Excretion in human beings
Excretion in human beings
Excretory system-
Excretory system in human beings (also known as urinary system) consists of a pair of kidneys, a pair of ureters ,a urinary bladder and a urethra .
The two kidneys are located towards the back of the lower part of the abdominal cavity, one on either side of the backbone. Left kidney is slightly larger and placed a little higher than the right kidney. The blood from aorta enters into kidneys via the renal arteries and returns to the posterior Vena cava via renal veins. Urine formed in the kidneys passes by a pair of ureters to the bladder where it is stored until it is released via the urethra.
Structure and function of kidneys-
There are two kidneys in humans each kidney is purplish- brown, slightly flattened and shaped somewhat like rajma Bean. It is about 12 centimetre long, about 6 CM thick and wait about 150 grams. Internally a kidney is made of numerous microscopic excretory units called nephrons. Single kidney contains about a million nephrons each approximately 3 centimetre long.
The most important function of kidney is filtration of blood to excrete the waste products of metabolism. If these waste products mainly nitrogenous waste such as urea and uric acid are not removed from the blood they will start accumulating to unbearable toxic levels. Besides filtering out the waste products the kidneys perform other functions such as osmoregulation, secretion of erythropoietin, enzyme - renin and conversion of inactive form of vitamin D to the active form. The kidney filter about 190 litres of blood to produce 0.9 to 1.9 litres of urine daily.
Structure and function of nephrons -
Each nephron has a cup shaped upper end called Bowmen's capsule. It contains a bundle of blood capillaries called glomerulus. The blood entering into the glomerulus carries waste materials which are filtered out in the Bowmen's capsule. Filtration is possible because the walls of glomerular capillaries and Bowmen's capsule are very thin and are selectively permeable. This property of membranes allows water and small molecules in the blood to pass through them.
Once the waste material is filtered out the blood free from these waste materials goes into the renal veins from where it goes into the heart through posterior vena cava. The fluid containing waste material is forced out of the glomerular capillaries in the bowman's capsule. The filtered out fluid is known as glomerular filtrate which contains sodium, potassium and chloride ions, glucose and amino acids along with urea, uric acid and a large amount of water.
Bowmen's capsule leads into a long tubular structure into which the glomerular filtrate moves away. The tubular structure is convolued, twisted, folded and has U- turn before meeting the collecting duct. During the flow of glomerular filtrate in this long tube reabsorption of useful materials and secretion of certain substances takes place. The materials reabsorbed are glucose and amino acids sodium ion, potassium ion and chloride ion, water etc. The fluid reaching the end of collecting duct is called urine. The urine is fluid and dissolved waste substances excreted by the kidneys. Human urine contains about 95% water and 5% nitrogenous substances (mostly urea and uric acid etc) and a few other substances. Finally the urine moves through the ureter and collects in the urinary bladder till thrown out of the body through urethra and urinary opening.
Excretory system-
Excretory system in human beings (also known as urinary system) consists of a pair of kidneys, a pair of ureters ,a urinary bladder and a urethra .
The two kidneys are located towards the back of the lower part of the abdominal cavity, one on either side of the backbone. Left kidney is slightly larger and placed a little higher than the right kidney. The blood from aorta enters into kidneys via the renal arteries and returns to the posterior Vena cava via renal veins. Urine formed in the kidneys passes by a pair of ureters to the bladder where it is stored until it is released via the urethra.
Structure and function of kidneys-
There are two kidneys in humans each kidney is purplish- brown, slightly flattened and shaped somewhat like rajma Bean. It is about 12 centimetre long, about 6 CM thick and wait about 150 grams. Internally a kidney is made of numerous microscopic excretory units called nephrons. Single kidney contains about a million nephrons each approximately 3 centimetre long.
The most important function of kidney is filtration of blood to excrete the waste products of metabolism. If these waste products mainly nitrogenous waste such as urea and uric acid are not removed from the blood they will start accumulating to unbearable toxic levels. Besides filtering out the waste products the kidneys perform other functions such as osmoregulation, secretion of erythropoietin, enzyme - renin and conversion of inactive form of vitamin D to the active form. The kidney filter about 190 litres of blood to produce 0.9 to 1.9 litres of urine daily.
Structure and function of nephrons -
Each nephron has a cup shaped upper end called Bowmen's capsule. It contains a bundle of blood capillaries called glomerulus. The blood entering into the glomerulus carries waste materials which are filtered out in the Bowmen's capsule. Filtration is possible because the walls of glomerular capillaries and Bowmen's capsule are very thin and are selectively permeable. This property of membranes allows water and small molecules in the blood to pass through them.
Once the waste material is filtered out the blood free from these waste materials goes into the renal veins from where it goes into the heart through posterior vena cava. The fluid containing waste material is forced out of the glomerular capillaries in the bowman's capsule. The filtered out fluid is known as glomerular filtrate which contains sodium, potassium and chloride ions, glucose and amino acids along with urea, uric acid and a large amount of water.
Bowmen's capsule leads into a long tubular structure into which the glomerular filtrate moves away. The tubular structure is convolued, twisted, folded and has U- turn before meeting the collecting duct. During the flow of glomerular filtrate in this long tube reabsorption of useful materials and secretion of certain substances takes place. The materials reabsorbed are glucose and amino acids sodium ion, potassium ion and chloride ion, water etc. The fluid reaching the end of collecting duct is called urine. The urine is fluid and dissolved waste substances excreted by the kidneys. Human urine contains about 95% water and 5% nitrogenous substances (mostly urea and uric acid etc) and a few other substances. Finally the urine moves through the ureter and collects in the urinary bladder till thrown out of the body through urethra and urinary opening.
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