Lecture 15 - The Heart and Circulation - Central

Question 1

What are the 4 major parts of the cardiovascular system?

Answer 1

• heart (pump)
• arteries (outflow conduits)
• capillaries (drop/pick-up site)
• veins (return flow conduits)

Question 2

what are the 4 chambers of the heart?

Answer 2

• right atria
• left atria
• right ventricle
• left ventricle

Question 3

what is the role of the atria?

Answer 3

• receiving chambers (top)

Question 4

what is the role of the ventricles?

Answer 4

• pumping chambers (bottom)

Question 5

what is the “right heart”?

Answer 5

• pulmonary circulation
• pumps deoxygenated blood from body to lungs
• superior/inferior vena cava –> RA –> tricuspid valve –> RV –> pulmonary valve –> pulmonary arteries –> lungs

Question 6

what is the “left heart”?

Answer 6

• systemic circulation
• pumps oxygenated blood from lungs to body
• lungs –> pulmonary veins –> LA –> mitral valve –> LV –> aortic valve –> aorta

Question 7

what is cardiac muscle? and its characteristics?

Answer 7

• muscle of the heart
• contracts as one single unit
• fibres are interconnected end-to-end by intercalated discs
• “all or nothing” muscle

Question 8

what is coronary circulation?

Answer 8

• primary blood supply to heart is provided by coronary arteries which arise from aorta
• cardiac veins return deoxygenated blood to the inferior and superior vena cava
• requires oxygen and energy for contraction

Question 9

how do you match O2 supply with O2 demand?

Answer 9

• as ATP demand increases, demand for oxygen increases
• oxygen supply also increases because they have to be equal/equivalent (supply and demand)

Question 10

What is the heart’s contribution to exercise?

Answer 10

• generates pressure to drive oxygenated blood through vessels to skeletal muscle
• driven by the demands for active skeletal muscle for O2
• also driven by the need to remove CO2, transport hormones, support temperature, fluid regulation and acid-base balance (pH)
• works harder when O2 demands are higher

Question 11

what is the equation for matching systemic O2 with O2 demand?

Answer 11

• VO2 = Q x a-vO2difference
• where VO2 = O2 uptake
• Q = HR x SV, flow of O2 rich blood
• a-vO2difference = CaO2 - CvO2 (O2 extraction)
• this is known as Fick’s principle

Question 12

how can you measure CaO2?

Answer 12

• with a catheter
• with hemoglobin –> concentration of hemoglobin, saturation of hemoglobin and partial pressure of O2 in the blood

Question 13

what has the biggest influence on Vo2 uptake?

Answer 13

• Q
• cardiac output needs to increase significantly to keep us exercising for long periods of time or at higher levels

Question 14

what is normal VO2 at rest?

Answer 14

• 4-6 L/ minute
• Q increases at a 6:1 ratio as VO2 increases

Question 15

what is cardiac output (Q)?

Answer 15

• total volume of blood pumped by the ventricle each minute
• measured in L/min
• HR x SV

Question 16

how does HR contribute to Q? (2)

Answer 16

• intrinsic control
• extrinsic control

Question 17

what is intrinsic control?

Answer 17

• internal rhythm controls in the heart
• heart can generate it’s own electrical signal
• pacemaker (SA node) - establishes sinus rhythm
• can reach 100 bpm without external control

Question 18

what is extrinsic control?

Answer 18

• systems that modulate intrinsic electrical impulses
• causes HR to increase
• adjusts HR at rest (for endurance athletes, it’s very low)
• HR can reach up to 220 during maximal effort
• works like a dial
• requires brain signals

Question 19

what are the components of an ECG?

Answer 19

• P wave = atrial depolarization
• QRS wave = ventricular depolarization
• ST segment= ventricular repolarization
• T wave = ventricular repolarization
• PR interval = includes AV delay
• QT interval = ventricular depolarization and repolarization

Question 20

what is the route of myocardial impulse transmission?

Answer 20

1. sinoatrial node
   1.5. atria
2. atrioventricular node
3. A-V bundle or bundle of His
4. Purkinje fibres (AV bundle)
   4.5. ventricles

Question 21

what happens in the SA node?

Answer 21

• spontaneous depolarization and repolarization to provide “innate” heart stimulus

Question 22

what happens in the AV node?

Answer 22

• delays impulse around 0.10 second to provide sufficient time for atria to contract and force blood into the ventricles

Question 23

what is the role of Purkinje fibres?

Answer 23

• speed impulse rapidly through ventricles

Question 24

what 3 extrinsic systems modulate HR?

Answer 24

• parasympathetic nervous system
• sympathetic nervous system
• endocrine system

Question 25

what is the role of the parasympathetic nervous system in modulating HR?

Answer 25

• vagus nerve
• slows the heart rate and conduction velocity
• uses acetylcholine

Question 26

what is the role of the sympathetic nervous system in modulating HR?

Answer 26

• from the ganglia
• increases HR
• uses norepinephrine (improves conduction)
• dilate coronary arteries

Question 27

what is the role of the endocrine system in modulating HR?

Answer 27

• releases epinephrine (from adrenal medulla)
• slows heart rate
• dilates coronary vessels
• accelerates SA node discharge
• increases myocardial metabolism

Question 28

how does SV contribute Q?

Answer 28

• stroke volume is the amount of blood pumped in one heartbeat
• pressure changes/generation throughout the heart
• through the cardiac cycle

Question 29

what is normal SV?

Answer 29

• 70mL/beat

Question 30

what are the phases of the cardiac cycle?

Answer 30

• contraction phase = systole
• relaxation phase = diastole
• always some volume in the left ventricle (never at 0)
• *understand the cardiac cycle image (slide 19)

Question 31

how do you calculate SV?

Answer 31

• during systole
• EDV - ESV = SV

Question 32

what is EF?

Answer 32

• ejection fraction
• % of EDV pumped (end-diastolic volume)
• SV /EDV = SV
• clinical index of heart contractile function
• typically between 60-65%

Question 33

what is preload?

Answer 33

• the volume of blood received by the heart during diastole (EDV)
• a component of SV
• increased venous return

Question 34

what is the Frank-Starling Law of the Heart?

Answer 34

• the relationship between contractile force and resting length of heart’s muscle fibres
• force is proportional to it’s initial length
• preload stretches the ventricle is diastole to produce a more forceful ejection of blood (increased EDV = increased SV)

Question 35

what is contractility?

Answer 35

• a component of SV
• can we get cells to contract more forcefully
• inotropy

Question 36

what is inotropy?

Answer 36

• enhanced contractile force (increased tension)
• augments stroke power and facilitates emptying
• length-independent
• increased inotropy = increased SV
• fires sympathetic nerves, decreases parasympathetic nerves, increases circulation of Epi and NE

Question 37

what is afterload?

Answer 37

• a component of SV
• pressure the heart must generate to open aortic valve
• higher afterload = higher pressure needed to open aortic valve

Question 38

how do you overcome afterload?

Answer 38

• reduction of afterload is normal during exercise
• high afterload = greater pressure generated by left ventricle

Question 39

what is the relationship between stroke volume and oxygen uptake?

Answer 39

• consistent relationship
• exponential relationship (ending with evening out)

Question 40

what are the 5 determinants off cardiac output?

Answer 40

• heart rate
• stroke volume
• preload
• contractility
• afterload

Question 41

what is the Fick Principle?

Answer 41

• need to match O2 supply with O2 demand
• cardiac output is very closely linked to oxygen supply and demand