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
What is urine made up of?
Water, urea, ions
What occurs at the loop of Henle?
Concentrates urine by transporting salts into blood by active transport, therefore causing some water to move into the blood by osmosis.
Further water is removed from filtrate (not related to osmoregulation)
How is the PCT adapted to absorb glucose?
Folded membrane to increase surface area
Many mitochondria to provide ATP for active transport of glucose
Describe the order of the nephron
Glomerulus, bowman’s capsule, PCT, loop of Henle, (DCT), collecting duct
What links the kidney to the bladder?
Ureter
What links bladder to outside of body?
Urethra
Describe order of ureter, urethra, kidneys and bladder
Kidney, ureter, bladder, urethra
