Heart structures

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HEART

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

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Cardiac cycle

Referred as one complete heart beat

Systole – contract

Diastole – relax

‘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

- 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 valve 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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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

Question : 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

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

- sinoatrial node (SA node) generate impulse to atria

- atria contract

- signal passes to AV node

- ventricle contract

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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

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

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Figure 1 : Conduction system (Nodal System)

Electrocardiogram (ECG)

- Recording of electrical changes

- Occurred in myocardium

- Detected on the skin surface

P wave : atria about to contract

QRS wave : ventricles about to contract

T wave : ventricle diastole (relax)

Blood vessels

1. Artery

2. Vein

3. Capillaries

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)

1st step Cardiac

cycle

2nd step CC

3rd step CC

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Layers of blood vessels

1. Tunica intima

2. Tunica tunica media

3. Tunica adventitia/externa

Tunica intima

- Inner lining

- Consist of endothelium and thin layer of connective tissue

- Provides smooth surface

- Minimize resistance

Tunica media

- is the middle muscular and/or elastic layer,

- containing smooth muscle and elastic tissue in varying proportions.

Tunica adventitia

- Is the outer, fibrous connective tissue layer.

- This elastic fibres allow the blood vessel to stretch and recoil

Differences between artery, capillary and vein

Artery Capillary Vein

Has no valve Except : semilunar valve in

aorta

Has no valve Has valve

Tunica media thick No tunica media Tunica media thinner than in artery

Tunica externa thick No tunica externa Tunica externa thinner than in artery

Has 3 layers Only one layer : endothelium cell

Has three layers

Highest blood pressure Lowest blood pressure Lower blood pressure than artery, higher than in capillary

capillary<vein<artery

Highest velocity Lowest velocity Lower than artery, higher than capillary

capillary<vein<artery

Smallest TCSA Highest TCSA Higher TCSA than artery, smaller TCSA than capillary

Transport oxygenated blood Except: pulmonary artery

Transport both oxygenated and deoxygenated blood

Transport deoxygenated blood Except : Pulmonary vein

No gas exchange occur Gas exchange occur No gas exchange occur

No absorption of nutrient occur Absorption of nutrient occur No absorption of nutrient occur

- *Note : TCSA is Total Cross sectional area

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Internal elastic lamina and external elastic lamina can be found only in artery

Gases and nutrient cannot pass through artery and veins because of thick wall

Only can pass through capillaries

Capillaries only have endothelial layer. One cell thick

Blood flow velocity

velocity depend on

total cross sectional

area of the blood

vessels. From the

graph all information

can be obtained.

This is based on the

law of continuity.

!! Imagine that the

blood is the water in

the pipe.

Arterial pulse

- Can be detected in radial artery and carotid artery

- Radial artery : border of the palm side of a wrist

- Carotid artery : side of trachea of the neck

- Pulse indicate the rate of heart beat

Blood pressure

- Pressure of blood against the wall of blood vessels

- Use sphygmomanometer to measure blood pressure

- Detected at the brachial artery

- Example : (120/80)

- 120 is systolic pressure

- 80 is the diastolic pressure

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Blood pressure

will decrease as

it move from

the aorta to the

vena cava

In the venules and veins, blood pressure is low.

Therefore, venous return depends on :

1. Skeletal muscle contraction

2. Presence of valves in the veins

3. Respiratory movements

Inhalation (respiratory movement) :

1. Thoracic P decreases

2. Abdominal P increases because chest expands

3. Allows blood in veins to return back to the heart