Class 10, Science, Chapter-5, Lecture-6, Excretion (Notes)
EXCRETION:
The biological process involved in removal of the excess or toxic wastes from the body is called Excretion.
Two vital functions of the kidneys:
- To remove toxic wastes from the body.
- To control water balance, and levels of mineral ions in the body.
FORMATION OF URINE:
In human being, blood enters into the kidney through renal artery.
Kidney contains excretory units called nephrons.
Ultrafiltration:
Blood is filtered, from the blood capillaries into Bowman’s Capsule of nephrons.
Selective Absorption:
The useful products in the filtrate are reabsorbed by collecting capillaries and the
nitrogenous wastes are drained into the ureter and finally collected in urinary bladder.
Thus, urine is formed.
Steps of urine formation (in detail, not for CBSE Exam):
The Glomerular Filtration:
- Each kidney contains over 1 million nephrons.
- Glomerulus is a network of capillaries surrounded by a Bowman’s capsule.
- As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane.
- The filtration membrane, allows water and small solutes to pass but blocks blood cells and large proteins
- This glomerular filtration begins the urine formation process
Reabsorption:
- The Glomerular filtrate contains waste, but also some vital substances such as essential ions, glucose, amino acids, and smaller proteins.
- When the filtrate exits the glomerulus, it flows into a duct in the nephron called the renal tubule.
- As it moves, the vital substances and some water are reabsorbed through the tube wall into adjacent capillaries.
- This reabsorption of vital nutrients Moves Nutrients and Water Back into the Bloodstream.
- Reabsorption helps in osmoregulation.
Secretion:
- Waste ions and hydrogen ions pass from the capillaries into the renal tubule.
- The secreted ions combine with the remaining filtrate and become urine.
- The urine flows out of the nephron tubule into a collecting duct.
- It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.