Cardiac Function 2 Flashcards
What is CO (or Q)?
- cardiac output
- volume of blood pumped out by each ventricle per minute
CO =
SV (stroke volume) x HR
Average CO =
~5 L/min at rest
Average blood volume in body =
~5.5 L
How is CO controlled?
- through regulation of HR and SV
- extrinsic and intrinsic regulation
What are extrinsic mechanisms? Give an example.
- from external
- neural and hormonal
What are intrinsic mechanisms?Give an example.
- from within
- autoregulation
How is HR determined?
by SA node firing frequency
SA node intrinsic firing rate = . This means that HR =
- 100/min
- no extrinsic control on heart; HR = 100
SA node is under control of ____ and ______.
- ANS
- hormones
What system dominates HR changes at rest?
- parasympathetic system
- HR = 75
What system dominates HR changes during excitement/exercise?
- sympathetic system
- HR increases
Describe how increased sympathetic activity leads to increased heart rate.
- increased sympathetic activity (nerves or epinephrine)
- targets SA node
- opens funny & Ca 2+ channels
- increase rate of AP firing
- increase heart rate
In looking at the effects of the autonomic nervous system on SA nodal cell potentials, the slope of the depolarization period to threshold is…
steep
In looking at the effects of the autonomic nervous system on SA nodal cell potentials, how does is slowly turn into parasympathetic?
- slope slowly decreases
- membrane potential slowly decreases
Describe how increased parasympathetic activity leads to decreased heart rate.
- increased parasympathetic activity
- targets SA node
- K+ channels open; Ca 2+ channels close
- decrease rate of AP firing and hyperpolarize cell
- decrease heart rate
How does epinephrine effect HR?
- same effect as sympathetic nervous system
- increases action potential frequency at SA node
- increases velocity of action potential conduction in muscle fibres
How do thyroid hormones, glucagon, and insulin have an effect on HR?
contraction
Activity of sympathetic neurons projecting to SA node does what to HR?
raises HR
Activity of parasympathetic neurons projecting to SA node does what to HR?
lowers HR
Levels of circulating epinephrine does what to HR?
raises HR
What are the 3 primary factors affecting stroke volume?
- ventricular contractility
- end-diastolic volume
- afterload
Describe the influence of ventricular contractility.
- more forceful contraction will expel more blood
- sympathetic control of ventricular contraction
Describe the sympathetic control of ventricular contraction.
- sympathetic innervation of muscle cells
- Norepinephrine → β1 adrenergic receptors → cAMP
