The document describes the structure and function of the human heart. It discusses the layers of the heart, including the epicardium, myocardium, and endocardium. It also describes the heart valves, cardiac cycle, conduction system, regulation of heart rate, and blood vessels. In summary, the document provides an overview of the anatomy and physiology of the heart and circulatory system.

1. 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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2. Cardiac cycle
Referred as one complete heart beat
Systole – contract
Diastole – relax
1 - atrial - Blood flow into atria 2- atrial - remaining blood is pushed out from
and and ventricle through systole atria to ventricle
ventricular AV valve ventricular - blood rushes out from ventricle due to
diastole - AV valve open, diastole high pressure
semilunar valve closed -AV open
- semilunar valve closed
3- atria
diastole
ventricular - blood pushes out
from ventricle
systole completely
-semilunar valve open
-atrioventricular
closed
‘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
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3. 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
- signal passes to AV node
- ventricle contract
- sinoatrial node (SA node) generate impulse
to atria
- atria contract
- 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
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4. 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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5. SA node
generate
impulse
causing atria
to contract
muscle of
ventricle wall impulse then
passes to AV
(ventricle node
contract)
from bundle
from AV node
of his to
to bundle of
Purkinje
His
fibers
Figure 1 : Conduction system (Nodal System)
Electrocardiogram (ECG)
- Recording of electrical changes
- Occurred in myocardium
- Detected on the skin surface 1st step Cardiac
cycle
2nd step CC
3rd step CC
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
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6. 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 Has no valve Has valve
Except : semilunar valve in
aorta
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 Has three layers
cell
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 Transport both oxygenated and Transport deoxygenated blood
Except: pulmonary artery 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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7. 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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8. 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
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