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BIO 238 Heart and blood vessels are part of the cardiovascular system Heart pumps blood Arteries carry blood away from the heart to capillaries Veins carry blood from capillaries to heart Heart Chambers ◦ 2 atria Receive blood from veins ◦ 2 ventricles Pump blood to arteries ◦ Atrial septum ◦ Interventricular septum ◦ Heart is a double pump Left atria and ventricle: left pump Right atria and ventricle: right pump ◦ Differences in wall thickness depend upon work performed by the chamber Ventricles have more muscle then atria: atria pump to ventricle, ventricles pump out to body areas Left ventricle is most muscular: pumps blood to body Right ventricle has less muscle: pumps blood to lungs only Heart Valves: ◦ Allows blood to flow in one directionAtrioventricular valves Allows flow from atria to ventricles Tricuspid valve: between R atrium and ventricle Bicuspid (mitral) valve: between L atrium and ventricle ◦ Semilunar valves Located at base of blood vessels attached to ventricles Pulmonary semilunar valve: between R ventricle and pulmonary trunk Aortic semilunar valve: between L ventricle and aorta Includes: ◦ Systole: contraction phase ◦ Diastole: relaxation phase When atria and ventricles are relaxed, blood flows into atria, then through open AV valves into ventricles ◦ Semilunar valves closed due to greater pressure in arteries than in ventricles Atrial systole forces more blood into relaxed ventricles Ventricular systole (atrial diastole) increases blood pressure in ventricles ◦ Closes AV valves, opens semilunar valves ◦ Blood moves from ventricles and into arteries Ventricular diastole (atrial diastole) follows ◦ Allows AV valves to open and semilunar valves close ◦ Cycle repeats Heart Sounds ◦ Lub-dup (pause) lub-dup ◦ Lub: closing of AV valves during ventricular diastole ◦ Dup: closing of semilunar valves during ventricular systole Flow of Blood Through the Heart ◦ Two basic circuits of blood flow Pulmonary circuit Deoxygenated blood flows from R ventricle to lungs Oxygenated blood flows from lungs to L atrium Systemic Circuit Oxygenated blood flows L ventricle to body Deoxygenated blood flows from body to R atrium Steps of heart circulation ◦ Superior and inferior vena cava return blood from body to R atrium ◦ Pulmonary veins return blood from lungs to L atrium ◦ Atria push blood into ventricles ◦ R ventricle pumps blood into pulmonary trunk Blood moves into R and L pulmonary arteries, which head to lungs ◦ L ventricle pumps blood into the aorta, which carries blood out to body Conduction system consists of specialized muscle tissue that acts as neural tissue ◦ Spontaneously form impulses ◦ Impulses cause myocardium to contract Components include ◦ ◦ ◦ ◦ Sinoatrial (SA) node Atrioventricular (AV) node AV bundle Purkinje fibers Sinoatrial node ◦ Pacemaker of the heart ◦ Rhythmically forms impulses to initiate each heartbeat ◦ Impulses cause simultaneous contraction of atria Atrioventricular node ◦ Receives impulse from SA node ◦ Delay in passing through node allows time for ventricular filling and the completion or atrial contraction ◦ Passes impulse to the AV bundle AV bundle ◦ Divides into L and R branches ◦ Carries impulse down ventricular septum and up lateral ventricle walls ◦ Forms Purkinje fibers Purkinje fibers ◦ Carry impulse to myocardium of ventricles ◦ Contraction occurs from the apex upward Electrocardiogram (ECG or EKG) ◦ Recording of the electrical current generated during heart contraction ◦ Performed by an electrocardiograph ◦ Electrocardiogram has three distinct waves P wave: atrial depolarization QRS wave: ventricular depolarization T wave: ventricular repolarization Numerous factors can act on the SA node to increase or decrease heart rate Autonomic Regulation ◦ Cardiac center in the medulla oblongata Stimulated by excessive blood pressure and emotional factors, such as grief and depression Sympathetic neurons in the cardiac center cause an increase in heart rate Parasympathetic neurons in the cardiac center cause a decrease in heart rate Other factors affecting heart rate ◦ Age: resting rate declines with age ◦ Sex: females slightly faster than males ◦ Physical condition: good condition means lower heart rate ◦ Temperature: increase in temperature increases rate ◦ Epinephrine: increases strengthens heart rate ◦ Thyroxine: produces a lesser but longer lasting increase in heart rate ◦ Blood calcium levels Low levels slow heart rate Increased levels increase heart rate and prolong contraction ◦ Blood potassium levels Increased levels decrease both heart rate and force of contraction Low levels can cause abnormal heart rhythms Arteries ◦ Carry blood away from the heart ◦ Branch into smaller arteries, eventually forming arterioles Play an important role in controlling blood flow and blood pressure Capillaries ◦ Most numerous and smallest vessels ◦ RBCs pass through one at a time ◦ Thin walls allow exchange of materials between blood and cells Veins ◦ Blood flows from capillaries into venules ◦ Venules unite to form larger veins, which in turn unite to form even larger veins ◦ Valves exist in large veins to prevent blood backflow and aid in venous blood return ◦ Veins hold ~60% of blood volume at any instant Reducing venous volume can compensate for blood loss or increase in muscle activity Blood flows from high pressure areas to low pressure areas ◦ Greatest in ventricles and lowest in atria Ventricles create the pressure Pressure decreases with increased distance from the heart ◦ Due to increase in overall cross-sectional area of vessels due to branching ◦ Due to low pressure, veins require assistance to return blood to the heart Skeletal muscle contractions Contraction compresses veins, forcing blood from one valved segment to another Important in arms and legs Respiratory movements Downward contraction of diaphragm during inspiration Decreases thoracic pressure and increases abdominal pressure High pressure in abdominal veins forces blood into low pressure thoracic veins Arterial blood pressure in the systemic circuit ◦ Systolic blood pressure Highest pressure during ventricular systole ◦ Diastolic blood pressure Lowest pressure during ventricular diastole ◦ Pulse pressure is difference between systolic and diastolic blood pressures Causes the pulse: expansion and contraction of arterial walls ◦ Cardiac output Volume of blood pumped by heart in one minute Determined by heart rate and blood volume pumped in contraction Increase cardiac output, increase blood pressure Decrease cardiac output, decrease blood pressure ◦ Blood volume Decrease in blood volume, decrease in blood pressure Increase in blood volume, increase in blood pressure ◦ Peripheral resistance Friction of blood against blood vessel walls Constriction of arterioles increase both resistance and blood pressure Dilation of arterioles decreases both resistance and blood pressure ◦ Viscosity Thickness of blood Determined by blood cell concentration and plasma proteins Increase viscosity increases blood pressure Decrease viscosity decreases blood pressure Control of Peripheral Resistance ◦ Vasomotor center in the medulla Increases frequency of sympathetic impulses to cause vasoconstriction Increases blood pressure and velocity Accelerates oxygen and carbon dioxide transport rates Decreases frequency of sympathetic impulses to cause vasodilation Lowers blood pressure and velocity Activity of vasomotor area can be modified Affected by epinephrine, impulses from higher brain area, impulses from pressure and chemoreceptors Decrease in pressure, pH, or oxygen causes vasoconstriction ◦ Autoregulation Blood vessels are affected by localized changes in blood composition Oxygen, carbon dioxide, pH Effects can override vasomotor control Increases rate of exchange of materials between cells and capillaries Example: decrease in oxygen and increase in carbon dioxide causes vasodilation to increase blood flow Arrhythmia ◦ Abnormal heart beat ◦ Caused by factors such as damage to conduction system and drugs Bradycardia Heart rate less then 60 beats/min Tachycardia Heart rate over 100 beats/min Heart flutter Heart rate over 200-300 beats/min Fibrillation Very rapid heart rate with uncoordinated contraction Blood is not pumped from ventricles Congestive heart failure (CHF) Heart murmurs Myocardial infarction Pericarditis ◦ Acute or chronic inability of hear to pump out returned to it ◦ Symptoms include fatigue, edema, accumulation of blood in organs ◦ Possible cause is atherosclerosis ◦ Unusual heart sounds associated with defective heart valves ◦ Death of myocardium due to coronary artery blockage ◦ Heart attack ◦ Inflammation of pericardium due to viral or bacterial infection Aneurysm ◦ Weakened vessel wall bulges, forming balloon-like sac filled with blood ◦ Rupture can be fatal Arteriosclerosis ◦ Hardening of the arteries ◦ Due to calcium deposits accumulating in tunica media Atherosclerosis ◦ Formation of fatty deposits in the tunica interna of arteries ◦ Plagues reduce lumen size and increase probability of blood clot formation Hypertension ◦ Chronic high blood pressure ◦ Pressure exceeds 140/90 ◦ Pre-hypertension A systolic pressure between 120-139 and diastolic pressure between 80-89 Phlebitis Varicose veins ◦ Inflammation of a vein ◦ Most common in the legs ◦ Thrombophlebitis involves the formation of blood clots at the inflammation site ◦ Dilated, swollen veins due to malfunctioning valves ◦ Causes include heredity, pregnancy, and lack of physical activity ◦ Hemorrhoids