Lecture 31 - Cardiovascular System: Regulation of Blood Pressure in the Short and Long Term

Question 1

What are 2 factors that blood pressure is affected by?

Answer 1

1. Total blood volume (how much blood is present)
2. Total resistance (what is the diameter of the vessels)

All across blood vessels

Question 2

What regulates vasoconstriction?

Answer 2

The autonomic nervous system regulates vasoconstriction through (sympathetic) vasomotor fibres that make synapses on vascular smooth muscle. APs in vasomotor fibres lead to enhanced contraction in smooth muscle

Question 3

What are the general sensors, integrator, and effector of mean arterial blood pressure?

Answer 3

Sensors - neurons in large elastic arteries
Integrator - neurons in hindbrain
Effectors - organs of the cardiovascular system

Question 4

What are baroreceptors?

Answer 4

They are mechanosensory neurons that monitor mean arterial blood pressure found within the carotid sinus and aortic arch

These neurons send their axons (via CN IX and CN X) to the medulla oblongata

Question 5

What are the 3 cardiovascular centres that baroreceptor info is integrated?

Answer 5

Integrated within cardiovascular monitoring centres in the brainstem within the medulla oblongata:

1. Cardioinhibitory centres
2. Cardioacceleratory centres
3. Vasomotor

Question 6

What is the function of the cardiac centres in the medulla oblangata?

Answer 6

They drive changes in cardiac output (CO) by altering activity in ANS inputs to the SA node of the heart and the myocardium

Question 7

What is the function of the vasomotor in the medulla oblangata?

Answer 7

It drives changes to blood vessel diameter (in both arteries and veins) by altering activity in sympathetic vasomotor fibres

Question 8

What can cause changes in overall chemical composition of blood in the systemic circuit?

Answer 8

Increased metabolic demands from peripheral tissues, where metabolic demands > current levels of CO:

• decreased PO2
• increased PCO2
• decreased pH (acidosis)

Question 9

How does blood chemistry restore its levels?

Answer 9

Arterial chemoreceptors - drive homeostatic reflexes that alter blood flow throughout the circulatory system:

Sensors - neurons in large elastic arteries (and hindbrain)
Control center - integrator; neurons in hindbrain
Effectors - organs of the respiratory and cardiovascular system

This leads to blood chemistry being restored

Question 10

What monitors blood gas composition?

Answer 10

Chemoreceptors - monitor mean arterial pH, P_O2, P_CO2. Found within the carotid bodies and aortic bodies

Question 11

Where is chemoreceptor info integrated within?

Answer 11

It’s integrated within cardiovascular monitoring centres in the brainstem

Peripheral neurons send axons (via CN IX and CN X) to three cardiovascular centres and respiratory centre within the medulla oblongata

Question 12

What are the effectors for short term alterations in blood gas composition?

Answer 12

Heart and blood vessel walls

Question 13

Difference between homeostasis and allostasis in blood pressure regulation

Answer 13

Homeostasis - when BP is disrupted, BP is restored to the set point

Allostasis - when blood chemistry is disrupted, BP is moved to a new set point

Question 14

T/F? Mechanisms of altering blood pressure over short terms are ideal for long term regulation

Answer 14

False - it is NOT ideal. Why?

• Energy intensive
• Maintain central pressure

Question 15

What is needed for long-term regulation of BP?

Answer 15

Changes in blood volume - to maintain oxygen delivery at normal rates, blood volume changes must involve changes to both plasma and RBC levels

Adjustments to blood volume are slow, but they can maintain blood pressure throughout the circulatory system without constant energy input

Question 16

Which organ is the long-term response to low BP, and which 2 hormones do they release?

Answer 16

Kidney; low BP (or blood volume) lead to lower levels of perfusion through kidney tissue, stimulating the release of 2 hormones:

1. Renin - leads to increased plasma volume
2. Erythropoietin (EPO) - drives RBC production

Question 17

How does renin play a role in the hormonal axis

Answer 17

It takes part in the hormonal axis Renin-Angiotensin-Aldosterone System (RAAS)

Question 18

What are the 3 components to RAAS?

Answer 18

1 . Renin is secreted by the kidney (note: it’s not a true hormone)

2a. Angiotensinogen is a plasma protein which is always present in circulation

2b. Angiotensin I is also inactive

2c. Angiotensin II has short-term and long-term effects on BP. It produces vasoconstriction and increase thirst (water intake)

3 . Aldosterone is a mineralocorticoid hormone that acts on the kidney

Question 19

What does angiotensin II stimulate?

Answer 19

Stimulates the release of aldosterone and ADH/vasopressin

Aldosterone influences Na+ retention by the kidneys, which indirectly contributes to water retention

ADH directly stimulates water retention by the kidney

Question 20

Which muscle is the long-term response to high BP, and which 2 hormones do they release?

Answer 20

Heart muscle; high BP (or blood volume) leads to increased stretching in heart chamber walls, which leads to the release of:

1. ANP - atrial natriuretic peptide, released by the atria
2. BNP - brain natriuretic peptide, released by the ventricles

Question 21

3 functions of natriuretic peptides

Answer 21

1. They stimulate the kidneys to increase excretion of Na+, which also leads to water loss
2. They also have short term effects on BP; they produce vasodilation in most blood vessels
3. Natriuretic peptides are regulatory hormones that inhibit the release of renin (and therefore, aldosterone), ADH, and epinephrine

Question 22

What do short term responses to blood loss involve?

Answer 22

Neural reflexes and the physiological stress response

Systemic veins can hold large volumes of blood, so venoconstriction can return a large amount of blood from these venous blood reservoirs without affecting perfusion

Question 23

What will occur in medium to long term loss of blood volume?

Answer 23

Blood contents will be replaced

Medium term - reductions in BP lead to dec. CHP, which leads to recall of fluid in the ISF

Long term - increases in ATII, ADH, aldosterone leads to inc. fluid intake and inc. fluid retention. EPO restores RBCs

Question 24

What does hypovolemic shock mean and when does it occur?

Answer 24

“Shock” means an acute cardiovascular crisis involving hypotension. Occurs when more than 20% of blood volume is lost (major blood loss) or if the loss of body fluids is faster than physiology can replace them

Question 25

5 major symptoms of circulatory shock

Answer 25

1. Rapid, weak pulse
2. Cold
3. Pale
4. Thirst
5. Sweating