Regulation Of Arterial Pressure Flashcards
How does the baroreceptor reflex occur?
Using classical reflex arc
- Detector
- Afferent neural pathway
- Coordinator center
- Efferent neural pathway
- Effectors
What is the Baroreceptor reflex?
‣ Fast, neural mediated reflexes that attempt to keep arterial pressure constant via changes in the output of the SNS and PNS to the heart and blood vessels
What can alter the sensitivity of baroreceptors?
Disease
I.e. chronic hypertension - will reset them to a higher set point
Where are baroreceptors located?
Where wil they lead to?
- carotid sinus
- aortic sinus
Lead to Nucleus tractus solitaries (NTS)
What types of detectors are present in baroreceptors?
Mechanoreceptors - changes in pressure
Chemoreceptors - reponse to PO2, PCO2, pH
How will firign rate change iwth increased stretch on vessel wall?
Increased firing rate
How will firing rate change with decreased stretch on vessel wall?
Decreased firing rate
What are the baroreceptors most responsive to?
Rate of change in pressure
Not just the magnitude of change
What 3 systems regulate MAP?
- Baroreceptor reflex
- Endocrine wise via RAAS
- Input from ADH & ANP
What does “decreased firing rate” refer to?
Refers to firing rate of afferent neurons
-decreased when decrased stretch
Where will efferent from the Baroreceptor pathway go to?
To cerebral cortex and hypothalamus
What is the region associated with PNS activity in the Nucleus of Tractus solitarius (NTS) ?
Dorsal motor nucleus of CN 10 and Nucleus ambiguus
What is the region associated with SNS activity in the Nucleus of Tractus solitarius (NTS) ?
Rostral ventrolateral medulla
How does the aortic sinus differ from the carotid?
‣ Aortic sinus = high threshold for activation
• Will continue to respond above saturation
• Less sensitive to rate
• Less affected by decreases
What effects does the SNS have on the CV system? (4)
‣ 1. SA node = increase HR (beta-1)
‣ 2. cardaic muscle = increase Contractility and SV
‣ 3. Arterioles to produce vasoconstriction = increase TPR (alpha-1)
‣ 4. veins to produce venoconstriction = decrease unstressed volume
How does the SNS influence the kidney for the CV system?
Goes to adrenal gland via splanchnic n.
-fluid retention by kidney du to afferent arteriole constriction and RENIN SECRETION
What is the influence of the PNS on CV system?
- SA node via CN 10 = decrease HR (Musc. Rs.)
- increased baroreceptor firing rate
- INDIRECT vasoDILATION via NO release stimulation
How does decreased symapthetic influence affect tone of blood vessels?
- decreased A. Constriction = decrased TPR
- decreased V. Constriction = incr. compliance = increased unstressed volume
What can cause a decrease in blood volume?
Hemorrhage
Dehydration
Loss of body fluids
What will happen with decreased blood volume?
VR, preload, SV, CO, MAP, vascular function curve?
Decrease in VR, SV, CO, and MAP
-vascular function curve will shift left
What will the compensatory response be to decreased blood volume?
- decrease in carotid sinus nerve firing
- decreased afferents
- decreases HR, contractility, Cardiac Output
- decreased unstressed (want more stressed to bring up pressure)
- increased TPR
- increased Epi, ADH, Renin, Angiotensin II, aldosterone
How does a hemorrhage affect the body?
- decreases Partery (bc BV and stressed volume =decreased)
- Baroreceptor reflex activated by acute decr.
- decreased stretch = decr. Firing rate
- will increase SNS, decrease PNS
How is blood pushed upward?
Normal upright movement initiates muscle pumps which push blood upward toward heart past valves in limb
What happens to blood if there is no movement?
- VR accumulates in lower limbs
- increases venous and capillary hydrostatic pressure
- venous pooling —> edema & HYPOtension
- reflexes to bring BP back up (increase SNS)
What is orthostatic hypotension?
Decrease in arterial BP upon standing
Why does orthostatic hypotension occur?
-going from supine to standing —> blood pools in veins of LEs
-decreases VR —> decreases CO
—> decreased MAP
- edema also occurs bc increased hydrostatic pressure =increased filtration
- if decrease in Partery is dramatic, then cerebral BP may decrease and cause fainting
What can cause long term adjustments of arterial pressure?
Hormonal responses can begin w/in minutes and build over a period of days
How does the Renin-Angiotensin II aldosterone system affect BP?
What other system does it overlap with?
Controls BP by regulating BV and TPR
Overlaps w/ SNS
What is renin?
‣ Enzyme secreted by kidney into blood in response to DROP in BP
• If BP is high - less renin secreted
When is renin secreted and by what?
Secreted when BP is LOW
Or
in response to SNS stimulation
By juxtaglomerular cells in walls of renal afferent arterioles
What r. Is activated to release renin?
Beta 1 adrenergic r.
What effect does renin have on NaCl?
NaCl will decrease at macula dense
What is the downstream effect of renin?
Renin —>
angiotensin —>
angiotensin I (inactive) —>
angiotensin II (active, converted in lungs/kidneys) —>
aldosterone
What is the effect of ANgiotensin II?
‣ Causes secretion of aldosterone from adrenal cortex
What are the effects of Aldosterone?
- na and H2O retention by kidney
- increases BV, SV, CO
—> increases BP
Where does ADH/vasopressin act?
At V1 receptors (sm. M.) and V2 receptors (collecting ducts)
What is ADH secreted in response to? (4)
‣ 1. Angiotensin II
‣ 2. Atrial receptors in presence of low preload - decreased atrial receptor firing
‣ 3. Increased osmolality of blood - hyperosmolarity
‣ 4. Sympathetic stimulation
What is effect of ADH?
Increases TPR and water retention
What will increase the secretion of ANP/BNP?
When there is Excessive Preload of atria and ventricles (high BP)
What effect does ANP have?
‣ Arteriolar dilation - decreases TPR
‣ Increases fluid loss - decreases preload
‣ Inhibits renin- decreases both TPR and preload
‣ Will decrease Blood Volume and BP
What does ANP protect against?
Protects against overdilation or over stretching of cardiac chambers
What is the central command response during exercise?
Increase SNS
- increase HR, contractility, CO
- constricts Arterioles (constricts skin, splanchnic regions, kidneys, inactive m.)
- constricts veins (decreasing unstressed volume and increasing VR)
Decrease PNS (to HR only)
What is the local response during exercise?
Increase vasodilator metabolites
-increased release of lactate, K+, adenosine
—> dilation of skeletal msucle arterioles —> decrased TPR
How do the cardaic function curve and vascular function curve change w/ exercise?
Both increase slope
How is TPR during exercise?
Decreased
Even though there is a bunch of constriction bc of SNS, local dilation allows for overall TPR decrease
