6.4.3 Osmoregulation Flashcards
Define osmoregulation
The control of the water potential of the blood
Describe and explain the effects of a fall in blood water potential (stages in brain)
- Osmoreceptors in hypothalamus detect water potential of blood being too low
- Hypothalamus increases ADH production
- More ADH passes to posterior pituitary gland, so more ADH is secreted into bloodstream
- More ADH binds to receptors on collecting duct cells
Describe and explain the effects of a fall in blood water potential (stages in kidney)
- More ADH binds to receptors on collecting duct cells
- Causes more vesicles containing aquaporins to fuse with cell-surface membrane
- More aquaporins increase the collecting duct’s cells permeability to water
- More water reabsorbed from filtrate by osmosis, down water potential gradient
- Smaller volume of more concentrated urine produced
Describe and explain the effects of an increase in blood water potential (stages in brain)
- Osmoreceptors in hypothalumus detect water potential of blood being too high
- Hypothalumus decreases ADH production
- Less ADH passes to posterior pituitary gland, so less ADH is secreted into blood stream
- Less ADH binds to receptors on collecting duct cells
Describe and explain the effects of an increase in blood water potential (stages in kidney)
- Less ADH binds to receptors on collecting duct cells
- Causes less vesicles containing aquaporins to fuse with cell-surface membrane
- Less aquaporins decreases collecting duct’s cells permeability to water
- Less water reabsorbed from filtrate by osmosis, down water potential gradient
- Larger volume of less concentrated urine produced
Describe and explain the formation of glomerular filtrate
- High hydrostatic pressure generated in glomerular capillaries
- As afferent arteriole is wider than efferent arteriole
- Ultrafiltration occurs as small molelcules (glucose + urea) forced out of gaps in capillary endothelium into Bowman’s capsule, through basement membrane
- Basement membrane acts as a filter, preventing large proteins from entering the glomerular filtrate, so they remain in blood
- Gaps between podocytes allow filtration
How is a high hydrostatic pressure generated in glomerular capillaries
Afferent arteriole is wider than efferent arteriole
Describe the process of ultrafiltration
- Small molecules (glucose + urea) forced out of gaps in capillary endotheliium into Bowman’s capsule, through basement membrane
- Basement membrane acts as a filter preventing large proteins from entering glomerular filtrate, so they remain in the blood
Role of podocytes
Gaps between podocytes allow filtration
Describe and explain the process of selective reabsorption in kidney
- Na+ actively transported out of tubule epithelial cell into blood by a sodium-potassium pump, using ATP
- Produces a Na+ concentration gradient, with a higher concentration in filtrate, and lower in tubule epithelial cells
- Glucose co-transported into tubule epithelial cells with Na+ by a co-transport protein
- Glucose moves by facilitated diffusion from tubule epithelial cell into blood
- Loss of glucose from filtrate increases it’s water potential, so water moves by osmosis from filtrate into cells into bloodstream
Apart from glucose, what else is reabsorbed into the blood during selective reapsorption
Water
Effect of glucose being selectivly reabsobed to filtrate
- Increases water potential of filtrate
- Water moves by osmosis from filtrate into cells into bloodstream, down water potential gradient
What are the specialisations of the proximal convoluted tubuele cells that increase the rate of reabsorption
- Many mitochondria provides more ATP for active transport
- Many carrier proteins allow for more active transport of Na+
- Microvilli provides a large surface area for absorption
Effect of many mitochondria specialisation of the proximal convoluted tubuele cells that increase the rate of reabsorption
Provides more ATP for active transport of Na+
Effect of many carrier proteins specialisation of the proximal convoluted tubuele cells that increase the rate of reabsorption
Allow more active transport of Na+
Effect of Microvilli specialisation of the proximal convoluted tubuele cells that increase the rate of reabsorption
Provides a large surface area for absorption
Describe and explain how having diabeties affects the reabsorption of glucose
- High concentration of glucose in blood
- High concentration of glucose in glomerular filtrate
- Glucose carrier proteins that reabsorb glucose by active transport are saturated
- Not all glucose is reabsorbed (some lost in urine)
State the permeabilites of collecting duct limbs
Descencing limb is permeable to water, ascencing limb in impermeable
Describe and explain the control of blood water potential in the decending limb of Loop of Henle
- Decending limb is permeable to water
- Water moves out of decending limb by osmosis, into medulla tissue fluid, down water potential gradient
- The longer the loop, the lower the water potential of medulla tissue fluid
- High concentration of sodium ions at base of loop
Effect of long loop of Henle
lower the water potential of medulla tissue fluid, so more water reabsorbed
Describe and explain the control of blood water potential in the ascending limb of Loop of Henle
- Ascending limb is impermeable to water
- Sodium ions actively transported out of filtrate, against their concentration gradient
- Into medulla tissue fluid, by tubule epithelial cell
- High concentration of sodium ions at base of loop
How does the couter-current multiplief affect apply to the Loop of Henle
Filtrate in ascending limb and decending limb flow in opposite directions, allowing for a counter-current multiplier effect
What is it when filtrate in ascending limb and desending limb flow in opposite directions
Counter-current multiplier effect
