CVS Histology Cardiac muscle & blood vessels PDF

Histology of cardiac muscle & blood vessels Ref: Junqueira’s basic histology, chapters 10, 11  Learning Objectives 1- Describe Microscopic structure of the wall of the heart 2- Identify characteristic Microscopic Features of the Cardiac muscle 3- Describe the Mi...

Histology of cardiac muscle & blood vessels Ref: Junqueira’s basic histology, chapters 10, 11  Learning Objectives 1- Describe Microscopic structure of the wall of the heart 2- Identify characteristic Microscopic Features of the Cardiac muscle 3- Describe the Microscopic structure of the wall of blood vessels 4- Compare and contrast the Microscopic structure of Arteries and Veins 5- Identify Microscopic characteristics of Various Types of Arteries 6- Identify Microscopic characteristics of Various Types of Veins 7- Compare and contrast the Microscopic structure of Various Types of Capillaries Cardiovascular system The cardiovascular system consists of: ❖Heart: which pumps blood throughout the body ❖Blood vessels: which are closed network of tubes that transport the blood. Types of blood vessels: ❑ Arteries: a series of efferent vessels that become smaller as they branch and their function is to transport blood away from the heart ❑ Veins: result from the convergence of capillaries into a system of larger channels that continue enlarging as they approach the heart, and their function is to transport blood toward the heart ❑ Capillaries: the smallest blood vessels, constituting a complex network of thin tubules that branch profusely in almost every organ they connect the arteries and veins, and through their walls the interchange between blood and tissues takes place  Heart The walls of all four heart chambers consist of three major layers or tunics: ❑ Endocardium (the internal layer) ❑ Myocardium (the middle layer) ❑ Epicardium (the external layer)  Endocardium Endocardium consists of: 1- Endothelium: Single layer of squamous endothelial cells 2- Subendothelial C.T: thin layer of loose connective tissue containing elastic, collagen fibers and smooth muscle cells The Subendocardial layer (SEn): Connective tissue layer Connects the subendothelial layer to the myocardium - SEn contains veins, nerves, and branches of the impulse-conducting SEn system of the heart (Purkinje fibers (P) - Note: The in-folding of Endocardium makes up the ‘valves’ of the heart  Myocardium It is the thickest of the tunics and consists of cardiac muscle cells arranged in layers that surround the heart chambers in a complex spiral ❑ Cardiac muscle characterized by: 1- Each fiber consist of elongated individual cells(cardiomyocytes) -The bundles of cells are branched tightly knit together (syncytium) by intercalated discs, interwoven in a fashion that provides a characteristic wave of contraction 2- Has Cross-striations like Skeletal ms. But fainter 3- Each cell has one or two centrally located pale-staining nuclei 4- Surrounded by a delicate sheath of endomysium containing a rich capillary network 5- The cell membranes of adjacent cardiac cells interlock with each other through ‘finger-like’, dark-staining junctions called the ‘intercalated discs’. Intercalated discs: - They are found only in cardiac muscle - Bind cardiac cells firmly together to prevent their pulling apart under constant contractile activity - They contain anchoring desmosomes and gap junctions - Desmosomes are abundant in The transverse regions of the step like intercalated disc - gap junctions found in the longitudinal portions of each disc -These gap junctions provide ionic continuity between adjacent cells and act as "electrical synapses" that allow cells of cardiac muscle to act as a syncytium 6- Cardiac muscle Contain numerous mitochondria which occupy 40% or more of the cytoplasmic volume, reflecting the need for continuous aerobic metabolism in heart muscle 7- Cardiac muscle cells contain numerous lipid droplets, Glycogen particles and Lipofuscin pigment granules  Epicardium It covers the external surface of the heart It corresponds to the visceral layer of the pericardium It is the site of the coronary vessels It is formed of: 1- Mesothelium: a layer of Simple Squamous-to-Cuboidal epithelium, which secrete a lubricate fluid to prevent fractioning between layers of the pericardium 2- loose connective tissue contains, coronary vessels, nerves, and many adipocytes  Blood Vessels ❑ Arteries: - Large Elastic arteries - Muscular arteries - Arterioles - Metarterioles ❑ Veins - Large veins - Medium and small veins - Venules (postcapillary venules, collecting venules, muscular venules) ❑ Capillaries - Continuous capillaries - Fenestrated capillaries - Sinusoids  Blood Vessels Blood vessels are usually composed of the following layers, or tunics: Tunica intima, Tunica media, Tunica adventitia Tunica intima Consists of: 1- Endothelium: Simple squamous cells connected by occluding junctions 2- Subendothelial layer of loose connective tissue 3- A layer of elastin (internal elastic lamina) formed of fenestrated elastic lamellae, which separates the intima from the media  Blood Vessels Tunica media (the middle layer): consists of: 1- Concentric layers of helically arranged smooth muscle cells 2- Elastic fibers and Reticular fibers interposed among the smooth muscle cells 3- external elastic lamina, separates tunica media from the tunica adventitia. Tunica adventitia or tunica externa consists of: 1- Connective tissue, Collagen (mainly) and Elastic fibers 2- Vasa vasorum ("vessels of the vessel"): small blood vessels to nourish the wall of big vessels large veins typically have more vasa vasorum than arteries. 3- Nervi vasorum, (autonomic nerves) Clinical Notes Atherosclerotic lesions: characterized by focal thickening of the intima proliferation of smooth muscle cells and connective tissue elements deposit of cholesterol in smooth muscle cells and macrophages (foam cells) These changes may extend to the inner part of the tunica media and occlude the vessel Coronary arteries are among those most predisposed to atherosclerosis. Aneurysm: It is a localized, blood-filled balloon-like bulge in the wall of a blood vessel It occurs due to weakening of tunica media of an artery by an embryonic defect, disease, or lesion It may rupture and brings severe consequences and may cause death.  Characteristics of Various Types of Arteries Artery Tunica intima Tunica media Tunica adventitia Elastic Represent 10%, Formed of - Represent 70% of Represent 20% (e.g aorta, Endothelium with basal the wall, formed of wall, formed Carotids, lamina of 1- 40- 70 of Pulmonary, Subendothelial layer with thin fenestrated elastic 1- Thin layer of Common Iliac) incomplete internal elastic laminae fibro-elastic lamina (not easily discerned) 2- Smooth muscle connective tissue - Contain few macrophages cells interspersed 2- Prominent - Has large ‘subendothelial between elastic vasa vasorum space’ (the ultimate site of fat laminae deposition in case of 3- Thin external Atherosclerosis). elastic lamina Muscular - Relatively thin, formed of - Represents - Represent (e.g Femoral, 1-Endothelium with basal lamina 50% of the 50% of wall Brachial, 2- Very thin Subendothelial layer wall, formed of formed of, radial……) with prominent internal elastic 1- Up to 40 layers 1-Thin layer of lamina of smooth muscle fibro-elastic C.T 2- Thick external 2-Less prominent elastic lamina vasa vasorum  Artery Tunica intima Tunica Tunica media adventitia Arteriole -Endothelium with basal lamina - 1 or 2 layers Very thin, )Arteries with a - Very thin Subendothelial layer of smooth inconspicuous, diameter less and may be absent muscle cells fibro-elastic than 0.5 mm( - No internal elastic lamina -No external connective tissue They have thick wall compared to elastic lamina -No vasa vasorum their lumen Metarteriole -Endothelium with basal lamina Smooth Sparse loose (smaller - Subendothelial layer (absent) muscle cells connective tissue branches of dispersed& arterioles that form supply blood to capillary bed) precapillary sphincter  Characteristics of Various Types of Veins Vein Tunica intima Tunica media Tunica adventitia Large veins -Endothelium with basal lamina, - 30% of wall, formed of: -70% of wall (Vena cavae, valves in some -few layers of circular Formed of: Portal vein, -Thin Subendothelial connective smooth muscle + longitudinal smooth subclavian vein tissue abundant connective muscle cells, collagen etc. - No internal elastic lamina tissue layers with fibroblasts - No external elastic - Numerous vasa lamina vasorum Medium -Endothelium with basal lamina, - Reticular and elastic Well developed (limb valves in some fibers, some smooth fibroelastic: veins)& -Thin Subendothelial connective muscle cells longitudinally small tissue arranged collagen Veins - No internal elastic lamina - No external elastic fibers with fibroblasts (Their diameter lamina less than 1 Cm) Venules -only Endothelium with basal - In Large venules: In Large venules: lamina (No Subendothelial Sparse connective tissue Some collagen& a few connective tissue) and some smooth muscle fibroblast - postcapillary venules, has cells pericytes surrounding the endothelial layer Small Vein Medium Vein Large Vein  postcapillary venules (range in diameter Postcapillary from 15 to 20 µm) are similar structurally to venule capillaries (No Tunica media or Tunica adventitia) postcapillary venules converge into larger collecting venules which have more contractile cells With greater size the venules become surrounded by recognizable tunica media with two or three smooth muscle layers and are called muscular venules Muscular Collecting venule venule  Difference between arteries& veins Large Artery Large Vein Tunica -No valves -Folded& form intima valves Tunica -Thick -Thin media -more elastic - less elastin& laminae no laminae - many layers - few layers of of smooth smooth muscle muscle Tunica Thin Thick& well- adventitia developed - Contains longitudinal bundles of smooth muscle Medium Artery Medium Vein  Capillaries Are composed of a single layer of endothelial cells rolled up in the form of a tube (No Tunica media or adventitia) The average diameter of capillaries varies from 5 to 10 µm and their individual length is usually not more than 50 µm At various locations along capillaries and postcapillary venules are cells called pericytes Pericytes are cells with long cytoplasmic processes surrounding the endothelial layer and have contractile function Also, they can proliferate and differentiate to form both tunica media of new blood vessels and cells with various other functions Characteristics of Various Types of Capillaries Continuous capillaries Fenestrated Sinusoids capillaries -The most common type - found in the - found in the liver, of capillary kidney, the spleen, some - found in muscle intestine and the endocrine organs, tissue, connective endocrine glands and bone marrow tissue, exocrine - characterized by - irregularly glands, and nervous the presence of shaped and have tissue small circular diameters as large as - characterized by the fenestrae 30–40 µm distinct continuity of through the - endothelial cells have the endothelial cells squamous large fenestrae in its wall endothelial cells without - Each fenestra diaphragms covered by a - cells form a diaphragm discontinuous layer - The basal lamina and are separated is continuous, from one another by covering the wide spaces; the fenestrae basal lamina is also discontinuous Fenestrations of endothelial cell Sinusoid Vasa vasorum are present in which of the following layers of the wall of blood vessel? a) Internal elastic lamina b) Subendothelium c) Tunica media d) Adventitia Internal and external elastic lamina are found in the wall of which of the following? a) Large arteries b) small veins c) Arterioles d) Venules Which of the following layers of the wall of the heart is homologous to adventitia of blood vessels? a) Endocardium b) Subendocardium c) Epicardium d) Myocardium Which one of the following vessels has a recognizable tunica media? a) Post capillary venule b) Thoroughfare channel c) Muscular venule d) Continuous capillary https://youtu.be/XhOi4yOFX-c?si=1u9J9T1iOPBywv8w