I hate hormones

tubularglomeric feedback

• responds to status downstream of tubular fluid 

• responds to high GFR

How does tubular glomeric feedback work?

high GFR → increased NaCl in nephron loop → macula densa cells secrete ATP → mesangial cells metabolize ATP to adenosine → adenosine stimulates granular cells → afferent arteriole contract -→ GFR is reduced

what stimulates the renin-angiotensin-aldosterone mechanism

• any substantial drop in BP due to bleeding/dehydration

Renin

• sympathetic fibers stimulate granular cells to release this

• acts on angiotensinogen and turns it into angiotensin I

angiotensin II main goal

• restore fluid volume and blood pressure

How can angiotensin II restore fluid volume and blood pressure

• potent vasoconstrictor= raises MAP in body

• constricts efferent arterioles more than afferent

• stimulates water reabsorption in the PCT

• stimulates aldosterone, ADH

• stimulates sense of thirst 

What does angiotensin II do to kidneys

• strongly constrict efferent arteriole more than afferent arteriole

  • raises glomerular BP and GFR

  • ensures normal continued filtration during drop in MAP

What does angiotensin II do to peritubular capilaries

• lowers BP in peritubular capillaries downstream of efferent arterioles 

  • this encourages reabsorption of NaCl and water so more water can be returned to bloodstream

What are the main effects of angiotensin II

• raise BP

• reduce water loss

• encourage water intake 

• constrict blood vessels

What is the effects of sympathetic control

• responds to strenuous exercise/circulatory shock 

  • stimulates epinephrine → constricts afferent arteriole→ reduces GFR/urine output 

  • redirects blood to where it is more needed 

How does angiotensin II aid in uptake of peritubular capilaries

• constricts mainly efferent but also afferent arteriole

• maintains glomerular BP/ filtration 

• reduces BP of peritubular capilaries

• reduces resistances to reabsorption 

• tubular reabsorption increases

• urine volume less but very concentrated 

What hormones regulate DCT and Collecting Duct

• aldosterone

• natriuretic peptides 

• ADH

• parathyroid hormone 

Aldosterone

• steroid secreted by adrenal cortex

• “salt retaining hormone”

What would cause aldosterone to be secreted

• decreased blood Na+ concentration 

• increased K+ concentration 

how does a drop in BP indirectly induce aldosterone secretion? 

• drop in BP leads to renin secretion

  • produces angiotensin II

  • angiotensin II stimulates aldosterone secretion

what does aldosterone target

• thick segment of ascending limb 

• DCT

• cortical portion of collecting duct 

What does aldosterone do? 

• stimulate reabsorption of Na+

  • water and Cl will follow 

• stimulate secretion of K+

what is the overall effect of aldosterone

• body retains NaCl and water

• urine volume is reduced 

• urine has elevated K+

Why is water retention important

• helps maintain blood volume and pressure 

when are natriuretic peptides secreted

• in response to high BP

  • will result in excretion of water and salts in urine

  • this will reduce BP and blood volume

What do natriuretic peptides do?

• dilate afferent arteriole/ constrict efferent arteriole 

  • increases GFR

• inhibit renin and aldosterone secretion 

• inhibit ADH

• inhibit NaCl reabsorption by collecting duct 

what would cause ADH to be released? 

• dehydration

• loss of blood volume

• rising blood osmolarity 

what does ADH do

• make collecting duct more permeable to water 

• water in tubular fluid reenters blood 

What would cause Parathyroid hormone to be released?

• calcium deficiency 

What does PTH do?

• acts on PCT to inhibit

  • phosphate reabsorption

• acts on DCT/thick nephron loop 

  • increases calcium reabsorption 

what is the main effect of PTH?

• increase phosphate in urine

• decrease calcium in urine

** lets calcium ions stay in circulation rather than being precipitated into bone as calcium phosphate 

What hormone is used to control water loss in the collecting duct? 

• ADH 

What stimulates the pituitary to release ADH?

• high blood osmolarity of a dehydrated person

How does ADH increase water reabsorption?

• collecting duct transfers aquaporins from storage vesicles to apical/basal cell surface

• cells transcribe aquaporin gene to make more aquaporins to further raise water permeability of collecting duct 

What happens if you are well hydrated?

• ADH secretion falls

• tubule removes aquaporins and duct is less permeable to water

• you produce more abundant, dilute urine

What does aldosterone target

• nephron loop 

• DCT

• CD

What does angiotensin II target?

• afferent and efferent arterioles

• PCT

What does ADH target

• collecting duct

What do natriuretic peptides target?

• afferent/efferent arterioles

• collecting duct 

What do epinephrine and norephrine target?

• juxtaglomerular apparatus

• afferent arteriole 

What do PTH targt

• PCT

• DCT

• nephron loop 

Effects of Aldosterone

• promote Na+ reabsorption 

• promote K+ secretion 

• indirectly promote Cl- and H2O reabsorption 

• maintain blood volume

• reduce urine volume

Effects of angiotensin II

• reduce water loss

• stimulate thirst

• encourage water uptake

• constrict blood vessels to raise BP

• stimulate PCT to reabsorb NaCl and H2O

• stimulate aldosterone/ADH secretion 

Effects of ADH

• promote H2O reabsorption

• reduce urine volume

• increase urine concentration 

Effects of Natriuretic Peptides

• dilate afferent and constrict efferent arteriole

• increases GFR

• inhibit renin, ADH, and aldosterone secretion 

• inhibit NaCl reabsorption in CD

• increase urine volume

• lowers BP

epinephrine/norephrine effects

• induce renin secretion

• constrict efferent arteriole

• reduce urine volume and GFR

effects of PTH

• promotes Ca2+ reabsorption by loop and DCT

• increases phosphate excretion by PCT 

• promotes calcitriol synthesis 

what do osmoreceptors respond to?

• angiotensin II and rising osmolarity of ECF

when causes action of osmoreceptors

• dehydration 

  • reduces blood volume

  • raises blood osmolarity

What do osmoreceptors do?

• communicate with hypothalamic neurons to produce ADH

  • promote water conservation, and make sense of thirst 

what hormone helps control water output independently of sodium?

• ADH

Dehydration

• low H2O,  increased Na+ 

  • elevated blood osmolarity

dehydration stimulates what?

• hypothalamic osmoreceptors 

what do hypothalamic osmoreceptors stimulate? 

• posterior pituitary to release ADH

When controling water output, what does ADH stimulate

• DCT and collecting duct 

  • increases water reabsorption 

    • reduces urine volume

    • increases Na:H2O ratio in urine

what is another effect of ADH when trying to overcome dehydration? 

• stimulating thirst

  • leads to water ingestion to increase H2O levels