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Cardiovascular system Heart Blood vascular system Artery, capillary, vein Pumping mechanism (+) Lymph vascular system Passive drainage Pumping mechanism (-) Heart: ventricle Fig. 8.1 Endocardium (E) Myocardium (M) Papillary muscles (P) chordae tendinae valves Epicardium (Epi) = visceral pericardium Coronary artery (A) Heart: endocardium & myocardium Endocardium A single layer of flattened epithelium endothelium of great vessels Contains vessels, nerves & conduction system Subendocardial tissue thin, collagen Endocardium & Myocardium Endocardium (E) Subendocardial tissue continuous with perimysium of cardiac muscle Masson’s trichrome: blue (collagen) red (cardiomyocytes) Epicardium Visceral pericardium Coronary vessels (opposing parietal pericardium) Fibroelastic tissue (F) with 8.3a Myo adipose tissue (A) connecting to myocardium (Myo) Lined w/ mesothelium (M) Epicardium Mesothelium (M) secrete serous fluid for lubrication Fibroelastic tissue adipose tissue, coronary vessels, and autonomic nerves Conduction system Specialized cardiomyocytes initiate contraction; conduct the impulse Sinoatrial node (SA node) Pacemaker at right atrium Influenced by autonomic nerves Atroventricular node (AV node) Atriventricular bundle (bundle of His) Divided in interventrivular septum Purkinje fibers Pass subendocardium to penetrate myocardium Purkinje fibers Rich in glycogen/mitochondria; no T-tubules Few myofibrils in irregular manners Desmosomes & gap junctions Larger, paler cytoplasm c.f. cardiomyocyte Sometimes binucleate Purkinje fibers Subendocardial Purkinje fibers in bundles Mallory-Azan SA node / AV node Small specialized myocardial fibers Little contractile proteins / glycogen (c.f. Prukinje fibers) Gap junctions to transmit electrochemical stimuli Embedded in dense vascular collagenous tissues / autonomic nerve endings Heart valve Vascular structures composed of connective tissue w/ overlying endocardium Heart valve H/E 8.6 EVG Lamina fibrosa (F) main bulk of valve Condensed at margin to form ring (valve annulus); part of cardiac “skeleton” Dense collagenous tissues Elastic fibers: particularly prominent in subendocardial area Cardiac “skeleton” Fibrous core of heart Fibrous ring of valves Collagenous tissues of Endocardium Myocardium Epicardium Chordae tendinae (to connect papillary muscle) Vessel Tunica intima Endothelium Basement membrane Tunica media Tunica adventitia Vasa vasorum Heart Endocardium Endothelium Subendothelium Myocardium Epicardium = Visceral pericardium Coronary arteries Pericardial cavity Parietal pericardium Vascular system: basic organization Tunica intima endothelium, basal lamina subendothelial layer smooth muscle cells Tunica media layers of smooth muscle cells elastin, reticular fibers, ECM Tunica adventitia longitudinal collagenous vasa vasorum, nervi vascularis Arterial system: Overview Systole: pumping of blood into artery expansion of arterial walls Diastole: recoil of arterial walls assists in maintaining blood pressure Recoil: a function of elastic tissue in arterial walls Blood flow: regulated by Ø of distributing vessels Circumfrentially smooth muscles Sympathetic nerves / adrenal medulla hormone Arterial system: Classification Determinants Elastin Smooth muscle Wall thickness relative to Ø Elastic arteries: as conduction tube Aorta, Innominate, Subclavian, Common carotid, Pulmonary Muscular arteries Radial, Femoral, Coronary, Cerebral a. Arterioles: terminal branches to supply capillary beds . in elastic fibers / - in smooth muscles as vessels become smaller (gradually) Elastic artery: Aorta Tunica intima Endothelial cell flat & elongate; long axis tight & gap junctions Subendothelial layer collagen and elastic fibers smooth muscle cells occasional macrophages Elastic artery: Aorta Tunica media thickest of three layer concentric fenestrated sheets of elastin (elastic lamella) collagenous tissues smooth muscle cells in layers collagen fibers & proteoglycan fibroblasts are not present Tunica adventitia – thin (relatively) Elastic artery: Aorta Tunica intima 8.7a endothelial cell subendothelial elastin smooth muscle cells Elastic artery: Aorta Tunica media elastin (black) collagenous tissues (red) smooth muscles (yellow) Elastic van Giesson Elastic artery: Aorta Tunica adventitia 8.7a Elastic van Giesson: black (elastic fibers) I: intima, M: media, A: adventitia collagen (red) elastic fibers fibroblasts & macrophages vasa vasorum penetrating into outer ½ of media nervi vascularis (nerve of vessel) Muscular artery Intima: very thin Media: thick layer of circumferential smooth m. internal elastic membrane (lamina) well defined fenestrated elastic sheet external elastic membrane (lamina) less defined, sometimes duplicated Adventitia: thick (relatively) Muscular artery IEL: internal elastic lamina EEL: external elastic lamina Adventitia: with elastic / collagen fibers Small muscular artery / Large arteriole Intima: thin, little supporting tissues, IEL Media: almost by smooth muscles Adventitia: as thick as Media; merge w/ surrounding tissues Absence of EEL Arteriole: lumen Ø < 0.3 mm (artificial definition) Small arterioles 8.10a Example: arterioles in dermis Intima: only nuclei of endothelium are visible Media: layers of smooth muscles Adventitia: merge with surrounding tissues Small arterioles Arrows: endothelium junctions basement membrane SM: smooth muscle in tunica media F: fibroblasts Capillaries Ø ~ RBC Intima: endothelium only connected by tight junctions Media and adventitia: absence Pericytes embrace capillary Capillaries Capillary: EM EM Fig. 8-13 M: marginal folds; C: collagen fibrils; BMp: BM of pericyte; F: fibroblast; P: pericyte; E: endothelium Exchange across continuous-type capillary Passive diffusion Gases, ions, low MW metabolites Pinocytotic vesicles Proteins, lipids Endothelial intercellular junctions Blood cells Fenestrated capillary In tissues with frequent exchange: intestine, endocrine glands, kidney F: fenestration, attenuation of endothelial cytoplasm BM: basement membrane; continuous over fenestrations Pericytes: rare in fenestrated capillaries Fenestrated capillary 8.14b Fenestration is traversed by electron-dense line (D); probably diaphragm Diaphragm: nature unknown; not in glomerular capillary of kidney Permeability: rapid passage of macromolecules smaller than plasma proteins Postcapillary / Collecting venules Postcapillary venules (PCV) Fig 8.16 Union of capillaries Similar structure to capillaries with wider lumen Sluggish blood flow Entrance / Exit of WBCs Collecting venules (CV) increase in lumen w/ pericytes Muscular venules (MV) w/ smooth muscle layer Very small arterioles (A) single smooth muscle layer Venous system Low pressure conducting system for returning of blood by Negative intra-thoracic pressure Contraction of skeletal muscles Valves in medium-sized veins Varicose veins due to failure of valves 3-layered arrangement with variations in elastic fibers / smooth muscles c.f. arterial system Smooth muscles in tunica media to control luminal diameter of muscular venules and veins Muscular venules (MV) / small veins MV: intima (w/o elastic fibers) + 1~2 layers of smooth m. Vein: thicker muscular layers poorly developed IEL V1, V2: MV; V3: small vein Vein: relative larger lumen compared to wall thickness Vein with valve Masson’s trichrome Semilunar projections of intima Fibroelastic tissues lined by endothelium on both sides 2 leaflets with free edges project in the direction of flow In veins > 2 mm in Ø; mainly in extremities Small- and medium-sized veins fig 8.19 Intima: endothelium only (some with folds) Media: 2 or more layers of circular muscles Adventitia: the broadest of wall; with longitudinal collagen fibers; merge with surrounding tissues Lumen > wall thickness (c.f. in arteriole: lumen~wall thickness) Medium vein most named vein femoral, renal veins Medium vein Intima: endothelium + elastic fibers Media: circular layers of smooth m. layers of collagen fibers some elastic fibers no IEL Elastic van Giesson: Smooth m. (yellow), collagen (red), elastin (black) Broad Adventitia: with lymphatics vasa vasorum (V) Large muscular vein (Vena Cava: with longitudinal layers of smooth muscles) lumen Small neurovascular bundle 8.21 A: arteriole V: venule N: nerves L: lymphatics Endothelial cells Structure Flat, polygonal cells, junctional complexes, basement membrane Pinocytotic vesicles Weibel-Palade bodies: membrane-bound organelles store von Willebrand factor (factor VIII) Functions Permeability barrier Metabolic functions Blood coagulation / thrombosis Blood flow Inflammatory reactions Trophic factors Microcirculation Fig 8.11 C: capillary, single endothelial layer; precapillary sphincter mechanism M: metarterioles, larger Ø capillaries, an outer discontinuous layer of smooth muscles S: arteriovenous shunts direct communication between arterioles & venules Small lymphatic vessels 8.22 Small lympatic thin layer of endothelium No RBC Plasma proteins Some lymphcytes Venule thin layer of endothelium RBC (+)
