Control of Arterial Blood Pressure Lecture 2 Flashcards
how is blood volume and MAP controlled?
by controlling the extracellular fluid volume
60 percent of body weight is water. what are the two fatcors contributing to total body fluid?
intracellular fluid (2/3rd) and extracellular fluid (ECF) - normally 1/3rd of the total
what two things make yo the ECF?
plasma volume (PV) and interstitial volume (IFV)
what is the IFV?
the fluid which bathes the cells and acts as the go between the blood and body cells
what happens to the volume in the IFV when PV falls?
compensatory mechanisms move fluid from the IFVto the PV
what two main factors affect EFV?
- water excess or deficit
2. Na excess or deficit
how is the EFV regulated?
by hormones that regulate the water and salt balances in our bodies
healthy people stay in a stable water and salt balance where…
water input = water output
what three hormones regulate the EFV ?
- the renin-angiotensin-aldosterone - RAAS
- atrial netriuretic peptide - ANP
- Antidiuretic hormone (arginine vasopressin)
what are the three components of RAAS?
renin
angiotensin and aldosterone
where is renin released?
from the kidneys
what does renin stimulate?
the formation of angiotensin 1 in the blood from angiotensinogen
where is angiotensinogen produced?
in the liver
what is the angiotensin 1 converted to?
angiotensin 2 by the angiotensin converting enzymes
where is ACE produced?
by the pulmonary vascular endothelium - the inner lining of blood vessels
what does angiotensin 2 stimulate?
the release of aldosterone
where is aldosterone released from?
the adrenal cortex
what does angiotensin do?
causes systemic vasoconstriction which increases the TPR
it also stimulates thirst and ADH release i.e. contributes to increasing PV mainly brought about by aldosterone
what effect does aldosterone have on the kidneys?
increases sodium and water retention - increases the PV
what is the renin angiotensin aldosterone system regulated by?
mechanisms which stimulate the release of renin from the juxtaglomerular apparatus in the kidney
what are the three reasons for increased renin release?
- renal artery hypotension - casued by systemic hypotension (low BP)
- stimulation of renal sympathetic nerves
- decreased Na in renal tubular fluid
what senses the decreased Na in renal tubular fluid?
macula densa (specialised cells of the kidney tubules)
what is the juxtaglomerula apparatus ?
a region comprising the macula densa, extraglomerular mesangial cells and granular cells (release renin)
what do granular cells do?
release renin
where is the atrial Natriuretic peptide synthesised?
28 amino acid peptide hormone synthesised and stored by atrial muscle cells (atrial myocytes)
what stimulates the release of ANP?
atrial distension - hypervolaemic states
what does ANP cause?
the excretion of salt and water in the kidneys
acts as a vasodilator
decreases renin release so acts as a counter regulatory mechanism for RAAS
what does the excretion of salt and water in the kidneys due to ANP lead to?
a reduced blood volume and blood pressure
what is ADH?
peptide hormone derived from a prehormone precursor
where is ADH synthesised and stored?
synthesised in the hypothalamus and stored in the posterior pituitary
what stimulates the release of ADH? 2 things
- reduced EFV
2. increased EF osmolarity (main stimulus)
what is the normal osmolarity of EF?
about 280 milli-osmoles
what is plasma osmolarity monitored by?
osmoreceptors mainly in the brain in close proximity to the hypothalamus
what does ADH do?
acts on the kidney tubules to increase reabsorption of water (conserve water) i.e. concentrate urine (antidiuresis)
WHAT DOES THIS INCREASE in water reabsorption by ADH do?
increases the extracellular and plasma volume and hence CO and BP
what does ADH do to the blood vessels ?
causes vasoconstriction which increases TPR and blood pressure; the effect is small in normal people but becomes important in hypovolaemic shock ( haemorrhage)
