BSCI450: Water Salt Homeostasis

how does dehydration affect GFR

dehydration -> low blood volume -> low BP -> low GFR

GFR calculation formula

([creatinine in urine]*urine production rate)/[creatinine in plasma]

clearance

use

rate at which solute leaves body by excretion

measure GFR

does GFR typically deviate

no

what is the MAP range of consistent GFR

80-180 mm Hg

what does it take to change GFR

really high or low BP

how can you regulate the amount of blood in/out of glomerulus

efferent/afferent arteriole radius

how to restore GFR when BP drops

increase resistance in efferent arteriole

how to restore GFR when BP rises

increase resistance in afferent arteriole

how does nephron know GFR has changed

stretch receptors in arterioles

sympathetic innervation (baroreceptors sense BP)

tubular flow rate

hormones

how can tubular flow rate be measured

cilia detection

NaCl concentration

what is angiotensin

main mechanisms

peptide hormone that increases blood pressure

vasoconstriction, salt/water retention

vasopressin is also known as

antidiuretic hormone (ADH)

juxtaglomerular complex

parts

what it does

location

macula densa, granular cells, arteriole smooth muscle

sense GFR

between DCT and glomerulus

macula dense

sense tubule flow rate and regulate GFR via paracrine signalling

describe linear GFR feedback regulation (high GFR)

high GFR -> faster filtrate flow velocity -> sensed by cilia mechanosensors -> paracrine mechanisms -> afferent arteriole constriction -> low GFR

high GFR -> higher [NaCl] after PCT (should’ve been reabsorbed but saturated) -> sensed by macula densa -> paracrine mecahnisms -> afferent arteriole constriction -> low GFR

key sensors of water level and electrolytes

brain and kidneys

what two variables affect homeostasis in regards to water

volume and osmolarity

how to decrease osmolarity and increase water

drink water

how to increase osmolarity and not change water

eat salt w/o drinking water

how to decrease volume and without changing osmolarity

hemorrhage

how to increase osmolarity while decreasing volume

dehydration

what drives water intake

thirst

what drives water excretion

key influences

kidney

GFR, reabsorption

how can water come into the body

food/drink + metabolism

how can water exit the body

skin, lungs, urine, feces

what does the nephron do if plasma is hypotonic

reabsorbs electrolytes and excretes water

what allows water pernability in LOH

aquaporin

diuretic

increase urine production and Na excretion

antidiuretic

decrease urine production and increase water retention

how come birds and reptiles can drink salt water

NKCC transporters allow excretion of salt via glands

what mechanism concentrates loop filtration

countercurrent flow