ANAT2411-2023 - Cardiovascular System - Lecture Slides - RS.pdf

ANAT2241 Histology: Basic & Systematic Cardiovascular System Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter...

ANAT2241 Histology: Basic & Systematic Cardiovascular System Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Wheather's online): Cardiovascular System Textbook chapter (Junqueira’s Basic Histology: Text and Atlas, 16e online): Cardiovascular System University of Michigan Histology and Virtual Microscopy Learning Resources Chapman Histology https://www.youtube.com/channel/UCvSvCkHjCbHn8aGd6OPno_A/featured Learning Objectives 1. To understand the function and components of circulatory system 2. To understand the histological features of the heart (epicardium, myocardium and endocardium) 3. To understand the architecture of vascular structures 4. To understand the tunica intima, media and adventitia in arteries and veins 5. To understand the types of capillaries and sinusoids and their features 6. To understand the histological features of lymphatic vessels Circulatory System Cardiovascular System Function of circulatory system: • Pumping and directing blood to all tissues Composed of two systems: 1- Blood vascular system (or cardiovascular system 2- Lymphatic vascular system Total length of vessels in human body: • 100,000-150,000 kilometers Lymphatic Vascular System Blood Vascular System / Cardiovascular System Components: 1- Heart: propelling blood through the system 2- Arteries: a series of vessels efferent from the heart carrying blood to the tissues 3- Capillaries: sites of exchange between blood and tissues 4- Veins: carrying blood from tissues to the heart to be pumped again Blood Circulation Blood circulation: • Vena cava -> Right atrium -> right ventricle -> pulmonary arteries -> lungs -> pulmonary veins -> left atrium –> left ventricle -> aorta 1- Systemic circulation 2- Pulmonary circulation Heart o A modified large vessel o A muscular four-chambered with rhythmic contraction to pump the blood through the circulatory system • Ventricles: propelling blood to the pulmonary and systemic circulation • Atria: receiving blood from the body and the pulmonary veins Anatomy of the Heart Fibrous pericardium Serous pericardium: 1- Parietal layer of serous pericardium (parietal pericardium) 2- Visceral layer of serous pericardium (visceral pericardium or epicardium) Heart wall: 1- Endocardium 2- Myocardium 3- Epicardium (visceral pericardium) Anatomy of the Heart Heart chambers: 1- Atria: • Right atrium • Left atrium 2- Ventricles: • Right ventricle • Left ventricle Heat valves: 1- Atrioventricular valves • Right atrioventricular (tricuspid) valves • Left atrioventricular (bicuspid/Mitral) valves 2- Semilunar valves • Pulmonary valves • Aortic valves Septa: 1- Atrial/interatrial septum 2- Ventricular/interventricular septum Anatomy of the Heart Heart Histological structure of the heart: 1- Internal layer: endocardium 2- Middle layer: myocardium 3- External layer: epicardium (or visceral layer of the pericardium) (X34; H&E staining; Atrial wall) • *: atrial chamber • En: endothelium • CT: loose connective tissue • Ep: epicardium Histological Structure of the Heart 1- Internal layer: endocardium a. Inner layer: endothelium and supporting connective tissue (lamina propria) b. Middle (myoelastic) layer: smooth muscle fibers (cells) and connective tissue c. Outer layer: subendocardial layer containing Purkinje fibers (X200; H&E staining; Ventricular wall) • En: endothelium • SEn: subendocardial layer • P: Purkinje fibers • M: myocardium (X200; H&E staining; Atrial wall) Histological Structure of the Heart (X35; H&E staining; Ventricular wall) • Arrowheads: endothelium (X120; H&E staining; Ventricular wall) • End: endothelium • SMC: smooth muscle cells • DCT: dense connective tissue • PF: Purkinje fibers • CMF: cardiac muscle fibers Histological Structure of the Heart (X180; H&E staining; Atrial wall) • *: atrial chamber • En: endothelium • CT: connective tissue Histological Structure of the Heart 2- Middle layer: myocardium • Thickest layer • Consists mainly of cardiac muscle • Much thicker in the wall of the ventricles particularly the left one than in the atrial walls (X200; H&E staining; Ventricular wall) • En: endothelium • SEn: subendocardial layer • P: Purkinje fibers • M: myocardium (X100; H&E staining; Atrial wall) • Ep: epicardium • Mes: mesothelium • CT: connective tissue • N: nerves • F: fat • M: myocardium (X200; H&E staining; Atrial wall) Histological Structure of the Heart 3- External layer: epicardium / visceral layer of the pericardium • A simple squamous mesothelium • Supported by a layer of loose connective tissue containing adipose tissue (X100; H&E staining; Atrial wall) • Ep: epicardium • Mes: mesothelium • CT: connective tissue • N: nerves • F: fat • M: myocardium Histological Structure of the Heart (X28; H&E staining; Outer layer of ventricular wall) • NF: nerve fibers • BV: blood vessels (X28; H&E staining; Ventricular epicardium) • Arrows: endothelial cells Specialized Structures within the Heart 1- Cardiac skeleton: dense irregular connective tissue 2- Conducting system of the heart Conducting System Cardiac Skeleton Cardiac Skeleton Features: o Dense irregular connective tissue o Forms parts of interventricular and interatrial septa o Surrounds all valves of the heart o Extends into the valve cusps and the chordae tendineae Cardiac Skeleton Function: o Separates the musculature of the atria from that of the ventricles o Anchoring and supporting the heart valves o Providing firm points of insertion for cardiac muscle o Helping coordinate the heartbeat by acting as electrical insulation between atria and ventricles (X20; Masson trichrome staining; Valve leaflet) • Arrow: cusp of AV valve • C: connective tissue • CT: chordae tendineae • En: endocardium • M: myocardium • A: atrium • V: ventricle Conducting System of the Heart Features: o Generates and propagates waves of depolarization to stimulate rhythmic contractions o Modified cardiac muscle cells (X20; Mallory-Azan staining; ventricular wall containing the conducting system) • E: endocardium • N: nuclei of Purkinje fibers • Arrow: intercalated discs • M: myocardium≈ Conducting System of the Heart Components: a. Nodes: i. Sinoatrial (SA) node / Pacemaker ii. Atrioventricular (AV) node Features of the cells in nodes: • Smaller size • Fewer myofibrils • Fewer intercalated discs b. Fibers i. Internodal pathway ii. Atrioventricular bundle / bundle of His iii. Subendocardial conducting network of cardiac muscle fibers: Purkinje fibers • Pale-staining fibers • Larger than the adjacent contractile fibers • contain large amounts of glycogen Wall of vessels 1- Innermost tunica/layer: Intima 2- Middle tunica/layer: media 3- Outer tunica/layer: adventitia or tunica externa Wall of vessels: (1) Intima Components: • • • Endothelium Subendothelial layer of loose connective tissue sometimes containing smooth muscle fibers Internal elastic lamina: in arteries (X122; Elastic staining; a: Aorta; b: Vena cava) • I: intima • IEL: internal elastic lamina • M: media • EF: elastic fibers • A: adventitia • V: vasa vasorum Endothelial Cells Function of endothelial cells: 1- Maintaining a selectively permeable barrier between blood and interstitial tissue fluid 2- Antithrombogenic (inhibitory to clot formation) barrier 3- Determining when and where white blood cells leave the circulation for the interstitial space of tissues 4- Secretion of a variety of paracrine factors for vessel dilation, constriction, and growth of adjacent cells Wall of vessels: (2) Media Composed of: • Concentric layers of helically arranged smooth muscle cells • Variable amounts of elastic fibers and elastic lamellae, reticular fibers, and proteoglycans interposed among the muscle fibers • External elastic lamina: separating media from the outermost tunic; in arteries (X122; Elastic staining; a: Aorta; b: Vena cava) • I: intima • IEL: internal elastic lamina • M: media • EF: elastic fibers • A: adventitia • V: vasa vasorum Wall of vessels: (3) Adventitia / Tunica Externa Features: • Connective tissue consisting principally of type I collagen and elastic fibers • Continuous with and bound to the stroma of the organ through which the blood vessel runs (X122; Elastic staining; a: Aorta; b: Vena cava) • I: intima • IEL: internal elastic lamina • M: media • EF: elastic fibers • A: adventitia • V: vasa vasorum Vasa Vasorum Vasa vasorum: vessels of the vessel • Arterioles, capillaries, and venules in the adventitia and outer part of the media • Provide metabolites to cells in those tunics in larger vessels because the wall is too thick to be nourished solely by diffusion from the blood in the lumen • Large veins commonly have more vasa vasorum than arteries (X100; H&E staining; Adventitia of a large artery) • A: arterioles • V: venules • N: sympathetic nerves • SM: smooth muscle fibers • E: elastic lamellae Vasomotor Nerves Vasomotor nerves: • The adventitia of larger vessels also contains a network of unmyelinated autonomic nerve fibers • Release the vasoconstrictor norepinephrine • Greater density of this innervation in arteries than in veins (X100; H&E staining; Adventitia of a large artery) • A: arterioles • V: venules • N: sympathetic nerves • SM: smooth muscle fibers • E: elastic lamellae Elastic Arteries/Conducting Arteries o Aorta o Pulmonary artery o Their largest branches Tunica intima: • Well developed, with many smooth muscle cells in the subendothelial connective tissue • Internal elastic lamina: more welldefined than the elastic laminae of the media Tunica media: • Thick; in which elastic lamellae alternate with layers of smooth muscle fibers • Most prominent feature of elastic arteries Adventitia: • Much thinner than the media (X200; PT staining; Elastic artery) • I: intima • M: media • A: adventitia Muscular Arteries / Distributing Arteries o Distribute blood to the organs o Help regulate blood pressure by contracting or relaxing the smooth muscle in the media Intima: • Thin subendothelial layer • A prominent internal elastic lamina Media: • May contain up to 40 layers of large smooth muscle cells interspersed with a variable number of elastic lamellae • External elastic lamina: only in the larger muscular arteries Adventitia: • Contains lymphatic capillaries, vasa vasorum, and nerves (X100; H&E staining; Muscular artery) • E: endothelial cells • IEL: internal elastic lamina • SM: smooth muscle • V: vasa vasorum Small Arteries o Three or four layers of medial smooth muscle o adventitia: very thin and inconspicuous (X100; H&E staining; Muscular artery) • E: endothelial cells • IEL: internal elastic lamina • SM: smooth muscle • V: vasa vasorum Arterioles • • Beginning of an organ's microvasculature Less than 0.1 mm in diameter, with lumens approximately as wide as the wall is thick • Subendothelial layer: • Very thin • No elastic lamina • Media: circularly arranged smooth muscle cells (only one or two smooth muscle layers) • Adventitia: very thin and inconspicuous (X100; H&E staining; Microvasculature) • A: Arterioles • C: capillaries • V: venules • L: lymphatic vessels Capillaries • • • • Permit and regulate metabolic exchange between blood and surrounding tissues Smallest blood vessels Function in networks called capillary beds Density of the capillary bed: related to the metabolic activity of the tissues • High metabolic rates, more capillary bed: such as the kidney, liver, and cardiac and skeletal muscle • Low metabolic rates, less capillary bed: such as smooth muscle and dense connective tissue Structure of Capillaries • Simple layer of endothelial cells rolled up as a tube surrounded by basement membrane • Average diameter of capillaries: 4-10 micrometers • Individual length: usually not more than 50 micrometers • Make up over 90% of the body’s vasculature • Exchange site of water and solutes between blood and tissues • Major structural variations in capillaries are related to the level of metabolic exchange Histologic types of capillaries 1- Continuous capillaries 2- Fenestrated capillaries 3- Discontinuous capillaries / sinusoids Continuous capillaries o Many tight, well-developed occluding junctions between slightly overlapping endothelial cells o Continuity along the endothelium o Well-regulated metabolic exchange across the cells o Found in muscle, connective tissue, lungs, exocrine glands, and nervous tissue Continuous capillaries Fenestrated capillaries o Sieve-like structure that allows more extensive molecular exchange across the endothelium o Endothelial cells are penetrated by numerous small circular openings or fenestrations o Membrane however is continuous and covers the fenestrations o Found in organs with rapid interchange of substances between tissues and the blood, such as the kidneys, intestine, choroid plexus, and endocrine glands Fenestrated capillaries Discontinuous capillaries / sinusoids o Permit maximal exchange of macromolecules as well as allow easier movement of cells between tissues and blood o Endothelium here has large perforations without diaphragms and irregular intercellular clefts, forming a discontinuous layer with spaces between and through the cells o Have highly discontinuous basement membranes o Found in the liver, spleen, some endocrine organs, and bone marrow Venules o Postcapillary venules: • Similar to capillaries with pericytes but larger • Primary site at which white blood cells adhere to endothelium and leave the circulation at sites of infection or tissue damage o Collecting venules: • Formed by the convergence of postcapillary venules • Have more distinct contractile cells o Muscular venules • Surrounded by a recognizable tunica media with two or three smooth muscle layers Veins o Carry blood back to the heart from microvasculature all over the body o Forces help veins move blood toward the heart: • Contraction of the smooth muscle fibers in the media • External compressions from surrounding skeletal muscles and other organs Small Veins & Medium Veins o With diameters of 10 mm or less o Usually located close and parallel to corresponding muscular arteries o Tunica intima: • Usually thin o Tunica media: • Small bundles of smooth muscle cells mixed with a network of reticular fibers and delicate elastic fibers o Tunica adventitia • Collagenous thick layer • Well developed Large Veins o Big venous trunks, paired with elastic arteries close to the heart o Tunica intima: • Well-developed intimal layers o Tunica media: • Relatively thin media with alternating smooth muscle and connective tissue o Tunica adventitia: • Thicker than the media in large veins and frequently contains longitudinal bundles of smooth muscle o Both the media and adventitia: • Contain elastic fibers o Internal elastic lamina like those of arteries may be present Valves in Veins o An important feature of large and medium veins o Especially numerous in veins of the legs o Consist of: • Thin, paired folds of the tunica intima projecting across the lumen • Rich in elastic fibers • Covered on both sides by endothelium Lymphatic Vascular System Lymphatic Vascular System Returns fluid from tissue spaces all over the body to the blood o Lymphatic capillaries: • Beginning of the system • Very thin-walled, closed-ended tubules • Very thin endothelial cells, which lack tight junctions and rest on a discontinuous basal lamina • Fine anchoring filaments of collagen extend from the basal lamina to the surrounding connective tissue • Collect excess interstitial fluid from the tissue spaces as lymph • Returning lymph to the blood • Merging to form larger lymphatic vessels • Connect with the blood vascular system and empty into the large veins Lymphatic Vessels o Formed by the convergence of lymphatic capillaries o Thin walls and increasing amounts of connective tissue and smooth muscle that never form clearly distinct outer tunics o Have valves comprised of complete intimal folds o Lymph nodes interposed in the path of these larger lymphatic vessels o Large lymphatic trunks: thoracic duct & right lymphatic duct • • Similar to that of small veins Adventitia: § Relatively underdeveloped, but contains vasa vasorum and a neural network Lymphatic Vessels o Lymph • Usually rich in lightly staining proteins • Does not normally contain red blood cells • Lymphocytes and other white blood cells may normally be present • No lymph in bone marrow and most of the CNS