Blood Circulatory System

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MD 3Y1 - 6

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Blood Circulatory System

  1. 1. BLOOD VASCULAR SYSTEM MD 3Y1-6 Midterm Discussion 3 bonto, mae willrose c.
  2. 2. ● Circulatory system: 1. blood vascular system 2. lymphatic vascular system ● Blood Vascular System: 1. Heart 2. Arteries - carry blood to tissues - become smaller as they branch 3. Capillaries - smallest blood vessel - interchange b/w blood & tissues 4. Veins - carry blood to heart - become larger as they converge
  3. 3. ● Vessels of the blood circulatory system: 1. principal organ: heart - pumps blood throughout body - provides for nutrients to leave capillaries and enter tissues 2. large elastic arteries (leave heart & branch to form muscular arteries) 3. muscular arteries (branch & enter organs) 4. arterioles 5. capillaries 6. venules 7. veins
  4. 4. ● Macrovasculature: - vessels more than 0.1mm in diameter - large arterioles - muscular & elastic arteries - muscular veins ● Microvasculature: - visible only w/ microscope - arterioles - capillaries - postcapillary venules - site of interchanges b/w blood & surrounding tissues under: 1. normal conditions 2. inflammatory processes
  5. 5. ● Macrovasculature: - vessels more than 0.1mm in diameter - large arterioles - muscular & elastic arteries - muscular veins ● Microvasculature: - visible only w/ microscope - arterioles - capillaries - postcapillary venules - site of interchanges b/w blood & surrounding tissues under: 1. normal conditions 2. inflammatory processes
  6. 6. ● General Plan of the Vascular Wall: 1. Tunica intima - 1 layer of endothelial cells supported by a thin subendothelial layer of loose CT w/ occasional smooth muscle cells - internal elastic lamina: separates the intima from the media in arteries - composed of elastin - has fenestrae (holes) - allows diffusion of substances to cells deep in vessel wall - slightly folded appearance in tissues at death
  7. 7. 2. Tunica Media: - middle layer - concentric layers of helically arranged smooth muscle cells - elastic fibers & lamellae, reticular fibers of collagen type III, proteoglycans & glycoproteins are interposed among & produced by smooth muscles - external elastic lamina: thin layer separating the media & the adventitia in arteries 3. Tunica Adventitia/Externa - consists of type I collagen & elastic fibers - gradually continuous w/ stromal CT of the organ through w/c b.v. runs
  8. 8. – Arteries: - thicker tunica media - narrow lumen – Veins: - thicker tunica externa - large lumen - tunica intima often folded to form valves – Capillaries: - only have an endothelium - no subendothelial later/ other tunics
  9. 9. ● Vasa vasorum: - “vessels of the vessels” - often present in large vessels - arterioles, capillaries, venules in adventitia & parts of the media - provides metabolites to cells of respective layers since walls of large vessels are often too thick to be nourished solely by diffusion - luminal blood alone does not provide nutrients & O2 for tunica intima - veins have more vasa vasorum than arteries since they carry deoxygenated blood - large arteries supplied more sparesly w/ small sympathetic nerves for control of vasoconstriction
  10. 10. ● Vasomotor nerves - network of of unmyelinated nerve fibers - neurotransmitter is norepinephrine - discharge of norepinephrine from nerves produce vasoconstriction - nerves do not enter media of arteries - neurotransmitter diffuses for several um to affect smooth muscle cells where gap junctions propagate response to inner layers of muscle cells - nerve endings found in adventitia & media of veins but its density is less than that of arteries - Acetylcholine released by nerves act on endothelium producing nitric oxide w/c diffuses into smooth muscle cells - muscle cells relax & vessel lumen is dilated
  11. 11. ● Blood Vessels 1. Capillaries - “exchange vessels” - composed of a single layer of endothelial cells in the form of a tube - ave. diameter: 5- 10 um - individual length: <50 um - comprise 90% of all b.v. in body - total length: 96,000 km - velocity of blood flow: 0.3 mm/s - favourable site for exchange of H2 O, CO2 , substrates, metabolites, solutes, macromolecules b/w blood & tissue b/c of thin walls & slow blood flow
  12. 12. Endothelial Cells: - polygonal & elongated in direction of blood flow - nucleus causes bulge into capillary lumen - cytoplasm: small Golgi body, mitochondria, free ribosomes, sparse cisternae of RER 1. small molecules diffuse/actively transported to plasmalemma of capillary endothelial cells 2. substances diffuse through endothelial cytoplasm to opposite cell surface 3. discharged into extracellular space - water & some hydrophobic molecules w/ <1.5 nm diameter & <10 kDain molec.mass diffuse through intercellular junctions (paracellular pathway) - pathways for large molecules: pores of fenestrated capillaries, spaces b/w endothelial cells of sinusoidal capillaries & pinocytotic vessels
  13. 13. Pericytes/Adventitial cells - cells of capillaries & venules of mesenchymal origin - long cytoplasmic processes partly surrounding the endothelial layer - enclosed in their own basal lamina - well-developed networks of myosin, actin & tropomyosin: contractile function - proliferate & differentiate to form tunica media of new b.v. & cells w/ functions in re-establishing the microvasculature & its extra-cellular matrix
  14. 14. Types of Capillaries 1. Continuous/tight capillary - most common - allows regulated exchange of material - characterized by continuity of cells - tight occluding junctions seal intercellular clefts b/w all endothelial cells for minimal fluid leakage - found in muscles, CT, exocrine glands & nervous tissues - in some places (except NS) numerous pinocytotic vesicles present on endothelial cell surfaces - vesicles appear isolated in cytoplasm - resp. for transcytosis of macromolecules across endothelial cytoplasm
  15. 15. 2. Fenestrated capillary - allows more extensive exchange - characterized by presence of small circular fenestrae through endothelial cells - each fenestra usually covered w/ very thin diaphragm containing heparan proteoglycans w/o lipid bilayer - continuous basal lamina covers fenestrae - macromolecules can cross through fenestrae - found in tissues where rapid interchange of substances occurs b/w tissues & blood - ex. Kidneys, intestine, choroid plexus & endocrine glands
  16. 16. 3. Sinusoid/ Discontinuous capillary - allows maximal exchange of macromolecules & cells b/w tissues & blood; easy movement of blood cells - greater diameter than most capillaries - found in liver, speen, bone marrow & some endocrine glands - characterized by: 1. endothelial cells w/ large fenestrae w/o diaphragm 2. discontinuous layer separated by wide spaces 3. discontinuous basal lamina
  17. 17. ● Tissues w/ high metabolic rates - abundant capillary network: kidney liver cardiac muscles skeletal muscles ● Tissues w/ low metabolic rates - less capillary network: dense CT smooth muscle
  18. 18. ● Arterioles - repeated branches of muscular arteries - 1-2 muscle layers - smallest arteries - indicate organ's microvasculature where exchanges of blood & tissue fluid occur - diameter: <0.5 mm - lumens as wide as wall is thick Metarterioles - smaller branches of arterioles - layer of smooth muscle disperse as bands of cells acting as precapillary sphincters - allow blood to enter bed of capillaries in a pulsatile manner Thorough Channel - lacks smooth muscle
  19. 19. ● Post capillary Venules - convergence of capillaries & metartioles ● Arteriovenous shuts/ anastomoses - regulates blood flow by allowing direct communication b/w arterioles & venules - richly innervated by sympathetic & parasympathetic nervous system - abundant in skeletal muscles, skin of hands & feet - when vessels contract, all blood must pass through capillary network - when vessels relax, some blood flows to venules instead of circulating in capillaries
  20. 20. ● Anastomoses (cont.,) - changes in diameter of vessels regulate: blood pressure blood flow temperature heat conservation - arterioles in shunts: - thick, capsule-like adventitia - thick smooth muscle layer ● Venules - diameter of lumen in all venules are large compared w/ thickness of its wall
  21. 21. ● Venules (cont.,) 1. post capillary venules - diameter: 15-20 um - w/ pericytes - participate in exchanges b/w bood & tissues - primary site where WBC leave circulation at sites of infection/tissue damage 2. collecting venules - convergence of postcapillary venules - more contractile cells 3. muscular venules - surrounded by tunica media - 2-3 smooth muscle layers
  22. 22. ● Blood Vessels 2. Arteries Elastic arteries help stabilize blood flow - incl. aorta & its larger branches - b/w elastic laminae: smooth muscles, reticular fibers, proteoglycans, glycoproteins Media: - elastin produces yellowish colour - consists of: elastic fibers + series of concentrically arranged, perforated elastic laminae whose no. increase w/ age ≈40: newborn ≈70: adults Intima: thicker than those of muscular artery Adventitia: underdeveloped
  23. 23. ● Blood Vessels 2. Arteries Elastic arteries help stabilize blood flow - incl. aorta & its larger branches - b/w elastic laminae: smooth muscles, reticular fibers, proteoglycans, glycoproteins Media: - elastin produces yellowish colour - consists of: elastic fibers + series of concentrically arranged, perforated elastic laminae whose no. increase w/ age ≈40: newborn ≈70: adults Intima: thicker than those of muscular artery Adventitia: underdeveloped
  24. 24. - largest arteries are elastic & expand when heart contracts - several elastic laminae function to make blood flow more uniform: Systole: elastic laminae of large arteries stretch, reducing the force of pressure Diastole: elastic rebound of large arteries help maintain arterial pressure when ventricular pressure drops = arterial pressure & blood velocity decrease & become less variable as distance from heart increases - w/ increasing distance from the heart, arteries gradually have less elastin and more smooth muscle
  25. 25. Muscular arteries Media: contraction/relaxation of smooth muscle cells control blood flow to organs - contains up to 40 layers of prominent smooth muscle cells w/c intermingle w/ a no. of elastic laminae, reticular fibers & proteoglycans - external elastic lamina present only in larger muscular arteries Intima: - thin subendothelial layer - prominent internal elastic lamina Adventitia: - consists of CT - lymphatic capillaries, vasa vasorum, nerves may penetrate to outer part of media
  26. 26. ● Blood Vessels 3. Veins - blood entering veins under low pressure - move towards heart by contraction of tunica media & external compressions from surrounding muscles & other organs -valves from tunica intima prevent back-flow of blood - most are small or medium veins <1cm - usually travel parallel w/ corresponding arteries Intima usually has a thin subendothelial layer Media consists of small bundlesof smooth muscle cells intermixed with reticular fibers & a delicate network of elastic fibers Adventitia is collagenous & well-developed
  27. 27. Small veins: - very thin - 2-3 layers of smooth muscle Large veins: - big venous trunks, paired w/ elastic arteries close to heart Media: - thin w/ few thin layers of smooth muscles - abundant CT (elastic fibers Intima: well developed Adventitia: - thick & often contains longtitudinal bundles of smooth muscle - elastic fibers
  28. 28. Valves - most prominent in large veins - consists of paired semi-lunar folds of tunica intima projecting across parts of the lumen - rich in elastic fibers - lined both sides by endothelium - esp. numerous in veins of legs - help keep flow of venous blood directed towards the heart ● HEART - muscular organ contracting rhythmically, pumping blood throughout circulatory system - ventricles pump blood to lungs & body - atria receives blood from body
  29. 29. - walls of all 4 heart chambers consist of 3 tunics: 1. internal endocardium 2. middle myocardium 3. external epicardium Endocardium - single layer of squamous endothelial cells on a thin layer of loose CT (elastic + collagen fibers + smooth muscle cells) - subendocardial connects subendothelial layer to mycardium - veins, nerves, branches of impulse- conducting system of heart
  30. 30. Myocardium - thickest tunic - consists of cardiac muscle cells arranged in layers surrounding heart chambers in a complex spiral - thicker in ventricles than in atria Epicardium - covers the heart - simple squamous epithelium (mesothelium) supported by a thin layer of CT - subepicardial layer of loose CT: veins, nerves, adipocytes - corresponds to visceral layer of pericardium (serous membrane of heart) - small amount of lubricant fluid facilitates heart's movements in space b/w epicardium & parietal layer
  31. 31. Sinoatrial (SA) node - located at right atrium - “pace maker” - small mass of modified cardiac muscle cells - in fusiform smaller, w/ fewer myofibrils than neighbouring muscle cells Atrioventricular (AV) node - located at right atrium - cytoplasmic projections branch in various directions, forming a network Atrioventricular bundle - originates from AV node - passes interventricular septum & splits into L & R bundles then branch further to ventricles
  32. 32. - cells/fibers of impulse-conducting system are modified cardiac muscles functionally integrated by gap junctions Purkinje fibers (conducting myofibers) - 1 or 2 central nuclei - cytoplasm rich in mitochondria & glycogen - myofibrils are sparse & restricted to periphery of cytoplasm - fibers penetrate myocardial layer of ventricles, allowing stimulus for contraction to reach innermost layers of ventricular musculature
  33. 33. - parasympathetic & sympathetic neural components innervates heart - ganglionic nerve cells & nerve fibers present in areas close to SA & AV nodes - affects heart rate & rhythm ex. physical excersize emotional stress - stimulation of parasympathetic division (vagus nerve) slows heart beat - stimulation of sympathetic nerve accelerated rhythm of pacemaker

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