Lecture 21: Regulation of Arterial Pressure Flashcards
What are the equations for calculating Mean Arterial Pressure?
- Mean Arterial Pressure = Cardiac Output x Total Peripheral Resistance
- Mean Arterial Pressure = Heart Rate x Stroke Volume x Total Peripheral Resistance
- Mean Arterial Pressure = 2/3 (Diastolic BP) + 1/3 (Systolic BP)
What regulates mean arterial pressure?
- Baroreceptor Reflex
- RAAS System
- ADH
- ANP
Where are baroreceptors located?
- Carotid sinus
- Aortic sinus
What nerves are involved in the carotid sinus?
Where do they send their information?
- CN IX
- Sinus nerve of Hering
What nerves are involved in the aortic sinus?
- CN X
- Aortic Nerve
Where do nerves from the aortic and carotid sinus send their information?
Nucleus Tractus Solitatrius
What neurotransmitter do afferent signals from baroreceptors use when sending information to the nucleus tractus soliatrius?
Glutamate
What do chemoreceptors respond to?
- PO2
- PCO2
- pH
What do mechanoreceptors respond to?
- Changes in arterial pressure
What causes increased firing in a baroreceptor?
Increased pressure/stretch
What causes decreased firing in a baroreceptor?
Decreases in pressure/stretch
Where do baroreceptors send their signals to?
Medulla: Vasomotor center
What area of the brainstem is involved in parasympathetic activity in cardiovascular function?
- Dorsal motor nucleus of the vagus
- Nucleus ambiguus
What area of the brainstem is involved in sympathetic activity in cardiovascular function?
Rostral ventrolateral medulla
What is stroke volume is dependent on?
- Sympathetic stimulation of the heart
- Preload (EDV)
Heart rate is dependent on?
- Sympathetic stimulation
- Parasympathetic stimulation
Total peripheral resistance (TPR) is dependent on?
Sympathetic stimulation of arterioles
What is the difference between aortic and carotid baroreceptors?
- Aortic baroreceptors has higher threshold for activation
- Continues to respond above saturation
- Less sensitive to rate
Sympathetic nervous system causes _ baroreceptor firing rate
Decreased
What are the effects of the sympathetic nervous system on HR, contractility, vein and arteriolar radius, fluid retention?
- Constriction of arterioles and veins (alpha receptors)
- Increases HR and contractility (beta 1)
- Renin secretion and increased fluid retention
Parasympathetic nervous system causes _ baroreceptor firing rate
Increased
What are the effects of the parasympathetic NS on arterial pressure?
- We want to decrease MAP
- Decrease HR
- Vagus nerve signal to SA node
- Muscarinic receptors
- Also indirect vasodilation on blood vessels via NO
How does hypertension saffect baroreceptors?
Changes “normal” set point to something higher, which becomes the new “normal”
What enzyme is secreted by the kidney in response to drops in BP? What type of cell secretes this?
Juxtaglomerular cells produces renin.
What stimulates the release of renin?
- Sympathetic Nervous System
- *Specifically beta 1 adrenergic receptor activation*
What does renin do as an enzyme?
Converts angiotensinogen to angiotensin I
Angiotensin I is converted to Angiotensin II via which enzyme?
Where is this occurring?
Converted by ACE in lungs
What does angiotensin II do in its active form?
- Causes secretion of aldosterone from the adrenal cortex
- Stimulates secretion of ADH/Vasopressin
- Causes global constriction of arterioles by binding to AT1 receptors
What does aldosterone do?
- Increases Na+ and H2O retention
- Increases blood volume, preload, SV, CO, and MAP
What does ADH/Vasopressin do?
It is not only secreted in response to angiotensin II, but what other factors?
- Acts on V1 and V2 receptors of smooth muscle, and collecting ducts, respectively and increases TPR and water retention
- Atrial receptors during low preload, increased osmolarity of blood
What are the three natriuretic peptides that affect arterial pressure?
When are they secreted?
What are their effects?
- ANP, BNP, CNP
- Excessive preload of atria and ventricles
- Effects
- Arteriolar dilation: decrease TPR
- Increases fluid loss: decreases preload
- Inhibits renin: decreases TPR and preload
What happens when you have a hemorrhage?
- Decrease in blood volume and MAP
- Decreased firing of mechanoreceptors
- Increase sympathetic activation to bring MAP back up
- Sympathetics will:
- Increase HR, CO and contractility via alpha ine adrenergic receptors
- Constrict arterioles to increase TPR
- Constrict the veins to decrease unstressed volume and increase venous return
- Increased RAAS activation
What happens when you have too much blood?
- Increase in blood volume and increase in MAP
- Activate parasympathetics to bring MAP back down
- Increased ANP secretion
- Decreased ADH secretion
- Renal vasodilation
- Increased HR? (d/t increased preload?)*
What happens during exercise?
- Most important thing is getting blood to heart and skeletal muscle-increased sympathetic activation and decreased parasymp activation
- Central command
- Increase HR/contractility via Beta 1 adrenergic receptors
- Increase venous return
- Alpha one receptor activation leads to SELECTIVE vasoconstriction in skin, kidney, splanchnic regions, and inactive muscle
- Vasodilation in active muscles due to metabolites such as K+, adenosine and lactate
- Effects:
- Increase in pulse pressure
- SBP increases
- DBP should not change much
- Overall TPR will decrease (d/t dilation of skeletal muscle arterioles
What happens during orthostatic hypotension?
What happens in response?
- Decreased MAP; no change in HR and TPR, CO goes down from decreased venous return, central venous pressure decreases d/t pooling of blood in lower extremities
- Increase sympathetic activation
- Increase HR, contractility and CO via beta 1 adrenergic receptors
- Want to increase TPR via constriction of arterioles
- Want to decrease unstressed volume and increase venous return so we constrict the veins
