THE CIRCULATORY SYSTEMTHE CIRCULATORY SYSTEM

Heart and Vessels

Basic Structure of CirculatoryBasic Structure of Circulatory System

• Tunica intima– Endothelium supported by basement membraneEndothelium supported by basement membrane

and delicate collagenous tissue.• Tunica mediaTunica media

– Muscle and CT• Tunica adventitia• Tunica adventitia

– CT

Layers of ArteryA mediumsized

lmuscularartery,showing its layers.

The usual histologic preparations cause the layers to appear thicker than those shown here; the drawing is actually similar to the in vivo architecture of the vessel. At the moment of death, the artery experiences c ec u e o e vesse . e o e o de , e e y e pe e cesan intense contraction; consequently, the lumen is reduced, the internal elastic membrane undulates, and the muscular tunica thickens.

Types of Vessels

• Elastic artery• Muscular arteryMuscular artery• Arteriole

C ill• Capillary• Muscular venule, small vein• Vein• Muscular veinMuscular vein

Layers of Aorta

• Tunica intima– Endothelium– Collagenous fibers, elastic fibers & elastin sheets

• Tunica media– Extremely elastic (sheets of elastin), smooth muscle

• Tunica adventitia– Collagenous, elastic fibers

AORTA: Elastic Artery (x4)

Aorta: Tunica Media (x20)

ELASTIC ARTERY: AORTA

Tunica Media: H&E stain

Muscular Artery

• Tunica intima– Endothelium

i ll fib h l– Fine collagenous fibers, smooth muscle– Internal elastic lamina clearly evident

• Tunica media• Tunica media– Smooth muscle– Collagenous, reticular, elastic fibers – External elastic lamina clearly evident

• Tunica adventitia– Thick collagenous, elastic tissue

Muscular Artery (x4)

Muscular Artery x10

Muscular Artery x10

Muscular Artery (L) vs Elastic A t (R)Artery (R)

Arteriole

• Tunica intima– Endothelium– Some CT– Internal elastic lamina may be present

• Tunica media• Tunica media– Muscle layer several layers thick– External elastic lamina may be present

• Tunica adventitia– Collagenous, elastic CT as thick as tunica media

Arteriole

LargeSmall

Venules

Veins

• Tunica intima– Endothelium– Scant CT

• Tunica media– Thin muscle layer– Collagen, elastic fibers

• Tunica adventitia– Bulk of vessel wall

Vein x10

Vein x10

Muscular Vein

Artery, Vein

HEART

• Epicardium– (Tunica adventitia)(Tunica adventitia)

• Myocardium(Tunica media)– (Tunica media)

• Endocardium( i i i )– (Tunica intima)

• Surrounded by pericardium

HEART

Myocardium and EndocardiumEndoEndo

Myo

Endocardium consists of endothelium which is supported by a pp ydelicate layer of collagenous tissue beneath which lies a fibro-elastic layer.

HEART

Epicardium

Mesolthelium (single layer of epithelium) surrounds think layer of fibro elastic tissue Adipose tissue connects epicardium tofibro-elastic tissue. Adipose tissue connects epicardium to Myocardium.

Elastic Artery

Notice the elasticlaminas in the tunicalaminas in the tunicamedia.

ARTERY WALL

Adventitia

Tunica media

Lamina propria

EndotheliumExt. elastic m

MuscularMuscular Artery

Muscular Artery

Muscular Artery

Muscular Artery: internal elastic lamina

ARTERY

Artery, Vein

Small A iArteries

ARTERIOLESARTERIOLES

Lumen: < 0.3mm dia

Thin tunica intimaEndothelium

i l ll iLittle collagenous support tissueThin IEL

Tunica mediaTunica media

T i d titiTunica adventitia

Arteriole, Venule

CAPILLARIESCAPILLARIES

• Diameter 3 - 40 um• EndotheliumEndothelium

– ContinuousDiscontinuous– Discontinuous

– Fenestrated

CAPILLARY

E d th liEndothelium

Microcirculation

Mi i l iMicrocirculation

FENESTRATED CAPILLARY

ARTERY and VEIN

VEINS

Tunica intimaLittl th d th liLittle more than endothelium

Tunica mediaThin layer of smooth muscle

Tunica adventitiaThickest layer

VEINVEIN

A little of everything....

Lymphatic CapillaryLymphatic Capillary

fibroblastfibroblast

Atherosclerotic Plaque in CoronaryAtherosclerotic Plaque in Coronary Artery

Atherosclerotic Lesions

• Focal thickening of intima.• Proliferation of smooth muscle cellsProliferation of smooth muscle cells,

increased deposition of CT fibers, lipoproteinslipoproteins.

• Macrophages engulf lipoproteins, become foam cellsfoam cells.

• Thickening occludes vessel.