The Heart YC Wong, PhD 王雲川 The University of Hong Kong [email protected].

The Heart YC Wong, PhD 王雲川

The University of Hong [email protected]

Scope• Overview of anatomy of the heart• Surface markings and gross anatomical

structure• Vascular system of the heart• Impulse conducting system• Histology of the heart

• Located in middle mediastinum 纵隔• Locate the sternal angle• Point one: right 3rd costal cartilage 1

cm from sternum border• Point 2: 6th costal cartilage, 1 cm from

sternum• Point 3: 5th left intercostal space just

medial to mid clavicular line• Point 4: 2nd left intercostal space at

the border of sternum• Join the 4 points to mark the outer

shape of the heart

Location and surface markings

Sternal angle

The Pericardium 心包膜• Fibrous capsule enclosing the heart• Separated by pericardial cavity filled with fluid• To reduce the friction of heart during pumping• Lined by serous pericardium 浆膜心包• Subdivided into parietal and visceral layers• The parietal layer closely adheres to fibrous pericardium 纤

维心包 ; the visceral layer reflected on the outer surface of heart, the external limit of epicardium 心外膜 , lined by mesothelium 间皮

• Perforated only at the roots of major vessels• Reflections of serous pericardium forms transverse sinus 横

窦 and oblique sinus 斜窦

The Pericardium 心包膜

R. Pulmonary V L pulmonary V

Trans Sinus

Oblique Sinus

Anatomy of the Heart• Located in middle mediastinum• Surrounded by pericardium• Apart from attachment to

major vessels, the rest is basically free within pericardial cavity

• Three surfaces: sternocostal surface, diaphramatic surface and base, i.e. the posterior surface

• The apex 心尖 of the heart is directed forward, downward and to the left

Right ventricle

Left ventricle

Right atriumLeft auricle

Apex

Four Chambers• Divided by vertical septa to form 4 chambers• Right atrium and left atrium, separated by

interatrial septum• Right ventricle and left ventricle, separated by

interventricular septum• Right atrium and right ventricle is guarded by a

valve, the tricuspid valve, 三尖瓣• Left atrium and left ventricle is guarded by

mitral valve 二尖瓣• Deoxygenated blood returns to right atrium

then to right ventricle which is pumped to the lungs via pulmonary trunk, guarded by pulmonary valve 肺动脉瓣

• Oxygenated blood from the lungs enters the left atrium, then to left ventricle

• This blood is pumped through aorta guarded by aortic valve 主动脉瓣

Right Atrium

Right ventricle

Left atrium

Left ventricle

Tricuspid v

Mitral v

Pulmonary v Aortic v

Right atrium 右心房• Receive blood from superior

vena cava 上腔靜脈• Inferior vena cava 下腔靜脈• Venous blood from the heart,

the coronary sinus 冠状窦• Interior surface, musculi

pectinati 梳状肌• Fossa ovale 卵圆窝 , on

interatrial septum• Crista terminalis 界嵴• Right auricle 心耳 , an

extension from atrium, irregular surface

• Location of sinoatrial node 竇房結 at junction with superior vena cava

Superior vena cava

Inferior vena cava with valve

Fossa ovale

Right auricle

Musculi pectinati

• Fairly common• Hidden condition• No obvious symptoms• Left atrium pressure higher

than right, the potent opening is physiologically closed

• Reason for the opening to stay patent, and not fused afterbirth remains unclear.

• No treatment is needed in most cases

Patent foramen ovale

Atrial Septal Defect (ASD)

• Hole in interatrial septum• Allow left atrial blood

(oxygenated) to enter right atrium (lower pressure)

• Increased work load of right ventricle

• Small hole, no significant effect

• Medium or large hole may require surgical repair

Ventricular Septal Defect

• Hole in interventricular septum

• Can be in different location along the septum

• Blood flow from left ventricle through hole to right venricle

• Increased right ventricle work load

• Increase pulmonary pressure, pulmonary hypertension

• Require surgical intervention

Right ventricle 右心室• Wall much thicker than

atrium• Separated from atrium by

tricuspid valve• With anterior, posterior

and septal cusps• Papillary muscle for the

attachment of heart valve tendons, chordae tendineae 腱索

• Moderator band 节制带• Pumps blood into

pulmonary trunk• Guarded by semilunar

valves 半月瓣

Anterior cusp

Septal cusp

Posterior cusp of tricuspid valve

Papillary muscle

Chordae tendinease

Moderator band

Left atrium 左心房• The wall is thin, like right

atrium, • Located mainly at the

posterior surface• A large portion is formed

by absorption of major blood vascular wall during development

• Extension of left auricle to the stenocostal surface

• Smooth interior surface receive 4 pulmonary veins from the lungs

Left ventricle 左心室• Wall very thick, twice as thick as right

ventricle• Separated from left atrium by mitral

valve, with only two leaflets• Responsible for systemic circulation• Interior surface is rough with trabeculae

carneae 心肉柱 , papillary muscles, but no moderator band

• Chordae tendineae 腱索 , to strengthen the leaflets of the valve

• Pumps blood out through aorta• Guarded by aortic valve, semilunar valve• The part of heart immediately below

the aortic orifice is known as aortic vestibule

Mitral valve

Chordae tendinease

Papillary muscle

Cardiac skeleton 心骨架• Not a true skeleton• Fibrous connective tissues located between

atria and ventricles• One ring between right atrium and right

ventricle• The other between left atrium and left ventricle• Forms an 8 shape figure• For the attachment of atrial fibres and

ventricular fibres as well as attachment of tricuspid and mitral valves

• Extensions of fibrous connective tissues to the roots of pulmonary trunk and aorta for attachment of semilunar valve leaflets

• No direct connection/contact between atrial and ventricular muscle fibres

Mitral valve ring

Tricuspid valve ring

Fibrous ring of pulm trunk Fibrous ring

at aortic valve

Heart valves 心瓣• Atrio-ventricular valves 房室瓣

– Tricuspid valve: between right atrium and right ventricle• Three leaflets anchor through tenon-like structure, chordae

tendineae

– Mitral valve: between left atrium and left ventricle• Two leaflets

• Pulmonary valve: at the junction of pulmonary trunk with right ventricle– Semilunar valve: three leaflets of half moon shape

• Aortic valve: junction of aorta with left ventricle– Semilunar valve with three leaflets of half moon shape– Origin of coronary arteries from aortic sinus

The coronary arteries 冠狀動脈• Left coronary artery: larger, from left

posterior aortic sinus. It enters atrioventricular groove and gives rise to:– Anterior interventricular branch,

anastomoses with posterior interventricular branch from right coronary artery

– Left circumflex branch, anastomosing with right coronary artery

• Right coronary artery: from anterior aortic sinus runs between pulmonary trunk and right auricle, and atrio-ventricular groove– Marginal branch– Posterior interventricular branch

L coronary a

L circumflex b

Anterior interventricular branch

Posterior interventricular branch

R coronary a

Marginal b

Variations of coronary arteries

A. Left coronary artery dominantB. Only one coronary artery, the right one is missingC.Circumflex artery is arising from right coronary artery

Coronary arteries and heart diseases

• Crucial for heart health• Anastomoses between artery branches

though occur, but most branches supply a secluded area

• Blockage of vessels or branches of vessels often results in death of cardiac muscle fibres in the affected, myocardiac infarction 心肌梗塞

• Serious cases result in death

Venous drainage of the heart

• Venous blood returns to right atrium via coronary sinus

• It is a continuation of great cardiac vein running parallel to anterior interventricular artery

• Small and middle cardiac veins are tributories of coronary sinus

• Anterior cardiac vein empties directly into right atrium

Coronary sinus

Great cardiac vein

Small cardiac vein

Middle cardiac vein

Coronary sinus

Middle cardiac vein

Impulse conducting system of heart

Impulse conducting system 心臟之傳導系統

• Specialized cardiac muscle to regulate the rhythm of heart• Sinoatrial node , 窦房结 pace-maker of the heart, to set the

pace of heart beat• Initiates atrial heart muscle contraction as well as spreading the

signals to AV node 旁室結• Atrioventricular node passes the singals to Purkinje fibres• Two branches extended out from here, known as bundle of HIS• Bundles of His run down along the sides of interventricular

septum and give off Purkinje fibres• Purkinje fibres spread contraction signals to ventricular cardiac

fibres, to start ventricular contraction• Cardiac arrththmia 心律失常

PA X-ray of the Heart

Auscultation points of heart sounds

• A for aortic valve• P for pulmonary

valve• T for tricuspid

valve• M for mitral valve

Aortic valve

Tricuspid valve

Right atrium

Right ventricle

Histology of the heartWith three basic layersEndocardium 心內膜Myocardium 心肌膜Epicardium 心外膜

Endocardium • Inner most• Endothelium• Sub-endothelial

connective tissue• Sub-endocardial layer

which may contain conducting system of heart, Purkinje fibres

Myocardium • Substantially thicker• Contains cardiac muscle• With intervening collagen

tissue and smaller vessels• Atrial walls are much

thinner than myocardium in ventricles

• Muscles are attached to cardiac skeleton between atria and ventricles

• Typical cardiac fibre morphology with striations and intercalated disks

Epicardium • Rich in fat (A; adipose

tissue)• Free surface covered by

mesothelial (M) cells• Connective tissue • Blood vessels, coronary

vesselsM

Heart valves 心瓣• Aortic valve: semilunar valve with three leaflets,

each is shaped as half-moon• Pulmonary valve: same as aortic valve with three

leaflets• Left atrioventricular valve or mitral valve: two

leaflets reinforced with tendinous cords known as chordae tendineae, to prevent eversion

• Right atrioventricular valve or tricuspid valve: three leaflets, also reinforced with chordae tendineae

Structure of heart valves• Attached to fibrous cardiac skeleton• Formed as a flap extending from tunica intima• Normally avascular in nature• Supported by a core of irregular dense

connective tissue continuous with cardiac skeleton

• Covered on both side by endothelial cells

Impulse conducting system (structure)

• Sinuatrial (SA) node, pacemaker, specialized group of cardiac fibres located at junction between superior vena cava and right atrium– Smaller than ordinary fibres

• Atrioventricular (AV) node• AV bundle of His, further divide to left and right

bundles and then into subendocardial fibres • Purkinje fibres

– Larger in diameter, paler staining and carry impulses to ordinary cardiac muscle in ventricles

– Rich in sarcoplasm, scarce myofibrils

Purkinje fibres (P)

Myocardium

Summary• Surface anatomy of the heart• Structure of the heart• Common septal defects• The coronary vessels • Impulse conducting system• Histological organization of the heart

End