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

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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)

Pulmonarytrunk

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

Pulmonarytrunk

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 temporalvein

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 veinInferior 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!