[HISTO]LEC_201_CARDIOVASCULAR-SYSTEM-HEART.pdf

(001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20...

(001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 OUTLINE I. CARDIOVASCULAR SYSTEM a. Structures b. At Rest II. HEART A. Two main divisions of circulation B. Layers of the heart C. Innervation of the Heart I. CARDIOVASCULAR SYSTEM Pumps and directs blood cells and substances carried in blood to all tissues of the body. Composed of the heart, arteries, capillaries and veins. Figure 1. Arteries, Veins, and Capillaries. A. CONSIST OF THE FOLLOWING STRUCTURES B. AT REST 1. Heart 70% of blood in systemic circulation Propels blood through the system. 18% pulmonary circulation 12% through the heart 2. Arteries Two major divisions of arteries, microvasculature, and veins make up the pulmonary circulation, where blood Efferent vessels / conducting / distributing vessels is oxygenated in the lungs, and the systemic Become smaller as they branch into various organs circulation, where blood brings nutrients and removes Carry oxygenated blood wastes in tissues throughout the body. Largest blood vessel in the body. The walls are made up of elastic connective tissue fibers. These fibers provide great resilience and flexibility during II. HEART blood flow A. TWO MAIN DIVISIONS OF CIRCULATION 3. Capillaries Pulmonary Circulation - consists of the heart, arteries, Smallest vessels, sites of O2, and CO nutrient, and waste veins and microvascular bed. Blood is oxygenated in the lungs. product exchange bet blood and tissues - Pumps blood from the right atrium → right Average diameter is 8um, which is about the size of an ventricle → pulmonary artery → pulmonary erythrocyte. circulation where blood becomes oxygenated in Smallest arterial and venous - Microvasculature or the lungs; capillaries in the lungs for microvascular bed of the system. oxygenation → oxygenated blood enters the pulmonary vein → left atrium → systemic 4. Veins circulation Systemic Circulation - blood brings nutrients and From convergence of venules into larger channels that remove wastes in tissues throughout the body. continue enlarging as they approach the heart. - Pumps blood from the left atrium → left ventricle Carry deoxygenated the blood to the heart. → Aorta (main artery) →other arteries→ The internal surface of all components of the blood and capillaries in the body for waste and product lymphatic systems is lined by a simple squamous exchange→veins → vena cava (main vein) → epithelium called ENDOTHELIUM – this endothelium right atrium → pulmonary circulation. forms a permeability barrier between blood and interstitial tissue. Page 1 of 6 CMED 1E  (001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 Figure 3. Anterior view of the Human heart (cut) B. LAYERS OF THE HEART 1. The heart wall can be viewed as a three-layered structure. a. Inner layer = Endocardium b. Middle Layer = Myocardium c. Outer layer = Epicardium (also called the pericardium) 2. Except for the smallest vessels, blood and lymphatic vessel walls can also be viewed as three-layered Figure 2. Pulmonary circulation and Systemic circulation of the Cardiovascular system structures. a. Inner layer = Tunica intima, consist of endothelium and subendothelial connective tissue Ventricular myocardium thicker than atria b. Middle layer = Tunica media, composed mainly of Valves-flaps of connective tissue anchored in heart’s smooth muscle fibers dense connective tissue (cardiac skeleton) c. Outer layer = Tunica adventitia, contains primarily CHORDAE TENDINEAE collagen and elastic fibers - Cords that extend from cusps of both atrio- ventricular valves (passageway: from the atria going to the ventricles) and attach to papillary muscles, preventing the valves from turning inside-out during ventricular contraction Valves and cord covered by NON-THROMBOGENIC endothelium. Figure 4. Layers of the heart Page 2 of 6 CMED 1E  (001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 Pericardium has fibrous and serous layer - Consists of: Serous pericardium includes the visceral layer of o Thin inner layer of endothelium (En) and pericardium and the parietal layer of pericardium where supporting connective tissue in between of these two is the pericardial cavity with o SEn (subendocardial layer) lacked in pericardial fluid. smooth muscle with variable thickness o Middle myoelastic layer of smooth muscle fibers and connective tissue o Deep layer of connective tissue subendocardial layer that merges with myocardium - Branches of the heart’s impulse-conducting system (Purkinje) consisting of modified cardiac muscle fibers, are also located in the subendocardial layer Figure 5. Internal endocardium, Middle myocardium, External pericardium Cardiac muscle in the four chambers of the heart wall contracts rhythmically, pumping the blood through the circulatory system. The right and left ventricles propel blood to the pulmonary and systemic circulation, respectively; right and left atria receive blood from the body and the pulmonary veins, respectively. The walls of all four heart chambers consist of three major layers: the internal endocardium; the middle myocardium; and the external epicardium. Figure 7. Endocardium, Myocardium, and fibers of the subendocardial conducting network. Below the endothelium (En) and myoelastic layer, the subendocardial layer (SEn) in the ventricles contains the conducting (Purkinje) fibers (P) of the heart’s impulse conducting network. These fibers are cardiac muscle cells joined by intercalated disks but specialized for impulse conduction rather than contraction. With glycogen filling much of the cytoplasm and displacing myofibrils to the periphery, Purkinje fibers typically are more pale staining than contractile cardiac muscle fibers (M). 2. Myocardium - Composed mainly of cardiac muscle Figure 6. Posterior view of the heart (cut) - The thickest layer - Middle layer 1. Endocardium - Cardiac muscle with fibers arranged spirally - Endocardial layer is the layer nearest to the around each heart chamber atrial and ventricular cavity - Because strong force required to pump blood - Inner layer of the heart wall through systemic and pulmonary circulations, Page 3 of 6 CMED 1E  (001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 - thicker myocardium in ventricle > atrium and - Corresponds to visceral layer of the pericardium left > right. (membrane surrounding the heart) - Where large vessels enter and leave heart, epicardium is reflected back as parietal layer lining the pericardium. - During heart movements, underlying structures are cushioned by deposits of adipose tissue in epicardium - Friction prevented by lubricant fluid produced by both layers of serous mesothelial cells - Dense fibrous connective tissue of the cardiac skeleton forms part of the interventricular and interatrial septa, surrounds all valves of the heart, and extends into the valve cusps and the chordae tendineae to which they are attached. Figure 9. Cardiac conducting system Figure 8. Myocardium and Epicardium of the outer ventricular wall. These regions of dense irregular connective tissue The epicardium and part of the myocardium can be seen. Nerve perform the following functions: fibers (NF) and large blood vessels (BV), which are branches of - Anchoring and supporting the heart valves coronary arteries and cardiac veins, run through the adipose tissue - Providing firm points of insertion for cardiac of the epicardium. 48×. H&E. muscle The external tunic of the heart, the epicardium, is the site Helping coordinate the heartbeat by acting as electrical of the coronary vessels and contains considerable adipose tissue. insulation between atria and ventricles This section of atrium shows part of the myocardium (M) and Within the subendocardial layer and adjacent epicardium (Ep). The epicardium consists of loose connective myocardium, modified cardiac muscle cells make up the tissue (CT) containing autonomic nerves (N) and variable amounts impulse conducting system of the heart, which of fat (F). The epicardium is the visceral layer of the pericardium generates and propagates waves of depolarization that and is covered by the simple mesothelium (Mes) that also lines the spread through the myocardium to stimulate rhythmic pericardial space. The mesothelial cells secrete a lubricant fluid contractions. that prevents friction as the beating heart contacts the parietal Consist of 2 nodes of specialized myocardial tissue that pericardium on the other side of the pericardial cavity. is difficult to distinguish histologically from surrounding cardiac muscle: 3. Epicardium - SINOATRIAL (SA) NODE (PACEMAKER) - Outer layer/portion that covers the myocardial o In right atrial wall near superior vena layer cava - Simple squamous mesothelium supported by a o 6- to 7-mm3 mass of cardiac muscle layer of loose connective tissue containing cells with smaller size, fewer blood vessels and nerves myofibrils, and fewer typical Page 4 of 6 CMED 1E  (001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 o intercalated disks than the neighboring muscle fibers. o Impulses initiated by these cells move along the myocardial fibers of both atria, stimulating their contraction. o Impulses from this node travel from the right atrium going to the left atrium and the AV node - ATRIOVENTRICULAR (AV) NODE o Continuous with specialized bundles of cardiac muscle fiber (AV Bundles of HIs) that at run along the o Interventricular septum to the apex of the heart where they branch as conducting Purkinje fibers o Lies near the interventricular septum towards the apex of the heart o That extend into myocardium of ventricles o Slightly smaller o floor of RA near AV valve Figure 10. Endocardium, Myocardium, and fibers of the o Cells similar to SA node subendocardial conducting network. Below the o Conducting muscle fibers from the AV endothelium (En) and myoelastic layer, the node form the AV bundle of HIS subendocardial layer (SEn) in the ventricles contains the o Conduct fibers from AV node, pass conducting (Purkinje) fibers (P) of the heart’s impulse through an opening in the cardiac conducting network. These fibers are cardiac muscle skeleton into interventricular septum ; cells joined by intercalated disks but specialized for bifurcate into RBB and LBB into wall of each ventricle. impulse conduction rather than contraction. With Purkinje fiber glycogen filling much of the cytoplasm and displacing - AKA impulse-conducting fibers myofibrils to the periphery, Purkinje fibers typically are - Are thicker and larger cardiac muscle fibers and more pale staining than contractile cardiac muscle fibers contain greater amount of glycogen. (M) - They also contain contain fewer contractile filaments. - Located at the subendocardial connective tissues. - This Subendocardial connective tissues will present a BLUE-STAINED COLLAGEN FIBERS with MALLORY-AZAN STAIN are 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. Figure 11. Endocardium, Myocardium, and fibers of the subendocardial conducting network. In the atria Purkinje fibers (P) are often closer to the endothelium (En) and Page 5 of 6 CMED 1E  (001) CARDIOVASCULAR SYSTEM (HEART) DR. PEEBLE NARITA AGDAMAG | 12/14/20 intermingle with the contractile fibers within the myocardium (M). Both X200. H&E. C. INNERVATION OF THE HEART Innervation of the heart - Both parasympathetic and sympathetic neural components innervate the heart - Ganglionic nerve cells and nerve fibers present in regions close to the SA and AV nodes - Affect heart rate and rhythm - Parasympathetic stimulation (vagus nerve) slows heartbeat. - Sympathetic nerve: accelerates pacemaker. - Between fibers of myocardium afferent free nerve endings that register pain, discomfort Figure 13. Valve leaflet and cardiac skeleton. Micrograph shows (angina pectoris) that occurs when partially a section through a cusp of an atrioventricular valve (arrow) and occluded coronary arteries cause local oxygen attached chordae tendineae (CT). These structures are largely deprivation. dense connective tissue (C) covered with a thin layer of endothelium. The collagen-rich connective tis- sue of the valves is stained pale blue here and is continuous with the fibrous ring of Fibrous cardiac skeleton connective tissue at the base of the valves, which fills the - consists of dense irregular connective tissue, endocardium between the atrium (A) and ventricle (V). The thick primarily in endocardium (En) ventricular myocardium (M) is also shown. X20. Masson trichrome. - anchors the valves and surrounds the AV canals, maintaining their proper shape. - A cusp of the Atrioventricular valve - AV valves: Mitral/Bicuspid, Tricuspid, TEST YOUR KNOWLEDGE Pulmonary and Aortic valves- made up of dense irregular connective tissue 1. Impulses from this node travel from the right atrium going to the left atrium and the AV node. 2. Also known as specialized impulse conducting fibers. 3. It consists of dense irregular connective tissue which anchors the valves and surrounds the AV canals, maintaining their proper shape. 4. True or False. The myocardium is thicker within the atria, as this muscle must pump all blood returning to the heart into the lungs for oxygenation. 5. It is reflected back as parietal layer lining the pericardium. a. Endocardium b. Myocardium c. Epicardium d. Pericardium thicker), 5. C (Epicardium) Fibrous cardiac skeleton, 4. False (Ventricular myocardium is Answers: 1. Sinoatrial Node (SA Node), 2. Purkinje fibers, 3. Figure 12. Heart in diastole viewed from base with atria removed REFERENCES Mesher, A (2016). Junqueira’s Basic Histology Text and Atlas. McGraw-Hill Education. Page 6 of 6 CMED 1E