Coordinated response of CVS

Question 1

Orthostasis

Answer 1

On standing up the CVS changes according to the effect of gravity

Question 2

What occurs when orthostasis occurs

Answer 2

Blood pressure falls at first - postural hypotension, lack of blood flow to brain - faint
Quickly recovers - due to homeostatic mechanisms such as baroreflex

Question 3

What 3 things does the baroreflex integrate

Answer 3

Increase heart rate
Increase heart contractility
Increase TPR

Question 4

Bernoulli’s law

Answer 4

Blood flow = pressure energy + potential energy + kinetic energy

Question 5

Gravity induced high venous blood pressure

Answer 5

High BP in venous system at feet is due to hydrostatic pressure

Question 6

How does orthostasis cause hypotension when standing

Answer 6

1) Fall in CVP
2) Decreased end diastolic volume
3) Decreased SV
4) Decreased CO
5) Poor perfusion of brain -dizziness and fainting

Question 7

How does orthostasis cause hypotension when lying down

Answer 7

1) Increased central venous pressure
2) Increased end diastolic volume
3) Increased SV
4) Increased CO

Question 8

Reflex response to orthostasis

Answer 8

1) Less stimulation (unloading) of baroreceptors
2) Lower afferent fibre activity
3) Switches off inhibitory nerves that go from CVLM to RVLM
4) Results in RVLM being more active sending efferent signals to heart and arterioles
5) Increased sympathetic drive to SA node and Increased HR
Myocardium increased contractility.
Vasoconstriction increases TPR
Less vagal parasympathetic activity to SA node - overall increase in BP

Question 9

What makes postural hypotension worse

Answer 9

• α-adrenergic blockade, generalized sympathetic blockade or other drugs that reduce vascular tone
• Varicose veins
• Lack of skeletal muscle activity
• Reduced circulating blood volume
• Increased core temperature

Question 10

The initial effect of microgravity (space) on CVS

Answer 10

• Blood not pooling in feet and returning to the heart easily, increases atria/ventricle volume so increase CO and preload
• Sensed by cardiac mechanoreceptors leading to a reduction in sympathetic activity
• Reduces ADH and RAAS
• Increases ANP and GFR
• Overall reduction in blood volume by 20%

Question 11

Long term effect of microgravity on CVS

Answer 11

Less BV, reduced stress on heart, heart reduces in muscle mass, genreal drop in BP

Question 12

Effect of returning to gravity on CVS

Answer 12

Severe postural hypotension due to lower blood volume and smaller heart
Baroreflex can’t compensate

Question 13

Cardiovascular response to the exercise

Answer 13

Increase sympathetic activity and reduce vagal inhibition
Increase lung O2 uptake
Control BP
Dynamic
Static

Question 14

CVS response to dynamic excercise

Answer 14

Constantly shortening and relaxing with lots of different muscle groups involved - lower BP and sympathetic tone

Question 15

CVS response to static exercise

Answer 15

1 specific muscle group is being worked without constant movement - Higher BP, local metabolic hyperaemia

Question 16

What are some small adaptations that will increase pulmonary circulation

Answer 16

Increase HR
Increase SV
Increase atriovenous O2 difference

Question 17

Exercise induced tachycardia

Answer 17

Maximum HR = 220
Decrease vagal tone
Increase sympathetic activity

Question 18

Exercise induced stroke volume

Answer 18

• INCREASE END DIASTOLIC VOLUME
• FASTER EJECTION
• DECREASED END SYSTOLIC VOLUME

Question 19

What does an increase end-diastolic volume mean in exercise induced SV

Answer 19

increase venous return/CVP through veno-constriction

Increase sympathetic activity and calf muscle pump - activates starling law increasing preload

Question 20

What does a faster ejection mean in exercise induced SV

Answer 20

increase contractility by sympathetic activation of β1 receptor (inotropic increase in Ca2+)

Question 21

What does a decreased end systolic volume mean in exercise induced SV

Answer 21

Accounts for increase SV. Increase contractility by sympathetic activation of β1 receptors and starling’s law

Question 22

What does compensatory vasoconstriction of non-essential circulations do

Answer 22

Prevent hypotension due to exercise induced decreased TPR

Prevent BP from falling

Question 23

What does RVLM control

Answer 23

Specific pre-ganglionic sympathetic nerves in spinal cord which send out post ganglionic nerves to specific tissues

Question 24

Metaboreceptors

Answer 24

Small diameter sensory fibres in skeletal muscle

Are chemosensitive

Question 25

What stimulates metaboreceptors

Answer 25

K+, H+, Lactate which increase in exercising muscle

Question 26

Reflex effects of metaboreceptors

Answer 26

• Tachycardia (via increased sympathetic activity)
• Increased blood pressure
• ‘Pressor response’ to exercise

Question 27

What do metaboreceptors do

Answer 27

• Important during isometric exercise (increased muscle load). Static exercise raises BP more than dynamic exercise
• Raised BP maintains blood flow to contracted muscle to try force blood into the contracted muscle
• Contracted muscle supplied by dilated resistance vessels due to metabolism – selective metabolic hyperaemia