Control Of ABP Flashcards
How can blood volume and MAP be regulated
By regulating extracellular fluid volume (ECF)
How much of our body weight is water (in a 70kg individual)
60%
42L
Total body fluid =
Intracellular fluid (2/3) + extracellular fluid (1/3)
Extracellular fluid volume (ECFV) =
Plasma volume (PV) + interstitial fluid volume (IFV)
What two factors affect ECFV
- Water excess or deficit
- Na+ excess or deficit
Healthy people stay in a stable ….. balance, where water input = water output
Water and salt
What hormones regulate ECFV
Renin-angiotensin-aldosterone system - RAAS
Natriuretic peptides - NPs
Antidiuretic hormone (arginine vasopressin) - ADH
What does RAAS regulate
Plasma volume and SVR —> MAP
3 components of RAAS
Renin
Angiotensin
Aldosterone
Describe the RAAS
When plasma volume decreases, BP decreases
Renin released from kidneys causes angiotensinogen (produced by liver) —> angiotensin 1 (in blood)
ACE (produced by pulmonary vascular endothelium - lungs) converts angiotensin 1 —> angiotensin 2
What does angiotensin 2 do
Stimulates release of aldosterone from adrenal cortex
Systemic vasoconstriction —> increases SVR and BP
Increases ADH release and thirst —> increases plasma volume and BP
What does aldosterone released by adrenal cortex do
Increases Na+ and water reabsorption in kidneys (decreases Na+ and water excretion - PRESERVES WATER)
—> increases plasma volume
—> increases BP
Rate limiting step of RAAS
Renin secretion
What are NPs released by
Heart
(Also brain and other organs)
Role of NPs
—> cause excretion of salt and water in kidneys (reduce blood volume and BP)
—> decrease renin release (decrease BP)
—> cause vasodilation (decrease SVR and BP)
Counter-regulatory system for RAAS
What are the two types of NPs released from the heart
Atrial natriuretic peptide (ANP)
Brain-type natriuretic peptide (BNP)
ANP released in response to atrial distension (hypervolemic states) by atrial myocytes
BNP released by brain and heart ventricles
What is measured in patients with suspected heart failure
Serum BNP
What causes ADH release
ADH release is stimulated by increased plasma osmolality
Role of ADH
Acts in kidney tubules to increase water reabsorption - concentrate urine
Increase ECFV and plasma volume —> CO and BP
ADH causes vasoconstriction —> increase SVR and BP
Conclusion of what RAAS, NPs and ADH do
Short term regulation of MAP = baroreceptor reflex
Long term = control of blood volume and hormones
ADH regulates ECFV and osmolality to deal with fluid loads
RAAS = long term regulation of MAP
NPs counter-regulate RAAS
