Blood Pressure Regulation - Lecture 13 Flashcards
What is blood pressure?
The force exerted upon vessel walls as blood flows through
What is the equation for blood pressure?
Cardiac output x Total peripheral resistance
How is blood pressure regulated when at rest?
Autoregulation of local flow
What can disturb blood pressure?
○ Physical stress e.g. high temperature
○ Chemical changes e.g. low oxygen, low pH
○ Increased tissue activity e.g. lactate
How does autoregulation correct blood pressure and blood flow?
○ If a tissue is active: vasodilatory metabolites increase in production which causes prepcapillary sphincters to relax
○ If a tissue becomes inactive: precapillary sphincters constrict
What are vasodilatory metabolites?
○ NO
○ CO2
○ K+
○ H+
○ Lactate
If BP is still low with autoregulation, what is activated?
Sympathetic system activates short term regulation
How does the sympathetic system increase blood pressure?
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
What detects pressure and chemical changes?
○ Pressure: baroreceptors
○ Chemical: chemoreceptors
Where are baroreceptors located?
○ Aortic sinus
○ Carotid sinus
How do baroreceptors respond in response to fall in BP?
○ 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
How do baroreceptors respond in response to increase in BP?
○ 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
Where are chemoreceptors located?
○ Carotid body
○ Aortic body
○ Medulla oblogata
How does the chemoreceptors in the blood respond?
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
How does the chemoreceptors in the medulla oblongata respond?
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
What systems are there for long term regulation of blood pressure?
○ Renin-Angiotensin-Aldosterone System (RAAS)
○ Anti-Diuretic Hormone (ADH/vasopressin)
○ Erythropoietin (Epo)
What are the steps in the RAAS?
○ 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
What does angiotensin II do?
○ Causes vasoconstriction
○ Stimulates adrenal glads in the kidneys to secrete aldosterone
○ Aldosterone increases Na+ reabsorption and fluid retention
What does ADH do?
○ 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
What does Epo do?
○ 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
What happens when blood pressure is too high?
○ Stretching of right atrium and ventricle causes release of natriuretic peptides:
- Atrium: secretes ANP
- Ventricle: secretes BNP
○ Causes renal effect and vascular effects
What are the renal effects?
Decreased blood volume due to:
○ Increased Na+ loss in urine
○ Increased water loss in urine
○ Reduced thirst
What are the vascular effects?
Decrease in blood pressure due to:
○ Inhibition of ADH, aldosterone, NA & adrenaline release
○ Peripheral vasodilation
Which mechanisms would be activated following severe haemorrhage?
○ Baroreceptor reflex
○ Chemoreceptor reflex
○ RAS activation
○ Catecholamine release
○ Vasopressin release
How is blood flow regulation different in the pulmonary circuit?
In lungs, arterioles constrict in regions of low oxygen to shunt blood flow to oxygen rice areas
How is blood flow regulation different in cerebral circulation?
In emergencies there is vasodilation of cerebral vessels while there is vasoconstriction in the periphery
How is blood flow regulation different in coronary circulation?
SNS activity leads to coronary artery vasodilation due to predominance of beta adrenergic receptors
