Module 6: Section 7

Question 1

What is the main driving force to keep blood circulating throughout the body?

Answer 1

mean arterial pressure (MAP)

Question 2

How is MAP regulated?

Answer 2

• It’s constantly being monitored by baroreceptors in the circulatory system
• Allows body to make short and long term adjustments to maintain MAP

Question 3

Short term control of MAP

Answer 3

• Mediated by the autonomic nervous system
• Can make beat-to-beat changes in cardiac output and total peripheral resistance
• Within seconds

Question 4

Long term control of MAP

Answer 4

• Long term adjustments regulate blood volume through kidney function and salt and water balance
• Regulates bulk flow in the capillaries
• Minutes to days

Question 5

Baroreceptors

Answer 5

• Any change in mean arterial pressure activates the autonomic baroreceptor reflex
• Baroreceptors adjust cardiovascular responses to restore MAP to its homeostatic set point

Question 6

Where are baroreceptors found?

Answer 6

In the carotid sinus and in the aortic arch

Question 7

What Baroreceptors Monitor

Answer 7

• Baroreceptors monitor mean arterial pressure for blood flow to the brain and systemic circulation
• They also detect pulse pressure changes, since pulse pressure can fluctuate without changing MAP

Question 8

Baroreceptor reflex

Answer 8

Baroreceptors are constantly firing action potentials at a rate proportional to the arterial pressure

Question 9

Baroreceptor reflex - normal

Answer 9

• Most of the time MAP or pulse pressure is stable
• Baroreceptor firing is stable

Question 10

Baroreceptor reflex - increased

Answer 10

When MAP or pulse pressure increases, the baroreceptors increase their firing rate

Question 11

Baroreceptor reflex - decreased

Answer 11

When MAP or pulse pressure decrease, the baroreceptors decrease their firing rate

Question 12

The cardiovascular control centre

Answer 12

• Output from the baroreceptors project to the cardiovascular control centre
• It receives signals and uses the efferent pathways of the autonomic nervous system to initiate a response
• Response is a balance of sympathetic and parasympathetic activity

Question 13

Where is the cardiovascular control centre located?

Answer 13

In the medulla within the brain stem

Question 14

Step 1 of how sympathetic and parasympathetic pathways are able to mediate changes in blood pressure

Answer 14

• Parasympathetic nervous system slows heart rate by releasing ACh at the SA node
• This increases K+ permeability, decreasing cardiac output and decreasing blood pressure

Question 15

Step 2 of how sympathetic and parasympathetic pathways are able to mediate changes in blood pressure

Answer 15

• The sympathetic nervous system increases heart rate, contractile strength of the heart and vasoconstriction
• All of these increase stroke volume, which increases cardiac output and increases blood pressure

Question 16

Other reflexes that help regulate the cardiovascular system (5 types)

Answer 16

1. Left atrial volume receptors and hypothalamic osmoreceptors
2. Chemoreceptors in the carotid and aortic arteries
3. Emotions
4. Hypothalamic control of skin arterioles for temperature regulation
5. Vasoactive substances

Question 17

Left atrial volume receptors and hypothalamic osmoreceptors - reflex that helps regulate the cardiovascular system

Answer 17

These receptors are important in long term control of MAP as they are important in water and salt balance

Question 18

Chemoreceptors in the carotid and aortic arteries - reflex that helps regulate the cardiovascular system

Answer 18

• Receptors are sensitive to low oxygen or high acid levels in the blood
• Their activity projects to the respiratory centre to increase ventilation and to the cardiovascular centre to increase blood pressure

Question 19

Emotions - reflex that helps regulate the cardiovascular system

Answer 19

• Certain responses are pre programmed through the cerebral cortex-hypothalamic pathways to initiate cardiovascular responses
• Ex: generalized fight-or-flight response and localized skin responses associated with blushing

Question 20

Hypothalamic control of skin arterioles for temperature regulation - reflex that helps regulate the cardiovascular system

Answer 20

• Pathway can override the cardiovascular control centre
• If body temp is above normal and there is a decrease in blood pressure that would normally result in the constriction of arterioles, the skin arterioles will still dilate to help reduce body temp

Question 21

Vasoactive substances - reflex that helps regulate the cardiovascular system

Answer 21

• Many substances are released in response to local changes in the cardiovascular system
• Nitric oxide and endothelin are produced and released by endothelial cells through pathways that are independent of autonomic input

Question 22

What is the most common disorder of blood pressure?

Answer 22

Hypertension

Question 23

What is normal blood pressure considered to be?

Answer 23

120/80 mmHg

Question 24

Hypertension

Answer 24

• Chronic elevation of blood pressure to greater then 140/90 mmHg that can possible reach ~180/110 mmHg
• 35-50% of the Canadian adult population is affected and prevalence increases with age

Question 25

How is hypertension diagnosed?

Answer 25

- By measuring blood pressure on 3 separate visits at least 2 weeks apart each - This is because blood pressure can be elevated due to exercise, stress, or White Coat syndrome

Question 26

Hypertension symptoms

Answer 26

- For mild or moderate cases symptoms are usually not present so it isn't diagnosed - Symptoms can include fatigue, blurred vision, and headaches

Question 27

Hypertension - Morbidity and mortality

Answer 27

- Untreated hypertension can shorten lifespan by 10-20 years - Even when treated ~50% still develop end-organ damage

Question 28

3 different types of hypertension

Answer 28

1. Primary hypertension 2. Secondary hypertension 3. "other", which includes malignant hypertension or hypertension associated with pregnancy

Question 29

Primary hypertension

Answer 29

- Also called essential hypertension - 90% of hypertensive patients fall into this category - Underlying cause is unknown - Risk factors include obesity, smoking, stress and diet (salt) - Strong genetic component - Treatment can help normalize MAP but the disease still progresses

Question 30

Secondary hypertension

Answer 30

- Seen in ~10% of patients - Cause of hypertension is secondary to another problem

Question 31

Diseases involved in secondary hypertension

Answer 31

1. Pheochromocytoma (adrenal medulla tumours), they secrete excessive norepinephrine and epinephrine which leads to an increase in cardiac output and MAP 2. Some kidney diseases since the kidney is involved in long term regulation of blood pressure

Question 32

Consequence 1 of hypertension

Answer 32

Damage to retinal blood vessels leading to blindness

Question 33

Consequence 2 of hypertension

Answer 33

Damage to cerebral arteries leading to stroke

Question 34

Consequence 3 of hypertension

Answer 34

Damage to arterial walls leading to atherosclerosis

Question 35

Consequence 4 of hypertension

Answer 35

Damage to renal blood vessels leading to kidney failure

Question 36

Consequence 5 of hypertension

Answer 36

Increased workload of the heart can initially lead to hypertrophy and ultimately heart failure

Question 37

Initial Orthostatic Hypotension (IOH)

Answer 37

- Condition when an individual stands and gravity forces blood from the central to the peripheral compartments - The body can sometimes not correctly adjust for this increase in arterial outflow and there is a temporary drop in MAP

Question 38

Circulatory shock

Answer 38

What happens when blood pressure decreases to the point where adequate blood flow to the tissues is compromised

Question 39

4 main categories of circulatory shock

Answer 39

1. Hypovolemic shock 2. Cardiogenic shock 3. Vasogenic shock 4. Neurogenic shock

Question 40

Hypovolemic shock

Answer 40

Occurs when severe blood or fluid loss reduces blood volume, lowering cardiac output and mean arterial pressure

Question 41

Cardiogenic shock

Answer 41

- Occurs when the heart is not strong enough to pump blood - Happens during heart failure

Question 42

Vasogenic shock

Answer 42

occurs when infection or a severe allergic reaction releases vasodilators, causing widespread vasodilation, decreased total peripheral resistance, and reduced MAP

Question 43

Neurogenic shock

Answer 43

Occurs when a loss of sympathetic nerve activity causes loss of vascular tone and widespread vasodilation, reducing total peripheral resistance and MAP