BSC 2086 1st Edition Lecture 11 Outline of Last Lecture I. Myocardial InfractionII. The Conducting System III. Cardiac CycleOutline of Current Lecture I. Introduction to Blood Vessels and CirculationII. Structure of Blood VesselsIII. ArteriesIV. Capillaries Current LectureI. Introduction to Blood Vessels and Circulation a. Blood vessels are classified by size and histological organizationb. Types: i. Arteries carry blood away from heartii. Arterioles smallest branches of arteries iii. Capillaries smallest blood vessels which allow for exchange between blood and interstitial fluidiv. Venules get blood from the capillariesv. Veins return blood to the heart c. Largest blood vesselsi. Connected to the heartii. Pulmonary trunk carries blood into pulmonary circulation from the right ventricleiii. Aorta carries blood into systemic circulation from the left ventricle d. Smallest blood vessels i. Capillariesii. Small diameteriii. Thin wallsiv. Exchange nutrients, chemicals, gases and wastes across wallsII. Structure of Blood Vessels a. Not all vessels have the 3 layersb. Arteries and veins have all 3 layers but the composition and thickness of each layer will be differentc. Walls have 3 layers: i. Tunica intima 1. Inner layer2. Includes:a. Endothelial liningb. Connective tissue layerc. Internal elastic membranei. In the arteries, this layer is found in the outer margin of the tunica intima ii. Tunica media 1. Middle layer2. Concentric sheets of smooth muscle in the connective tissuea. Smooth muscles under autonomic control3. Binds to both inner and outer layers4. External elastic membranea. Separates the tunica media from the tunica externa iii. Tunica externa1. Outer layer2. Attaches vessel to adjacent tissues in the arteriesa. Collagen and elastic fibers3. 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 roundii. Thick wall made up mostly of tunica media1. Dominated by smooth muscle cells and elastic fibers e. Typical Vein:i. Flattened or collapsed, with a thin wallii. Absent internal and external elastic membrane f. Differences between arteries and veins:i. They run side by sideii. Arteries have thicker walls and higher blood pressure iii. A collapsed artery has a small round lumen1. Lumen = internal spaceiv. Vein has a large flat lumenv. The lining of the vein contracts unlike the lining of the arteryvi. Artery lining folds and they are more elasticvii. Veins have valvesIII. Arteriesa. Able to absorb pressure waves that come with each heart beat due to their elasticityb. Contractility:i. Change diameterii. Controlled by sympathetic innervationiii. Vasoconstriction contraction of smooth muscle by the ANSiv. Vasodilation relaxation of smooth muscle which enlarges the lumen c. Affects of vasoconstriction and vasodilationi. Afterload on heart1. Resistance against the flow of blood (stroke volume) out of the heartii. Peripheral blood pressureiii. 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 aortaiii. Their tunica media has few muscle cells and a lot of elastic fibersiv. Elasticity is able to even out pulse force1. Stretches when the ventricles contract and pushes blood into vessel2. Recoils back to normal state when ventricles relax3. This recoil allows blood to retain pressure f. Muscular arteries i. Aka. distribution arteriesii. Medium sized iii. Tunica media is composed of many smooth muscle cells g. Arterioles i. Small arteriesii. Little or no tunica externaiii. Thin or incomplete tunica media h. Diameter of arteriesi. Small arteries and arteriolesii. Change with either endocrine or sympathetic stimulation1. Sympathetic stimulation can cause them to constrict or dilate2. 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 actioniii. Resistance (R) – arterioles, also known as resistance vessels1. Constricted arteries that oppose blood flow i. Aneurysm i. Bulge in the arterial wall caused by weak spot in the elastic fibersii. Pressure created may rupture the vessel if the elastic component failsIV. Capillaries a. Smallest vessels with thin wallsb. Function:i. All exchange functions of the cardiovascular systemii. Materials diffused between the interstitial fluid and bloodc. Structurei. Endothelial tube with a thin basement membrane inside ii. Diameter is similar to that of a red blood celliii. NO tunica media or tunica externa d. Continuous capillariesi. Complete endothelial lining ii. Found in all tissues except cartilage and epitheliaiii. Functions:1. Allow diffusion of water, small solutes and lipid soluble materials2. Blood plasma proteins and blood cells3. Specialized continuous capillaries in the central nervous system have strict permeability a. Responsible for blood brain barriere. Fenestrated capillariesi. Pores in endothelial liningii. Allow rapid exchange of water and large solutesiii. Found in: 1. Endocrine organs2. Choroid plexus3. Kidneys4. Intestinal tractf. Sinusoidal Capillaries i. Gaps between adjacent endothelial cells ii. Found in:1. Spleen2. Liver make plasma proteins that enter blood3. Bone marrow 4. Endocrine organs iii. Allow free exchange of water and large plasma proteins between blood and interstitial fluidiv. Phagocytic cells monitor blood at the sinusoids 1. Engulf damaged red blood cells, pathogens and wastes v. Capillary Beds1. Aka. capillary plexus2. Connect one arteriole and one venule3. Precapillary sphincter – smooth muscle cellsa. Guard the entrance to each capillaryb. Capillary blood flows in pulses due to them opening and
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