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Heart structures (human)

- Enclosed by pericardium (double sac of serous membrane)

- Pericardium lined by squamous serous membrane

- Filled with serous fluid

- Serous fluid produced by serous pericardial membrane

- Serous fluid function to eliminate friction during beating

Layers :

- Epicardium

- Myocardium

Act as barrier from spread of infection and inflammation from adjacent structures

- Endocardium

Valves

- Artrioventricular valve (AV)

Between atria and ventricles

Right side referred as tricuspid valve

Left side referred as bicuspid valve or mitral valve

- Semilunar valve

Between ventricle and artery

At Pulmonary artery (pulmonary semilunar valve)

At aorta known as Aortic semilunar valve

Why pulmonary circuit is a short loop?

- Because start at heart right half and go to the lung and into heart left half

Systemic circuit is a longer loop

- Because start at heart left half and end at the heart right half

Cardiac cycle

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‘lup’ – closing of atroventricular valve

‘dup’ – closing of semilunar valve

Cardiac output

- Amount of blood pumped by each ventricle in one minute

- Product of heart rate and stroke volume

- Normal : 5liter/min

Heart rate

- Pulse/number of heart beat per minute

- Normal : 75 beats/min

Stroke volume

- Amount of blood pumped out by each ventricle in each heart beat

- 70ml/beat

- Regulation depend on venous return

Venous return

- Amount of blood entering the heart

Why our heart beat become fast after exercise?

- Skeletal muscle contract and relax causing blood flow to be faster

- Speed up venous return

- Venous return increase, stroke volume increase

- Causing more contraction

- Blood flow into atria and ventricle through AV valve

- AV valve open,

semilunar valve closed

1 - atrial and

ventricular diastole

- remaining blood is pushed out from atria to ventricle

- blood rushes out from ventricle due to high pressure

-AV open

- semilunar closed

2- atrial systole

ventricular diastole

- blood pushes out from ventricle completely

-semilunar valve open

-atrioventricular closed

3- atria diastole

ventricular systole

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Regulation of heart beat

- During stress or physical activities nerves of sympathetic division triggers AV and SA node to

increase heart beat.

- Parasympathetic nerves slow down heart rate.

- Hormone :

Epinephrine and thyroxine increase heart rate

- Ions :

Low ion, low heart rate

- Other factors affecting heart rate :

Age

Gender

Body Temp.

Activities

Conduction system of the heart

Two systems :

Autonomic nervous system

- Slow down or speeds heart rate

- Depend on which division it activated

Nodal system or intrinsic condustion system

- A specialized tissue

- Function as it is a combination of muscle and nervous tissue

Nodal system

1) Depend on AV node and SA node

2) SA node located at right atrium

3) Also called as pacemaker because it starts the heart beat

From SA node, impulse spread to the atria

Atria contract

Then spread to AV node

4) AV node located at the junction of atria and ventricle

5) Then impulse send to bundle of His

- sinoatrial node (SA node) generate impulse to atria

- atria contract

- signal passes to AV node

- ventricle contract

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6) Then spread to Purkinje fibers

7) From purkinje spread to muscle of ventricle walls

At AV node, impulse is delayed because to wait for atria to finish contract

Figure 1 : Conduction system (Nodal System)

SA node generate impulse

causing atria to contract

impulse then passes to AV

node

from AV node to bundle of

His

from bundle of his to Purkinje

fibers

muscle of ventricle wall

(ventricle contract)