Lecture 16: Responses of the Cardiovascular system

Question 1

Do reflexes induced by haemorrhage
become counterproductive?

Answer 1

Yes

Question 2

Describe haemorrhage

Answer 2

rapid loss of blood

1. Respond to reduction in blood volume

2. Maintains blood pressure and cardiac output

3. Restore circulating fluid volume

Question 3

Does blood pressure mainatin caridac output?

Answer 3

Yes

Question 4

During haemorrhage, what does a loss of pressure
leads to?

Answer 4

During haemorrhage a loss of pressure leads to lowered cardiac output due to a fall in venous return.

Question 5

the total peripheral resistance doesn’t immediately compensate enough, then what might happen?

Answer 5

If CO drops, and TPR doesn’t immediately compensate enough, BP falls.

Question 6

Blood Pressure =

Answer 6

(Blood Pressure = Cardiac Output × Total Peripheral Resistance)

Question 7

Haemorrhage = less blood → less pressure → weaker heart pumping → lower blood pressure → dangerous for survival if not fixed fast.

Answer 7

Haemorrhage = less blood → less pressure → weaker heart pumping → lower blood pressure → dangerous for survival if not fixed fast.

Question 8

🩸 Bleeding happens →
🫥 Veins have less blood →
🫀 Heart has less to pump out →
💔 Arteries lose pressure →
🆘 Body goes into shock if not fixed.

Answer 8

🩸 Bleeding happens →
🫥 Veins have less blood →
🫀 Heart has less to pump out →
💔 Arteries lose pressure →
🆘 Body goes into shock if not fixed.

Question 9

During haemorrhage, what do the intial corrections come from?

Answer 9

During haemorrhage inital corrections
come from baroreceptor reflexes

Question 10

Baroreceptors -> Vasomotor centres -> Autonomic nervous system

Answer 10

Baroreceptors -> Vasomotor centres -> Autonomic nervous system

Question 11

During a haemorrhage, the first thing your body tries to do to save itself is use baroreceptor reflexes to correct the falling blood pressure. Describe this process

Answer 11

• Baroreceptors (pressure sensors) detect the drop in blood pressure (because of blood loss).
• They send a signal to the vasomotor centres in the brainstem (medulla).
• The vasomotor centres activate the autonomic nervous system (especially the sympathetic branch).

Question 12

What does the autonomic nervous system do after being activated by the baroreceptors?

Answer 12

• (A) Increase cardiac output (make the heart pump harder and faster):
• Elevating heart rate — via sympathetic nerves (and less parasympathetic “braking”).
• Enhancing contractility — so the heart squeezes stronger.
• (B) Increase drive to blood vessels (mainly sympathetic):
• Constriction of arterioles in areas like skin, gut (GI), and skeletal muscle — to raise TPR (Total Peripheral Resistance) and maintain blood pressure.
• Constriction of veins (“raising venometer tone”) — pushing more blood back to the heart (increasing venous return).

Question 13

How may increasing cardiac output increase the rates of haemorrhage?

Answer 13

• raising blood pressure too much can sometimes worsen bleeding if the wound isn’t sealed (but the body prioritises perfusion of vital organs first).

Question 16

When increasing the drive to the vasculature, more blood will be sent back to the brain and heart, but this limits blood and oxygen supply to other organs. So a person may recover from the haemorrhage with significant organ damage, even though it keeps them alive in the moment.

Answer 16

When increasing the drive to the vasculature, more blood will be sent back to the brain and heart, but this limits blood and oxygen supply to other organs. So a person may recover from the haemorrhage with significant organ damage, even though it keeps them alive in the moment.

Question 17

During haemorrhage what happens when hydrostatic pressure decreases below oncotic pressure?

Answer 17

• Extreme Reabsorption of fluid into the capillary bed at the expense of viscosity

Question 18

Is angiotensin II one of the most powerful vasoconstrictors found in the body?

Answer 18

Yes

Question 19

How does the secretion of renin correct for the loss of blood volume?

Answer 19

• It secretes Angiotensinogen
• This eventually allows for the secretion of angiotensin II , which in the short term will result in: Constriction of arterioles, Increase TPR, Constriction of veins, Restore filling pressure.
• In the long term: Secretion of aldosterone, Fluid retention, Thirst, Restoring ECF

Question 20

What does the secretion of erythropoietin do?

Answer 20

Secretion of erythropoietin corrects
for loss of red blood cells

Question 21

Secretion of erythropoietin corrects
for loss of red blood cells

Answer 21

• Reabsorption of interstitial fluid partially restores blood volume
• Expense of haematocrit and plasma proteins (colloid osmotic pressure will fall)
• Other longer term physiological mechanisms will restore extracellular fluid volume :
• Secretion of aldosterone, anti-diuretic hormone,
• Atrial natriuretic peptide.
• Secretion of erythropoietin will restore red cell count

Question 22

How many classes of heamorrhage are there?

Answer 22

4

Question 23

Describe Class I Hemorrhage

Answer 23

• Loss of 15% of blood volume
• No change in vital signs (i.e. blood donation)

Question 24

Describe Class II Hemorrhage

Answer 24

• Loss of 15-30% of total blood volume.
• Tachycardia, narrowing of the difference between the systolic and diastolic blood pressures, peripheral vasoconstriction.
• Skin looks pale and is cool to the touch.
• The patient may exhibit changes in behavior.

Question 25

Describe Class III Hemorrhage

Answer 25

- The loss of 30-40% of blood volume - Heart rate increases, blood pressure drops, the peripheral hypoperfusion (shock), mental status worsens. - Fluid resuscitation with crystalloid and blood transfusion are necessary.

Question 26

Describe Class IV Hemorrhage

Answer 26

- loss of >40% of circulating blood volume. - The limit of the body's compensation is reached and aggressive resuscitation is required to prevent death.

Question 27

What clinical interventions are required when someone is undergoing haemorrhage?

Answer 27

1. Treat the cause of blood loss - prevent further bleeding 2. Give fluids – preferably blood, but otherwise saline with colloid to maintain oncotic pressure 3. Monitor oxygen saturation (oximetry) 4. In severe situations, monitor the filling pressure of the heart (left atrial pressure) with catheter.

Question 28

What is needed for exercise?

Answer 28

Provide skeletal muscle with radically increased blood supply Raise cardiac output and balance changes in peripheral resistance Increase coronary blood flow

Question 29

Is it true that exercise requires the redistribution of blood supply to the skeletal muscles?

Answer 29

Yes

Question 30

How is the blood supply redistributed to the skeletal muscles during exercise?

Answer 30

Vasoconstriction in peripheral tissues Vasodilatation in muscle blood vessels

Question 31

Athletes do a lot of training that increases their sympatheic output and descreases parasympathetic output.

Answer 31

Athletes do a lot of training that increases their sympatheic output and descreases parasympathetic output.

Question 32

Sympathetic drive increases adrenaline. Vasoconstriction occurs through adrenaline acting at α-receptors But the muscle has β2 receptors. And adrenaline causes vasodilation via β2 receptors. So blood flow will be constricted to all other organs and places in the body, except for the skeletal muscle.

Answer 32

Sympathetic drive increases adrenaline. Vasoconstriction occurs through adrenaline acting at α-receptors But the muscle has β2 receptors. And adrenaline causes vasodilation via β2 receptors. So blood flow will be constricted to all other organs and places in the body, except for the skeletal muscle.

Question 33

Local vasodilator metabiolites..

Answer 33

- Potassium concentration will increase. This potassium relaxes vascular smooth muscle. - ATP will be converted to adenosine, which is an important paracrine vasodilator. -Anaerobic respiration will cause lactate to be produced. The acidification from lactate will lead to vasodilation

Question 34

Is it true that the local effects that cause vasodilation will override any sympathetic vasoconstriction?

Answer 34

Yes (Vasoconstriction= - Sympathetic tone - Angiotensin II - ADH )

Question 35

Staling's law

Answer 35

Normally, Starling’s law states that if you increase venous return (blood returning to the heart), the heart stretches more, and it pumps out more blood (higher stroke volume → higher cardiac output). But during exercise, the body does not just rely on that Starling mechanism.

Question 36

During exercise, blood flow to muscles needs to increase massively. This increase can't just depend on Starling’s law (venous return stretching the heart). Instead, cardiac output must be actively increased — not just passively by more filling.

Answer 36

During exercise, blood flow to muscles needs to increase massively. This increase can't just depend on Starling’s law (venous return stretching the heart). Instead, cardiac output must be actively increased — not just passively by more filling.

Question 37

How is cardiac output actively increased during exercise?

Answer 37

- Skeletal muscle movements (like when you run or lift weights) push blood back to the heart, increasing venous pressure. - Higher venous pressure → helps increase cardiac output (the amount of blood pumped by the heart). - Cardiac output and total peripheral resistance (TPR) together determine blood pressure (BP = CO × TPR).

Question 38

"Starling’s Law: Increasing venous return, increases stroke volume, increases cardiac output" is crossed out because that's the classic rule — but exercise needs more than that.

Answer 38

"Starling’s Law: Increasing venous return, increases stroke volume, increases cardiac output" is crossed out because that's the classic rule — but exercise needs more than that.

Question 39

Why does diastole reduce during exercise?

Answer 39

To stop the heart from overfilling

Question 40

During exercise, heart rate and contractility increase through signals from the cerebral motor cortex and central command. These signals activate vasomotor centers, leading to inhibition of the parasympathetic system (which normally slows the heart) and recruitment of the sympathetic system (which speeds it up and strengthens contractions). As a result, both heart rate and contractility rise to meet the body's demands. These cardiovascular changes can even anticipate exercise before it starts, preparing the body in advance. Vasodilation in skeletal muscle is also partly anticipatory.

Answer 40

During exercise, heart rate and contractility increase through signals from the cerebral motor cortex and central command. These signals activate vasomotor centers, leading to inhibition of the parasympathetic system (which normally slows the heart) and recruitment of the sympathetic system (which speeds it up and strengthens contractions). As a result, both heart rate and contractility rise to meet the body's demands. These cardiovascular changes can even anticipate exercise before it starts, preparing the body in advance. Vasodilation in skeletal muscle is also partly anticipatory.

Question 41

What are the 4 phases of exercise?

Answer 41

- Phase 1, phase 2, phase 3, recovery

Question 42

What counters the increased blood pressure during exercise?

Answer 42

Reduced total peripheral resistance counters the increased blood pressure

Question 43

IS it true that those whose ability to increase heart rate is compromised have limited ability to exercise?

Answer 43

yes

Question 44

What contributes to thermoregulation during exercise?

Answer 44

Cutaneous vasodilation (widening of the blood vessels in the skin)

Question 45

Cutaneous vasodilation: sympathetic vasodilation system

Answer 45

Cutaneous vasodilation: sympathetic vasodilation system

Question 46

What is the problem with cutaneous vasodilation ?

Answer 46

Cutaneous vasodilation reduces peripheral resistance and will divert blood from muscles - Initially thermoregulation wins out - If central venous pressure falls sufficiently than thermoregulation is abandoned. - In hot climates, this may cause heat stroke

Question 47

Coronary circulation ceases during systole because the contracting heart muscle compresses the coronary arteries, reducing blood flow to the heart, and blood flow resumes during diastole when the heart relaxes.

Answer 47

Coronary circulation ceases during systole because the contracting heart muscle compresses the coronary arteries, reducing blood flow to the heart, and blood flow resumes during diastole when the heart relaxes.

Question 48

Coronary circulation flows during diastole

Answer 48

- Blood flow to myocardium occurs in diastole. - Heart needs more blood flow, due to increased workload - Heart very good at extracting oxygen (70% efficient) Can not increase O2 extraction - Vasodilator metabolites : - principally adenosine - Ensure that blood flow matches O2 consumption. - Coronary artery disease first expresses itself as angina during exercise, when compromised blood supply becomes insufficient

Question 49

Cardiovascular changes during Exercise

Answer 49

- Baroreceptor reflexes keep blood pressure from rising substantially - Blood pressure = cardiac output x TPR - Arterial pressure- rises slightly - Heart rate- rises substantially - Stroke volume- rises 10- 20% - Cardiac output- rises substantially - Total peripheral resistance- falls (Increased blood flow to skeletal muscle and heart ) - Oxygen consumption- rises

Question 50

To summarise this lecture has covered:

Answer 50

The responses to haemorrhage, particularly in terms of immediate and medium term responses The responses of the heart and circulation to exercise in terms of changes of CO and TPR The changes of the circulation to skeletal muscle and heart in exercise The pulmonary circulation and its low perfusions pressures and its regulation by oxygen levels.