Cardiovascular System Lecture 5 Flashcards
(34 cards)
What is Intrinsic HR?
the natural rate at which the SA node generates electrical impulses to initiate heartbeats in the absence of external influences or neural inputs.
- ~100 bpm
What is Cardiac Output (Q)?
The volume of blood pumped out of each ventricle per unit time (L/min)
How to calculate Cardiac Output?
Q= HR x SV
where HR = bpm
Stroke Volume
SV = EDV - ESV
What is Extrinsic HR?
Need other influences beyond SA node to get a faster or slower heart rate, particularly the sympathetic and parasympathetic nervous sytems
What is the Chronotropic effect?
Alters Heart Rate
What is Positive Chronotropic?
- Positive chronotropic – increase HR
- Sympathetic nervous system, calcium
What is Negative Chronotropic?
- Negative chronotropic – decrease HR
- Parasympathetic nervous system, sodium, potassium
What is a “Center”
A “center” is a cluster of neurons acting as a control area.
* Receives sensory input.
* Generates motor output (in this case alters HR)
Where is the Cardiovascular Center?
What are the 3 Centers that it is composed of?
Cardiovascular (CV) center:
* In medulla oblongata.
* Composed of 3 smaller centers:
* Cardioacceleratory center.
* Cardioinhibitory center.
* Vasomotor center.
What is the Sympathetic HR?
(7)
Cardioacceleratory center sends neural signal to heart.
* Releases norepinephrine (NE).
* Binds β1 receptors.
Cardioacceleratory center sends neural signal to adrenal gland (inner layer – adrenal medulla).
* Releases epinephrine into blood circulation.
* Travels to heart.
* Binds β1 receptors
β1 = beta1 receptors
What is Parasympathetic HR?
(3)
Cardioinhibitory center sends neural signal to heart.
* Releases acetylcholine (Ach).
* Binds M receptors.
M = muscarinic receptors
Stimulation of β1 Receptors on SA Node (5)
SA Node Response to β1 Receptors
* Pacemaker potential rises steeply.
* Reaches threshold quickly.
* More AP’s per unit time
* Increases heart rate (HR).
Occurs during “fight or flight” response.
Stimulation of M Receptors on SA Node (5)
SA Node Response to M Receptors
* Pacemaker potential rises shallower.
* Takes longer to reach threshold.
* Less AP’s per unit time
* Decreases heart rate (HR).
Occurs during Rest and Digest.
Stimulation of β1 Receptors in AV Node (4):
Alter length of AV Node Delay:
* Shortened time to get through the AV node.
* More action potentials (APs) transmitted per unit of time.
* Increases heart rate (HR).
Occurs during “fight or flight” response.
Stimulation of M Receptors (M2) in AV Node:
Alter Length of AV Node Delay:
* Prolonged time to get through the AV node.
* Fewer action potentials (APs) transmitted per unit of time.
* Decreases heart rate (HR).
Part of “rest and digest” response.
What is Intrinsic SV?
SA node pacemaker generated with no other influences.
* ~70 mL/beat
What is Extrinsic SV?
What are the 3 Primary Influences?
Need other influences beyond SA node to get lesser or greater stroke volume.
Primary influences:
* Preload.
* Contractility.
* Afterload.
What is “Preload”?
stretch on cardiac muscle fibers before systole
(by altering ventricular volume)
What is Frank–Starling’s law of heart?
ventricle contracts more forcefully during systole when filled to a greater volume during diastole.
- More forceful contraction produces a greater SV
Example:
EDV 135 mL to 205 mL = SV 70 mL to 105 mL
What is the Key to EDV?
Key to EDV is venous return (volume of blood returned from venous system back into heart).
* Controlled by venous pressure / ventricle filling time
What is Contractility?
cardiac muscle fibers contraction strength
(by altering something other than ventricular volume)
What is the Inotropic effect?
alters contraction strength
