Microanatomy: Cardiovascular System

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components of cardiovascular system

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heart, arteries, arterioles, capillaries, venules, veins, lymphatic vessels

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all components of CV system have three layers, which include

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innermost layer, middle layer, outermost layer

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innermost layer of CV (histology)

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tunica intima - endocardium

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middle layer of CV (histology)

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tunica media - myocardium

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outermost layer of CV (histology)

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tunica adventitia - epicardium

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heart develops from a

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simple tube

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three layers of CV tissue are developed to a greater or lesser degree depending on

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function

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arterovenous shunts found in

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in beds of capillaries

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tunica intima lies closest to

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the lumen of a CV vessel

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tunica intima, tissue type

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simple squamous epithelium (endothelium)

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beneath endothelium in CV system is

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a subendothelial layer

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subendothelial layers, thickness

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variable

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composition of endothelium (in CV system)

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loose connective tissue containing some smooth muscle cells

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endothelium & elements of subendothelium is oriented

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longitudinally (in same axis as blood flow)

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7 important functions of endothelium

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maintains selective permeability barrier; maintins non-thrombogenic barrier; modulates blod flow & vascular resistance; regulates cell growth; regulates immune response; maintains ECM; involved in lipoprotein metabolism

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tunica media is most prominent layer in

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arteries

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tunica media, composition

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concentric layers of smooth muscle & elastic membranes

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tunica media, ratio of components

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relative amounts of smooth muscle & elastic membranes dependent upon type of vessel (type IV collagen)

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in arteries, tunica media separated from tunica intima by

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internal elastic lamina

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reticular fibers formed from type _____ collagen

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III

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tunica media contains two types of fibers

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reticular fibers and proteoglycans

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in elastic arteries, _______ predominate

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elastic lamellae

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all ECM in the tunica media is synthesized by

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smooth muscle cells

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elements of tunica media are arranged in a

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circle

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layers of tunica arranged, external to internal

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longitudinally, circularly, longitudinally

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tunica adventitia is most prominent layer in

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veins

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tunica adventitia comprised of

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connective tissue sheath

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connective tissue sheath of tunica adventitia contains mainly

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type I collagen

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connective tissue sheath of tunica adventitia also contains these two other types of fibers

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elastic fibers & smooth muscle fibers

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ratio of components in connective tissue depends upon

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type of vessel

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large vessels may have

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their own blood vessels, aka vasa vasorum

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______ form a network in the adventitia

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vasomotor nerves

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vasomotor nerves aka

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nervi vascularis

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nervi vascularis innervate

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smooth muscle of tunica media

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elements of tunica adventitia are arranged

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longitudinally (in same axis as blood flow)

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lymphatic vessels are distinguishable from vascular vessels because

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they don't have distinguishable layers

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tunica media, on slide, appears

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prominent in comparison to rest of vessel

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on slides, arteries stand out as compared to veins because

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the veins collapse but the arteries don't

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moderator band of heart carries

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purkinje fibers

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ischemia to purkinje fibers can cause

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tricuspid valve prolapse (rare)

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heart has ____ distinct layers

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three

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three distinct layers of heart

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endocardium (inside), myocardium, epicardium (outside)

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epicardium composed of

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connective tissue with vessels & nerves

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heart has internal conducting system composed of

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highly specialized cardiac muscle cells

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endocardium is homologous to

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tunica intimia

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endocardium composed of

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endothelial lining with underlying subendocardium

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subendocardium composed of

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loose connective tissue containing elastic & collagen fibers & smooth muscle cells

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subendocardium contains

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some small veins, nerves, and in some locations, purkinje fibers

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conduction system of heart comprised of

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highly specialized cardiac muscle cells called purkinje fibers

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purkinje fibers, in comparison to ordinary cardiac muscle cells are

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much larger

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purkinje fibers have fewer ______ than ordinary cardiac muscle cells

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myofibrils (thus they stain lighter)

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purkinje fibers, histological appearance

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central, often binucleate, nucleus surrounded by a very prominent light area where glycogen accumulates

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impulses initiated at the sinoatrial node travel to

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the AV node and then via bundle of His & its branches to the apex of the heart

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ischemic attack involving areas where purkinje fibers are located can be

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fatal, since damae to these fibers can result in inability of heart to contract rythmically & effectively

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myocardium is homologous to

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tunica media

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mycoardium is thicker in

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the ventricles than the atria

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two layers of myocardium in the ventricle

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inner circular layer & outer spiral layer

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cardiac skeleton

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dense fibrous connective tissue layer

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anchored to cardiac skeleton

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cardiac muscle

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stage of heart muscle

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postmitotic

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ischedmia due to coronary artery insufficiency can cause

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focal death of myocardial fibers (can't regenerate because they're postmitotic)

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following ischemic death, myocardial fibers are replaced by

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scar tissue

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myocardium accumulates _____ over time during normal conditions

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lipofuschin

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lipofuschin appears as

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a brownish-gold pigment

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epicardium is homologous to

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tunica adventitia

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epicardium composed of

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thick layer of loose connective tissue with variable amounts of adipose tissue

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epidcardium contains

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arteries, veins, & nerves

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outermost layer of epicardium comprised of

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simple squamous epithelium

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outermost layer of epicardium aka

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mesothelium, a serous membrane

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mesothelium is the

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visceral pericardium

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mesothelium functions to

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allow smooth movement (sliding) of heart within pericardial sac

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heart valves, two atrioventricular

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right = tricuspid; left = bicuspid/mitral

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heart valves, other

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pulmonic & aortic

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aortic valve can be identified on histologic slide because

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it has a coronary artery branching off of it

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there is no hyperplasia in heart muscle, just

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hypertrophy (cells postmitotic, so they can't regenerate more, they can just get bigger)

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hypertrophy of cardiac muscle occurs with

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different kinds of resistance (systemic vs. pulmonic, etc)

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heart change, in people who exercise a lot

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thickened myocardial fibers

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circulation to muscle reduced with

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hypertrophy

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two classifications of arteries

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large elastic arteries & muscular arteries

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elastic arteries aka

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conducting arteries

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elastic arteries, three layers

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intima, media, adventitia

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intima of elastic arteries

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consists of layer of endothelial cells resting on thick subendothelium; CT oriented longitudinally; internal elastic lamina not clearly defined

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elastic arteries contain ____ cells

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smooth muscle cells

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media of elastic arteries, composition

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concentrically arranged membranes of elastin (spiral)

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media of elastic arteries contain

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smooth muscle

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media of elastic arteries, arrangement aka

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lamellae

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thickness of lamellae in media of elastic aa

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40-70

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lamellae increase in number from

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infancy to adulthood

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portion of media in elastic arteries that helps maintain blood pressure during diastole

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elastin portion of media

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adventitia of elastic aa

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relatively thin compared to size of vessel

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adventitita of elastic aa contains

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vasa vasorum that extend into media

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smooth muscle cells in elastic aa are oriented

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longitudinally

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marfan's syndrome, cause

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abnormal expression of the fibrillin 1 gene

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marfan's syndrome, consequence

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abnormal elastic tissue

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marfan's syndrome, CV effects

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causes dissecting aneurysm of aorta; life threatening

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marfan's syndrome, characteristics

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pts are tall, arachnodactylic, have mitral valve prolapse, dilation of root of aorta, & aortic dissection

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marfan's syndrome, histological appearance

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disruption of elastic lamellae in tunica media

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muscular aa aka

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distributing aa

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muscular aa, tunica intima consists of

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layer of endothelial cells resting on subendothelial layer containing some smooth muscle

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muscular aa, tunica intima, arrangement

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longitudinally

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muscular aa, tunica intima, most prominent feature

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scalloped internal elastic lamina

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scalloped internal elastic lamina of muscular aa separates

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intima from media

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muscular aa, tunica intima, histological appearance

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easy to see, particularly in larger muscular aa, with routine H & E stain

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muscular aa, tunica media consists of

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3 to 40 concentric layers of smooth muscle cells organized circularly

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muscular aa, tunica media, histological appearance

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elastin membrane between smooth muscle cells can only be seen with special stains

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muscualar aa, tunica adventitia, feature

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external elastic lamina that separates media from adventitia

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muscular aa, tunica adventitia, composition

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longitudinally oriented fibroblasts, collagen fibers, & elastic fibers

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muscular aa, tunica adventitia, contents

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vasa vasorum, lymphatics, vasa nervorum

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vasa vasorum of tunica adventitia in muscular aa can extend into

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tunica media

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atherosclerosis, prevalence

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affects more americans than any other disease process

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atherosclerosis, risk factors

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age, gender (males>females), genetics, obesity, htn, smoking, diabetes mellitus

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smoking, affect on vasculature

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nicotine causes vascular constriction

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atherosclerosis, histological presence

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intimal thickening with proliferation of intimal smooth muscle cells & accumulation of lipid

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in atherosclerosis, lipids accumulate in

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macrophages & smooth muscle cells (foam cells)

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growth factor implicated in smooth muscle cell proliferation in atherosclerosis

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platelet-derived groth factor (PDGF)

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atherosclerosis, mechanism

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endothelium breaks down, platelets are deposited, plaque forms, plaque vascularized by "vasa plaquorum," lesion expands & fibrosis leads to vascular occlusion

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atherosclerosis, pathogenesis

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endothelial damage or monoclonal hypothesis (I.e. smooth muscle proliferation)

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arterioles, tunica intima

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layer of endothelial cells resting on a very thin subendothelium; internal elastic lamina not usually visible

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arterioles, tunica media

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one or two layers of concentrically arranged smooth muscle cells

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arterioles, tunica adventitia

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very thin

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arterioles, histological appearance

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endothelium bulges out because it's longitudinal; smooth muscle & endothelial cells can be seen

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capillaries, function

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exchange vessels

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capillaries, three types

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continuous, fenestrated, sinusoidal

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continuous capillaries aka

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somatic capillaries

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continuous capillaries consist of

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continuous endothelium joined by tight junctions (zonula occludens)

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continuous capillaries found in

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CNS, PNS, muscle (esp. heart), connective tissue, & exocrine glands

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means by which something can cross a continuous capillary

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pinocytosis

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CNS capillaries, continuous

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have continuous endothelium resting on basal lamina; basal lamina surrounded by astrocytotic endfeet

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astrocytotic endfeet in CNS capillaries, function

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form blood-brain barrier via endothelial tight junctions & paucity of pinocytotic vesicles

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fenestrated capillaries aka

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visceral capillaries

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fenestrated capillaries, characterized by

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continuous endothelium interrupted by pores/fenestrae

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pores of fenestrated capillaries sometimes have

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thin diaphragms over them

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location where fenestrated capillaries do not have diaphragms

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renal glomeruli

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renal glomerulus, histological appearance

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"tuft" of fenestrated capillaries

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sinusoidal capillaries aka

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discontinuous capillaries

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sinusoidal capillaries, characteristics

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specialized, very large lumens, many open fenestrations & absence of basal lamina, macrophages present in walls

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sinusoidal capillaries, location

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structures where fluid moves v. slowly, eg liver, lympoid, & hematopoietic organs

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liver, sinusoidal capillaries, characterization

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capillaries with macrophages that sit in the lumen, called Kupffer cells

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diabetes mellitus & microvascular disease, interaction

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capillary basal laminae (basement membrane) thickens abnormally, with evidence of increased laminin & collagen type IV synthesis by endothelial cells

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venules, definition

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small, postcapillary vessels

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venules, characterostcs

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very thin walls rel. to size of limen & rel. to paired arterioles; exchange vessels

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venules, histologically present next to

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arterioles

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venules, histological appearance

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thin wall with irregular lumen

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veins, characteristics

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thin intima, poorly developed media, v. well developed adventitia

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veins, small & medium sized, special feature

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have valves in their interiors

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valves in veins formed by

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subendothelial connective tissue and have covering of endothelium

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veins, large, special features

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thick intimas, relatively thin medias, & prominent, well-developed adventitias

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veins, largest, special characteristc

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have very prominent longitudinal bundles of smooth muscle in the adventitia

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distinguishing features, arteries v. veins

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large arteries have thick intimas, thick medias, & v. underdeveloped adventitias; large veins have thick intimas, thin medias, & v. well developed adventitias freq characterized by longitudinal bundles of smooth muscle

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distinguishing features, muscular aa

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appear v. round in cross section, thick wall rel. to diameter, prominent internal elastic lamina, v. well developed media

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distinguishing features, veins comp sized to muscular aa.

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seldom regularly shaped in cross section, wall thin rel. to vessel diameter, no prominent internal elastic lamina, thin media & thick adventitia

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lymphatic vessels, characteristics

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v. thin-walled, capillaries usually have larger irregular lumens (compared to vascular capillaries)

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larger lymphatics, characteristics

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do not have well-defined tunics; can have valves