Cardiac output

• What is cardiac output?

  Cardiac output is the volume ejected from a ventricle per minute (L/m).
• How is cardiac output calculated?

  Cardiac output is the product of stroke volume and heart rate.
• What controls cardiac output?

  Cardiac output is controlled by regulating either or both heart rate and stroke volume.
• Which system regulates cardiac output?

  Cardiac output is regulated by the autonomic nervous system (ANS).
• How do the sympathetic and parasympathetic nervous systems affect heart rate?

  Both the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) innervate the SA node, controlling heart rate through their balance.
• What is tachycardia a sign of?

  Tachycardia is a sign of sympathetic activation.
• Are both the SNS and PNS active at rest?

  Yes, both the sympathetic and parasympathetic nervous systems are active at rest.
• What effect do beta-blockers have on heart rate?

  Beta-blockers can drop heart rate from 70 to 60 bpm, showing sympathetic nervous system action.
• What type of receptor is the beta-adrenoceptor?

  The beta-adrenoceptor is a G-protein coupled receptor linked to adenylate cyclase.
• What does increased cAMP activate in the heart?

  Increased cAMP activates protein kinase A (PKA).
• What is the main depolarizing current in the SA node?

  The main depolarizing current in the SA node comes from the Na+/K+ HCN channels.
• How does cAMP/PKA affect myocytes in the heart?

  cAMP/PKA increases the entry of Ca$^{2+}$ into myocytes, increasing the force of contraction.
• What does the parasympathetic nervous system affect in the heart?

  The parasympathetic nervous system only affects heart rate.
• What does the sympathetic nervous system do to heart rate and force of contraction?

  The sympathetic nervous system increases both heart rate and force of contraction.
• What are positive chronotropes?

  Positive chronotropes increase heart rate.
• What are positive inotropes?

  Positive inotropes increase the force of contraction.
• What does intrinsic regulation of stroke volume refer to?

  Intrinsic regulation refers to the heart's ability to adapt to changes in blood volume without dependence on nerves or hormones.
• What does the Frank-Starling mechanism state?

  The Frank-Starling mechanism states that the greater the degree of stretch, the greater the force of contraction.
• How does increasing preload affect stroke volume?

  Increasing preload increases stroke volume.
• What happens as the myocardium is stretched according to Starling's law?

  As the myocardium is stretched, more cross bridges form between actin and myosin, allowing greater force to be generated.
• Is the relationship between stretch and force generated linear?

  No, it is not a linear relationship; if stretched too much, the number of cross bridges falls, and so does the force generated.
• What is the Starling cardiac function curve?

  • Represents the relationship between stroke volume and preload
  • Illustrates how stroke volume increases with greater preload until a certain point
  • Shows the decline in stroke volume if the myocardium is overstretched
• What is preload?

  Preload is the term that describes ventricular filling during diastole.
• What factors affect preload?

  Preload is affected by atrial pressure, venous pressure, gravity, and blood volume in circulation.
• How does gravity affect venous return?

  When upright, gravity negatively affects venous return, while in the supine position, venous return is increased.
• What role do veins play in blood circulation?

  Veins act as capacitance vessels for the storage of blood.
• What happens to central venous pressure with increased blood volume?

  An increase in blood volume results in increased central venous pressure and hence increased preload.
• What is the muscle pump's role in venous return?

  The muscle pump displaces blood in veins as muscles contract, aided by valves that prevent backflow.
• How does the thoracic pump assist venous return?

  The thoracic pump raises abdominal pressure and lowers thoracic pressure during inspiration, aiding venous return.
• What is arterial blood pressure (BP) a driving force for?

  Arterial blood pressure is the driving force of tissue perfusion.
• What is tissue perfusion?

  Tissue perfusion is the process of delivering blood to the tissues and organs of the body.
• Why is blood pressure important?

  Blood pressure ensures that tissues receive oxygen and nutrients and that waste products are removed.
• What happens if blood pressure is too low?

  If blood pressure is too low, brain blood flow and kidney filtration fall.
• What happens if blood pressure is too high?

  If blood pressure is too high, pathological damage occurs in many tissues.
• What is the formula for mean arterial pressure (MAP)?

  MAP = cardiac output (CO) × total peripheral resistance (TPR).
• How does blood volume affect blood pressure?

  Blood volume via venous return affects cardiac output and blood pressure.
• What is the renin-angiotensin system (RAS)?

  The renin-angiotensin system increases resistance and stimulates aldosterone, increasing Na+ and water reabsorption from urine.
• What does anti-diuretic hormone do?

  Anti-diuretic hormone drives water reabsorption from the kidney and decreases diuresis.
• What is the function of atrial natriuretic peptide (ANP)?

  Atrial natriuretic peptide inhibits salt reabsorption and promotes salt and water loss.
• What is the baroreceptor reflex?

  The baroreceptor reflex is a short-term control mechanism of blood pressure involving sensory afferents, central relays, and effector efferents.