B2050/2051: Human Anatomy and

Embryology

Lecture 6: Anatomy of the adult heart and

great vessels

Pulmonary

circuit (lungs)

Systemic circuit

(rest of body)

Aorta (principal artery

of systemic circuit)

Superior vena cava

(head, thorax

& arms)

Inferior

vena cava

(legs, abdomen,

pelvis)

Pulmonary veins

Pulmonary

arteries

Outline of the human circulatory system

The heart lies within the chest cavity, to the left of the midline, protected by the

ribs and sternum

Pectoral muscles sternum

arm

Aorta

Oesophagus

Heart

Lung

The heart forms the main mass of the mediastinum. In this view there is little in front of the

heart (anterior mediastinum) but structures like the oesophagus, thoracic aorta and thoracic

duct lie behind it (posterior mediastinum).

The heart forms most of the mediastinum – the wall of tissue that separates the

two pleural cavities.

Diagrammatic sagittal section of thorax

Heart

Superior mediastinum

(great vessels – aorta,

vena cava, trachea,

oesophagus)

Inferior mediastium

(heart)

+ thoracic aorta, oesophagus,

azygous vein, thoracic duct

Anterior Posterior

The green dotted line marks the boundary between the superior and inferior mediastinum.

Superior

Inferior

The heart is enclosed in a fibrous bag

- the fibrous pericardium – that is

fused inferiorly to the central

tendon of the diaphragm

The inner surface of the fibrous pericardium and the outer surface of the heart

are covered by a thin layer of serous pericardium. Like the pleura, the layer

attached to the wall (fibrous pericardium) is called the parietal layer and the layer

attached to the heart is the visceral layer. Between them is a pericardial cavity

containing a small amount of fluid. The fibrous and parietal layers are supplied

by somatic nerves (phrenic) and are sensitive to pain.

Fibrous

pericardium

lined with

parietal serous

pericardium

Apex

Right border

(R.A)

Inferior border

(Mostly R.V)

Left border

(L.V)

Superior border

(Great vessels)

In reality the human heart

is not ‘heart-shaped’

at all – but trapezoid

Apex

Right border

Inferior border

Left border

Superior

border

Normal chest Xray

Enlargement of RA

The four border of the heart can be seen on a normal chest X-ray.

Compare it with the X-ray on the right and you can see there how the right border

is more expanded – showing enlargement of the right atrium

Fibrous skeleton of the heart

Although most of the heart is cardiac

muscle, there is a fibrous skeleton,

roughly at the junction of the atria and

ventricles, that supports the valves

Right atrium Blood from:

Superior &

inferior vena

cava, coronary

sinus

Right ventricle

- To pulmonary trunk

Left atrium Blood from:

Pulmonary

veins

Left ventricle

- To aorta

Pulmonary arteries Aorta

Superior vena cava

Inferior vena cava

Right auricular process

Arch of aorta

Pulmonary trunk

Left auricular process

Main external features of the heart

Ligamentum

arteriosum

Vagus nerve

Pectinate muscle

Crista terminalis (= boundary between

smooth and

rough walled parts

of the atrium)

Fossa ovalis Remnant of foramen

ovale in embryo)

Auricular

process

Opening of coronary sinus

Right atrium

SVC

Aorta

IVC

The atria are formed from two different regions in the embryo – the ‘true’ atrium and the

sinus venosus, a sac into which all the veins empty. The sinus becomes incorporated

into the atria, as do parts of the pulmonary vein on the left. The sinus/veins form the

smooth part of the atrial wall; the rough part is formed by the true atria.

Right atrium

Fossa ovalis

Ligamentum

arteriosum

These two structures are remnants of the foetal circulation:

a) The fossa ovalis is a remnant of the foramen ovale between the right and left

atria. In the foetus, this carries oxygenated blood from the placenta (coming via

the left umbilical vein and IVC) across to the left side for circulation to the growing

body and, especially, the brain.

b) The ligamentum arteriosum is a remnant of the ductus arteriosus which carries

blood from the pulmonary trunk into the aorta to bypass the lungs

Papillary muscles

Moderator band (Enlarged trabecula that carries

a branch of the conducting

system directly to the base of

the papillary muscles)

Pulmonary semi-lunar

valve

Chordae tendinae

Cusps of tricuspid

valve (3 cusps)

Right ventricle

(run from the edges of the

cusps to the papillary muscles)

(Contract before the ventricular wall

to ensure the valve does not flip ‘inside out’ and

let blood back into the atrium)

Vagus nerve

Atrioventricular valve in a fresh heart

Trabeculae carnae

Chordae tendinae

Papillary muscle

Valve cusplet

Pulmonary semi-lunar valve Aortic semi-lunar valve

Bicuspid (mitral) valve Tricuspid valve

View of heart from above with major vessels and atria removed –

showing the valves. Anterior is at the top.

Left side of the heart

Trabeculae carnae

Bicuspid valve =

Mitral valve

Most of the left atrium is

At the back of the heart.

It receives four pulmonary

veins – two from each

lung.

Bishop’s mitre

The right ventricle has thinner walls than the left – the resistance in the

pulmonary circuit (lung capillaries) is less than that in the systemic circuit

(capillaries of the rest of the body) so less pressure is required.

Cross section through

ventricles shows right chamber

wrapped around thicker left

Coronary arterial blood supply to the heart

The coronary arteries branch from aorta immediately above the semi-lunar valves

and form a ‘crown’ (=coronet) around the top of the heart

Great cardiac vein

Middle cardiac vein

Anterior cardiac veins

Coronary sinus

Cardiac veins The veins of the heart do not form a ‘crown’ like the arteries and are therefore called cardiac

(not coronary) veins.

Pulmonary veins

(2 left, 2 right)

Pain travels with

sympathetic nerves:

Mainly T1,T2

Parasympathetic

(vagus)

The cardiac muscle has its own intrinsic beat but the speed and strength

of the beat is moderated by autonomic nerves

The beat is initiated at the

sino-atrial (SA) node which lies at

the junction of the superior vena

cava and the sinus part of the

heart.

The wave of contraction crosses

the atria and stimulates the atrio-

ventricular (AV node) which lies

close to the opening of the

coronary sinus in the wall of the

right atrium.

It then crosses the atrioventricular

junction in the AV bundle, which

then divides into left and right

branches that travel in the

interventricular septum to the

base of the heart.

One large branch from the right

(the septomarginal trabecula or

moderator band) passes to the

base of the right side papillary

muscles to ensure they contract

in time to tense the tricuspid valve

Placement of an artificial pacemaker where parts

of the conducting system or nodes have failed Conducting system

The major blood vessels of the thorax

The heart and great vessels

Descending

thoracic

(dorsal) aorta

Ascending

(ventral) aorta

Aortic arch Brachiocephalic a.

R. Subclavian a.

R. Common

Carotid a.

L. Common

Carotid a.

L. Subclavian a.

Summary of the branches from the aortic arch

RSc

RCC LCC

LSc

BC

Sub-clavian = under clavicle

Brachio = arm; cephalic=head

Vertebral a.

Intercostal a.s

(=thoracic

segmental a.)

Vertebral artery

Vertebral a. Branch of subclavian

artery.

Runs up within cervical

vertebrae, enters

skull, and joins with

opposite vertebral

artery to help supply the

brain .

In the skull – form

anastomoses with

internal carotid branches

Superior vena cava (SVC) and its tributaries (head, thorax, arms) Inferior vena cava (IVC) and its tributaries (abdomen, pelvis, legs)

Venous system

Tributaries of the superior vena cava: Left and right brachiocephalic v. Azygous vein

Superior

vena cava

R. Internal

Jugular v.

R. Subclavian v.

L. Subclavian v.

L. Internal

jugular v.

Hemiazygous vein Azygous vein

Thoracic

duct

IVC

View of right mediastinum showing

azygous vein draining into SVC

Azygous v.

SVC

Superior vena cava drainage

SVC Azygous v.

L. Brachiocephalic v. R.Brachiocephalic v.

Internal jugular v.

External jugular v.

External jugular vein

By the end of this lecture, you should be able to answer MCQ’s and

write short answers on:

a) The internal anatomy of the heart

b) The external anatomy of the heart and the coronary blood vessels

c) The conducting system of the heart

d) The position of the heart in the chest

e) The mediastinum

f) The arrangement of the major arteries and veins of the thorax

For those in the Dissecting Room Group this afternoon (L-Z):

You MUST bring a valid student photocard with you – you will not be

admitted without it.

Mobile phones may not be carried in the Dissecting Room –

even switched off. Put them into your bag and keep them there until

you have left the room.

Bags may be left at the back of the Dissecting Room with coats – don’t

leave them in the hallway outside