Unit 2 - Blood Flow & Blood Pressure PART E Flashcards
How does the body homeostatically regulate BP?
by regulating mean arterial pressure (MAP)
Arterial pressure
is a balance b/t BF into the arteries & BF out of the arteries
If flow in exceeds flow out…
blood volume in the arteries ↑’s & MAP ↑’s
If flow out exceeds flow in…
volume ↓’s & MAP falls
What will happen if MAP is too low or too high?
If MAP is too LOW, blood does not perfuse organs fast enough to clear wastes and bring in nutrients/oxygen.
If MAP is too HIGH, perfusion is too fast to allow for adequate exchange between the blood and the tissues.
MAP =
CO x TPR
What can MAP be regulated by controlling?
- Cardiac Output
- TPR (Total Peripheral Resistance)
- Blood Volume
MAP can be regulated by controlling:
Cardiac output; how?
- By increasing or decreasing HEART RATE
- By increasing or decreasing the FORCE OF CONTRACTION TO ALTER STROKE VOLUME.
- By increasing or decreasing VENOUS RETURN.
MAP can be regulated by controlling:
TPR (Total Peripheral Resistance); how?
- By increasing or decreasing VASOCONSTRICTION/VASODILATION (arteriolar radius)
What is BF out of the arteries primarily influenced by?
TPR
TPR (Total Peripheral Resistance)
resistance to flow offered by the arterioles
MAP can be regulated by controlling:
Blood Volume; how?
- Increasing/decreasing blood volume increases/decreases venous return, increases/decreases stroke volume.
- Also increases MAP directly, by increasing the hydrostatic pressure of the blood pressing harder against the walls of the vessels).
(if BV ↑’s, BP ↑’s & if BV ↓’s, BP ↓’s)
- small ↑’s in BV occur throughout the day due to ingestion of food & liquids, but usually don’t create long-lasting changes in BP b/c of homeostatic compensations
- if BV ↓’s, the kidneys cannot restore the lost fluid (can only conserve BV & thereby prevent further ↓’s in BV)
What happens if CO ↑’s?
the heart pumps MORE blood into the arteries per unit time
What happens if resistance to BF out of the arteries doesn’t change?
flow into the arteries is GREATER than flow out, BV in the arteries ↑’s, & arterial BP ↑’s
What happens if CO remains unchanged but peripheral resistance ↑’s?
- flow into arteries is UNCHANGED but flow out is ↓’ed
- blood again accumulates in the arteries, & the arterial pressure again ↑’s
BF into the aorta is = to…
the CO of the LV
Most cases of hypertension are believed to be caused by…
↑’ed PR without changes in CO
What is MAP?
Mean arterial pressure is a function of CO & PR
- illustrates mass balance: the volume of blood in the arteries is determined by input (CO) & flow out (altered by changing PR)
- as arterial volume ↑’s, pressure ↑’s
Specific Control Mechanisms…
use negative feedback to keep MAP constant
What are the specific control mechanisms that use negative feedback to keep MAP constant?
- Baroreceptor Reflex Control (for short-term regulation of MAP)
- Blood Volume Control (for long-term regulation of MAP)
Baroreceptor Reflex Control (for short-term regulation of MAP)
An autonomic reflex that is the single most import mechanism for short term regulation of MAP. Causes changes in TPR and CO.
What is the Baroreceptor Reflex Control (for short-term regulation of MAP) stimulus?
Stimulus: changes in blood pressure (MAP) and pulse pressure
What is the Baroreceptor Reflex Control (for short-term regulation of MAP) receptors?
Receptors: Mechanical stretch receptors (BAROreceptors) in aortic arch and carotid sinuses (where they continuously monitor the pressure of blood flowing to the brain (carotid baroreceptors) & to the body (aortic baroreceptors))
Describe Baroreceptors discharge rate
Their discharge rate is directly proportional to MAP within physiological limits (so as MAP increases, so does the frequency of action potentials in the baroreceptor cells).
- when ↑’ed BP in the arteries stretches the baroreceptor membrane, the firing rate of the receptor ↑’s
- if BP falls, the firing rate of the receptor ↓’s