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CARDIOVASCULAR SYSTEM ANATOMY AND PHYSIOLOGY
Functions of the Heart Managing blood supply: Variations in the rate and force of heart contraction Match blood flow to the changing metabolic needs of the tissues during: Rest, exercise, and changes in body position Producing blood pressure: Contractions of the heart produce blood pressure Need for blood flow through the blood vessels Securing one- way blood flow: Valves of the heart secure a one-way blood flow through the heart and blood vessels Transmitting blood: Heart separates the pulmonary and systematic circulations Ensures the flow of oxygenated blood to tissues Anatomy of the Heart o Cardiovascular system can be compared to a muscular pump equipped with one- way valves o System of large and small plumbing tubes within which the blood travels Heart Structure and Functions o Modest size and weight of the heart o Give few hints of its incredible strength Weight: Approximately the size of a person’s fist Hollow, cone-shaped Weight less than a pound Mediastinum: Snugly enclosed within the inferior mediastinum Medial cavity of the thorax Heart is flanked on each side by the lungs Apex: ^ Directed toward the^ left hip^ and^ rests^ on the^ diaphragm Approx. at the level of the fifth intercostals space Base: Broad posterosuperior aspect Great vessels of the body emerge Points toward the right shoulder and lies beneath the 2 nd^ rib Pericardium: Enclosed in a double-walled sac (pericardium) Outermost layer of the heart Fibrous pericardium: Loosely fitting superficial part of the sac Helps protect the heart Anchors it to surrounding structures such as the diaphragm and
sternum Serous pericardium: Slipper, two-layer serous pericardium Parietal layer lines the interior of the fibrous pericardium Layers of the Heart o Heart muscles has 3 layers Epicardium: ^ Also known as the^ visceral Outermost layer Actually part of the heart wall Myocardium: ^ Consists of^ thick bundles^ of cardiac muscle^ twisted^ and^ whirled into ring-like arrangements Layer that actually contracts Endocardium: Innermost layer Thin, glistening sheet of endothelium hat Lines the heart chambers Chambers of the Heart o Heart has 4 hollow chambers or cavities Two atria, and Two ventricles o Receiving chambers: Two superior atria – primarily the receiving chambers Play a lighter role in the pumping activity of the heart o Discharging chambers: Two inferior Thick-walled ventricles are the discharging chambers Actual pumps of the heart When they contract, blood is propelled out o Septum: Divides the heart longitudinally depending on which chamber it separates Interventricular septum, or Interatrial septum Associated Great Vessels o Provide a pathway for the entire cardiac circulation to proceed Superior and inferior vena cava: Heart receives relatively oxygen-poor blood from the veins of the body through the large superior and inferior vena cava Pumps blood through the pulmonary trunk Pulmonary arteries: Carry blood to the lungs Lung is where oxygen is picked up and carbon dioxide is unloaded Pulmonary veins: Oxygen-rich blood drains from the lungs Returned to the left side of the heart through the 4 pulmonary veins Aorta: Systematic arteries branch to supply essentially all body tissues
Tunics o Walls of the blood vessels have three coats or tunics Tunica intima: Lines the lumen or interior of the vessels Thin layer of endothelium resting on a basement membrane Decreases friction as blood flows through the vessel lumen Tunica media: Bulky middle coat Consists of smooth and elastic fibers that constrict or dilate Make blood pressure increase or decrease Tunica externa: Outermost tunic Composed largely of fibrous connective tissue Function is basically support and protect the vessels Major Arteries of the Systematic Circulation o Major branches of the aorta and the organs they serve are listed next in the sequence from the heart
Arterial Branches of the Ascending Aorta o Aorta springs upward from the left ventricle of the heart Coronary arteries Only branches of the ascending aorta Serve the heart Arterial Branches of the Aortic Arch o Aorta arches to the left as the aortic arch Brachiocephalic trunk: 1 st^ branch of the aortic arch Splits into the: o Right common carotid artery, and o Right subclavian artery Left common carotid artery: 2 nd^ branch of the aortic arch Divides into 2: o Left internal carotid – serves the brain o Left external carotid – serves the skin and muscles (head and neck) Left subclavian artery: 3 rd^ branch of aortic arch Gives off an important branch vertebral artery o Serves as part of the brain Axillary artery: Subclavian artery becomes the axillary artery (axilla) Brachial artery: Subclavian artery continues into the arm as the brachial artery Supplies the arm Radial and ulnar arteries: Brachial artery at the elbow splits to form: o Radial arteries, and o Ulnar arteries Serve the forearm Arterial Branches of the Thoracic Aorta o Aorta plunges downward through the thorax o Following the spine as the thoracic aorta Intercostals arteries: 10 pairs Supply the muscles of the thorax wall Arterial Branches of the Abdominal Aorta o Aorta passes through the diaphragm into the abdominopelvic cavity o Becomes the abdominal aorta Celiac trunk: 1 st^ branch of abdominal aorta Consists of 3 branches: o Left gastric artery – supplies the stomach o Splenic artery – supplies the spleen o Common hepatic artery – supplies the liver Superior mesenteric artery: Unpaired Supplies most of the small intestine and the 1 st^ half of the large intestine or colon Renal arteries: Serve the kidneys Gonadal arteries: ^ Supply the^ gonads They are called Ovarian arteries (females) and, Testicular arteries (males) Lumbar arteries: Serve the heavy muscles of the abdomen and trunk walls Inferior mesenteric artery: Small, unpaired artery Supply the 2 nd^ half of the large intestine Common iliac arteries: Final branches of the abdominal aorta
internal jugular veins on their respective sides Azygos vein: Single vein Drains the thorax Enters the superior vena cava just before it joins the heart Veins Draining into the Inferior Vena Cava o Much longer than the superior vena cava o Returns blood to the heart from all body region below the diaphragm Tibial veins: Anterior and posterior tibial veins o Fibular vein – drain the leg o Posterior tibial veins – become the popliteal vein (knee) o Femoral vein – in the thigh, it becomes the external iliac vein as it enters the pelvis Great saphenous veins: Longest veins in the body Begin at the dorsal venous arch in the foot and travel up the medial aspect of the leg to empty into the femoral vein in the thigh Common iliac vein: Formed by the union of the external iliac vein Internal iliac vein drains the pelvis Gonadal vein: Drains the right ovary (females) Right testicles (males) Left Gonadal vein empties into the left renal veins superiorly Renal veins: Right and left drain the kidneys Hepatic portal vein: Single vein Drains the digestive tract organs Carries blood through the liver before it enters the systematic circulation Hepatic veins: Drain the liver Physiology of the Heart o As the heart beats or contracts, the blood makes continuous round trips – in and out of the heart Intrinsic Conduction System of the Heart o Spontaneous contractions of the cardiac muscle cells occurs in a regular and continuous way o Giving rhythm to the heart
Cardiac muscle cells: Can and do contract spontaneously and independently Even if all nervous connections are severed Rhythms: ^ Cardiac muscles^ can beat^ independently Muscle cells in the different areas of the heart have different rhythms Intrinsic conduction system: Also known as nodal system Built into the heart tissue sets the basic rhythm Composition: Intrinsic conduction system is composed of a special tissue found nowhere else in the body Much like a cross between a muscle and nervous tissue Function: ^ Heart muscle^ depolarization^ in only^ one direction o From the atria to the ventricles Enforces a contraction rate of approx 75 beats per minute Heart beats as a coordinated unit Sinoatrial (SA) node: “Pacemaker” Highest rate of depolarization in the whole system Start the beat and set the pace for the whole heart Atrial contraction: Impulse spread through the atria to the AV node Atria contract Ventricular contraction: Passes through the AV bundle, the bundle branches, and the Purkinje fibers resulting in a “wringing” contraction Ejection: This contraction effectively ejects blood superiorly into the large arteries leaving the heart The Pathway of the Conduction System o Conduction system occurs systematically through SA node: Depolarization wave is initiated by the Sinoatrial node Atrial myocardium: Wave then successively passes through the atrial myocardium Atrioventricular node: Depolarization wave then spreads to the AV node Atria contracts AV bundle: ^ Passes rapidly through the^ AV bundle Bundle branches and Purkinje fibers: Wave then continues on through the right and left bundle branches The Purkinje fibers in the ventricular walls o Resulting in a contraction that ejects blood, leaving the heart Cardiac Cycle and Heart Sounds o Healthy heart, the atria contract simultaneously then as they start to relax o Contraction of the ventricles begins Systole: ^ Means heart^ contraction Diastole: ^ Means heart^ relaxation Cardiac cycle: Refers to the events of 1 complete heartbeat During both atria and ventricles contract and then relax Length: Average heartbeats approx 75 times per minute Length of the cardiac cycle is normally about 0.8 seconds Mid-to-late diastole: Cycle starts with the heart in complete relaxation Pressure in the heart is low and blood is flowing passively Semilunar valves are closed and the AV valves are open Atria contract and force the blood remaining in their chambers into the ventricles Ventricular systole: Ventricular contraction begins and the pressure within the ventricles increases rapidly
Measuring blood pressure: The off-and-on flow of the blood into the arteries causes the blood pressure to rise and fall during each beat 2 arterial blood pressure measurements o Systolic pressure – pressure at the peak of ventricular contraction o Diastolic pressure – pressure when the ventricles are relaxing Peripheral resistance: Amount of friction the blood encounters as it flows through the blood vessels Neural factors: Parasympathetic division of the autonomic nervous system Little or no effect on blood pressure Sympathetic division has the major action of narrowing of the blood vessels (vasoconstriction) o Increases blood pressure Renal factors: When blood pressure increases beyond normal, kidneys allow more water to leave the body in the urine Blood volume decreases which turn decreases blood pressure Temperature: ^ Cold^ has a^ vasoconstricting effect Heat has a vasodilating effect Chemicals: Epinephrine - increases both heart rate and blood pressure Nicotine - increases blood pressure’ Alcohol and histamine - cause vasodilation and decreased blood pressure Diet: Diet low in salt, saturated fats, and cholesterol help to prevent hypertension, or high blood pressure Blood Circulation Through the Heart o Right and left sides of the heart work together in achieving a smooth-flowing blood circulation
Entrance to the heart: Blood enters the heart through 2 large veins o The inferior o Superior vena cava Emptying oxygen-poor blood from the body into the right atrium of the heart Atrial contraction: Blood flows from the right atrium to the right ventricle through the open tricuspid valve Closure of the tricuspid valve: Ventricle is full Tricuspid valve shuts to prevent blood from flowing backward into the atria (ventricle contracts) Ventricle contraction: Blood leaves the heart through the pulmonic valve Into the lungs where it is oxygenated Oxygen-rich blood circulates: Pulmonary veins empties oxygen-rich blood from the lungs into the left atrium of the heart Opening of the mitral valve: Blood flows from your left atrium into your left ventricle through the open mitral valve Prevention of backflow: Ventricle is full, mitral valve shuts o Prevents blood from flowing backward Blood flow to the systematic circulation: Blood leaves the heart through the aortic valve, into the aorta, and to the body
