Responses to CVS stress Flashcards
When you stand up, what happens to the blood above your heart due to gravity?
Blood is forced to the heart so arteries above the heart will have low pressure
When you stand up, what happens to the blood below your heart due to gravity?
Blood is forced to the toes and pressure is high there
Why is blood pressure taken from the arm?
The artery is in line with the heart so won’t be affected by gravity
What effect does gravity have on arteries and veins?
Little effect on arteries as they are muscular
Effect veins - causes distention as blood pools in the veins
What effect does pooling in legs have on blood pressure?
HINT: hydrostatic pressure
High hydrostatic pressure in the legs in addition to gravity so lots of fluid leaved capillaries. This leads to a reduction in blood plasma volume- hypotension could occur
What is transient hypotension?
When you stand up too fast can cause a drop in blood pressure
Which mechanisms occur following a haemorrhage?
- heart rate increases
- heart contractility changes
- organ specific vasoconstriction
How is it that following a haemorrhage, less fluid is lost and more is retained?
Hydrostatic pressure in capillaries is lower so more fluid is retained
What is autotransfusion?
a significant reasbsorption of fluid into capillaries follow decrease in blood pressure
Which hormones are used following a hemorrhage?
- angiotensin 2
- aldosterone
- vasopressin
What does angiotensin 2 do to increase blood pressure?
Vasoconstrictor so reduces blood flow to kidney so less urine produced
What do aldosterone and vasopressin do?
In collecting duct they work. Aldosterone increases sodium reabsorption hence water and vasopressin stimulates water retention
When will you experience shock - how much blood must be lost?
Over 30%
During exercise what happens to the blood vessels?
Vasodilation and a decrease in TPR
What is active hyperemia?
During exercise skeletal muscle uses lots of glucose and oxygen. This causes local vasodilation to increase supply. The process is active hyperaemia
What are the control mechanisms to deal with exercise?
- Preprogrammed pattern which is autonomic activation of the medullary CV centre before exercise
- Chemoreceptors in the muscle detect change and send impulse to CV centre
How is total peripheral resistance changed?
Sympathetic NS vasoconstricts to counteract fall in TPR caused by vasodilation. Lots of constriction in the abdominal region.
What are the negative effects of changes caused by exercise?
- Increased capillary pressure so more fluid is lost
- sweating causes more fluid loss
- plasma volume decreases
What is the overall effect of exercise on blood pressure?
The CO greatly increases due to greater venous return and sympathetic effects and there is a fall in TPR. But CO is greater than TPR fall so overall BP increases
What effect does the sympathetic system have on the skin and why?
The sympathetic system has a negative effect on the skin - allows dilation to allow heat to radiate
What is the overall effect of exercise on TPR?
TPR falls due to vasodilation but less of a fall due to sympathetic activity
What effect does exercise have on cardiac output and why?
Increased because increased sympathetic activity causes stroke volume and heart rate to increase. The skeletal muscle contraction squeezes veins so more venous return which also increases heart rate.
What is the compensatory response to standing up?
Carotid baroreceptors input to brainstem ↓ due to fall in pulse pressure
Cardiopulmonary receptors input to brainstem ↓ due to fall in cardiac blood volume
These reduced inputs to the brainstem elicit a reflex reduction in parasympathetic activity to the heart and an increased sympathetic outflow to the heart and vasculature. Heart rate and contractility increase.
Vasoconstriction in skeletal muscle, splanchnic & renal vascular beds so peripheral resistance ↑ there. Arterial pressure and cerebral perfusion are safe.
What happens when low pressure is detected at the kidney following a haemoorhage?
↑ renin release and angiotensin activation ↑ = aldosterone
Reflex ↑ secretion of vasopressin
