BIOL 221 Lecture Notes - Lecture 2: Sinoatrial Node, Chronotropic, Thyroid Hormones

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Heart rate is the number of contractions (beats) per minute. The intrinsic rate is set by the sinoatrial (sa) node and altered by several factors such temperature and chronotropic agents such as hormones, ion autonomic postganglionic neurons. neurotransmitters from concentrations and. The faster sodium can diffuse into the cells, the faster action potentials can be generated at the sinoatrial node and the faster they can spread through the heart. Hormones that affect the increase heart rate include epinephrine. & norepinephrine (with what receptors do these interact?) and thyroxine. Ionic conditions that increase heart rate include decreased plasma calcium (hypocalcemia). Ionic conditions that decrease heart rate include increased plasma calcium (hypercalcemia), decreased potassium (hypokalemia), and highly increased potassium (severe hyperkalemia). In fact, if potassium levels get high enough, they can cause cardiac arrest. Heart rate can be controlled clinically using beta-adrenergic blockers (beta-blockers) such as propranolol (e. g. , inderal). Abnormal bradycardia and cardiac arrhythmias may require treatment with an artificial pacemaker.

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