For sustenance and maintenance of an organism, various life processes must go on at all times. These processes involve numerous biochemical reactions such as the synthesis of proteins, fats, carbohydrates, hormones, etc. The biological process involved in the removal of these harmful metabolic wastes from the body is called excretion. Let us discover more about the human excretory system.
These biochemical reactions of the many life processes lead to the production of harmful by-products which need to be removed from the body. Varied strategies are observed in different organisms for excreting out the metabolic waste from the body. In this module, let us learn about the process of excretion in human beings.
To understand the excretory system of human beings, we must be aware of its components.
The main components or organs of human excretory system are-
- A pair of kidneys, located in the lower part of the abdominal cavity, one on either side of the back bone.
- A pair of ureters, a urinary bladder, and…a urethra
- The blood from aorta enters into the kidneys via the renal arteries. And after filtration, it returns to the posterior vena cava via renal veins.
- The nitrogenous wastes such as urea and uric acid are removed from the blood in the kidneys through urine.
- The urine formed in the kidneys is passed through the pair of ureters into the urinary bladder where it is stored until being released through the urethra.
Human Excretory System: Process
We now know the reason for the production of urine. But are you aware of how urine is produced?
Let us try to understand the process of urine formation.
Urine is produced to filter out the waste products from the blood which is filtered out by the kidneys.
Each kidney possesses a cluster of thin-walled blood capillaries each of which is associated with the cup-shaped end of a tube called the bowman’s capsule that collects the filtered urine. These filtration units are called nephrons.
The nephrons are present in large numbers in each kidney. The blood entering the capillaries contains waste materials which are filtered out in the bowman’s capsule. The thin walls of these capillaries and the bowman’s capsule allow water and other small molecules in the blood to pass through them. The filtered blood then goes into the renal veins from where it reaches the heart through the posterior vena cava. The fluid containing the waste material is forced out of the capillaries in the bowman’s capsule.
The filtered out fluid contains sodium ions, potassium ions, chloride ions, glucose, amino acids along with other wastes such as urea, uric acid, and a large amount of water. The bowman’s capsule opens into a long tubular structure, thus passing the filtrate into it. As this filtrate flows along this long tube, some useful materials like glucose, amino acids, sodium, potassium and chloride ions, and water, etc. are selectively reabsorbed. The fluid reaching the end of the collecting duct is the urine.
Fact- Human urine contains about 95% water and 5% nitrogenous substances along with a few other substances.
Finally, the urine produced in each kidney moves into the urinary bladder through the ureters till it is released out of the body through the urethra. In this way, the human excretory system functions and removes the toxic metabolic wastes from the body.
Excretion : Renal failure and Dialysis
We all know that the kidneys are one of the most vital organs for our survival. They are involved in the removal of harmful nitrogenous wastes produced by our body during various metabolic processes.
Though the kidneys remain active throughout life, their efficiency gradually declines with the normal aging process. Infections, injury, or restricted blood flow to the kidneys are some other factors that are responsible for the decline in the normal functioning of kidneys.
What is a kidney failure?
Loss of the ability of kidneys to function properly is generally referred to as Kidney Failure.
In case of failure of both kidneys, immediate medical intervention is sought. There are two alternative treatments for kidney failure. First, a kidney transplant from a healthy person, and second, using an ‘artificial kidney’ to get rid of harmful metabolic wastes from the blood and maintain a normal level of water and mineral ions in the body fluids.
What is a dialysis?
With the help of an artificial kidney, blood is pumped out of the body into the artificial kidney. Heparin is added to the blood to prevent it from clotting. The blood then circulates slowly through the long tubes with semi-permeable lining, coiled in a tank filled with dialyzing solution.
During this passage, the waste products such as ions, small molecules, and water diffuse into the dialyzing fluid, thus leaving the blood purified. Molecules such as blood corpuscles, platelets, and proteins being too large, do not pass through the membrane. Finally, the purified blood is pumped back into the patient. This entire process of purifying blood using an artificial kidney is termed dialysis.