Circulatory System PDF

CHAP 11 - CIRCULATORY SYSTEM Tuesday, March 25, 2025 23:26 CIRCULATORY SYSTEM - Pumps and directs blood cells and substances carried in blood to all tissues of the body - Includes both the blood and lymphatic vascular systems - In an adult the total length of its vessels is estimated a...

CHAP 11 - CIRCULATORY SYSTEM Tuesday, March 25, 2025 23:26 CIRCULATORY SYSTEM - Pumps and directs blood cells and substances carried in blood to all tissues of the body - Includes both the blood and lymphatic vascular systems - In an adult the total length of its vessels is estimated at between 100,000 and 150,000 kilometers - Heart ○ Propel blood through the system - Arteries ○ Carry blood to tissue - Capillaries ○ Sites if O2, CO2, nutrient, and waste product exchange - Veins ○ Carry blood to the heart - Endothelium ○ Lines the internal surface of all components of the blood and lymphatic systems ○ Specific subtype: Simple Squamous epithelium ○ Maintain a selectively permeable, antithrombogenic barrier ○ Determine when and where white blood cells leave the circulation for the interstitial space of tissues and secrete a variety for the interstitial space of tissues and secrete a variety of paracrine factors for vessel dilation, constriction, and growth of adjacent cells HEART - Cardiac muscle in the four chambers of the heart wall contracts rhythmically ○ Right ventricle § To the pulmonary ○ Left ventricle § To the systemic circulation ○ Right atria § Receive blood from the body ○ Left atria § Receive blood from the pulmonary veins ○ - Walls of the heart chambers ○ Endocardium § Thin inner layer of endothelium and supporting connective tissue § Middle myoelastic layer of smooth muscle fibers and connective tissue § Deep layer of connective tissue called subendocardial layer □ Also located here are modified cardiac muscle fibers (Purkinje fibers) § Purkinje Fibers □ At the apex of the heart □ Subendocardial conducting network of myofibers □ Pale-staining fibers, larger than the adjacent contractile muscle fibers, with sparse, peripheral myofibrils and much glycogen □ Mingle distally with contractile fibers of both ventricles and trigger waves of contraction through both ventricles simultaneously. □ ○ Myocardium § Thickest layer § Consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber § Much thicker in the walls of ventricles, particularly left. § Cardiac muscle cells □ Striated □ Involuntary □ Cylindrical with branching □ Mononucleated or binucleated □ Centrally-located nucleus □ Intercalated discs § ○ Epicardium § Simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves § Corresponds to the visceral layer of the pericardium, the membrane surrounding the heart § Subepicardium □ thin layer of loose connective tissue □ elastic fibers, BV, nerves § - Pericardium ○ Outer fibrous layer or fibrous pericardium ○ Inner serous layer or serous pericardium § External parietal layer § Inner visceral layer (epicardium) ○ Pericardial Cavity § Space between epicardium and parietal pericardium § Pericardial fluid - serous fluid secreted by mesothelial cells § Layers glide freely - Cardiac Skeleton ○ Dense irregular connective tissue ○ Functions: § Anchoring and supporting the heart valves § Providing firm points of insertion for cardiac muscle § Helping coordinate the heartbeat by acting as electrical insulation between atria and ventricles ○ Components § Septum membranaceum § Trigona fibrosa § Annuli fibrosi - Cardiac Valves ○ Central core of dense fibrous tissue (collagen and elastic fibers) ○ Lined on both sides by endothelium ○ Bases of valves attached to annuli fibrosi ○ Types § Atrioventricular: □ Tricuspid Valve, Bicuspid Valve (Mitral) § Semilunar □ pulmonary, aortic valves ○ Function § Prevent the reflux of blood during relaxation of heart ○ - Conducting System ○ Both parasympathetic (vagus nerve) and sympathetic neural components innervate the heart § Parasympathetic – slows heartbeat § Sympathetic - accelerates ○ Ganglionic nerve cells and nerve fibers are present in the regions close to the SA and AV nodes ○ Between fibers of the myocardium are afferent free nerve endings that register pain § such as the discomfort called angina pectoris BLOOD VESSELS - Tissues of the vascular wall ○ Endothelium ○ Smooth muscles ○ Connective tissue - Macrovasculature ○ Vessels more than 0.1 mm in diameter ○ Large arterioles, muscular and elastic arteries, muscular veins - Microvasculature ○ Visible only under the microscope (< 0.5 mm) ○ Small arterioles, capillaries, postcapillary venules ○ Important site of exchange between blood and surrounding tissues - Walls of Blood Vessels ○ ○ Tunica intima § Innermost layer § Consists of the endothelium and a thin subendothelial layer of loose connective tissue sometimes containing smooth muscle fibers § Internal Elastic Lamina □ In arteries, forms the boundary between the tunica intima and tunica media □ Structure absent in all but the largest veins □ Thin layer composed of elastin, with holes allowing better diffusion of substances from blood deeper into the wall. ○ Tunica media § Middle layer § Consists chiefly of concentric layers of helically arranged smooth muscle cells § Variable amounts of elastic fibers and elastic lamellae, reticular fibers, and proteoglycans § Much thicker in large arteries than veins § External elastic lamina □ In arteries, separates tunica media from tunica adventitia ○ Tunica adventitia § AKA Tunica Externa § 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 § Relatively thicker in large veins ○ - Vasa Vasorum ○ "Vessels of the vessel” ○ Arterioles, capillaries, and venules in the adventitia and outer part of the media ○ Required to provide metabolites to cells in those tunics in larger vessels ○ Large veins commonly have more vasa vasorum than arteries - - Nervi Vasorum ○ Vasomotor nerves ○ Nerve supply of blood vessels ○ A network of unmyelinated autonomic nerve fibers in the adventitia of larger vessels ○ Releases Norepinephrine ○ The density of this innervation is greater in arteries than in veins. ○ - - - Elastic Arteries ○ Aorta, the pulmonary artery, and their largest branches ○ Large elastic arteries ○ Aka conducting arteries - carry blood to smaller arteries ○ Lumen is larger while wall is thinner ○ Tunica Intima - well developed, with many smooth muscle cells in the subendothelial connective tissue § internal elastic lamina (IEL) – not prominent ○ Tunica media – thick; the most prominent feature § elastic lamellae alternate with layers of smooth muscle fibers § The adult aorta has about 50 elastic lamellae ○ Tunica adventitia – much thinner ○ ○ - Capillaries ○ Simple layer of endothelial cells rolled up as a tube surrounded by basement membrane ○ Average diameter: 4-10 um, which allows transit of blood cells only one at a time ○ Individual length: not > 50um ○ Most capillaries are essentially empty at any given time ○ Their thin walls, extensive surface area, and slow, pulsatile blood flow optimize capillaries for the exchange of water and solutes between blood and tissues ○ Pericytes § Mesenchymal cells at various locations along continuous capillaries and postcapillary venules § long cytoplasmic processes partly surrounding the endothelial layer § Secrete many ECM components and form their own basal lamina § Well-developed cytoskeletal networks of myosin, actin, and tropomyosin § Dilate or constrict capillaries, helping to regulate blood flow in some organs § CNS: maintaining the endothelial blood-brain barrier § § After injuries pericytes proliferate and differentiate to form smooth muscle and other cells in new vessels as the microvasculature is reestablished ○ Capillaries are generally grouped into three histologic types, depending on the continuity of the endothelial cells and their basement membrane: § Continuous type □ Tight capillaries □ tight, well-developed occluding junctions ® provide for continuity along the endothelium and well-regulated metabolic exchange □ Most common type of capillary □ Found in muscle, connective tissue, lungs, exocrine glands, and nervous tissue □ § Fenestrated type □ Visceral capillaries □ have a sievelike structure that allows more extensive molecular exchange □ endothelial cells are penetrated by numerous small circular openings or fenestrations (approx. 80 nm diameter) □ The basement membrane however is continuous and covers the fenestrations □ Found in kidneys, intestine, choroid plexus, and endocrine glands □ § Sinusoidal (discontinuous) □ Commonly called sinusoids □ Permit maximal exchange of macromolecules as well as allow easier movement of cells between tissues and blood □ The endothelium here has large perforations without diaphragms and irregular intercellular clefts □ Have highly discontinuous basement membranes and much larger diameters, often 30-40 μm, which slows blood flow □ Found in the liver, spleen, some endocrine organs, and bone marrow □ - Veins ○ Carry blood back to the heart from microvasculature all over the body ○ Blood entering veins is under very low pressure and moves toward the heart by contraction of the smooth muscle fibers in the media and by external compressions from surrounding skeletal muscles and other organs ○ Most veins are classified as small or medium veins ○ diameters of 10 mm or less ○ usually located close and parallel to corresponding muscular arteries ○ Tunica Intima: usually thin ○ Tunica media: small bundles of smooth muscle cells mixed with a network of reticular fibers and delicate elastic fibers ○ Tunica adventitia: collagenous, thick, well developed ○ ○ ○ Valves § Important feature of large and medium veins § consist of thin, paired folds of the tunica intima projecting across the lumen § rich in elastic fibers and covered on both sides by endothelium § especially numerous in veins of the legs § Help keep the flow of venous blood directed toward the heart § - -