BIOL 1344 Lecture 8Outline of Last Lecture I. Path of Action Potential in the HeartII. Cardiac CycleA. Ventricular Filling and EjectionB. Cardiac OutputIII. Control of Heart RateOutline of Current Lecture IV. Preload and Afterload of the HeartV. Blood VesselsA. Layers of Blood VesselsB. VeinsC. ArteriesD. CapillariesCurrent LecturePreload is the point of EDV (End Diastolic Volume) or when the heart is filled with blood. This can be increased by stretching the cardiac muscles which results in more blood volume filling the heart and also more force which increases cardiac output. This is called the Frank-Starling Law. Too much calcium flowing through calcium channels plays a big role in the heart having toomuch force which can be dangerous. If necessary, channel blockers can be administered throughmedications which will block calcium flow and reduce force which will lower blood pressure.Afterload is the tension developed in the wall of the heart at the point of contraction or when blood is leaving the heart. It is the resistance against which the blood pushes to get out. If bloodvessels are narrow, hard, or less elastic there is an increased afterload which can cause an enlarged heart. Blood vessels have three layers:1. Tunica externa – made of areolar tissue, fibrous, tissue, and vaso vasorum which means blood vessel for the blood vessel. These supply blood to the wall of the large blood vessel.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Tunica media – made of smooth muscles and elastic tissue which are made up of the protein elastin3. Tunica intima – endothelium of blood vessels, made of simple squamous cells, secretes endothelin which causes vasoconstriction as well as EDRF (endothelium derived relaxing factor) which is a vasodilator.Veins- thin walls, have valves, contain 60-70% of the bloodArteries-elastic arteries are close to the heart and include the aorta, they are 1-2.5 cm/diameter. These are also called conducting arteries. Muscular arteries are less elastic and a bit smaller which a diameter of 3mm-1 cm. They are also called distributing arteries. Arterioles are narrow, elastic, smooth muscles. They provide resistance to blood flow as well as blood pressure regulation. They are very tiny at 10micrometers-3mm. Capillaries are endothelial cell about 1mm long and 8-10micrometers in diameter. There are three types. Continuous capillaries are the most common and only allow small substances such as water and ions through. Fenestrated capillaries have small holes and are responsible for filtration, they are found in the kidneys. Sinusoidal capillaries have large holes and allow larger substances such as proteins
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