01/20/16 Flashcards
1
Q
Background of Cardiac Output
A
- Heart pumps blood around the body
- Left heart pumps oxygenated blood
- Right heart pumps deoxygenated blood
2
Q
Anatomy of the heart
A
3
Q
Anatomy of the heart; cartoon illustration
A
4
Q
The Cardiac Cycle
A
- Molecular/electrical/physiologicaleventsthat occur from the start of one heartbeat to the start of the next heartbeat
- Consists of 2 periods:
-
Diastole:
- relaxation,heart fills with blood
- BP~80mmHg
-
Systole:
- contraction, heart ejects blood
- BP~120mmHg
5
Q
Diastole
A
- Venous return fills atria
- AV valve opens
- ~75% blood flows directly into ventricles
-
Atrial priming
- pumps remaining 25% blood into ventricles
- AV valve closes
6
Q
Systole
A
- Ventricles fill with blood
- Increase in pressure
- Isometric contraction
- Aortic/pulmonary valves open
- Blood ejected
- 70% fast, 30% slow
- Ventricles relax
- Aortic/pulmonary valves close
7
Q
What is cardiac output?
A
- Cardiac output=Stroke volume * Heart Rate
- CO=SV*HR
- Stroke Volume
- Blood volume ejected by ventricles/beat
- Heart Rate
- # heart beats/min
8
Q
Calculating Cardiac Output
A
- Cardiac output (mL/min)=Stroke volume (mL/beat)*Heart rate (beats/min)
- Average resting heart rate:
- ~70 beats/min
- Average resting stroke volume:
- ~70 mL/beat
- Cardiact output=70*70=4900 mL/min
- or ~5 L/min
- During exercise, CO increases 7 fold
9
Q
Preload and Afterload
A
- Determinants of stroke volume
- Preload
- Tension of ventricular muscle before contraction
- Determined by left ventricular end diastolic volume/pressure (LVED/LVEP)
- Afterload
- Pressure against which ventricles pump blood
- Determined by total peripheral resistance
10
Q
Excitiation-Contraction Coupling
A
- Generation of electrical impulses:
- Sinus node
- AV node
- Propogation of impulses:
- Internodal pathways
- Bachmann’s bundle
- AV node, Bundle of His
- Purkinje fibers
11
Q
Cardiac Electrophysiology
A
12
Q
Ion Channels Confirmational States
A
- Resting
- Closed, can be opened
- Activated
- Open, ions flowing
- Inactivated
- Closed, can’t be opened
13
Q
Generation of Cardiac Rhythmicity
A
- Sinus (sinoatrial) node
- “Pacemaker region”
- Small specialized muscle
- Located in right atrium
- Controls heart rate
- Origin of spontaneous action potential
14
Q
Spontaneous Action Potentials
A
- HCN channels
- hyperpolarization cyclic nucleotide gated
- Phase 0:
- Ca2+ enters: ICa-L
- Phase 3:
- K+ exits: IKS/IKR
- Phase 4:
- Na+ enters: If
- Ca2+ enters: ICa-T/ICa-L
- Key:
- L: long
- S: short
- T: transient
- F: funny
- KS: slow delayed rectifier
- KR: rapid delayed rectifier
15
Q
Transmission of Cardiac Current
A
- Internodal pathways/Bachmann’s bundle
- Spread current through atria
- AV node/Bundle of His
- Electrically separate atria and ventricles
- Delays current transmission to ventricles
- Has spontaneous activity
- Ectopic pacemaker
- Purkinje Fibers
- Spreads currents through ventricles
16
Q
Transmission of Cardiac Impulses
A
17
Q
Non-spontaneous action potential
“cardiac action potential”
A
- Phase 0
- Na+ enters: INa
- Phase 1
- K+/Cl- exits: Ito1/Ito2
- Phase 2
- K+ exits: IKs
- Ca2+ enters: ICa-L
- Phase 3
- K+ exits: IKs/IKR/IK1
- Phase 4
- Resting membrane potential
18
Q
Cardiomyocyte Contraction
A
- Increase [Ca2+]i through L-type Ca2+ channels
- Ca2+ spread through transverse T-tubules
- Ca2+ opens rynodine receptors on sarcoplasmic reticulum
- Calcium induced calcium release
- Ca2+ binds troponin-C
- Releases tropomyosin from actin
- Increases actin-myosin cross-bridging
19
Q
Channels and Proteins in Cardiomyocyte Contraction: Illustration
A
20
Q
Troponin and Myosin Chains in Cardiomyocyte Contraction: Illustration
A
21
Q
Thick/Thin Filament in Cardiomyocyte Contraction: Illustration
A
22
Q
Factors affecting Cardiac Output
A
- Frank-Starling Mechanism
- Autonomics
- Sympathetic nervous system
- Parasympathetic nervous system
- Renin-Angiotensin-Aldosterone System
23
Q
Frank-Starling Mechanism
A
- “Within physiological limits, the heart pumps all the blood that it receives without allowing excessing damming of blood in the veins”
- Increase in venous return
- Cardiomyocyte contractility
- Increase stroke volume
24
Q
Autonomic Regulation of Cardiac Output
A
- Parasympathetic Nervous System
- Decrease HR and SV
- Dominant at rest
- Sympathetic Nervous System
- Increase HR and SV
- Dominant during exercise/stress
25
Autonomic Nervous System: Innervation Illustration
26
Parasympathetic Effects
* Vagal nerves release acetylcholine
* SA and AV nodes
* Acetylcholine stimulates M2-muscarinic receptors
* Increase K+ channel opening
* Decrease sinoatrial node rhythm
* Decrease AV node transmission
27
Sympathetic Effects
* Sympathetic nerves release norepinephrine throughout heart
* Stimulates Beta-1-adrenergic receptors
* Increase Ca/Na channel opening
* Increase SA node rhythm
* Increase AV node transmission
* Increase force of atrial/ventricular contraction
28
Autonomic nervous system regulation of spontaneous action potential
* PSNS→rest
* Decrease AP frequency
* Increase phase 4 duration
* Decrease HR→Decrease CO
* SNS→excercise, stress
* Increase AP frequency
* Decrease phase 4 duration
* Increase HR→Increase CO
29
Baroreceptor Reflex
* Rapid, fine control of CVS
* Sensory baroreceptors
* Carotid sinus/aortic arch
* Detect BP changes
* Increase BP
* Increase PSNS activity
* Decrease CO
* Decrease BP
* Increase NS activity
* Increase CO
30
Renin-Angiotensin-Aldosterone System
* Decrease BP in kidney nephron macula densa
* Renin secreted into circulation
* Renin→angiotensin to angiotensin I
* Angiotensin converting enzyme (ACE)
* angiotensin-I to angiotensin-II
* Increase aldosterone
* Increase plasma volume
* Increase BP
* Increase CO
