Blood Pressure Regulation - Lecture 13

Question 1

What is blood pressure?

Answer 1

The force exerted upon vessel walls as blood flows through

Question 2

Why do we need blood pressure?

Answer 2

Capillary hydrostatic pressure is required to exchange substances/fluids across capilary networks

Question 3

What is the equation for blood pressure?

Answer 3

Cardiac output x Total peripheral resistance

Question 4

How is blood pressure regulated when at rest?

Answer 4

Autoregulation of local flow

Question 5

How is blood pressure regulated when autoregulation is not enough?

Answer 5

○ Short term regulation - neural
○ Long term regulation - endocrine

Question 6

What can disturb blood pressure?

Answer 6

○ Physical stress e.g. high temperature
○ Chemical changes e.g. low oxygen, low pH
○ Increased tissue activity e.g. lactate

Question 7

How does autoregulation correct blood pressure and blood flow?

Answer 7

○ If a tissue is active: vasodilatory metabolites increase in production which causes prepcapillary sphincters to relax allow
○ If a tissue becomes inactive: precapillary sphincters constrict

Question 8

What are vasodilatory metabolites?

Answer 8

○ NO
○ CO2
○ K+
○ H+
○ Lactate

Question 9

If BP is still low with autoregulation, what is activated?

Answer 9

Sympathetic system activates short term regulation

Question 10

How does the sympathetic system increase blood pressure?

Answer 10

Increase in cardiac output:
○ Increase in heart rate and stroke volume
○ Positive inotrophic and chronotrophic effects
Increase in total peripheral resistance:
○ Adrenoreceptors in smooth muscle are activiated
○ Arterioles constrict
○ Increase vasoconstriction

Question 11

What detects pressure and chemical changes?

Answer 11

○ Pressure: baroreceptors
○ Chemical: chemoreceptors

Question 12

Where are baroreceptors located?

Answer 12

○ Aortic sinus
○ Carotid sinus

Question 13

How do baroreceptors respond in response to fall in BP?

Answer 13

○ Baroreceptors are inhibited:
- Activation of cardioacceleratory } Increase in HR and CO
- Inhibition of cardioinhibitory } increase in HR and CO
- Activation of vasomotor centre -> vasoconstriction of arterioles

Question 14

How do baroreceptors respond in response to decrease in BP?

Answer 14

○ Baroreceptors are activated:
- Inhibition of cardioacceleratory } decrease in HR and CO
- Activation of cardioinhibitory } decrease in HR and CO
- Inhibition of vasomotor centre -> vasodilation of arterioles

Question 15

Where are chemoreceptors located?

Answer 15

○ Carotid body
○ Aortic body
○ Medulla oblogata

Question 16

How does the chemoreceptors in the blood respond?

Answer 16

If there is a fall in pH, Fall in O2 or rise in CO2:
○ Cardioacceleratory centre activation } increase in HR and CO
○ Cardioinhibitory centre inhibition } increase in HR and CO
○ Vasomotor Centre activation -> peripheral vasoconstriction

Question 17

How does the chemoreceptors in the medulla oblongata respond?

Answer 17

Sensitive to changes in CO2
Rise in CO2:
○ Respiratory system activation -> increase in respiratory rate
○ Vasodilation of cerebral vessels -> increase blood flow to the brain

Question 18

What systems are there for long term regulation of blood pressure?

Answer 18

○ Renin-Angiotensin-Aldosterone System (RAAS)
○ Anti-Diuretic Hormone (ADH/vasopressin)
○ Erythropoietin (Epo)

Question 19

What are the steps in the RAAS?

Answer 19

○ Kidney detects low blood pressure and secretes renin
○ Renin cleaves angiotensinogen (plasma protein secreted from the liver) to angiotensin I
○ Angiotensin I is converted to angiotensin II by an enzyme secreted by lung cells

Question 20

What does angiotensin II do?

Answer 20

○ Causes vasoconstriction
○ Stimulates adrenal glads in the kidneys to secrete aldosterone
○ Aldosterone increases Na+ reabsorption and fluid retention

Question 21

What does ADH do?

Answer 21

○ Hormone secreted by the pituitary gland when there is a fall in blood volume or increased osmolality
○ Causes vasoconstriction
○ Increases permeability so increases fluid retention
○ Makes us thirsty

Question 22

What does Epo do?

Answer 22

○ Hormone secreted by the kidneys when there is a fall in BP or O2
○ Vasoconstriction
○ Increases blood volume as it is responsible for RBC formation

Question 23

What happens when blood pressure is too high?

Answer 23

○ Stretching of right atrium and ventricle causes release of natriuretic peptides:
- Atrium: secretes ANP
- Ventricle: secretes BNP
○ Causes renal effect and vascular effects

Question 24

What are the renal effects?

Answer 24

Decreased blood volume due to:
○ Increased Na+ loss in urine
○ Increased water loss in urine
○ Reduced thirst

Question 25

What are the vascular effects?

Answer 25

Decrease in blood pressure due to:
○ Inhibition of ADH, aldosterone, NA & adrenaline release
○ Peripheral vasodilation

Question 26

Which mechanisms would be activated following severe haemorrhage?

Answer 26

○ Baroreceptor reflex
○ Chemoreceptor reflex
○ RAS activation
○ Catecholamine release
○ Vasopressin release

Question 27

How is blood flow regulation different in the pulmonary circuit?

Answer 27

In lungs, arterioles constrict in regions of low oxygen to shunt blood flow to oxygen rice areas

Question 28

How is blood flow regulation different in cerebral circulation?

Answer 28

In emergencies there is vasodilation of cerebral vessels while there is vasoconstriction in the periphery

Question 29

How is blood flow regulation different in coronary circulation?

Answer 29

SNS activity leads to coronary artery vasodilation due to predominance of beta adrenergic receptors