The Physiology of Cardiac Function Flashcards
What is the role of ATPase in Myosin?
Hydrolysis of ATP is necessary to allow actin / myosin cross-bridge formation
Describe the structure of Actin
A long filament of Globular actin, forming two helices. Between the two helices are rod-shaped proteins called Tropomyosin. Attatched to tropomyosin is the Troponin regulatory complex
What three units comprise the Troponin complex?
TnT
TnC
TnI
Briefly describe what occurs during Excitation-Contraction-Coupling
A process where an action potential triggers a myocyte to contract
Describe the structure of a Myosin molecule
A myosin molecule has a rod-like tail and two heads (ATPase). Hinge region between the head and tail
What is the functional unit of a cardiac myocyte?
Sarcomere
What are the two ways in which extracellular Ca2+ can enter a Cardiac myocyte?
- T tubules
- L-type Ca2+ channels
Describe “Calcium-induced-calcium-release”
Whereby extracellular calcium is able to activate calcium release from intracellular Ca2+ stores
Following muscular contraction, how is Ca2+ pumped out of the cardiac myocyte for relaxation (Lusitropy)
- Ca ATPase (SERCA)
- Na-Ca exchanger
- Phospholamban
Upon the arrival of an action potential, what type of Calcium ion channels open?
L-type Ca2+ channels
Cardiac glycosides inhibit which pump?
Na-K pump
The Na-Ca exchange transports how many Na and Ca’s?
3 Na in
1 Ca out
Define “dromotropy”?
Ionotropy (force) + Chronotropy (rate)
In the heart, what does the Vagus nerve ennervate?
AVN and SAN
Define “chronotropy”?
Heart rate
Sympathetic nerves act via which NT, which receptor, to induce what effect on the cardiomyocyte?
Sympathetic nerves act on Noradrenaline, which act on B1 and B2 adrenergic receptors, to INCREASE chrono/iono/dromo/lusitropy
Define “Ionotropy”
Muscular contraction force
Parasympathetic (Vagus) nerves act via which NT, which receptor, to induce what effect on the cardiomyocyte?
Parasympathetic nerves act on Acetylcholine, which act on M2 muscarinic receptors, to DECREASE chrono/iono/dromo/lusitropy
Describe the 3 phases of the SAN Action Potential
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Phase 4:
- Pacemaker Na2+ influx
- Ca2+ channels recover from inactivation
- Pumps restore ion gradients
Phase 0:
Ca2+ influx
Phase 3:
Ca2+ channels inactivate
K+ efflux delayed
Describe the 5 phases of the Ventricular Action Potential
40123(4)
Phase 4:
- Na+ and Ca+ channels recover from inactivation
- Pumps restore ion gradients
Phase 0:
- Na+ influx
Phase 1:
- Na+ channels inactivate
- Fast K+ efflux
Phase 2:
- Ca2+ influx
Phase 3:
- Ca2+ channels inactivate
Delayed K+ efflux
Describe the sequence for the Conductive Pathway through the Heart
SAN AVN Bundle of His Bundle branches Purkinje Fibres
What is ESV?
End Systolic Volume, volume of blood remaining if the ventricles at the end of a contraction = 65 mL
How long is the sub-stages for Atrial Systole, Ventricular Systole and Diastole?
Atrial Systole: 0.1 s
Ventricular Systole: 0.3 s
Diastole: 0.4 s
What is EDV?
End Diastolic Volume, maximum amount of blood in ventricles at the end of ventricular relaxation = 135 mL
Define “stroke volume”
Stroke volume (SV) is the volume of blood pumped from the left ventricle per beat
What is the equation for Cardiac Output (CO)?
CO = HR x SV
HR = Heart rate SV = Stroke Volume
How can you calculate Stroke Volume (SV)?
Stroke Volume = EDV - ESV`
What is the Frank-Starling relationship?
An increase in EDV causes stroke volume to increase
