What is excretion?
The removal of waste products from the body
What are kidneys?
They are excretion organs
What are the kidney’s 3 main roles?
- Remove urea from the blood (urea is excess amino acids produced by the liver)
- Adjusting salt levels in the blood
- Adjust amount of water in the blood
(Do this by filtering substances out of the blood using HIGH PRESSURE, and reabsorb only the useful stuff. What is left outside the blood is called urine.)
What are nephrons?
Also known as kidney tubules, it is found in the kidney
Where does blood get filtered?
In the nephrons
What 3 steps happen when blood is passing through the kidney?
- Ultra-filtration
- Re-Absorption
- Release of waste
How does Ultrafiltration occur in the kidney?
When blood passes through the kidney, the first step is ultrafiltration- p99
- High pressure in the nephron squeezes out water, urea, salts and glucose out of the blood and into the capsule.
- Blood is inside the glomerulus, just under the glomerulus is the capsule where ALL the substances where pushed into.
- The membrane between the glomerulus and the capsule acts like a filter (therefore big molecules like proteins and blood cells are NOT squeezed out of the glomerulus, but stay in the blood)
Remember that all of these (glomerulus and capsules) is from a single nephron!
How does Reabsorption occur in the kidney?
When blood passes through the kidney, the second step is reabsorption - p99
- After all substances where squeezed out into the capsule and were travelling into the nephron ‘‘coiled tubule’’ (relax, its just a tube), useful substances are being reabsorbed.
- All the sugars are being reabsorbed through diffusion (involves active transport - p79)
- Enough salt is being reabsorbed
(also using active transport - forcing salt to diffuse from the coiled tubule to the capillary network [capillary network is connected to the glomerulus] using energy from respiration) - Sufficient water is reabsorbed (this depends on the level of ADH Hormone
How does the release of wastes occur in the kidney?
When blood passes through the kidney, the third step is releasing waste - p99
- When the capillary network absorbed all its useful substances, the excess is thrown out
- Excess salt, water and other substances that has not been reabsorbed continue down the nephron (coiled tubule)
- go into the ureter and down the bladder as urine.
