Intro to CVS (#2) Flashcards
List 3 ways cardiac output is regulated
- Preload
- Afterload
- ANS
What is preload?
degree of stretch at end of diastole just before vent begin to pump
How does preload affect CO?
- inc CVP stretches RV which responds by beating more forcefully + pumping more blood into the lungs
- this inc pul vascular P + therefore P in LV which stretches + beats more forcefully
- inc CO as pushing heart to work harder
- also works with EDP (amount of blood in vent just before contraction) as more blood in vent make them more stretched
How do venous P differ between R + L side of heart?
- CVP on R side
- pul venous P on L side
What is afterload + what is it determined by?
- load against which heart works to eject blood
- determined by aortic P
How does afterload affect CO?
- inc afterload works against heart which caused dec ejection of blood
- dec CO
What causes inc afterload?
- if mean BP v.high
- aortic stiffness - gets stiffer with age - causes inc P within it which inc afterload
How does ANS affect CO?
- SNS inc HR, cardiac contractility (strength of contraction) through beta 1 receptors + SV which inc CO
- PNS dec HR through muscarinic receptors which dec CO
What happens to ESV at end of systole?
- dec as heart pumped out more blood
What does the Frank-Starling curve show?
relationship between SV + EDP
How does F-S curves affected by inc afterload + inc SNS activity?
- inc afterload: inc EDP means less inc in SV so curve shifts down showing that for any given EDP, SV dec - less blood ejected
- inc activity of cardiac symp nerve fibres: dec EDP means greater in SV so shifts curve up showing that for any given EDP, SV inc - more blood ejected
What is rel low arterial P gen by + why is it sufficient to drive blood through pul circ?
- gen by RV (~ 16mmHg)
- bc pul vascular R v. low
What is Poiseuille’s law?
R prop to r to power of 4 of vessel
What is r + R of pul arteries + why?
- shorter + so have larger radius which dec R
- also cap network supplying alveoli with blood forms v.dense mesh lowers R
What is sig of cap network surrounding alveoli?
massive SA for gas exchange of O2 + CO2 between blood + alveoli due to small diffusion distance between them
Why must R of lungs be low?
- receiving same vol of blood as rest of body
- R must be low to accomm high CO from R side
What is pO2, Hb O2 binding site sat, O2 content of blood in systemic vascular system?
- pO2: ~ 100mmHg (higher due to gas exchange in lungs)
- Hb O2 binding site sat: >/= 97%
- O2 content: ~ 200ml/l
What is pCO2 + CO2 content of blood in systemic vascular system?
- pCO2: ~ 40mmHg
- CO2 content: ~ 480ml/l (dec as its diffused into alveoli)
What is P in aorta in systemic circ?
- 120 (diastolic)/80 (systolic)mmHg
- oscillating P
How does diastolic + systolic P change with age?
- diastolic inc until middle age + then dec
- systolic P inc through life so chances of high BP is 50% by 50 which continues to inc
What is blood velocity during systole + why?
- ~ 70cm/sec
- blood has lots of momentum as just been pumped out of L vent + quicker than velocity going into heart
Describe passage of blood flow from heart to body
- Blood pumped from LV into aorta
- Blood vessels branch out aorta to main organs: heart, brain, muscle, GIT, liver
- Blood then flows into microcirc
- Blood returned to RA
- Enters RV then pumped to lungs
- Blood returns to LA
What is function of arterial system + its P?
- high P
- regulates distribution of blood to diff regions of body mainly by small arteries + arterioles
- does this by changing R through contraction + P of arteries in diff organs
What is R of arterial system also known as + why?
- peripheral R
- systemic peripheral R
- systemic vascular R
- TPR
- biggest contributor to reg of BP +, vas R etc
How does liver get arterial supply + why does it need it?
- hepatic artery
- venous blood from GIT goes to liver but not getting enough O2
What is portal system and why is it needed?
- blood moves sequentially through 2 cap beds in series connected by a larger vessel
- in liver, kidneys + part of brain
- process ingested toxins from GIT before it gets to rest of body
What is org of microcirc?
large arteries —> muscular arteries —> arterioles —> cap —> venules —> small veins —> large veins
What is function of venous system?
collects blood from tissues + returns it to the heart
How much blood do the veins contain?
70% - acts as blood reservoir
What does contraction of veins cause?
redis blood to arteries, maintaining BP
What is arterial BP like?
- pulsatile
- osc between 80 + 120mmHg
How do you calc MABP?
diastolic + (systolic - diastolic)/3 or 1/3 pulse P
What is the pulse P?
diff between systolic + diastolic P
Why is MAP not av of sys + dia?
Heart spends more time in diastole so MABP closer to diastolic P bc its longer than systolic
What is incisura/notch due to?
closure of aortic valve
What is the P wave that occurs during diastole?
- aorta + arteries already full of blood so need to expand for blood to eject from heart
- causes P wave where blood that’s entered pushes against blood already there
- propagated v. fast along aorta into large arteries which expand so can accept more blood
What causes a large pulse P?
large arteries bring blood to vas beds
Where is 75% of ejection fraction stored?
- transiently in aorta + large arteries where energy stored in elastic walls
- already blood in aorta so expands to take on extra blood entering
What causes inc P in aorta?
- vent pump distends aorta
- aortic valve shuts at end of so blood can only go forwards
What happens to 25% of blood in aorta?
pushed forward out of other end of aorta into small arteries + rest of body in stuttering motion with each heartbeat
