Lecture 3.2: The Heart as a Pump Flashcards
What is Negative Chronotropy?
A decreased rate of contraction
What is Negative Inotropy
Decreased force of contraction
What are Chronotropic Drugs?
• Drugs that may change the heart rate & rhythm
• Affect the electrical conduction system of the heart and the
nerves that influence it
• Such as by changing the rhythm produced by the sinoatrial node
What is the structure of cardiac muscle cells (myocytes)? (7)
• Striated (less well organised than skeletal muscle cells)
• Small (diameter 20μm, length 100μm)
• Branched
• Single Nucleus (generally)
• Coupled to other myocytes
• Branching+coupling = functional syncytium
• Intercalated Disks
What are Desmosomes? Why are they important?
They are intercellular junctions that provide strong adhesion between cells
What are Fascia Adherens? Why are they important?
• Ribbon like structures that help stabilise
tissue
• A broad intercellular junction in the
intercalated disk of cardiac muscle anchoring
actin filaments
What is the Mechanism of Heart Contraction (SA…etc)?
• Depolarisation of SA node spreads to atrial
myocytes
• Wave of depolarisation halted by fibrous
skeleton, insulates the atria from the ventricles
• Delay here allows atrial emptying
• Bridge across the fibrous skeleton, begins at
the AV node
• AP passes via Bundle of His into the right and
left bundle branches
• These deliver the AP to the Purkinje fibres
• Purkinje fibres deliver the AP to the contractile
myocytes of the ventricles
What is Wiggers Diagram?
Wiggers diagram is a graphical representation of the cardiac cycle = the alternate contraction and relaxation of the heart
What does the P wave represent?
Atrial Depolarisation
What does the QRS wave represent?
Ventricular Depolarisation
What does the T wave represent?
Ventricular Repolarisation
Systole vs Diastole
• Systole occurs when the heart contracts to
pump blood out (ventricular contraction)
• Diastole occurs when the heart relaxes after
contraction (atrial contraction)
What Valves open during Systole?
• Semilunar valves are open (aortic and
pulmonic)
• Atrioventricular valves are closed
What Valves open during Diastole?
• Atrioventricular are open
• Aka Mitral and Tricuspid Valves
Mitral Valve Open: Atrial vs Ventricular Pressure
(Ap > Vp)
Aortic Valve Closed: Aortic vs Ventricular Pressure
(Aop > Vp)
What is Diastasis?
Filling slows down
What is meant by End Diastolic Volume (EDV)? In ml?
• It is the amount of blood that is in the ventricles
before the heart contracts
• About 120 mL
Jugular veins openly communicate with RA therefore…?
… pressure changes in RA produce a visible JVP
Atria and JVP Waves: A-Wave
• Caused by atrial systole
• Reflux of blood – minimal since incoming blood
has inertia
Atria and JVP Waves: C-Wave
• Bulging of AV valves into atrium as they close • Jugular some distance from the AV valves,
therefore delay in seeing the wave
Atria and JVP Waves: X-Wave
• Rapid drop in atrial pressure, caused by atrial
relaxation
• Base moves towards apex resulting in blood
being sucked into atria
Atria and JVP Waves: V-Wave
• Increased atrial pressure as a consequence of
their filling
Atria and JVP Waves: Y-Wave
• AV valves open, blood leaves ventricle, rapid
drop in atrial pressure
