E4 L23 ion & water balance

How is homeostasis maintained

input matching output

What is the main regulator to match input to output

urine

Baroreceptors detect changes in pressure as a result of

Sodium chloride

Osmreceptors detect ECF osmolarity changes due to

Pure water gains

Na and H2O are ______ at the _____ and mostly _______

freely filtered, glomerulus, reabsorbed (99%)

Where does most Na reabsorption occur

Proximal tubule (65%)

How is Na reabsorbed at the proximal tubule

Primary active: basolateral membrane, Na to ISF, K into cell

Secondary active: cotransport (x and Na) or counter (Na in H out) transport

Facilitated diffusion of X from cell to ISF

The reabsorption of Na at the proximal tubule is ___________

non-regulated

How is Na reabsorbed at the ascending loop (25%)

Primary active: basolateral membrane, Na to ISF, K into cell

Secondary active: cotransport of Na and Cl from lumen to cells

Leak channels for Cl and K

The reabsorption of Na at the ascending limb is ______

non-regulated (ascending)

How is Na reabsorbed at the cortical collecting duct

Primary K Na pump

Aldosterone secreted from adrenal builds more pumps

Results in more Na reabs and more K excretion

Reabsorption of Na at the cortical collecting duct is ________

Regulated

Processing

always happening, intrinsic property

Regulation

Endocrine and nervous systems changing processing to meet homeostatic demands

Three methods of Na reabsorption

Cortical collecting duct

Ascending limb

Proximal tubule

Two methods of water reabsorption

Transcellular and paracellular

Paracellular water reabsorption

between/around, proximal tubule, non regulated, 65%

Transcellular water reabsorption

across/through the cell, collecting ducts, requires aquaporins, regulated by ADH

How does ADH regulate water reabs

Secreted from posterior pituitary cAMP - kinase, inserts AQP2 into luminal membrane to facilitate movement of water

What nephrons contribute to the renal medullary gradient

Juxtamedullary nephrons

What two mechanisms create this gradient

Countercurrent multiplier system

Urea recycling

What maintains the renal medullary gradient

Vasa recta circulation

What is the counter multiplier system

Movement of H2O out of the descending limb, movement of solutes of out the ascending limb, water is reabs at the ascending limb

Where does urea recycling take place

Bewteen the ascending limb and collecting duct

How does urea recycling maintain the renal medullary gradient

reabs at collecting, secreted at ascending, draws water with it

Renal countercurrent multiplier system

Active transport of NaCl out of ascending and distal, water reabs at distal, recycling of urea promoted by ADH, increased ADH, increased H2O reabs, increased urea reabs

Medullary circulation at the vasa recta

Solutes from asc to desc

Water from desc to asc

Results in 2x fluid volume at distal

How does ADH control urine volume and osmolarity

ADH inserts aquaporing into collecting ducts, concentrates urine, hyperosmotic medullary ISF, increased water & urea reabs

What happens if you're over hydrated

Decreased ADH from the posterior pituitary

Renal sodium regulation equation

Na excreted= Na filtered - Na reabs

Is Na secreted

no

What are the two ways to alter Na excretion to maintain homeostasis

Regulating filtered load by changing GFR, regulating rate of reabs

How does changing GFR alter the amount of Na filtered

Increased Na, decrease P venous/atrial/arterial, baroreceptors sense and constrict afferent arterioles of kidney = decreased filtration (reverse for dilation)

How is the reabs rate of Na controlled

Occurs at juxtaglomerular cells - less MAP (increased symp, decreased art P and GFR) - increased Renin secretion - converts ag-gen to AG1/AG2 - vasoconstrict, increase aldosterone (up BP)

Acute: increase TPR

Longterm: increased Na and H20 retention

Common hypertension medications

ACE inhibitors

AngII blockers

Aldosterone receptor blockers

What does the enzyme ACE do

converts angiotensin I into angiotensin II

What does AngII do in Na reabs

causes vasoconstriction and increased levels of angeotensin

What does angiotensin (from AM) do in Na reabs

Increase Na and H2O retention long term

How does the atrial natriuretic peptide control Na reabs

Increased MAP = increased ANP secretion from atrial muscle cells - decreased aldosterone - afferent dilation, decreased Na reabs, increased Na excretion

Acute: alters arterioles to increase GFR

Long term: decreases Na reabs