Systemic circulation Flashcards
What is pressure?
force per unit area
What is transmural pressure?
pressure tending to distent/collapse a vessel
What is pressure gradient?
Pressure differential b/w inflow and outflow
What is hydrostatic pressure?
generally used as blood pressure
pressure caused by the height of a fluid column
What is the mean arterial pressure?
avg pressure existing in the aorta and proximal arterial system during one cardiac cycle
Diastolic pressure + 1/3 pulse pressure
What are the physiological factors that determine arterial blood pressure?
- cardiac output (SV x HR)
-primary affect systolic pressure
regulated by ANS - peripheral resistance
-primary affects diastolic pressure
regulated by local metabolic activity
What is the baroreceptor reflex?
acts via ANS to affect Co and peripheral resistance
*maintains arterial BP moment to moment
What is the effect of exercise on mean arterial pressure?
systolic P increases and diastolic same or decr
pulse pressure widens
-MAP increases
What diseases affect blood pressure?
CHF (decr SV & contractility), IM, Bradycardia, sepsis -> decrease BP
hypertension: increase BP
What are physical factors that affect arterial blood pressure?
- arterial compliance
affects systolic + diastolic P
determined by age, blood volume, symp tone, pregnancy - blood volume: affects SV and arterial compliance
How does changing peripheral resistance affect arterial pressure?
if keep compliance constant,
as peripheral resistance increases, both systolic and diastolic P increase
How does changing compliance affect arterial pressure?
if keep peripheral resistance constant,
as decrease compliance, the pulse pressure widens
(increase systolic and decrease diastolic)
What are the factors that affect total peripheral resistance?
“runoff of blood”
blood viscosity and arteriolar radius
What are the global (extrinsic) factors that control arteriolar radius?
- baroreceptors
- hormonal effects
- sympathetic activity
What are the local (intrinsic) factors that control arteriolar radius?
- myogenic response
- endothelium-mediated regulation
- local metabolic changes
What effect does parasympathetic stimulation have on mean arterial pressure?
decr HR so decr CO and lower BP
What effect does sympathetic stimulation have on mean arterial pressure?
- affect the heart: incr HR and contraction strength -> both increase C.O. which increases BP
- affect veins: venoconstrict to increase venous returns so increase SV which increases CO and thus BP
- affects arterioles: vasoconstrict to increase peripheral resistance and prevent run off! increase BP
What is the effect of sympathetic activity on exercise?
increase HR
increase contractility
increase CO
What is the effect of sympathetic vasoconstriction?
increases vascular resistance
diverts blood away from skin, kidneys, splanchnic regions and inactive muscle
doesn’t affect cerebral, pulmonary and cardiac vasculature
What is the effect of metabolic vasodilation?
lowers vascular resistance and increases blood flow
to skeletal muscle and heart
change in total peripheral resistance dep on level of exercise and mass of active muscle
*overcomes but still limited by sympathetic innervation
What other strategies are used to help during exercise?
capillary recruitment
ehanced O2 extraction for muscles (not heart)
What helps to increase venous return?
sympathetic venoconstriction: decr venous compliance and shunts blood back to heart
muscle pump
respiratory pump
What happens to arterial pressure during exercise?
systolic pressure is increased (cuz SV), vasoconstriction also helps
diastolic pressure is determined by changes in total peripheral resistance
*pulse pressure widens
What are the pre capillary resistance vessels?
arterioles
metarterioles
precapillary sphincters
What are some characteristics of capillary blood flow?
- low velocity
- intermittent (vasomotion: not cont, chaotic -> some open, others closed
- direction (pressure gradients)
- not uniform
- rouleaux formation
How does oncotic pressure affect transcapillary fluid exchange?
proteins are more concentrated in the capillaries so it pulls water in to balance (absorption)
How does hydrostatic pressure affect fluid exchange?
it decreases as you go from arterial to venous side
all pressure is inside the capillary
push fluid outside to balance it
Describe pressures on the arterial side
hydrostatic pressure higher then oncotic
net: fluid out
e.g. kidneys
Describe pressures on the venous side
oncotic pressure higher then hydrostatic
net: fluid in
What is the function of lymphatic vessels?
pick up extra fluid that ended up in the interstitial space and shut it back to the heart
What determines oncotic pressure?
albumin concentration
What is the effect of arterial pressure on capillary hydrostatic pressure?
small effect!
cuz too much pre-capillary resistance
What is the effect of venous pressure on capillary hydrostatic pressure?
larger cuz few resistance
What determines capillary hydrostatic pressure?
pre/post capillary resistance ratio
What are some substances secreted from the endothelium?
- prostaglandins
- EDRF
- NO
- metabolites
- all vasodilate
-endothelin: vasoconstrict
What is the structure of lymphatics?
- unidirection flow back to heart
- valves
- non-fenestrated endothelium, lil to no basal lamina, no smooth muscle
- large collecting vessels return fluid to subclavian veins
What factors govern lymph flow?
- amount of capillary filtration
- skeletal muscle activity
- lymphatic unidirectional valves
What is edema?
accumulation of excess fluid within the interstitial space
What precipitates peripheral edema?
- reduction in plasma protein concentration (liver or renal disease)
- increase in capillary hydrostatic pressure (CHF- back up fluid)
- increased permeability of capillary membrane (burns)
- lymphatic obstruction (tumor)
