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Humoral and intra cardiac mechanisms of heart ‘ regulation. Humoral regulation of heart. Effects of thyroid hormones
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Humoraland intra cardiac mechanisms of heart ‘ regulation.
Humoral regulation of heart • Effects of thyroid hormones • Thyroid hormones increase transmission process in ribosome and nucleus of cells. Intracellular enzymes are stimulated due to increasing protein synthesis. Also increases glucose absorption and uptake of glucose by cells, increases glycolisis and gluconeogenesis. In blood plasma increases contents of free fatty acids. • All these effects of thyroid hormones lead to increase activity of mitochondria in heart cells and ATP formation in it. So, both activity of heart muscle and conduction of impulses are stimulated.
Effects of adrenocortical hormones • Aldosterone causes increasing Na+ and Cl- in blood and decreases K+. This is actually for producing action potential in the heart. Cortisol stimulates gluconeogenesis and increase blood glucose level. • Amino acids blood level and free fatty acids concentration in blood increases also. Utilization of free fatty acids for energy increases. These mechanisms actual in stress reaction. So heart activity is stimulated.
Hormones of Langerhans’ islets effects • Insulin promotes facilitated diffusion of glucose into cells by activation glucokinase that phosphorilates glucose and traps it in the cell, promotes glucose utilization, causes active transport of amino acids into cells, promote translation of mRNA in ribosome to form new proteins. Also insulin promotes glucose utilization in cardiac muscle, because of utilization fatty acids for energy. • Clucagone stimulate gluconeogenesis, mobilizes fatty acids from adipose tissue, promotes utilization free fatty acids foe energy and promotes gluconeogenesis from glycerol. So both hormones can increase strength of heartbeat.
Endocrine function of heart • Myocardium, especially in heart auricles capable to secretion of regulatory substances as atria Na-ureic peptide, which increases loss of Na+ in increase of systemic pressure, or digitalis-like substances, which can stimulate heart activity.
Intrinsic regulation • Intrinsic regulation is performed in response changes of blood volume, flowing into the heart. It is known as Frank Starling low. Within physiological limits heart pumps all blood that comes to it without allowing excessive damming of blood in veins. • Cardiac contraction is directly proportional to initial length of its fibers. In end-diastolic volume over 180 ml excessive stretching heart fibers occurs and strength of next cardiac contraction decreases.
Anrep's effect • Increase of blood flow in aorta and so coronary arteries leads to excessive stretching surrounding myocardial cells. • According to Frank Starling low cardiac contraction is directly proportional to initial length of its fibers. So increase of coronary blood flow leads to stimulation heartbeat.
Boudichi phenomenon • In evaluation heart beat rate increase of every next heart contraction is observed. • It caused by rising of Ca2+ influx into myocardial cells without perfect outflow, because of shortening of cardio cycle duration.
Effects of nn. vagi • Effects of nn. vagus on the heart activity. Parasympathetic stimulation causes decrease in heart rate and contractility, causing blood flow to decrease. • It is known as negative inotropic, dromotropic, bathmotropic and chronotropic effect.
Effects of acetylcholin • Effects of acetylcholin leads to increase of K+ permeability through cell membrane in conductive system, which leads to hyper-polarisation and cause such effects to the heart activity: • - Negative inotropic effect - decreasing strength of heart contractions; • - Negative chrono-tropic effect - decreasing heartbeat rate; • -Negative dromo-tropic effect - decreasing heart conductibility; • - Negative bathmo-tropic effect - decreasing excitability of heart muscle.
Location of receptors in the heart • Heart muscle contains, both chemical and stretch receptors in coronary vessels, all heart cameras and pericardium. Stretch receptors are irritated by changing blood pressure in heart cameras and vessels. • Chemo sensitive cells, which are stimulated by decrease O2, increase of CO2, H+ and biological active substances also, are called as chemoreceptors.
Reflexes from atria • When atria pressure increase due to increasing blood volume, atria stretched. Signals pass to afferent arterioles in kidneys to cause vasodilatation and glomerullar capillary pressure, thereby increasing glomerullar filtration. Signals also pass to hypothalamus to decrease antidiuretic hormone secretion and so fluid reabsorbtion. It causes decreasing both blood volume and arterial pressure to normal. • Other reflex reaction is known as atria and pulmonary artery reflex. When atria pressure increase due to increasing blood volume, atria stretched. Low-pressure receptors, similar to baroreceptors, in atria and pulmonary arteries stretched and stimulated. Signals pass to vasomotor center and inhibit vasculomotor area. Arterial pressure decreases to normal.
Reflex reactions from receptors of pericardium, endocardium and coronary vessels • Reflex reactions from receptors of pericardium, endocardium and coronary vessels lead to stimulation n. vagus. It leads to parasympathetic stimulation of the heart. • Parasympathetic stimulation causes decrease in heart rate and contractility, causing blood flow to decrease. It is known as negative inotropic, dromotropic, bathmotropic and chronotropic effect.
Baroreceptor reflexes • Increasing arterial pressure stretched and stimulated baroreceptors in carotid sinus and aortic arc. Signals pass through glossopharyngeal and vagal nerve to tractus solitarius in medulla. Secondary signals from tractus solitarius inhibit vasoconstrictor center and excite vagal center. • Peripheral vasodilatation and decrease both heart rate and contractility occur. Arterial pressure decreases to normal. When arterial pressure decreases, whole process occurs, causing opposite result.
Irritation of visceroreceptors • Irritation of visceroreceptors results in stimulation of vagal nuclei, which cause decreasing blood pressure and heartbeat. Parasympathetic stimulation causes decrease in heart rate and contractility, causing blood flow to decrease. It is known as negative inotropic, dromotropic, bathmotropic and chronotropic effect. • This mechanism is important for doctor in performing diagnostic procedures, when probes from apparatuses are attached into visceral organs. This may cause excessive irritation of visceral receptors.
Mechanisms of heart auto regulation • Greater rate of metabolism or less blood flow causes decreasing O2 supply and other nutrients. Therefore rate of formation vasodilator substances (CO2, lactic acid, adenosine, histamine, K+ and H+) rises. When decreasing both blood flow and oxygen supply smooth muscle in precapillary sphincter dilate, and blood flow increases. • Moderate increasing temperature increases contractile strength of heart. Prolonged increase of temperature exhausts metabolic system of heart and causes cardiac weakness. Anoxia increases heart rate. Moderate increase CO2 stimulates heart rate. Greater increase CO2 decreases heart rate.
Atria and pulmonary artery reflex • When arterial pressure increases due to increasing blood volume, atria stretched. Low-pressure receptors, similar to baroreceptors, in atria and pulmonary arteries stretched and stimulated. Signals pass to vasomotor center and inhibit vasculomotor area. Arterial pressure decreases to normal. • Excessive stretching of lung tissue causes excitation of n. vagus. It leads to parasympathetic stimulation of the heart. Parasympathetic stimulation causes decrease in heart rate and contractility, causing blood flow to decrease.
