6: Control of arterial blood pressure (2) Flashcards
Long-term control of blood volume and MAP is achieved by controlling…
extracellular fluid volume
What two volumes make up the extracellular fluid volume (ECF)?
ECF = Plasma Volume (PV) + Interstitial Fluid Volume (IFV)
Interstitial fluid bathes ___.
cells
If plasma volume falls, compensatory mechanisms shift ___ ___ back to the plasma compartment.
interstitial fluid
Which two factors affect extracellular fluid volume?
- Water excess or deficit
2. Na+ excess or deficit
Extrinsic control of MAP is carried out by…
the nervous system and hormones.
How do hormones regulate the extracellular fluid volume?
They regulate the water and salt balance in our bodies
Which three hormone systems regulate extracellular fluid volume?
- Renin-Angiotensin-Aldosterone System (RASS)
- Atrial Natriuretic Peptide (ANP)
- Antidiuretic Hormone (Vasopressin) or ADH
What two constituents of MAP does the RAAS system regulate?
Plasma volume
Total peripheral resistance
Where is renin released?
The kidneys
What molecule does renin act on to produce angiotensin I?
Angiotensinogen
Where is angiotensinogen produced?
The liver
Renin stimulates the formation of ___ _ from angiotensinogen.
Angiotensin I
Which enzyme converts angiotensin I to angiotensin II?
Angiotensin converting enzyme (ACE)
Where is ACE produced?
Pulmonary vascular endothelium
ACE converts angiotensin I into ____ _.
Angiotensin II
What stimulates the release of aldosterone from the adrenal cortex?
Angiotensin II
What is released from the adrenal cortex when the cortex is stimulated by angiotensin II?
Aldosterone
Where is aldosterone released after stimulation by angiotensin II?
Adrenal cortex
Angiotensin II stimulates the release of aldosterone from the adrenal cortex.
Name another effect it has.
Causes vasoconstriction, increasing TPR and therefore MAP
Increases thirst and ADH release, increasing plasma volume and therefore MAP
Where does aldosterone act?
The kidneys
What is the effect of aldosterone once it has stimulated the kidneys?
Increases Na+ and water retention, increasing plasma volume –> increases MAP
What is the rate limiting step for the RAAS system?
Renin secretion (from the juxtaglomerular apparatus) from the kidney
Name three conditions which stimulate renin secretion from the kidneys.
1) Renal artery hypotension (decreased blood pressure)
2) Stimulation of renal sympathetic nerves
3) Decreased [Na+] in renal tubular fluid
What does ANP stand for?
Atrial natriuretic peptide
Where is the hormone ANP stored?
Atrial myocytes
What is ANP released in response to?
Atrial distension / hypervolaemic states in the atrium
What are two effects of ANP on the renal system once it has been released following atrial distension?
Decreased excretion of Na+ and water from the kidneys, reducing blood volume and therefore MAP
Decreased renin secretion
What is an effect of ANP on the vascular system?
Vasodilator - decreases MAP
Which mechanism does ANP serve as a counter to?
Renin-Angiotensin-Aldosterone system
What does ADH stand for?
Antidiuretic hormone
What is ADH also known as?
Vasopressin
Where in the brain is ADH synthesised?
Hypothalamus
Where in the brain is ADH stored?
Posterior pituitary gland
What is the main stimulator of ADH release from the posterior pituitary gland?
Increased extracellular fluid osmolarity
Also: reduced extracellular fluid volume
What is the normal osmolarity of extracellular fluid?
280 milli-osmoles/L
Which receptors in the brain monitor plasma osmolarity?
Osmoreceptors
Where does ADH act?
The kidney tubules
What effect does ADH have once it has acted on the kidney tubules?
Increases reabsoprtion of water, increasing ECF volume and hence cardiac output and MAP
What effect does ADH have on blood vessels?
Vasoconstriction - increases TPR and therefore MAP
What achieves short-term regulation of MAP?
Baroreceptor reflex
What achieves long-term regulation of MAP?
Control of blood volume by hormones
