Control of Blood Water Potential Flashcards
what is osmoregulation?
- control of water potential of the blood
what is the hormone involved in osmoregulation?
antidiuretic hormone
where is ADH produced?
hypothalamus
where is ADH stored?
posterior pituitary gland
what is the mechanism of ADH action?
- ADH binds to receptors on the surface of cells in the DCT and collecting duct
- triggers activation of enzyme phosphorylase
- caused water channel proteins called aquaporins to be integrated into the cell surface membrane
- water then moves through aquaporins by osmosis from the DCT and collecting duct into the surrounding interstitial space
- water is then reabsorbed into surrounding blood vessels
what does ADH do for osmoregulation?
changes water content of blood when it is too high or too low
what happens when the blood water content is too low?
- osmoreceptors in the hypothalamus detect the fall in water potential
- posterior pituitary gland is stimulated to release more ADH into blood
- more ADH means DCT and collecting duct are more permeable, so more water is reabsorbed into blood by osmosis
- small amount of highly concentrated urine is produced, so less water is lost
what happens when the blood water content is too high?
- osmoreceptors in the hypothalamus detect the rise in water potential
- posterior pituitary gland releases less ADH into blood
- less ADH means that the DCT and collecting duct are less permeable, so less water is reabsorbed into the blood by osmosis
- large amount of dilute urine is produced, so more water is lost
what is the role of the proximal convoluted tubule?
reabsorption of glucose and water
what is the role of the loop of Henle in the medulla?
maintains a gradient for sodium ions in the medulla
what is the role of the distal convoluted tubule and the collecting duct?
reabsorption of water
where does ultrafiltration occur?
glomerulus
what is ultrafiltration?
- small molecules like water, glucose, mineral ions and urea are filtered out of blood and into Bowman’s capsule = glomerular filtrate
- larger molecules remain in the bloodstream
what is the process of ultrafiltration?
- blood enters glomerulus through afferent arteriole
- blood leaves glomerulus through smaller efferent arteriole, this maintains a high hydrostatic pressure
- high hydrostatic pressure forces molecules like water and small flutes out of blood though pores in capillary endothelium
- molecules moves through basement membrane, has collage fibres which acts as selective filter prevent large molecules + blood cells passing into Bowman’s capsule through the podocytes on the epithelium
- filtered fluid collects in the Bowman’s capsule
what are the key features of the epithelial cells in the proximal convoluted tubule?
- microvilli = increases surface area
- basal infoldings = increases surface area
- many mitochondria = provides ATP for active transport
- co transporter porteins in plasma membrane = filtrate
what is the process of reabsorption by the proximal convoluted tubule?
- sodium ions are actively transported into blood capillaries, reduces Na+ concentration in epithelial cells lining the PCT
- Na+ moves from PCT lumen into epithelial cells, down conc gradient
- Na+ is cotransported with substances like glucose and amino acids into the epithelial cels
- these reabsorbed molecules can diffuse into blood capillaries
what are the two sections of the loop of Henle?
- ascending limb
- descending limb
what are features of the descending limb?
- where the filtrate arrives
- narrow
- highly permeable to water
- impermeable to ions
what are features of the ascending limb?
- where the filtrate leaves
- wider than descending limb
- impermeable to water
- highly permeable to ions
explain the process of water reabsorption of the loop of Henle
- descending limb’s walls are permeable to water, so water leaves filtrate via osmosis into the interstitial space
- filtrate loses water as it moves down descending limb, so reaches a low water potential at tip of medulla
- water which is lost is reabsorbed into blood in surrounding capillaries by osmosis
- ascending limb is impermeable to water, but permeable to sodium and chloride ions
- ions diffuse out of filtrate into interstitial space at Botton of ascending limb sue to low water potential
- ions are actively transported out of top of ascending limb as their conc in filtrate decreases as it ascends due to water potential increasing
what is the system that the loop of Henle operates on?
countercurrent multiplier system
what is the counter current multiplier system?
- as filtrate moves down collecting duct, it loses water, decreasing water potential
- due to pumping of ions out of ascending limb of loop of Henle, deeper in the medulla the water potential of surrounding tissue is lower than in collecting duct
- allows water to continue to move out of filtrate down the whole length of collecting duct
