Urinary system of humans
The excretory system of humans is also called urinary system.it is formed of one pair of kidney,a pair of ureters,a urinary bladder and a urethra.kidney filter the blood to produce urine and the ureter carry urine from kidney to urinery bladder.
the bladder temporarily store urine until is realesed from the body.urethre is a tube that carry urine from urinary bladder to the out side of body.
Structure of kidney.
Kidney is a dark-red bean shaped organ.each kidney is 10Cm long,5Cm wide and 4 kg thick and about 120 gram weight.they are located against the back wall of renal cavity just below the diaform,one on either side of vertebral column.the left kidney is little higher than the right one.
The concave side of kidney faces vertibral column.there is a depression called hilus,near the centre of the concave area of kidney.this area of kidney through which ureter keaves kidney and other structure including blood vessels,lymphatic vessels and nerves enter and kidney leaves.
The lingutidnal section of kidney shoes two reigons.the cortex is outer part of kidney and its dark red in colour.renal medulla is the inner part of kidney and is pale red in colour.renal pyrmaid projects into a funnel-shaped cavity called renal pelvis, which is base of ureter.
The functional unit of kidney is called nepron.there are over one million neprons in each kidney.there are two parts of each nepron i.e renal corposcle and renal tubule.
The renal corpuscle is not tubular and has two parts i.e glomerulus and bowman,s capsule.
Glomerulus is a network of cappilaries while bowman,s capsule is cup-shaped structure enclosed glomerulus.
The renal tubule is part of nepron which starts after bowman,s capsule .its first portion is called the proximal convluted tubule.next portrion is u-shaped and is called the loop of henle.the last portion of renal tubule is the distal convolated tubule.
The distal convolated tubules of many neprons open in a single collecting duct join tegether to form several hundred papillary ducts which drain into renal pelvis.
Function of kidney.
The main function of kidney is urine formation,which takes place in three steps.the first one is pressure filtration.when blood enter the kidney via renal artery,it goes to many arterioles,and then to the glomerulus.
the pressure of blood is very high so most of the water ,salt,glucose and urea of blood is forced out of glomerulus cappilaries.this material passes into the bowman,s capsule and is now called glomerular filtrate.
The second step is selective re- absoption.in this step about 99% of the glomerular filtrate is reabsorbed into the blood cappilaries surronding the renal tubule.
it is occuring through osmosis ,diffusion and active transport.some water and most of the glucose is reabsorbed from the proximal convoluted tubule.here,salt are re- absorbed by active transport and then water follows by osmosis.
The descending limb of loop of henle allows the re- absoption os the salts.the distal convoluted tubuke again allows the re- absoption of water into the blood.
The third part is the tubular secretion.different ions,creatine,urea etc,aresecreated from the blood into the filtrate in renal tubule.this is done to maintain blood at a normal ph.
After the above mentioned steps,the filtrate present in renal tubule is known as urine.it moves into collecting ducts and then into pelvis.
Osmoregulatory function of kidney
Osmoregulation is defined as the regulation of the concentration of water and salts in the blood and other body fluids.kidneys play important role in the osmoregulation by regulating the water contens of blood .
it is an important process as excressive loss of water concentration of the body fluids where as excess take of water dilutes them.
When there is excess water in body fluids,kidneys forms dilutes(hypotonic) urine.for this purpose,kidney filters more water from the glomerlus cappilaries into the bowman,s capsule.
Similarly less water is re- absorbed and abundant dilute urine is produced.it is brings dowm the volume of body fluids to normal.
When there is shortage of water in body fluids,kidney filters less water from glomerular cappilaries and the rate of re –absoption of water is increased.
less filtration and more re-absoption produce small amount of concentrated (hypertonic)urine.it increases the volume of the body fluid to normal.this whole process is under the hormonal control.
This mean the whole urinary system is dependent on kidney.
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published to @the biotech centre
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