20c- Water Handling and Osmolarity

What regulates water balance?

ADH/AVP

How does ADH/AVP increase water reabsorption in CD?

increases πISF of medulla

stimulates aquaporin-2 channels

How does ADH/AVP affect πISF of inner medulla?

stimulates UT-1 on collecting duct, allowing urea reabsorption + recycling, adding 600mOsml/L to ISF for a total of 1200 mOsm/L

How does ADH/AVP increase blood pressure (mechanism)?

1. low BP: SNS + Ang II stimulate ADH/AVP release

2. vasoconstriction (systemic + kidneys)

3. Decreases filtration/preurine

4. ADH/AVp stimulates UT-1, urea recycling adds 600 mOsm/L to ISF

5. Vasa recta requilibrates with ISF

6. ADH/AVP adds aqp-2 to CD

7. Water reabsorption into plasma

8. decreased water in urine, increased water in blood, increased BP

Osmolarity of tubule, intermedullary ISF, urine with ADH/AVP.

inner medullary ISF: 1200mOsm/L

tubule: 300-1200 mOsm/L

urine: 1200 mOsm/L

Osmolarity of tubule, intermedullary ISF, urine without ADH AVP?

inner medullary ISF: 600 mOsm/L

tubule: 300-600 mOsm/L

urine: ≤100mOsm/L

When is urine < 100 mOSm/L?

when there is low/no ADH/AVP and high aldosterone

When would there be high aldosterone but low ADH/AVP?

when the person have normal BP, but is hyperkalemic

What is the syndrome of inappropriate ADH (siADH)?

ADH/AVP hypersecretion due to complication of pituitary surgery or small cell lung cancer

What does siADH cause + put you at risk for?

causes HTN, at risk for hypertensive retinopathy

What causes ADH/AVP hyposecretion?

alcohol

caffeine

immature pituitary (kids)

diabetes insipidus

vaptan

Central Diabetes Insipidus

brain not making ADH/AVP

nephrogenic diabetes insipidus

kidney ADH/AVP receptors not working

Presentation of diabetes insipidus

dehydration/polydipsia

polyuria

How does the kidney self regulate BP?

macula densa sense chronic changes in GFR + signals to JG cells to alter renin secretion

Kidney response to chronic low BP

1. chronic low BP--> chronic low GFR

2. macula densa senses chronic low Cl-, secretes substance onto JG cells

3. JG cells stimulated to secrete renin

4. Renin causes vasoconstriction of afferent arteriole

5. decreases GFR, less fluid in nephron, more fluid in blood

6. increased BP

Kidney response to chronic high BP

1. chronic high BP --> chronic high GFR

2. macula densa senses chronic high Cl-, secretes substance onto JG cells

3. JG cells stimulated to decrease renin secretion

4. afferent arteriole vasodilates

5. increased GFR, more urine, less blood volume

6. decreased BP

Tubule regulation of renin/BP vs tubuloglomerular feedback (regulation of GFR). What do they respond to + what are there goals?

tubule regulation of BP/renin:

-responds to chronic low or high levels of BP

- goal it to increase or decrease BP to normal

tubuloglomerular feedback:

-responds to sudden changes in GFR

- goal is to increase or decrease GFR

Tubule regulation of renin/BP vs tubuloglomerular feedback (regulation of GFR). How does GFR change and what is secreted + by what cells?

tubule regulation of BP/renin:

-GFR does NOT change

-secretes different levels of renin from JG cells

tubuloglomerular feedback:

-GFR increases or decreases (depending on goal)

-secretes adenosine or PGE2 from macula densa (depending on goal)

Where are baroreceptors located?

carotid sinus and aortic arch

Where are osmoreceptors located?

hypothalamus

adrenal cortex

How does the body respond to hyposomotic blood?

decrease ADH/AVP

increase aldosterone

How does the body respond to hyperosmotic blood?

increase ADH/AVP

decrease aldosterone