SRA 2107 THE CIRCULATORY SYSTEM
THE HEART
Mr. S. T Gashirai

Lesson Objectives
 Describe the location of the heart.
 Describe the structure of the pericardium and the heart
wall.
 Discuss the external and internal anatomy of the chambers
of the heart.
 Relate external and internal structure of heart to function.
 Describe structure and function of heart’s valves.
 Outline flow of blood through the systemic and pulmonary
circulations.

The Heart
•Cone shaped
•Roughly size of clenched fist 0.2 -
0.3kg weight.
•Pointed apex formed by tip of Lt
ventricle.
•Base formed by the atria.
•12 cm long, 9cm wide at its widest
point a 6cm thick.
•Located in mediastinum, rests on
diaphragm in the midline.
• of the heart lies on the left side of the
midline
•Anterior surface – deep to sternum
•Inferior surface – btwn apex & rt surface
•Rt surface & Lt surface facing lungs

The Heart

The Heart
• Circulates blood
throughout the body.
• Beats about 100 000
times in a day.
• Right side pumps blood
through the lungs
(pulmonary circulation).
• Left side responsible for
systemic circulation.

The Heart - Pericardium• A membrane that surrounds the
heart
• Confines heart to mediastinum
but allows for sufficient
movement for vigorous &rapid
contraction.
• Consists of a superficial fibrous
pericardium (FP)and a deeper
serous pericardium (SP).
• FP composed of tough, inelastic,
dense irregular connective
tissue.
Fibrous Pericardium
Resembles a bag with open end fused to
blood vessels entering and leaving heart
Prevents overstretching of heart, protects and anchors heart in mediastinum.

The Heart - Pericardium
• Serous pericardium (SP)
Composed of a parietal and
visceral layer.
• Visceral layer a.k.a Epicardium
• Epicardium adheres tightly to
heart.
• Potential space formed is called
pericardial cavity, contains
pericardial fluid for lubrication.
•Pericarditis – inflammation of pericardium.
•Can be acute or chronic.
•Acute is idiopathic, sometimes linked to a viral infection.
•Characterised by chest pain due radiating to left shoulder and
arm.

Clinical Note – Cardiac Tamponade
• Chronic Pericarditis is gradual and long standing.
• May be associated with build up of pericardial fluid resulting in cardiac
tamponade.
• Results in compression, reducing ventricular filling and cardiac output.
• Venous return to heart is diminished, BP falls, and breathing is difficult.
• Usually associated with cancer and TB.
• Fluid has to be aspirated from pericardial cavity

The Heart – Layers of the Heart
• 3 layers: Epicardium, Myocardium and Endocardium.
• Epicardium - visceral layer of serous pericardium
• Adheres tightly to surface of heart
• Composed of mesothelium, fibro elastic tissue and fat
• Contains lymphatics and blood vessels that supply myocardium.

Myocardium
• Responsible for pumping action of heart.
• Composed of cardiac muscle tissue.
• Has muscle fibres like those of striated skeletal muscle
tissue wrapped in connective tissue sheaths.

Endocardium
• Endocardium is a thin layer of endothelium overlying a thin layer
of connective tissue.
• Provides smooth lining of the chambers of the heart and covers
valves.
• Minimises surface friction as blood passes through.

• Has 2 receiving (atria) and 2 pumping (ventricles) chambers
Right atrium
• Receives deoxygenated blood from body, via three openings:
• Superior vena cava (SVC), Inferior vena cava (IVC) &Coronary sinus
• Inter-atrial septum has an oval depression, the fossa ovalis – a remnant of
the foramen ovale.
• Blood passes from Rt atrium to Rt ventricle through the tricuspid valve.
Heart
Chambers

Fossa Ovalis
Patent Foramen
Ovale
Failure of Foramen ovale to
close post birth results in:
Foramen ovale should close
post birth resulting in.

Heart Chambers
Right ventricle
• Forms most of the anterior surface of the heart.
• Receives blood from the Rt atrium then sends the blood to
the lungs via the pulmonary trunk after it passes through
the pulmonary semilunar valve.
valve).

Heart Chambers
Left atrium
• The left atrium receives oxygenated blood from the lungs via
the pulmonary veins.
• Blood passes from the left atrium to the left ventricle through
the bicuspid valve (aka: mitral valve)

Heart Chambers
Left ventricle
• The left ventricle forms the
apex of the heart.
• Blood passes from the left
ventricle through the aortic
semilunar valve into the aorta
to systemic circulation.
• During fetal life the ductus
arteriosus shunts blood from
the pulmonary trunk into the
aorta.
• At birth, the ductus arteriosus
closes and becomes
the ligamentum arteriosum.

External view of heart
• On the surface of the heart are the auricles and sulci
1. Auricles are small pouches on the anterior surface of each atrium
that slightly increase the capacity of each atrium
2. Sulci are grooves that separate the chambers and contain blood
vessels and fat.

Posterior view of heart

Internal View of Heart

Myocardial Thickness and Function
• The thickness of the myocardium of the four chambers varies according
to the function of each chamber.
• Atria walls are thin - deliver blood only to the ventricles.
• Ventricle walls are thicker - pump blood to greater distances
• Rt ventricle walls are thinner than the Lt - pump blood to the lungs
(pulmonary).
• Lt ventricle walls are thicker - pump blood through the body (systemic
circulation) resistance to blood flow is greater.

Heart Valves
• Valves open and close in response to pressure changes as the heart
contracts and relaxes.
• AV valves are flaps of tissue which closes off the passageway between
the atria and ventricles
• Permit blood flow from atria to ventricles only.
• Back flow is prevented by contraction of papillary muscles thus
tightening the chordae tendinae which prevent eversion of valve cusps.

Heart Valves
• Atrioventricular valves (aka: cuspate valves or cuspid
valves) These include:
The tricuspid valve
• Located between the right atrium and right ventricle
• Consists of three cuspate or pointed flaps of tissue
(cusps)
The bicuspid valve (aka: mitral valve)
• Located between the left atrium and left ventricle
• Consists of two cuspate or pointed flaps of tissue
(cusps)

Bicuspid Valve

Heart Valves
Semilunar valves
• Found between a ventricle and its associated great vessels
that leaves the heart
• Consist of three semilunar-shaped (or pocket-like) flaps of
tissue
• These valve only permit outflow of blood from the heart
• There are two semilunar valves are associated with the
heart:
1. The aortic semilunar valve--found at junction between
the left ventricle and the origin of the aorta
2. The pulmonary semilunar valve--found at the junction
between the right ventricle and the origin of the
pulmonary trunk.

Heart valves

In atria, backflow is
minimised by collapse of all
venous entry points as atrium
contracts. (no valves to manage
backflow)

Fibrous Skeleton of the Heart
• Heart also has dense connective
tissue that forms the fibrous
skeleton of the heart.
• Consists of 4 dense connective
tissue rings around the valves.
• Fuse with each other & with the
interventricular septum as well.
• Form a structural foundation for
valves
• Prevent overstretching of valves
• Point of insertion for bundles of
cardiac muscle fibres
• Electrical insulator btwn atria &
ventricles

Circulation of
Blood

Systemic and Pulmonary Circulations
• The left side of the heart is the pump for the
systemic circulation.
• It pumps oxygenated blood from the lungs out
into the vessels of the body.
• The right side of the heart is the pump for the
pulmonary circulation.
• It receives deoxygenated blood from the body
and sends it to the lungs for oxygenation.

Blood Circulation
Coronary circulation
• Flow of blood through the many vessels that pierce the
myocardium of the heart is called the coronary (cardiac)
circulation;
• it delivers oxygenated blood and nutrients to and removes
carbon dioxide and wastes from the myocardium.
• The principle arteries, branching from the ascending aorta
and carrying oxygenated blood, are the right and left
coronary arteries.
• Deoxygenated blood returns to the right atrium primarily
via the largest cardiac venous structure: the coronary
sinus.

Blood Circulation
• From aorta, blood divides into separate
streams, entering progressively smaller
systemic arteries that carry it to all organs
throughout the body
• In systemic tissues, arteries give rise to
smaller-diameter arterioles, which finally lead
into extensive beds of systemic capillaries.
• Exchange of nutrients and gases occurs across
the thin capillary walls.

Blood Circulation
• Blood unloads O2 (oxygen) and picks up CO2
(carbon dioxide).
• In most cases, blood flows through only one
capillary and then enters a systemic venule.
• Venules carry deoxygenated (oxygen-poor)
blood away from tissues and merge to form
larger systemic veins.
• Ultimately the blood flows back to the right
atrium