Cardiovascular System PDF

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Cardiovascular System Describe the electrical events of the heart? – AP propogation The sinoatrial (SA) node generates impulses

The impulses pause at 0.1seconds at the atrioventricular (AV) node The atrioventricular (AV) bundle connects the atria to the ventricles The bundle brances conduct the impluses through the interventricular septum The purkinje fibres depolarize the contractile cells of both ventricles The heart works as a dual pump, simulatenously pumping blood between the left and right sides but separately into systemic and pulmonary vessels Sympathetic postganglionic fibers innervate the heart as efficient pumping of the blood causes the atria to contract Contraction of cardiac muscles are triggered by depolarizing the plasma membrane via L Type Ca+ channels. AP propagate along the gap junctions that interconnect myocardial cells allowing them to move from one to another. An initial AP of a single cardiac muscle subsequently initiates the rest of the cardiac muscles to become excited. The initial depolarization normally arises in SA node (conducting system cells) located in the right atrium which generates the first pacemaker potential which creates the an initial impulse to create the depolarization of other cardiac cells The discharge of the AP determines the heart beat rate of how many times a heart contracts per minute The AP spreads from the SA node to the AV node through intermodal pathways This allows for the atrial contraction before ventricular contraction occurs After excitation of the AV node the AP propagates down to the interventricular septum Interventricular septum contains conducting system fibres call “bundle of His”

AV node and bundke if his constitute electrical connection between atria and venticles In the interventricular septum the bundle of his divides into left and right bundle branches at the apex of the heart Fibers make contact with purkinje fibers and distribution of fibers cause depolarization of all right and left ventricular cells to occur and ensure single coordinated contraction

What factors determine the blood flow through any particular part of the body In the circulatory system blood flow is directly proportional to the pressure difference between relative points and inversely proportional to resistance. Blood flow is always from a region of higher pressure to lower pressure The force is generated in the blood by the contraction of the heart. The units for the rate of flow are volume per unit time (L/min). The units for pressure difference are the milimeters of mercury. It is the difference in pressure between relevant points that determine flow. Total blood flow is Cardiac Output (CO) which is the volume of blood that circulates through the pulmonary or systemic blood vessels. CO = HR x SV

How is blood flow to any particular organ regulated Mainly regulated at the arterioles. Arterioles are major sites of resistance to flow; responsible for the pattern of blood flow distribution to the various organs and participate in the regulation of arterial blood pressure. (MABP)

Explain how the movements of the heart are initiated and coordinated during one cardiac cycle? The SA Node is the pacemaker cell that stimulates the first impulse. AP must be initiated in cardiac cells for the contraction to occur

Blood composition and effects on pressure

How are electrical impulses conducted across the interventricular septum especially at SA node

Pressure changes

High pressure baroreceptors vs low pressure baroreceptors High pressure baroreceptors found in high pressure regions of the cardiovascular system such as the aortic arch and carotid sinus. They are stretch sensitive mechanoreceptors that detect changes in arterial pressure and relay information back to the medulla Low pressure baroreceptors are found in low pressure regions of the cardiovascular system Reflect changes in venous volume Relay info back to the CNS via the vagal nerve trunk Impulses regulate the secretion of ADH, renin and aldosterone Stretching of atrial receptors increases secretion of ANP which promotes water and sodium excretion through urine.

Functions of the chordae tendineae and papillary muscles and where are they located in relation to one another? To prevent the AV valves from being pushed up and opening backwards into the atria when the ventricles are contracting, the AV valves are fastened to muscular projections (papillary muscles) of the ventricular walls by fibrous strands (chordae

tendinae). Therefore when the AV valves contract, the papillary muscle contract and pull downward on the chordae tendinae. This mechanism helps stabilise the AV valves during contraction. The papillary muscles don’t open or close the AV valves, they act only to limit the valves movements and prevent the backflow of blood. The chordae tendinae connect the papillary muscles to the tricuspid and mitral valve.

Coronary circulation The coronary circulation supplies blood to the working heart. The left main coronary artery arises from the aorta travels behind the pulmonary artery and branches into the cicumflex artery and left anterior descending artery (LAD) The circumflex and LAD artery supply blood to the left ventricle The right main artery arises from the aorta and travels behind the right atrium and ventricle towards the posterior regions of the heart and supply blood to the right ventricle and atrium. These coronary ateries are on the surface of the heart. They divide into smaller branches that dive into the myocardium. Resistance vessels regulate coronary blood flow During systole the contraction of the myocardium compresses the small coronary vessels within the ventricular wall thereby increasing resistance. During diastole the compressive forces are removed and blood flow is increased. Coronary blood flow reaches a peak in early diastole then falls passively as the aortic pressure falls towards its diastolic value.

Net filtration pressure Depends directly upon 4 factors Capillary hydrostatic pressure (favours fluid movement out of the capillary) Interstitial hydrostatic pressure (favouring fluid movement into the capillary) The osmotic force due to plasma protein concentration (favouring fluid movement into the capillary) The osmotic force due to interstitial fluid protein concentration (favouring fluid movement out of the capillary).

Heart beat co-ordination

The heart works as a dual pump pumping blood through pulmonary and coronary vessels simultaneously between left and right sides. Action potentials must be initiated in cardiac cells for contraction to occur The rapid depolarization of the AP in atrial and ventricular muscle cells is due to a positive feedback increase in Na+ permeability. Following the initial depolarization, the cardiac cell membrane remains depolarized for the entirety of the contraction because of prolonged entry of Ca+ into the cell through L Type Ca+ channels The SA node generates the AP that leads to the depolarization of other cardiac cells The SA node initiates a pacemaker potential involving Ca+ and cation channels which brings it to threshold and stimulates an action potential The action potential spreads from SA node to AV node located in the right atrium at the apex of the heart where a small delay of approx.. 0.1 seconds occurs to empty the blood from the atria to the ventricles and then passes through the interventricular septum which contains a bundle of conducting system fibers known as the bundle of his which extend to right and left bundle branches and then to the purkinje fibers and ventricular muscle cells. Ca+ mainly released from the sarcoplasmic reticulum functions in cardiac excitation – contraction coupling as in skeletal muscle by combining with troponin A major signal for Ca+ release from SR is extracellular Ca+ travelling through L type voltage gated ca+ channels during AP. This opens Ca+ (ryanodine receptor) ca+ channels in SR membrane. Cardiac muscle cannot undergo tetanic contractions because it has a long refactory period.

How is Cardiac Output regulated & DEFINED Total blood flow is CO. CO = HR x SV It is the volume of blood that flows through the systemic or pulmonary blood vessels each minute. It is the volume of blood each ventricle pumps out per unit time and equals the product of heart rate and stroke volume.

Heart rate is increased by stimulation of the sympathetic neurons to the heart or by epinephrine It is decreased by stimulation of parasympathetic neurons or norepinephrine Stroke volume is increased by increased end diastolic volume and increase in contractility due to the sympathetic/epinephrine stimulation. Generally blood flows from higher pressure to lower pressure. Resistance increases as blood flow decreases.

Describe the anatomy of the heart. The heart is a muscular organ enclosed in a protective fiborous sac called the pericardium. The heart is located in the left side of the chest. The fiborous layer that is also closely affixed to the heart is called the epicardium. The myocardium, is the wall of the heart primarily composed of cardiac cells. The inner surface of the cardiac chambers, as well as the inner wall of all blood blood vessels, is lined by endothelial cells. The heart is divided into right and left halves each consisting of an atrium and a ventricle. The two ventricles are separated by the interventricular septum. Between the atrium and ventricle one way atrioventricular valves (AV) permit blood flow from atrium to ventricle but not backwards from ventricle to atrium. The right AV is called the tricuspid valve, it has 3 fibrous flaps. The left AV is called the bicuspid valve also known as the mitral valve . Valves are fastened to papillary muscles of the ventricular walls by chordae tindinae.

Name the heart valves and describe their location, function and mechanism of operation. Tricuspid valve – located at the right atrioventricular valve

Bicuspid (mitral) valve – located at the left atrioventricular valve Pulmonary semilunar valve – Located at the opening of the right ventricle into the pulmonary trunk Aortic semilunar valve – Located at the left opening of the left ventricle into the aortic valves

The tricuspid valve and mitral valve are one way atrioventricular valves which permit blood to flow from the atrium to the ventricle but not backwards from the ventricle to the atrium. The opening and closing of the valves result from pressure differences across the valves. When the blood pressure in an atrium is higher than the corresponding ventricle, the valve is pushed open so blood can flow from atrium to ventricle. In contrast when blood pressure is higher in the ventricle than the connected atrium the AV valve is forced shut. This is so blood does not flow backwards but is forced into the pulmonary trunk from right side and aortic trunk from the left side. The semilunar valves permit blood flow into the arteries during ventricular contraction but prevent blood flow from moving in the opposite direction during ventricular relaxation.

Understand the components of the conduction system of the heart. Describe the functional unit of contraction in the cardiac muscle cell and explain how a contraction comes about. Describe the pressure changes in the heart during the cardiac cycle. The cardiac cycle is divided into 2 divisions of systole and diastole. Systole is contraction and diastole is ventricular relaxation. PRESSURE CHANGES IN THE LEFT SIDE At the beginning, the heart muscle is relaxed, blood flows into the atrium and ventricle. The left AV valve is open and the pressure in both is low. The aortic valve is closed because pressure in the aorta is high. The atria receive the depolarising stimulus and contract. Atrial pressure increases slightly. When the ventricle starts to contract, the pressure in the ventricle rises rapidly As soon as pressure in the ventricle is greater than the pressure in atrium, the left AV valve closes. The aortic valve is still closed because pressure in the aorta is still higher than pressure in the ventricle but the pressure in the ventricle continues to increase which opens the valve. Blood is forced into the aorta at high pressure

As the ventricle empties, pressure begins to fall in both the ventricle and aorta. As the ventricle relaxes, pressure in the left ventricle falls rapidly and the aortic valve closes. When pressure in the ventricle falls below pressure in the atrium the AV opens and ventricle begins to fill. At the onset of systole, ventricular pressure rapidly exceeds the atrial pressure and the AV valves close. The aortic and pulmonary valves are not yet open therefore no ejection can occur, this is called isolvolumetric ventricular contraction When ventricular pressures exceed aortic and pulmonary pressures, aortic and pulmonary valves open and ventricles eject the blood When the ventricles relax at the diastole, the ventricular pressures decrease significantly below the pulmonary and coronary trunk and then the aortic and pulmonary valves close Because the AV valves are still closed no change in ventricular volume occurs during this isovolumetric ventricular relaxation When ventricular pressures decrease below the pressures in the right and left atria, the AV valves open and the ventricular filling phase of diastole begins. Filling occurs rapidly at first so that atrial contraction which occurs at the end of diastole, adds small amount of blood to ventricles.

Describe the components of the blood & Blood Composition Blood contains plasma and cells. The liquid portion of the blood is the plasma in which contains dissolved nutrients, ions, wastes, gasses and other substances. Its composition equilibrates with that of the IF at the capillaries. The cells in which make up blood include erythrocytes (in RBC) that function in mainly gas transport (oxygen) and leukocytes that function in immune defenses against cancer and infections, and platelets (cell fragments) for blood clotting. Erythrocytes are forced to the bottom of the centrifuge tube, the plasma remains on top and the leukocytes and platelets form a very thin layer between them called a buffy coat. Plasma volume equals the difference between blood volume and erythrocyte volume.

Describe the three layers that typically form the wall of a blood vessel. 1. Tunica intima

2. Tunica media 3. Tunica externa

Compare and contrast the structure and function of arteries, capillaries and veins. Arteries are low resistance tubes conducting blood to the various organs with little loss in pressure They act as pressure reservoirs for maintaining blood flow during ventricular relaxation Capillaries are a major site of nutrient, metabolic end product and fluid exchange between blood and tissues. Veins are low resistance conduits for blood flow back to the heart.

Discuss the fluid dynamics at the capillary bed. The capillary beds are between the arterial and venous systems They are the exchange tissues for regulating filtration and absorption of gases, nutrients and waste products between blood and interstitial fluid. The capillaries are made of a basement membrane and endothelium. When blood goes through the terminal arteriole, in the arterial side where it is oxugentated it travels through the capillary bed and goes out the venous side, the postcapillary venule The Exchange between blood and tissues can occur in 4 different ways 1. Diffusion through membrane (lipid soluble substances) Bulk flow 2. Movement through intercellular clefts (water soluble substances) 3. Movement through fenestrations (water soluble substances) Always moves from high concentration to low concentration 4. Transport via vesicles or caveolae (large substances) When the membrane catches large molecules Water and solutes can move from the blood into the capillary through fenestrations and clefts between cells Plasma proteins cannot cross capillary walls Bulk flow is driven by blood pressure (hydrostatic pressure) and osmotic pressure As fluid moves through the capillary, forces will act upon it to force fluid out force material in. The physical forces that govern the movement of fluid into and out of the capillaries are called starling forces

These forces come from pressures Capillary blood pressure drives fluid out of the capillary

Describe the function of the lymphatic system. Define blood flow, blood velocity and blood pressure. Blood flow is the volume of blood flowing through a vessel, organ or entire circulation at any given period. In the entire circulation blood flow is equivalent to cardiac output The blood flow through organs vary and depend on the organs needs. Blood Velocity is the distance per unit time with which blood flows through a given segment of the circulation It varies throughout the vasculature and inversely proportional to the total cross sectional area The velocity of flow is slowest in the capillaries as they allow time for exchange of nutrients, wastes and gases. Blood Pressure is the force per unit area exerted on the wall of a blood vessel by the blood. It is expressed as millimeters of mercury and measured as the pressure gradient systemic arterial pressure – venous pressure. Blood pressure and blood flow are proportional.

Describe the relationship between blood flow, blood pressure and resistance. Blood flow = pressure gradient / resistance Blood flow is inversely proportional to peripheral resistance. If the resistance decreases blood flow increases. If resistance increases blood flow decreases. If blood pressure increases, blood flow increases.

For the flow of blood in a blood vessel, the ΔP is the pressure difference between any two points along a given length of the vessel.

When describing the flow of blood for an organ, the pressure difference is generally expressed as the difference between the arterial pressure (PA) and venous pressure (PV) The blood flow across a heart valve follows the same relationship as for a blood vessel; however, the pressure difference is the two pressures on either side of the valve The pressure difference across the aortic valve that drives flow across that valve during ventricular ejection is the intraventricular pressure (PIV) minus the aortic pressure (PAo). The resistance (R) is the resistance to flow that is related in large part to the size of the valve opening.

Volume of blood flowing through a vessel, an organ or the entire circulation in a given period of time. Explain how the body monitors and regulates blood pressure. Blood pressure is regulated by cardiac output, blood volume, and Total peripheral resistance Short term regulation - Baroreceptors – mechanoreceptors part of the ANS Long term regulation – Renal system The instantaneous regulating blood pressure are through the baroreceptors. They are specialized mechanoreceptors located in high pressure regions such as the aortic arch, carotid sinuses and the walls of the arteries in the neck and thorax. When BP increases, this causes a stretch in blood vessels and the stretch in baroreceptors. This increases afferent nerve firing of signals to the cardiovascular control center in the brain, located in the medulla oblongata. This activates the parasympathetic system as the sympathetic nervous system becomes more inhibited, which subsequently decreases heart rate, decreases heart contractility, decreases stroke volume and the more inhibited the sympathetic nervous system is, the less constriction of arterioles will also decrease stroke volume resistance. Overall this decreases mean arterial blood pressure. When blood pressure is increased, the process occurs conversely. As there will be decreased stretch in blood vessels, there will be a decrease stretch in baroreceptors, which will decrease the activation of the parasympathetic nervous, decrease the inhibition of sympathetic nervous system, increasing heart rate and contractility, stroke volume will increase and there will be an increase in the constriction of

arterioles, and increase stroke volume resistance. This increas...