Increased contractility ESV because of increased volume of ejected blood

Increased contractility esv because of increased

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Increased contractility ESV ↓ because of increased volume of ejected blood Because both EDV and ESV decrease, SV can remain unchanged Parasympathetic NS opposes sympathetic effects ACh hyperpolarizes pacemaker cells by opening K + channels, which slows HR Has little to no effect on contractility Autonomic Nervous System regulation of HR Regulation of Heart Rate
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Autonomic Nervous System regulation of HR cont. Regulation of Heart Rate Heart at rest exhibits vagal tone Parasympathetic is dominant influence on heart rate Decreases rate about 25 beats/min Cutting vagal nerve leads to HR of 100 beats/min When SNS is activated, PNS is inhibited, and vice-versa Atrial ( Bainbridge ) reflex : sympathetic reflex initiated by increased venous return , hence increased atrial filling Atrial walls are stretched with increased volume Stimulates SA node, which increases HR
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Chemical regulation of heart rate Hormones Epinephrine from adrenal medulla ↑ HR & contractility Thyroxine ↑ HR; enhances effects of NE & E Ions Intra- and extracellular ion concentrations (e.g., Ca 2+ and K + ) must be maintained for normal heart function Imbalances are very dangerous to heart Hypocalcemia : depresses heart Hypercalcemia : increases HR and contractility Hyperkalemia : alters electrical activity, which can lead to heart block and cardiac arrest Hypokalemia : results in feeble heartbeat; arrhythmias Regulation of Heart Rate
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Regulation of Heart Rate Other factors that influence heart rate Age Fetus has fastest HR; declines with age Gender Females have faster HR than males Exercise Increases HR Trained athletes can have slow HR Body temperature HR increases with increased body temperature
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Fill in the blanks: The contraction of the ventricles is referred to as and the period of ventricular relaxation is called . The first heart sound is a result of closure of the valves and closure of the valves causes the second heart sound. The heart chambers that have just been filled when you hear the first heart sound are the . The chambers that have just emptied when you hear the first heart sound are the . Immediately after the second heart sound, the are filling and the __________________ have emptied. Abnormal sounds, or usually indicate valve problems. 1 . During atrial systole: a) the atrial pressure exceeds ventricular pressure b) 70% of ventricular filling occurs c) the AV valves are open d) valves prevent backflow into the great veins e) a and c 2. Threshold in pacemaker cells is marked by: a) opening of sodium gates b) opening of calcium slow channels c) opening of calcium fast channels d) opening of potassium gates CHECK YOUR UNDERSTANDING
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  • Winter '16
  • Josef Buttigieg
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