YR1 Lecture 1H - Tissues & Organs - Dr Morven Cameron 2022 PDF

Learning objectives Appreciate that organs are built up from the four basic tissue types: epithelial tissue, connective tissue, muscle tissue and nervous tissue. Compare and contrast the organisation and function of the four major types of tissues in blood vessels (arteries, veins and capillaries)....

Learning objectives Appreciate that organs are built up from the four basic tissue types: epithelial tissue, connective tissue, muscle tissue and nervous tissue. Compare and contrast the organisation and function of the four major types of tissues in blood vessels (arteries, veins and capillaries). Tissues and Organs - an Overview ~200 distinctly different cell types. Organized into 4 basic tissues – Epithelial – Connective – Nervous – Muscle Basic tissues are organised into organs. Organs An organ is a structure that has at least two different types of tissues. Tissues within an organ function together for the same goal. When looking at organs, question: – Which basic tissues? – How are they organised? – Specialisations? – What does each basic tissue contribute to the organ? Three Main Classes of Blood Vessels Arteries convey blood away from the heart to the body tissues. Arteries branch, or bifurcate, into smaller and smaller vessels until they feed into the Capillaries, where gas and nutrient exchange occurs. From the capillaries, veins return blood to the heart. Veins become progressively larger as they merge and get closer to the heart. Copyright © The McGraw-Hill Companies, Inc. Types of Epithelia Tunica Intima (or Interna) – Innermost layer of a blood vessel wall – 2 major components – Endothelium – Simple squamous epithelium – Provide smooth surface for passage of blood – Secrete pro/anticoagulent factors: endolthelin, Von Willebrand factor (vWF), NO; basement membrane components: collagen, laminin – Membrane bound enzymes e.g. ACE – Cell adhesion proteins. – Subendothelium – Loose connective tissue – Dispersed smooth muscle cells – Internal elastic lamina - especially developed in muscular arteries Endothelium Subendothelium Internal elastic lamina Basement Membrane Acellular region between epithelium and connective tissue Composed of: – basal lamina (glycoproteins & collagens) – Lamina lucida and lamina densa – lamina reticularis (collagens) Basal lamina secreated by epithelium Lamina reticularis secreated by connective tissue. **NOT A BLOOD VESSEL** Tunica Media – Middle layer of the vessel wall – Thickest layer – Composed of helically arranged layers of smooth muscle cells – Vasoconstriction (narrowing of the blood vessel lumen) – Sympathetic function – Absent in capillaries and post-capillary venules Tunica media Tunica Externa or Tunica Adventitia – Outermost layer of the blood vessel wall – Composed of an areolar connective tissue that contains elastic and collagen fibers. – Helps anchor the vessel to other tissues – Vasa vasorum - small arteries that enter the vessel wall – Blends into surrounding connective tissue Tunica Externa or Tunica Adventitia – Outermost layer of the blood vessel wall – Composed of an areolar connective tissue that contains elastic and collagen fibers. – Helps anchor the vessel to other tissues – Vasa vasorum - small arteries that enter the vessel wall – Blends into surrounding connective tissue Arteries and Veins Copyright © The McGraw-Hill Companies, Inc. In prepared specimens, arteries usually retain their shape Walls of veins collapse when not filled with blood Arteries In the systemic circulation, carry oxygenated blood to the body tissues. Pulmonary arteries carry deoxygenated blood to the lungs. Three basic types of arteries: – elastic arteries, muscular arteries, and arterioles – as an artery’s diameter decreases – decrease in elastic fibers – relatively more smooth muscle Transition between the types Tunica externa Elastic Artery e.g. Aorta Tunica Intima – Endothelium axes parallel to the longitudinal axis of vessel. – Internal elastic lamina Elastic Artery e.g. Aorta Tunica Intima – Endothelium axes parallel to the longitudinal axis of vessel. – Inclusions containing von Willebrand factor. – Internal elastic lamina Tunica Media – Fenestrated elastic membrane – Organised as lamellae and alternate with smooth muscle cells – Number of lamellae increases with age – 40 in newborn, 70 in adults – External elastic lamina Tunica Adventitia – Relatively thin layer fibroelastic tissue – Vasa vasorum. Tunica adventitia Muscular Artery or Distributing Artery Tunica Intima – Thinner than in elastic arteries but, pronounced internal elastic lamina Tunica Media – Up to 40 layers of smooth muscle cells, as little as 4 for smaller. – Vasoconstriction/dilation controls blood flow. Tunica Adventitia – Relatively thin layer fibroelastic tissue Arterioles - Terminal Arteries Tunica Intima – Sub-endothelial layer virtually absent – Note endothelial nuclei protruding into lumen Tunica arteriole Media – 1 - 3 layers of smooth muscle cells Tunica Adventitia – Scant, loose fibroelastic connective tissue – Larger arterioles have the 3 tunics – Smaller arterioles limited to endothelium + layer of smooth muscle fibres – Metarterioles contain sphincters to control the blood flow to capillary beds. venule Arterioles - Terminal Arteries Tunica Intima – Sub-endothelial layer virtually absent – Note endothelial nuclei protruding into lumen Tunica Media – 1 - 3 layers of smooth muscle cells Tunica Adventitia – Scant, loose fibroelastic connective tissue – Larger arterioles have the 3 tunics – Smaller arterioles limited to endothelium + layer of smooth muscle fibres – Metarterioles function as sphincters for capillary beds Capillaries Capillaries Arteriole Capillaries Only have the tunica intima, which consists of a basal lamina and endothelium. Numerous pinocytotic vesicles Allow gas and nutrient exchange between the blood and the body tissues to occur rapidly. Smallest blood vessels, connect arterioles to venules. Are called the functional units of the cardiovascular system. A group of capillaries (10–100) functions together and forms a capillary bed. Copyright © The McGraw-Hill Companies, Inc. Basal lamina surrounds external surface of endothelial cells (arrows) Pericytes surround capillaries and venules Regulate blood flow Basic Types of Capillaries (Basal lamina) (Basal lamina) Copyright © The McGraw-Hill Companies, Inc. Muscle Pancreas Bone marrow Nervous Intestine Liver Connective tissue Endocrine glands Spleen Veins Drain capillaries and return the blood to the heart. Walls are relatively thin and the vein lumen is larger. Systemic veins carry deoxygenated blood to the right atrium of the heart Pulmonary veins carry oxygenated blood to the left atrium of the heart. Blood pressure is substantially reduced by the time blood reaches the veins. Hold about 60% of the body’s blood at rest. Veins also function as blood reservoirs. Structure of Veins Layered like Arteries – Tunica intima – Tunica media – Tunica adventitia Lumen larger Adventitia thicker Valves for blood flow direction Questions?