Renal 2 Flashcards
Renal Lectures 5-7
organ systems involved in integrative process of maintaining fluid and electrolyte balance
respiratory, CV, renal, behavioural responses
T or F: 2/3 of body water is ECF
F: intracellular
diuresis osmolarity
removal of excess urine (dilute urine), 50 mOsM
if kidneys need to conserve water, what urine is produced, osmolarity
low volume of conc urine, up to 1200 mOsM
renal cortex is what osmolarity to plasma
isosmotic
renal medulla is what osmolarity to plasma
hyperosmotic, progressively more concentrated as filtered through nephron
vasopressin does what
alter membrane permeability to water by inserting or removing water pores in the apical membrane in collecting duct, signals from posterior pituitary hormone vasopressin (AVP), antidiuretic hormone (ADH)
T or F: insertion of AQP2 is graded
T: depends on amount of vasopressin (AVP) present
4 steps of AQP2 channel insertion
- vasopressin released from posterior pituitary travels via blood and binds to membrane receptor on blm
- receptor activates cAMP second messenger system
- cells insert AQP2 water pores into apical membrane via exocytosis of storage vesicles
- water enters cell via AQP2 and diffuses into blood via osmosis
what stimulates vasopressin secretion
decreased blood pressure:
carotid and aortic baroreceptors -> sensoru neuron to hypothalamus
decreased atrial stretch bc of low blood volume:
atrial stretch receptor-> sensory neuron to hypothalamus
osmolarity greater than 280mOsM:
hypothalamic osmoreceptors -> interneurons to hypothalamus
all = increased vasopressin synthesis in hypothalamus then stored and released from posterior pituitary
what cells produce AVP? how is it secreted?
magnocellular neurosecretory cells (MNC’s) produce and release AVP
-osmolarity monitored by osmoreceptors neurons. stretch sensitive that increase firing as osm increase (shrink, opposite of normal stretch receptors)
- signal to MNCs, APs fire in the MNCs causing release of AVP containing vesicles
-baro and atrial receptors also signal
what creates the hyperosmotic interstitium and why isn’t it reduced as water is reabsorbed?
- the loop of Henle is a countercurrent multiplier - kidneys transfer water and solute instead of heat
- Urea contributes to hyperosmotic interstitium
The renal countercurrent exchange system- two components
multiplier: loop of henle, create hypertonic interstitium
exchanger: peritubular capillaries (vasa recta), prevent dilution of the hypertonic interstitium
-as filtrate enters descending limb, progressively more conc as it loses water
- the ascending limb pumps out solutes and filtrate becomes hyposmotic
-blood in vasa recta removes water leaving the loop
countercurrent multiplier osmolarities
start of descending limb: 300 = interstitium
middle (bottom): 1200 bc water pumped out
ascending limb: 100, solutes pumped out, no AQP2, becomes hyposmotic
% of reabsorption taking place in ascending limb
25% of Na and K
what transporter actively transports solutes to create countercurrent multiplier
NKCC transporter: Na, K, 2 Cl
apical membrane (out of tubule, through epithelial cells, to interstitium to vasa recta)
active transport: uses Na gradient energy
how does urea contribute to the hyperosmotic interstitium
about half of solute in interstitium is urea
- 50% urea reabsorbed in the proximal tubule
- 50% of urea is secreted back into loop of henle
- 30% reabsorbed in distal portion of nephron
- 50% reabsorbed from end of collecting duct
makes recycling loop
homeostatic mechanisms to maintain mass balance - response to salt ingestion
no change in volume, increase osmolarity
- Vasopressin secretion
- increase water reabsorption = kindeys conserve water in body
a. increase water reabsorption -> increase ECF -> increase bp -> CV reflexes (rapid response)
- thirst
- increase water intake
a. “”
b. increase ECF volume -> kidneys excrete salt and water = osmolarity returns to normal + volume and bp (slow response)
what endocrine pathway helps control Na balance
renin-angiotensin-aldosterone system
what does aldosterone do
aldosterone is a steroid hormone that is regulates Na reabsorption and K secretion
targets end of distal tubule and cortex/ start of collecting duct
zona glomerulosa cells
what cells does aldosterone act on
principal cells
principal cells vs intercalated cells
2 types of cells in collecting duct
principal cells: Na and water regulation
intercalated: acid-base balance, type A and B
5 steps of aldosterone pathway
- aldosterone combines with cytoplasmic receptor in cell
- hormone-receptor complex initiates transcription in nucleus
- translation and protein synthesis makes new protein channels and pumps
- aldosterone-induced proteins modulate existing channels and pumps
- Results: increased Na reabsorption and K secretion
what is the cytoplasmic aldosterone receptor called
mineralocorticoid receptor
