Control of arterial blood pressure - 2 Flashcards
What are the components of the total body fluid?
- 2/3 are intracellular fluid
- 1/3 are extracellular fluid
What makes up the extracellular fluid volume (ECFV)?
Plasma volume (PV) + interstitial fluid volume (IFV)
What happens if plasma volume falls?
Compensatory mechanisms shifts fluid from the interstitial compartment to the plasma compartment
What happens if ECFV is controlled?
Plasma volume (PV), blood volume and MAP would be controlled
How do hormones act as effectors to regulate the extracellular fluid volume (including plasma volume)?
Regulating the water and salt balance in our bodies
What is the water and salt balance in healthy people?
water input=water output
What 3 hormones regulate extracellular fluid volume?
- The renin-angiotensin- Aldosterone system- RAAS
- Atrial natriuretic peptide -ANP
- Antidiuretic hormone (arginine vasopressin)- ADH
What is the role of renin-angiotensin-aldosterone system?
Regulates plasma volume and TPR and hence the regulation of MAP
Where is renin released from?
Kidneys
What does renin do?
Stimulates the formation of angiotensin I in the blood from angiotensinogen (produced by the liver)
What converts angiotensin I to angiotensin II?
Angiotensin coverting enzyme -ACE
What are the roles of angiotensin II?
1) stimulates the release of Aldosterone from the adrenal cortex
- Causes systemic vasoconstriction which increases TPR and BP
- Also stimulates thirst and ADH release - i.e. contributes to increasing plasma volume and BP
What is the function of aldosterone?
- steroid hormone
- acts on kidneys to increase sodium and water retention which increases plasma volume
What 2 main factors affect extracellular fluid volume?
- water excess or deficit
2. Na+ excess or deficit
What 3 mechanisms regulate the RAAS ?
(1) Renal artery hypotension -caused by systemic hypotension ( blood pressure)
(2) stimulation of renal sympathetic nerves
(3) Decreased [Na+] in renal tubular fluid – sensed by macula densa (specialised cells of kidney tubules
What Is the rate limiting step for RAAS?
Rennin secretion
What is the role of atrial natriuretic peptide and when is it secreted?
- released in response to atrial distension
- causes excretion of salt and water in the kidneys, thereby reducing blood volume and blood pressure
- decrease rennin release
- counter-regulatory mechanism for RAAS
What is antidiuretic hormone (ADH)?
Peptide hormone derived from a prehormone precursor synthesised by the hypothalamus and stored in the posterior pituitary
What is secretion of ADH stimulated by?
1) reduced extracellular fluid volume
2) increased exrtracellular fluid osmolarity (main stimulus)
What is the normal osmolarity of extracellular fluid?
280 milli-osmoles/l
What is plasma osmolarity is monitored by?
Osmoreceptors mainly in the brain in close proximity to hypothalamus -
What does increased plasma osmolarity lead to?
stimulation the release of ADH
What is the role of ADH?
-acts in the kidney tubules to increase the reabsorption of water (conserve water) which increase extracellular and plasma volume and hence CO and BP
What effect does ADH have on blood vessels?
- cause vasoconstriction which increases TPR and BP
- the effect is small in normal people but becomes important in hypovolaemic shock
