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CIRCULATORY SYSTEM

CIRCULATORY SYSTEM. Kristina C. Erasmo , M.D. Function. Transport – oxygen, carbon dioxide, nutrients, hormones, waste products Immune defense. CIRCULATORY SYSTEM. Cardiovascular system Heart Two systems of blood vessels: Systemic circulation Pulmonary circulation Lymph vascular system.

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CIRCULATORY SYSTEM

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  1. CIRCULATORY SYSTEM Kristina C. Erasmo, M.D.

  2. Function • Transport – oxygen, carbon dioxide, nutrients, hormones, waste products • Immune defense

  3. CIRCULATORY SYSTEM • Cardiovascular system • Heart • Two systems of blood vessels: • Systemic circulation • Pulmonary circulation • Lymph vascular system

  4. Heart • Muscular pump that propels blood to the arteries of both systemic and pulmonary circulation • Systemic circulation – brings blood from the heart to the rest of the body then back to the heart • Pulmonary circulation – brings blood from the heart to the lungs and then back to the heart

  5. Heart • Located in the central mediastinum of the thoracic cavity • Four chambers: • Left ventricle – systemic circulation • Right ventricle – pulmonary • Left atrium • Right atrium

  6. Pericardium • Connective tissue sac covering the heart • Outer sac (fibrous pericardium) • Inner sac (serous pericardium) • Parietal pericardium • Visceral pericardium • Pericardial cavity – with fluid

  7. Pericardium • Fibrous and parietal pericardia – dense CT (collagen and elastic fibers, fibroblasts, other CT elements) • Inner aspect of parietal pericardium – simple squamous epithelium (mesothelium) • Visceral pericardium a.k.a. epicardium

  8. Histologic Layers of Heart Wall • Epicardium • Myocardium • Endocardium

  9. Epicardium • a.k.a. visceral pericardium • Outermost layer of heart wall • Lining epithelium of external surface: mesothelium

  10. Myocardium • Thickest (thickness varies for different parts) • Thickest: left ventricle • Thinnest: atria • Mainly cardiac muscle fibers

  11. Purkinje Fibers • Modified cardiac muscle cells • Initiate and conduct the electrical impulse that controls the contraction of the heart • Form the impulse-conducting system of the heart • Larger, contain more glycogen than ordinary cardiac muscle cells

  12. Myocardium • Atrialnatriuretic peptide (ANP) – polypeptide hormone secreted by cardiac muscle cells in atria and interventricular septum • Causes natriuresis– excretion of sodium by the kidneys

  13. Endocardium • Thinnest • Lining epithelium: endothelium • Continuous with innermost layer of the great blood vessels • Lines all internal surfaces of heart

  14. Endocardium • Subendothelial layer – loose CT • External to subendothelial layer – dense CT, thickest portion of endocardium

  15. Blood Vascular System • Refers to the system of blood vessels within which blood circulates • 3 types of blood vessels: • Arteries • Veins • Capillaries

  16. Blood Vascular System • Arteries – carry blood from the heart to the capillaries • Veins – carry blood from the capillaries to the heart

  17. Endothelium • Lining of the luminal surface of all blood vessels • Functions: • Lining blood vessels to facilitate blood flow • Secretes components of underlying CT

  18. Endothelium • Functions: • Secrete prostacyclin – inhibits platelet aggregation, promotes vasodilation • Nitric oxide and endothelin I – vasodilator • Von Willebrand factor – blood coagulation

  19. VasaVasorum • Network of small blood vessels that supply large blood vessels • Veins: present in the tunica adventitia and media • Arteries: confined to adventitia

  20. Capillaries • Smallest blood vessels (5-10 um) • Connect arterioles and venules • Function: Allow exchange of gases and materials between blood and surrounding tissue

  21. Capillaries • Wall consists of single layer of endothelial cells and its associated basal lamina • Surrounding connective tissue elements

  22. Pericytes • Slender, elongated, perivascular cells that usually accompany capillaries • Look like fibroblasts • Not part of the endothelium • Contain tropomyosin • Function: contractile cells that influence the luminal size of capillaries

  23. Types of Capillaries • Continuous (Type I) • Fenestrated (Type II) • Sinusoids

  24. Continuous Capillary • Found in muscles, lungs, CNS, skin • The endothelial cell and the basal lamina do not form openings (which would allow substances to pass the capillary wall without passing through both the endothelial cell and the basal lamina)

  25. Fenestrated Capillary • Mucous membranes of GIT, renal glomerulus, pancreas, some endocrine glands • Endothelial cell body forms small openings (fenestrations) which allow components of the blood and interstitial fluid to bypass the endothelial cells

  26. Sinusoids • a.k.a. discontinuous capillaries or sinusoidal capillaries • Formed by fenestrated endothelial cells, (which may not even form a complete layer of cells) • Basal lamina is also incomplete • Found in liver, spleen, red bone marrow (free exchange of substances or even cells between bloodstream and organ is advantageous)

  27. Histologic Layers of Arteries and Veins • Tunica adventitia • Tunica media • Tunica intima

  28. Tunica Adventitia • Outermost coat of arteries and veins • Chiefly made up of connective tissue with cells and fibers arranged longitudinally

  29. Tunica Media • Middle coat of arteries and veins • Concentrically arranged smooth muscle fibers • Interspersed between the muscle cells are connective tissue elements (collagen and elastic fibers)

  30. Tunica Media • In large arteries: • External elastic lamina/membrane – outer layer of elastin which demarcates the tunica media from the tunica adventitia

  31. Tunica Intima • Innermost coat of arteries and veins • Consists of a layer of endothelium that rest on a basal lamina • Subendothelial layer of loose CT • In arteries: • Internal elastic lamina/membrane – demarcates tunica intima from tunica media

  32. Arteries • Classification: • Small (arteriole) • Medium (muscular or distributing) • Large (elastic or conducting) • Decrease in size but increase in number as they go farther from the heart

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