Responses to CVS stress

Question 1

When you stand up, what happens to the blood above your heart due to gravity?

Answer 1

Blood is forced to the heart so arteries above the heart will have low pressure

Question 2

When you stand up, what happens to the blood below your heart due to gravity?

Answer 2

Blood is forced to the toes and pressure is high there

Question 3

Why is blood pressure taken from the arm?

Answer 3

The artery is in line with the heart so won’t be affected by gravity

Question 4

What effect does gravity have on arteries and veins?

Answer 4

Little effect on arteries as they are muscular

Effect veins - causes distention as blood pools in the veins

Question 5

What effect does pooling in legs have on blood pressure?

HINT: hydrostatic pressure

Answer 5

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

Question 6

What is transient hypotension?

Answer 6

When you stand up too fast can cause a drop in blood pressure

Question 7

Which mechanisms occur following a haemorrhage?

Answer 7

• heart rate increases
• heart contractility changes
• organ specific vasoconstriction

Question 8

How is it that following a haemorrhage, less fluid is lost and more is retained?

Answer 8

Hydrostatic pressure in capillaries is lower so more fluid is retained

Question 9

What is autotransfusion?

Answer 9

a significant reasbsorption of fluid into capillaries follow decrease in blood pressure

Question 10

Which hormones are used following a hemorrhage?

Answer 10

• angiotensin 2
• aldosterone
• vasopressin

Question 11

What does angiotensin 2 do to increase blood pressure?

Answer 11

Vasoconstrictor so reduces blood flow to kidney so less urine produced

Question 12

What do aldosterone and vasopressin do?

Answer 12

In collecting duct they work. Aldosterone increases sodium reabsorption hence water and vasopressin stimulates water retention

Question 13

When will you experience shock - how much blood must be lost?

Answer 13

Over 30%

Question 14

During exercise what happens to the blood vessels?

Answer 14

Vasodilation and a decrease in TPR

Question 15

What is active hyperemia?

Answer 15

During exercise skeletal muscle uses lots of glucose and oxygen. This causes local vasodilation to increase supply. The process is active hyperaemia

Question 16

What are the control mechanisms to deal with exercise?

Answer 16

• 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

Question 17

How is total peripheral resistance changed?

Answer 17

Sympathetic NS vasoconstricts to counteract fall in TPR caused by vasodilation. Lots of constriction in the abdominal region.

Question 18

What are the negative effects of changes caused by exercise?

Answer 18

• Increased capillary pressure so more fluid is lost
• sweating causes more fluid loss
• plasma volume decreases

Question 19

What is the overall effect of exercise on blood pressure?

Answer 19

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

Question 20

What effect does the sympathetic system have on the skin and why?

Answer 20

The sympathetic system has a negative effect on the skin - allows dilation to allow heat to radiate

Question 21

What is the overall effect of exercise on TPR?

Answer 21

TPR falls due to vasodilation but less of a fall due to sympathetic activity

Question 22

What effect does exercise have on cardiac output and why?

Answer 22

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.

Question 23

What is the compensatory response to standing up?

Answer 23

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.

Question 24

What happens when low pressure is detected at the kidney following a haemoorhage?

Answer 24

↑ renin release and angiotensin activation ↑ = aldosterone

Reflex ↑ secretion of vasopressin