Veins Histology PDF

(004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 OUTLINE I. VENULES II. VEINS...

(004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 OUTLINE I. VENULES II. VEINS A. SMALL OR MEDIUM VEINS B. LARGE VEINS III. VALVES I.VENULES -The smallest veins that receive blood from converging capillaries Size varies from 10 microns (post-capillary venules) to 1 mm (muscular venules) Larger diameter than capillaries; consist of endothelium surrounded by pericytes Attenuated endothelium that is 0.2-0.4 μm wide lines these venules. A few intercellular junctions link adjacent endothelial cells of venules The endothelium, usually resting on a thin basal lamina, is loosely organized and relatively leaky compared with other parts of the vascular system Functions: 1) Collect blood from capillaries 2) Respond to vasoactive agents (e.g., histamine, serotonin) by altering permeability 3) Also, a site of exchange of materials between tissue fluid and blood 4) Site of exit of WBCs from blood into tissue Transition from capillaries to venules occurs gradually Fig. 1. Venule Immediate postcapillary venules similar to capillaries with Pericytes, range diameter from 15 to 20 μm A series of increasingly larger and more organized venules lie between Primary site at which white blood cells adhere to endothelium and capillaries and veins. leave the circulation at sites of infection or tissue damage. (a) Compared to arterioles (A), postcapillary venules (V) have large lumens and an intima of simple endothelial cells, with occasional pericytes (P). These vessels are preferred sites for exchange of blood cells and X400. Toluidine blue (TB). tissue exudate from the circulation to surrounding tissues, (b) Larger collecting venules (V) have much greater diameters than especially during acute inflammation. arterioles (A), but the wall is still very thin, consisting of an endothelium with more numerous pericytes or smooth muscle cells. Postcapillary venules converge into larger collecting venules that X200. Toluidine blue. have more contractile cells. With greater size, venules become surrounded by tunica media with two or three smooth muscle layers ( muscular venules) characteristic feature of all venules is large diameter of lumen compared to the overall thinness of the wall Venule walls are also thinner than walls of companion arterioles. Intraluminal pressure differences often cause venules to appear collapsed in section and with an irregular contour; The thin venule wall is adapted to functions in fluid exchange and as common sites of trans endothelial leukocyte migration, known as diapedesis. Page 1 of 5 CMED 1F  (004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 A. SMALL OR MEDIUM VEINS diameters of 10 mm or less located close and parallel to corresponding muscular arteries A. tunica intima – thin subendothelial layer B. tunica media - small bundles of smooth muscle cells + reticular fibers + delicate network of elastic fibers. C. tunica adventitia well developed collagenous layer Function - to collect blood from smaller venous vessels Fig.2. Light Microscopy of a venule and arteriole in transverse section The venule has a thin wall and a relatively larger lumen than the arteriole. The lumen of each vessel holds many erythrocytes, but the venule lumen also has many white blood cells, a feature often seen in sections of venules. Fig. 4. Light Microscopy of the wall of a muscular artery (Left) and Venules have thin walls and are thus the main site of migration of leukocytes muscular vein (Right). from the bloodstream to tissues. Via contraction, smooth muscle in arterioles regulates pressure in the arterial system. 450×. H&E. The arterial wall has more elastic fibers (in black), whereas the vein has more collagen (in orange). Smooth muscle in the artery imparts an intense eosinophilia to the media (TM). Internal elastic lamina (IEL), external elastic lamina (EEL), adventitia (TA), and lumen (*) are indicated. 320×. II. VEINS Gomori aldehyde fuchsin. Carry blood back to heart from microvasculature all over the body Blood under very low pressure B. LARGE VEINS Moves toward heart by contraction of smooth muscle fibers in Big venous trunks, paired with elastic arteries close to heart, media and by external compressions from surrounding muscles Tunica intima – well developed and other organs Tunica media- thin with alternating layers of smooth muscle and Valves project from the tunica intima to prevent backflow of blood connective tissue. Tunica adventitia thicker than media in large veins and frequently contains longitudinal bundles of smooth muscle. Both the media and adventitia contain elastic fibers, but internal and external elastic laminae like those of arteries are not present Function - to collect blood from medium sized veins and return it to heart HISTOLOGY OF LARGE VEINS: THE VENAE CAVAE The superior and inferior venae cavae are large veins that deliver deoxygenated blood to the right atrium. Others similar histologic features: o Porta Vein o Pulmonary Vein o Azygos o Renal Vein o Suprarenal Vein o Splenic Vein o Superior Mesenteric Veins. They all have a thin intima with one layer of endothelial cells resting on an incomplete basement membrane. Fig. 3. Veins Subendothelial connective tissue in these veins contains a network of Veins usually travel as companions to arteries and are classified as small, elastic fibers with scattered fibroblasts. medium, or large based on size and develop- ment of the tunics. Micrograph The media is not well developed, and its content of circularly arranged of small vein (V) shows a relatively large lumen compared to the small smooth muscle varies greatly according to location muscular artery (A) with its thick media (M) and adventitia (Ad). The wall of a small vein is very thin, containing only two or three layers of smooth muscle. X200. H&E. Page 2 of 5 CMED 1F  (004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 Example: media in uterine veins has several layers of smooth muscle, whereas that in meningeal and retinal veins has no smooth muscle. III.VALVES Paired folds of the intima projecting across the lumen in medium In contrast, the adventitia—the thickest layer in large veins—may and large veins contain bundles of longitudinally oriented smooth muscle cells Rich in elastic fibers lined on both sides by endothelium interspersed with collagen and elastic fibers. Numerous in veins of the legs The abundant collagen fibers have either a longitudinal or helical Help keep the flow of venous blood directed toward the heart orientation. Leukocytes from the bloodstream to tissues. Via contraction, At their entrances to the heart, venae cavae and pulmonary veins have smooth muscle in arterioles regulates pressure in the arterial a small amount of cardiac muscle in the adventitia. system. Compared with arterial walls, walls of veins have more extensive vasa vasorum, penetrating from the adventitia into deeper regions. Fig.5. LM of the wall of the superior vena cava. Elastic fibers stain black and are seen in the intima (arrows) and scattered Fig.7. Wall of large vein with valve in the media (TM) and adventitia (TA). The media also contains layers of Large veins have a muscular media layer (M) which is very thin compared smooth muscle (SM) oriented in different directions. A small muscular artery to the surrounding adventitia (A) of dense irregular connective tissue. The (Ar) is part of the rich vasa vasorum feature of veins of this caliber. The wall is often folded as shown here, with the intima (I) projecting into the intima (TI) is indicated, and lumen of the vessel (*) is at the left. 100×. lumen as a valve (V) composed of the subendothelial connective tissue Verhoeff-van Gieson. with endothelium on both sides. (X100; PT Fig.6. LM of the wall of the inferior vena cava. The lumen (*) is lined by an attenuated intima (TI). A few layers of circular smooth muscle cells occupy the thin media (TM). The adventitia (TA), the thickest layer, contains longitudinal bundles of smooth muscle (SM) interspersed with collagen fibers, as well as vasa vasorum (arrow). 60×. H&E. Page 3 of 5 CMED 1F  (004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 IV.APPENDIX Page 4 of 5 CMED 1F  (004) VEINS DR. PEEBLE AGDAMAG | 01/18/21 TEST YOUR KNOWLEDGE C B A D C A C D B A D FALSE TRUE ANSWER KEY: 1-5 Choices: a. Elastic artery c. Small artery b. Muscular artery d. Arteriole 1. The connective tissue of adventitia layer of this artery is thinner than media and has no vasa vasorum. 2. It distributes blood to all organs and maintains steady blood pressure; and maintains steady blood pressure and flow with vasoldilation and constriction. 3. Its outer diameter is approximately >10mm 4. Endothelium in the intima has no connective tissue or smooth muscle. 5. Its Media has 3-10 layers of smooth muscle 6. They have thick layer of muscles and elastic fibers; narrow lumen and thick outer wall. a. Arteries b. Veins c. Capillaries d. NOTA 7. Which of the following correctly describe the vessel in the photo above? a. It is situated deep to the body surface b. It has a very small lumen c. It has a thin layer of muscles and elastic fibers d. It does not have any semi lunar valves. 8. Venules: a. Primary site at which white blood cells adhere to endothelium. b. Leave the circulation at sites of infection or tissue damage. c. Size of its diameter is at 15 to 20 μm d. AOTA 9. The last segment of the microvasculature and is the primary site at which white blood cells enter damaged or infected tissues A. Arterioles B. Venules C. Veins D. Capillary beds 10. A characteristic feature of veins and venules are valves that function to: A. Prevent backflow of blood B. Keep the flow of venous blood directed away from the heart C. Provide extra strength for the vessels D. Serve as attachments for WBC's 11.. Compared to arterioles, venules have A. Thicker wall and larger lumen B. Smaller diameter of lumen C. Thinner wall and smaller lumen with RBC's and WBC's D. Relatively larger lumen with RBC's and WBC's 12. True or False. With greater size, venules become surrounded by tunica media with three or five smooth muscle layers. 13. True or False. Valves project from the tunica intima to prevent backflow of blood. Page 5 of 5 CMED 1F