Cardiovascular

• Gap Junctions

  Responsible for the transmission of current between neighboring cells. In the heart, gap junctions allow current to be transmitted rapidly between each cardiac muscle cell. Ca2+ is the major ion responsible for the current.
• Desmosomes

  Responsible for the transmission of force between neighboring cells.
• Gap junctions and desmosomes are found in intercalated discs that connect cardiac myocytes end to end.
• Difference between skeletal and cardiac excitation-contraction coupling

  • In skeletal muscle, DHPR acts as voltage-sensor only. In cardiac muscle, DHPR acts as voltage-gated Ca2+ channel, allowing Ca2+ to enter from extracellular fluid.
• Sympathetic nervous system activation

  Increases the rate of depolarization of the pacemaker action potential, increasing heart rate
• Parasympathetic nervous system activation

  Decreases the rate of depolarization of the pacemaker action potential, decreasing heart rate
• What happens to heart rate when the sympathetic nervous system becomes activated?

  1. Heart rate increases

  2. Sympathetic nervous system INcreases the rate of DE-polarization of the unstable resting membrane potential in the pacemaker action potential
• What happens to heart rate when the parasympathetic nervous system becomes activated?

  1. Heart rate decreases

  2. Parasympathetic nervous system DEcreases the rate of DE-polarization of the unstable resting membrane potential in the pacemaker action potential
• Ejection fraction

  Evaluates the fraction of blood that leaves the ventricles during ejection to the amount of blood in the ventricles at the end of diastole
• Factors that regulate stroke volume

  • Preload: The degree of stretch on the ventricles before ejection (aka end diastolic volume)
  • Contractility: The force and intensity of contraction
  • Afterload: The pressure the ventricle must generate to eject blood
• Contractility

  Intensity and strength of contraction
• Positive inotropes

  Increase contractility
• Negative inotropes

  Decrease contractility
• Frank-Starling Law of the Heart

  The greater the volume of blood in the ventricles at the end of diastole (EDV), the stronger the ventricles will contract during systole, causing increased stroke volume
• Afterload

  The amount of pressure that the ventricles must overcome to open the aortic valve
• Chronic hypertension

  Increases afterload, decreases stroke volume
• Cardiac output is roughly equal to venous return
• Compliance

  The ability to stretch because of a change in pressure
• The compliance and elastic recoil of the aorta allows it to accommodate blood during systole and return to its original shape during diastole
• Arteries have high elastic recoil, veins are compliance vessels
• The greatest change in pressure occurs at the arterioles
• During exercise, arterioles in the kidneys vasoconstrict while arterioles in skeletal muscles vasodilate, diverting blood flow
• Intrinsic (local) factor

  A chemical/substance produced within the vasculature that regulates blood pressure
• Intrinsic factors that cause vasodilation

  • Increased CO2
  • Increased metabolites
  • Increased nitric oxide
  • Decreased systemic O2
• Intrinsic factors that cause vasoconstriction

  • Decreased oxygen in the lungs
  • Decreased CO2
  • Increased endothelin
• Norepinephrine binds to β2 adrenergic receptors

  Increases arteriole radius, causing vasodilation
• Norepinephrine binds to α1 adrenergic receptors

  Decreases arteriole radius, causing vasoconstriction
• Baroreceptors

  Mechanoreceptors that detect changes in pressure, located in the aortic arch and carotid artery
• Neural (baroreceptors) and hormonal (RAAS) mechanisms

  Work together to maintain BP
• Baroreceptors

  Mechanoreceptors that detect changes in pressure, located within the aortic arch and carotid artery
• Baroreceptor reflex arc

  1. Stimulus: Change in blood pressure

  2. Receptor: Baroreceptors

  3. Afferent Pathway: Sensory neuron

  4. Integrating Center: Cardiovascular control center

  5. Efferent Pathway: Autonomic nervous system

  6. Effectors: Sympathetic and parasympathetic systems

  7. Response: Changes in heart rate, contractility, and vasoconstriction
• Orthostatic hypotension

  Decrease in blood pressure when changing position rapidly
• Intrinsic factors that can lead to precapillary vasodilation

  • Increased CO2
  • Decreased O2
• Capillaries have the highest total cross-section area, slowest blood flow velocity, and greatest drop in blood pressure
• Starling's forces

  Hydrostatic pressure (favors filtration), Oncotic pressure gradient (favors absorption)
• Edema arises when filtration far exceeds absorption
• Oncotic pressure

  Pressure exerted by proteins
• Respiratory pump

  Diaphragm contraction/relaxation creates pressure gradients that move blood toward the heart
• Factors that can impact venous return

  • Venous pressure gradients
  • Valves
  • Skeletal muscle pump
  • Respiratory pump
  • Venoconstriction
• Venous return is roughly the same as cardiac output