control of blood volume Flashcards
what happens to urine production when arterial pressure increases?
urine production increases (so blood volume decreases)
what happens to urine production when arterial pressure decreases?
urine production decreases (so blood volume increases)
where is ADH released from?
the pituitary gland
what causes ADH to be released?
- an increase in osmotic pressure ( i.e. higher concentration of solute in the blood)
- hypovolemaia (low blood volume)
- hypotension
- angiotensin II
do atrial baroreceptors normally inhibit or promote ADH release?
inhibit
how does ADH increase blood volume?
by increasing water permeability in renal collecting ducts, therefore decreasing urine production
what does ADH cause in severe hypovolemic shock?
a high release of ADH causes vasoconstriction, increasing total peripheral resistance
what area of the brain detects a change in blood osmotic pressure, causing a release of ADH?
the hypothalamus
what type of protein is Renin?
a proteolytic enzyme
what causes renin release?
- sympathetic nerve activation
- renal artery hypotension
- decreased sodium in kidney distal tubules
which cells in the kidneys release Renin?
juxtaglomerular cells
what is the substrate for renin?
angiotensinogen
where is the angiotensin converting enzyme (ACE) found?
in the lungs (converts angiotensin 1 to angiotensin 2)
what is the DIRECT effect of renin on the kidneys?
constricts renal arteries, therefore decreasing blood flow to the kidneys and less urine output
what substance does renin cause to be released which increases sodium and water resorption?
aldosterone (released from adrenal glands)
what other hormone does renin cause to be released?
ADH
what is the name of the hormone released in response to stretch of the atria which increases urine output and so decreases blood volume?
atrial natriuretic hormone (28 amino acid peptide)
a 10-15% blood loss results in which class of shock?
class 1
a >40% blood loss results in which class of shock?
class 4
a 15-30% blood loss results in which class of shock?
class 2
a 30-40% blood loss results in which class of shock?
class 3
what happens to stroke volume (SV) in response to hypovolemia?
sympathetic activity results in an increase in contractility which increases stroke volume
what happens to heart rate (HR) in response to hypovolaemia?
reflex actions increase heart rate
what happens to CO in response to hypovolaemia?
as SV and HR have both increased, CO also increases
what happens to total peripheral resistance in response to hypovolaemia?
increases to try and restore mean arterial blood pressure to as near normal values as before
what are the three main LATER responses to hypovolaemia?
- arterial constriction (decreases fluid loss from capillaries and favours fluid reabsorption)
- decreased renal blood flow
- thirst
how does the cerebral cortex affect the control of blood pressure?
conscious effects of emotions send nerves to the medullary CVC centre
how does the time of day affect the control of Bp?
diurnal variations in circulation of hormones and cortical input
how does respiration affect control of Bp?
mechanical movements (decrease/increase in pressure in blood vessels inside/outside the thorax) - also via chemoreceptors (aortic and carotid bodies detect changes in pO2 and alter rate of firing)
