Control of BP

Question 1

What is the main short-term mechanism that regulates the MAP?

Answer 1

Baroreceptor reflex

Question 2

What is the main long-term mechanism that regulates the MAP?

Answer 2

Renin-angiotensin11-aldosterone system

Question 3

What are the other things that regulate the MAP?

Answer 3

MAP = CO * TPR

Question 4

How do the baroreceptors work?

Answer 4

The controlled variable is the arterial blood pressure

• The set point for the MAP is usually 100mmHg
• When the arterial pressure falls below 100mmHg, sympathetic (fight or flight) activation occurs, and parasympathetic (rest) activation is reduced, increasing the HR, contractility, and vascular resistance, and vice versa once the arterial pressure goes above 100mmHg

Question 5

Where are the baroreceptors located?

Answer 5

1) Carotid sinus

2) Aortic Arch

Question 6

What is the mechanism by which the baroreceptors control hemorrhage?

Answer 6

In case of hemorrhage, the BP will go down thus, the stretch of the carotid sinus baroreceptor will decrease, hence the firing rate of the carotid sinus nerve will decrease, therefore the parasympathetic stimulation to the heart will decrease increasing the heart rate, and the sympathetic stimulation will increase, increasing the HR, Contractility of the heart, constriction of the arterioles (Increased TPR), and constricting the veins (Increasing the SV and CO), this will all get the BP back to normal

Question 6

Which nerves carry the signal from the baroreceptor in the carotid sinus?

Answer 6

glossopharyngeal (carotid sinus nerve to Nerve IX)

Question 7

Which nerve carries the signal from the baroreceptors in the aortic arch?

Answer 7

Vagus nerve

Question 8

What is the mechanism by which the baroreceptors control a high MAP?

Answer 8

1) Carotid sinus (Cranial nerve IX) & Aortic arch (CNX)

Medulla

2) Nucleus tractus solitarius

3) Increases the cardiac decelerator (Parasympathetic)

4) The increased parasympathetic stimulation will decrease the stimulation of the sinoatrial node (decreased HR)

Question 9

What is the Valsalva maneuver?

Answer 9

It is a technique where you take a breath close your mouth and nose push against them for 15-20 seconds this will increase the thoracic pressure and BP thus lower our HR, this technique can help us know if the baroreceptor is working properly, but it is not useful for people with chronic hypertension as they have a higher set point and their baroreceptor have a decreased sensitivity to high BP

Question 10

What happens when you massage the carotid sinus?

Answer 10

When you massage the carotid sinus the BP will increase thus the parasympathetic stimulation will increase decreasing the sympathetic stimulation, HR, and BP

Question 11

wHAT HAPPENS WHEN YOU GO TO SPACE (NO GRAVITY)

Answer 11

The BP in the upper body will increase, increasing the Para, decreasing the HR, Symp, and BP

Question 12

What happens when you have orthostatic hypotension?

Answer 12

Your symp, HR, and BP will increase, Para will decrease

Question 13

What happens if the cranial nerve IX is cut?

Answer 13

The parasympathetic stimulation will decrease, and the sympathetic, HR, and BP stimulation will increase

Question 14

What happens in case the carotid sinus is occluded?

Answer 14

The BP will go down, para stimulation will decrease, and Smp will increase along with the HR and BP

Question 15

What is the renin-angiotensin-aldosterone response?

Answer 15

It is a long-term mechanism by which the body adjusts the BP

Question 16

What are the major causes of increased renin secretion?

Answer 16

1) Increased renal sympathetic stimulation

2) Decreased renal perfusion (detected by renal baroreceptors)

3) Decreased NaCl in the distal tube

Question 17

What are the steps by which the renin-angiotensin-aldosterone mechanism works by?

Answer 17

When stimulated:

1) Angiotensin (a renin substrate) will get converted into angiotensin-I via the enzyme renin

2) Angiotensin-I will then get converted into angiotensin-II via angiotensin converting enzyme

3) Angiotensin-II will then:

• Cause the secretion of aldosterone (from the adrenal cortex, zona glomerulosa cells) which will increase the absorption of Na+ and thus water retention
• Increase the Thirst
• Vasoconstric the vessels, increasing the TPR
• Increase the Na+-H+ exchange, increasing the absorption of Na+

All of these will return the aortic pressure back to normal

Question 18

What is the other mechanism by which the MAP is regulated?

Answer 18

REFLEXES

Question 19

What are the different reflexes that regulate the MAP?

Answer 19

1) Chemoreceptor reflex

2) Cushing Reflex

3) Volume reflex

4) Bainbridge reflex

5) Respiratory sinus arrhythmia

Question 20

Where are the chemoreceptors located?

Answer 20

1) Peripheral chemoreceptors are located in the carotid bodies and aortic bodies

2) Central chemoreceptors are located in the medulla of the brain

Question 21

What is the mechanism of action of the peripheral chemoreceptors?

Answer 21

• It is mainly sensitive to arterial PO2

When there is a decrease in arterial PO2 levels and an increase in the levels of PCO2 & pH, the peripheral chemoreceptors will increase the sympathetic outflow causing arteriolar vasoconstriction, they will also increase the parasympathetic outflow decreasing the HR and finally, it will increase the ventilation

Question 22

Describe the mechanism of action of the central chemoreceptors

Answer 22

• It is mainly sensitive to the PCO2 and pH

when PCO2 and the pH are high in the brain it will increase the sympathetic outflow, causing arteriolar vasoconstriction and redirecting blood to the brain

Question 23

What is the cushing’s reflex?

Answer 23

• It maintains the cerebral blood flow via cerebral chemoreceptors
• Same as the central chemoreceptors, but what triggers it is different which is a change in the intracranial pressure like when there is a tumor that is compressing the cerebral arteries, which in turn will increase both PCO2and pH levels

Question 24

What is the volume receptor?

Answer 24

• Volume/Low-pressure receptor
• They are a type of mechanoreceptor that checks the blood volume, especially in the right atrium and large veins
• They minimize changes in arterial pressure when the blood volume changes

Question 25

What is the mechanism of action of the low pressure receptors (volume receptors)?

Answer 25

• They work by secreting two hormones (ADH & ANP)

When the stretch decreases due to low BP
- ADH (vasopressin), secreted due to the increase in the serum osmolarity and decrease the BP, where ADH will act on V2 receptors to increase water reabsorption and V1 receptors to constrict the smooth muscles

When the stretch increases due to high BP
- ANP, secreted due to the increase in the extracellular fluid and BP, causing vasodilation (decreasing the TPR), and increasing the excretion of Na+ and water from the kidneys

this mechanism is combined together with the renin-angiotensin mechanism

Question 26

What is the Bainbridge reflex?

Answer 26

• Its physiologic significance isn’t well known
• It ensures that blood volume does not back on the venous side (when the HR is low) increasing the venous pressure and the HR

Question 27

What is the respiratory sinus arrhythmia reflex?

Answer 27

it is a combination of several reflexes where the inspiration will lead to an increase in the VR and thus the HR will increase

Question 28

Define the different stages of hypertension

Answer 28

As of 2017:

1) Normal: >120/80
2) Elevated: 120-129/<80
3) Stage 1: 130-139/80-89
4) Stage 2: >=140/>=90

Question 29

Describe the negative feed-back control of the BP

Answer 29

1) Elevated BP

2) Arteries are stretched

3) Baroreceptors increase the firing rate

4a) Stimulation of the cardioinhibitory neurons, increasing the vagal tone, reducing the HR, decreasing the BP

4b) Stimulation of the vasomotor center in inhibited, reducing the sympathetic and vasomotor tone causing vasodilation, decreasing the BP