Chapter 11 : Cardiovascular System The Heart - Consists of the heart, blood vessels, and blood. - This system has 3 main functions: 1.Transport of nutrients, oxygen, hormones to all cells and removal of metabolic wastes 2. Protection of the body by WBCs that circulate in the blood and defend the body against foreign microorganisms. It also has a clotting mechanism 3. Regulation of body temperature It involves 2 separate circuits: 1. Pulmonary circuit 2. Systemic circuit Anatomy of the Heart - The Heart lies in the medical section of the thoracic cavity called the mediastinum. - Its apex rests on the diaphragm. - The heart is held in a sac called the pericardium which is formed of three layers: Fibrous pericardium, Parietal pericardium and Visceral pericardium. Coverings and Walls of the Heart *important to know - The heart itself is formed of three layers: ●Endocardium: the innermost layer of the heart formed of endothelium ●Myocardium: the thick muscular layer of the heart; formed of cardiac muscle ●Epicardium: the outermost layer of the heart, the visceral pericardium Why is the left ventricle thicker than the right ventricle? Because it has a bigger job, it has to pump enough blood from top of body to feet. - Atrium - receiving chambers - Ventricles - discharging chamber Pulmonary Circuit: The circuit of blood moving from the right atrium, to the lungs, and to the left atrium is called the pulmonary circuit. Systemic Circuit: Carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body. Heart Valves *must know all steps for AV and SL valves AV valves 1) Blood returning to the atria puts pressure against AV valves; the AV valves are forced open 2) As the ventricles fill, AV valves cusps hang limply into ventricles 3) Atria contract, forcing additionally blood into ventricles 4) Ventricles contract, forcing blood against AV valve cusps 5) AV valves close 6) Chordae tendineae tighten, preventing valve cusps from everting into atria Semilunar valves 1) As ventricles contract and intraventricular pressure rises, blood is pushed up against SL valves, forcing them open 2) As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of SL valves and forcing them to close. AV Valves - It is important that the blood flow goes in one direction in the heart. - The valve helps the direction and the flow of blood, prevents backflow - On the right side of the heart, the atrium and ventricles are separated by the tricuspid valve - On the left side, the atrium and ventricles are separated by the bicuspid valve (mitral valve) - These valves are held in place by cords called chordae tendineae, which are attached to the papillary muscles within the ventricles - When ventricles contract they pull on these cords and close the AV valves, which prevents any backflow of blood and also produces the first heart sound (“lub” or S1). Semilunar Valves - The pulmonary semilunar valve and the aortic semilunar valve are essentially always closed until the ventricles contract (60-100 bpm is normal). - When the ventricles contract, the pressure pushes the SL valves open, allowing blood to move to both the lungs and the body. First heart sound results from tricuspid and bicuspid valves closing. - When the ventricles relax, blood flows back against the SL valves, causing them to shut, which produces the second heart sound (“dub” or S2). Blood supply of the heart - Although there is blood in the heart at any given moment, the blood in the chambers does not feed the heart tissue itself. Instead, the heart is supplied by coronary arteries that branch off the aorta. Intrinsic Conduction System - Although external forces can modify your heart rate, the heart can regulate its own contractions. It does this via nodal tissue. Components are: - Sinoatrial (SA) node: “the pacemaker of the heart” - sends an impulse across the atria leading to depolarization of the atria and therefore contraction (systole). - AV node - Bundle branches - Purkinje fibres Cardiac Cycle The cardiac cycle refers to all the events that occur in one heart beat. The terms that we use during cardiac cycle are: - Heart contraction → systole - Heart relaxation → diastole The average heart beat is approx 75 bpm and the cardiac cycle is normally about 0.8 seconds *for cardiac cycle know what's happening to the chambers, atriums and ventricles Steps: 1) All chambers of the heart are relaxed, the AV valves are open and the heart begins to passively fill with blood. 2) The atria contracts and forces blood into the ventricles. 3) Atria relaxes and the ventricles begin to contract. This build up of pressure causes the AV valves to close and the 1st heart sound is heard. “Lub” 4) The ventricles continue to contract and the buildup of pressure forces the SL valves open, allowing blood to move into the pulmonary trunk and the aorta. 5) When the ventricles relax, the SL valves are closed, and the 2nd heart sound is produced “dub” or s2 Cardiac Output - Cardiac output is the amount of blood pumped out by each side of the heart in 1 minute. It is the product of heart rate (HR) and stroke volume (SV). - SV is the volume of blood pumped out by a ventricle with each heartbeat, each “lub dub.” Stroke volume - Stroke volume is the volume of blood pumped from the left ventricle per beat. - 3 factors influence SV: 1. Preload - How much the cardiac muscles are stretched by filling the chambers just before they contract. - The more muscles are stretched, the higher the stroke volume - The account of venous return (1) and the length of time the ventricles are relaxed and filling (2) affects preload. - Ex. A slow heartbeat allows more time for the ventricles to fill, while exercise speeds venous return because it results in increased heart rate. 2. Contractibility - ability of cardiac muscle to generate tension 3. Afterload - amount of pressure the ventricles must overcome to eject blood. Factors modifying heart rate 1. Neural (ANS) controls - During physical or emotional stress, the sympathetic division of the autonomic nervous system stimulates the SA and AV nodes and the cardiac muscle itself which causes the heart to beat faster. - Parasympathetic nerves slows and steadies the heart, giving it time to rest during noncrisis - *sympathetic - fight or flight 2. Hormones and ions - Epinephrine (which mimics sympathetic nerves) is released in response to sympathetic nerve stimulation - Thyroxine increases heart rate and contractility - Reduced level of calcium ions in the blood depresses heartbeat , but excessive amounts of calcium ions causes contractions and the heart may even stop 3. Physical factors - Age, gender, exercise, and body temperature affect heart rate - Heat increases heart rate by boosting metabolic rate of heart cells - Cold decreases heart rate - Exercise acts through nervous system controls to increase heart rate. Microscopic Anatomy of Blood Vessels Blood Vessels - As the heart beats, it moves blood into the large arteries leaving the heart. - Large arteries branch into smaller and smaller arteries called arterioles. - Arterioles feed into capillaries in the tissues. - Clusters of capillaries called capillary beds are drained by venules; they in turn empties into veins Arteries - away Veins - towards Tunics Tunica intima : innermost layer Tunica media: medial muscle layers Tunica externa : the outermost layer formed of connective tissue - The valves operate with skeletal muscle interaction and prevent blood from moving back down. Structural Difference Between Arteries, Veins, and Capillaries Arteries - Arteries carry blood away from the heart. - The walls of arteries are much thicker than veins because they must be able to expand and stretch in response to the force of blood that goes through them. -Their walls are more stronger and can stretch to take continuous changes in pressure - Doesn’t have valves Veins: - Veins carry blood back to the heart and tend to have low pressure, thus walls are thinner. - Has valves Capillaries - Capillaries are found throughout the body’s tissues but are not all active at the same time. - They are equipped with vascular shuts to ensure blood still flows between the arteries and the venules. Walls of arteries vs Veins - The walls of arteries are much thicker than veins because they must be able to expand and stretch in response to the force of blood that goes through them, their walls are stronger and can stretch to take continuous changes in pressure. -Veins carry blood back to the heart and tend to have low pressure, thus walls are thinner Pulse is the expansion and recoiling of an artery as the left ventricle beats and forces blood through them. Pulse is determined by your heart rate which is an average of 60-100 (75 bpm) Blood Pressure - Blood pressure is the pressure the blood exerts against the inner walls of the blood vessels, and it is the force that keeps blood circulating continuously between heartbeats. Blood Pressure Gradient - When ventricles contract, they force blood into arteries that expand as blood is pushed into them. The high pressure in the arteries forces the blood to move into areas where the pressure is lower. - Pressure is highest in the large arteries closest to the heart, as it moves down its pathway to the heart it flows down a pressure gradient (high to low). Veins have a low pressure gradient. - Ex. if you cut yourself in the veins the blood flows evenly from the wound, however in the artery the blood is produced in rapid spurts Factors that Influence Blood Pressure - If blood volume increases, BP increases Neural factors Renal factors: the kidneys Temperature - Cold causes vasoconstriction (increases BP) - Heat causes vasodilation (decreases BP) Chemical that increase BP - Epinephrine increases heart rate and BP - Nicotine increases BP because it causes vasoconstriction of the blood vessels Chemicals that decrease BP - Alcohol and histamine cause vasodilation thus decreasing BP Diet - Diet with high cholesterol, sodium, and sugars causes high HP -Recommended to eat foods with low sodium, low cholesterol, and saturated fats to prevent increase in BP Capillary Exchange of Gases and Nutrients - Recall that capillaries are small blood vessels found in beds in tissues. -Gas, nutrients and waste exchange occur across capillary beds. - Methods of crossing capillary bed: 1. Through membrane 2. Intercellular clefts 3. Pores 4. Vesicles 1. Direct Diffusion through membrane - Substances diffuse directly through across the plasma membrane if the substances are lipid-soluble - Like simple diffusion of O2 and CO2 2. Diffusion through intercellular clefts - Fluids and small solutes can move through here 3. Diffusion through pores - Occurs in fenestrated capillaries that are found in the area of absorption and filtration (Kidney and intestines). - They allow passage of small solutes and fluids 4. Transport via Vesicles - If a product a liquid-soluble, it can be transported via exocytosis or endocytosis Fluid movements in Capillary Beds Osmotic pressure vs blood pressure How substances move across the capillary bed and into the tissues: Arterial end: Blood pressure is higher than osmotic pressure which causes net movement of fluid and small solutes out of the capillary. This process is filtration. Venous end: Blood pressure is decreased to less than osmotic pressure causing the net movement in. Most of the fluid that left at the arterial end re-enters the tissues at the venous end
