Histology LC10: The Heart (BATCH TANNAWAG 1C) PDF

Lymphatic vascular system - begins with the COURSE OUTLINE lymphatic capillaries, which are thin-walled, closed-ended tubules carrying lymph that I. INTRODUCTION...

Lymphatic vascular system - begins with the COURSE OUTLINE lymphatic capillaries, which are thin-walled, closed-ended tubules carrying lymph that I. INTRODUCTION merge to form vessels of steadily increasing A. Components size. B. Divisions ○ The largest lymph vessels connect with the II. HEART blood vascular system and empty into the A. Blood Circulation Summary large veins near the heart. These returns B. Heart Chambers fluid from tissue spaces all over the blood. III. MAJOR LAYERS OF THE HEART When body is at rest: A. Endocardium ○ 70% of blood moves through systemic B. Myocardium circulation, C. Epicardium or Pericardium ○ 18% through pulmonary circulation, and IV. CARDIAC SKELETON ○ 12% through the heart. V. RECITATION QUESTIONS I. INTRODUCTION The circulatory system pumps blood (blood cells and related substances) to all parts of the body. It 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 km. A. COMPONENTS Heart − propels blood Arteries − different vessels / conducting / Figure 1. Cardiovascular system. distributing vessels. It carries oxygenated blood and becomes smaller as they branch into various organs. II. HEART Capillaries − smallest vessels; site for the exchange of oxygen, nutrients, carbon dioxide A. BLOOD CIRCULATION SUMMARY and waste products between blood and the tissues. Capillaries together with the smallest Cardiac muscle in the four chambers of the arterial and venous are collectively called as heart wall contracts rhythmically, pumping the microvasculature or microvascular bed. blood through the circulatory system. Veins − from convergence of venules into ○ Blood from the body (through Superior & larger channels that continue enlarging as they Inferior Vena Cava) – Right Atrium (RA) – approach the heart. It carries the deoxygenated Tricuspid Valve (Right Atrioventricular blood to the heart. Valve) – Right Ventricle (RV) – Pulmonary Valve (Pulmonary Semilunar Valve) – B. DIVISIONS Pulmonary Artery – Pulmonary Circulation – Pulmonary Vein – Left Atrium (LA) – Pulmonary Circulation - where blood is Bicuspid Valve (Mitral Valve) – Left oxygenated in the lungs. Ventricle (LV) – Aortic Valve (Aortic ○ In the pulmonary circulation the right side Semilunar Valve) – Aorta –Systemic of the heart pumps blood through Circulation. pulmonary vessels, through the lungs for Pulmonary artery is the only artery that carries oxygenation, and back to the left side of deoxygenated blood. the heart. In terms of thickness, ventricles are thicker Systemic Circulation - where blood brings than atria. nutrients and removes wastes in tissues Left ventricle is thicker than the right ventricle throughout the body. because of the high pressure in the aorta which ○ Systemic circulation pumps blood from the the blood may pass through going to the left side of the heart through vessels systemic circulation. supplying either the head and arms or the lower body, and back to the right side of the heart. BATCH TANNAWAG 1C 1 HISTOLOGY LC10: THE HEART Dr. Agdamag, P. N. 11/25/2024 Loose connective tissues and nerves can be seen. Consists of: ○ Thin inner lining layer of endothelium and supporting connective tissue with scattered fibers of smooth muscle. ○ Middle myoelastic layer of smooth muscle fibers and connective tissue ○ Deep layer of connective tissue called subendocardial layer that merges with myocardium. Branches of the heart’s impulse-conducting system (purkinje fibers), consisting of modified cardiac muscle fibers are also located in the subendocardial layer. Figure 2. Blood circulation. B. HEART CHAMBERS Atria Right and Left Atria - receive blood from the body and the pulmonary veins, respectively. Ventricles Right and Left Ventricle - propel blood to the pulmonary and systemic circulation. Other Structures: Valves - flaps of connective tissue anchored in heart’s dense connective tissue (cardiac Figure 4. Subendocardial layer (En : Endothelium; SEn : skeleton) Subendocardial layer; P : Purkinje fiber; M : Muscle fiber) Chordae tendineae - cords that extend from cusps of both atrioventricular valves (AV valve) and attach to papillary muscles, preventing the valves from turning inside-out during ventricular contraction. ○ Valves and cord covered by nonthrombogenic endothelium Figure 5. Subendocardial layer, atrial walls. Figure 3. The Heart. B. MYOCARDIUM Middle layer III. MAJOR LAYERS OF THE HEART Cardiac muscle with fibers arranged spirally around each heart chamber A. ENDOCARDIUM It has strong force required to pump blood through systemic and pulmonary circulations, Innermost layer thus thicker myocardium is found in the Near the atrial and ventricular cavity ventricle compared to the atria and thicker on Endothelial cells - simple squamous epithelium the left side of the heart than on the right side. Could be medial or lateral Thicker layer than endocardium Next to a space Myocardial cells Dense, bright, pink-staining Blood vessels and nerve fibers can be seen BATCH TANNAWAG 1C 2 HISTOLOGY LC10: THE HEART Dr. Agdamag, P. N. 11/25/2024 C. EPICARDIUM OR PERICARDIUM ○ Helping coordinate the heartbeat by acting as electrical insulation between atria and Simple squamous mesothelium supported by ventricles. a layer of loose connective tissue containing blood vessels and nerves. Conducting System of the Heart During heart movements, underlying structures Made up of modified cardiac muscle cells to are cushioned by deposits of adipose tissue in generate and conduct waves of depolarization, epicardium. which stimulate rhythmic contractions in Friction is prevented by lubricant fluid produced adjacent myocardial fibers. by both layers of serous mesothelial cells. Sinoatrial (SA) node (or pacemaker) - located It is divided into two layers: in the right atrial wall near the superior vena ○ Parietal epicardium - membrane cava surrounding the heart. ○ Described as a 6-7mm3 region of less ○ Visceral epicardium - the outermost well-stained cardiac muscle cells with layer, where the large vessels enter and smaller size, fewer myofibrils, and fewer leave the heart. typical intercalated disks than the neighboring contractile fibers ○ Impulses initiated by these cells move along myocardial fibers of both atria, stimulating their contraction. Atrioventricular (AV) node - located in the floor of the right atrium near the AV valve and composed of cells similar to those of the SA node, which stimulate depolarization myocytes. AV bundle (Bundle of His) - conducting myocytes passes through an opening in the cardiac skeleton into the interventricular septum where it bifurcates into left and right bundles of myocytes located within the myocardium and subendocardial layer. Figure 6. Epicardium/visceral pericardium (Mes : Mesothelium; CT: connective tissue (loose); N : nerve (autonomic); Ep : Purkinje fibers - located at the apex of the Epicardium; F : Fat / Adipocytes; M : Myocardium) heart, where branches subdivide further into a subendocardial conducting network of cardiac muscle fibers. ○ Pale-staining fibers, larger than the adjacent contractile fibers, with sparse, peripheral myofibrils, and much glycogen. ○ Mingle distally with contractile muscle fibers of each ventricle and trigger waves of contraction through both ventricles simultaneously. Innervation of the Heart Both parasympathetic and sympathetic neural components innervate the heart. Ganglionic nerve cells and nerve fibers are present in the regions close to the SA and AV nodes, where they affect heart rate and rhythm, Figure 7. Myocardium, epicardium, and surround blood vessels and nerve fibers (NF : Nerve fibers; BV :Blood vessels (arteriole such as during physical exercise and emotional and venule)) stress. Parasympathetic division (vagus nerve) - slows the heartbeat IV. CARDIAC SKELETON Sympathetic nerve - accelerates activity of the pacemaker. Consists of dense irregular connective tissue, Between fibers of the myocardium are afferent primarily on the endocardium, that separates free nerve endings that register pain, such as the musculature of the atria from that of the the discomfort called angina pectoris that ventricles. occurs when partially occluded coronary Forms part of the interventricular and interatrial arteries cause local oxygen deprivation. septa, and extends into the valve cusps and Abnormal heart valves, caused by defects or the chordae tendineae to which they are conditions like hypertension, can lead to attached. regurgitation, heart murmurs, and increased Functions: heart workload, causing enlargement. ○ Anchors the valves and surrounds the AV Valve defects may be surgically repaired or canals, maintaining their proper shape. replaced with artificial or animal valves, ○ Providing firm points of insertion for requiring anticoagulants to prevent thrombus cardiac muscle in the atria and ventricles. formation due to the lack of endothelial covering. BATCH TANNAWAG 1C 3 HISTOLOGY LC10: THE HEART Dr. Agdamag, P. N. 11/25/2024 Systolic BP: 120mmHg (also your systemic blood pressure) Pulmonary pressure: 40mmHg or less Right ventricle will pump against a 40mmHg pressure while the left ventricle will pump against 120mmHg. Since the right ventricle will pump against lower pressure, its myocardium doesn’t have to be very thick. 13. Main difference between atria and ventricle? Figure 8. Valve leaflet and cardiac skeleton (En : Endocardium; ➝ Atria: thinner myocardium; Arrow : Atrioventricular valve; CT : Chordae tendineae; C : Dense receives blood connective tissue; A : Atrium; V : Ventricle; M : Myocardium). ➝ Ventricles: thicker myocardium; propels blood V. RECITATION QUESTIONS 14. Does the atria pump? ➝ Yes, but not definitely 1. What is the main function of the heart? ➝ To pump blood Note: 3 phase diastole: 2. Who is in-charge of the blood pressure? First phase: Early rapid filling a. Arteries Second phase: Slow filling b. Veins Third phase: Atrial filling c. Capillaries 3. At rest, how many percent of the blood is 15. What attaches the valve? A cord that in the Heart? extends from cusps of both atrioventricular ➝ 12% valves (AV valve) and attach to papillary 4. At rest, how many percent of the blood is muscles. in the Systemic Circulation? ➝ Chordae tendineae ➝ 70% 16. When you have occluded coronary arteries 5. At rest, how many percent of blood is in (ex. on stable coronary heart disease), the Pulmonary Circulation? what do you call the type of pain that you ➝ 18% have? 6. What is the largest vein? ➝ Angina pectoris ➝ Inferior & superior vena cava 17. How can you tell if it's angina? 7. From the right atrium to the right ventricle, ➝ Because of lack of supply, the what do you call the valve? supply is occluded. Not always chest pain, ➝ Tricuspid valve there is chest pain if there is increase in 8. Which artery carries the deoxygenated demand of oxygen (e.g. physical activity, blood? exercise, stress, anger). ➝ Pulmonary artery 18. What are the 3 layers of the blood 9. In between the left atrium and left ventricle, vessels? what do you call the valve? ➝ Innermost layer: Tunica ➝ Mitral valve intima 10. How many layers does the capillary have? ➝ Middle layer: Tunica media ➝ Two layers ➝ Outermost layer: Tunica 11. Before it goes to the aorta, what do you adventitia / Tunica externa call the valve? 19. Cross sectional view of the heart: what are ➝ Aortic valve the 3 layers of the heart? 12. Difference between the right ventricle & left ➝ Innermost layer: ventricle? Endocardium ➝ Left ventricle is thicker ➝ Middle layer: Myocardium because it is a higher pressure ➝ Outermost layer: chamber compared to the right Epicardium/ Pericardium ventricle. 20. Endocardium consists of 3 layers? ➝ Inner layer thin endothelium Note: Both ventricles have afterload (which is the ➝ Middle myoelastic (smooth pressure by which your heart pumps against/ muscle fibers) & the connective generally known as the blood pressure). tissues Diastolic BP: 80mmHg ➝ Deep subendocardial layer BATCH TANNAWAG 1C 4 HISTOLOGY LC10: THE HEART Dr. Agdamag, P. N. 11/25/2024 21. Endocardium is special because of these special fibers which run just beneath the endocardium and part of the conduction system of the heart. ➝ Purkinje fibers Note: Electrical activity goes through SA-AV- Bundle branch-Common bundle branch-Right and Left-Purkinje fibers, which go on top of your atria into your ventricles. 22. What are the two pericardium present in your heart? ➝ Visceral and Parietal pericardium Note: Directly surrounding your heart is the visceral; parietal is the one that is further away from the heart. 23. A normal or "pacemaker" is the: ➝ Sinoatrial (SA) Node 24. Innervations of the heart: between your sympathetic and parasympathetic, which one will slow down your heart rate? ➝ Parasympathetic Note: Sympathetic: Accelerates heart rate. References: Mescher, A. L. (2021). Junqueira's basic histology: Text and atlas (17th ed.). McGraw Hill. Eroschenko V.P. diFiore’s Atlas of Histology with Functional Correlation. 13th ed, 2017. Dr. Agdamag’s PowerPoint Presentation. S.Y. 2024-2025 - CV Heart. University of Northern Philippines. College of Medicine. BATCH TANNAWAG 1C 5