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Embryology and histology of bloodvessels
- 1. Embryology and Histology of BloodVessels Edited by: Std.Dr.Orlando Joseph Course: System Pathology Institution: Georgetown American University
- 2. EMBRYOLOGY
- 3. Early Development of Cardiovascular System At the end of the second week, embryonic nutrition is obtained from the maternal blood by diffusion through the extraembryonic coelom and umbilical vesicle. At the beginning of the third week, blood vessel formation begins in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion. Embryonic blood vessels begin to develop approximately 2 days later. The early formation of the cardiovascular system is correlated with the urgent need for blood vessels to bring oxygen and nourishment to the embryo from the maternal circulation through the placenta. Blood and blood vessels originates from mesoderm
- 4. Development of chorionic villi Shortly after primary chorionic villi appear at the end of the second week, they begin to branch. Early in the third week, mesenchyme grows into these primary villi, forming a core of mesenchymal tissue.The villi at this stage—secondary chorionic villi—cover the entire surface of the chorionic sac. Some mesenchymal cells in the villi soon differentiate into capillaries and blood cellsVilli are called tertiary chorionic villi when blood vessels are visible in them. The capillaries in the chorionic villi fuse to form arteriocapillary networks, which soon become connected with the embryonic heart through vessels that differentiate in the mesenchyme of the chorion and connecting stalk
- 5. By the end of the third week, embryonic blood begins to flow slowly through the capillaries in the chorionic villi. Oxygen and nutrients in the maternal blood in the intervillous space diffuse through the walls of the villi and enter the embryo’s blood . Carbon dioxide and waste products diffuse from blood in the fetal capillaries through the wall of the chorionic villi into the maternal blood. Concurrently, cytotrophoblastic cells of the chorionic villi proliferate and extend through the syncytiotrophoblast to form an extravillous cytotrophoblastic shell ,which gradually surrounds the chorionic sac and attaches it to the endometrium.
- 6. Villi that attach to the maternal tissues through the cytotrophoblastic shell are stem chorionic villi (anchoringvilli). The villi that grow from the sides of the stem villi are branch chorionic villi. It is through the walls of the branch villi that the main exchange of material between the blood of the mother and the embryo takes place. The branch villi are bathed in continually changing maternal blood in the intervillous space
- 11. Vasculogenesis and Angiogenesis Blood vessels begins to develop at the ending of second week to the begin of third week of pregnancy during cardiovascular development. The formation of the embryonic vascular system involves two processes, vasculogenesis and angiogenesis. Vasculogenesis is the formation of new vascular channels by assembly of individual cell precursors (angioblasts) and occurs in mesoderm. Angiogenesis is the formation of new vessels by budding and branching from preexisting vessels and occur Occurs in adult life. Blood vessel formation in the embryo and extraembryonic membranes during the third week begins when mesenchymal cells differentiate into endothelial cell precursors, or angioblasts (vessel-forming cells).
- 12. Angioblasts aggregate to form isolated angiogenic cell clusters, or blood islands, which are associated with the umbilical vesicle or endothelial cords within the embryo. Small cavities appear within the blood islands and endothelial cords by confluence of intercellular clefts. The angioblasts flatten to form endothelial cells that arrange themselves around the cavities in the blood islands to form the endothelium. Many of these endothelium-lined cavities soon fuse to form networks of endothelial channels (vasculogenesis). Additional vessels sprout into adjacent areas by endothelial budding (angiogenesis) and fuse with other vessels.The mesenchymal cells surrounding the primordial endothelial blood vessels differentiate into the muscular and connective tissue elements of the vessels.
- 14. Blood cells develop from specialized endothelial cells (hemangiogenic epithelium) of vessels as they grow on the umbilical vesicle and allantois at the end of the third week and later in specialized sites along the dorsal aorta. Progenitor blood cells also arise directly from hemangiopoietic stem cells. Blood formation (hematogenesis) does not begin in the embryo until the fifth week. It occurs first along the aorta and then in various parts of the embryonic mesenchyme, mainly the liver and later in the spleen, bone marrow, and lymph nodes. Fetal and adult erythrocytes are derived from hematopoietic progenitor cells
- 16. Summary
- 18. Lymphatic Vessels The lymphatic system begins to develop at the end of the sixth week, approximately 2 weeks after the primordia of the cardiovascular system are recognizable. Lymphatic vessels develop in a manner similar to that previously described for blood vessels, and make connections with the venous system. The early lymphatic capillaries join each other to form a network of lymphatics .
- 19. Development of the lymphatic system. A, Left side of a 712- week embryo showing the primary lymph sacs. B,Ventral view of the lymphatic system at 9 weeks showing the paired thoracic ducts. C, Later in the fetal period, illustrating formation of the thoracic duct and right lymphatic duct.
- 20. Development of LymphSacs and Lymphatic Ducts There are six primary lymph sacs present at the end of the embryonic period: Two jugular lymph sacs near the junction of the subclavian veins with the anterior cardinal veins (the future internal jugular veins) Two iliac lymph sacs near the junction of the iliac veins with the posterior cardinal veins One retroperitoneal lymph sac in the root of the mesentery on the posterior abdominal wall One cisterna chyli (chyle cistern) located dorsal to the retroperitoneal lymph sac
- 21. Lymphatic vessels soon connect to the lymph sacs and pass along main veins: to the head, neck, and upper limbs from the jugular lymph sacs; to the lower trunk and lower limbs from the iliac lymph sacs; and to the primordial gut from the retroperitoneal lymph sac and the cisterna chyli. Two large channels (right and left thoracic ducts) connect the jugular lymph sacs with this cistern. Soon a large anastomosis forms between these channels
- 22. Embryology of Blood vessels
- 23. HISTOLOGY
- 24. Histological Techniques/ Examination Microscopic view Light microscope Electron microscope(TEM&SEM) Histological stains Hematoxylin and Eosin (H&E) Reticular stain Alkaline Phosphatase Elastic stain Luna Stain Trichrome stains Blood vessels and its structures Capillaries Arteries Veins Capillaries Continuous Discontinuous Fenestrated Arteries Elastic arteries Muscular arteries Arterioles Veins Large veins Medium size veins Venules Lymphatics Lymph capillaries Lymph vessels
- 25. BLOODVESSEL
- 35. Blood vessel
- 36. CAPILLARIES
- 37. Capillary
- 38. Capillary (H&E)
- 39. Capillary (TEM)
- 42. Microcopy of types of capillaries Fenestrated Continuous Discontinous
- 44. Fenestrated Capillary (non glomerular region of kidney) TEM
- 49. Artery
- 50. Artery (TEM)
- 53. MuscularArtery External elastic fiber Lumen Tunica adventia Tunica Media Internal elastic fiber
- 55. Arteriole (H&E)
- 58. VEINS
- 59. Vein
- 60. Veins (H&E)
- 63. Vales inVeins Trichrome stain Vein with valve Masson trichrome (MP)
- 65. Venule (H&E)
- 66. LYMPHATICVESSELS
- 70. Lymphatic valves
- 72. References Moore.L.Keith PHD.Persuad.T.V.N.PHD.Torschia.G.Mark PHD.Developing Human.10th Edition. Elsevier Inc.chapter4,Third week of human development.early cardiovascular development.pg 64 Southern Illinois University School of Medicine.cardiovascular.retrived .Histology of the bloodvessels .retrived from http://www.siumed.edu/~dking2/crr/cvguide.htm#vessels
Editor's Notes
- Diagrams illustrating development of secondary chorionic villi into tertiary chorionic villi. Early formation of the placenta is also shown. A, Sagittal section of an embryo (approximately 16 days). B, Section of a secondary chorionic villus.
- C, Section of an implanted embryo (approximately 21 days). D, Section of a tertiary chorionic villus. The fetal blood in the capillaries is separated from the maternal blood surrounding the villus by the endothelium of the capillary, embryonic connective tissue, cytotrophoblast, and syncytiotrophoblast. A BCDSecondary chorionic villusSyncytiotrophoblastCytotrophoblastDeveloping blood vesselWall of chorionic sacMesenchymal coreEndometriumCytotrophoblastic shellTertiary chorionic villusConnective tissueCapillaries containing fetal bloodIntervillous spaceMaternal bloodMaternal sinusoid
- Diagram of the primordial cardiovascular system in an embryo of approximately 21 days, viewed from the left side. Observe the transitory stage of the paired symmetric vessels. Each heart tube continues dorsally into a dorsal aorta that passes caudally. Branches of the aortae are (1) umbilical arteries establishing connections with vessels in the chorion, (2) vitelline arteries to the umbilical vesicle, and (3) dorsal intersegmental arteries to the body of the embryo. Vessels on the umbilical vesicle form a vascular plexus that is connected to the heart tubes by vitelline veins. The cardinal veins return blood from the body of the embryo. The umbilical vein carries oxygenated blood and nutrients to the chorion, which, in turn, provides nourishment to the embryo. The arteries carry poorly oxygenated blood and waste products to the chorionic villi for transfer to the mother’s blood.
- Successive stages in the development of blood and blood vessels
- Arterioles (A), small capillaries (C) and venules (V) make up the microvasculature where, in almost every organ, exchange takes place between blood and the interstitial fluid of the tissues. X200. Masson trichrome.
- Peripheral arteries, veins, and nerves tend to travel and branch in parallel. Wherever one of these structures is found, the other two are likely to be closeby. In this specimen, elastic tissue is colored dark purple, cytoplasm (in smooth muscle and nerve) is lighter purple, and collagen is pale pink. The background is adipose connective tissue.
- Peripheral arteries, veins, and nerves tend to travel and branch in parallel. Wherever one of these structures is found, the other two are likely to be closeby. In this trichrome stained specimen, collagen is colored blue and smooth muscle is red. Red blood cells in the venous lumen are brighter red. The background is adipose connective tissue. Note differences between artery and vein, not only the thickness of the vessel wall relative to the lumen but also the overall shape (artery rounder, vein flatter). The intima is not noticable at this magnification. The media is the thickest, most conspicuous layer of the artery, much less pronounced in the vein. In this loose connective tissue, the adventitia comprises distinct layer.
- Histologically, blood vessels consist of concentric layers or "tunics" of different tissue types. The tunica intima is the inner lining, consisting of endothelium and a relatively thin layer of supporting connective tissue. The tunica media is the middle muscular and/or elastic layer, containing smooth muscle and elastic tissue in varying proportions. The tunica adventitia is the outer, fibrous connective tissue layer. Nervous tissue is generally inconspicuous in blood vessels but serves to regulate smooth muscle function and to mediate pain sensation.
- Image display endothelial lining and smooth muscle nuclei
- Capillaries are the smallest of blood vessels, with diameter close to that of red blood cells (RBCs). Capillaries are seldom conspicuous in sectioned specimens, unless (as shown here) the capillary lies within the plane of section and contains RBCs. (RBCs are often rinsed out during specimen preparation.)
- Capillary in the brain
- Three basic types of blood capillaries are illustrated. They are differentiated by the continuity of the endothelial cell and the basal lamina. A, continuous capillary; b, fenestrated capillary; c, discontinuous capillary (sinusoid). Rat diaphragm, pancreas and liver, respectively. Weiss, L. ed., Cell and Tissue Biology, 6th ed., Urban & Schwarzenberg, Baltimore, 1988, p. 381.
- Arrows indicate fenestrae closed by diaphragms. In this cell the nucleus (N), Golgi complex (G), and centrioles (C ) can be seen. Note the continuous basal lamina on the outer surface of the endothelial cell (double arrows). Junqueira, LC and Carneiro, J, Basic Histology, 11th ed., McGraw-Hill, New York, 2005. p. 216.
- Liver sinusoid in cross section (rat). Open fenestrae are evident in the endothelial cell cytoplasm. The space of Disse is between the sinusoidal wall and the hepatocytes. Cormack, D.H. Ham’s Histology, 9th ed., Lippincott, Philadelphia, 1987, p. 531.
- FIG. 8.14╇ Capillaries H&E (HP) The vessels seen here in longitudinal and transverse section illustrate the characteristic features of capillaries. A single layer of flattened endothelial cells lines the capillary lumen. The thin layer of cytoplasm is difficult to resolve by light microscopy. The flattened endothelial cell nuclei E bulge into the capillary lumen. In longitudinal section, the nuclei appear elongated, whereas in transverse section they appear more rounded. Muscular and adventitial layers are absent. Occasional flattened cells called pericytes P embrace the capillary endothelial cells and may have a contractile function. Note that the diameter of capillaries is similar to that of the red blood cells contained within them.
- FIG. 8.13╇ The microcirculation, mesenteric spread H&E (MP) This image demonstrates a network of anastomosing capillaries between an arteriole At and a venule V. The capillary network comprises small-diameter capillaries C with a single layer of endothelial cells and basement membrane, as well as largerdiameter capillaries known as metarterioles Ma. These are characterised by a discontinuous outer layer of smooth muscle cells. Small capillaries arise from both arterioles and metarterioles. At the origin of each capillary, there is a sphincter mechanism, the precapillary sphincter, which is involved in regulation of blood flow. There is also a direct wide-diameter link between the arteriole and venule, an arteriovenous shunt S. Metarterioles also form direct communications between arterioles and venules. Contraction of the smooth muscle of shunts and metarterioles directs blood through the network of small capillaries. Thus arterioles, metarterioles, precapillary sphincters and arteriovenous shunts regulate blood flow in the microcirculation. The smooth muscle activity of these vessels is modulated by the autonomic nervous system and by circulating hormones (e.g. adrenal catecholamines).
- In this trichrome stained specimen, collagen is colored blue and smooth muscle is red. Red blood cells (RBCs) in the arterial lumen are brighter red. The red texture in the upper-left corner of the image is cross-sectioned smooth muscle in wall of the (unidentified) organ from which this specimen was taken. The intima is inconspicuous, consisting of little more than very thin endothelial cells. The internal elastic lamina is unstained but distinctly visible as a sinuous band between the intima and the media. The media is the thickest, most conspicuous layer, in which individual smooth muscle fibers are clearly visible. The adventitia is not a distinct layer but merges with surrounding connective tissue.
- Internal elastic lamina Tunica media External elastic lamina Tunica adventitia Lumen
- FIG. 8.9╇ Elastic artery: aorta (a) Elastic van Gieson (LP) (b) Elastic van Gieson (HP) The highly elastic nature of the aortic wall is demonstrated in these preparations in which the elastic fibres are stained brownish-black. In micrograph (a), the three basic layers of the wall can be seen: the narrow tunica intima I, the broad tunica media M and the tunica adventitia A. The tunica intima consists of a single layer of flattened endothelial cells (not seen at this magnification) supported by a layer of collagenous tissue rich in elastin disposed in the form of both fibres and discontinuous sheets. The subendothelial supporting tissue contains scattered fibroblasts and other cells with ultrastructural features akin to smooth muscle cells and known as myointimal cells. Both cell types are probably involved in elaboration of the extracellular constituents. The myointimal cells are not invested by basement membrane and are thus not epithelial (myoepithelial) in nature. With increasing age, the myointimal cells accumulate lipid and the intima progressively thickens. If this process continues, atherosclerosis will develop. The tunica media is particularly broad and extremely elastic. At high magnification in (b), it is seen to consist of concentric fenestrated sheets of elastin (stained black) separated by collagenous tissue (stained reddish-brown) and smooth muscle fibres (stained yellow). As seen in micrograph (a), the collagenous tunica adventitia (stained reddish-brown) contains small vasa vasorum V which also penetrate the outer half of the tunica media. Blood flow within elastic arteries is highly pulsatile. With advancing age, the arterial system becomes less elastic, thereby increasing peripheral resistance and thus arterial blood pressure.
- The intima of the small artery is visible only as a "dotted line" of nuclei of endothelial cells, exactly at the edge of the arterial lumen. These nuclei look round rather than flat because post-mortem contraction of smooth muscle in the media has caused longitudinal wrinkles in the endothelium. The internal elastic lamina is inconspicuous. The media is the thickest, most conspicuous layer, in which nuclei of individual smooth muscle fibers are clearly visible. The adventitia is not a distinct layer but merges with surrounding connective tissue.
- FIG. 8.12╇ Arterioles (a) Large arteriole H&E, TS (MP) (b) Small arteriole, EM ×5250, TS Small muscular arteries merge into large arterioles, which eventually become small arterioles. These transitions are gradual with no sharp demarcations and involve loss of the internal elastic lamina and progressive reduction of the number of muscle layers in the media. Micrograph (a) shows two large arterioles, with a thin intima lined by endothelial cells E and a tunica media M comprising only 2 to 3 layers of muscle. The adventitia is thin and merges imperceptibly with surrounding supporting collagenous fibrous tissue. Micrograph (b) is an electron micrograph of a small arteriole, with a single layer of smooth muscle cells SM separated from endothelium E by basement membrane BM. The endothelium is prominent because the arteriole is constricted.
- FIG. 8.23╇ Large muscular vein Elastic van Gieson (HP) Large veins such as the femoral and renal veins again have a very narrow tunica intima, but the media M is more substantial, consisting of several layers of smooth muscle (stained yellow in this stain), separated by layers of collagenous connective tissue (red) and scanty elastic fibres (black). The tunica adventitia Ad is broad and is composed of collagen (red) and contains numerous vasa vasorum VV. Elastic fibres are particularly prominent at the junction between media and adventitia, but there are no distinct elastic laminae as there are in arteries.
- f.G masson trichome. This micrograph demonstrates a valve in a small vein. The valve consists of delicate semilunar projections of the tunica intima of the vein wall. These projections are composed of a layer of fibroelastic tissue which is lined on both sides by endothelium. Each valve usually consists of two leaflets L, the free edges of which project in the direction of blood flow. These serve to prevent backflow of blood due to the effects of gravity. Valves only occur in veins which are more than 2╯mm in diameter, particularly those draining the extremities. Varicose veins are abnormal dilatations of superficial veins which typically occur in the lower legs. These form due to incompetence of valves in the leg veins.
- Lymphatic capillaries drain interstitial fluid produced when the plasma forced from the microvasculature by hydrostatic pressure does not all return to blood by the action of osmotic pressure. (a): Micrograph showing a lymphatic capillary filled with this fluid called lymph (L). Lymphatics are blind-ended vessels with a wall of very thin endothelial cells (E) and are quite variable in diameter (10-50 m). Lymph is rich in proteins and other material and often stains somewhat better than the surrounding ground substance, as seen here. X200. Mallory trichrome. (b): Diagram indicating details of lymphatics, including the openings between the endothelial cells. The openings are held in place by anchoring filaments containing elastin and are covered by flaps of endothelium. Interstitial fluid enters primarily via these openings and the endothelial folds prevent backflow of lymph into tissue spaces. Lymphatic endothelial cells are typically larger than those of blood vessels.
- Medium-sized lymphatic vessel H&E (MP) Fig. 8.25 shows small lymphatic vessels containing only a very small amount of smooth muscle in their walls. As lymphatic channels become larger, the muscle layer ML becomes thicker and its contraction makes a greater contribution to the movement of lymph along the vessel. Backflow of lymph fluid is prevented by valves (not illustrated here). The muscle layers are most prominent in the largest lymphatic vessels which drain into the venous system (the thoracic duct and right lymphatic duct).
- (b): Lymphatic vessel (LV) in muscle is cut longitudinally showing a valve, the structure responsible for the unidirectional flow of lymph. The solid arrow shows the direction of the lymph flow, and the dotted arrows show how the valves prevent lymph backflow. The lower small lymphatic vessel is a lymphatic capillary with a wall consisting only of endothelium. X200. PT.
- Valve of a lymphatic vessel H&E (LP) A characteristic feature of the lymphatic system is the presence of numerous delicate valves within small and medium-sized vessels. The structure of these valves V is similar to that of valves in the venous system, but the supporting tissue core includes only some reticulin fibres and a little ground substance. Note the presence of light pink–stained proteinaceous lymph fluid in the channels, with scattered lymphocytes around the periphery.