The Circulatory System 5

Question 1

what is the efficiency + work of the heart as a pump measured as?

Answer 1

cardiac output

Question 2

what is cardiac output?

Answer 2

vol of blood heart pumps out every min (ml/min or L/min)

Question 3

what is cardiac output determined by?

Answer 3

• stroke vol

- heart rate

Question 4

formula to find CO?

Answer 4

CO = SV x HR

Question 5

what is stroke volume?

Answer 5

vol of blood ejected by the left ventricle with each heart beat (ml/beat)

Question 6

what are the determinants of heart rate?

Answer 6

ANS/autonomic tone on heart

• inc in SNS/sympathetic tone INC heart rate
• inc in PNS/parasympathetic tone DEC heart rate

Question 7

what are the determinants of stroke volume?

Answer 7

• preload
• afterload
• cardiac contractility

Question 8

what is preload?

Answer 8

workload imposed on heart before contraction begins

Question 9

what does preload =

Answer 9

end-diastolic vol / pressure

Question 10

what is EDV/EDP?

Answer 10

vol of blood/pressure in ventricle prior to contraction (i.e at end of diastole)

Question 11

what does EDV =

Answer 11

venous return (VR)

Question 12

what is Frank-Starlings law of the heart?

Answer 12

SV = directly proportional to preload (or VR)

Question 13

what does an inc in preload lead to?

Answer 13

• inc in stretch of cardiac muscle fibres
• inc in contraction
• inc in SV

Question 14

what is afterload?

Answer 14

pressure heart must generate/overcome in order to eject blood into aorta

Question 15

what does afterload =

Answer 15

aortic pressure = systemic arterial BP

Question 16

what is afterload determined by?

Answer 16

systemic/total peripheral resistance (TPR)

Question 17

what is SV inversely proportional to?

Answer 17

afterload (or TPR)

Question 18

what does an increase in afterload lead to?

Answer 18

decrease in SV

Question 19

what is contractility?

Answer 19

ability of heart to change its force of contraction without changing rest of muscle length

Question 20

what does contractility =

Answer 20

strength of contraction at any given EDV

Question 21

what does contractility depend on?

Answer 21

availability of intracellular ca2+ to participate in contractile process

Question 22

what is SV directly proportional to?

Answer 22

cardiac contractility

Question 23

what does an inc in [Ca2+]i lead to?

Answer 23

• inc in actin-myosin crossbridge formation
• inc in contractility
• inc in SV

Question 24

what is cardiac contractility inc by?

Answer 24

SNS activation

- inc in SV

Question 25

control of cardiac output

Answer 25

- inc in symp activity (+ epinephrine) inc heart rate and SV —> inc cardiac output (via EXTRINSIC control) - inc in end-diastolic vol inc SV —> inc CO (via INTRINSIC control) - inc in venous return —> inc SV —> CO (via INTRINSIC control)

Question 26

what is systolic BP?

Answer 26

force exerted by blood on arterial walls during systole

Question 27

what is diastolic BP?

Answer 27

force exerted by blood on arterial walls during diastole

Question 28

what is the mean arterial BP?

Answer 28

average pressure responsible for driving blood forward into tissues

Question 29

formula to find pulse pressure?

Answer 29

systolic BP - diastolic BP

Question 30

formula to find mean BP?

Answer 30

diastolic BP + (1/3 x pulse pressure)

Question 31

what is BP determined by?

Answer 31

- cardiac output | - total peripheral resistance (TPR)

Question 32

formula to find BP?

Answer 32

CO x TPR

Question 33

what is TPR determined by?

Answer 33

- sympathetic tone: vascular alpha 1 + beta 2 adrenoreceptors - circulating hormones - Ang II + catecholamines - local hormones - NO, ETs, PGs + adenosine

Question 34

cardiac output is determined by HR and SV. give further examples within these 2 points

Answer 34

HR- autonomic tone, catecholamines SV- cardiac contractility, venous return

Question 35

the mean BP is closely regulated + kept within narrow physiological range. give the 2 reasons why?

Answer 35

- must = high enough to ensure adequate perfusion of organs + tissues - must not be so high that places undue strain on heart + risks damaging blood vessels

Question 36

homeostatic control involved 2 mechanisms give the 2 mechanisms?

Answer 36

- short-term control mechanism: via baroreceptors | - long-term control mechanisms: via kidneys

Question 37

short term control adjustments

Answer 37

- happens in seconds - involves alterations in CO + TPR - mediated via autonomic nervous system influences on heart, arterioles + veins

Question 38

long term control adjustments

Answer 38

- needs minutes to days | - involves renal mechanisms of normal salt + water balance —> adjustments in total blood vol

Question 39

short term BP control mechanism (parasympathetic output)

Answer 39

- inc in BP - inc in firing of baroreceptors in carotid arteries + aorta - sensory neurones - medulla oblongata - inc in parasympathetic output - more ACh on muscarinic receptor - SA node - dec heart rate - dec CO - dec BP

Question 40

short term BP control mechanism | sympathetic output

Answer 40

- inc in BP - less NE released - alpha receptor —> arteriolar smooth muscle —> vasodilation - dec peripheral resistance - beta receptor —> ventricular myocardium —> dec force of contraction. —> dec CO - dec BP

Question 41

what kind of mechanism is the short control BP control mechanism?

Answer 41

negative feedback

Question 42

long term BP control mechanism | kidneys

Answer 42

- dec in extracellular fluid - dec in arterial BP - renin released - convertes angiotensinogen to angiotensin I - angiotensin I converted into angiotensin II - goes to adrenal cortex + arterioles - adrenal cortex rel aldosterone —> Na+ reabsorption by kidney - —> inc in vascular vol - arterioles vasoconstrict - —> inc in arterial BP

Question 43

long term BP control mechanism | hypothalamic neuron

Answer 43

- hypothalamic osmoreceptors stimulate hypothalamic neurons - inc thirst - —> water intake - —> inc in plasma bol and plasma osmolarity - —> relieves inc in osmolarity - —> relieves dec in ECF vol + arterial blood pressure - stimulates left atrial volume receptors - stim hypothalamic neurones - inc in vasopressin - —> water permeability of DCT and PCT - —> inc in water reabsorption - dec in urine output - inc in plasma vol

Question 44

integrated BP control mechanism

Answer 44

- inc in blood vol - —> inc BP - triggers compensation by cardiovascular system (FAST**) + compensation by kidneys (SLOW*) - ** —> vasodilation + dec CO —> dec BP to normal - * —> excretion of fluid in urine dec blood vol - —> dec BP