Excretion Flashcards
Definition of excretion
Removal of toxic waste products which have been made by cells.
Waste product of lungs
Carbon dioxide
Waste product of skin
Sweat that contains water, urea and salts
Waste product of kidneys
Urea
Where is urea made?
Liver
Describe how ultrafiltration occurs
Higher pressure in capillaries forces small molecules (glucose, urea, salts, amino acids) out of the capillaries of the glomerulus and into the Bowman’s capsule. Forms glomerular filtrate. Larger molecules such as proteins or red blood cells are unable to fit across the capillary walls so stay in the blood.
Composition of the glomerular filtrate
Glucose, amino acids, urea, salts (water)
Where does selective reabsorption take place?
Proximal convoluted tubule (first loop after bowman’s capsule)
How is the proximal convoluted tubule adapted for its function?
Many mitochondria to provide ATP (energy) for active transport.
Folded membrane to increase surface area
How does selective reabsorption work?
Useful substances (glucose, amino acids) move by active transport (using energy back into the bloodstream. Some water and salts also move back into the bloodstream
Describe how the body responds when the body is dehydrated
Osmoregulation
Hypothalamus detects low water in blood
Pituitary releases ADH
ADH increases permeability of collecting duct
More water is reabsorbed back into the blood
Less water enters urine, making it more concentrated
What gland is ADH released by?
Pituitary gland
