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CIRCULATORY SYSTEM

Dr Iram Tassaduq

OVERVIEWTransport of nutrients, hormones, gases, & other vital materials requires highly controlled flow.

Body has 2 circulatory systems.• Blood vascular system• Lymph vascular system

BLOOD VASCULAR SYSTEM

The heart, which is a pump for propelling the fluid.

The arteries which are tubes for conveying the blood toward the organs & tissues. The capillaries, which are anastomosing channels of small caliber with thin walls providing for much of the interchange of substances between the blood & tissue fluids.The veins, which in their initial segment also provide for blood-tissue fluid interchange but in addition serve for the return of blood to the heart.

LYMPH VASCULAR SYSTEM

Consists of lymphatic capillaries & various sized lymphatic vessels which ultimately drain into main trunks, the thoracic duct & the right lymphatic duct, which empty into large veins in the neck.

VESSEL WALLSTUNICA INTIMA

TUNICA MEDIA

TUNICA ADVENTITI

A

ELASTIC ARTERY (AORTA)Also called conducting arteries.Diameter: >1cmIntima:

Endothelium Connective tissue Smooth muscles 1 - Tunica intima

2 - Tunica media3 - Tunica externa

Stained with orsein

TUNICA MEDIA

Smooth muscles

Elastic lamellae

TUNICA ADVENTITIA

Thinner than tunica media

Connective tissue

Elastic fibers

MUSCULAR ARTERY2-10 mm in diameter

Intima: Endothelium Connective tissue Smooth muscle Internal elastic

membrane

MUSCULAR ARTERYMedia:

25-40 layers of Smooth muscle fibers

Collagen fibers

Elastic tissue

MUSCULAR ARTERYAdventitia:

Thinner than media

Connective tissue

Some elastic fibers

MUSCULAR ARTERY

SMALL ARTERY0.1-2 mm in diameter

Internal elastic membrane present

8-10 layers of smooth muscles.

Very thin tunica adventitia

SMALL ARTERY

LOW POWER VIEW OF SMALL ARTERY

HIGH POWER VIEW OF SMALL ARTERY

& ARTERIOLE

ARTERIOLEArterioles can be differentiated from arteries by the numbers of layers of smooth muscle.No more than 6 layers.A “precapillary arteriole” (1-2 layers)

VEINSVeins are distinguished by their thinner wall, valves, collapsed state.

The tunica media does not look as well organized as that in the artery or arteriole. 

VENULEMUSCULAR VENULE:

50-100 µm in diameter

1-2 layers of smooth muscles in media

V A N

SMALL SIZE VEIN

0.1-1 mm in diameter

2-3 layers of smooth muscles in tunica media

Thicker adventitia

MEDIUM VEIN

1-10 mm in diameter

Media is considerably thinner

Adventitia is well developed & forms bulk of the wall.

LARGE VEIN

LARGE VEIN>1mm in diameter

2-15 layers of smooth muscles

Much thicker adventitia containing connective tissue & some elastic fibers.

CAPILLARIESThin walled tubules with an average diameter of about 4-10 µm.Branch extensively without much change in caliber, & the branches anastomose to form networks which vary in density & pattern in different tissues & organs.The tissues with the highest metabolic activity have networks of elaborately branched & closely packed capillaries.

TYPES OF CAPILLARIES

MICROSCOPIC VIEW

MEDIUM SIZE ARTERY AND VEIN

ARTERIOLE & VENULE

ARTERIOLE & VENULES SMALL ARTERY

& VEIN