Cardiovascular Physiology Part A

Question 1

Heart

Answer 1

1. Dual pump with valves

2. muscle cells connected by gap junctions

Question 2

Conduction System

Answer 2

1. non-contractile cardiac muscle cells
2. initiate and distribute impulses through heart
3. produce APs spontaneously (no stimulus) BUT at different rates

Question 3

Parts of Conduction System

Answer 3

1. Sinoatrial (SA) node
2. Atrioventricular (AV) node
3. Bundle of His (AV) bundle
4. Purkinje Fibers

Question 4

Sinoatrial node

• where is it?
• rate

Answer 4

1. In RA
2. rate= 100 APs/min
3. produces APs faster than other areas. Therefore, is the pacemaker

Question 5

Atrioventricular node

• where is it?
• rate

Answer 5

1. In RA

2. rate= 50 APs/min

Question 6

Bundle of His

• where is it?
• rate

Answer 6

1. Originate at AV node
2. ONLY route for electrical activity to go from atria to ventricles + bundle branches
3. 30 APs/min

Question 7

Purkinje Fibers

• where is it?
• rate

Answer 7

1. terminal fibers- stimulate contraction of ventricular myocardium
2. 30 APs/min

Question 8

Damaged Conduction System

-what is an artificial pacemaker?

Answer 8

• next fastest part becomes pacemaker
  ex) damaged SA, AV node takes over (atria may not contract + ventricles contract at AV speed= 50 beats/mon
• Artificial pacemakers- stimulate if SA or AV nodes damaged

Question 9

APs of SA & AV nodes

Answer 9

1. cells= non-contractile autorythmic cardiac muscle cells
2. threshold = -40mV
3. NO RMP

Question 10

APs of SA & AV nodes:

Phases of Pacemaker Activity

Answer 10

1. Pacemaker Potential
2. AP Depolarization
3. AP Repolarization
4. Na+ channels open at -60mV

Question 11

APs of SA & AV nodes:

Pacemaker potential

Answer 11

1. Low K+ permeability (K+ voltage gates closed)

2. Slow inward leak of Na+ (Na+ voltage gates open) which cause slow depot. to threshold (-40mV)

Question 12

APs of SA & AV nodes:

AP Depolarization

Answer 12

1. at threshold -> AP
2. Ca2+ voltage gates open and move in
3. Na+ voltage gates close at threshold- not involved in AP
4. Ca2+ voltage gates close at peak

Question 13

APs of SA & AV nodes:

AP Repolarization

Answer 13

1. K+ voltage gates open at peak, K+ out

2. K+ gates close below threshold

Question 14

APs of SA & AV nodes:

Na+ channels open at ____

Answer 14

-60mV

Starts pacemaker potential again (continuous cycle)

Question 15

APs in Ventricular Myocardium

Answer 15

1. cells= contractile
2. purkinje fiber AP -> ventricular myocardial AP (spread cell to cell by gap junction)
3. RMP= -90mV

Question 16

APs in Ventricular Myocardium:

Phases

Answer 16

1. Depolarization
2. Plateau
3. Repolarization

Question 17

APs in Ventricular Myocardium:

Depolarization

Answer 17

1. Na+ voltage gates open (fast) = same gate as neutron, skeletal muscle
2. MP to +30mV

Question 18

APs in Ventricular Myocardium:

Plateau

Answer 18

1. Na+ channels close and inactivate (slight drop in MP)

2. Ca2+ slow voltage gates are open (Ca2+ IN maintains depol.)

Question 19

APs in Ventricular Myocardium:

Repolarization

Answer 19

1. Ca2+ channels close

2. K+ voltage gated channels open (increased K+ OUT -> MP decrease to RMP

Question 20

APs in Ventricular Myocardium:

Absolute Refractory Period

Answer 20

Long- Na+ channels inactivated until MP is close to -70mV

Question 21

APs in Ventricular Myocardium:

Excitation-Contraction Coupling in Myocardial Cells

Answer 21

1. open voltage-gated Ca2+ channels of AP = small ⇑ cytosolic Ca2+ (from ECF) ⇒ not enough to trigger contraction BUT…
2. opens chemically-gated Ca2+ channels on SR ⇒ ⇑⇑ cytosolic Ca2+ ⇒ binds to troponin, etc, etc ⇒ leads to contraction
3. Contraction
   - sliding filaments
   - begins a few msec after AP begins
   - duration of AP =~250 msec and duration of twitch = ~ 300 msec
   - ∴ contraction almost over when AP ends
   - Result = NO summation ∴ NO tetanus - get alternation of contraction/relaxation