Excretion Flashcards
Excretion Definition
The process by which metabolic waste products and toxic materials are removed from an body of an organism
Metabolic Waste
Metabolic waste products can be damaging and harmful if they are accumulated in the body
Metabolism (anabolic and catabolic)
Anabolic: Formation/ synthesis of larger molecules
E.g Photosynthesis, glucose to glycogen
Catabolic: Break down of larger molecules/ oxidation of food
E.g Deamination (urea), Respiration (carbon dioxide and water)
Ultrafiltration
Caused by high blood pressure and the membrane around the glomerular blood capillaries acts like a filter. Membrane that wraps around the glomerular blood capillaries is the basement membrane
Why is the blood in glomerulus under high pressure?
The blood comes directly from the heart via the aorta and renal artery.
Efferent arteriole leaving the glomerulus is much narrower than the afferent arteriole entering. Therefore the increased pressure forces filtrate out of the glomerulus into the capsule.
Why must the basement membrane be present?
It will only allow water and small molecules to pass through. High blood pressure in glomerulus forces water and small molecules (glucose, amino acids, mineral salts and urea) out of the glomerulus into the Bowman’s Capsule. Red blood cell, platelets and large molecules such as proteins e.g Albumin, fats are retained in the glomerular capillaries.
Selective reabsorption
Is needed to absorb back useful materials into the bloodstream as the filtrate pass through the tubule
Proximal Convulated Tube
Water (osmosis)
Glucose, amino acids and minerals salts (diffusion and active transport)
Loop of Henle
Water (osmosis)
Distal Convulated Tube
Water (osmosis)
Mineral Salts ( Diffusion and active transport)
Collecting Duct
Water (osmosis)
Why are kidneys important?
It allows the excretion or removal of metabolic waste products e.g urea, excess water and mineral salts.
It also allows osmoregulation to help maintain water potential in blood.
Maintain blood pressure.
Normal Constitution of Urine
Total: 100g
96.0g of water, 1.8g of mineral salts (mainly sodium chloride), 2g of urea, 0.2g of other nitrogenous substances
Factors of composition of urine
Intake of water, salt and protein rich food
Health Status: Kidney failure, Diabetic
Osmoregulation
Changes in water detected by the hypothalamus. Hypothalamus produces an anti-diuretic hormone and is secreted by the pituitary gland into blood. Increase in ADH will increase the permeability of cells in the walls of the collecting duct to water, hence more water will be reabsorbed from the collecting duct into blood capillaries.
