Excretion Flashcards
What is excretion?
Removal of metabolic waste from the body that is by products or unwanted substances from normal cell processes
The liver
All cells carry out same function
Regenerates itself
Body can’t store amino acids or proteins so it is processed by liver where toxic groups are removed and useful energy is preserved
Processing of amino acids in the liver: deamination
Toxic amino group removed
Amino acid+ oxygen — Keto acid + ammonia
Processing of amino acids in the liver: formation or urea
Ornithine cycle
Ammonia + carbon dioxide — urea + water
Urea compared to ammonia
Urea is less soluble and less toxic than ammonia so it can be safely transported in blood to kidneys
What is the function of a nephron
Remove excess of water waste and other substances from the blood
Regulate water levels
Regulate electrolyte levels
What is ultrafiltration?
Fluid from the blood is pushed into the bowmans capsule
Why does the afferent arteriole have a larger lumen than the efferent arteriole
Creates high pressure forcing liquid out
Stages of excretion
Ultrafiltration
Tubular reabsorption
Countercurrent multiplication
Distal convoluted tubule
Collecting duct (osmoregulation)
Ultrafiltration: what 3 layers does the barrier between the blood in the capillary and the linen of the bowmans capsule consist of?
Endothelium of capillary
Basement membrane
Epithelial cells of bowmans capsule (podocytes)
What does the glomerular filtrate contain?
Water Amino acids Glucose Urea Inorganic ions Waste products
Where does tubular reabsorption take place
The proximal convoluted tubule
Process of tubular reabsorption
Active transport move sodium ions from surrounding cells to the blood
Co transport of glucose and amino acid’s with sodium as the concentration gradient has been established
All glucose and amino acid’s are reabsorbed
Water potential in plasma is lower than filtrate so water moves by osmosis from nephron into blood
Where does counter current multiplication take place
Loop of Henle
Process of counter current multiplication
Salts are actively pumped out of wider part of ascending limb into surrounding tissue
Water potential is reduced in tissues
Water leaves descending limb by osmosis into tissues
Filtrate in the thin part of ascending limb is more concentrated so salts diffuse out passively
Results of counter current multiplication
Consistently higher salt concentration in tissues so more water is reabsorbed
The kangaroo rat
Has a longer Medulla and a long loop of Henle so more water can be reabsorbed as it’s a steep concentration gradient
What happens at the distal convoluted tubule?
Active reabsorption of sodium ions followed by osmotic movement of water
What happens at the distal convoluted tubule when the salt conc is low in the body?
Aldosterone stimulates reabsorption of sodium by making it permeable to salts
Osmoregulation in the collecting duct
Walls not permeable to water
High salt conc in tissues so water reabsorbed making urine more concentrated
What happens in the collecting duct if dehydrated?
ADH released to make duct permeable to water
