what is excretion
= process of removing metabolic waste products, toxic substances and excess substances from the body
why is excretion important
-> chemical / metabolic activities produce harmful / toxic substances, metabolic waste products / excretory products, that need to be removed by the body
-> prevents harmful substances from building up in the body and causing harm
what is ultrafiltration
= process by which small molecules are filtered out of the blood by the glomerulus into the Bowman’s capsule to form glomerular filtrate
process of ultrafiltration
- afferent arteriole wider than efferent arteriole -> creates high blood pressure in glomerulus -> more efficient ultrafiltration
- blood plasma forced out of glomerular blood capillaries into Bowman’s capsule
- filtered blood plasma known as glomerular filtrate
-> contains small molecules such as salts, water, glucose, amino acids and waste products such as urea
-> forced out into Bowman’s capsule
features of glomerulus
- is a knot or network of glomerular blood capillaries -> provides large surface area for filtration process
- glomerular blood capillaries have walls one-cell thick + tiny pores in capillary wall
- glomerular blood capillaries covered by thin selectively permeable membrane that only allows very small soluble molecules or ions to pass through -> impermeable to red and white blood cells, platelets and large molecules such as proteins that are too large to pass through pores of glomerular blood capillaries -> left in efferent arteriole after ultrafiltration
what is selective reabsorption
= process occurring mainly in proximal convoluted tubule in which useful substances that the body needs are reabsorbed back into blood capillaries
process of selective reabsorption
- all glucose and amino acids are reabsorbed by active transport from proximal convoluted tubule to blood capillaries
- most water is reabsorbed by osmosis from proximal convoluted tubule to blood capillaries
- most mineral salts are reabsorbed by facilitated diffusion and active transport from proximal convoluted tubule to blood capillaries
- anything not reabsorbed, waste products such as urea and excess water and mineral salts, will form urine at the collecting duct and be passed out of the nephron
what is osmoregulation
= maintenance of a constant water potential by controlling the water potential and solutions concentration in the blood involving the kidneys and skin
water potential in blood
- dependent on amount of water and mineral salts in blood plasma
- controlled by antidiuretic hormone
◦ produced in hypothalamus
◦ released by pituitary gland
◦ increases water reabsorption in nephrons
