cardiac anatomy in detail

1. Cardiac Anatomy

2. Outline
 Heart Anatomy
 Muscle Layers of the heart
 Myocardial muscle fibres
 Atria and Ventricles
 Semilunar and Atrioventricular Valves
 Blood flow through the Heart
 Cardiac Cycle
 Coronary Circulation
 Coronary Artery Blood flow
 Nervous supply to the heart

3. Heart
 The heart is a four chambered
muscular organ located in the chest
behind the sternum in the mediastinal
cavity between the lungs and rest on
the diaphragm.
 The heart is usually the size of a
person’s fist and typically weighs 225-
340gm, with size varying upon height,
age, sex, athletic condition and heart
disease.
 The heart’s function is to pump blood
throughout the body in response to
the body’s metabolic requirements.

4. Muscle Layers of the Heart
The heart is composed of three distinct
muscular layers and a dense fibrous tissue
which makes up the “skeleton” of the heart.
 The muscular layers are made up of:
 Endocardium.
 Myocardium
 Epicardium
 Pericardium,
 Within the myocardium consists a
specialized electrical conduction
system consisting of the :
 Sinoatrial (SA) Node,
 Atrioventricular (AV) Node,
 the Bundle of HIS
 Purkinje Fibres.

5. Endocardium
Endocardium:
The endocardium is a
thin, smooth layer of
epithelium and connective
tissue membrane which
lines the heart’s inner
chambers, valves,
chordae tendineae and
papillary muscles.
The endocardium also
extends into the lumen of
the coronary arteries
(tunica intima), systemic
arteries, veins and
capillaries; creating a
continuous closed
circulatory system

6. Myocardium
 The myocardium is the muscular middle layer of
the heart consisting of cardiac muscle fibres
which are responsible for contraction in a
twisting motion
 Is divided into two areas:
 Innermost half subendocardial
 Outermost half subepicardial
 The muscle fibres are of the myocardium are
separated by connective tissue which have a
rich supply of capillaries and nerve fibres
 Thickness of the myocardium varies from one
chamber to another and is related to the amount
of resistance that must be overcome to pump
blood from each chamber i.e:
 the atria encounter little resistance and
hence are thinned walled
 The LV is three times thicker than the RV
because the pressure in the pulmonary
circulation is much less than the arterial
circulation

7. Epicardium
 The heart’s outer most layer is called
the epicardium and is continuous with
the inner lining of the pericardium at the
heart’s apex.
 Epicardium contains:
 Blood capillaries
 Lymph capillaries
 Nerve fibres
 Fat
 The main coronary arteries lie on the
epicardial surface and feed this layer
before entering the myocardium and
supplying the heart’s inner layers
 The subendocardial area is at greatest
risk of ischaemia because:
 This area as a high demand for O2
 This area is fed by the most distal
branches of the coronary circulation

8. Pericardium
 Is a double walled sac consisting of two
layers which encase the heart and attaches
to the roots of the great vessels and the
fascia of the diaphragm which helps protect
the heart from trauma and infection.
 The pericardium has two portions:
 The outer layer is called the parietal
pericardium and is fibrous and non
distensible.
 It then doubles back to form the visceral
pericardium (also termed the epicardium)
which directly adheres to the surface of the
myocardium.
 The space between the two (pericardial
Space) usually contains 10-20ml of serous
fluid, termed pericardial fluid
 The pericardial fluid and acts as a
lubrication to enable the heart to beat within
without friction.
 Excess pericardial fluid (pericardial
effusion) can compromise the heart’s ability
to function by causing a tamponade.

9. Pericardium
 If the pericardium becomes inflamed
(pericarditis) more serous fluid is
secreted
 Pericarditis can be caused by bacterial or
viral infection, rheumatoid arthritis
destruction of the heart muscle post MI
and many other causes
 A build up of blood and fluid within this
space can compress the heart and impair
contraction by impairing chamber filling
and the stoke volume
 As a result blood returning to the heart is
also decreased. These changes can
result in a life threatening condition call
Cardiac Tamponade

10. Cardiac Muscle
 Cardiac muscle is only found within the heart and makes up the wall of the heart
 Each muscle is made up of thousands of muscle cells, which is enclosed in a
membrane called sarcolemma, which:
Have holes within leading to T-tubules which are extensions of the cell
membrane
Other tubules the sarcoplasmic reticulum located within store calcium
Muscles need calcium to contract
 Within each cell are mitochondria, the energy producing parts of the and hundreds of
long tube like structures called myofibrils
 Myofibrils are made up of many sarcomeres, the basic protein units responsible
for contraction
 Channels within the cell membranes allow electrolytes such as Na, K and Ca to pass
through during various phases of the cell cycle
 When the myocardium is relaxed the calcium channels are closed
 T-tubules conduct impulses form the cells membrane down into the sarcoplasmic
reticulum, where the Ca Channels open, where the cells are stimulated to contract
 Thus the force of contraction depends largely on the concentration of Ca within the
blood

11. Cardiac Muscle Fiber

12. Cardiac Muscle
 Each sarcomere is compose of thin and thick filaments:
 Thin filaments are made up of actin and actin binding proteins which are made up of
tropomyosin, troponin-T, troponin-C and troponin-I
 Thick filaments are made up of hundreds of myosin molecules
 Contraction occurs when projections on the thin filaments interact with the thick
myosin an form cross bridges
 This allows the actin filaments to slide over the myosin filaments causing
shortening of the muscle cells
 The force of contraction is directly related to the amount of end-diastolic stretch,
determined by the amount of blood within the heart at end-diastole. Increased stretch
of the myofibrils results in increased force which can be compared to that of a rubber
band.
 When myocardial cells die as in MI, substances within the cells pass through the
ruptured membranes and into the blood stream. These substance involve the
troponins, creatinine kinase and myoglobin
 Blood tests are used the measure the presence of these markers and verify MI

13. Atria and Ventricles
 The heart is effectively divided into four
chambers and functions as a two sided
pump.
 The left and right sides are separated by
a muscular wall called the septum.
 The right side of the heart accepts blood
form the venous system from 3 different
vessels:
 Superior vena cava
 Inferior vena cava
 Coronary sinus
 Venous blood is deoxygenated and from the
RA is pumped to the lungs where it
becomes oxygenated.
 Once oxygenated it travels through the left
side of the heart where it is pumped
throughout the circulatory system. .

14. Atria
 Atria
 The atria are thin walled, low pressured chambers, act as a reservoir to facilitate the
passage of blood through to the ventricles.
 The wall thickness of both atria vary slightly:
 The right atrium is 2mm thick
 The left atrium is 3mm thick
 When the valves open 70-75% of this blood flows directly into the ventricles, they
then contract to push the remaining volume through.
 This contraction termed the atrial kick contributes to 25-30% of cardiac output and
also prevents the pooling of blood within the atria which has the potential to develop
into life threatening clots.

15. Ventricles
The ventricles are larger and thicker walled chambers than the atria and are responsible
for pumping blood to the lungs and systemic circulation.
 When the LV contracts it normally produces an impulse which can be felt at the apex
of the heart (apical impulse). This occurs because when the LV contracts it rotates
forward and can be felt 5th
intercostal space mid clavicular and is called the point of
maximal impulse (PMI)
 The outside surface of the hearts has grooves called sulci, in which the coronary
arteries and their branches lie in.
 The coronary sulcus (groove) encircles the outside of the heart and separates the
atria from the ventricles
 The Right Ventricle pumps low pressured venous blood to the pulmonary circulation
 The Left Ventricle is responsible for pumping high pressured oxygenated blood
throughout systemic circulation, its wall thickness is triple that of the RV and is to
facilitate this.
 The diameter of the ventricular walls:
 Right ventricular wall thickness is 3-5mm
 Left ventricular wall thickness is 13-15mm

16. Ventricles
 Each ventricle holds approx 150ml and
normally ejects about half this volume
70-80ml with each contraction also
termed stroke volume.
 The percentage of blood ejected from
the LV with each contraction is called
ejection fraction, one of the most
important piece of diagnostic information
reflecting cardiac function.
 A normal ejection fraction is 50-60%. A
person is said to have impaired
ventricular function when the ejection
fraction is less than 40%
 Ejection Fraction is estimated on
echocardiograms and left ventricular
angiograms

17. Valves
The heart has a skeletal fibrous tissue located within which supports its structure. The
skeleton is made up of four rings of thick connective tissue which surrounds the base of
the pulmonary trunk, aorta and heart valves.
 The skeleton:
 Helps from the partitions (septum) which separate atria and ventricles
 Provides secure attachments for the valves and chambers
 There are 4 valves within the heart:
 Two sets of atrioventricular valves
 Two sets of semilunar valves
 The flow of blood through the heart is only made possible by the valves which lie
within, separating the chambers and great vessels.
 The valves’ function is to isolate blood in each chamber and to prevent backflow
during contraction.
 They open and close in response to the changes in pressure within the chambers,
thus ensuring blood is always pumped in a forwards motion preventing backflow.

18. Valves

19. Valves
Atrioventricular Valves
 Separate atria from ventricles, tricuspid and mitral and consist of:
• Tough, fibrous rings (annuli fibrosi)
• Leaflets or cusps of endocardium
• Chordae tendinae
• Papillary muscles
 Tricuspid valve lies between the right atrium and right ventricle
 Mitral valve lies between left atrium and left ventricle
 Tricuspid consists of three leaflets
 Mitral consists of two leaflets (bicuspid)
 Tricuspid valve is larger in diameter
and thinner than the mitral

20. Valves
Chordae Tendineae
Are thin strands of connective tissue which attach to under side of the valve
and small mounds attached to the endocardium called papillary muscles
Papillary muscles project inward from the ventricles and contract and relax
with the ventricles
When the ventricles contract the papillary muscles pull on the chordae
tendineae stretching them thus preventing the leaflets from bulging back into
the atria

21. Valves
Semilunar Valves
Consist of the pulmonic and aortic valves
Their role also is to prevent back flow from the pulmonary vein and aorta
into the ventricles
Have three cusps shaped like half moons
Their openings are small than those of the AV valves
Have thicker leaflets than those of the AV valves
SL valves are not attached to chordae tendineae

22. Blood flow through the Heart
 The right atrium receives venous (deoxygenated) blood from:
 Superior vena cave (from head and upper extremities)
 Inferior vena cave ( form lower body)
 Coronary sinus (from coronary circulation)
 Blood then flows into right ventricle through the tricuspid valve
 When Right ventricle contracts tricuspid valve closes and blood is ejected into the
pulmonary trunk via the pulmonary artery.
 The pulmonary trunk divides into the right and left pulmonary artery which carries
blood to each lung where gaseous exchange occurs
 Once oxygenated blood flows form capillaries into pulmonary veins where it drains
into the left atrium
 Blood flows form the left atrium into the left ventricle through the mitral valve
 When the left ventricle contracts the aortic valve opens and blood is ejected into he
aorta where it is then distributed throughout the systemic circuit.
 The mitral valve closes during left ventricular contraction to prevent back flow into the
left atrium

23. Blood flow through the heart

24. Reference List
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W.B. Saunders Compamy
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2004. Mosby – Year Book, Incorporated.
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Springhouse Corporation.
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Company
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MediMedia, Inc