 2-3 litres, which help in the proper functioning of our kidneys. For example, we consume lots of water during summers, but still, we urinate fewer times in summers than winters and the concentration of the urine is also more. The reason is that we lose lots of water from our body in summers through sweating. Thus, to maintain the fluid balance in the body our kidneys reabsorb more water.

$\star\textsc{hope it helps}\star$