Histology LC11 Cardiovascular System Histology PDF

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC11 Cardiovascular System Histology COLLEGE OF MEDICINE, BATCH 2026...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC11 Cardiovascular System Histology COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05, 2022 Editors: Gadut, Gorospe, Kwaw, Lucas LECTURE OUTLINE 2. Systemic Circulation: − Where blood brings nutrients and removes wastes in tissues I. INTRODUCTION TO CVS throughout the body A. Components of the CVS − Systemic circulation pumps blood from the left side of the B. Two Divisions of Circulation heart through vessels supplying either the head and arms or the lower body, and back to the right side of the heart. II. HEART A. Summary of Blood Circulation B. Four Chambers of the Heart C. Three Major Layers of the Heart and Blood Vessels D. Endocardium E. Myocardium When body is at rest, 70% of blood moves through systemic circulation, F. Epicardium 18% through pulmonary circulation, and 12% through the heart. G. Cardiac Conducting System H. Innervation III. FIBROUS CARDIAC SKELETON IV. TEST YOUR KNOWLEDGE V. REFERENCES I. INTRODUCTION TO CVS − The circulatory system pumps and directs blood cells and Substances carried in blood to all parts of the body. A. Components of the CVS 1. Heart − Propels blood 2. Arteries − Efferent vessels / conducting / distributing vessels − Become smaller as they branch into various organs − Oxygenated blood 3. Capillaries Figure 1. Blood vascular system or the cardiovascular system − Smallest vessels, sites of O2, and CO nutrient, and waste product exchange bet blood and tissues. II. HEART − Together with the smallest arterial and venous --> microvasculature or microvascular bed. A. Summary of Blood Circulation 4. Veins − From convergence of venules into larger channels that continue enlarging- Cardiac muscle in the four chambers of the heart wall contracts as they approach the heart. rhythmically, pumping the blood through the circulatory system. − Carry the deoxygenated blood to the heart.  Blood from the body (through Superior & Inferior Vena Cava) – Right Atrium (RA) – Tricuspid Valve (Right Atrioventricular Valve) B. Two Divisions of Circulation – Right Ventricle (RV) – Pulmonary Valve ((Pulmonary Semilunar Valve) – Pulmonary Artery – Pulmonary Circulation – Pulmonary 1. Pulmonary Circulation: Vein – Left Atrium (LA) – Bicuspid Valve (Mitral Valve) – Left − Where blood is oxygenated in the lungs. Ventricle (LV) – Aortic Valve (Aortic Semilunar Valve) – Aorta – − In the pulmonary circulation the right side of the heart pumps blood Systemic Circulation. through pulmonary vessels, through the lungs for oxygenation, and back to the left side of the heart. Page 1 of 6 [HISTOLOGY] LC.12 CARDIOVASCULAR SYSTEM HISTOLOGY – Dr. Peeble Narita Agdamag - Pulmonary artery is the only artery that carries deoxygenated blood. - In terms of thickness, ventricles are thicker than atria. - Left ventricle is thicker than the right ventricle because of the high pressure in the aorta which the blood may pass through going to the systemic circulation. Figure 3. As seen in the diagram, the human heart has two atria and two ventricles. The myocardium of the ventricular walls is thicker than that of the atria. The valves are basically flaps of connective tissue anchored in the heart’s dense connective tissue, or cardiac skeleton, concentrated in the regions shown in white. This fibrous tissue includes the chordae tendineae, cords which extend from the cusps of both atrioventricular valves and attach to papillary muscles, preventing the valves from turning inside-out during ventricular contraction. Valves and cords are covered by the nonthrombogenic endothelium. C. Major Layers of the Heart - The walls of all four heart chambers consist of three major layers: the internal endocardium, the middle myocardium, and the external epicardium. Figure 2. The system consisting of the heart, arteries, veins, and micro- 1. Endocardium vascular beds is organized as the pulmonary circulation and the systemic - Inner layer circulation. In the pulmonary circulation the right side of the heart pumps - Consists of the lining endothelium blood through pulmonary vessels, through the lungs for oxygenation, and - supporting layer of fibroelastic connective tissue with scattered fibers of back to the left side of the heart. The larger systemic circulation pumps smooth muscle blood from the left side of the heart through vessels supplying either the - Deep layer of connective tissue called subendocardial layer that merges head and arms or the lower body, and back to the right side of the heart. with myocardium. - Branches of the heart’s impulse-conducting system (Purkinje Fibers) - modified cardiac muscle fibers that are also located in the subendocardial layer. 2. Myocardium B. Chambers of the Heart - Middle layer - Cardiac muscle with fibers arranged spirally around each heart chamber  Right & Left Atria - receive blood from the body and the - It has strong force required to pump blood through systemic and pulmonary veins, respectively. pulmonary circulations  Right & Left Ventricle - propel blood to the pulmonary and systemic circulation. 3. Epicardium - Simple squamous mesothelium supported by a layer of loose connective Other Structures: tissue containing blood vessels and nerves - During heart movements, underlying structures are cushioned by deposits  Valves - flaps of connective tissue anchored in heart’s dense of adipose tissue in epicardium connective tissue (cardiac skeleton) - Friction is prevented by lubricant fluid produced by serous mesothelial  Chordae Tendineae - cords that extend from cusps of both cells atrioventricular valves (AV valve) and attach to papillary muscles, - divided into two layers: preventing the valves from turning inside-out during ventricular Visceral Layer - membrane surrounding the heart contraction. Parietal Layer - where large vessels enter and leave heart.  Valves and cord covered by non thrombogenic endothelium - Outermost layer Page 2 of 6 [HISTOLOGY] LC.12 CARDIOVASCULAR SYSTEM HISTOLOGY – Dr. Peeble Narita Agdamag merging with the contractile fibers of the myocardium (M), which is organized into many partially separated bundles and muscles. Figure 6: The external tunic of the heart, the epicardium, is the site of the coronary vessels and contains considerable adipose tissue. This section of atrium shows part of the myocardium (M) and epicardium (Ep). The epicardium consists of loose connective tissue (CT) containing autonomic nerves (N) and variable amounts of fat (F). The epicardium is the visceral Figure 4: The subendocardial layer of connective tissue (SEn) in the layer of the pericardium and is covered by the simple mesothelium (Mes) ventricles surrounds Purkinje fibers (P) of the heart’s impulse conducting which also lines the pericardial space. The mesothelial cells secrete a lubri- network. These are modified cardiac muscle fibers joined by intercalated cant fluid which prevents friction as the beating heart contacts the parietal disks but specialized for impulse conduction rather than contraction. pericardium on the other side of the pericardial cavity. Containing glycogen but relatively few organelles and peripheral myofibrils, Purkinje fibers typically are paler staining than contractile muscle fibers (M). C. Layers of the Blood Vessels  Smooth muscle – present in the walls of large blood vessels. - arranged helically in layers  Connective tissue - present in vascular walls in variable amounts.  3 Concentric layers, or tunics (L. tunica, coat): 1. Tunica Intima - Inner layer - Consists of the endothelium - Subendothelial layer of loose connective tissue - In arteries the intima includes a thin layer, called internal elastic lamina (composed of elastin). 2. Tunica Media - Middle layer - Consists chiefly of concentric layers of helically arranged smooth muscle cells - Variable amounts of elastic fibers, elastic lamellae, reticular fibers, and proteoglycans - In arteries may also have an external elastic lamina separating it from tunica adventitia. 3. Tunica Adventitia - Also known as Tunica Externa - Outermost layer - Contains connective tissue (Type 1 Collagen) Figure 5: In the atrial walls conducting Purkinje-like fibers (P) often occupy most of the subendocardial layer, lying close to the endothelium (En), and Page 3 of 6  [HISTOLOGY] LC.12 CARDIOVASCULAR SYSTEM HISTOLOGY – Dr. Peeble Narita Agdamag - Continuous with and bound to the stroma of the organ through which the blood vessel runs. Figure 8. Tissue slide showing the endocardium and myocardium, as well as the subendocardial layer where Purkinje fibers are found. (En) endothelium, (P) Purkinje fibers, (SEn) Subendocardial layer, (M) muscle fibers. Figure 7: Walls of both arteries and veins have three tunics called the intima, -Because strong force required to pump blood through systemic media, and the adventitia (or externa), which correspond roughly to the and pulmonary circulations, thicker myocardium is found in the heart’s endocardium, myocardium, and epicardium. An artery has a thicker ventricle compared to the atria and thicker on the left side of media and relatively narrow lumen. A vein has a larger lumen and its the heart than on the right side. adventitia is the thickest layer. The intima of veins is often folded to form valves. Capillaries have only an endothelium, with no subendothelial layer F. Epicardium or other tunics. − Simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves D. Endocardium − Innermost layer of the heart wall − Fat cells can also be seen − Near the atrial and ventricular cavity − Corresponds to visceral layer of the pericardium − Endothelial cells − Membrane surrounding the heart − Could be medial or lateral − Where large vessels enter and leave heart, epicardium is − Next to a space reflected back as parietal layer lining the pericardium. − Loose connective tissues and nerves can be seen. − During heart movements, underlying structures are cushioned by Consists of: deposits of adipose tissue in epicardium 1. Thin inner layer of endothelium and supporting connective tissue − Friction prevented by lubricant fluid produced by both layers of 2. Middle myoelastic layer of smooth muscle fibers and connective tissue serous mesothelial cells. 3. 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. E. Myocardium − Thicker layer than endocardium − Myocardial cells − Dense − Bright − Pink-staining − Cardiac muscle with fibers arranged spirally around each heart chamber − Blood vessels and nerve fibers can be seen Because strong force required to pump blood through systemic Figure 9. In the atria of the Purkinje fibers (P) are often closer to the and pulmonary circulations, thicker myocardium ventricle > endothelium (En), and intermingle with the contractile fibers within the atrium and left > right. myocardium (M). Page 4 of 6 [HISTOLOGY] LC.12 CARDIOVASCULAR SYSTEM HISTOLOGY – Dr. Peeble Narita Agdamag Located in the right atrial wall near SVC 6 to 7 mm3 mass of cardiac muscle cells with smaller size, fewer myofibrils, and fewer typical intercalated disks than the neighboring muscle fibers. Impulses initiated → atrial myocardial fibers of both atria → Contraction 2. Atrioventricular Node Smaller Found on the floor of the right atrium near AV valve Cells similar to SA node Conducting muscle fibers from the AV node form the AV bundle of HIS Conduct fibers from AV node, pass through an opening in the cardiac skeleton into interventricular septum → Bifurcate into RBB and LBB into wall of each ventricle. Purkinje fibers - Mingle distally with contractile fibers of both ventricles and trigger waves of contraction through both ventricles simultaneously. Figures 10&11: Tissue slides showing the epicardium and distinguishing structures (BV, NF, and Adipocytes) H. Innervation G. Cardiac Conducting System − Both parasympathetic and sympathetic neural components innervate the − Modified cardiac muscle cells specialized to generate and conduct waves heart. of depolarization which stimulate rhythmic contractions in adjacent − Ganglionic nerve cells and nerve fibers present in regions close to the SA myocardial fibers. and AV nodes: Consists of Two Nodes: 1. Sinoatrial Node (Pacemaker) Page 5 of 6 [HISTOLOGY] LC.12 CARDIOVASCULAR SYSTEM HISTOLOGY – Dr. Peeble Narita Agdamag  Affect heart rate and rhythm a. Found on the floor of the right atrium near AV valve Parasympathetic stimulation (Vagus nerve) slows heartbeat b. Conduct fibers from AV node, pass through an opening in the cardiac Sympathetic nerve: accelerates pacemaker skeleton into interventricular septum and bifurcate into RBB and LBB into wall of each ventricle 3 − Between fibers of myocardium afferent free nerve endings that register c. 6 to 7 mm mass of cardiac muscle cells with smaller size, fewer pain, myofibrils, and fewer typical intercalated disks than the neighboring muscle Discomfort (Angina pectoris) that occurs when partially occluded fibers. coronary arteries cause local oxygen deprivation. d. NOTA 6. At rest, the percentage of blood in the systemic circulation is III. FIBROUS CARDIAC MUSCLE a.12% b.18% − Consists of dense irregular connective tissue, primarily in endocardium, c.70% which anchors the valves and surrounds the AV canals, maintaining their d.60% proper shape 7. 6- to 7-mm3 mass of cardiac muscle cells with smaller size, fewer myofibrils, and fewer typical intercalated disks found in the wall of the right atrium a. Atrioventricular node b. Sinoatrial node c. Bundle of His d. Purkinje Fiber 8. Which of the following is/are incorrectly paired. a. Bathmotropy: degree of excitability b. Chronotropy: rate of heartbeat c. Inotropy: the strength of contractility d. Dromotropy: rate of chemical impluses in the heart 9. Which of the following is/are true about heart a. It beats normally 100,000 times a day, b. Pumps 1.5 gallon of blood every minute. c. Has its own electrical impulse and will continue to pump to beat when separated from your body for period of time. IV. TEST YOUR KNOWLEDGE d. Every cell in the body gets blood from the heart. 1. True or False. The myocardium is thicker within the atria, as this muscle 10. These are contractile fibers joined by intercalated disks specialized for must pump all blood returning to the heart into the lungs for oxygenation. impulse conduction a. Purkinje fibers 2. It is reflected back as parietal layer lining the pericardium. b. Collagen fibers a. Endocardium c. Nerve fibers b. Myocardium d. Elastic fibers c. Epicardium d. Pericardium ANSWERS: 1. False (Ventricular myocardium is thicker) 2. C 3. A 4. B 5. C 6. C 7. B 8. D 3. Fat cells can also be seen in the: 9. D 10. A a. Epicardium b. Myocardium V. REFERENCES c. Endocardium Mescher, A.L. (2016). Junqueira’s Basic Histology Atlas of Histology. d. Pericardium McGraw Hill Education.Eroschenko, V. P. (2017).Atlas of Histology withFunctional Correlations 13th Edition. Wolters Kluwer PPT of Dr. Peeble 4. What is the effect of the parasympathetic stimulation on heartbeat? Narita Agdamag a. Rapid heartbeat b. Slows heartbeat c. No effect d. Irregular beating 5. True about of AV node except; Page 6 of 6