What is excretion? Explain the mechanism of urine formation with a well labeled diagram of Nephorn.
Answers
excretion:Excretion is a process by which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell. Excretion is an essential process in all forms of life.
The process of urine formation in kidneys include the following steps:
(i) Glomerular filtration - Urine formation begins when the blood is filtered by the glomerulus and enters the Bowman's capsule and the glomerular filtrate is formed. The afferent arteriole entering the glomerulus is wider than the efferent arteriole in diameter. This increases the blood pressure within the glomerulus helps in the filtration. Glomerular filtrate is formed of all blood constituents except corpuscles and plasma proteins.
(ii) Tubular reabsorption - When the glomerular filtrate comes to the proximal tubule then the essential nutrients are reabsorbed. Glucose, amino acids, water, ions like sodium, potassium, chloride, bicarbonate, magnesium, calcium are reabsorbed from the glomerular filtrate. When the filtrate finally comes to the collecting duct ADH (anti-diuretic hormone) acts and reabsorbs the excess water and decreases the urine volume.
(iii) Tubular secretion - When the glomerular filtrate is in the proximal tubule cretinine, uric acid are secreted in it. When the filtrate goes to the distal part urea, potasium ion and some hydrogen ions are secreted in it.
and labelled diagram is attached.............
excretion is the removal of nitrogenous waste from body.
nephron is the filtration unit of kidney.
steps of urination
- ultra filtration
- tubular reabsorbption
- tubular secretion