Lab 2: Cardiovascular system

Valves in the heart include:

Atrioventricular: atrium to ventricle

• tricuspid valve

• bicuspid (mitral) valve

Semilunar: ventricle to artery

• pulmonary valve

• aortic valve

5- Left bundle branch

7- Atrioventricular node

1- Superior vena cava

3- Right bundle branch

6- Bundle of His

2- Sinoatrial node

4- Purkinje fibers

Self depolarization graph

Depolarization of the heart steps

1. Depolarization starts in SA node

2. Depolarization propagates through contractile cells with Gap Junctions

3. Continued depolarization of atria and AP passing through the Bundle of His and Purkinje fibre. *Note the electrical barrier

4. Starting at the apex, the ventricular heart muscles contract

ANS control of HR

• SA node is under nervous regulation

• Sympathetic activation will lead to increased heart rate; Increased Na+ leakage shortening the potential drift

• Parasympathetic activation will lead to decreased heart rate; Increased K+ permeability

• To maintain coordination between atrial and ventricular contraction, the sympathetic input proportionally increases the velocity of the AV node; This reduces the lag in conduction

Can the heart cramp?

The heart muscle itself can’t cramp, unlike skeletal muscles

Coupling of electrical activity, contraction, movement of blood, and valves diagram

Stage 1 of coupling of electrical activity, contraction, movement of blood, and valves

Refilling of the heart (diastole)

• The heart is relaxed

• Venous return fills the atria

• Pressure pushes the AV valves open

• Blood flows in the ventricles

• Not enough pressure to open the semilunar valves

Status of valves in stage 1

AV Valves - OPEN

SL Valves - CLOSED

Stage 2 of coupling of electrical activity, contraction, movement of blood, and valves

Atrial Contraction (part of diastole)

• SA node fires

• Atrial contraction

• Blood packed in ventricles through the AV valves which are pushed open

• Pressure in ventricles not sufficient to force the semilunar valves open

Status of valves in stage 2

AV Valves - OPEN

SL Valves - CLOSED

Stage 3 of coupling of electrical activity, contraction, movement of blood, and valves

Isovolumic contraction (part of systole)

• AV node transmit the AP between atria and ventricles with a lag

• Atria finished contracting, ventricles waiting for the AP wave

• Blood packed in ventricles, all valves are closed

• In between atrial and ventricular contraction

Status of valves in stage 3

AV Valves - CLOSED

SL Valves - CLOSED

Stage 4 of coupling of electrical activity, contraction, movement of blood, and valves

Ejection (systole per say)

• AP passed on to the bundle of Hiss and Purkinje fibers

• Ventricles depolarize and contract

• Pressure in ventricles increased, sufficient to force open the semilunar valves

• Blood rushes out of the ventricles into arteries

Status of valves in stage 4

AV Valves - CLOSED

SL Valves - OPEN

Stage 5 of coupling of electrical activity, contraction, movement of blood, and valves

Isovolumic relaxation (part of systole)

• Contraction is over

• The heart is empty

• Low pressure throughout, all the valves are closed

• Blood starts accumulating in the atria

Status of valves in stage 5

AV Valves - CLOSED

SL Valves - CLOSED

Full cycle diagram

Electrocardiogram parts

P: Atrial depolarization

PQ interval: Time taken by the AP to pass the AV node

QRS: Ventricle depolarization

T: Ventricle repolarization

Normal ECG

Sinus tachycardia

Increased HR

• decreases distance between P waves

Paroxysmal supraventricular tachycardia

Paroxysmal tachycardia: HR increases abruptly

Atrial flutter

Frequent, but rhythmic atrial contractions (P waves). Ever second atrial depolarization is propagated to the ventricles (2:1 rhythm)

1rst degree AV block

The propagation of the atrial depolarizations to the ventricles is slow, and the PQ interval is abnormally long

2nd degree AV block

Some of the atrial depolarizations are not conducted to the ventricles

3rd degree AV block

There is a complete failure of impulse conduction from the atria to the ventricles. QRS complexes originate in the tissues below the AV node. The ventricular rhythms are slow, but usually regular.

1 - aorta

2- superior vena cava

3 - pulmonary artery

4 - pulmonary vein

5 - pulmonary valve (semi-lunar)

6 - tricuspid valve

7 - left ventricle

8 - papillary muscle

Why is the aorta elastic

• To absorb pressure coming from left ventricle after ejection

• To keep pressure in the arterial side higher than in the veins

• To maintain the flow of blood in the body

1 - lungs

2 - non-oxygenated

3 - oxygenated

Steps on how electrical activity in the heart propagates

1. SA node is self excited (fires an action potential)

2. Depolarization travels through the atria to the AV node with little delay

3. AP propagates to bundle of His and purkinje fibers quickly

4. The contractile cells depolarize from the apex through the ventricular wall (ventricular depolarization)

1. diastole

2. atrial contraction

3. isovolumic contraction

4. ejection phase (systole)

5. isovolumic relaxation

Describe the status of each of the valves listed below (open/closed) during phase 1 of the cardiac cycle

Open

• tricuspid

• bicuspid

Closed

• pulmonary

• aortic

Describe the status of each of the valves listed below (open/closed) during phase 2 of the cardiac cycle

Open

• bicuspid

• tricuspid

Closed

• aortic

• pulmonary

Describe the status of each of the valves listed below (open/closed) during phase 4 of the cardiac cycle

Open

• pulmonary

• aortic

Closed

• bicuspid

• tricuspid

Describe the status of each of the valves listed below (open/closed) during phase 5 of the cardiac cycle

Closed

• bicuspid

• tricuspid

• pulmonary

• aortic

Match the electrical waves (episodes) during a normal electrocardiogram (ECG) with the electrical event they represent

P - atrial depolarization

QRS - ventricle depolarization

T - ventricle repolarization

PQ - time taken by the action potential to pass to the AV node (from the atria to the ventricles)