Homeostasis-control of blood water potential Flashcards
how is blood water potential controlled
by osmuregulation, controlled by hormones eg. ADH which affects the distal convoluted tubule and collecting duct
what is the effect of pressure on the formation of urine
- higher pa, more filterate produced, more urine produced
2. lower pa, less filterate produced, less urine produced
describe how the glomerular filterate is formed (5 marks)
- higher hydrostatic pressure in efferent arteriole, lower hydrostatic pressure in afferent arteriole
- difference in hydrostatic pressure forces out water, mineral ions, glucose and urea
- molecules pass through pores in the endothelium of the capilliaries. the basement membrane acts as filter and slits between podocytes
- proteins like antibodies and red blood cells are too large to pass through pores
- repelled by the basement membrane
how is the proximal convoluted tubule adapted for the reabsorption of glucose
- many mitochondria for the release of ATP for active transport
- microvilli on epithelieum cells to increase SA
- channel proteins for faciliated diffusion
explain how the body responds to a decrease in water potential
- detected by osmoreceptors in the hypothalamus; osmoreceptors shrink
- hypothalamus produces more ADH; the posterior pituitary gland secretes more ADH into the blood
- ADH travles to the kidneys and attaches to receptors on the collecting duct/ DCT
- receptors activate the phosphorylase enzyme, causes more vescicles containing aquaporins to fuse with the cell surface membrane
- so more water is absorbed from the DCT by osmosis
- so less water lost in urine, smaller volume; more concenterated
explain how the body responds to an increase in water potential
- detechted by osmorecptors in the hypothalamus ; osmoreceptors swell
- hypothalamus produces less ADH; posterior pituiary gland secretes less ADH into the blood
- less ADH travels to the kidneys and attaches to receptors on collecting duct/ DCT
- not as many phosphorylase enzymes activated; fewer vescicles containing aquaporins fuse with the cell surface membrane, decreasing permiability of the cells of the DCT to water
- less water absorbed from the DCT by osmosis
- so more water lost in ruine, larger volume; less concenterated
what is the role of the nephron in osmoregulation?
- where the glomerular filterate forms
- allows reabsorption of water and glucose by PCT
- maintains a Na+ gradient/ water potential gradient in the medulla by loop of henle
- allows reabsorption of water by DCT
describe the function of the PCT
- reabsorption of glucose and water
- Na+ actively transported out of the epithelial cells to the interstital space by Na+/K+ pump; lowers the Na+ conc inside of cell
- Na+ moves into the epithelial cells from the lumen of the PCT down its concenteration gradient by facilitated diffusion via co-transporter proteins. this brings in glucose against its concentration gradient; increasing the conc of glucose in cell
- glucose moves out of the cell into the interstital space then capilliary by faciliated diffusion, down the concentration gradient; lowers the water potential of the capillary
- water is reabsorbed by capillary via osmosis, down the water potential gradient
describe the function of the loop of henle
- maintains a gradient of Na+ ions in the medulla
- acts as a counter current multiplier
- Na+ actively transported out of the asending limb (AL), AL is impermiable to water so no water leaves by osmosis
- this increases solvent conc of Na+; lowers water potential of the medulla
- water moves out of the descending limb (DL) by osmosis into the medulla, water is reabsorbed by capilliaries, filterate becomes more concenterated down the DL, towards the hair pin structure
- Na+ diffuses into the DL, this recycles the Na+ in loop of henle; futher reducing water potential
how is water reabsorbed into the blood
- by the distal convoluted tubule and collecting ducts
- water moves out of the DCT and collecting duct by osmosis, down water potential gradient
- controlled by ADH, which changes the permiability of the walls of the DCT/collecting duct to water
how is the DCT adapted for the reabsorption of water
- cells of the DCT have receptors which are complementory to ADH
- ADH controls the permiabilty of the walls of the DCT
describe the structure of the loop of henle
- desending limb, thinner walls; permiable to water
- hair pin structure, where concentration of ions is highest
- ascending limb, thicker walls; impermiable to water
what is the osmolarity of the hair pin structure
1200 mosmo/L
what is the function of the DCT
helps maintain the pH of the blood by reabsorbing final ions and reabsorb some water
what happens to the water potential in the medulla and why is than an advantage
furthur down the medulla, the lower the water potential; higher concenteration of ions
allows water to be reabsorbed along the entire length
