Vascular Histology 2024 PDF

Cardiovascular Histology  Introduction to Histology, Cell Structure and Function Connect to this resource at: Click on this link: Junqueria's Basic Histology: Text and Atlas 17th Ed. by: publication date: 2024. Available Online From: AccessMedicine. 15th available in print on Re...

Cardiovascular Histology  Introduction to Histology, Cell Structure and Function Connect to this resource at: Click on this link: Junqueria's Basic Histology: Text and Atlas 17th Ed. by: publication date: 2024. Available Online From: AccessMedicine. 15th available in print on ReserveLinks. at Health Center Library. QS 504 J95h14 2016 Chapter 11: Circulatory System  Learning Objectives for Cardiovascular System 1. Describe the structure, function and characteristics of blood vessel including the cellular and non-cellular components 2. Describe the layers of blood vessels and the cells and components of these layers 3. Compare and contrast arteries and veins, arterioles and venules 4. Describe the capillary bed and distinguish the different types of capillaries found in different portions of the body 5. Describe the lymphatic system identify components of lymph vessels 6. Describe the chambers and layers of heart muscle 7. Describe the histologic and ultrastructural features of cardiomyocytes 8. Identify the heart valves and compare and contrast their features 9. Describe the features and layers of heart valve histology  The Cardiovascular System Function and Components  The main function of the cardiovascular system is to transport (and exchange) nutrients, oxygen, body fluids, waste material, heat and blood cells around the body  The cardiovascular system is a closed system of plumbing: blood circulates through blood vessels and is propelled by an the heart  Blood flows through the system from: heart  elastic artery  muscular artery  arteriole  capillaries  venules  vein  heart  Blood Vessels  The blood and lymphatic vascular systems are classified as specialized connective tissue  The blood vessels are part of the cardiovascular system consisting of: ► Heart (muscular pump) ► Pulmonary circulation (system of blood vessels to and from the lungs) ► Systemic circulation (system of blood vessels bringing blood to and from all the other organs >1cm >1cm 1-10mm 2-10mm 0.1-1mm 0.1-2mm Veins have valves! 10-50mm Circulatory System Artery Blood Vessels: Arteries Three-Layered Structures  Blood Vessels: Veins Vein Three-Layered Structures  Components of Blood Vessels Cells:  Endothelium, smooth muscle, fibroblasts, nerve Non-Cellular Components:  Collagen-types I, III, IV, V, VIII  Elastin  Proteoglycans-heparan sulfate  Others: fibronectin, laminin Normal Blood Vessel  Tunica Intima  Endothelium- simple squamous “epithelial” layer, actually mesodermal derived, on a basement membrane  Internal Elastic Lamina (IEL)  Collagen type IV, V, VI, VIII, others-FN, LN, HSP, vWF  Sub-IEL layer- Loose connective tissue  Smooth muscle cells  Collagens  Elastin  Others- fibronectin, laminin, proteoglycans  Normal Blood Vessel IEL IEL Endothelial cells Endothelial cells Smooth Muscle Cells Smooth Muscle Cells Fibroblasts Connective tissue- collagens, proteoglycans EEL  Endothelium  The endothelial cells are derived from embryonic mesenchyme and should not be regarded as epithelial, but as connective tissue cells. Characterized by presence of Weibel-Palade bodies. These store vWF and P-selectins  Endothelial cells line the lumina of all the vessels of the blood vascular and lymphatic vascular systems as well as heart.  The total number of endothelial cells in the body is enormous (estimated as 6x1023 cells) and cover a very large surface area (700-1000m2) and in total weigh about 1.5kg W-P bodies Endothelial Cell Functions  Tunica Media  Smooth muscle cells (circumferential, circular, spiral)  Connective tissue  Collagen  External elastic membrane  Elastin fibers, or fenestrated sheets Tunica media  Reticular fibers  Proteoglycans  Function  Vascular tone  Tunica Media IEL Smooth muscle EEL cell nuclei Tunica media Extracellular matrix  Tunica Adventitia (Externa)  Connective tissue  Elastic fibers  Collagen fibers  Smooth muscle cells (longitudinal) & fibroblasts  Vasa vasorum (arrows) “Vessels of the vessel”  Nerve (nervi vascularis) Tunica media  Vasa Vasorum Large arteries and veins have small blood vessels called vasa vasorum in the adventitia and outer media Vasa vasorum nourish the adventitia and outer tunica media Veins have more vasa vasorum than arteries because veins have a lower content of oxygen and nutrients in blood in the lumen  Classification of Arteries Based on Flow to Capillary Beds Arteries are classified into three main groups:  Conducting or Elastic Arteries: These are large arteries closest to the heart (aorta, renal artery) with very high blood pressure and flow, >1cm. Lots of elastin, vessel can expand during systole, recoil during diastole, allowing blood to be propelled into tissues  Distributing or Muscular Arteries: These are smaller diameter arteries with a slower blood flow, 2-10mm in diameter  Smallest Arteries are arterioles: 20-100mm in diameter Large Vessel-Elastin IEL IEL Elastin fibers stains black-Verhoff  Clinical Correlation Aortic Dissection Disorders associated with:  Hypertensive male, 40-60 yoa  Marfan Syndrome (fibrillin defect)  Pregnancy  Trauma  Connective Tissue Disorder Reticulin stain: Loss of elastin (left), often seen in Marfan’s Muscular arteries (medium size) Media- elastic lamina faint or nonexistent, mostly elastin fibers and SMCs Intima very thin Internal elastic lamina Adventitia Small muscular artery  Clinical Correlation-Atherosclerosis All of this is intima! Lumen Blue circle represents what the arterial lumen should be, without Atherosclerosis is an intimal disease anything in it  Arterioles  Arterioles are small vessels with a diameter of 20-100mm  They consist of three layers:  tunica intima with endothelium alone (no subendothelial layer) and a very thin inner elastic lamina  tunica media with only 4-5 layers of smooth muscle  adventitia that is fairly thin V=Vein, A=arteriole, artery, N=nerve  Arterioles Normal constriction (vasomotor response) is important for regulating capillary blood flow  Arterioles and Capillaries Capillaries Arteriole (not contracted) Arteriole (contracted) Clinical Correlation-Hypertension Medial lesions, hyalinized Pathologic Normal Hypertension is a small artery, arteriole disease AND medial disease  Capillary Bed  Capillaries branch extensively, forming a microvasculature network (capillary bed) with a huge surface area  Capillary beds are great places to exchange water, ions, and macromolecules between blood and tissue because:  Blood flows slowly  Surface area is huge  Capillaries  Blood capillaries have a diameter of about 4-10mm, which is close to the dimension of erythrocytes (about 7mm)  Movement across the capillary wall depends on  Size and charge of molecules  Structure of the capillary  The diameter of the capillaries varies according to the functional status of the tissue or organ. When functional demands rise, the diameter of the capillaries enlarges, allowing increased exchange of oxygen and metabolites. This may also lead to fluid into tissues (edema)  There are three different types of capillaries, however the differences are only visible at the ultrastructural level:  Continuous capillaries  Fenestrated capillaries  Sinusoids  Continuous Capillaries  These have continuous endothelial cells located on a continuous basal lamina, connected by tight junctions.  Abundant small invaginations of the cell surfaces (caveolae) and numerous pinocytotic vesicles in the cytoplasm.  Example: “Blood-brain-barrier" of the CNS or the "blood-thymus barrier”, most cardiovascular vessels  Fenestrated Capillaries  These possess endothelial cells with groups of very small "pores" or "fenestrae", about 80-100nm diameter Example: endocrine glands and renal glomeruli  Sinusoidal Capillaries  Are irregular vessels with large diameters (30-40nm) and often not cylindrical Examples: liver, endocrine glands and in the hematopoietic organs (bone marrow, spleen). Phagocytes are found in walls of the sinusoids called Kupffer cells  Veins  The veins constitute a low-pressure system of vessels  The return of blood to the heart from the capillary beds of the tissues follows a route of small venules, small veins and large veins  As the venous vessels near the heart they become large and with thicker walls. The route of the veins is in parallel to that of the arteries Artery & Vein Compared  Veins  Veins are classified as large, medium or small veins  Veins have three layers (tunica intima, tunica media and adventitia), however the borders between these layers are much less distinct than in arteries  Valves are found in veins  In veins the smooth muscles of the tunica media are all circular muscles, grouped in bundles, whereas smooth muscle present in the adventitia are longitudinal. Media has fewer layers of SMCs than similar sized artery  Medium and Large Veins Endothelial cells  Intima  Media Smooth muscle cells  Adventitia Media Adventitia Small vein with valves  Portal Systems  In typical configurations an artery or arteriole carrying oxygenated blood enters the capillary bed, where there is exchange of oxygen and metabolites, and the vessel exiting the capillary bed is a venule or vein with deoxygenated blood. Heart, kidney, endocrine systems  Portal systems describe unique situations where the blood vessel leaving the capillary bed is of the same category as the blood vessel entering the capillary bed. (e.g., vein-capillary bed-vein or artery-capillary bed-artery)  In a venous portal system (such as in the liver) a vein (hepatic portal vein) enters the capillary bed and a vein (hepatic vein) exits the capillary bed. A similar portal system is found in the hypothalamus-hypophysis  An example of an arterial portal system is found in the renal cortex. Afferent arterioles break up into the capillary bed of the glomerular tufts of the renal corpuscle and the blood exits in efferent arterioles  Venules Very thin walls Smaller venules are similar to capillaries in structure and function All 3 tunics are thin, but externa is relatively the thickest Tunica media contains a few smooth muscle cells and/or pericytes (not concentric rings of smooth muscle)  Venules  Venules  These have a very small diameter (20-50mm) but sometimes appear distended  Post-capillary venules  In lymphatic organs, such as the lymph nodes, the post- capillary venules have high or cuboidal endothelium. These specialized venules permit the recirculation of lymphocytes (especially T-lymphocytes) from the blood to the lymph Small artery Small vein Venule Major Feature of Blood Vessels  Lymphatics (in green)  The lymph vessels return to the blood extracellular fluid from connective tissue spaces and this is called lymph  Lymph is a fairly clear, transparent fluid that flows (passively) in small lymph capillaries  This system ensures the return of water, electrolytes and plasma proteins to the blood. Also returns lymphocytes from the lymph nodes to the blood and transports immunoglobulins (antibodies) from the lymph nodes to the blood  These are found in most organs close to blood capillaries (an exception is the CNS). Valves prevent backflow of lymph Lymphatic capillary  Lymphatics  Typical lymph capillaries have a diameter of 10-50mm only. Lymphatic vessels have very Endothelial cells thin walls lined by “high” endothelium.  Lymphatic capillaries (unlike Lymphoid cells endothelial cells of blood vessels) lack a basal lamina but like veins, have valves  Lymphatic vessels are hard to detect as the lumen tends to collapse. Heart and Valves  The Cardiovascular System Heart and Valves The heart beats independently (autonomic) of any nervous stimuli, but has postsynaptic and sympathetic input Has 2 circulatory systems: systemic and pulmonic  Heart Development cardiac linear chambered tube loop crescent heart heart heart twisting septation The heart is composed of three layers and surrounded by a pericardial cavity Layers of Cardiac Chambers Heart wall  Endocardium Right  Myocardium Coronary atrium  Epicardium artery Tricuspid valve Epicardi um Right Myocardiu ventricle m Myocardium Endocardi um Heart Structure & Blood Flow  Normal Heart LA RA RV LV  Clinical Correlation- Hypertrophic Cardiomyopathy Normal Septum and LV Hypertrophic Cardiac muscle  Clinical Correlation Cardiac Hypertrophy Normal LV Wall Normal RV Thickness Wall Thickness Hypertrophy Note RV hypertrophy Heart Layers  Epicardium  Myocardium  Endocardium  Endocardium Myocardium Lots of blood vessels! Layers of Cardiac Chambers Fat Epicardium  Epicardium Outer layer of the heart= visceral pericardium Consists of a surface of mesothelium (simple squamous type epithelium) supported by a thin layer of connective tissue Epicardium contains loose connective tissue, large amounts of adipose tissue, nerves, and blood vessels, including the coronary vessels, nerves and cardiac ganglia  Epicardium: outer mesothelial cells; Myocardium underlying dense connective tissue  Myocardium  Cardiomyocytes (multiple layers) ► Contractile, pulse-generating and conductive ► Myofibrils which are made of sarcomeres (basic contractile unit), contraction= +Ca, relaxation= minus Ca  Blood vessels ► Coronary artery and vein branches  Loose connective tissue septa ► Fibroblasts, collagen and elastin, extracellular matrix  Myocardium  Muscle fibers are arranged in a spiral pattern around the chambers of the heart. When the fibers contract, the heart twists and wrings out blood from the chambers  Cardiac muscle fibers are inserted into a dense fibrous connective tissue skeleton of the heart, multiple layers  Impulse-generating and conducting cells are also present in the myocardium  Lots of blood vessels!!  Cardiac Muscle/Cardiomyocytes  The muscle fibers branch (bifurcate) and are arranged in series to form an anastomosing network, The fibers have more sarcoplasm. All the fibers are Type I (red fibers, with abundant myoglobin, high oxidative slow-twitch)  Each myocyte has one or two central nuclei (unlike the many peripheral nuclei of syncytia of skeletal muscle fibers)  The mitochondria are larger and better developed. Glycogen is more common  Myocytes have specialized areas of contact - the intercalated disks. These are step-like areas of interdigitation between adjacent sarcomeres  Contractions are rhythmic, spontaneous and involuntary  Atrial Cardiomyocytes Mitochondrion ANF Granules Golgi ANF Granules Nucleus Nucleus Atrium and Atrial Natriuretic Factor (ANF): Released mostly by the right atrial cardiomyocytes, ANF decreases Na+ reabsorption by the kidney tubules: natriuresis followed by water loss: Blood pressure, atrium has granules, ventricles do not Myocardium: Cardiomyocytes ► Striated, short, branched, interconnected ► One central nucleus (at most, 2 nuclei) ► Numerous large mitochondria; glycogen deposits ► Wider but less numerous T tubules ► Less developed Sarcoplasmic reticulum: Diads ► Depolarization (Ca+2) occurs at T tubules, voltage sensor”  Myocardium: Cardiomyocytes Microscopic Anatomy of Cardiac Muscle Intercalated discs: step-like areas between adjacent cells that contain: Desmosomes Fascia adherens Gap junctions Keep cells together and electrically coupled, allowing heart to contract as a single coordinated unit Connexin 43 (Immunohistochemistry)  Sarcomere  Is the basic contractile unit of cardiac muscle  Each sarcomere is composed of two sets of protein filaments  thick myosin filaments  thin actin filaments  Each protein strand has a globular head at each end  Sliding filament model: Myosin heads bound to actin produce movement of thin filaments= sarcomere shortening I band H band I band  Cardiac Muscle Cells Bands & Sarcomeres- EM Level Thick Thin Z= tubulin + a-actinin I= Thin actin+ troponin A= Thick myosin + actin +tropomyosin Myocardium- Longitudinal Myocardium- Cross Sectional  Clinical Correlation Myocardial Infarction Normal Myocyte injury & coagulation necrosis, edema  Nervous System of the Heart SA node--Atrium--Internodal fibers--AV node--Bundle of His--Purkinje  Conducting System of the Heart Purkinje fibers: found in sub-endocardium  Larger than normal cardiac myofibers, has specialized junctions  Rich in glycogen  Sparse and peripheral myofibrils  Also: hormones, epinephrine, norepinephrine- which increase force of contraction, PARAHR, SYMPHR Myocardium Purkinje fibers Endocardium Sinoatrial (SA) node Atrioventricu lar (AV) node Atrioventricular (AV) bundle Lumen AV bundle branches Subendocardial conducting network (Purkinje fibers) SA---Internodal---AV---Bundle---Purkinje  Conducting System of the Heart Endocardium Purkinje fibers Purkinje fibers are larger than normal cardiac myofibers and each fiber possesses a large central nucleus, surrounded by perinuclear region rich in glycogen. Found in subendocardium Myocardium Note: Purkinje cells are in CNS  Endocardium Inner layer of heart (analogous to intima of blood vessels) Consists of endothelium and basal lamina resting on a thin layer of connective tissue Subendocardium is a layer of loose connective tissue between endocardium and myocardium. It contains nerves, blood vessels, and branches of the conducting system of the heart Valves are considered part of the endocardium  Endocardium Endocardium: Subendocardium and endocardium, left thin layer of endothelial cells atrium (endocardium thicker on this side because of high pressure)  Cardiac Valves  Two types:  Atrioventricular  Mitral or Tricuspid  Semilunar  Aortic or Pulmonary  Ensure unidirectional flow of blood  The thin cusps are normally avascular Atrioventricular Valves Cardiac Valves  Atrioventricular Valves Tricuspid Mitral Chordae tendinae  Semilunar Valves Aortic and Pulmonic Free edge Line of Closure Annulus Clinical Correlation Aortic Stenosis  Atrioventricular Cardiac Valves, Valves Muscle Chordae, Papillary  Histology of Cardiac Valves The heart valve layers are the fibrosa, spongiosa and endocardium (with an endothelial lining) The endocardial layers of the opposing surfaces of the each of the 4 heart valves have different names, and are simply named for the chamber they face  For the atrioventricular valves (mitral and tricuspid), the endocardial layers are called the auricularis (which faces the atrium) and ventricularis (which faces the ventricle)  For the semilunar valves (aortic and pulmonic), the endocardial layers are called the arterialis (which face the aorta and pulmonary artery, respectively) and ventricularis (which again faces the ventricle)  Atrioventricular Valves Cardiac Valves Aortic Mitral Aortic Valve  Aorta, Heart and Cardiac Valves Fibrosa Aortic valve Spongiosa Aorta Mitral valve Myocardium Fibrosa Spongiosa Mitral Valve Endothelium inflow surface Endocardium Spongiosa Fibrosa outflow surface Semilunar Valves Fibrosa Spongiosa Ventricularis  Summary 1. The histological features of arteries and veins are that they composed of three layers - tunica intima, tunica media and tunica adventitia with similar cellular and non-cellular components of these layers. 2. Variations of vessels depend on size and functional need. Veins have valves 3. Importance of endothelium and smooth muscle cells, extracellular matrix components 4. Lymphatic vessels are similar and different from the arteries and veins. Lymphatics have valves  Summary 4. There are three distinct layers, epi-, myo- and endocardium, of the heart with interspersed connective tissue and an extensive supply of blood vessels 5. Pericardium surrounds the heart, layers and space 6. Working myocardium of the heart, the myocytes are specialized cells with distinct morphology. Specialized conducting tissue/cells of the heart are Purkinje fibers 7. Heart valves have two (or more) layers, fibrosa and spongiosa, lined by endocardial endothelium 1) Go to PathPresenter: Website: https://cwru.pathpresenter.net Username: Your Case ID (i.e., [email protected]) Password: Your Case Password or just click “Login with SSO” 2) Click on words of each slide, i.e., first slide is hyperlinked, make sure your cursor is on the word “Artery, Vein Lymphatics” hhttps://cwru.pathpresenter.net/#/public/display?token=282b9e6e).  Artery, Vein & Lymphatics https://cwru.pathpresenter.net/public/display?token=0144d441  Vein with Valve https://cwru.pathpresenter.net/public/display?token=61ba83c8  Heart with Purkinje fibers https://cwru.pathpresenter.net/public/display?token=38db889c  Heart, Valves, Aorta https://cwru.pathpresenter.net/#/public/display?token=089d7eca Mitral valve Myocardium Fibrosa Aortic valve Fibrosa Aorta