Lecture 14 – Coordinated responses of the CVS – exercise, gravity hemorrhage

Question 1

Examples of coordianted responses of the CVS (5)

Answer 1

Exercise
FFF
Diving
Sleeping 
Gravity
- microgravity on CVS
- Orthostasis

Question 2

Orthostasis 3

Answer 2

standing up
Fall in BP due to postural hypotension (lack of blood flow to brain), after a long period
Recovers due to homestatic response, baroreflex

Question 3

Baroreflex integrates 3 smaller changes (3)

Answer 3

HR
Heart contractility
TPR
These IN perfusion to the brain

Question 4

effects of gravity on bp during orthostasis (5)

Answer 4

When lying down bp in head/feet is the same.
Standing up, bp in feet is greater as blood pools.
Pressure in heart is greater so for blood to get to the brain it considers BERNOULLIS LAW (PE/KE).
Blood leaving heart will have a higher PE/KE but will be at a lower pressure.
If there is an issue with CO fingers/toes will become poorly perfused.

Question 5

How to get blood flow from heart to feet to heart?

Answer 5

• How to get blood flow from heart to feet to heart?

Arterial pressure gradient is 95-185 mmHg

Question 6

Gravity induced high venous BP 3

Answer 6

High venous P due to HYDROSTATIC pressure.
Pressure in veins of feet = P x Height x Gravity constant.
Veins are complaint capacitance vessels and distend at the bottom, so blood can pool in the feet, lower pressure.

Question 7

how does orthostasis cause hypotension? 4

Answer 7

Venous pooling of 500ml in the legs reduces the return to the heart, fall in CVP.
EDV DE.
A lot of pooling = less blood fills LV (STARLINGS LAW), so stretched less, IN SNS, DE PNS.
Leads to dizziness and fainting.

Question 8

Reflex response to orthostasis

Answer 8

Basically FC - decrease in BP, unloading etc.
IN SNS
DE PNS

Question 9

What makes postural hypotension worse 5

Answer 9

Alpha adrenegic blockers - less SNS, reduces vascular tone e.g. side effect of VGCC blocker used to treat hypertension/angina.
Varicose veins - impairs venous return
Lack of skeletal muscle activity - due to paralysi/forced inactivity
Reduced circulating BV - e.g. haemorrhage
IN core T - so more peripheral VD

Question 10

effect of mimcrogravity on CVS 5

Answer 10

Doesnt matter if you sit or stand there is no blood pooling.
Preload and STARLINGS LAW is in account, loading of BR.
So DE in SNS, IN in PNS, VD.
Sensed by cardiac mechanoreceptors.
De in ADH, IN in ANP.
IN in GFR, reduced RAAS

Question 11

CVS response to exercise 3

Answer 11

IN SNS, DE PNS
IN O2 lung uptake (up to 10-15x), need to selectively target areas where the ocygen is delievered so coordinated VD/VC of vasuclar beds.
Controlled BP- despite changes in CO, as TPR DE.

Question 12

IN in O2 uptake from the lungs 3

Answer 12

• During light exercise, there is not a great arteriovenous difference and a lower cardiac output.
• As we get more extreme, there is a limit without the mount of oxygen released from the blood into the tissues.
• Arterio-venous oxygen difference will plateau at high exercise levels, the flow must be increased through the lungs during extreme exercise.

Question 13

IN in CO during exercise 3

Answer 13

• Stroke volume can reach a maximum value which will result in a plateau phase on the Starling Curve.
• This is because the heart rate will be too high and there will be less time for filling of the heart and the effect of Starling’s Law will be less.
• If the BP goes up too much, the heart can be overfilled and there will be less of a cardiac output.

Question 14

Compensatory vasoconstriction of non-essential circulations 3

Answer 14

• Compensatory vasoconstriction of non-essential circulations prevents hypotension due to exercise-induced decreased TPR.
• Compensatory vasoconstrictions in inactive or unrequired tissues e.g. kidney, GI tract.
• Active areas: metabolic vasodilation and central control of the RVLM.

Question 15

Metaboreceptors: metabolic hyperama = local muscles di (8)

Answer 15

• Small diameter sensory fibres in skeletal muscle
o Chemosensitive - stimulated by K+, H+, lactate, which increase in exercising muscle.
• Reflex effects
o Tachycardia (via increased sympathetic activity)
o Increased blood pressure
o ‘pressor response’ to exercise
o Especially important during isometric exercise (increased muscle load). Static exercise raises BP more than dynamic exercise.
o Raised BP maintains blood flow to contracted muscle to try to force blood into the contracted muscle.
o Contracted muscle supplied by dilated resistance vessels due to metabolism - selective metabolic hyperaemia.

Question 16

Demands on CVS during exercise and how they are met 5

Answer 16

WORD DOC