The Heart: Circulatory System

Dr. Mack MBBS, MS, Ph.D.

Assistant Professor

Department of Human Anatomy

Zhejiang Chinese Medical University

E-mail: drmack_zcmu@hotmail.com
 Cardiovascular System
• Cardiovascular system
– Heart and blood vessels

• Circulatory system
– Heart, blood vessels (arteries and veins),
and the blood.
 The Pulmonary and Systemic Circuits
Major divisions of circulatory system:
• Pulmonary circuit: right side of heart,

Carries blood to lungs for gas exchange and back to heart.

• Systemic circuit: left side of heart,

Supplies oxygenated blood to all tissues of the body and

returns it to the heart.
 The Pulmonary and Systemic Circuits
• Left side of heart
– Fully oxygenated blood arrives from
lungs via pulmonary veins
– Blood sent to all organs of the body via
aorta

• Right side of heart

– Lesser oxygenated blood arrives from
inferior and superior venae cavae
– Blood sent to lungs via pulmonary
trunk
 Pathway of Blood Through the Heart
o Pulmonary circuit
Ø Right ventricle
§ pulmonary semilunar valve
§ pulmonary trunk
§ pulmonary arteries
§ Lungs
Ø Lungs
§ pulmonary veins
§ left atrium
 Pathway of Blood Through the Heart
o Systemic circuit
Ø Left ventricle
§ aortic semilunar valve
§ Aorta
Ø Aorta
§ systemic circulation
§ superior and inferior venae cavae
§ right atrium
 Superior vena cava (SVC) Oxygen-poor blood
Inferior vena cava (IVC)
Oxygen-rich blood
Coronary sinus

SVC
Coronary
sinus

IVC
 Superior vena cava (SVC) Oxygen-poor blood
Inferior vena cava (IVC)
Right
Coronary sinus
atrium Oxygen-rich blood

SVC Coronary
sinus

Right
atrium

IVC
 Tricuspid
Superior vena cava (SVC) Right valve Right Oxygen-poor blood
Inferior vena cava (IVC) atrium ventricle
Coronary sinus Oxygen-rich blood

SVC Tricuspid
Coronary
valve
sinus

Right
atrium

Right
IVC ventricle
 Pulmonary
Tricuspid
Right
Semilunar
Pulmonary Oxygen-poor blood
Superior vena cava (SVC) valve Right valve
Inferior vena cava (IVC) trunk
Coronary sinus atrium ventricle Oxygen-rich blood
Pulmonary
arteries
SVC Coronary Tricuspid
sinus valve Pulmonary
trunk
Right
atrium
Pulmonary
Right semilunar
IVC ventricle valve
 Oxygen-poor blood
Oxygen-rich blood
Pulmonary
Tricuspid Semilunar
Superior vena cava (SVC) valve valve
Inferior vena cava (IVC) Right Right Pulmonary
Coronary sinus atrium ventricle trunk

Pulmonary
arteries
SVC Coronary Tricuspid
sinus valve Pulmonary
trunk
Right
atrium
Pulmonary
Right semilunar
ventricle valve
IVC

Oxygen-poor blood is carried

in two pulmonary arteries to the lungs To lungs
(pulmonary circuit) to be oxygenated.

Pulmonary
capillaries
 Oxygen-poor blood
Pulmonary Oxygen-rich blood

veins

Four
pulmonary
veins
 Oxygen-poor blood
Pulmonary Oxygen-rich blood
veins

Left
atrium

Four
Left
pulmonary
atrium
veins
 Oxygen-poor blood
Oxygen-rich blood

Pulmonary
veins

Mitral Left
valve atrium
Left
ventricle

Mitral Four
Left valve Left
ventricle atrium pulmonary
veins
 Oxygen-poor blood
Oxygen-rich blood

Aorta Pulmonary
veins

Aortic Mitral Left

semilunar valve atrium
valve Left
ventricle

Aortic
Semilunar Mitral
Left Four
valve Left valve
Aorta pulmonary
ventricle atrium
veins
 Oxygen-poor blood
Oxygen-rich blood

Systemic
capillaries

Oxygen-rich blood is
To body delivered to the body
tissue(ssystemic circuit).

Aorta Pulmonary
veins
Aortic Left
semilunar Mitral atrium
valve valve
Left
ventricle
Aortic
Semilunar Mitral
valve Left valve Left Four
Aorta ventricle atrium pulmonary
veins
Systemic Circulation: Arteries
 Systemic Circulation: Arteries
Aorta
From which all arteries are derived either directly or indirectly
Parts
• Ascending aorta
• aortic arch
• descending aorta
(thoracic and abdominal)
Bracheocephalic artery
Branches of the Ascending Aorta
Coronary arteries:
Supply the heart’s cardiac muscle with oxygen and
nutrients.
 Branches of the Aortic Arch
First branch
• Brachiocephalic trunk- divides
into :
• Right common carotid
• right subclavian
Second branch
• Left common carotid
Third branch
• Left subclavian
Branches of the AorticArch: Head and NeckArteries
Branches of common carotid
arteries
• Internal carotid arteries
• External carotid arteries
Branches of the subclavian
arteries
• Left and right vertebral
Internal carotid artery
arteries External carotid artery
Common carotid artery
• Internal carotids and Vertebral artery

Brachiocephalic trunk
vertebral arteries supply Subclavian artery

brain
 Thoracic cavity is divided into three compartments:

• Right and left pulmonary cavities, contain the lungs and pleurae
(lining membranes) and occupy the majority of the thoracic cavity.

• A central mediastinum,—the heart, thoracic parts of the great vessels,

thoracic part of the trachea, esophagus, thymus, and other structures
(e.g., lymph nodes).
Position, Size, and Shape of the Heart

Aorta
Superior Pulmonary trunk
vena cava
Right lung Base of heart
Parietal
pleura (cut)
Pericardial Apex of heart
sac (cut)

Diaphragm
 Position, Size, and Shape of the Heart
• Heart located in mediastinum, between lungs.

• Base—wide, superior portion of heart, blood vessels attach here.

• Apex—inferior end, tilts to the left, tapers to point.

• 3.5 inch (3.5x2.5 cm). wide at base,
5 inch. from base to apex, and 2.5 inch. anterior to posterior;
weighs 10 ounces.
Blood 5 liter/ 7-8% of body weight.
Position, Size, and Shape of the Heart

Sternum
Posterior
3rd rib
Lungs
Diaphragm Pericardial
Thoracic cavity
vertebra Left
Right ventricle
ventricle Interventricular
Sternum septum

Anterior
 The Heart Wall
• Pericardium—double-walled sac (pericardial sac) that encloses the
heart.
– Allows heart to beat without friction, provides room to expand,
yet resists excessive expansion
– Anchored to diaphragm inferiorly and sternum anteriorly

• Parietal pericardium—outer wall of sac

– Superficial fibrous layer of connective tissue
– Deep, thin serous layer
 The Heart Wall
• Visceral pericardium (epicardium)—heart covering
– Serous lining of sac turns inward at base of heart to cover the
heart surface

• Pericardial cavity—space inside the pericardial sac filled with 5

to 30 mL of pericardial fluid

• Pericarditis—inflammation of the membranes

– Painful friction rub with each heartbeat
 Pericardial cavity
Pericardial sac:

Fibrous layer

Serous layer
Epicardium

Myocardium
Endocardium
Epicardium
Pericardial sac
 Pericardium
The pericardium (in middle mediastinum) is a fibroserous
membrane that covers the heart and its great vessels.
A closed sac composed of two layers:

1. The fibrous pericardium (tough)

2. The parietal layer of serous pericardium.
3. This layer is reflected onto the heart at the great vessels (aorta,
pulmonary trunk and veins, and superior and inferior venae
cavae) as the visceral layer of serous pericardium.
 The Heart Wall
• Epicardium (visceral pericardium)
– Serous membrane covering heart
– Adipose in thick layer in some places
– Coronary blood vessels travel through thislayer

• Endocardium
– Smooth inner lining of heart and blood vessels
– Covers the valve surfaces and is continuouswith endothelium of
blood vessels.
 The Heart Wall
• Myocardium
– Layer of cardiac muscle proportional to work load
• Muscle spirals around heart which produceswringing
motion.
– Fibrous skeleton of the heart: framework of collagenous and
elastic fibers
• Provides structural support and attachment for cardiac
muscle and anchor for valve tissue.
• Electrical insulation between atria and ventricles; important in
timing and coordination of contractile activity.
 The Chambers
• Four chambers
– Right and left atria
• Two superior chambers
• Receive blood returning
to heart
• Auricles (seen on
surface) enlarge
chamber
– Right and left ventricles
• Two inferior chambers
• Pump blood into arteries
*
*
 Auricle refers to an ear-shaped pouch in the atrium of the
heart. Each auricle is attached to the anterior surface of each atrium.
Thereby, the two auricles are called the left auricle and the right
auricle. Auricle is a wrinkled structure.
The auricle's functions are to collect sound and transform it
into directional and other information. The auricle collects sound
and, like a funnel, amplifies the sound and directs it to the auditory
canal.
 The Chambers
• Atrioventricular
sulcus—separates atria
and ventricles
• Interventricular
sulcus—overlies the
interventricular septum
that divides the right
ventricle from the left *
*

• Sulci contain coronary

arteries
 The Chambers
• Interatrial septum
– Wall that separates atria

• Pectinate muscles
– Internal ridges of myocardium in right atrium and both auricles

• Interventricular septum
– Muscular wall that separates ventricles

• Trabeculae carneae*
– Internal ridges in both ventricles
*
* *

* *

* *
*
*

*
*
*
*

*
*
*
* *
 The Valves
• Valves ensure a one-way flow of blood through the heart and are of
four type.
• Atrioventricular (AV) valves—control blood flow between atria
and ventricles.
– Right AV valve has three cusps (tricuspid valve)
– Left AV valve has two cusps (mitral or bicuspid valve)
– Chordae tendineae: cords connect AV valves to papillary
muscles on floor of ventricles
• Prevent AV valves from flipping inside out or bulging into the
atria when the ventricles contract
 The Valves
• Semilunar valves—control flow into great arteries; open and close
because of blood flow and pressure

– Pulmonary semilunar valve: in opening between right

ventricle and pulmonary trunk
– Aortic semilunar valve: in opening between left ventricle
and aorta
 Left AV (bicuspid)
valve

Right AV
(tricuspid) valve

Fibrous
skeleton

Openings to
coronary arteries

Aortic
valve

Pulmonary
valve
The Valves: Endoscopic View
 The Valves

Tendinous
cords

Papillary
muscle
 Blood Flow Through the Chambers
• Ventricles relax (Diastole)
– Pressure drops inside the ventricles

– Semilunar valves close as blood attempts to back up into the

ventricles from the vessels
– AV valves open
– Blood flows from atria to ventricles
 Blood Flow Through the Chambers
• Ventricles contract (Systole)

– AV valves close as blood attempts to back up into the atria.

– Pressure rises inside of the ventricles

– Semilunar valves open and blood flows into great vessels.

Blood Flow Through the Chambers
 The Coronary Circulation
• 5% of blood pumped by heart is pumped to the heart itself through
the coronary circulation to sustain its strenuous workload.
– 250 mL of blood per minute
– Needs abundant O2 and nutrients.
 Arterial Supply
• Left coronary artery (LCA) branches off the ascending aorta
– Anterior interventricular branch
• Supplies blood to both ventricles and anterior two- thirds of the
interventricular septum

– Circumflex branch
• Passes around left side of heart in coronary sulcus
• Gives off left marginal branch and then ends on the posterior side of
the heart
• Supplies left atrium and posterior wall of left ventricle
 Arterial Supply
• Right coronary artery (RCA) branches off the ascending aorta
– Supplies right atrium and sinoatrial node (pacemaker)
– Right marginal branch
• Supplies lateral aspect of right atrium and ventricle

– Posterior interventricular branch

• Supplies posterior walls of ventricles
*

*
 Venous Drainage
• 5% to 10% drains directly into heart chambers—right atrium and
right ventricle—by way of the thebesian veins

• The rest returns to right atrium by the following routes:

– Great cardiac vein
• Travels alongside anterior interventricular artery
• Collects blood from anterior portion of heart
• Empties into coronary sinus
 Venous Drainage
• The rest returns to right atrium by the following routes (cont.):
– Middle cardiac vein (posterior interventricular)
• Found in posterior sulcus
• Collects blood from posterior portion of heart
• Drains into coronary sinus
– Left marginal vein
• Empties into coronary sinus
• Coronary sinus
– Large transverse vein in coronary sulcus on posterior side of heart
– Collects blood and empties into right atrium
 *

*
*

*
Cardiac Muscle and the Cardiac
Conduction System
 Structure of Cardiac Muscle
• Cardiocytes—striated, short, thick, branched cells, one central
nucleus surrounded by light-staining mass of glycogen.

• Intercalated discs—join cardiocytes end to end

– Interdigitating folds: folds interlock with each other, and increase

surface area of contact.
 Structure of Cardiac Muscle
Mechanical junctions tightly join cardiocytes
• Fascia adherens—broad band in which the actin of the thin
myofilaments is anchored to the plasma membrane.
– Each cell is linked to the next via transmembrane proteins

• Desmosomes—weldlike mechanical junctions between cells

– Prevents cardiocytes from being pulled apart
 Structure of Cardiac Muscle
• Electrical junctions (gap junctions) allow ions to flow between
cells; can stimulate neighbors

– Entire myocardium of either two atria or two ventricles acts like

single, unified cell

• Repair of damage of cardiac muscle is almost entirely by

fibrosis (scarring)
 Metabolism of Cardiac Muscle
• Cardiac muscle depends almost exclusively on aerobic
respiration used to make ATP
– Rich in myoglobin and glycogen
– Huge mitochondria: fill 25% of cell
• Adaptable to organic fuels used
– Fatty acids (60%); glucose (35%); ketones, lactic acid, and amino
acids (5%)
– More vulnerable to oxygen deficiency than lack of a specific fuel

• Fatigue resistant because it makes little use of anaerobic

fermentation or oxygen debt mechanisms
– Does not fatigue for a lifetime
 The Conduction System
• Coordinates the heartbeat
– Composed of an internal pacemaker and nervelike conduction
pathways through myocardium

• Generates and conducts rhythmic electrical signals in the

following order:
– Sinoatrial (SA) node: modified cardiocytes
• Pacemaker initiates each heartbeat and determines heart rate
• Pacemaker in right atrium near base of superior vena cava
– Signals spread throughout atria
– Atrioventricular (AV) node
• Located near the right AV valve at lower end of interatrial septum
• Electrical gateway to the ventricles
• Fibrous skeleton—insulator prevents currents from getting to
ventricles from any other route
– Atrioventricular (AV) bundle (bundle of Hiss)
• Bundle forks into right and left bundle branches
• Branches pass through interventricular septum toward apex
– Purkinje fibers
• Nervelike processes spread throughout ventricular myocardium
• Signal passes from cell to cell through gap junctions
The Conduction System
 The Heart: Conduction System
• Special tissue sets the pace
• Sinoatrial node = SA node (“pacemaker”), is in the right atrium

• Atrioventricular node = AV node, is at the junction of the atria

and ventricles

• Atrioventricular bundle = AV bundle (bundle of His), is in the

interventricular septum
• Bundle branches are in the interventricular septum

• Purkinje fibers spread within the ventricle wall muscles

Heart Contractions
 Heart Contractions
• Contraction is initiated by the sinoatrial node (SA node)

• Sequential stimulation occurs at other autorhythmic cells

• Force cardiac muscle depolarization in one direction—from atria to

ventricles.
 Heart Contractions
• Once SA node starts the heartbeat

– Impulse spreads to the AV node

– Then the atria contract

• At the AV node, the impulse passes through the AV bundle, bundle

branches, and Purkinje fibers

• Blood is ejected from the ventricles to the aorta and pulmonary

trunk as the ventricles contract
 Nerve Supply to the Heart
• Sympathetic nerves (raise heart rate)
– Sympathetic pathway to the heart originates in the lower cervical to
upper thoracic segments of the spinal cord
– Continues to adjacent sympathetic chain ganglia

– Some pass through cardiac plexus in mediastinum

 Nerve Supply to the Heart
– Some pass through cardiac plexus in mediastinum
– Continue as cardiac nerves to the heart

– Fibers terminate in SA and AV nodes, in atrial and ventricular

myocardium, as well as the aorta, pulmonary trunk, and coronary
arteries
• Increase heart rate and contraction strength

• Dilates coronary arteries to increase myocardial blood flow

 Nerve Supply to the Heart
• Parasympathetic nerves (slows heart rate)
– Pathway begins with nuclei of the vagus nerves in the medulla
oblongata
– Extend to cardiac plexus and continue to the heart by way of the
cardiac nerves
– Fibers of right vagus nerve lead to the SA node
– Fibers of left vagus nerve lead to the AV node
– Little or no vagal stimulation of the myocardium
• Parasympathetic stimulation reduces the heart rate
 Electrical and Contractile Activity
of the Heart
• Cycle of events in heart- 70/min

– Systole: atrial or ventricular contraction

– Diastole: atrial or ventricular relaxation

Surface Anatomy of Heart and Mediastinal Viscera
 Auscultatory Areas
• Clinicians’ interest in the surface anatomy of the heart and cardiac valves
results from their need to listen to valve sounds.
• The five areas (two areas are for the pulmonary valve) are as wide apart
as possible so that the sounds produced at any given valve may be clearly
distinguished from those produced at other valves.
• Blood tends to carry the sound in the direction of its flow;
• consequently, each area is situated superficial to the chamber or vessel
into which the blood has passed and in a direct line with the valve orifice.