Section 8

Question 1

Predict the sequence of events following severe blood loss (haemorrhage) in hypovolemic shock.

Answer 1

Haemorrhage → Blood Volume (immediate decrease) → Stroke Volume (decreased venous return) → Cardiac Output (decrease) → Arterial Pressure (decrease)

Question 2

What is the highest priority for the body following significant blood loss?

Answer 2

The highest priority is to return arterial pressure to a level adequate for tissue perfusion, especially of the brain.This is crucial for maintaining oxygen delivery to vital organs and preventing complications associated with inadequate perfusion.

Question 3

What are the compensatory measures in the short term (seconds) following haemorrhagic shock?

Answer 3

n the short term, the activation of the autonomic-mediated baroreceptor reflex is initiated to immediately respond and restore arterial pressure. This assumes that the cause of haemorrhage is fixed and the volume of blood lost isn’t greater than 40%

Question 4

What happens in the intermediate response (minutes to hours) after haemorrhagic shock?

Answer 4

The intermediate response involves fluid shifts between blood and interstitial fluid. Several other mechanisms contribute to compensatory increases in blood volume over minutes to hours. These mechanisms work to restore and stabilize blood volume, further supporting adequate tissue perfusion.

Question 5

How is the loss of red blood cells compensated for in the long term (hours to days) following haemorrhagic shock?

Answer 5

In the long term, the loss of red blood cells is compensated for by an increase in red blood cell production. This process occurs in the days following the shock, ensuring that the body can maintain oxygen-carrying capacity and overall cardiovascular function.

Question 6

What are the primary goals of the short term, intermediate, and long term compensatory responses following haemorrhagic shock?

Answer 6

Short term: Stabilize arterial pressure, especially for vital organ perfusion.

Intermediate: Increase plasma volume through various mechanisms.

Long term: Restore the number of red blood cells to ensure adequate oxygen-carrying capacity and overall cardiovascular function.

Question 7

As a result of the haemorrhage, would the baroreceptors increase or decrease their firing
rate?

Answer 7

DECREASE

Recall that baroreceptors fire action potentials at a rate proportional to the arterial pressure, and thus the decrease in pressure will be reflected by a decrease in baroreceptor firing
frequency.

Question 8

What changes to the autonomic input to the heart would the cardiovascular control centre
coordinate as a result?

a) increased sympathetic
b) decreased sympathetic
c) decreased parasympathetic
d) both a and c

Answer 8

both a and c.

Remember that parasympathetic (PS) control by the vagus nerve has rich innervation of the SA node, the pacemaker of the heart.

Therefore, a decrease in PS activity acts to increase the heart rate in order to offset the reduction in stroke volume brought about by the loss in blood volume. This is reinforced by the sympathetic system that also contributes to an
increase in heart rate.

Question 9

Define stroke volume.

Answer 9

Stroke volume refers to the amount of blood ejected by the left ventricle of the heart in one contraction or heartbeat. It is typically measured in milliliters per beat.

Question 10

What are the two parameters through which the baroreceptor reflex primarily accomplishes the adjustment of mean arterial pressure (MAP)?

Answer 10

Cardiac output and total peripheral resistance.

The baroreceptor reflex modulates MAP by regulating the product of cardiac output (CO) and total peripheral resistance (TPR), as represented by the equation:
CO x TPR = MAP.

Question 11

What is the primary function of the baroreceptor reflex concerning blood pressure?

Answer 11

Detecting changes in blood pressure and counteracting them to increase blood pressure, ensuring adequate tissue perfusion.

Question 12

the baroreceptor reflex brings about decreased parasympathetic and increased sympathetic activity to the heart, increasing the heart rate in response to the fall in blood
pressure.

This increases cardiac output.

How else is the baroreceptor reflex able to increase cardiac output following haemorrhage?
* Increase stroke volume
* Decrease urine volume
* Increase blood volume
* Increase interatrial pressure

Answer 12

increase stroke volume

Recall that cardiac output is defined as the volume of blood that is pumped by each ventricle over a
minute of time.

It is therefore determined by heart rate and stroke volume

Question 13

In order to increase TPR, there must be increased _______________activity to the _____________resulting in
vasoconstriction throughout the body, except for the _______

• parasympathetic, arterioles, heart
• parasympathetic, veins, brain
• sympathetic, veins, heart
• sympathetic, arterioles, brain

Answer 13

sympathetic, arterioles, brain

Question 14

What is the immediate response of the baroreceptor reflex to a fall in blood pressure?

Answer 14

Decrease parasympathetic activity and increase sympathetic activity to the heart.

Question 15

How does the baroreceptor reflex contribute to an increase in cardiac output during hypovolemic shock?

Answer 15

By inducing vasoconstriction of veins and arterioles (except in the brain).

Question 16

In the context of the baroreceptor reflex, what does sympathetically induced arteriolar vasoconstriction lead to?

Answer 16

A compensatory increase in total peripheral resistance.

Question 17

What is the primary goal of the baroreceptor reflex following hypovolemic shock?

Answer 17

To maintain adequate blood flow to the organs and tissues of the body.

Question 18

As you know, haemorrhage leads to a significant reduction in circulating blood volume. This leads to an
immediate fall in blood pressure, which is accompanied by a fall in capillary blood pressure.

Would the adjustments in autonomic innervation of the vasculature due to the baroreceptor reflex have an influence on the blood pressure within capillary beds?

• No, because there are no smooth muscle cells in capillary walls
• Yes, because capillary walls have several layers of smooth muscle cells
• No, due to the presence of metarterioles
• Yes, due to the presence of smooth muscle cells between arterioles and capillaries

Answer 18

Yes, due to the presence of smooth muscle cells between arterioles and capillaries.

Recall that metarterioles are vessels structurally in between arterioles and capillaries as they contain
some smooth muscle cells. Capillaries branch from these vessels, and the flow of blood into capillary beds is controlled by precapillary sphincters, which are the smooth muscle cells of metarterioles.

During an event such as haemorrhage, the body is able to use sympathetic activation to redistribute cardiac output away from less important organs, such as those involved in digestion, benefiting organs that are critical for survival, those being the heart and brain

Question 19

What is the role of thirst as a compensatory mechanism following a decrease in plasma volume?

Answer 19

Thirst is stimulated, leading to increased fluid intake, ultimately helping to raise plasma volume.

Question 20

How does the liver contribute to compensating for a decrease in plasma volume?

Answer 20

The liver synthesizes plasma proteins, exerting colloid osmotic pressure to retain extra fluid in the plasma. This is a long-term compensatory mechanism.

Question 21

What happens to urine output as a compensatory measure following haemorrhage?

Answer 21

Urinary output is reduced due to compensatory renal vasoconstriction, conserving water that would otherwise be lost from the body. Hormones like vasopressin and aldosterone also contribute to this reduction in urinary output.

Question 22

How does the drop in arterial pressure and constriction of arterioles and veins affect capillary exchange?

Answer 22

These changes lead to a significant increase in capillary reabsorption, transferring interstitial fluids to the plasma, thereby increasing blood volume.

Question 23

What is the approximate rate at which this mechanism can restore blood volume?

Answer 23

This mechanism can restore blood volume at a rate of up to 1 liter per hour or 20% of the total blood volume per hour.

Question 24

How does the body respond to the increase in plasma volume in terms of thirst and urine output?

Answer 24

There is an increased thirst and a renal response that decreases urine output, both contributing to the stabilization of plasma volume.

Question 25

What happens to sympathetic output as plasma volume increases and blood pressure is restored?

Answer 25

As plasma volume increases and blood pressure is restored, sympathetic output decreases.

Question 26

What is the primary aim of the intermediate and short-term responses following haemorrhagic shock?

Answer 26

Stabilizing blood pressure and flow to maintain nutrient and water delivery, heat and waste removal, and cellular communication.

Question 27

How does the loss of red blood cells affect the blood’s ability to transport oxygen and remove carbon dioxide?

Answer 27

The loss of red blood cells decreases the blood’s ability to transport oxygen to and remove carbon dioxide from the tissues.

Question 28

What is the role of decreased renal blood flow in the compensatory response?

Answer 28

Decreased renal blood flow triggers the release of hormones that stimulate red blood cell production.

Question 29

Over what time frame does red blood cell production occur in response to haemorrhagic shock?

Answer 29

Red blood cell production occurs over several days to weeks as part of the long-term compensatory mechanism.