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Blood circulation
Dr AA Adebesin,
Dept. of Anat. X4130
Objectives
• To understand the types and histological
organisation of blood vessels
• To understand the anatomy 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.
Endothelial function can be improved significantly by exercise and
improved diet
Arterial wall
Venous 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
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)
The chambers of the heart
Pulmonary
trunk
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
The heart and the lungs in situ
Left lung
Pulmonary
trunk
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
Blood supply of the heart
Coronary sinus
L. Coronary art.
R coronary art
Anterior interventricular art
Venous return of the heart
Coronary sinus
(vein)
Middle cardiac vein
The big vessels of the body
Common carotid
R Brachiocephalic vein
L subclavian
Arch of aorta
Superficial temporal
vein
Facial art
The deep arteries of the face
Internal
jugular
vein
Common
carotid
art.
Axillary artery
Subclavian v
Brachial art
Axillary vein
Brachial art
Radial art
Ulnar art
Thoracic aorta
Left Kidney
Inferior vena cava
Renal vein
The renal artery and branches
Renal art
Branches of renal artery are example of terminal arteries
Celiac art
Sup. Mesenteric art
Abdominal aorta
Common iliac
Internal iliac
External iliac
Femoral art
Popliteal art
Small saphenous vein
Portal circulation
Inf vena cava
Hepatic vein
sinusoids
Hepatic artery
Portal vein
(splenic + sup
Mesenteric vv)
Splenic vein
spleen
Inf. Mesenteric vein
sup. Mesenteric 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
Middle cerebral art
Basilar art
Vertebral art
Basilar art.
Middle cerebral art.
Anterior cerebral art.
Posterior cerebral 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!