Blood Vessels & Lymphatics (CB 007) PDF

B&C (007b) Blood Vessels & lymphatics Histopathology division Date : 2021 Aims and objectives By the end of this lecture and the practical class, students should be able to: Describe the histological structure of all major types of blood vessel Recognize blood vessels and their class,...

B&C (007b) Blood Vessels & lymphatics Histopathology division Date : 2021 Aims and objectives By the end of this lecture and the practical class, students should be able to: Describe the histological structure of all major types of blood vessel Recognize blood vessels and their class, in sections or light micrographs of compound tissues. Compare and contrast the structure of lymphatic capillaries and vessels with blood capillaries and vessels. M. Assaf 2 BLOOD VESSELS M. Assaf 3 M. Assaf 4 M. Assaf 5 M. Assaf 6 M. Assaf 7 General structure of blood vessel walls A blood vessel wall has three coats ( tunica): 1. Tunica intima 2. Tunica media 3. Tunica adventitia M. Assaf 8  Layers of blood vessel wall blood vessel need other blood vessels to supply them (vasa vasora) covered by endothelium followed by internal elastic lamina followed by fibro collagenous tissue fibro collagenous tissue followed by external elastic lamina M. Assaf 9  Large (elastic, conducting) arteries morphology function Aorta Pulmonary Common carotid supplies head and neck Common iliac supplies lower limbs Function: transport large volume of blood away from the heart Elastic tissue expands when heart contracts → enables the body to maintain blood pressure M. Assaf 10 Structure of the elastic artery wall 1. Tunica intima 2. Tunica media 3. Tunica adventitia Tunica intima Thick (1/4 of the wall) - Endothelial cells on a basal lamina - Sub-endothelial loose Connective Tissue - Internal elastic lamina is indistinct M. Assaf 11 Structure of large, elastic artery 1. Tunica intima 2. Tunica media 3. Tunica adventitia The tunica media Forms most of the wall of the aorta - Fenestrated elastic laminae intersected by circular smooth muscle fibers - External elastic lamina is indistinct M. Assaf 12 Structure of the large elastic artery 1. Tunica intima 2. Tunica media 3. Tunica adventitia The tunica adventitia Thin Loose connective tissue Contains vasa vasora, lymphatics and nerves M. Assaf 13 Muscular(small to medium, distribution) arteries any organ is supplied by medium sized artery Examples External carotid artery Splenic artery Function: 1. Draw blood from an elastic artery and branch into "resistance vessels" including small arteries and arterioles 2. The smooth muscle within the wall helps them to contract and relax changing the amount of blood delivered, as needed M. Assaf 14 Muscular artery M. Assaf 15 make a table comparing dff arteries, veins, capillaries Structure of a muscular artery Endothelial layer resting on a basal lamina Distinct wavy layer of internal elastic lamina (IEL) Note that the wall of the artery is mostly tunica media, is almost entirely smooth muscle. Thick collagenous tunica adventitia. Mainly collagen+ less elastic tissue. The external Connective Tissue (CT) investment anchors the artery to the surrounding CT. M. Assaf 16  Small muscular artery IEL CT E TM Separation of the lining endothelium (E) from the internal elastic lamina (IEL) by sub-endothelial CT is well seen. A few layers of smooth muscle constitute the tunica media (TM) M. Assaf 17  Contrast between the artery and vein in this photomicrograph ARTERY more smooth muscle VEIN M. Assaf 18  Arteriole skeletal muscle--> myofibril Diameter of 100 μm or less Thick wall in relation to lumen Structure: T. Interna: only endothelium& thin evident IEL (IEL is absent in small arterioles supplying capillaries) T. Media: 1-5 layers of smooth muscle fibers& few scattered elastic fibers (small arterioles have only a single layer of smooth muscle fibers) T. adventitia: Thin layer of few collagen and elastic fibers M. Assaf 19 Histology of an arteriole M. Assaf 20  Function of arterioles are not made for the process of diffusion Arterioles decrease pressure of the blood entering capillaries They have a thick muscle wall and a relatively narrow lumen through which arterial blood must pass and loose high pressure before entering into the capillaries Arterioles are relatively impermeable in comparison to capillaries → they are not involved in interchange between blood and tissues M. Assaf 21  Meta-arterioles (Arterial capillaries) Intermediate vessels between arterioles and capillaries ( Meta- arterioles = after arterioles) Structure: thin wall lined by endothelial cells and formed of layers of interrupted muscle cells At their junction with capillaries, they have a band of circular smooth muscle fibers (Pre- capillary sphincter) M. Assaf 22 Function of meta-arterioles: Control of blood flow into capillary bed M. Assaf 23  Capillaries Small, thin walled Diameter 8-10 μm Structure: a single layer of endothelial cells resting on a basal lamina. NO MUSCLE LAYER, YET: no contraction normally The basal lamina encloses slight contraction myoepithelial cells (pericytes)when volume of blood is high If pericytes contract they might close the capillary M. Assaf 24 Function of capillaries The capillary bed is the site for exchange of CO2, O2 , nutrients, waste products and hormones between the blood and cells of the body drains excess blood that hasn't been taken by vein non oxygenated blood M. Assaf 25  Types of capillaries Continuous Fenestrated tight junction --> doesn't allow exchange only allows diffusion Main sites: Nervous tissue (BBB) Main sites: tissues where a large amount of Fat molecular exchange occurs, such as the Muscle kidneys, endocrine glands, and small intestine Function: Trans-capillary transport transport blood to the next station M. Assaf 26  Continuous capillaries and Blood brain barrier Blood brain barrier is a barrier between blood stream in brain capillaries and neurons of the CNS. #prevent toxic materials from entering brain Structure of the blood brain barrier: Blood capillaries in the brain are lined by continuous endothelium. Endothelial cells are joined by tight junctions. Basal lamina is very thick Endothelial cells are covered by a perivascular feet of astrocytes. Function: Prevent toxic material from entering the brain. M. Assaf 27 Normal blood brain barrier  Sinusoids Thin - walled, capillaries Site: bone marrow, spleen, liver, endocrine glands Structure: Wide irregular lumen Interrupted basal lamina (may be absent) Endothelial cells separated by large gaps Function: Allow blood to pass from the blood stream to the interstitial tissue M. Assaf 29 M. Assaf 30  Venules Capillaries and sinusoids open into slightly wider thin-walled vessels called VENULES Structure: Lined by endothelium and its basal lamina Endothelial cells are connected by tight junctions No or thin media and very thin adventitia Function: Conduits (channels) for deoxygenated blood returning from capillaries where most gas exchange takes place M. Assaf 31 M. Assaf 32  Medium- sized, muscular veins Structure: 1. Tunica intima: endothelium and its basal lamina. Poor IEL (folds of tunica intima form the valves of veins) 2. Tunica media: thinner than the artery; contains circular smooth muscle fibers, few elastic fibers 3. Tunica adventitia: thickest layer; contains loose CT and vasa vasora M. Assaf 33  Function of muscular veins Un-oxygenated blood is collected from venules towards the heart by muscular veins. Valves prevent venous flow in the reverse direction M. Assaf 34 Compare between medium sized artery and vein M. Assaf 35  Large veins Superior and inferior vena cava Portal vein Common iliac vein Structure: T. intima: thicker than medium sized veins T. media: circular smooth muscle fibers with collagen and few elastic fibers T. adventitia: thick, well- developed, contains many vasa vasora M. Assaf 36 Large vein Largest adventitia of all vessels M. Assaf 37  How does the structure of a large vein relate to its function? Large veins contain circular smooth muscle fibers within the T. media and longitudinal smooth muscle fibers within the T. adventitia. in artery only T. media contains smooth muscle fibers Both help strengthening the vessel wall to prevent excessive distension M. Assaf 38 Can you define the two labeled vessels? A B M. Assaf 39 Can you define the two labeled vessels? M. Assaf 40 LYMPHATIC VESSELS M. Assaf 41 vein will contain remnants of interstitial tissue and deoxygenated blood Function of lymphatic vessels Remove tissue fluid from the interstitial tissue and return it to the blood Once tissue fluids enter lymphatic vessels it is known as lymph M. Assaf 42 M. Assaf 43 M. Assaf 44 Lymphatic vessels M. Assaf 45  Lymphatic capillaries Small, thin-walled, blind ended tubes How to differentiate lymphatic capillaries from blood capillaries? Larger diameter No associated pericytes in capillary ONLY M. Assaf 46 M. Assaf 47  Structure of lymphatic capillary Single layer of endothelial cells with GAPS between them Endothelial cells rest on an INTERRUPTED basal lamina Anchoring, fine filaments extend from the outer surface to the surrounding help anchor vessel to surrounding tissue connective tissue. Function: Essential in removing lymph from poor functions to help interstitial tissue and returning it pull lymph into vessel to the blood in ONE DIRECTION. M. Assaf 48  Medium sized lymphatic vessels Resemble veins Have more numerous bicaspid valves than veins Valves control the direction of lymph flow. Structure: T. intima: endothelial cells T. media: Connective tissue and both longitudinal and circular smooth muscle fibers T. adventitia: thinner and lacks smooth muscle inlongitudinal vein --> smooth muscle cells M. Assaf 49 Bi-caspid valves in lymphatic vessels M. Assaf 50 Lymphatic vessel M. Assaf 51 Comparison of a small vein and a lymphatic vessel contain lymph (plasma) M. Assaf 52  Lymphatic ducts Lymphatic vessels join one another to form two main lymphatic ducts: Thoracic duct Main lymphatic duct M. Assaf 53  Structure of a lymphatic duct T. Intima: Endothelial cells resting on a thin basal lamina& connective tissue T. media: smooth muscle fibers T. adventitia: connective tissue and occasional longitudinal smooth muscle bundles. M. Assaf 54 Compare& contrast M. Assaf 55 Contrast vascular structures within the interstitial tissue M. Assaf 56 Contrast elastic and muscular arteries M. Assaf 57 M. Assaf 58 Contrast artery and vein M. Assaf 59 Artery Vein M. Assaf 60 Compare lymphatic vessel and venule M. Assaf 61 By the end of this lecture and the practical class, you should be able to: Describe the histological structure of all major types of blood vessel Recognize blood vessels and their class, in sections or light micrographs of compound tissues. Compare and contrast the structure of lymphatic capillaries and vessels with blood capillaries and vessels. M. Assaf 62