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Regulation of cardiac activity Cardiac output Blood flow Blood pressure

Regulation of cardiac activity Cardiac output Blood flow Blood pressure. Cardiac output= stroke volume X cardiac rate (ml/min) (ml/beat) (beats/min) At 70 beats/min and 80 ml/beat, this comes to about 5.5 liters per minute— Equivalent to the total blood volume.

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Regulation of cardiac activity Cardiac output Blood flow Blood pressure

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  1. Regulation of cardiac activity Cardiac output Blood flow Blood pressure

  2. Cardiac output= stroke volume X cardiac rate (ml/min) (ml/beat) (beats/min) At 70 beats/min and 80 ml/beat, this comes to about 5.5 liters per minute— Equivalent to the total blood volume

  3. Autonomic system regulation at SA node • Heart cells will contract spontaneously; HCN channels open to cause depolarization • Sympathetic NS (E, NE) increases depolarization rate by keeping HCN channels open • PNS: Ach acts on muscarinic receptors for hyperpolarization • Chronotropic effect: aggregate effect on heart rate (positive= increase) • See table 14.1

  4. Exercise reduces vagus inhibition and increases sympathetic nerve activity Cardiac control center in medulla oblongata coordinates this activity This in turn is regulated by higher brain activity and pressure (baroreceptors) in aorta and carotid arteries

  5. Regulation of stroke volume EDV: end-diastolic volume (blood left in ventricles after diastole) increase in EDV increase in stroke volume Total peripheral resistance to arterial blood flow stroke volume is inversely proportional to this (temporarily)- heart compensates Strength of ventricular contraction increased as EDV increases; normal ejection fraction is about 60% of total volume

  6. Frank-Starling law of the heart Intrinsic variation as EDV increases, so does force of contraction (increased stretch) Increased peripheral resistance  Increased EDV  Increased stretch  Next contraction is stronger Highly adjustable

  7. Contractility • Positive inotropic effect (increased influx of calcium)increased contraction strength • Chronotropic effect and inotropic effect manipulated by ANS

  8. Venous return At rest, most of the blood is in the veins veins can “give” more and hold more blood than arteries; venous pressure is much lower (2 mm Hg vs. 90-100 mm Hg mean arterial pressure) Venous pressure determines rate of blood return to the heart

  9. And solutes

  10. Edema- excessive fluid in tissues Causes: high blood pressure venous obstruction leakage of plasma proteins into tissue fluid (as in inflammation) kidney or liver disease leading to protein loss or lack of formation obstruction of lymphatic vessels (filiarisis) myxedema- increased secretion of proteins into extracellular matrix

  11. Regulation of blood volume by kidneys Filtration of blood- almost all of filtrate is reabsorbed by the kidneys (out of daily production of ca. 180L of filtrate, only about 1.5 L actually excreted) Various hormones acting on, or produced by, the kidneys

  12. ANF responds to increased blood volume

  13. Resistance to blood flow Related to pressure difference between the ends of the vessel Inversely related to resistance of blood flow through vessel In body, vasodilation in one organ system might be offset by vasoconstriction in another

  14. Regulation of blood flow Sympathetic nervous system overall, increase in cardiac output and in peripheral resistance vasoconstriction in arterioles of viscera and skin vasodilation in skeletal muscles (depends on receptors) Parasympathetic- vasodilation effect confined to GI, genitalia, salivary glands

  15. Paracrine regulation, e.g., inflammation Intrinsic (autoregulation) myogenic- response to changes in blood pressure metabolic-oxygen, carbon dioxide levels local vasodilation

  16. How are aerobic requirements of heart met? Lots of capillaries Myoglobin releases oxygen during systole (blood flow is reduced at that time) capacity for aerobic respiration: extra mitochondria, enzymes Blockages in blood supply are corrected by angioplasty, bypass, etc.

  17. Blood flow to brain Intrinsic mechanisms maintain constant flow myogenic responses to changes in blood pressure sensitive to CO2 levels in arterial blood metabolic responses- local vasodilation

  18. Blood pressure Blood flow resistance highest in arterioles Flow rate lowest in capillaries Blood pressure can be raised by: vasoconstriction of arterioles increase in cardiac output (higher cardiac rate or stroke volume) Various factors can affect these: kidneys, sympathetic nervous system, etc.

  19. Pressure receptors (baroreceptors) Action potentials will increase or decrease as pressure rises or falls Baroreceptor reflex activated when blood pressure rises or falls. Activated when a person changes position Vasomotor control centers- constriction/dilation Cardiac control centers- cardiac rate

  20. And hormones; Stretch receptors

  21. Measurement of blood pressure sphygmomanometer Systolic/diastolic pressure, e.g., 120/80 exercise tends to raise systolic more changing position. Total peripheral resistance tends to affect diastolic Pulse pressure: systolic- diastolic reflects stroke volume drops in dehydration or blood loss Pulse rate reflects cardiac rate Mean arterial pressure= diastolic + 1/3 pulse pressure

  22. Pathophysiology of cardiovascular system Hypertension Secondary- results from known diseases (table 14.9) processes that affect blood flow; damage to tissue that results in release of vasoactive chemicals; damage to sympa- thetic nervous system, etc. Essential- accounts for most cases of hypertension

  23. Increased total peripheral resistance Low renin secretion? High salt intake? Stress? Inability of kidneys to regulation salt and water excretion?

  24. Consequences of high blood pressure Can damage cerebral blood vessels and lead to stroke Causes heart to work harder (harder to eject blood if peripheral resistance is high) Contributes to atherosclerosis Treatments are many and varied (table 14.10) diet, diuretics, various receptor blockers

  25. Shock due to loss of blood flow hypovolemic- blood LOSS septic- blood-borne infection; nitric oxide formation might be the culprit anaphylactic- severe allergic reaction (histamine) cardiogenic- infarction causes extensive damage to heart muscle

  26. Congestive heart failure- cardiac output is inadequate causes: heart disease, hypertension, electrolyte imbalance Digitalis increases contractility of heart muscle Diuretics lower blood volume Nitroglycerin is a vasodilator Make heart work more efficiently; reduce stress on heart

  27. Summary • Cardiac output is regulated by ANS, blood volume, venous return, and vascular resistance to blood flow • Vasodilation and vasoconstriction direct blood flow to different parts of the body in response to exercise or other stimuli • Baroreceptors, and well as mechanisms that adjust blood volume, regulate blood pressure • Hypertension, shock, and congestive heart failure are serious disorders that must be controlled by medication or other treatment

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