control of blood volume Flashcards
Where is blood volume controlled on the long term?
controlled in the kidneys. the renal body fluid feedback system
What effect does increased arterial pressure have on urine production?
increases urine production
What does an increase in hydrostatic pressure in the kidneys mean?
increase across the kidneys and the glomeruli will push out more fluid into the bladder
what effect does increase in blood pressure have on sodium ions? What effect do sodium ions have on water?
- more sodium ions are pushed out
- water follows sodium hence more water will be pushed out
what happens to renal output when salt and water intake is increased?
kidney function takes on a more chronic regulation to keep blood pressure low
what happens to renal output if blood pressure increases?
increases renal output of water and salt causing blood pressure to go back down again by reducing blood volume
what are the meanings of volume and osmolarity?
volume- total amount of blood in the system
osmolarity- right concentration of blood
how is blood osmolarity sensed?
osmotic receptors in the hypothalamus
what hormone is released by the hypothalamus?
antidiuretic hormone ADH
what stimulates ADH to be released?
released in response to increased osmotic pressure detected in the hypothalamus
what effect does hypovolemia have on ADH release? Explain the mechanism
- arterial baroreceptors normally inhibit ADH release however the decrease in volume therefore decreases the firing rate and hence
- increases ADH release
How does ADH reduce urine output?
increases water permeability in renal collecting ducts by increasing the tuber of aquoporins there hence decreasing urine production
Which system is involved in the long term control of blood volume and plasma salt composition?
renin angiotensin aldosterone system
RAAS
how is decreased blood volume controlled by the long term control RAAS?
- decrease in blood volume decreases mean arterial blood pressure sensed by baroreceptors
- baroreceptors feed the info to the MCVCC
- increase in renal sympathetic nerves increases kidney renin output decreasing urine formation
What are the component parts of the RAAS?
-renin (an enzyme)
angiotensin 2
what does Angiotensin 2 act on? what 2 things does it do?
- directly on the kidney
- constricts arteries in the kidneys decreasing blood flow to kidneys and stimulates the release of aldosterone from adrenal glands which increases sodium and therefore water reabsorption
how and where is angiotensin 2 formed?
- angiotensin 1 is pumped through the system to heart and then when it arrives in the pulmonary circulation it meets an enzyme
- enzyme converts 1 into 2
what are the 4 functions of angiotensin 2?
- vasoconstriction
- renal retention of sodium and therefore water
- increased arterial pressure
- increase release of ADH
what is produced by atrial cells when the atrial wall is stretched?
atrial natriuretic peptide ANP
what is the structure of ANP? Where is it stored? what is its function?
- 28 amino acid peptide
- stored in muscle cells of the atria
- released in response to the stretch of the atria and helps oppose effects of RAAS
what effect does haemorrhage have on the blood volume?
decrease blood volume, decreased venous return, decreased arterial pressure, decreased end diastolic volume
what features are involved in the baroreceptor reflex response to haemorrhage?
Stroke volume, hear rate, cardiac output, total peripheral resistance, mean arterial blood pressure
What happens to SV during haemorrhage?
- decreases at the point of haemorrhage
- then is increased since veins are squeezed in response however it does not increase to the same level it was at
what happens to heart rate during haemorrhage?
remains constant at time of haemorrhage then increases with sympathetic nerve stimulation to increase CO
what happens to total peripheral resistance as a result of haemorrhage?
increases because veins constrict to decrease capacity in order to push blood back to the heart in response to sympathetic innervation
What other conditions cause hypovolemia?
- decreased plasma as a result of burns
- decreased sodium form vomiting
- decreased blood pressure
what is the later response to hypovolemia since nerve innervation reflex mechanisms are short term?
- arteriole constriction to decrease hydrostatic pressure in capillaries favouring fluid reabsorption
- temporary redistribution of blood flow
- decreased renal blood flow, decreased urine output
what happens in severe hypovolemia?
if fluid lost can’t be compensated fro damage to tissue and organs may occur
-can lead to heart failure
how is severe hypovolemia treated?
-fluid replacement is required: resuscitation fluids, colloid, blood
what factors input into the medullary cardiovascular control centre?
cortex, blood hormone levels, posture and movements, hypothalamus and thalamus
