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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.