Coordinated responses of the CVS - gravity & exercise

Question 1

Describe orthostasis?

Answer 1

• Orthostasis= On standing up ( orthostasis) the cardiovascular system changes according to the effect of gravity
  1. Blood pressure falls at first
• postural hypotension occurs and there is a lack of blood flow to the brain. This makes an individual feel faint
  2. Quickly recovers
• individual will quickly recover due to homeostatic mechanisms such as baroflex.
  3. Baroflex integrates 3 smaller changes by increasing:

1. Heart rate
2. Force of contraction
3. Total peripheral resistance

HFT

Question 2

Describe the effect of gravity on blood pressure?

Answer 2

1. The arterial pressure gradient is 95-180mmHg
2. Gravity pulls down causing high pressure near the feet
3. We go against the pressure gradient to transport the blood from the heart to the feet
   4, Bernoulis law= pressure energy + potential energy+ kinetic energy
4. The total energies mean the blood will flow from the heart to the feet

Question 3

Describe hydrostatic pressure

Answer 3

1. The high pressure in the venous system at the feet is due to hydrostatic pressure
2. Pressure is higher at the feet

Question 4

Pressure equation?

Answer 4

Pressure= phg

Question 5

Describe how orthostaiss causes hypotension when you are standing up? (6pts)

Answer 5

1. Standing up
2. The blood pooling in the legs will decrease the amount of blood returning to the heart which will cause a fall in central venous pressure
3. This will cause decreased end diastolic volume- the heart doesn’t fill as much
4. This will cause decreased stroke volume- the heart does not stretch as much
5. This causes a decreased cardiac output- decreases the rate of contraction of the heart
6. This will cause poor perfusion of the brain which leads to dizziness and fainting

Question 6

What happens when you are laying down e.g in fainting? (5pts)

Answer 6

1. Lying down
2. This causes increased central venous pressure
3. This causes increased end diastolic volume
4. This causes increased stroke volume
5. This causes increased cardiac output

Question 7

What is the reflex response to orthostasis?

Answer 7

1. When you stand up there is less stimulation of baroreceptors
2. This lowers afferent fibre activity to the NTS. The NTS switches off inhibitory nerves that go from the CVLM to the RVLM
3. There is therefore less vagal parasympathetic activity to the SA node via the nucleus ambigious. This will increase blood pressure
4. This results in the RVLM being more active sending efferent signals to the heart and the arterioles
5. This increases the sympathetic drive to the SA node which causes increased contractility of the heart. This will cause an increase in heart rate. Myocaridum will increase contractility. Vasoconstriction of the arteries and the veins will increase total peripheral resistance and will send more blood to the heart

Question 8

What makes postural hypotension worse?

Answer 8

1. a- adrenergic blockers or generalised sympathetic blocake or other drugs that reduce vascular tone.

side effects= calcium channel blockers used to treat hypotension and angina

2. Varicose veins- impairs venous return. If valves cannot close in the veins then less blood returns to the heart
3. Lack of skeletal muscle activity- due to paralysis or forced inactivity e.g long term bed rest and soldiers on guard
4. Reduced circulating blood volume- reducing blood volume will reduce preload. This will cause haemorrhage
5. Increased core temperatyre- an increased temperature will cause increased peripheral vasodilation which will cause less blood volume to be available.

Question 9

What happens when you first go into space? (6pts)

Answer 9

1. Blood not pooling in the feet therefore it will return to the heart easily
2. This increases atria/ ventricle volume and so increases preload and cardiac output
3. This is sensed by cardiac mechanoreceptors leading to a reduction in sympathetic activity
4. This reduces ADH and increases ANP
5. There is increased glomelular filtration rate and reduced RAAS. This is due to the increased preload
6. Overall the blood volume will reduce by 20% and we adapt to a new normal

Question 10

What happens when you are long term in space?

Answer 10

1. There is a lower blood volume
2. There is reduced stress on the heart
3. Heart reduces in muscle mass
4. There is a general drop in blood pressure

Question 11

What happens on return to gravity? (2pts)

Answer 11

1. Severe postural hypotension due to much lower blood volume and a smaller heart
2. The baroreceptor reflex cannot compensate

Question 12

Describe the cardiovascular response to exercise?

Answer 12

1. There is a central command in the brain. Jus thinking of exercise will cause some changes to be imitated,
2. Once exercise commences there is feedback from the muscles via mechanoreceptors and metaboreceptors
3. All changes are going to affect sympathetic activity and vagus inhibition

causes

1. increased lung uptake- more oxygen is needed and more of it is transported around the body and supplies to exercising muscle . This increases heart rate and force of contraction
2. Control of blood pressure- despite huge changes in cardiac output and resistance, This protects the heart from excessive afterload which will reduce cardiac output
3. Coordinated dilation/ constriction of vascular beds- it specifically targets areas where the oxygen is delivered.

Question 13

What happens at high oxygen exercise levels?

Answer 13

The arterio-venous oxygen difference reaches a plateau

Question 14

Describe the increase in cardiac output during exercise? (2pts)

Answer 14

1. During light exercise heart rate increases slightly whilst stroke volume increases significantly due to starlings law
2. As levels of exercise increase eventually the increase in stroke volume will reach its max value and will plateau

Question 15

Describe exercise induced tachycardia? (3pts)

Answer 15

1. There is a decreased signal down the vagus nerve to the SA node and AV nodes
2. There is increased sympathetic activity to the SA and AV nodes
3. The maximum heart rate= 220-age

Question 16

Describe how sympathetic activity will increase stroke volume?

Answer 16

1. Increased end diastolic volume (filling pressure)

• there is increased sympathetic activity and calf muscle pump causes vasocosntirction which increases venous return and CVP
  2. Activates starlings law which increases preload

2. Faster ejection
3. increased sympathetic activation of B1 receptors which causes faster ejection of blood
4. This causes an intropic increase in calcium
5. Decreased end-systolic volume- increases ejection
   - increased contractility by sympathetic activation of B1 receptord aNd increased stretching e.g starlings law

Question 17

What happens during leg exercise?

Answer 17

1. As you do leg exercise there is an increase in blood flow in the leg muscle, heart and skin. The brain is unaffected
2. In the leg there is a local resistance force due to metabolic hyperemia vasodilation. This is a local sympathetic response. Hyperaemia causes vasodilatation by binding to the sympathetic nerve directly and causing vasodilation. B2-mediated vasodilation occurs via circulating adrenaline, B2 receptor expression is high in skeletal muscle and coronary arteries.

Question 18

What happens to cardiac output as we exercise? (3pts)

Answer 18

1. There is a large increase in cardiac output as we exercise
2. There is a small increase in mean blood pressure due to dilated skeletal muscle arterioles which decreases total peripheral resistance
3. There is a large decrease in total peripheral resistance

Question 19

Describe compensatory vasoconstriction of non essential circulation?

Answer 19

1. The compensatory vasoconstriction of non essentail circualtion prevents hypotension due to exercise-induced decreased total peripheral reistance
2. Compensatory vasoconstirction in inactive or unrequited tissues e.g kidneys, GI tract and inactive muscle. This prevents blood pressure from falling
3. The RVLM controls specific pre-ganglionic sympathetic nerves in the spinal cord which send out post ganglionic nerves to specific tissues

Question 20

Describe compensatory vasoconstriction of non essential circulation?

Answer 20

1. The compensatory vasoconstriction of non essentail circualtion prevents hypotension due to exercise-induced decreased total peripheral reistance
2. Compensatory vasoconstirction in inactive or unrequited tissues e.g kidneys, GI tract and inactive muscle. This prevents blood pressure from falling
3. The RVLM controls specific pre-ganglionic sympathetic nerves in the spinal cord which send out post ganglionic nerves to specific tissues

Question 21

What are metaborecptors?

Answer 21

1. Metaboreceptors are small diameter sensory fibres in skeletal muscle
2. They are chemorecptive- they are stimulated by H+, K+ and lactate which all increase in exercise.

Question 22

Name reflex effects

Answer 22

1. Tachycardia- via increased sympathetic activity
2. Increased blood pressure
3. Pressure respons to exercise

• reflex actions are important during isometric exercise which is increased muscle load
• statin exercise raises blood pressure more than dynamic exercise
• raised blood pressure maintains blood flow to contracted muscle to try to force blood into the contracted muscle
• contracted muscle supplied by dialated resistance vessels due to metabolism- selective metabolic hyperamia

Question 23

What is dynamic exercise

Answer 23

Constantly shortenting and relaxing with lots of different muscle groups involved- lower bp, lower sympathetic tone

Question 24

What is static exercise

Answer 24

One specific muscle group is being worked without constant movemnt- higher bp, local metabolic hyperaemia