Cardio Histology 10-1 PDF

Histology Cardiovascular system Name: dr. Khalid Alyodawi Email: [email protected] Lecture objectives Blood vessel types: Arteries, capillaries, and veins, including their distinct structural features and functional roles. The heart's structure and function: Its layers, muscle, conducti...

Histology Cardiovascular system Name: dr. Khalid Alyodawi Email: [email protected] Lecture objectives Blood vessel types: Arteries, capillaries, and veins, including their distinct structural features and functional roles. The heart's structure and function: Its layers, muscle, conduction system, and valves. The lymphatic system: Its structure and role in fluid movement and immunity. Type of blood vessels Permit exchange between Distribute blood to Arteries Capillaries blood and tissues tissues Veins Return blood to heart Structural Plan of Blood Vessels 1. The tunica intima is the innermost layer and has one layer of endothelial cells supported by a thin subendothelial layer of loose connective tissue with occasional smooth muscle cells. In arteries, this layer is separated from the media by an internal elastic lamina, the most external component of the intima. 2. The tunica media is the middle layer, consisting chiefly of concentric layers of helically arranged smooth muscle cells, variable amounts of elastic fibres and reticular fibres of collagen type III, proteoglycans, and glycoproteins. In arteries, the media has a thinner external elastic lamina, which separates it from the tunica adventitia. 3. The tunica adventitia or tunica externa consists principally of type I collagen and elastic fibres. This adventitial layer is gradually continuous with the stromal connective tissue of the organ through which the blood vessel runs. Arteries basic structure Tunica Intima Endothelium Basement membrane Delicate Connective T. Tunica Media Muscle Elastic T. Tunica Adventitia Connective Tissue Large Elastic Arteries The intima is thicker than the corresponding tunic of a muscular artery. The media consists of elastic fibres and a series of concentrically arranged perforated elastic laminae whose number increases with age (there are about 40 in the newborn and 70 in the adult). Between the elastic laminae are smooth muscle cells, reticular fibres, proteoglycans, and glycoproteins. The tunica adventitia is relatively underdeveloped. Example: Aorta and its large branches. The muscular arteries The intima has a very thin subendothelial layer and the internal elastic lamina, the most external component of the intima, is prominent The tunica media may contain up to 40 layers of more prominent smooth muscle. An external elastic lamina, the last component of the media, is present only in the larger muscular arteries. The adventitia consists of connective tissue, lymphatic capillaries, vasa vasorum, and nerves. Arterioles Less than 0.5 mm in diameter. The subendothelial layer is very thin, the elastic laminae are absent and the media is generally composed of circularly arranged smooth muscle cells. In both small arteries and arterioles, the tunica adventitia is very thin. Function of Arteries Permit elastic recoil of vessels. Ensure blood flow during diastole. Varied blood flow requirements. Control flow to large area e.g. Femoral to leg. Control blood flow into capillary beds. Affect peripheral resistance, if resistance increases leads to an increase in BP. Target of some hypertension drug (relax in smooth m.). Capillaries Permit different levels of metabolic exchange between blood and surrounding tissues. Composed of a single layer of endothelial cells rolled up in the form of a tube. 5- 10 µm in diameter and 50 µm in length. Represent over 90% of all blood vessels in the body. The total length of nearly 96,000 km. The velocity of blood in the aorta averages 320 mm/s compared to 0.3 mm/s in capillaries. Favorable place for the exchange of water, solutes, and macromolecules between blood and tissues because of their thin walls and slow blood flow. Types of capillaries Continuous (type I) Found in muscle tissue, lung, CNS, skin, CT, and exocrine gland. The endothelial cytoplasm contains small vesicles (pinocytotic vesicles) of (50-70) nm in diameter. Functionally, it appears that they are involved in the transport of fluid and macromolecules across the capillary Wall. Few or no pinocytotic vesicles are encountered in the continuous capillaries of the nervous system. This feature accounts for the existence of Blood Brain Barrier Fenestrated (type II) Found in the intestinal mucosa, endocrine glands, renal glomerulus, and pancreas. Peripheral cytoplasm of endothelium is perforated at intervals by pores ranging (30-50) nm. The pores are closed by a thin diaphragm except in the capillary of renal glomeruli (pores have no diaphragm). The basal lamina is continuous Sinusoidal (type III) It has a tortuous path and the lumen is greater than other types of capillaries (30-40 µm in diameter) The wall of the sinusoid is composed of a discontinuous layer of endothelial cells separated from one another by wide space. Cytoplasm of endothelial cells shows multiple fenestrations without diaphragm. Macrophages are closely associated with endothelial cells both within and around the sinusoidal wall. Basal lamina is incomplete or discontinuous. Sinusoids are found in liver & haemopoietic organs (ex, bone marrow and spleen) Pericytes Cells of mesenchymal origin with long cytoplasmic processes partly surrounding the endothelial layer at various locations along capillaries and postcapillary venules. Primary has contractile function. It perfoliates after tissue injuries and differentiates to form new blood vessels. Further function of microcirculation Control blood perfusing. The pre-capillary sphincters (PS) can restrict the flow into capillaries. Thoroughfare channels (TC) provide a route for blood to enter the venous system without traversing the capillary bed Veins Same layers of Arteries 1. The tunica intima 2. The tunica media 3. The tunica adventitia Venules Have a typical endothelium of simple squamous epithelial cells but the intima lacks sub-endothelial tissue. The media consists of a few smooth muscle cells. The adventitia is very thin and consists of a few strands of collagen.  Small and medium sized veins Characterized by an intimal layer (I) containing subendothelial tissue. Tunica media (M) containing a small amount of elastic tissue and smooth muscle and an adventitia (A) which is thicker than the media and contain collagen with small amount of smooth muscle and elastic fibres. Smooth muscle amount increase with diameter increase in both media and adventitia. The larger vessel contain valves which are intimal extensions and ensure unidirectional blood flow.  Large veins Such as vena cava. Well-developed layers. The media contains smooth muscle, reticular fibres and collagen. The adventitia is the most developed layer. It contains collagen smooth muscle fibres running longitudinally and may contain adipose tissue (A) and blood vessels (V) that supply nutrients to the vessel wall and are called vasa vasorum. Contain valves. Functional Importance of Veins Any smooth muscle in the veins walls is innervated by the sympathetic nervous system and hence the veins can constrict. As such they assist venous return and therefore cardiac output. The venules are important sites of migration of leucocyte into surrounding connective tissue.  The heart The walls of all four heart chambers consist of three major layers or tunics: the internal endocardium; the middle myocardium; and the external epicardium Cardiac Muscle Cardiac muscle is striated as the actin and myosin are arranged in sarcomeres, just as in skeletal muscle. However, cardiac muscle is involuntary. Cardiac muscle cells usually have a single (central) nucleus. The cells are often branched and are tightly connected by specialised junctions. The region where the ends of the cells are connected to another cell is called an intercalated disc. The conducting system These conducting myofibers or Purkinje fibres have one or two central nuclei. Myofibrils are sparse and restricted to the periphery of the cytoplasm. Purkinje fibres play a major role in electrical conduction and spread of impulses to the ventricular muscle.  Valves and fibrous skeleton The fibrous skeleton of the heart consists of masses of dense connective tissue in the endocardium which anchors the valves and surrounds the two atrioventricular canals, maintaining their proper shape. Section through a leaflet of the left atrioventricular valve (arrows) shows that valves are largely dense connective tissue (C) covered with a thin layer of endothelium. The collagen-rich connective tissue of the valves is stained light blue here and is continuous with the fibrous ring of connective tissue at the base of the valves, which fills the endocardium (En). Lymphatic Vascular System The lymphatic capillaries originate in the various tissues as thin, closed-ended vessels that consist of a single layer of endothelium and an incomplete basal lamina.  The larger lymphatics have a structure similar to that of veins except that they have thinner walls and lack a clear-cut separation between tunics They also have more numerous internal valves