The Circulatory System 3

Question 1

general properties of cardiac cells

automaticity

Answer 1

• ability to initiate/fire APs spontaneously
• called automatic/pacemaker activity
• normal cardiac/automatic/pacemaker cells: SA node, AV node, His-Purkinje system
• primary vs latent/subsidiary pacemakers
• intrinsic + extrinsic control

Question 2

what is the basis of automaticity?

Answer 2

I^f current + spontaneous phase 4 depolarisation

Question 3

natural pattern of excitation of the heart

Answer 3

• heart beats spontaneously + rhythmically
• triggered by spread of AP across muscle cell memb
• AP CYCLICALLY initiated + conducted in ORDERLY SEQ

SAN -> atria -> AVN -> bundle of his -> purkinje fibres -> ventricles

Question 4

how are electrical currents generated?

Answer 4

by cardiac muscle during depolarisation + repolarisation

conducted through bodily fluids + into tissues around heart

detected on body surface + recorded as ECG/EKG (electrocardiogram)

Question 5

what is an ECG?

Answer 5

summation of overall spread of electrical activity throughout heart during depolarisation and repolarisation

Question 6

what are the standard 12-lead ECG recordings?

Answer 6

six limb heads (I-III, aVR, aVL + aVF)

six chest leads (V1-V6)

Question 7

what are the 3 distinct waveforms a normal ECG has?

Answer 7

• P wave
• QRS complex
• T wave

Question 8

P wave represents…

Answer 8

atrial depolarisation

Question 9

the QRS complex represents…

Answer 9

ventricular depolarisation

Question 10

the T wave represents…

Answer 10

ventricular repolarisation

Question 11

individual cardiac muscles … to form branching fibres

Answer 11

interconnect

Question 12

what are intercalated discs?

Answer 12

adjacent cells joined end to end at specialised structures

Question 13

what are the 2 types of membrane junctions present within intercalated disc?

Answer 13

• desmosomes

- gap junctions

Question 14

desmosomes

Answer 14

cell to cell anchoring junctions

Question 15

gap junctions

Answer 15

cell to cell communication junctions

Question 16

muscle mass forms a ….

Answer 16

functional syncytium (becomes excited + contracts as single unit)

Question 17

systole

Answer 17

• ventricular contraction + emptying

- 2 sub phases / periods = isovolumetric contraction + ejection periods

Question 18

diastole

Answer 18

• ventricular relaxation + filling

- 2 sub phases / periods = isovolumetric relaxation + filling periods

Question 19

cardiac cycle?

Answer 19

1. LATE DIASTOLE - both sets chambers relaxed + ventricles fill
2. ATRIAL SYSTOLE - atrial contraction forces small mount blood into ventricles
3. ISOVOLUMETRIC VENTRICULAR CONTRACTION - 1st phase of v. contraction pushes AV closed but doesn’t create enough pressure to open SL valves
4. VENTRICULAR EJECTION - ventricular pressure rises + exceeds pressure in arteries.
   SL valves open + blood = ejected
5. ISOVOLUMETRIC VENTRICULAR RELAXATION - ventricles relax, pressure in ventricles falls.
   blood flows back into cups of SL valves and snaps them closed

Question 20

1st heart sound (Lub)?

Answer 20

closure of AV valves at start of ventricular contraction

Question 21

2nd heart sound (Dub)?

Answer 21

due to closure of aortic + pulmonary valves at end of v.systole

Question 22

3rd heart sound?

Answer 22

heard in early diastole

due to inrush of blood during rapid ventricular filling

Question 23

4th heart sound (Dub)?

Answer 23

heard immediately before 1st sound (in late diastole)

due to ventricular filling

Question 24

excitation contraction coupling process

Answer 24

• action potential enters from adjacent cell
• voltage-gated Ca2+ channels open. Ca2+ enters cells
• Ca2+ induces release through ryanodine receptor channels
• local release -> Ca2+ spark
• summed Ca2+ sparks -> Ca2+ signal
• Ca2+ ions bind to troponin to initiate contraction
• relaxation happens when Ca2+ unbinds from troponin
• Ca2+ pumped back into SR for storage
• Ca2+ exchanged with Na+
• Na+ gradient maintained by Na+-K+-ATPase

Question 25

excitation contraction coupling (troponin-tropomyosin complex) process

Answer 25

• AP in cardiac contractile cell
• travels down T tubules
• —> entry of small amount Ca2+ from ECF through L-type Ca2+ channels
• —> release of large amount Ca2+ from SR through ryanodine Ca2+ release channels
• —> inc in cytosolic Ca2+
• troponin-tropomyosin complex in thin filaments pull aside
• cross bridge cycling bet thick + thin filaments
• thin filaments slide inwards between thick filaments
• —> contraction

Question 26

where are the sounds of the aortic semilunar valve heard?

Answer 26

2nd intercostal space at right sternal margin

Question 27

where are the sounds of the pulmonary semilunar valve heard?

Answer 27

2nd intercostal space at left sternal margin

Question 28

where are the sounds of the mitral valve heard?

Answer 28

over apex in 5th intercostal space in line with middle of clavicle

Question 29

where are the sounds of the tricuspid valve heard?

Answer 29

right sternal margin of 5th intercostal space

variations inc over sternum/over left sternal margin in 5th intercostal space

Question 30

intercalated discs contain 2 types of membrane junctions

what are these?

Answer 30

• mechanically important desmosomes

- electrically imp gap junctions