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23 Cards in this Set

  • Front
  • Back

General layers of the heart and vessels

Heart- endocardium, myocardium, epicardium


Vessels- Tunica intima, tunica media, tunica adventitia

Layers of the heart

Endocardium- made up of a layer of endothelial cells and a sub endothelial layer of connective tissue (containing nerves, veins and Purkinje fibres)


Myocardium- highly vascularised, made up of cardiac muscles


Epicardium- Made up of fibroelastic connective tissue, containing blood vessels, lymphatics, nerves and adipose tissue, covered by a layer of simple squamous epithelium

Features of cardiac muscle

Branched


Striated


Involuntary


Centrally placed nucleus


Adjacent cardiac muscles form a syncytium to act in a coordinated contraction through intercalated discs (allows rapid transmission of electrical impulses, consists of three cell to cell junctions- gap, adhering and desmosomes)

Purkinje fibres features

Found in endocardium (specifically sub-endocardium)


Specialised cardiac muscle cells, generates and conducts impulses to created synchronised contraction


Larger, has more glycogen and mitochondria, fewer myofibrils, no t-tubules and no intercalated discs (only desmosomes and gap junctions) compared to cardiac muscle

features of the tunica intimate (general)

Innermost layer


One layer of simple squamous epithelium- known as endothelial


Encircled by a layer of sub endothelial- made up of loose connective tissue


Internal elastic lamina, a fenestrated sheet of elastic fibres, separates intima from tunica media


Role of endothelial

(found in tunica intimate)


regulates transport of substances from lumen to vessel wall


controls local clotting through secretion of soluble factors


enables migration of WBCs from blood to tissue

Tunica media

middle layer


consists of circularly arranged smooth muscle


contraction of this regulates blood flow


if muscles are weakened, walls become dilated, causing aneurysms


Matrix consists of elastic and collagen fibres


external elastic lamina separates tunica media from the outer tunica adventitia

tunica adventitia

outermost layer


connective tissue layer- many collagen and elastin fibres


blends in with surrounding connective tissue, providing anchoring


contains vasa vasorum, small nutrient arteries and veins providing blood supply to walls of larger vessels

types of arteries

elastic, mucular, arterioles

elastic arteries

also known as large/conducting arteries


transports blood away from heart


tunica intima is thick, made up of endothelium with thick loose connective tissue sublayer


tunica media made up of 50 - 70 concentrically arranged fenestrated elastic membranes (laminae) with smooth muscle cells and collagen fibres between them (internal and external lamina not readily visible)

Why do elastic arteries need to be elastic

large diameter, yet walls are very thin


undergo expansion with each systole


have to recoil during diastole to maintain BP and continue to move blood

Muscular artery

also known as medium or distributing, as it distributes blood to various parts of the body


thick wall (25% of diameter)


tunica intima consists of endothelium and flattened sub endothelial layer of collagen and elastic fibres


tunica media is the major identifying characteristic- thick smooth muscular layer with 10-40 layers of smooth muscle, w/ much less elastic fibres, external elastic lamina readily recognisable in larger elastic arteries


tunica adventitia is well developed, contains mainly collagen, elastin and vasa vasorum

Features of arterioles

small arteries, 0.004 - 0.4mm in diameter


delivers blood to capillaries


retain general features of muscular arteries


regulates blood flow to capillaries by met arterioles, which connect small arterioles to capillaries- junctions are surrounded by a ring of smooth muscle, which act as a pre capillary sphincters and can cause arteriovenous shunting (important in thermoregulation)


Tunica intima- very thin sub endothelial layer of loose connective tissue


tunica media- 1 - 3 layers of smooth muscle (key feature!)


tunica adventitia- fairly prominent

capillaries

usually 7 - 9 um in diameter


walls consist of a single layer of endothelium, surrounded by a basement membrane


pericytes found between basement membrane and endothelium


Capillaries allow passive diffusion + pinocytosis of nutrients and wastes


WBCs can move through intercellular junctions (diapedesis)


Types of capillaries

Continuous


Fenestrated


Discontinuous

continuous capillaries

most common, found in muscle, fat, connective tissue, lungs, brain


no pores or spaces between cells in walls, tight junctions between cells in walls


continuous basement membrane


cells can move in.out by diapedesis


macromolecules can pass through endothelial cells by pinocytotic vesicles


fenestrated capillaries

found in tissues where rapid exchange occurs (glomeruli of kidney, villi of intestinal wall)


have pores which penetrate endothelial cells, covered by a thin diaphragm (not found in glomeruli)


have a continuous basement membrane

discontinuous capillaries

aka sinusoids


larger, more irregularly shaped


found in liver/haematopoietic organs (spleen, bone marrow)


gaps between adjacent endothelial cells


lacks basement membrane


no continuous lining between lumen and surrounding tissue- not a barrier to blood constituents


phagocytic cells are present (kupffer in liver)

Types of veins

venules, medium + large

venules

formed by the confluence of capillaries


tunica intima lacks subendothelial layer


tunica media consists of 1 -2 layers of muscle fibre, increases with size


tunica adventitia fuses with surrounding connective tissue

medium and large veins

all three tunica present


intima- well developed, but thin, folds in endothelium forms valves


media- thin, muscular, can regulate diameter (useful due to low BP)


adventitia- predominant layer, thickest and best developed, spirally arranged collagen and elastic fibres, longitudinal smooth muscle and more vasa vasorum than arteries

Lymphatic capillaries

thin endothelial lined tubes that...


- drain interstitial fluid


-resemble blood capillaries, but begin as blind-ending vessels, have incomplete.absent basement membranes, lack pericytes, have larger irregular lames, lack tight junctions, have anchoring filaments which contract to allow fluid to enter and lacks RBCs

medium/large lymphatic vessels

resemble veins, consist of three basic laters containing much less smooth muscle.elastic or collagen fibres


have valves


(but still lacks RBCs)