L7.1 The Heart

Question 1

Why is the cardiovascular system important?

Answer 1

• transports O2 and nutrients to the cells
• removes waste products from the body
• transports hormones around the body
• helps maintain body temperature

Question 2

what are the layers of the heart?

Answer 2

1. epicardium: outer layer = visceral pericardium
2. myocardium: cardiac muscle layer
3. endocardium: simple squamous epithelium, smooth layer to minimise friction

Question 3

describe the features of cardiac muscle cells

Answer 3

branched cells, interconnected, join at intercalated disc, 99% contractile muscle cells, 1% auto-rhythmic cells (non-contractile, generate action potentials)

Question 4

describe intercalated disc

Answer 4

• junction between cardiac cells
• desmosomes: mechanical anchor
• gap junctions: tunnels connecting cells; allows the passage of ions (transmission of action potentials)
• cardiac cells contract simultaneously

Question 5

describe the cardiac conduction system

Answer 5

• controls the route and timing of cardiac action potentials - coordinated contraction of heart chambers
• consists of autorhythmic cells (sinoatrial node, bundle of His, purkinje fibres, atrioventricular node, bundle branches)

Question 6

what node is the pacemaker of the heart?

Answer 6

SA node

Question 7

spread of excitation through the heart must meet 3 criteria. what are they?

Answer 7

1. each heart chamber must pump as a unit
2. atria should contract together; ventricles should contract together
3. atrial excitation and contraction must complete before ventricular contraction

Question 8

describe the electrical conduction through the heart

Answer 8

action potentials start in the SA node (spreads through atria); action potentials must travel through the AV node to reach ventricles (AV nodal delay); ventricular contraction (AV bundle, bundle branches; purkinje fibres)

Question 9

what is the cardiac cycle?

Answer 9

period between one heart beat and the next; periods of contraction and relaxation

Question 10

describe systole and diastole

Answer 10

systole: contraction
diastole: relaxation

Question 11

describe the first heart sound and second heart sound

Answer 11

first sound: closure of the AV valve; beginning of ventricular systole
second sound: closure of semilunar valves; during ventricular diastole

Question 12

what is fluid pressure

Answer 12

force exerted on a container by the fluid

Question 13

decreasing the size of a fluid-filled container will _____ fluid pressure, causing …

Answer 13

decreasing the size of a fluid-filled container will INCREASE fluid pressure, causing:

• ventricular contraction
• constriction of vessels

Question 14

increasing the size of a fluid-filled container will _____ fluid pressure, causing …

Answer 14

increasing the size of a fluid-filled container will DECREASE fluid pressure, causing:

• ventricular relaxation
• dilation of vessels

Question 15

describe the steps of the cardiac cycle

Answer 15

the flow of blood is between chambers is determined by the pressure changes in the heart

1. ventricular and atrial diastole: blood entering atrium; atrial pressure > ventricular pressure = AV valve open (passive flow of blood into the ventricles)
2. atrial contraction: atrial pressure increases and ventricular volume increases until end diastolic volume (EDV)
3. isovolumetric ventricular contraction:
   - ventricular pressure > atrial pressure: AV valve closes (1st heart sound)
   - ventricular pressure < aortic pressure: semilunar valves closed
4. ventricular ejection:
   - ventricular pressure > aortic pressure = semilunar valves open
   - ventricular volume decreases until end systolic volume (ESV)
5. isometric ventricular relaxation:
   - ventricular pressure < aortic pressure = semilunar valves close (2nd heart sound)
   - ventricular pressure > atrial pressure = AV valves close