HISTO_LC11_ARTERIES.pdf

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas OUTLINE I. MICROANATOMY OF BLOOD VESSELS II. STRUCTURES FOUND BETWEEN THE LAYERS OF THE BLOOD VESSEL A. Endothelium B. Smooth Muscle Fibers C. Connective Tissue III. LAYERS OF THE BLOOD VESSELS A. Tunica Intima B. Tunica Media C. Tunica Adventitia IV. VASA VASORUM V. CLASSIFICATION OF ARTERIES Figure 1 Artery vs, Vein VI. ELASTIC ARTERIES/ LARGE ARTERIES A. Elastic Arteries Layers B. Medical Application: atherosclerosis VII. ARTERIAL SENSORY STRUCTURES VIII. MUSCULAR ARTERIES IX. ARTERIOLES A. Structure of Arterioles B. Function of Arterioles C. Microvascular Bed Structure and Perfusion D. Medical Application X. TEST YOUR KNOWLEDGE XI. REFERENCES Figure 2. Flow of blood through the blood vessel II. STRUCTURES FOUND BETWEEN THE LAYERS OF THE BLOOD VESSEL I. MICROANATOMY OF BLOOD VESSELS A. ENDOTHELIUM - Semipermeable barrier between two major internal compartments: - Most larger blood vessel walls contain three major layers with sublayering. blood plasma and interstitial tissue fluid. - Vascular endothelial cells are squamous, polygonal, and elongated tong  Tunica intima- Luminal layer axis in direction of blood flow. a. Lumen is lined by an endothelium of simple squamous - With its basal lamina is highly differentiated to mediate and actively epithelium. monitor the bidirectional exchange of molecules by simple and active b. A subendothelial layer of loose FECT is present in most diffusion, receptor-mediated endocytosis, transcytosis, and other medium to large vessels and may contain scattered mechanisms. smooth muscle in larger vessels. - Functions: c. This layer is closest to the lumen.  Nonthrombogenic surface on which blood will not clot and actively secretes agents that control local clot formation (such as - An internal elastic lamina (elastica interna) marks the boundary between heparin. Tissue plasminogen activator, and von Willebrand the tunica intima and the tunica media. Factor). -The tunica media contains layers of either elastic laminae/lamellae  Regulate local vascular tone and blood flow by secreting various (fenestrated sheets) or FECT alternating with layers of smooth muscle. factor that stimulate smooth muscle contraction (such as - If present, the external elastic lamina (elastica externa) marks the endothelin 1 and angiotensin-converting enzyme [ACE]) or boundary between the tunica media and the tunica adventitia. relaxation (including Nitric Oxide [NO] and prostacyclin). - The tunica adventitia (tunica externa) contains loose to moderately dense  Inflammation and local immune response FECT, +/- scattered smooth muscle cells. Small and medium arteries and veins present in the tunica adventitia of large arteries and veins. B. SMOOTH MUSCLE FIBERS - Occur in the walls of all vessels larger than capillaries. - Arranged helically in layer. - In arterioles and small arteries, smooth muscle cells are connected by gap Page 1 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas junctions and permit vasoconstriction and vasodilation (regulate BP) IV. VASA VASORUM C. CONNECTIVE TISSUE - Also known as “Vessels of the Vessel” - Collagen fibers - Arterioles, capillaries, and venules are present in the tunica adventitia and  Are found in the subendothelial layer, between smooth muscle outer part of the tunica media layers, and in the outer covering. - Provide metabolites to cells in those tunics in larger vessels because wall - Elastic fibers is too thick to be nourished solely by diffusion from the blood in the lumen  Provide the resiliency for vascular wall expansion under pressure. - They carry deoxygenated blood  Elastin is a major component in large arteries where it forms - Large veins commonly have more vasa vasorum than arteries parallel lamellae, gradually distributed between muscle layers. - Vasomotor nerves network of unmyelinated autonomic nerve fibers, which release the vasoconstrictor, norepinephrine. III. LAYERS OF THE BLOOD VESSELS *Density is greater in arteries than in veins. - Transitions such as those from “small arteries” to “arterioles.“ - All larger vessels have walls with three concentric layers, or tunics (L. tunica, coat) A. TUNICA INTIMA - Innermost - Consists of:  Endothelium  This subendothelial layer of loose connective sometimes containing smooth muscle fibers. - Arteries and large veins  Includes prominent limiting later, internal elastic lamina: composed of elastin, with holes allowing better diffusion of substances from blood deeper into the wall.  B. TUNICA MEDIA - Middle layer  Concentric layers of helically arranged smooth muscle cells  Interposed among the muscle fibers are variable amounts of Figure 11-8 The adventitia of the larger arteries contains a supply of elastic fibers and elastic lamellae, reticular fibers, and microvasculature to bring O2 and nutrients to local cells that are too far proteoglycans, produced by smooth muscle. from the lumen to be nourished by blood there. These arterioles (A), cap-  In arteries, the media may have thin external elastic lamina, illaries, and venules (V) constitute the vasa vasorum (vessels of vessels). The separating it from outermost tunic. adventitia of large arteries is also supplied more sparsely with small sympathetic nerves (N) for control of vasoconstriction. Above the C. TUNICA ADVENTITIA adventitia in this section can be seen muscle fibers (SM) and elastic lamellae - Outermost adventitia or tunica externa (E) in the media. - A connective tissue consisting principally of Type I Collagen and elastic fibers. V. CLASSIFICATION OF ARTERIES - Continuous with and bound to the stromal connective tissue of the organ through which the blood vessel runs. A. Elastic Arteries - Conducting or Conduit Arteries - Closes to heart - Largest, > 10 mm in diameter - Conduct blood from heart with elastic recoil help move blood forward under steady pressure - E.g. aorta and pulmonary, common carotid, subclavian and common iliac arteries B. Muscular Arteries - Distributing Arteries Figure 3 Walls of Arteries and Veins - 10-1 mm in diameter Page 2 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas - Consists mainly of collagen fibers, blood vessels, nerve, elastic fibers, - Regulate blood flow to organs and parts of the body by contraction and fibroblasts, & macrophages (maybe present). relaxation of smooth muscle in their walls - Distribute blood to all organs and maintain steady blood pressure and flow with vasodilation and constriction - E.g. femoral and brachial arteries C. Arterioles - 100 mm or less in diameter - Small-resistance vessels that mainly regulate systemic blood pressure - Walls contain one or two layers of circularly arranged smooth muscle - Eesist and control blood flow to capillaries - Major determinant of systemic blood pressure VI. ELASTIC/LARGE ARTERIES - Major role is to carry blood to smaller arteries - Ventricular Contraction (Systole)  Forceful movement of blood through arteries  Elastin stretched  Distend wall within limit set by the wall’s collagen. - Ventricular Relaxation (Diastole)  ventricular pressure drops  Elastin rebounds passively, helping to maintain arterial pressure - Aortic and pulmonary valves prevent backflow of blood into the heart, so the rebound continues the blood flow away from the heart - Arterial blood pressure and blood velocity decrease and become less variable as the distance from the heart increases A. LAYERS OF ELASTIC ARTERIES 1. Tunica Intima - thin (relative to other layers in this type of vessel) - endothelium - Subendothelial Layer contains some smooth muscle, elastic fibers & collagen fibers - connective tissue with smooth muscle  Internal elastic lamina - not as distinct as in other arteries because it is similar to elastic laminae of next layer. Figure 11-7 Comparison of the three major layers or tunics in the largest artery and vein. (a) Aorta, (b) vena cava. Simple squamous endothelial cells  Elastic laminae (arrows) line the intima (I) that also has subendothelial connective tissue - making blood flow more uniform and in arteries is separated from the media by an internal elastic lamina (IEL), a structure absent in all but the largest veins. The media (M) contains 2. Tunica media many elastic lamellae and elastic fibers (EF) alternating with layers of - thick smooth muscle. The media is much thicker in large arteries than veins, with - elastic lamellae alternate with layers of smooth muscle fibers relatively more elastin. Elastic fibers are also present in the outer tunica - adult aorta has 50 elastic lamellae (more in hypertensive patients) adventitia (A), which is relatively thicker in large veins. Vasa vasorum (V) - between elastic laminae is consists of, fibroblasts, elastic fibers, collagen are seen in the adventitia of the aorta. The connective tissue of the fibers & spiral (to circular) smooth muscle adventitia always merges with the less dense connective tissue around it. 3. Tunica adventita - Thinner that tunica media - Presence of vasa vasorum Page 3 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas - Decreased blood flow to downstream vessels, leading to ischemic heart disease VII. ARTERIAL SENSORY STRUCTURES - Carotid sinuses Slight dilations of bilateral internal carotid arteries where they branch from the (elastic) common carotid arteries Baroreceptors - monitoring arterial blood pressure Media is thinner - allow greater distension when BP Adventitia contains sensory nerve endings from cranial nerve IX, the glossopharyngeal nerve Brain’s vasomotor centers process afferent impulses and adjust vasoconstriction, maintaining normal blood pressure. Similar baroreceptors present in aortic arch. Complex chemoreceptors Monitor blood levels of CO2 and O2, H+ found in carotid bodies (in walls of carotid sinus) and aortic bodies (wall of aortic arch) Parts of ANS called paraganglia with rich capillary networks Large, neural crest-derived glomus (type I) cells surround capillaries Filled with dense-core vesicles containing dopamine, acetylcholine, and other neurotransmitters supported by smaller satellite (type II) cells. Figure 11-9 The largest arteries contain considerable elastic material and Respond to stimuli in the arterial blood, primarily hypoxia (low expand with blood when the heart contracts. A transverse section through O2), hypercapnia (excess CO2), or acidosis, o Glossopharyngeal nerve part of a large elastic artery shows a thick media (M) consisting largely of sensory fiber form synapses with glomus cells and signal brain centers many well-developed elastic lamellae. Strong pressure of blood pulsating to initiate cardiovascular and respiratory adjustments that correct the into such arteries during systole expands the arterial wall, reducing the condition. pressure, and allowing strong blood flow to continue during diastole. The intima (I) of the empty aorta is typically folded, and the dense irregular VIII. MUSCULAR ARTERIES connective tissue of the adventitia (A) is thinner than the media. - Small to medium arteries MEDICAL APPLICATION - also known as Muscular Arteries  Atherosclerosis LAYERS OF MUSCULAR ARTERIES - Disease of elastic arteries and large muscular arteries - Play a role in nearly half of all deaths in developed parts of the world. 1. Tunica intima - Initiated by damaged or dysfunctional endothelial cells oxidizing low which − Thin is the low density lipoproteins (LDLs) in the tunica intima - Endothelium - which Induces adhesion and intima entry of monocytes/macrophages to remove the modified LDL - Thin subendothelial layer consisting of scattered fine collagen and elastic - Lipid-filled macro- phages (called Foam Cells) accumulate and, along with fibers and a few fibroblasts the free LDL, produce a pathologic. - Internal elastic lamina – prominent very distinct, usually folded - A sign of early atherosclerosis is called fatty streaks - During disease progression, these develop into fibro-fatty plaques or 2. Tunica media atheromas, consisting of a gruel-like mix of smooth muscle cells, collagen - Thick fibers, and lymphocytes with necrotic regions of lipid, debris, and foam - Contain up to 40 layers of large smooth muscle cells interspersed with a cells. variable number of elastic lamellae (depending on the size of the vessel) - Elastic arteries, atheromas produce localized destruction within the wall, - Thickness decreases as diameter of vessel decreases weakening it and causing arterial bulges or aneurysms that can rupture. - External elastic lamina presents only in the larger muscular arteries (May - Muscular arteries such as the coronary arteries, atheromas can be be indistinct in smaller muscular arteries) occluded. 3. Tunica adventitia - Thick Page 4 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas - Lymphatic capillaries, vasa vasorum, and nerves are also found in the with only sparse connective tissue between the endothelial cells (E) and adventitia, and these structures may penetrate to the outer part of the internal elastic lamina (IEL). Multiple layers of smooth muscle (SM) in the media. media (M) are thicker than the elastic lamellae and fibers with which they intersperse. Vasa vasorum (V) are seen in the adventitia. X100. H&E. Function: - Distribute blood to the organs and help regulate blood pressure by contracting or relaxing the smooth muscle in the media. IX. ARTERIOLES A. STRUCTURES OF ARTERIOLES A. Tunica intima − Very thin consisting only of endothelium − Elastic lamina absent B. Tunica media − Circularly arranged 1 or 2 layers of smooth muscle, some elastic fibers C. Tunica adventitia − Thin, consisting of longitudinally arranged collagen and elastic fibers B. FUNCTIONS OF ARTERIOLES − To redistribute blood flow to capillaries and to alter blood pressure by altering peripheral resistance to blood flow Figure 6. LM wall of a muscular artery. In this partly constricted artery, the − Arterioles can change diameter very drastically therefore affecting blood lumen caliber is small relative to the muscular wall thickness. A prominent pressure and flow patterns. internal elastic lamina (IEL) looks corrugated. Several layers of circular − Major determinant of systemic BP smooth muscle occupy the media (TM); loose connective tissue, the − Arterioles are referred to as peripheral resistance vessels. adventitia (TA). Figure 8 Arterioles (A), capillaries (C), and venules (V) comprise the micro- vasculature where, in almost every organ, molecular exchange takes place between blood and the interstitial fluid of the sur- rounding tissues. Lacking media and adventitia tunics and with diameters of only 4-10 μm, capillaries (C) in paraffin sections can Figure 7. Muscular Artery. With distance from heart, arteries have relatively be recognized by nuclei adjacent to small lumens or by highly eosinophilic less elastin and more smooth muscle in their walls. Most arteries, large red blood cells in the lumen. As described in Figure 5–20, not all interstitial enough to have names, are of the muscular type. A transverse section fluid formed at capillary beds is drained into venules; the excess is called through a muscular (medium-caliber) artery shows a slightly folded intima lymph and collects in thin-walled, irregularly shaped lymphatic vessels (L), such as those seen in connective tissue and smooth muscle here. Page 5 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas − Precapillary sphincters Sphincters regulate blood flow into true capillaries. Figure 9 (A) Arterioles are microvessels with an intima (I) consisting only of endothelium (E), in which the cells may have rounded nuclei. They have media (M) tunics with only one or two layers of smooth muscle, and usually thin, inconspicuous adventitia (Ad). (X350; Masson trichrome) (b) Three arterioles (A) of various sizes and a capillary (C) are shown here. Figure 11 Part (a) shows a well-perfused capillary bed with all the sphincters relaxed and open; part (b) shows a capillary bed with the blood shunted away by contracted sphincters. At any given moment, most sphincters are at least partially closed and blood enters the capillary bed in a pulsatile manner for maximally efficient exchange of nutrients, wastes, O2, and CO2 across the endothelium. Except in the pulmonary circulation, blood enters the microvasculature well oxygenated and leaves poorly oxygenated. D. MEDICAL APPLICATION Figure 10 Under LM of an arteriole in transverse section. Tightly arranged − Blood Pressure (BP) depends on cardiac output (CO) and the total smooth muscle cells (SM) are oriented more or less circularly relative to the peripheral resistance (TPR) to blood flow lumen. Their contraction causes the internal elastic lamina (IEL) to appear − Peripheral resistance - mostly due to arteriolar resistance corrugated and endothelial cell (En) nuclei to bulge into the lumen. The − Hypertension (HTn) or elevated BP may occur secondarily to renal or adventitia (TA) contains connective tissue cells (mostly fibroblasts) and endocrine problems, but more commonly essential hypertension, due to a collagen fibers. wide variety of mechanisms that increase arteriolar constriction. C. MICROVASCULAR BED STRUCTURE AND PERFUSION X. REFERENCES - Continuation of the functions of capillaries) Mescher, A.L. (2016). Junqueira’s Basic Histology Atlas of Histology. − Arterioles supplying a capillary bed typically form smaller branches called McGraw Hill Education.Eroschenko, V. P. (2017).Atlas of Histology metarterioles in which the smooth muscle cells are dispersed as bands that withFunctional Correlations 13th Edition. Wolters Kluwer PPT of Dr. Peeble act as precapillary sphincters Narita Agdamag − Thoroughfare channels Distal portion of the metarteriole, lacks smooth muscle cells and merges with the post-capillary venule. XI. TEST YOUR KNOWLEDGE − True capillaries Smallest vessels branching from 1. The semipermeable barrier between two major internal compartments metarteriole and thoroughfare channel of blood vessels. Lack smooth muscle cells (although pericytes may be present) A. Endothelium B. Collagen Page 6 of 7  UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC12 Arteries COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Peeble Narita Agdamag | Dec. 05 2022 Editors: Gadut, Gorospe, Kwaw, Lucas C. Elastic muscle fibers D. Connective Tissue 2. This layer of the blood vessels is composed of concentric layer of helically arranged smooth muscle cells. A. Tunica intima B. Tunica Media C. Tunica adventitia D. Endothelium 3. The major determinant of systemic blood pressure. A. Veins B. Arteries C. Capillaries D. Arterioles 4. Which of the following is/are true about artery? A. It has a thin wall compare to vein. B. Presence of valve which is absent in vein. C. It has thick layer of muscle tissue compare to vein. D. Usually located superficial in the muscle. 5. Monitor blood levels of CO2 and O2, H+ found in carotid bodies (in walls of carotid sinus) and aortic bodies (wall of aortic arch) A. Carotid sinuses B. Baroreceptors C. Complex chemoreceptors D. Glomus (type I) cells 6. Thin subendothelial layer consisting of scattered fine collagen and elastic fibers and a few fibroblasts. A. Tunica intima B. Tunica media C. External elastic lamina D. Tunica adventitia 7. True or False. Tunica adventitia is thin, consisting of circularly arranged collagen and elastic fibers. 8. True or False. Arterioles can change diameter very drastically therefore affecting blood pressure and flow patterns. Answer: 1. A, 2. B, 3. D, 4. C, 5. C, 6. A, 7. False. Longitudinally, not “circularly,” 8. True Page 7 of 7