Blood pressure Flashcards
bloodpressure regulation overview
Short term regulation
* Cardiovascular system ==>Baroreceptor reflex
Long term regulation
* Kidneys
* Blood volume alterations
what is MAP
- Mean arterial pressure (MAP)
- Average pressure driving blood forward into the tissues
- Averages 93 mm Hg (not 100 because it spends more time in diastole so we have to consider that, and make it less)
MAP = diastolic pressure + 1/3 (pulse pressure)
- Arteries offer little resistance to flow, therefore MAP is similar in all arteries
What determines MAP?
- Determined by cardiac output and peripheral resistance
MAP proportion to CO X Resistance inarterioles - Blood flow in the arteries must be balanced in order to maintain pressure
- If flow in > flow out, MAP increases (exerting more force to the walls of these vessels, more accommodation and stretching)
- If flow out > flow in, MAP decreases (less blood accumulating and less stretch)
MAP ∝ CO X Resistancearterioles - Flow in = CO
- Flow out is influenced by peripheral resistance (arterioles) == blood entering capillaries
factors that influence MAP
1. blood volume => fluid intake (water) /loss (sweating or urination)
2. cardiac output => heart rate/ stroke volume
3. resistance => diameter of arterioles
4. distribution of blood in vessels = > diameter of veins
when blood volume increases
- leads to increase BP
=> need to reduce total peripheral resistance
so less blood acculumlates in tubules
2a) fast response : compensation by cardiovascular system
- vasodilation and decrease in CO
2b) slow response : compensation by kidney
- excretion of fluid in urine, decrease in BV
–> need to get rid of extra volume
two processes go hand in hand, both pathways are triggered to lower BP to normal
baroreceptors
found in carotid sinus and aortic arch
(carotid sinus baroreceptors and aortic arch baroreceptors)
monitors MAP, changes in pressure can triggere downstream effect to alter processes
MAP controlled by baroreceptor reflex
- blood flows past receptors
–> baroreceptors continously monitor blood pressure and sending signals to brain - change in pressure is detected, sends sensory signals to brain
- integrates response by ANS
- para : alters autorhythmic firing rate (SA node) to alter heart rate
- sym : influence cardiovascular system (SA node, ventricles = muscles to change contractability // veins and arterioles to vasodilate or constrict ==> restore BP to normal
Baroreceptor reflexes, BP too high
- Baroreceptors in the carotid sinus and aortic arch detect an increase in blood pressure
- Increased rate of firing in afferent nerves sends signals to the cardiovascular center in the medulla
- The Medulla Oblongata (MD = BP/RP mnemonic) integrates the information and adjusts autonomic output:
- Decreased Sympathetic Activity cardiac and vasoconstrictor nerve activity AND Increased Parasympathetic Activity: Increases parasympathetic nerve activity, releasing more ACh
- Decreased heart rate and stroke volume and Vasodilation (relaxation of arterioles and veins)
- Decreased cardiac output and total peripheral resistance
- lower blood pressure back toward normal.
Baroreceptor reflexes, BP too low
- Baroreceptors in the carotid sinus and aortic arch detect an decrease in blood pressure
- Decreased rate of firing in afferent nerves sends signals to the cardiovascular center in the medulla
- The Medulla Oblongata (MD = BP/RP mnemonic) integrates the information and adjusts autonomic output:
- Increase Sympathetic Activity cardiac and vasoconstrictor nerve activity AND Decreased Parasympathetic Activity: decreased parasympathetic nerve activity, releasing less ACh
- Increased heart rate and stroke volume and Vasodilation (relaxation of arterioles and veins)
- Increased cardiac output and total peripheral resistance
- higher blood pressure back toward normal.
effect of ACH on heart rate and blood pressure
ACh binds to muscarinic (M2) receptors on SA node cells.
Hyperpolarization: Increases K+ efflux and decreases Ca2+ influx, hyperpolarizing the cell membrane.
Slower Depolarization: Leads to a slower rate of depolarization and reaches threshold for AP less quickly
–> decrease in Heart Rate, Cardiac Output and Blood Pressure
Para and sympathetic response to baroreceptor reflex when pressure too high
- decrease in sympathetic activity
–> less NE released (norepinephrine used for vasconstriction)
=> Results in vasodilation of arteriolar smooth muscle, decreasing peripheral resistance.
–> ventricular myocardium (muscular tissue of the heart) causes reduced force in contraction and CO - increase in parasympathetic activty
–> more ACh on muscarinic receptor, causing hyperpolarisation and decreasing heart rate and CO
negative feedbac to stop firing after BP restored to normal, send normal tonic signals to the brain knows the Bp is normal
Abnormalities in blood pressure : hypertension
- hypertension puts on a lot of stress to blood vessels walls with “shear stress”
–> increase in BP damages cell lining in blood vessel/ endothelium damage - damaged endothelial exposes underlying collagen/matrix within arteries
- recruits platelets to kick start clotting cascade
- clots formed or formation of plaque (atherosclerosis)
–> occulusion (blockage/closing of blood vessels or organs)
damage can lead to fibrosis
–> scarring in blood vessels and thickening in vessel wall
heart, due to high BP, muscle pumps more blood, muscle wall thickens and heart can store less blood now
Abnormalities in blood pressure : hypotension
Too little blood to fill vessels – Circulatory shock
–> bloods circulation is inadequate to maintain oxygen supply to tissues and organs
reasons : low volume, heart muscles no contracting properly, sudden loss of sympathetic signals to increase HR, toxins in blood damages vessels and decrease blood flow, reaction to toxins to alter dilation and blood pressure
hypertension: Adaptation to baroreceptors
- During hypertension, baroreceptors are unable to bring MAP back to normal
- “Reset” to new set-point
adapts to new BP, can no longer sense CHANGE in MAP
–> constantly firing to brain this tonic input “this is normal”
hypovolemic shock
caused by severe hemorrhage / excessive vomiting, diarrhead, urinary losses => loss of fluids derived from plasma
–> loss of blood volume
–> CO
–> circulatory shock, and decrease in MAP
vasogenic shock
caused by septic shock => vasodilator subtances from bacteria / anaphylactic shock => histamine released from allergic reaction
–> widespread vasodilation
–> decrease in totall peripheral resistance
–> circulatory shock, and decrease in MAP
