Histology II Blood Vessels - Medicine PDF

Blood Vessels S. THEMISTOCLEOUS, MSc. BSc Medicine Program Medical School Blood Vasculature Blood vessel walls are formed of: smooth muscle connective tissue endothelial lining. Concentration and arrangement of tissues in the vascular wall is dependent on metabolic factor...

Blood Vessels S. THEMISTOCLEOUS, MSc. BSc Medicine Program Medical School Blood Vasculature Blood vessel walls are formed of: smooth muscle connective tissue endothelial lining. Concentration and arrangement of tissues in the vascular wall is dependent on metabolic factors and mechanical factors such as blood pressure  Layers of Blood Vessels The tunica intima is the inner lining, consisting of endothelium and is supported by a thin layer of connective tissue. In larger vessels it may also contain elastin The tunica media is the middle muscular (helically arranged) and/or elastic layer, containing smooth muscle and elastic tissue in varying proportions. The tunica adventitia is the outer, fibrous connective tissue layer (Type I collagen). Vasa Vasorum- vessels of vessels Endothelium Epithelial lining of the cardiovascular system Simple squamous epithelium whose elongated Semi-permeable allowing for exchange between blood & interstitial fluid (simple and active diffusion) The cells control how tight or relaxed blood vessels are and how blood flows by releasing different substances. Some of these substances, like endothelin 1 and ACE, make the muscles around the blood vessels tighten. Others, like nitric oxide (NO) and prostacyclin, help the muscles relax. Endothelium Non-thrombogenic surface = secrete agents such as heparin, tissue plasminogen activator and con Willebrand factor Role in inflammation & local immune response Secrete growth factors Vascular endothelial cells in contact with blood in the lumen of blood vessels Lymphatic endothelial cells are in contact with the lymph" means that the cells lining the lymphatic vessels (called lymphatic endothelial cells) are directly touching or interacting with the lymph, which is the fluid that circulates within the lymphatic system https://doi.org/10.3390/cells10102712  Tunica Media -Smooth Muscle Wall of all blood vessels except capillaries They are arranged in a spiral or helical pattern increasing structural support and allowing for changes to the diameter of vessels Contraction = vasoconstrictions Relaxation = vasodilation Some vessels also contain elastic fibers for stretching & recoil Tunica Adventitia Outermost layer of a blood vessel Provides protection & support Larger blood vessels contain their own small blood vessels (vasa vasorum) supplying them with nutrients & oxygen they cannot receive through diffusion Nervi Vascularis –nerve fibers regulating contraction of smooth muscle in tunica media  https://news.yale.edu/2020/06/30/yale -ids-test-detect-blood-vessel-injury- predict-survival-covid-19 Blood Vessels https://www.physio- pedia.com/Veins  Elastic Arteries Muscular Artery Arteriole Intima- Endothelium- Intima-endothelium, Intima-endothelium, no C.T with smooth muscle C.T & smooth muscle & connective tissue or Tunica Media- elastic elastic lamina smooth muscle lamellae with smooth Media- smooth muscle, Media- 1-3 layers of muscle fewer elastic fibers smooth muscle Adventitia- C.T, thinner Adventitia-regulates Adventitia- very thin than media with vasa systemic BP connective tissue vasorum Distributes blood to all Regulate systemic blood Provide elastic recoil to organs & maintain BP pressure guide blood forward (vasodilation under a steady pressure &vasoconstriction)  Large veins Intima- Endothelium- C.T with smooth muscle. Prominent valves Tunica Media- >5 layers of smooth & collagen Adventitia- bundled longitudinal smooth muscle Medium Veins Intima-endothelium, C.T & valves Media- more smooth muscle Adventitia-thicker than media, longitudinal smooth muscle Venules Intima-endothelium, no valves Media- pericytes & scattered smooth muscle Adventitia- N/A  Elastic Artery Includes the aorta, pulmonary artery and their largest branches Tunica intima contains endothelial cells and is supported by a subendothelial layer of connective tissue that may contain some smooth muscle cells. The internal elastic lamina, located between the tunica intima and the tunica media, is present but may be less distinct in elastic arteries due to the abundance of elastic fibers in the media. Thick tunica media filled with elastic fibers mixed with smooth muscle arranged helically Tunica adventitia much thinner than tunica media. Consists of connective tissue , vasa vasorum & nervi vaorum Ageing With aging, the number of elastic lamellae in the tunica media increases, but the elasticity of the vessels decreases due to changes in the composition of elastin and collagen. This change can lead to conditions such as arteriosclerosis (stiffening of arteries) over time.  Muscular Vein Lumen of muscular veins is typically wider and more irregular shaped compared to arteries of similar size Tunica Intima- endothelium with a sparse subendothelial connective tissue layer and few smooth muscle cells. Internal elastic lamina absent or poorly defined Tunica Media- few layers of circularly arranged smooth muscle cells. Much less elastin & smooth muscle than in muscular vein. Some collagen fibers Tunica Adventitia – thickest layer composed primarily of collagen fibers with some elastic fibers, vasa vasorum  Arterioles Tunica Intima is lined with an endothelium, a layer of connective tissue below this and some smooth muscle Tunica Media is 3-4 layers of smooth muscle Tunica Adventitia is so thin it is difficult to define  Arteriole Sensors Peripheral Chemoreceptors- Baroreceptors located in the carotid and Mechanoreceptors found in aortic bodies and detect carotid sinus and the aortic changed in chemical arch that sense the stretch composition of the blood. or tension in the arterial A chemical substance is walls, which corresponds to converted into a biological changes in blood pressure. signal. This signal may be an action potential or neurotransmitter 25 Sinusoid-= discontinuous endothelium and basement membrane with large gaps between endothelial cells, making them the most permeable type (e.g. liver, spleen, lymphoid tissues and bone marrow) Fenestrated = small pores (fenestrations) within the endothelial cells, which increase permeability. However, the basement membrane remains continuous (e.g. kidneys, endocrine glands and intestines) Continuous= have a continuous, uninterrupted endothelial lining with tight junctions between endothelial cells. The basement membrane is also continuous. (e.g. muscle tissue, lung and brain) Sinusoids in Adrenal Glands  Valves within bood vessels Flaps of connective tissue form valves within the vessels and are held in position by the chordae tendinae. These extend into the muscle and attach to papillary muscle which and are covered by the endothelium Erythrocytes Neutrophils Lymphatic Vessels Lymphatic capillaries→ thin,-less organized walls than blood vessels, but are more permeable. Endothelium- loosely connected with overlapping junctions permitting interstitial fluid and larger molecules to enter. Collect excess interstitial fluid from tissue and return it to the blood Tunica Media- primarily smooth muscle in larger vessels but absent in smaller ones Adventitia found in larger vessels and anchors them to surrounding tissue connective tissue Lymphatic Vessels Capillaries The End