Urinary System: Structure, Function and Osmoregulatory Function of Kidney


Urinary System of  Humans

The excretory system of humans (peoples) is also known as the urinary system. It is framed of one couple of kidneys, a couple of ureters, a urinary bladder, and urethra. Kidneys filter blood to create urine and the ureters convey urine from kidneys to the urinary bladder. the bladder briefly stores urine until it is discharged from the body. The urethra is the pipe that conveys urine from the urinary bladder to the outside of the body.


Structure of Kidney

Kidneys are dark-red, bean-shaped organs. Every kidney is 10 cm long, 5 cm wide and 4 cm thick (dense) and weighs about 20 grams. They are placed/put against the back wall of the abdominal/stomach cavity just below the diaphragm, one on either side of the vertebral column. They are protected/secured by the last 2 ribs. The left kidney is somewhat higher than the right (privilege).

The curved side of the kidney faces the vertebral column/line. There is a gloom, known as hilus, near the center of the concave area of the kidney. This is the territory of the kidney via which ureter leaves the kidney and various structures including blood vessels (veins), lymphatic vessels and nerves enter and leave kidney locales.

The longitudinal segment of the kidney indicates two regions. The renal cortex is the outer/external piece of the kidney and it is dark red in color. The renal medulla is the internal/interior piece of the kidney and is light red in color. The renal medulla consists of several cone-shaped areas known as renal pyramids. Renal pyramids venture into a funnel-shaped pit known as the renal pelvis, which is the base of the ureter.


The working unit/component of the kidneys is known as nephron. There are over (more than) one million nephrons in every kidney. There are two pieces of a nephron (uriniferous tubule) i.e. renal corpuscle (blood cell) and renal/nephritic tubule.

The renal corpuscle is not rounded and has two parts/sections i.e. glomerulus and Bowman’s capsule.

The glomerulus is a network of vessels while Bowman’s capsule is a cup-shaped texture that encases glomerulus.

The renal tubule is the piece of nephron which begins after Bowman’s container. Its first part is known as the proximal tangled tubule. The next part is U-molded and is known as the loop/circle of Henle. The last part of the renal tubule is the distal tangled tubule.

The distal tangled tubules of numerous nephrons open in a solitary gathering conduit. Many gathering conduits combine to shape a few hundred papillary channels that channel into the renal pelvis.


Function of Kidney

The primary function of the kidney is pee arrangement, which takes place in three stages.

i)  Pressure Filtration

When blood enters the kidney through the renal artery, it goes to numerous arterioles, and after that to the glomerulus. The pressure/weight of blood is very/extremely high and thus the greater part of the water, salts, glucose, and urea of blood is constrained out of glomerular capillaries. This material passes into the Bowman’s capsule and is now known as glomerular filtrate.

ii)  Selective Re-absorption

In this stage, about 99% of the glomerular filtrate is reabsorbed into the blood capillaries surrounding the renal tubule. It occurs via osmosis diffusion and dynamic transport. Some water and most of the glucose is reabsorbed from the proximal tangled tubule. Here, salts are reabsorbed by dynamic transport, and after that water follows by osmosis. The dropping limb of the circle of Henle permits the reabsorption of water while the ascending limb of Loop of Henle allows the reabsorption of salts. The distal tangled tubule again permits the reabsorption of water into the blood.


iii)  Tubular secretion

Various ions, creatinine, urea, etc. are secreted/emitted from the blood into the filtrate in the renal tubule (nephritis). This is done to keep up the blood at an ordinary pH (7.35 to 7.45).
After the above-mentioned stages, the filtrate present in renal tubules is known as urine. It moves into gathering ducts and then into the pelvis.


Osmoregulatory Function of Kidney

Osmoregulation is defined as the regulation of the grouping of water and salts in blood and other body fluids/liquids. Kidneys perform a significant role in osmoregulation by regulating the water substances of blood. It is a significant procedure as excessive loss of water focuses the body liquids whereas excess intake of water dilutes them.
When there is surplus water in body liquids, kidneys form dilute (hypotonic) urine. For this motive, kidneys filter more water from glomerular vessels into Bowman’s capsule. Likewise, less water is reabsorbed and bottomless weaken urine is produced. It brings down the volume of body liquids to typical.


At the point when there is a deficiency of water in body fluids, kidneys filter less water from glomerular vessels and the rate of reabsorption of water is expanded. Not so much filtration but rather more reabsorption produce a little amount of concentrated (hypertonic) urine. It builds the volume of body fluids/liquids to ordinary. This entire procedure is below hormonal control.

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