Blood circulation

Dr AA Adebesin, Dept. of Anat. X4130

Objectives

• To understand the types and histological

organisation of blood vessels

• To understand the anatomical design of the

heart

• To understand the systemic circulation

• To understand the pulmonary circulation

• To understand the coronary circulation

• To understand the hepatic portal circulation

• To understand the brain circulation

Blood circulation

• The essential components of the human

cardiovascular system are the heart, blood and

blood vessels

• There are three types of blood vessels: arteries,

veins, and capillaries

• Blood under high pressure leaves the heart and

is distributed to the body by a branching system

of thick-walled arteries.

• The final distributing vessels, arterioles, deliver

oxygen-rich blood to capillaries.

• Capillaries form a capillary bed, where the

interchange of oxygen, nutrients, waste

products, and other substances with the

extracellular fluid occurs.

• The heart is a dual suction and pressure pump

that propels blood through the infinite double

loop formed by the pulmonary and systemic

circuits

•

Structure of the vessels

The tunics

The tunica externa, (or adventitia), is the

outermost layer of a blood vessel, surrounding

the tunica media. It is mainly composed of

collagen and is supported by external elastic

lamina.

The collagen serves to anchor the blood vessel to

nearby organs, giving it stability.

It also contains nerves (Vasa nervorum) that

supply the vessel as well as nutrient capillaries

(vasa vasorum) in the larger blood vessels.

The tunica media or middle coat (the thickest

layer): has circularly arranged elastic fibre,

connective tissue, polysaccharide substances.

The tunica media is distinguished from the inner

(tunica intima) by its colour and by the transverse

arrangement of its fibres.

In the smaller arteries it consists principally of

plain muscle fibres in fine bundles, arranged in

lamellae and disposed circularly around the

vessel.

These lamellae vary in number according to the

size of the vessel; the smallest arteries having

only a single layer, and those slightly larger three

or four layers.

These vascular smooth muscles control the

calibre of the vessels

It is this coat that determines the thickness of the

wall of the artery,

Exceptions: arteries of cranium and vertebral

column. .

The tunica intima or intima (the thinnest layer)

It is the innermost layer of an artery or vein.

It is made up of a single layer of simple squamous

endothelial cells glued by a polysaccharide

intercellular matrix.

There is a thin layer of subendothelial connective

tissue interlaced with a number of circularly

arranged elastic bands called the internal elastic

lamina

The endothelial cells are in direct contact with the

blood flow

The arteries and veins have similar structures,

veins having reduced tunica media than the

arteries

Capillaries consist of little more than a layer of

endothelium and occasional connective tissue.

Arterial wall

A key and quantifiable feature of endothelial dysfunction is the

inability of arteries and arterioles to dilate fully in response to an

appropriate stimulus that stimulates release of vasodilators from

the endothelium like nitric oxide

Endothelial function can be improved significantly by exercise and

improved diet

Venous wall

When blood vessels connect to form a region of

diffuse vascular supply it is called an

anastomosis.

Anastomoses provide critical alternative routes

for blood to flow in case of blockages.

Arteries that do not anastomose with adjacent

arteries are true terminal arteries (end arteries).

Occlusion of an end artery interrupts the blood

supply to the structure or segment of an organ it

supplies

The design of the heart

• The atria and ventricles are attached to pair of

conjoined fibrous rings that bound the orifices

• The muscle cells are shorter than in the skeletal

muscle

• Boundary membrane of adjacent cells

interdigitate to increase surface area for

conduction of impulses

• Cells are arranged in whorls and spirals

enabling each chamber to empty by mass

contraction

• Primarily to aid circulation of blood

• Enclosed in the pericardium

• 3 layered muscle : epicardium,

myocardium, endocardium

• 4 chambers

• Muscular wall of left ventricle is thicker

than the right

The valves and cusps

• Tricuspid valve

• Mitral valve

• Aortic valve

• Pulmonary valve

• All have 3 valves and cusps except mitral (has only

2)

Pulmonary

trunk

The chambers of the heart

Pulmonary circulation

•Between the heart and the Lungs

•From Rt ventricle via pulmonary (trunk) arteries

to the lungs

•Return to Lf atrium via pulmonary veins

•Essentially for oxygenation

Left lung

Pulmonary

trunk

The heart and the lungs in situ

The pulmonary circulation loop is virtually bypassed in

fetal circulation.

The fetal lungs are collapsed, and blood passes from the

right atrium directly into the left atrium through the

foramen ovale, an open passage between the two atria

Fossa ovalis

Systemic circulation

•Blood circulation of the body excluding

pulmonary circulation

•From the Lt ventricle (via the aorta) and

returns via venae cavae and coronary sinus

to (the Rt atrium)

•Transports oxygenated blood away and

return deoxygenated blood to the heart

Blood circulation of the heart

• The right and left coronary arteries are

responsible for supplying the heart.

• The circulatory system of the myocardium is

unique in that the coronary arteries fill during

ventricular diastole as a result of aortic recoil

L. Coronary art.

R coronary art

Coronary sinus

Blood supply of the heart

Anterior interventricular art

Coronary sinus

(vein)

Venous return of the heart

Middle cardiac vein

Arch of aorta

L subclavian

Common carotid

R Brachiocephalic vein

The big vessels of the body

Superficial temporal

vein

Facial art

The deep arteries of the face

Internal

jugular

vein

Common

carotid

art.

Axillary artery

Brachial art

Subclavian v

Axillary vein

Brachial art

Radial art

Ulnar art

Renal vein Inferior vena cava

Thoracic aorta

Left Kidney

Renal art

Branches of renal artery are example of terminal arteries

The renal artery and branches

Abdominal aorta

Common iliac

Internal iliac

External iliac

Femoral art

Sup. Mesenteric art

Celiac art

Popliteal art

Small saphenous vein

Portal circulation

Inf vena cava

Hepatic vein

Hepatic artery

Portal vein (splenic + sup

Mesenteric vv)

sinusoids

spleen

sup. Mesenteric vein

Inf. Mesenteric vein

Splenic vein

Blood circulation of the brain

Principal arteries

•Vertebral art

•Internal carotid artery

Internal carotid art

Post communicating art

Basilar art

Brain circulation

• Internal carotid artery supplies the forebrain

except the occipital lobes

• The vertebral artery supplies the brainstem and

the occipital lobes

• The vertebral and internal carotid artery form

circulus arteriousus

• The final branches from this circle of Willis that

supply the cortical tissues are end arteries

Int. carotid art

Vertebral art

Basilar art

Middle cerebral art

Anterior cerebral art.

Posterior cerebral art.

Middle cerebral art.

Basilar art.

Small artery and vein, pia mater of sheep. X 250. Surface view

above the interrupted line; longitudinal section below. Artery in

red; vein in blue

Important branches to note

Perforating branches: lenticulostriate

arteries, i.e. medial and lateral striate

arteries supply the basal nuclei

Middle meningeal artery: found in epidural

space outside of the brain i.e. between the

cranium and the meninges

Venous drainage

Blood from the brain eventually drains into

the

sigmoid sinus internal jugular vein

What to expect……………

The test questions!

Concerning the blood vessels, which of the

following statements is (are) true?

a. arteries are vessels that transport blood from the

periphery to the heart

b. the diffusion of gases, nutrients and wastes occurs in

the venules

c. an end artery is an artery with sufficient anastomosis

to maintain viability of the tissue supplied if an arterial

occlusion occurs

d. arteries are vessels that transport blood from the

heart to the tissues or the lung

Thank you 4 your attention!