FE balance Flashcards
Osmolarity changes through the nephron
- isosmotic fluid leaving the proximal tubule becomes progressively more concentrated at the descending limb. Only water reabsorbed.
- removal of solute in the thick ascending limb creates hyposmotic fluid. ions reabsorbed but no water
- permeability to water and solutes in the distal tubule and collecting duct is regulated by hormones. Variable reabsorption of water and solutes based on body’s needs
- final urine osmolarity depends on reabsorption in the collecting duct
what is vasopressin released by
posterior pituitary gland
explain how vasopressin is released into the blood
- made and packaged in cell body of neuron
- vesicles are transported down the cell
- vesicles containing AVP are stored in posterior pituitary
- AVP is released into blood
what is the stimulus for vasopressin release
when we need more water
- high plasma osmolarity
- low blood volume
- low blood pressure
what does vasopressin do
controls the addition of water pores (aquaporin-2; AQP2) into the apical membrane of collecting duct cells
results in increased water reabsorption and more concentrated urine. Pulling back water if it is needed
- response may be graded (need a bit of h2o, secrete a little vasopressin, more if needed) and depends on the amount of hormone released
what kind of relationship is the effect of plasma osmolarity on vasopressin secretion
linear relationship
what is the the homeostatic response to decreased blood pressure
sensor: carotid and aortic baroreceptors
input signal: sensory neuron to hypothalamus
integrating center: hypothalamic neurons that synthesize vasopressin
output signal: vasopressin released from posterior pituitary
target: collecting duct epithelium
tissue response: insertion of water pores in apical membrane
systemic response: increased water reabsorption to conserve water
what is the homeostatic response to decreased atrial stretch due to low blood volume
sensor: atrial stretch receptor (if there is less blood it will not need to stretch)
input signal: sensory neuron to hypothalamus
integrating center: hypothalamic neurons that synthesize vasopressin
output signal: vasopressin released from posterior pituitary
target: collecting duct epithelium
tissue response: insertion of water pores in apical membrane
systemic response: increased water reabsorption to conserve water
what is the homeostatic response to osmolarity greater than 280 mOsM
sensor: hypothalamic osmoreceptors
input signal: interneurons to the hypothalamus
integrating center: hypothalamic neurons that synthesize vasopressin
output signal: vasopressin released from posterior pituitary
target: collecting duct epithelium
tissue response: insertion of water pores in apical membrane
systemic response: increased water reabsorption to conserve water
what type of hormone is aldosterone
steroid hormone
where is aldosterone made and released
adrenal cortex
what does aldosterone do
acts on principal (P) cells of the distal tubule and collecting duct to increase sodium reabsorption
if we turn this up to increase sodium gradient, water will follow via osmosis
what is the stimulus of aldosterone release
angiotensin 2 (low blood pressure and the Renin-Angiotensin system; RAS)
hyperkalemia (High potassium concentration in plasma)
renin-angiotensin-aldosterone system
stimuli is low BP or BV
granular cells of the afferent arteriole produce the enzyme renin which is released into circulation to act of angiotensinogen (inactive, produced by liver)
renin converts angiotensinogen to ANG 1 and then ACE (angiotensin-converted enzyme located on all vascular endothelial cells) which is active and acts on adrenal cortex
aldosterone is released from adrenal cortex to increase sodium reabsorption
what are the other targets of ANG 2
cardiovascular control center - increase CO, SV, HR
arterioles: powerful vasoconstrictor, increase R and BP
hypothalamus: increases vasopressin release, thirst and salt appetite
what are the buffers in acid base balance
bicarbonate in extracellular fluid
proteins, hemoglobin and phophates in cells
phosphates and ammonia in urine
what are the three mechanisms to maintain normal pH
buffers, regulation of ventilation and kidneys (in this order)
renal compensation in pH homeostasis
H+ secreted and bicarbonate reabsorbed at the proximal tubule
fine regulation of acid-base balance occurs at the collecting duct
interaclated 1 cells (interspersed between P cells) contain high levels of carbonic anhydrase
type A I cells
secrete H+ and reabsorb bicarbonate
response to acidosis
type B I cells
secrete bicarbonate and reabsorb H+
response to alkalosis
