Circulatory System PDF

Circulatory system Shiping Ding (丁世萍） School of Medicine, Zhejiang University  Learning Objectives describe how blood vessels (arteries, arterioles, capillaries, venules and veins) are named. describe the structure of different types of blood vessels in...

Circulatory system Shiping Ding (丁世萍） School of Medicine, Zhejiang University  Learning Objectives describe how blood vessels (arteries, arterioles, capillaries, venules and veins) are named. describe the structure of different types of blood vessels in relation to their function in supplying blood to and from the tissues of the body. You should also revise the structure of cardiac muscle covered in the Tissues of the Body module.  Concepts of organs and systems Organ: composed of four kinds of the tissues in a particular way Hollow organs: studied from inside to outside Types parenchyma Substantial organs: interstitium System: composed of many organs which have relationship with each other in structure and function.  General outline According to the circulating fluid in the tubes blood or lymph: Cardiovascular system Lymphatic vascular system  Cardiovascular System The histological study of the cardiovascular system includes two major components Heart – mainly functions as a pump to move blood (and all the things blood carries) through the body. Blood vessels – are the tubes that distribute the blood to the cells and then back to the heart. --Arteries: deliver blood from heart to capillaries --Capillaries: the smallest blood vessels and closest to body cells, the interchanges between blood and tissues occur there --Veins: carry blood from body to the heart Histological Structure of Blood Vessels Structural Plan of Blood Vessels 1.The tunica intima : (endothelial cells, a thin subendothelial layer of loose con. T. with occasional smooth muscle cells and internal elastic membrane). In arteries, the intima is separated from the media by an internal elastic membrane 2.The tunica media: (consists of concentric layers of smooth muscle cells and amounts of elastic fibers and reticular fibers of collagen type III, proteoglycans, and glycoproteins)  In arteries, the media has a thinner external elastic membrane 3.The tunica adventitia: consists of : Connective tissue. Lymphatic capillaries, vasa vasorum, and nerves. Figre : summarized the comparison between veins & arteries  Large (elastic) artery  Aorta, the pulmonary trunk and their main branches  With a large lumen relative to wall thickness (diameter >10mm)  subendothelial layer is thicker with a few smooth muscles  tunica media is thick, contains a 40-70 concentrically-arranged elastic lamina  internal and external elastic lamina are not distinguished  tunica adventitia are thinner, abundant vasa vasorum  Tunica intima Tunica media Tunica adventitia  Medium-sized artery  muscular artery: diameter (2mm~ 10mm) Endothelium Tunica intima Subendothelial layer: LCT Internal elastic lamina: clear Classic muscular artery- elastic stain Tunica media: contain 10~40 layers of circular smooth muscle External elastic lamina Tunica adventitia LCT: contain vasa vasorum nerve tissue Elastic artery Muscular artery Medium artery Elastic artery vs muscular artery  Small artery muscular artery (diameter 0.1mm~2mm)  internal elastic lamina is clear, while external elastic lamina is not distinguished  the tunica media contains 3~9 layers of smooth muscles  Arterioles  Less than 0.1mm in diameter. Have similar and simpler structure as that of muscular artery.  1~2 layers of smooth muscle in tunica media.  Responsible for the presence of blood pressure.  In both small arteries and arterioles, the tunica adventitia is very thin. ? Identify the characteristic tunica of arteries?  Capillaries Capillaries are the site where materials carried in the blood are unloaded and other materials are loaded into the blood. In many organs the capillaries form a network. Consist of a single layer of simple squamous epithelium. the average diameter about 8um. Stomach, vascular injection of mucosa  Capillaries L/M:  A single layer of endothelial cells  A basement membrane  pericyte: Structure: Along capillaries and postcapillary venules. Capillary(b) and venule (a) Long cytoplasmic processes surround the endothelial cells. Function: After tissue injuries, proliferate and differentiate to form new blood vessels and C.T. cells. Contractile function. Capillary - pericyte Capillary Endothelial cell capillary podocyte pericyte  E/M According to the appearance of the endothelium and basement membrane: Continuous capillary Fenestrated capillary Sinusoid  Continuous capillary  distributed in muscle tissue, brain, lung and connective tissue, etc.  endothelial cell: large number of pinocytotic vesicles, cell junctions between the endothelia (tight junction), no pores, no gaps  basement membrane: integrity Tight junction Basement membrane Continuous capillary pinocytotic vesicles  Fenestrated capillary  distributed in tissues where rapid interchange of substances occurs between the tissue and the blood, as in the kidney glomerulus, mucosa of gastrointestine, some endocrine glands  endothelial cells: present abundant perforated pores (60-80nm in D, with 4-6 nm diaphragm of proteoglycans), have or haven’t diaphragm on them  basement membrane: integrity Fenestrated capillary (kidney)  Sinusoid  distributed in tissues where interchange of substance in big size occurs, as in the liver, spleen, and some endocrine glands  a greatly enlarged diameter (30~40um)  endothelial cell: intercellular clefts are large between cells, many pores without diaphragm  absence of a continuous basement membrane  macrophages are located either among or outside the cells of the endothelium Continuous capillary Fenestrated capillary Sinusoid ? Memorize types of capillaries.  Vein  large lumen, thin wall, irregular  Internal and external elastic lamina are not clear  Tunica media is thin, with a few elastic fibers and smooth muscles  Tunica adventitia is thick (well-developed)  Some veins have valves  Large Vein Diameter >10mm T. media: 3~15 layers of smooth muscle T. Adventitia: well-developed layer (longtitudinally arranged smooth muscle cells, adipose A and vessels V =vasa vasorum) T.In Contain valves. T.me T.adv  Medium-sized  Diameter 1mm~10mm  T. media: 3~5 layers of smooth muscle  T. Adventitia: thicker than the media, well-developed layer (longtitudinally arranged smooth muscle cells)  Vein valve Distributed in large vein and medium vein Ensure unidirectional blood flow intimal extensions  Vein valves: Bag-like protrusion of tunica intima, which prevents the blood flow from running to opposite direction. Exists only in the vein that has low position or far away from heart. Vein with valve  small vein Diameter 0.1～1mm T. media: 2~3 layers of smooth muscle  Venules Venules have a typical endothelium but the intima lacks sub-endothelial tissue. The media consists of a few smooth muscle cells or pericytes. The adventitia is very thin and consists of a few strands of collagen. Postcapillary Venules T. intima: endothelium, a very thin subendothelial layer. T. media : may contain: only contractile pericytes. vasa vasorum (vessels of vessels). Amicrovasculature lie in the tunica adventitia of large blood vessels ( ex. Aorta ). function: to bring O2 and nutrients to local cells too far from the lumen to be nourished by blood there. arterioles (A), capillaries and venules (V) constitute the vasa vasorum (vessels of vessels). A Comparison of a Typical Artery and a Typical Vein ? Can you diffrentiate between veins & arteries?  Heart  Muscular organ , when contracts, pumping the blood through the circulatory system.  Producing a hormone called atrial natriuretic factor.  Endocardium Consists of: squamous endothelial cells. subendothelial layer of fine C. T. Subendocardial layer: LCT, blood vessels, nerves and the impulse-conducting system of the heart   thickest layer, consists of cardiac muscle, is richly supplied with capillaries myocardium  the myocardium, consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber.  Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls Cardiac Muscle Functions 1. Contraction ( Ordinary fibers) 2. Conduction ( Conducting System ) 3. Secretion Atrial Natriuretic Peptide (ANP) N.B: Main function of ANP is causing a reduction in expanded extracellular fluid (ECF) volume by increasing renal sodium excretion.  LCT: contain adipose cells, blood vessels and nerves epicardium Methothelium  Where the large vessels enter and leave the heart, the epicardium is reflected back as the parietal layer lining the pericardium.  Friction within the pericardium is prevented by lubricant fluid produced by both layers of serous mesothelial cells.  Cardiac valve  Endocardium extensions  Endothelium on both sides and dense connective tissue in the middle  Cardiac conducting system The heart has a specialized system to generate a rhythmic stimulus (spread to the entire myocardium) consist of: sinoatrial node (pacemaker): modified cardiac muscle cells (fusiform), with fewer myofibrils atrioventricular node: similar to those of the sinoatrial node, but their cytoplasmic projections branch ,forming a network. atrioventricular bundle (bundle of His): formed by cells similar to those of the atrioventricular node. Purkinje fibers: the cardiac conducting system  Purkinje fibers Structure --End of atrioventricular bundle --specialized conducting fibers, --larger than cardiac muscle cells --Fewer myofibrils --a large number of mitochondria and glycogen --intercalated disc Function: conduct cardiac action potentials more quickly and efficiently than any other cells in the heart The Lymphatic Vascular System (Learned by yourself) Lymphatic capillaries: In the various tissues as thin, closed-ended vessels , consist of: A single layer of endothelium An incomplete basal lamina. The larger lymphatics: similar to veins except: They have thinner walls and lack separation between tunics. More numerous internal valves Thank you for listen!