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HEART AND VASCULAR SYSTEM CAPILLARIES Function = exchange of gas, nutrients, metabolites, water Structure = Endothelium +pericyte + basement membrane Pericyte =undifferentiated cells that becomes smooth muscle or fibroblast CAPILLARY SYSTEMS Vary regarding: Diameter 3-4 μm to 30-40 μm Abundance Heart, liver > Tendon Arterio-venous shunts Direct connections between arterial + venous system Types of endothelium 1. Continuous: 1. Most common 2. Basement membrane is present 3. Uninterrupted lining with tight junctions 2. Fenestrated: 1. Found in gut, kidney, endocrine glands 2. Basement membrane is present 3. Large pores From: Wheater’s Functional Histology, B Young and JW Heath 3. Discontinuous: No basement membrane Large diameter Continuous interface between lumen and surrounding tissue Sinusiods of liver, spleen and bone marrow ARTERIES AND VEINS Inner Tunica intima: endothelium Tunica media: elastic and/or smooth muscle Tunica adventitia: collagen, elastic fibres Outer ARTERIES ARTERIOLI Control blood flow by dilation or constriction Tunica intima Endothelium Lamina elastica interna (2 or more layers of a fenestrated elastic membrane) Tunica media Few layers smooth muscle cells Tunica adventitia Loose connective tissue MUSCLE/MEDIUM SIZED ARTERIES Blood flow to organs Tunica intima: 1. 2. Endothelium Either Lamina elastica interna or Subendothelial layer of thin loose connective tissue MUSCLE/MEDIUM SIZED ARTERIES Tunica media: 1. 2. 3. 4. Most prominent Spirally arranged smooth muscle Little connective tissue Lamina elastic externa MUSCLE/MEDIUM SIZED ARTERIES Tunica adventitia: Usually thinner, loose connective tissue lamina elastica interna smooth muscle of tunica media lamina elastica externa ELASTIC ARTERIES Pulmonary trunk/aorta + major branches Stretch/systole/heart contracts/blood ejected from ventricles – diastole/recoil Tunica intima: 1. 2. Endothelium Subendothelium layer 3. Lamina elastica interna ELASTIC ARTERIES Tunica media: 1. 40-70 fenestrated concentric layers of elastic fibre 2. Amorphic ground substance with collagen & smooth muscle cells Tunica adventitia: 1. Irregular connective tissue, few elastic fibers endothelium tunica intima subendothelium layer lamina elastica interna tunica media tunica adventitia THE VENOUS SYSTEM Thinner walls than arteries, larger lumen VENULES Tunica intima: Endothelial layer Tunica media: Pericytes ____ smooth muscle fibres Tunica adventitia: Longitudinal collagen fibres SMALL /MEDIUM VEINS Small= 0.2-1 mm + Medium =1-10 mm Tunica intima: 1. Endothelium 2. Subendothelial layer 3. Lamina elastica interna (poorly developed) Tunica media: 1. Layers of circular smooth muscle fibres 2. Loose connective tissue SMALL /MEDIUM VEINS Tunica adventitia: 1. Thick, longitudinal collagen fibres 2. 3. 4. Loose connective tissue Elastic fibres Fibroblasts and macrophages Valves Folds intima strengthened with connective tissue & elastic fibres NB! Note difference to heart valve structure LARGE MUSCULAR VEINS Tunica intima: Similar to medium veins Tunica media: Similar to medium veins Tunica adventitia: Thick, bundles longitudinal collagen Elastic fibres Smooth muscle Numerous vasa vasorum tunica intima endothelium subendothelial layer lamina elastica interna collagen fibers smooth muscle bundles tunica media tunica adventitia From Basic Histology, 4th Ed, LC Junquera, J Carneiro LYMPHATIC SYSTEM Begin blind in connective tissue as lymph capillaries Large pores- cells, bacteria and macromolecules LYMPH CAPILLARIES Similar structure to blood capillaries Large lumen No pericytes Basal membrane is often absent SMALL/LARGER LYMPH VESSELS Layers difficult to distinguish Tunica intima: Similar to large veins Tunica media: Concentric/diagonal muscle bundles Tunica adventitia: 1. Longitudinal/diagonal bundles of smooth muscle 2. Bundles of collagen fibres 3. Outer layer of collagen fibres From Basic Histology, 4th Ed, LC Junquera, J Carneiro NERVE SUPPLY Most blood vessels have a well developed nerve supply Efferent, Afferent, Motor, Baro and chemoreceptors HEART Tunica intima= Endocardium (inner) Tunica media = Myocardium (middle) Tunica adventitia= Epicardium (outer) pericardium Epicardium (t.a.) Myocardium (t. m.) Subendocardium (s.e.) Endocardium (t.i.) A: ENDOCARDIUM (inner/contact with blood) 1. 2. 3. Endothelium Delicate layer of collagenous tissue Robust fibro-elastic layer -contains smooth muscle cells B: SUBENDOCARDIUM 1. Loose connective tissue 2. 3. 4. Fat cells Purkinje fibers Small blood vessels+ nerves + branches of conducting system C: MYOCARDIUM Bundles of cardiac muscle (thickest) Pericardium Epicardium (t.a) Myocardium (t. m.) Subendocardium (s.e.) Endocardium (t.i.) D: EPICARDIUM (Outer) External 1. 2. 3. 4. Mesothelium - flattened epithelial cells Fibroelastic tissue (thin) Broad layer adipose tissue Coronary vessels + autonomic nerves pass through the epicardium to supply the myocardium pericardium Epicardium (t.a.) Myocardium (t. m.) Subendocardium (s.e.) Endocardium (t.i.) SKELETON OF THE HEART Thick fibrous rings at the origin of aorta + pulmonary arteries Connected by trigonum fibrosum with rings at arterio-ventricle openings VALVES Plate/flap of fibroelastic connective tissue Extending from the fibrous skeleton Covered by endocardium CONDUCTING SYSTEM The coordinated contraction of the myocardium is mediated by a specialized conducting system of modified cardiac muscle fibers 1. SINOARTRIAL (SA) NODE - PACEMAKER REGION (Right atrium (top)) 2. ATRIOVENTRICULAR (AV) NODE (Right atrium (bottom)) 3. ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS) (interventricular septum) SA Node AV Node HOW DOES IT WORK? Impulse starts at SA node Spreads throughout atrium Causes contraction Blood into ventricles Then! Impulse spreads to AV node Passed via bundle of Hiss Divides into smaller branches bundles of Purkinje fibers Then! Passes to subendocardial connective tissue Penetrates the ventricular myocardium Depolarization and contraction SA Node LA RA Bundle of Hiss AV Node RV Right branch LV Left branch A: SINOARTRIAL (SA) NODE Group of collagen & elastic fibres Well developed capillary system In middle: Nodal myocyotes or P cells Borders on narrow transitional cells Border of the Purkinje Cardiac muscle cells Region contains many axons of sympathetic and parasympathetic nervous system Impulse moves from the → P-cells (Pale cells/pacemakers) → Transitional cells:fewer myofibrils → Purkinje cells: large, abundant glycogen, few myofilaments, extensive gap junctions → Cardiac muscle cells B: ATRIOVENTRICULAR(AV) NODE Right atrium, microscopically similar to the SA node C: ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS) Longitudinal transitional cells of AV node Down the interventricular septum Divide into left and right bundle Moves through subendocardium C: ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS) Half way down septum, transitional cells are replaced with Purkinje cells Two branches divide further, form the Purkinje cell network Contact between Purkinje cells and cardiac muscles cells of myocardium Practical Consider your practical as a self study period You will not be allowed into a practical without your textbooks (checks at door) Register Must be present for the first 30 minutes