CIRCULATORY SYSTEM Dr Iram Tassaduq

OVERVIEW Transport 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 WALLS TUNICA INTIMA TUNIC A MEDIA TUNICA ADVENTITI A

ELASTIC ARTERY (AORTA) Also called conducting arteries. Diameter: >1cm Intima :  Endothelium  Connective tissue  Smooth muscles 1 - Tunica intima 2 - Tunica media 3 - Tunica externa Stained with orsein

TUNICA MEDIA  Smooth muscles  Elastic lamellae

TUNICA ADVENTITIA  Thinner than tunica media  Connective tissue  Elastic fibers

MUSCULAR ARTERY 2-10 mm in diameter Intima:  Endothelium  Connective tissue  Smooth muscle  Internal elastic membrane

MUSCULAR ARTERY Media:  layers of Smooth muscle fibers  Collagen fibers  Elastic tissue

MUSCULAR ARTERY Adventitia:  Thinner than media  Connective tissue  Some elastic fibers

MUSCULAR ARTERY

SMALL ARTERY 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

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

VEINS Veins 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.

VENULE MUSCULAR VENULE:  µm in diameter  1-2 layers of smooth muscles in media VA N

SMALL SIZE VEIN 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

>1mm in diameter 2-15 layers of smooth muscles Much thicker adventitia containing connective tissue & some elastic fibers.

CAPILLARIES Thin 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