Microscopis Structure of CVS تفريغ PDF

‫نظرا الفتقار شرائح الدكتورة إلى كثير من‬ ‫تنبيه‪ً :‬‬ ‫المعلومات التي تذكرها خالل المحاضرة‪ ،‬فقد‬ ‫قمت بإدراج كثير منها ضمن الشرائح (ال أعني‬ ‫المربعات الخضر المعتادة‪ ،‬بل بين السطور في‬ ‫الشرائح) مع بعض التعديالت‪.‬‬ Cardiovascular System...

‫نظرا الفتقار شرائح الدكتورة إلى كثير من‬ ‫تنبيه‪ً :‬‬ ‫المعلومات التي تذكرها خالل المحاضرة‪ ،‬فقد‬ ‫قمت بإدراج كثير منها ضمن الشرائح (ال أعني‬ ‫المربعات الخضر المعتادة‪ ،‬بل بين السطور في‬ ‫الشرائح) مع بعض التعديالت‪.‬‬ Cardiovascular System: The cardiovascular system is part of the circulatory system. It consists of: 1. The heart 2. blood vessels. Blood vessels have two types: 1. Arterial bunches 2. Venous bunches that meet in capillary beds.  Blood vascular system General structure of blood vessel wall Blood vessels consist of 3 layers (tunics): 1. tunica intima: the innermost layer 2. tunica media: middle layer 3. tunica adventitia: outermost layer Blood vessels are divided into: Macrovasculature: Large vessels. Microvasculature: Capillary beds and the smallest connection of the arteries and veins which involves the exchange between blood and tissue fluid.  Tunica intima 1) Endothelium: Simple squamous epithelium. Subendothelium Why? To allow the optimum (the best) exchange between the blood and tissue fluid. rest on basal lamina. Endothelium 2) Subendothelial CT layer: loose connective tissue. To support the epithelium. few scattered smooth muscle cells. Internal elastic lamina 3) Internal elastic lamina: A layer of elastic tissue that looks like cheese. -Its function is to cover the vessels. Whenever you hear the word “elastic,” In (all) arteries (Only found in arteries) know it’s an artery, because veins are elastin not supported by elastic tissue. with fenestrae (holes): to allow better diffusion of nutrition from blood vessels lumen into the wall of the vessels (to provide nutrition to the vessel). CT = connective tissue  Tunica media ❖ (mainly) composed of concentric layers of smooth muscle arranged helically. Tunica media is the most ❖ other structures: well-developed layer in arteries. ▪ Elastic fibers and lamellae It’s prominent and thick in arteries, but thin in veins. in arteries. ▪ reticular fibers To support. ▪ proteoglycans To attach the components all together. o secreted by smooth muscle. NO fibroblast. Lamina = sheath Which surround blood vessels. e.g Aorta, pulmonary etc… external elastic lamina: only in large arteries, (it’s fenestrated). In capillaries: media is replaced by pericytes (elongated cells). Tunica media is NOT found in the capillaries, it is replaced by pericyte (this cell will be explained in the next slides). To allow diffusion of nutrients to the wall of the vessel.  It’s composed of dense CT and has Tunica adventitia Collagen type I which is the toughest type, also, it may have elastic fibers in arteries. ▪ C.T. containing fibroblast: To secret CT fibers. ▪ Collagen type I and elastic fibers. Small blood vessels that penetrate and Vasa vasorum (vessels of the vessel): supply the wall of the large vessel. ❑ Found in large vessels - more in veins. Why only in large vessels? Because their walls are thicker so they need additional blood supply. Why more in veins? Because the main supply of the vessels is from the lumen, and the lumen of the veins contains deoxygenated blood and metabolites which means they need more nutrition. Vasa vasorum Innervation of vessels in tunica adventitia: Vasomotor nerves Small unmyelinated autonomic nerve fibers Within the vessel, it’s impossible to find collagen, (vasomotor) Which is responsible for vasoconstriction or vasodilation. but in the adventitia, we’ll find collagen. The density of this innervation is greater in The doctor means that in intima and media, we’ll find reticular and elastic arteries than in veins. Because they control our blood pressure. fibers, not collagen type 1, but in the external wall (adventitia) we’ll find CT = connective tissue collagen.  General structure of blood vessels Got skipped because there was not enough time. Vasa vasorum nerves adventitia External elastic lamina Smooth muscle media Internal elastic lamina Subenothelial layer intima Basal lamina endothelium  “Large or conducting” We have veins and we have arteries which vary in size: large, medium-sized, and small arteries. You need to know the differences in the tunics between them. “ medium or distributing” Main differences between the wall of veins and arteries Veins Arteries thickness Thin Thick “Small or resistance” of the wall Prominent Tunica Tunica media layer adventitia  Large elastic (yellow) Arteries: The name indicates the most prominent component of the wall. Elastin is the most prominent Yellow due to the presence of Function: component of all of its tunics. high amount of elastin. Physiologically called: conducting arteries: they conduct blood from the heart to other arteries. they carry the blood without exchange. Role of elastic laminae: 1-Expansion of arteries during systole. 2-Passive rebound during diastole (maintain the blood pressure). Why the elastin is the most prominent here? What’s its function? Because large arteries undergo high blood pressure therefore elastin facilitates the expand of the arteries (e.g aorta and pulmonary) during systole Examples: then during diastole will allow for the passive contract/rebound/recoil. Aorta, pulmonary, and their large branches. Histological Features: 1-Tunica intima: Mainly in large vessels - Large, Thick, Well-developed. o Endothelium. o Subendothelium: rich in elastic fibers. o Internal elastic lamina: present but masked (covered) by elastic lamellae of the tunica media. Can’t be seen because its masked. These three picture are related to the next slide  Generally, the main component of tunica Continuation… media is smooth muscles, but in large arteries, elastin is the main component. Elastin here means two things: 1-elastic fibers: ‫خيوط‬ 2-Tunica media (the thickest layer): 2-elastic lamina/lamellae: sheath which surrounds. Mainly fenestrated elastic lamellae or laminae (Very large amount). (looks like curly hair) which alternate with the smooth muscle. Why fenestrated elastic lamellae? Alternating means: a layer of elastic then a layer of smooth muscle To allow the diffusion of nutrients. then another layer of elastic then a layer of smooth muscles etc… Smooth muscle cells external elastic lamina *Do not forget that tunica media in large arteries contains the external elastic lamina* 3-Tunica Adventitia: Thinner than media. Tunica media is the most prominent in any artery. Has vasa vasorum. Because large arteries have thick wall that needs nutrition. There is a large amount of elastin in all layers, especially in media. In media, elastin exists as lamella, not fibers, fibers exist in intima and adventitia. Baroreceptors & chemoreceptors: present in the wall of common carotid artery and aortic arch. Baroreceptors sense the blood pressure while chemoreceptors sense the chemical environment of the blood (pH, CO2, O2). Carotid arteries are considered large vessels as well. Medium sized (muscular) arteries: Function: Physiologically: distributing arteries because they distribute the blood to the organs. Histologically: muscular arteries, tunica media mainly contain smooth muscles. Regulation of blood pressure: by vasodilation and vasoconstriction. Role of smooth muscle: Most prominent factor of the function of these arteries is smooth muscles Histological features: which are present in tunica media. Tunica intima: (Thin) Tunica media: (the main layer) Tunica adventitia The surface is folded, has ❖ well-developed. Thinner, (less developed). undulation/irregularity. Mainly smooth muscle fibers + a It has Vasa vasorum/nerves to Endothelium - Subendothelium. few scattered elastic lamellae. supply the wall. Internal elastic lamina: Less than large arteries. prominent ‘undulating External elastic lamina: in large muscular arteries. (absent in surface’. which makes the small medium ones). surface irregular. Which of the following arteries has external elastic lamina? Femoral artery Even more than large arteries. or Tibial artery? It is Femoral artery.  Arterioles indicates the beginning of microvascular beds. Function: * Resistance vessels Size: less than 0.1 mm in diameter. Structure: Tunica intima: -Very thin with endothelium and subendothelium. - absent internal elastic lamina It is called Resistance vessels because the tone Tunica media: The (not the contraction) of the smooth muscle in the media makes the lumen and wall partially -1-3 layers of smooth muscle average is 2 layers closed, resisting the flow of blood into it. This -absent external elastic lamina will lead to the appearance of what is called peripheral vascular resistance. Adventitia: very thin Peripheral vascular resistance is the The arterioles resistance of the blood that normally occurs in the arteriole. It is also very important because it is the major metarterioles determinant of blood pressure. The medium-sized arteries only regulate the (discontinuous smooth muscle layer) blood pressure while arterioles create it ‘precapillary sphincter’ through peripheral vascular resistance. Arterioles Metaarteriole Thoroughfare channel  The sphincter open and close periodically Metarterioles: (in cyclic manner) 5-10 cycles per minute , The direct branching network coming out from the this allows pulsatile flow of the blood into arteriole. The metarteriole + thoroughfare channel the capillary bed and that’s allow efficient gives the true capillary bed. exchange of nutrients, wastes, gases and What is the difference between the arteriole and electrolytes between the blood and metarteriole? interstitial fluid. -The metarterioles are branches of the arteriole so it’s very small in diameter. -The main difference is the smooth muscle in: Arteriole: concentric layer around the wall. Metarteriole: doesn’t surround the wall instead it makes a band )‫ (حزمة‬at a start of each branch and it’s called precapillary sphincter. So the metarterioles are not completely surrounded by smooth muscle. The continuation of the metarteriole is called thoroughfare channel which is not surrounded by smooth muscle but instead by pericyte. Microvascular bed and arteriovenous connections Microvascular bed and arteriovenous connections The precapillary sphincters contract and relax cyclically, with 5-10 cycles per minute, causing blood to pass through capillaries in a pulsatile manner. During relaxation (opening)of precapillary sphincters: the blood flows (perfusion) to the capillary bed by the precapillary sphincter. When precapillary sphincters relax the capillary beds become wed perfused in order to take the metabolized nutrients from interstitial fluid. During contraction(closing) of precapillary sphincters: To have the optimum time for gas, metabolites, nutrients and ions exchange. the precapillary sphincter is closed but minimum blood moves from the arteriole to the venule by the thoroughfare channel(because it doesn’t have a sphincter) Microvascular bed and arteriovenous connections Connection between the arterioles and venule: 1-Simple (normal) pathway: the connection between the arteriole and the veniole is the capillary. 2-Arteriovenous shunt: helps the function of the skin. it is supplied by autonomic nerves so, it helps thermoregulation (vasodilation, vasoconstriction). In a hot atmosphere: the AV shunt will vasodilate so, it will increase the blood flow inside it and inside the capillary beds to lose the heat. In a cold atmosphere: the AV shunt constricts and reduces the blood flow inside it and inside the capillary beds to maintain the temp. 3-portal system: two capillary sets connected by portal vein. To collect the nutrients from the first capillary bed then discharge in the second one. Like in the intestine which collects nutrients then release them to the liver via the portal vein. 219: 1-1st capillary bed: a collection of nutrients, or hormones from an organ (such as the intestine) 2-Enters the portal vein to be delivered to another organ. 3- 2nd capillary set: in another organ (such as the liver for detoxification,, storage, or elimination) Or the hormones in the hypothalamus collected by portal vein to be released in pituitary gland through 2nd capillary set.  Blood capillaries Definition: -branching and anastomosing network between arterioles and venules. - Consist of Branches of metaarteriole + thoroughfare channel. Function: Exchange vessels: Because through it happens the exchange of blood and tissue fluid. N.B “ functions of pericytes” Its Importance is to know that it’s narrow at the size of RBCs approximately. Scattered Pericytes are contractile cells (like smooth muscle). Diameter: 4-10 µm in diameter. it can contract contains actin and myosin. Total length/surface area: about 100.000 km/5000 m² Its function: It’s scattered (spread) and has its own contract to control the lumen of the capillary to basal lamina which is fused with the regulate blood flow inside the capillary bed. Structure: capillary basal lamina Acts as a stem cell it can regenerate to replace the -Squamous endothelial cells rolled into a tube. damaged vessel so it is very important in -Rest on basal lamina. angiogenesis/vessel repair. Other function: -Surrounded by pericytes with their own In the brain, it helps to make the BBB, it separates basal lamina. the blood from the nerves. Also, it has an immunological function.  Types of capillaries 3 types: Continuous Capillaries means: completely closed there is no chance of leakage or 1 ​Continuous Capillaries: pass/diffusion of the fluid from the lumen unless it is from the cell (endothelium). The most common type When there is an exchange between the lumen and the extracellular space, there will be no leakage of substances, only very very little. Structure: exchange of molecules by transcytosis through the cytoplasm of the - continuity of endothelium endothelium. The structures that make it completely closed: 1-endothelial cells connected by tight junction. The ends of the endothelium cell overlap each other. 2-continuous basal lamina (no clefts or opening ‘Tight or occluding junction’ Transcytosis occurs through pinocytotic vesicles (‫( ) مثل القارب‬to allow the or pores) exchange of substances between -continuous basal lamina (no holes) capillaries and outside). -pinocytotic vesicles: exchange of molecules by transcytosis /diffusion/minimal fluid leakage in places where protection is required. It’s present in the lung and the basic tissues Site: muscles, C.T., lung, exocrine glands e.g connective, muscle, nerve tissue except and nervous tissue. the epithelium because it avascular.  Types of capillaries The fenestrated capillaries may have diaphragm (‫ )حاجز‬or not 2a- Fenestrated Blood capillaries with It has pores that diaphragms: allow rapid Structure: exchange of fluids -Pores ‘fenestrations’ covered by a diaphragm The importance of pores - continuous basal lamina. (fenestrae) in the endothelial - Tight junctions cells: to increase the gas exchange (Rapid exchange of Site: in the sites where rapid exchange is required. molecules) intestinal mucosa, endocrine glands and choroid plexus. Choroid plexus: in brain and produce CSF (Cerebral Spinal Fluid) These are the fenestrations Rapid exchange of molecules which can be covered by diaphragms or not. 2b- Fenestrated Blood capillaries without diaphragms: Structure: - As in type 2 but pores are not covered with diaphragm. in the sites where more rapid exchange is required. Site: The glomerular capillaries in kidney 219: what is the difference between fenestrated capillaries and continuous capillaries? continuous capillaries: continuity of endothelium and continuous basal lamina. fenestrated capillaries: -The endothelial cells are fenestrated (there are pores) but still held by tight junctions so the diffusion occurs by pores or some cells by pinocytotic vesicles. -continuous basal lamina Fenestrated Blood capillaries are two types: Fenestrated Blood capillaries with diaphragms ( pores have covers called diaphragms ) Fenestrated Blood capillaries without diaphragms ( pores without diaphragms ) The importance of pores (fenestrae): to increase the gas exchange or in another word Rapid exchange of molecules. Types of capillaries 3- Discontinuous capillaries ‘capillary sinusoids’: It’s the largest type Structure: - larger diameter 30-40um. -irregular shape - discontinuous basal lamina. It is not intact -large fenestrae without diaphragm. -wide intercellular cleft. - Macrophages may be located either in or along the outside of the endothelial wall. Site: bone marrow, liver & spleen. Maximal exchange of molecules Sinusoidal Continuous Fenestrated capillaries capillaries capillaries Functions of Blood capillaries 1- Gaseous exchange 2-Exchange of metabolites, nutrients and wastes 3- Metabolic function Angiotensin I → angiotensin II Inactive active angiotensin causes vasoconstriction and an increase in blood pressure.  veins 220: The important here that in large veins there is no elastic fibers tunica adventitia is very prominent Difference between artery and vein The major layers in Arteries: Tunica media Veins: Tunica adventitia To direct the blood flow toward the heart. Summary of the differences This slide is added by the writer, If you don’t have time just skip it. between arteries and veins: Feature Arteries Veins Thicker walls (especially tunica Thinner walls (especially Wall Thickness media) tunica adventitia) All arteries have internal elastic More elastic fibers for pressure Less elastic, more collagen lamina, but only large arteries Elasticity have external elastic lamina. regulation fibers Carry oxygenated blood away Carry deoxygenated blood Main Function Both arteries and veins have from the heart toward the heart three main layers (tunics): Valves Contain valves to prevent tunica intima, media, and Do not contain valves backflow adventitia. Both contain Layers Prominent tunica media Prominent tunica adventitia connective tissue and smooth More prominent in larger muscles. Vasa Vasorum Present in larger arteries veins More dense innervation Vasa vasorum are more in veins Innervation Less dense innervation Vasomotor is more in arteries (vasomotor) (reasons are mentioned earlier)  The first part of the veins is the postcapillary venule. Postcapillary venule is a large capillary which means it contains pericytes instead of smooth muscles. The importance of the postcapillary venules site is that it’s the site of the high endothelial venules (HEV) which are present in organs for WBC emigration. (Similar to capillaries but larger) &Collecting (Media present containing smooth muscle)  1- Venules -postcapillary venules: Resemble larger capillaries “15 to 20 µm”. Endothelium with occasional pericytes sites of WBCs emigration types of venules: 1-postcapillary venules: -collecting venules: It is the first part of the venules it comes after capillary. More contractile cells larger than capillaries. Scattered smooth muscles start to appear It consists of Endothelium, Basal lamina, and -muscular venules: pericytes (no smooth muscle). 2-collecting venules: 2 or 3 layers of smooth muscle cells. -it comes after the postcapillary venules. Surrounded by a well-defined layer of smooth muscle. -have the same structure as the postcapillary venule but it is larger than the postcapillary this is the difference between the collecting and the muscular. venule. postcapillary venules and collecting Venules have wide collapsed venules involved in the exchange of metabolites lumen/thin wall and they are parts of the capillary bed 3-muscular venules: It comes after the collecting venules muscular venules  2- Veins No internal or external elastic lamina M A Medim sized veins: Tunica intima: very thin A v Tunica media: Thin -few layers of smooth muscle fibers. Medim sized veins Tunica Adventitia: Is the most prominent, it’s very thick, has vasa vasorum Well developed/ vasa vasorum. Large veins: - As in inferior vena cava - Well-developed tunica intima Normally, there are no smooth - Relatively thin tunica media muscles in the tunica adventitia, but here we find them in veins - Bundles of smooth muscle in tunica adventitia *Valves: Valves are folds of intima (covered by it) and it’s CT. - semilunar folds of intima project into lumen. - Direct blood toward heart 1-thethesurrounding valves. 2-the contraction of skeletal muscles.  Heart Blood vessels Lymphatic vessels Arteries & veins  Lymphatic vascular system - lymphatic capillaries and vessels - lymph circulates only in one direction toward heart. - Lymph nodes interposed in their path Lymphatic capillaries: differs from blood What’s capillary in: the difference between the lymphatic 1 closed ended/no pericytes capillaries and blood capillaries? 1-lymphatic C. have blind ends e.g the lacteals 2 incomplete basal lamina. 2-fixed by anchoring fibers 3-have incomplete basal lamina around 3 are held open by anchoring filaments. them, as Discontinuous capillaries have. 4-no pericyte *Large lymphatic vessels are similar to veins but differ in: it is fixed on the surrounding connective tissue by the anchoring filament -thinner wall We can’t differentiate between the different tunics. -no clear separation/demarcation between tunics Between the valves, there is dilation which gives the lymphatic vessels its beaded (‫ )مثل المسبحة‬appearance. -more valves so it gives us a beaded appearance - beaded appearance as vessels slightly dilate between valves NO Pericytes Function of lymphatics: under microscope, we cannot differentiate between the large - Drain excess interstitial fluid lymphatic vessels and veins but they differ in content: - Major distributor of lymphocytes and other lymphatic vessels contain lymph immunecomponents (there is no blood) blood vessels contain blood Got skipped because there was not enough time. The doctor said it’s easy and Heart will be covered in the lab. Structure: Its wall is composed of 3 layers: endocardium: consists of a- endothelium b. subendothelial layer: -loose CT with smooth muscle “ myoelastic layer” c. subenocardial layer: -CT zone contains vessels, nerves and Purkinji cells (impulse conducting system). myocardium: thickest layer cardiac myocytes spirally arranged in layers in various directions. Got skipped because there was not enough time. The doctor said it’s easy and Heart will be covered in the lab. epicardium: outermost layer. - the visceral layer of serous pericardium. -the site of the coronary vessels -It is composed of : a. Subepicardial layer: Loose CT contact myocardium containing vessels, nerves and adipose tissue b. mesothelium: simple squamous epithelium -In the space between the serous pericardium's visceral layer (epicardium) and its parietal layer is a small amount of lubricant fluid that facilitates the heart's movements. Got skipped because there was not enough time. The doctor said it’s easy and Heart will be covered in the lab. Cardiac fibrous skeleton: Function: - Serve as base of valves - Site of insertion of cardiac muscle. - Help in coordinating heart beats Structure: -dense irregular CT of collagen fibers in various directions - Fibrous cartilage present in certain regions. valve Heart valves: Structure: -Core of dense fibrous CT lined on both sides with endothelium -Its base is attached to the fibrous skeleton Further Studying: This slide is added by the writer, If you don’t have time just skip it. 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 shows a lymphatic capillary filled with this fluid called lymph (L). Lymphatics are blind-ended vessels with a wall of very thin (b) Diagram indicating more details about lymphatics, endothelial cells (E) and are quite variable in including the openings between the endothelial cells. The diameter (10-50 µm). Lymph is rich in proteins and openings are held in place by anchoring filaments containing other materials and often stains somewhat better elastin and are covered by extensions of the endothelial cells. than the surrounding ground substance, as seen Interstitial fluid enters primarily via these openings, and the here. (X200; Mallory trichrome) endothelial folds prevent backflow of lymph into tissue Junqueiras Basic Histology – Page 233 spaces. Lymphatic endothelial cells are typically larger than those of blood capillaries.  This slide is added by the writer, Further Studying: If you don’t have time just skip it. As seen in the diagram, the human heart has two atria and two ventricles. The myocardium of the ventricular walls is thicker than that of the atria. The valves are basically flaps of connective tissue anchored in the heart’s dense connective tissue, or cardiac skeleton, concentrated in the regions shown in white. This fibrous tissue includes the chordae tendineae, cords that extend from the cusps of both atrioventricular valves and attach to papillary muscles, preventing the The epicardium is a simple squamous mesothelium valves from turning inside-out during ventricular contraction. Valves supported by a layer of loose connective tissue and cords are covered by the nonthrombogenic endothelium. Shown in containing blood vessels and nerves. The yellow are parts of the cardiac conducting system, which initiates the epicardium corresponds to the visceral layer of the electrical impulse for contraction (heartbeat) and spreads it through the pericardium, the membrane surrounding the heart. ventricular myocardium. Both the sinoatrial (SA) node (pacemaker), in Where the large vessels enter and leave the heart, the right atrial wall, and the atrioventricular (AV) node, in the floor of the epicardium is reflected back as the parietal the right atrium, consist of myocardial tissue that is difficult to layer lining the pericardium. During heart distinguish his tologically from surrounding cardiac muscle. The AV movements, underlying structures are cushioned by node is continuous with a specialized bundle of cardiac muscle fibers, deposits of adipose tissue in the epicardium and the AV bundle (of His), which gives rise to right and left bundle friction within the pericardium is prevented by branches that run along the interventricular septum to the apex of the lubricant fluid produced by both layers of serous heart. At the apex the bundle branches subdivide further as conducting mesothelial cells. (Purkinje) fibers that extend into myocardium of the ventricles. If you want to learn more about the histology of the heart continue Junqueiras Basic Histology – Page 217 reading from the reference page.  It’s important to know all of the questions. Some of them are mentioned by the doctor. Q1) Which layer (tunica) of a blood Q2) Which of the following layers of blood vessel contains vasa vasorum? vessels primarily contain smooth muscle? A-Tunica media By 220 A-Tunica media By 219 B-Tunica intima B-Tunica intima C-Tunica adventitia C-Tunica adventitia Q3) Which of the following is responsible Q4) Which of the following muscular for the undulation of the tunica intima in arteries contains external elastic muscular arteries? lamina? A-Internal elastic lamina A-Tibial artery B-External elastic lamina B-Coronary arterioles C-Smooth muscle fibers C-Femoral artery D-Subendothelial connective tissue D-Cerebral Arteries 1-C | 2-A | 3-A | 4-C Q5) What is function of the Q6) The examples of the portal fenestrations in the internal and capillary beds and arteriovenous external elastic lamina? shunt in order are: A-Facilitate elastic recoil A-Liver, Skin B-Provide structural support B-Kidney, Spleen C-Allow diffusion of nutrients C-Skin, Liver D-Enhance gas exchange D-Bone marrow, endocrine glands Q7) Which of the following is the major Q8) Which of the following is the determinant of blood pressure? main component of tunica media in large arteries? A-Arteries A-Collagen fibers B-Venules B-Elastin C-Veins C-Smooth muscles D-Arterioles D-Reticular fibers 5-C | 6-A | 7-D | 8-B  Q1) Slide (7) Q5) Slide (5) Q2) Slide (6) Q6) Slide (17) Q3) Slide (12) Q7) Slide (13) Q4) Slide (12) Q8) Slide (11) Q4)External elastic lamina is found in large muscular arteries but not in small muscular arteries. In this question the answer is Femoral artery because Q8) In general the main component of tunica media is it’s the only large muscular artery from the choices. smooth muscles but in large arteries it’s elastin. Q5) Each choice and the structure which performs the function: A-Facilitate elastic recoil (Elastic fibers within the tunica media) B-Provide structural support (Elastic laminae (internal and external)) (not the fenestrations) C-Allow diffusion of nutrients (Fenestrations in the internal and external elastic lamina) D-Enhance gas exchange (Capillary beds)