The Heart: Study Stack for Test (more info)
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| Timing of Cardiac Cycle - in resting person: | atrial systole, ventricular systole, quiescent (when all four chambers are in diastole)
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| Cardiac Output (CO): | the amount ejected by ventricle in 1 minute (rate)
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| Cardiac Output: | heart rate x stroke volume
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| Cardiac Reserve: | the difference between a person's maximum and resting CO (increases with fitness, decreases with disease) CO can increase in an athlete
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| As you get older: | stroke volume will decrease, you still want to maintain a constant CO
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| Heart Rate: | is measured by taking a pulse.
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| Pulse: | surge of pressure produced by each heart beat that can be felt by palpating a superficial artery with the fingertips.
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| Tachycardia: | resting adult heart rate above 100 bpm (stress, anxiety, drugs, heart disease, fever, blood loss, damage to myocardium)
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| Bradycardia: | resting adult heart rate of less than 60 bpm (sleeping/rest, low blood temp, endurance trained athletes)
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| Positive Chronotropic Agents: | factors/agents that raise heart rate.
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| Negative Chronotropic Agents: | factors/agents that lower heart rate.
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| Common Carotid Artery: | neck
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| Radial Artery: | wrist
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| Cardiac Centers: | in the medulla oblongata initiate autonomic output to the heart.
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| Cardiostimulatory Effect: | some neurons of the cardiac center transmit signals to the heart by way of sympathetic pathways (increases heart rate)
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| Cardioinhibitory Effect: | others transmit parasympathetic signals by way of the vagus nerve.
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| Infant Heart Rate: | 120 bpm or more
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| Young adult female Heart Rate: | 72-80 bpm
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| Young adult male Heart Rate: | 64-72 bpm
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| Chronotropic Effects of the Autonomic Nervous System: | MEMORIZE
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| Chronotropic Effects of the Autonomic Nervous System: | MEMORIZE
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| Parasympathetic Vagus Nerves: | have cholinergic, inhibitory effects on the SA node and AV nods. [acetylcholine (ACh) binds to muscarinic receptors, opens K+ gates in the nodal cells, as K+ leaves the cells, they become hyperpolarized and fire less frequently, heart slows down]
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| What happens without influence from the cardiac centers? | The heart will still beat. The heart has an intrinsic heart rate of 100 bpm.
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| Cardiac Centers in the Medulla: | receive input input from many sources and integrate it into the decision to speed or slow the heart rate.
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| Higher Brain Centers: | affect heart rate & will respond to sensory/emotional stimuli [cerebral cortex, hypothalamus, limbic system]
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| Medulla: | also receives input from muscles, joints, arteries, and brain stem.
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| Proprioceptors in the muscles and joints: | informs the cardiac center about changes in activity.
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| Baroreceptors: | signal cardiac center when there is a pressure change.
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| Barorecptors: | pressure sensors in aorta & internal carotid arteries.
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| baro = | pressure
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| Chemoreceptors: | in aortic arch, carotid arteries and medulla oblongata
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| Chemoreceptors: | sensitive to blood pH, CO2, and O2 levels.
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| If blood pressure drops: | signal rate drops, and heart rate increases
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| If blood pressure rises: | signal rates increase, and heart rate decreases
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| Chemicals: | affect heart rate as well as neurotransmitters from cardiac nerves.
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| Drugs that stimulate heart: | Nicotine, thyroid hormone, caffeine
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| Nicotine: | stimulates catecholamine secretion (NE,EPI)
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| Thyroid hormone: | increases number of adrenergic receptors on heart so more responsive to sympatheitc stimulation.
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| Caffeine: | inhibits cAMP breakdown prolonging adrenergic effect.
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| All positive = | increases prolonged effect.
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| Three variables govern stroke volume: | Preload, contractility, afterload
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| Preload & Contractility: | etiher or can cause increase in stroke volume.
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| Afterload: | increase afterload which causes a decrease in stroke volume.
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| Preload: | the amount of tension in ventricular myocardium immediately before it begins to contract.
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| Increased preload: | causes increased force of contraction
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| Exercise: | increases venous return and stretches myocardium
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| Cardiocytes: | generate more tension during contraction
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| Increased cardiac output: | matches increased venous return
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| Frank-Starling Law of Heart: | Stroke volume is propportional to the end diastolic volume, ventricles eject as much blood as they recieve, the more they are stretched the harder they contract.
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| Contractility: | refers to how hard the myocardium contracts for a given preload.
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| Positive Inotropic Agents: | increase contractility.
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| Hypercalcemia: | can cause strong, prolonged contractions and even cardiac arrest in systole.
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| Catecholamines: | Increases calcium levels (examples of catecholamines are: dopamine EPI, NE)
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| Glucagon: | stimulates cAMP production
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| Digitalis: | raises intracellular calcium levels and contraction strength
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| Negative Inotropic Agents: | reduce contractility
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| Hypocalcemia: | can cause weak, irregular heartbeat and cardiac arrest in diastole
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| Hyperkalemia: | reduces strength of myocardial action potentials and the realease of Ca2+ into the sarcoplasm.
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| Vagus Nerves: | have effect on atria but too few nerves to ventricles for a significant effect
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| Afterload: | the blood pressure in the aorta and pulmonary trunk immediately diastal to the semilunar valves [opposes the opening of theses valves, limits stroke volume]
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| Hypertension: | increases afterload and opposes ventricular ejection.
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| Anything that impedes aterial circulation: | can also increase afterload.
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| Increase afterload: | will reduce stroke volume.
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| Exercise: | makes heart work harder and increases cardiac output.
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| Proprioceptors: signal cardiac center - | at beginning of exercise, signals from joints and muscles reach the cardiac center of the brain, & sympathetic output from cardiac center increases cardiac output
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| Increased muscular activity: | increases venous return [increase preload and ultimately cardiac output].
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| Increase in heart rate and stroke volume: | cause an increase in cardiac output.
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| Exercise: | can produce ventricular hypertrophy.
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| The resting heart rates in athletes: | are lower
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| Increased stroke volume: | allows the heart to beat more slowly at rest (training athletes)
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