cardiac output

• What is cardiac output?

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

  It is the product of stroke volume and heart rate
• If a person has a stroke volume of approximately $70 \text{ ml}$ and a heart rate of $70 \text{ bpm}$, what is their cardiac output?


  Approximately $5 \text{ L/m}$
• What factors control cardiac output?

  Heart rate and stroke volume
• What regulates cardiac output?

  The autonomic nervous system (ANS), intrinsic regulation of myocytes, and atrial reflexes
• What is the resting membrane potential (RP) of the SA node?

  Approximately $-55 \text{ mV}$
• What is the action potential (AP) of the SA node?

  Approximately $-40 \text{ mV}$
• What happens during the SA node action potential?

  Ca$^{2+}$ channels open, followed by K$^{+}$ channels opening and Ca$^{2+}$ channels closing
• What is the role of cholinergic action on the heart?

  It involves the M2 cholinergic receptor and decreases heart rate
• What is the role of adrenergic action on the heart?

  It involves β-adrenoceptors that increase heart rate and force of contraction
• What is the intrinsic rate of the SA node?

  About $100 \text{ bpm}$
• What effect does vagal stimulation have on heart rate?

  It decreases heart rate to about $70 \text{ bpm}$
• What is the Frank Starling Law of the heart?

  The greater the degree of stretch, the greater the force of contraction
• How does preload affect stroke volume?

  Increasing preload increases stroke volume
• What factors affect preload?

  Atrial pressure, venous pressure, gravity, and blood volume
• What percentage of total blood volume do veins contain at any given time?

  60-70%
• How does blood volume affect preload?

  An increase in blood volume results in increased central venous pressure and preload
• What is the effect of gravity on venous return?

  It makes venous return more difficult when standing
• What is the muscle pump's role in venous return?

  It helps displace blood towards the heart during muscle contraction

  
• How does the thoracic pump assist venous return?

  It lowers thoracic pressure during inspiration, aiding blood movement into the thorax
• What is the difference between Starling's law and contractility?

  Starling's law increases stroke volume by changing fiber orientation, while inotropes increase contractility by altering Ca$^{2+}$ signaling
• What is mean arterial pressure (MAP) and how is it calculated?

  MAP = cardiac output x total peripheral resistance
• What role does blood volume play in blood pressure control?

  It affects cardiac output and thus blood pressure
• What is the renin-angiotensin system (RAS)?

  It regulates blood volume and pressure through vasoconstriction and sodium reabsorption
• What is the function of anti-diuretic hormone (ADH)?

  It drives water reabsorption from the kidney
• What is the role of Atrial Natriuretic Peptide (ANP)?

  It inhibits salt reabsorption, promoting salt and water loss
• What is the baroreceptor reflex?

  It is a short-term control mechanism for blood pressure

  
• Where are baroreceptors located?

  In the walls of the aortic arch and carotid sinus

  
• What happens when blood pressure drops?

  Baroreceptor firing decreases, leading to increased sympathetic outflow

  
• What is heart failure?

  It is the inability to maintain cardiac output
• How does the body respond to decreased cardiac output?

  It activates the SNS via the baroreceptor reflex
• What triggers the release of ANP and BNP?

  Increased blood volume that stretches the atria
• What is the effect of stretch on the heart's atria?

  It activates sensory afferents to the medulla, inhibiting the cardiovascular center
• What is the relationship between blood volume and urine loss?

  Increased blood volume leads to decreased SNS activity and greater urine loss
• What is the significance of stretch receptors in the heart?

  They detect changes in blood volume and help regulate cardiovascular responses