Blood Pressure Regulation - Lecture 13 Flashcards
(27 cards)
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
