LP #104 The Cardiac Cycle

Question 1

2 mechanisms control heart rate

Answer 1

• intrinsic

- extrinsic

Question 2

• mediates heart fxn to meet changing needs of the body
• responds to external & internal stimuli
• located in medulla oblongata (regulates vital autonomic fxns)
• fxn: CSN control of heart

Answer 2

Extrinsic mechanism

Question 3

ANS centres (medulla oblongata):

Answer 3

• CV
• respiratory
• coughing
• swallowing
• vomiting

Question 4

CV centres (medulla oblongata):

Answer 4

1. Cardiac centre

2. Vasomotor centre

Question 5

• 2 centres;
• cardioaccelatory
• cardiohibitory
• Controls contraction force & HR to meet body’s demands

Answer 5

Cardiac centre

Question 6

• regulates contraction of vascular smooth m (helps control BP)
• vasoconstriction:
• decrease lumen size= increase BP
• vasodilation:
• increase lumen size= decrease BP

Answer 6

Vasomotor centre

Question 7

Medulla oblongata sends signals to heart via:

Answer 7

Cardioaccelatory centre

Cardioinhibitory centre

Question 8

• sympathetic
• fibres projects from medulla to motor neurone at T1-T5 SC level
• innervates: SA & AV nodes, heart m, & coronary aa

Answer 8

Cardioaccelatory centre

Question 9

• parasympathetic
• fibres project from medulla to heart via vagus n
• innervates mainly SA & AV nodes
• damage to vagus n is life threatening
• if parasympathetic fibers damaged, sympathetic nn are unopposed

Answer 9

Cardioinhibitory centre

Question 10

• mediates ongoing control of HR, independent of NS
• found in myocardium
• fxn: excites heart m cells at a continuous/ constant pace

Answer 10

Intrinsic mechanism

Question 11

Myocardial cells:

• contractile?
• non-contractile (pacemaker cells)?

Answer 11

*responsible for contraction of heart m as a syncytium

• autorythmic
• found strategic sites in heart

Question 12

Depolarization?

Answer 12

Excites cell membrane

Question 13

Hyperpolarization?

Answer 13

Inhibits cell membrane

Question 14

Restoration of the RMP?

Answer 14

Returning ions to their place: NA+ is pumped out of cell & K+ brought into cell via ATPase pump (energy dependent)

Question 15

2 events in pacemaker cells during an AP?

Answer 15

• returning to pacemaker potential
• after hyperpolarization of the cell membrane, once an AP has be initiated
• initiating an AP
• rapid influx of calcium ions

Question 16

After AP event:

Answer 16

• cell membrane is hyperpolarized

- cycle begins again

Question 17

*decrease permeability to K+ & slow Na+ influx?

Answer 17

• depolarization

- pacemaker potential

Question 18

*increase per ability to Ca2+?

Answer 18

AP

Question 19

*decrease permeability to Ca2+ & K+, & increase permeability to Na+

Answer 19

Polarization

Question 20

Intrinsic mechanism locations:

• SA nodes?
• AV nodes?
• AV bundle (bundle of his)?
• Bundle branches?
• Purkinje fibres?

Answer 20

• R atrium
• R atrium
• W/in interventricular septum
• Ventricular myocardium
• Ventricular myocardium

Question 21

Cardiac cycle: Events associated w/BF through heart during 1 heartbeat (2 processes)?

Answer 21

1. electrical

2. mechanical

Question 22

Excitation of pacemaker cells

Answer 22

Electrical

Question 23

• contraction of cardiac m cells (entire heart)
• atrial contraction of cardiac m cells (entire heart)
• ventricular contraction forces blood out of ventricles into aorta & pulmonary trunk

Answer 23

Mechanical

Question 24

Heart alternately contracts & relaxes?

Answer 24

Diastole & systole

Question 25

Diastolic phase (diastole) ?

Answer 25

Relaxation

Question 26

Systolic phase (systole) ?

Answer 26

Contraction

Question 27

• cardiac m is relaxed
• blood is flowing passively through atria, open AV valves & into ventricles (~80% of ventricular filling)
• when atria contracts, remaining 20% pumped into ventricles
• ventricles in axiom diastole & blood capacity= end diastolic volume (EDV)

Answer 27

Ventricular filling (mid-late diastole)

Question 28

• as atria relax, ventricles begin contracting
• ventricular P increase rapidly & AV valves close
• increase ventricular P opens Sl valves & blood is expelled into aorta & pulmonary trunk
• ventricular ejection phase (peak P): P in aorta~ 120mm Hg
• atria is diastole begins to fill w/blood (from venae cavae & pulmonary vv)

Answer 28

Ventricular systole (atria diastole)

Question 29

-blood remaining in ventricles= end systolic volume (ESV)
-rapid decrease in ventricular P
-increase P in aorta & pulmonary trunks closes SL valves
-atria continue to fill w/blood
*atrial P > ventricular P
*AV valves open & blood flows into ventricles
…. & the cycle repeats….

Answer 29

Early ventricular diastol