BSC 2086 1st Edition Lecture 11 Outline of Last Lecture I Myocardial Infraction II The Conducting System III Cardiac Cycle Outline of Current Lecture I Introduction to Blood Vessels and Circulation II Structure of Blood Vessels III Arteries IV Capillaries Current Lecture I Introduction to Blood Vessels and Circulation a Blood vessels are classified by size and histological organization b Types i Arteries carry blood away from heart ii Arterioles smallest branches of arteries iii Capillaries smallest blood vessels which allow for exchange between blood and interstitial fluid iv Venules get blood from the capillaries v Veins return blood to the heart c Largest blood vessels i Connected to the heart ii Pulmonary trunk carries blood into pulmonary circulation from the right ventricle iii Aorta carries blood into systemic circulation from the left ventricle d Smallest blood vessels i Capillaries ii Small diameter iii Thin walls iv Exchange nutrients chemicals gases and wastes across walls II Structure of Blood Vessels a Not all vessels have the 3 layers b Arteries and veins have all 3 layers but the composition and thickness of each layer will be different c Walls have 3 layers i Tunica intima 1 Inner layer 2 Includes a Endothelial lining b Connective tissue layer c Internal elastic membrane i In the arteries this layer is found in the outer margin of the tunica intima ii Tunica media 1 Middle layer 2 Concentric sheets of smooth muscle in the connective tissue a Smooth muscles under autonomic control 3 Binds to both inner and outer layers 4 External elastic membrane a Separates the tunica media from the tunica externa iii Tunica externa 1 Outer layer 2 Attaches vessel to adjacent tissues in the arteries a Collagen and elastic fibers 3 In veins it contains elastic fibers and smooth muscle cells 4 Vasa vasorum a vessels of vessels b small arteries and veins which are found in the walls of large arteries and veins c supply the cells of the tunica media and externa d Typical artery i Usually round ii Thick wall made up mostly of tunica media 1 Dominated by smooth muscle cells and elastic fibers e Typical Vein i Flattened or collapsed with a thin wall ii Absent internal and external elastic membrane f Differences between arteries and veins i They run side by side ii Arteries have thicker walls and higher blood pressure iii A collapsed artery has a small round lumen 1 Lumen internal space iv Vein has a large flat lumen v The lining of the vein contracts unlike the lining of the artery III vi Artery lining folds and they are more elastic vii Veins have valves Arteries a Able to absorb pressure waves that come with each heart beat due to their elasticity b Contractility i Change diameter ii Controlled by sympathetic innervation iii Vasoconstriction contraction of smooth muscle by the ANS iv Vasodilation relaxation of smooth muscle which enlarges the lumen c Affects of vasoconstriction and vasodilation i Afterload on heart 1 Resistance against the flow of blood stroke volume out of the heart ii Peripheral blood pressure iii Capillary blood flow 1 Amount of blood that actually flows into the capillaries d Change of arteries from the heart to the capillaries i Elastic arteries muscular arteries arterioles e Elastic arteries i Aka conducting arteries ii Large vessels like the pulmonary trunk and the aorta iii Their tunica media has few muscle cells and a lot of elastic fibers iv Elasticity is able to even out pulse force 1 Stretches when the ventricles contract and pushes blood into vessel 2 Recoils back to normal state when ventricles relax 3 This recoil allows blood to retain pressure f Muscular arteries i Aka distribution arteries ii Medium sized iii Tunica media is composed of many smooth muscle cells g Arterioles i Small arteries ii Little or no tunica externa iii Thin or incomplete tunica media h Diameter of arteries i Small arteries and arterioles ii Change with either endocrine or sympathetic stimulation 1 Sympathetic stimulation can cause them to constrict or dilate 2 When you get scared the blood vessels in your skin will constrict pale skin and blood vessels going to skeletal muscles will dilate to give more blood to the muscles for action iii Resistance R arterioles also known as resistance vessels 1 Constricted arteries that oppose blood flow i IV Aneurysm i Bulge in the arterial wall caused by weak spot in the elastic fibers ii Pressure created may rupture the vessel if the elastic component fails Capillaries a Smallest vessels with thin walls b Function i All exchange functions of the cardiovascular system ii Materials diffused between the interstitial fluid and blood c Structure i Endothelial tube with a thin basement membrane inside ii Diameter is similar to that of a red blood cell iii NO tunica media or tunica externa d Continuous capillaries i Complete endothelial lining ii Found in all tissues except cartilage and epithelia iii Functions 1 Allow diffusion of water small solutes and lipid soluble materials 2 Blood plasma proteins and blood cells 3 Specialized continuous capillaries in the central nervous system have strict permeability a Responsible for blood brain barrier e Fenestrated capillaries i Pores in endothelial lining ii Allow rapid exchange of water and large solutes iii Found in 1 Endocrine organs 2 Choroid plexus 3 Kidneys 4 Intestinal tract f Sinusoidal Capillaries i Gaps between adjacent endothelial cells ii Found in 1 Spleen 2 Liver make plasma proteins that enter blood 3 Bone marrow 4 Endocrine organs iii Allow free exchange of water and large plasma proteins between blood and interstitial fluid iv Phagocytic cells monitor blood at the sinusoids 1 Engulf damaged red blood cells pathogens and wastes v Capillary Beds 1 Aka capillary plexus 2 Connect one arteriole and one venule 3 Precapillary sphincter smooth muscle cells a Guard the entrance to each capillary b Capillary blood flows in pulses due to them opening and closing
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