Excretion of waste Flashcards
What is the function of the thick ascending limb?
- Actively pumps out NaCl
- is impermeable to water so water does not follow
- NaCl raises the solute concentration in the surrounding interstitial fluid of the renal medulla
What is the function of the thin descending limb?
- highly permeable to water but not to Na+ or Cl-
- bc the surrounding interstitial fluid tissue is more concentration, water exits the descending loop by omsosis
- thus the renal fluid in the descending limb becomes more concentrated
What happens in the distal convoluted tubule?
- the renal fluid is LESS concentrated than the interstitial fluid
- reabsorption of salts, amino acids etc occurs.
- Some water moves out by osmosis
- renal fluid becomes iso-osmotic with the interstitial fluid
What happens as the filtrate moves down the collecting duct?
• it becomes highly concentrated as water is drawn out due to the high solute concentration in the interstitial fluid of the medulla
Describe the movement of urea
- some urea leaks from the collecting duct into the interstitial fluid of medulla, adding to increased osmotic concentration in renal medulla
- urea diffuses back into ascending limb and is returned to the collecting duct
What is the function of ADH (Antidiuretic hormone - aka vasopressin)?
- controls the permeability of the collecting duct to water - thus the amount of water reabsorbed from urine
- ADH stimulates expression of aquaporin 2 which is a water channel in the collecting duct cell membranes.
What signals does the brain receive for it to stimulate thirst?
- the amount of water in the body is too low
* some elements in the blood, such as sodium, are too concentrated
Explain with reference to kidney function the hormonal control of blood volume if blood pressure is too low.
- blood pressure is too low - kidney releases renin
- renin converts angiotensinogen to ang 1
- then converting enzyme ACE converts ang 1 to active form ang2
- ang2 stimulates adrenal cortex to release aldesterone
- there is enhanced Na+ reabsorption in the kidney and H2O is reserved
What effect angiotensin 2 have on the body?
- constriction of peripheral blood vessels (increase pressure)
- release of aldosterone (enhances Na+ reabsorption and hence water reabsorption in distal convoluted tubule and collecting duct)
- stimulation of thirst and drinking
What happens in the hypothalamus if blood osmolarity increases?
- high blood osmolarity or low blood pressure/volume
- stimulates the posterior pituitary to release ADH
- ADH increases permeability of distal tubule and collecting duct to H2O - water is conserved to restore the osmolarity
What receptors detect osmolarity?
Osmoreceptors in the hypothalamus
• they also detect changes in blood pressure
What happens if there is a mutation to the vasopressin/ADH gene?
- mice cannot produce AD/vasopressin so its kidneys don’t return water to the blood but instead secrete it
- mice is always drinking water to replenish the water lost in the urine
Why does alcohol increase frequency of urination?
- high blood alcohol levels block production of vasopressin in the pituitary gland
- kidney does not return water to the blood
- excess urination leads to dehydration and loss of electrolytes (K+, Mg2+)
what is RAAS?
Renin-Angiotensin - Aldosterone System
• An important autoregulatory mechanism is renin release by kidney when blood pressure falls
How is a decrease in blood pressure detected by the kidney?
- blood volume influences the pressure in the glomerulus which is regulated to maintain the glomerular filtration rate
- small changes in blood pressure are detected by baroreceptors in the afferent arterioles
