Cardiovascular System Histology PDF

Cardiovascular histology Prof.Dr. B.Zühal Altunkaynak AIMS 1. Wall structure of the heart 2. Cardiac muscle cell types 3. Wall structure of arterial and venous system vessels 4. Functional differentiation in the vessels Overview of the cardiovascular system (CVS) Transport system Blood and lymph flu...

Cardiovascular histology Prof.Dr. B.Zühal Altunkaynak AIMS 1. Wall structure of the heart 2. Cardiac muscle cell types 3. Wall structure of arterial and venous system vessels 4. Functional differentiation in the vessels Overview of the cardiovascular system (CVS) Transport system Blood and lymph fluid Cells; nutrients; waste products; hormones; antibodies Overview of the cardiovascular system (CVS) Blood vessels work in two directions Artery takes blood to tissue Vein carries blood from tissue to heart Lymph vessels work one way, collect the exess intercellular fluid from the stroma and empty to lymph sacs. Heart Wall  It is a muscular pump  Three layers  Epicardium  Outside layer  This layer is also called as the visseral pericardium  Connective tissue layer  Myocardium  Middle and thickest layer  Mostly cardiac muscle  Endocardium  Inner layer  Endothelium and subendocardial layer Heart Wall Myocardium Endocardium Epicardium Epicardium Outermost layer of the heart Composed of connective tissue with nerves, vessels, adipocytes and an outer layer of mesothelium Covers and protects the heart Myocardium Thickest layer of the heart Thickest in left ventricle because must pump hard to overcome high pressure of systemic circulation Right atrium the thinnest because of low resistance to back flow Consist of cardiac muscle cells = myocytes – Different from smooth or skeletal muscle cells due to placement of nuclei, cross striations, and intercalated disks Intercalated disks – Junctional complexes that contain fascia adherens, desmosomes, and gap junction to provide connection and communication. – Bind myocytes and allow ion exchange to facilitate electrical impulses to pass Cardiac Myocytes Oval, with central single nuclei It has a striated structure Cells have collaterals Intercalar disc is located between cells Some cardiocytes in the atria have secretory granules (ANF) Cardiac Myocytes Branching myocytes Central nuclei Fibers with Cross Striations Intercalated discs It is at the border where the heart muscle cells meet Includes multiple gap-junctions There are also fascia adherens and desmosomes It is also found at the border where Purkinje cells adjoin. Gap-junctions serve to speed up the message Endocardium Innermost layer Composed of: – Simple squamous epithelium (endothelium) – Connective Tissue – Subendocardium: in contact with cardiac muscle and contains small vessels, nerves, and Purkinje Fibers. Purkinje Fibers Impulse conducting fibers Large modified muscle cells – Cluster in groups together – 1-2 nuclei and stain pale due to fewer myofibrils AV bundle branches located in the subendocardial connective tissue Blood Vessels: The Vascular System  Taking blood to the tissues and back  Arteries  Arterioles  Capillaries  Venules  Veins The Vascular System Figure 11.8b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Blood Vessels:  Three layers (tunics)  Tunica intima  Endothelium  Tunica media  Smooth muscle  Controlled by sympathetic nervous system  Tunica externa  Mostly fibrous connective tissue Tunica intima It is the layer in contact with blood Consists of single layer of squamous cell layer (= endothelium) Basal lamina Loose connective tissue ENDOTELIUM 1.Provide an exceptionally smooth surface 2.Regulate hemostasis, leukocyte adhesion and leukocyte transmigration 3.Secrete types II, IV, and V collagens, lamin, endothelin, nitric oxide, and von Willebrand factor. SUBENDOTHELIAL LAYER A subendothelial layer lies immediately beneath the endothelial cells. It is composed of loose connective tissue and a few scattered smooth muscle cells, both arranged longitudinally. Beneath the subendothelial layer is an internal elastic lamina (rich from the elastin) that is especially well developed in muscular arteries. Tunica media Circularly located smooth muscle cells Elastic laminas between rows of smooth muscle cells Elastic laminas with pores (with windows) (for diffusion) Extracellular matrix (ECM) elements in T.media are produced by smooth muscle cells (eg elastic lamina) T.media is thicker in the arteries Larger muscular arteries have an external elastic lamina, which is more delicate than the internal elastic lamina and separates the tunica media from the overlying tunica adventitia. Tunica adventitia Loose connective tissue, the outermost layer of the vessel Collagen, elastic fibers ECM = produced by fibroblasts Vaza vasorum, nerve fibers, lymph vessels T. Adventitia is thicker in veins Tunika adventisia is also called "Tunika externa" Classification of the Vessels I. Arteries II. Veins III. Capillaries Elastic Arteries the aorta and its major branches Also called conductive vessels There are 40-70 layers of the muscle cells and more elastic laminae Function: Keeping blood pressure constant in the arterial system Elastic Arteries Diameter:> 10 millimeters (mm) T. intima: endothelium, connective tissue, smooth muscle and elactic laminae T. media: smooth muscle, elastic lamellas T. adventitia: connective tissue; elastic fibers; Thinner than T.media; vaza vazorums extend to T.media Largest, conducting arteries – lead directly from heart, subject to high pressures Superior & inferior vena cava and their tributaries Pulmonary trunk & aorta and their major branches Vasa vasorum. Walls of the larger vessels, as the aorta, contain in the tunica adventitia a supply of microvasculature to bring O2 and nutrients to local cells too far from the lumen to be nourished by blood there. These arterioles (A), capillaries and venules (V) constitute the vasa vasorum (vessels of vessels). The adventitia of large arteries is also supplied more sparsely with small sympathetic nerves (N) for control of vasoconstriction. X100. H&E. Muscular Arteries Medium diameter arteries Also called distributive arteries They are the vessels that deliver blood to the organs Their diameters are variable Most anatomically named arteries are muscular arteries. Muscular Arteries Diameter: 2 - 10 mm T.intima: Endothelium Basal lamina Membrana elastica interna (most prominent) T.media: Smooth muscle Collagen fibers Elastic fibers (less than elastic artery) Membrane elastica externa (prominent in large muscular arteries) T.adventitia: Connective tissue Elastic fibers (less) Thinner than T.media ARTERIOLES Diameter: 10 - 100 µm (micrometers) T.intima: Endothelium basal lamina Connective tissue T.media usually consists of one or two layers of smooth muscle cells arranged in a spiral. No outer elastic lamina T.adventitia: Thin Difficult to differ from the connective tissue sheath  They are Resistance vessels VEINS Veins are capacitance vessels At any time, approximately 70% of the blood (circulating in the veins) is in the veins Veins begin with the postcapillary venule Postcapillary venules Diameter: 10 – 50 µm T. İntima: – Endothelium – Basal lamina – Pericytes: » Contractile » Can divide » May differ T.media: Ø T.adventitia: Ø Small Veins Medium-Sized Veins Large Veins Capillaries  Arising from the terminal ends of the arterioles are capillaries which form, by branching and anastomosing, a capillary bed (network) between the arterioles and the venules.  Electron micrographs have revealed three types of capillaries: (1) continuous, (2) fenestrated, and (3) sinusoidal General Structure of Capillaries  These endothelial cells are flattened, with the attenuated ends tapering to a thickness to 0.2 µm or less, although an elliptical nucleus bulges out into the lumen of the capillary.  The cytoplasm contains a Golgi complex, a few mitochondria, some rough endoplasmic reticulum (RER), and free ribosomes Continuous Capillaries  Continuous capillaries have no pores or fenestrae in their walls.  Continuous capillaries are present in muscle, nervous, and connective tissues, whereas in the brain tissue they are classified as modified continuous capillaries.  The intercellular junctions between their endothelial cells are a type of fasciae occludentes, which prevent passage of many molecules. In continuous capillaries, basal lamina covers the endothelium and surrounding pericyte cells PERICYTES: The origin is plurıpotent stem cells according to the vessel type and specifically depending on injury or growth factors; it turns into endotel cell fibroblasts Smooth muscle cell Fenestrated Capillaries  Fenestrated capillaries have pores (fenestrae) in their walls that are 60 to 80 nm in diameter and covered by a pore diaphragm.  These capillaries are found in the pancreas, intestines, and endocrine glands.  The pores in fenestrated capillaries are bridged by an ultrathin diaphragm.  An exception is the renal glomerulus, composed of fenestrated capillaries that lack diaphragms. diaphragms. glomerulus Sinusoidal Capillaries  Sinusoidal capillaries may possess discontinuous endothelial cells and basal lamina and contain many large fenestrae without diaphragms, enhancing exchange between blood and tissue.  The vascular channels in certain organs of the body, including the bone marrow, liver, spleen, lymphoid organs, and certain of the endocrine glands, are called sinusoids, irregular blood pools or channels that conform to the shape of the structure in which they are located. 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