Heart

Question 0

cardiac action potential length (3)

Answer 0

1. last 20-50x longer than skeletal muscle
2. long plateau which allows for time for (slow) contraction of heart to occur
3. this also leads to a long refractory period

Question 1

resting membrane potentials

Answer 1

1. resting membrane porential for atrial and ventricular muscle = -80 mV

Question 2

cardial action potential stages (4)

Answer 2

1. depolarization produced by influx of Na+ and Ca2+ (fast Na, slow Ca)
2. early slight repolarization produced by Cl- ions
3. long plateau of depolarization, maintained by presence of Ca and decreased permeability to K
4. repolarization caused by closer of Ca channels and increase in K permeability

Question 3

spontaneous contractions

Answer 3

1. SA node can generate spontaneous contraction at any time because leaky K channels => variable resting potential

Question 4

differences in cardiac and skeletal muscle contractions (2)

Answer 4

1. cardiac action potential persists 70% of duration of mechanical contraction (= long refractory period)
2. cardiac muscle is more eleastic and has more passive tension at normal resting length

Question 5

2 phases of cardiac cycle

Answer 5

1. diastole (relaxation)

2. systole (contraction)

Question 6

3 phases of diastole

Answer 6

1. rapid filling
2. slow filling
3. atrial contraction

Question 7

3 phases of systole

Answer 7

1. isovolumic contraction
2. ejection
3. isovolumic relaxion

Question 8

heart conduction system order(3)

Answer 8

1. SA node -> AV node
2. AV node -> purjunkie fibers
3. purjunkie fibers -> bundle of hiss

Question 9

SA node beat and innervation (2)

Answer 9

1. SA node self activates 100x /min

2. vagus nerve (parasympathetic) slows this down to 60-70x/min

Question 10

AV node self activation (2)

Answer 10

1. 40 x/ min

2. can take over for SA node if needed, does not interrupt blood flow

Question 11

SA node -> AV node (2)

connection and reason for AV delay

Answer 11

1. AV node is only connection btwn SA node and rest of the heart (this is where problems occur)
2. AV delay slows the signal to allow reciprocal contraction of atria and ventricles. This allows complete filling of ventricles before contraction occurs

Question 12

slow speed of AV node due to: (2)

Answer 12

1. thin fibers

2. fewer gap junctions

Question 13

AV delay vs. palateau (2)

Answer 13

1. AV delay is entire conduction system

2. plateau = delay in cell depolarization

Question 14

common cardiac cycle (12)

Answer 14

1. AV valves close and ventricles contract (pushing blood out)
2. after blood is pushed out, BP drops in ventricle, allowing the AV valves to open = diastole = period of ventricular filling = relaxation
   
   3. 80% of blood flow into ventricles is from gravity = rapid filling
   4. this happens while signal flows from SA node -> AV node
3. after initial filling, right before contraction = diastasis
4. signal travels, causing contraction of atria - which causes final 20% of blood to flow into ventricles
5. papillary muscles depolarize and contract when signal travels thru AV node, this pulls flaps of AV valves down as pressure in ventricle builds
6. turbulence of blood hitting the closes valves = first heart sound
7. signal travels thru ventricles => contraction => systole => period of ejection
8. period of isometric contraction -> period of ejection = when pressure from blood from ventricles > pressure of blood in aorta and blood flows from ventricles into vessels
9. leads to period of isometric relaxation = ends of systole
10. after blood is ejected, semilunar valves both close and sound of blood backflow is 2nd heart sound

Question 15

intrinsic regulation of heart - frank starling law (what goes in must come out) (4)

Answer 15

1. preload = degree of tension on muscle when it begins to contract, end of diatolic pressure when ventricle is filled
   
   2. increased stretch in heart = increase contraction = larger afterload
2. afterload = load against which muscle exerts contractile force, eg pressure on artery leading to ventricle
3. higher preload = higher afterload

Question 16

sympathetic control of heart (2)

Answer 16

1. distributed to all parts of the heart

2. norepinephrine increases heart rate by increasing slope of diastolic depolarization (=> faster, shooting up)

Question 17

parasympathetic control of the heart (2)

Answer 17

1. fibers are distributed mainly to SA and AV nodes
2. acetylcholine hyperpolarizes nodal cell => decreased rate of depolarization => slower vagal tone, which is what slows the heart to 60-70bpm

Question 18

ionic control of the heart (3)

Answer 18

1. potassium- excess K slows heart rate because it can block conduction of impulses from SA to AV node
2. Ca- excess Ca leads to spastic contractions because Ca is what starts contractile process
   
   3. deficiency => cardiac flaccidity

Question 19

2 Factors that affect cardiac output

Answer 19

1. Stroke volume

2. Heart rate

Question 20

3 factors that affect BP

Answer 20

1. Cardiac output (stroke volume + HR)
2. Peripheral resistance
3. Blood volume