Hormonal and Diuretic Regulation

Purpose of renal system

maintain blood volume and composition

normal plasma osmolarity affected by

solute concentration

Total solute concentration is measured by

plasma osmolarity

Normal plasma osmolarity is

285 - 295 mOsm

Homeostasis typically prevents fluctuation more than

1-3 %

dehydration from heavy exercise can

increase osmolality by 10 mOsm

Collecting Duct receives \____ mOsm filtrate from DCT

100

filtrate from collecting duct is

hypotonic to renal cortex

As filtrate transports from cortex through renal pyramid,

interstitial fluid become increasingly concentrated

Osmotic pressure in collecting duct drives

water out of duct and into interstitial space

once solutes in the interstitial space they are removed by

capillaries

rate of osmosis is not

constant

rate of osmosis is regulated by

antidiuretic hormone

Antidiuretic hormone aka

vasopressin

adh produced by

neurons in hypothalamus

adh stored in

posterior pituitary gland

adh secreted in response to

increased plasma osmolarity

Osmoreceptors in hypothalamus can detect increases from

0.5 - 5 mOsm

ADH detects

Na+ only

ADH response triggered by

dehydration and increased salt intake

ADH stimulates

thirst and adh secretion from posterior pituitary gland

ADH binds to

target cells in collecting duct

ADH stimulated messengers,

cAMP 2nd messenger system.

Vesicles translocate to

cell surface

vesicle translocation increases

aquaporin water channels in the cell membrane

increase in aquaporins allows for

passive transport and simple diffusion of water to occur

more aquaporins effect on water

increases the rate of water reabsorption

increased water retention causes

increased blood volume and decreases blood osmolality

increased urine concentration causes

less urine to be produced

Absence of ADh induces

endocytosis of aquaporins

endocytosis of aquaporins due to ADH secretion causes

decreased water retention, lower blood volume, and increases urine production

Ethanol inhibits

ADH secretion

ethanol ingestion results in

increased urine production an increased dehydration

Juxtaglomerular apparatus

regions where afferent arterioles contact end os ascending limb of the nephron loop

Juxtaglomerular apparatus contains

granular cells in arterioles
macula densa in tubule

the granular cells of Juxtaglomerular apparatus

sense low blood pressure and secrete renin to stimulate aldosterone secretion

Macula Densa of Juxtaglomerular apparatus

senses increased NaCl and H2O in filtrate

how does the macula densa sense NaCl and H2O in filtrate

through Na+ , K+ and -2Cl cotransporters

The Macula densa releases

ATP

release of ATP stimulares

afferent arteriole construction and decreases GFR

decreased GFR

decreases flow of NaCl and H2O

Mascula densa inhibits

granular cell secretion of renin

kidneys produce renin in the

Juxtaglomerular apparatus

renin production in juxtaglomerular apparatus stimulated by

low NaCl concentration in filtrate
low blood volume in filtrate
low renal artery blood pressure

renin cleaves angiotensinogen into

angiotensin 1

angiotensin-converting enzyme ACE cleaves

2 more amino acids to produce angiotensin 2

angiotensin cleavage occurs in

lung capillaries

Angiotensin 2 effects

increase blood pressure
stimulates vasoconstriction of small arteries and arterioles
increases TPR

the macula densa is a

quality control aspect

increases in blood volume

stimulate thirst center in hypothalamus to increase water intake
- stimulates adrenal cortex to secrete alsosterone

secretion of aldosterone causes

decreased salt loss and thus water loss

ACE inhibitors

prevent conversion of angiotensin 1 into 2
- promotes vasodiltion to lower TPR and arterial blood pressure

Aldosterone

steroid hormone secreted by adrenal cortex

aldosterone secretion is indirectly stimulated by

salt deprevation and low blood volume and pressure

another way for aldosterone to be secreted

high potassium levels

aldosterone stimulated

reabsorption of salt in late DCT and cortical collecting duct

aldosterone in DCT and collecting duct causes

increased blood volume and thus pressure

aldosterone does not effect

plasma osmolarity

plasma osmolarity maintained by aldosterone because

salt and water are retained in equal portions

aldosterone functions with interactions with

ADH

Aldosterone regulates

the reabsorption of the remaining 8-10% of Na+

Aldosterone Na+ reabsorption occurs in the

collecting duct mainly - some in DCT

reabsorption without aldosterone

additional 8% of Na+ reabsorbed
2% or 30 g/day excreted in urine

Maximum aldosterone secretion

remaining 10% of Na+ completely reabsorbed - no salt excreted in urine

Maximum aldosterone secretion stimulates

Na/K+ pumps on basolateral surface of collecting duct epithelial cells

Na/K+ pumps on basolateral surface of collecting duct epithelial cells creates

concentration gradient to drive Na+ out of collecting duct
Cl- passively follows

Aldosterone regulation of K+

90% K+ reabsorbed in PCT and nephron loop

K+ secreted into DCT and collecting duct

increase K+ secreted where Na+ reabsorbed
- balances K+ plasma changes from consumption

Aldosterone-dependent K+ secretion

increased K+ plasma levels stimulates adrenal cortex to release aldosterone

hyperkalemia

increased potassium levels

aldosterone released due to hyperkalemia stimulates

increased K+ secretion through Na+ / K+ pumps on basolateral surface

Alsosterone independent K+ secretion

hyperkalemia induces insertion of additional K+ channels ( passive ) into collecting duct

Atrial netriuretic Peptide ANP produced by

atria

Atria produces ANP through

increased venous return stimulated by stretch receptors in atrial wall

ANP inhibits

ADH secretion

ANP stimulates

natriuresis and vasodilation

secretion means

back into filtrate

ANP is antagonistic to

ADH

ANP promotes

excretion of Na+ and thus water

ANP lowers

blood volume and pressure

ADH released due to

increased plsma osmolarity

effect of ADH

water reabsorbed

Aldosterone released due to

low blood pressure
low blood volume
low Na+
and high K+

Diuretics

increased volume of urine excreted

Aldosterone effect

Na+ reabsorbed with water following
K+ secretion increased

ANP released by

increased blood volume

ANP effect

Na+ reabsorption inhibited thus inhibiting water reabsorption
- inhibited ADH production

increaed volume of urine excreted directly lowers

blood volume and blood pressure

diuretics indirectly decrease

edema

decreased edema

lowers interstitial fluid volume

decreased plasma volume increases

plasma concentration

oncotic pressure drives

fluid from interstital space into capillaries

diuretics classified by

chemical structure and actions

Diuretics inhibit

water and salt reabsorption

loop diuretics

inhibits active NaCl transport out of ascending limb

loop diuretics are the

most powerful diuretic

Carbonic Anhydrase inhibitors

promotes HCO3- secretions and are a much weaker diuretic

increased HCO3- secretion inhibits

water reabsorption associated with HCO3- reabsorption in PCT

Osmotic diuretics

act as extra solutes within the filtrate

osmotic diuretics increase and decrease

increase filtrate osmotic pressure and decrease water reabsorption