Module 1 Lecture 2 Flashcards
Why is the cardiovascular system
important?
• Transports O2 & nutrients to tissues
• Removes waste products (e.g. CO2) from the
body
• Transports hormones around the body
• Helps maintain body temperature by shifting
heat around the body
What is the cardiac cycle?
The cardiac cycle is the period between one heartbeat
& the next
In each cycle, what happens to the Atria and ventricles?
In each cycle, the atria & ventricles undergo separate
phases of systole (contraction & emptying) and diastole
(relaxation & filling) in response to electrical activity
Recall that the atrioventricular (AV; tricuspid & mitral)
and semilunar valves (aortic and pulmonary) ensure
forward blood flow & prevent backwards flow
What is an ECG?
Electrical currents generated & transmitted throughout the heart spread throughout the body -> these can be measured by electrocardiography • An electrocardiograph (ECG) provides a graphical presentation • An ECG is the sum of all action potentials in the heart at a given time – not a single action potential
Label the eletrical events of the cardiac cycle!
–
What occurs in the P wave?
atrial depolarization
What is the QRS complex
ventricular depolarization
& atrial repolarization
What occurs in the T wave?
ventricular repolarization
What occurs in PR interval
AV node delay
What occurs in the ST segement?
Entire ventricle is depolarized
NOTE
Electrical events alwats precede contraction and relaxation
What happens in normal sinus rhythm?
8 beats in 6 seconds = 80bpm
What occurs in junctional rhythm
the SA node is non-functional, resulting in P waves being absent and AV node paces heart at 40-60bpm
What occurs in a second degree heart block?
The AV nodes fails to conduct some SA node impulses, resulting in more P waves than QRS waves, usually 2 P waves for each QRS wave
What occurs in ventricular fibrillation?
Electrical activity is disorganised, AP occur randomly throughout the ventricles, results in chaotic, grossly abnormal ECG deflections, seen in acute attacks and after electric shock
What are the mechanical phases of the cardiac cycle?
P-Q Interval: atria contract –> R-S interval: isovolumetric contraction phase (valves closed) –> S-T: ventricles contract and eject, atria relax –>Post T wave: ventricles relax (isovolumetric relaxation phase)
Label the diagram, pressure changes and valve closures/openings during a cardiac cycle
Valves open when pressure is higher in the first compartment (direction of blood flow) andValves close when pressure is higher in the next compartment (direction of blood flow)
Define heart rate
HR) – number of times the heart beats (i.e. completes one cardiac
cycle of systole & diastole) in 1 minute
Stroke volume (SV)?
Stroke volume (SV) - volume of blood pumped out by each ventricle with each beat
End diastolic volume (EDV)?
End diastolic volume (EDV) - volume of blood in ventricle when filling is
complete (‘preload’)
End systolic volume (ESV)
End systolic volume (ESV) - volume of blood remaining in ventricle when
ejection is complete
Cardiac output?
Cardiac output (CO) - amount of blood pumped out by each ventricle in 1
minute
CO (ml/min) = HR (beats/min) X SV (ml/beat)
average CO is 5L/min
Cardiac reserve?
- difference between resting and maximal CO (i.e. during
exercise CO ↑ 5-fold)
CO diagram !!
–
How is heart rate determined?
Determined by:
• Autonomic influences on the SA node:
– Sympathetic stimulation ↑ HR
– Parasympathetic stimulation ↓ HR
• Other factors: hormone adrenalin, thyroxine (T4), blood
ions (e.g. Ca2+, K+), age, body temperature
How is SV determined?
Determined by:
- EDV (venous return)
- Contractility
Regulation of SV by EDV?
Venous return affects stretch of cardiac muscle cells
(called preload). The relationship between preload & SV is
called the Frank-Starling Law
↑ venous return/EDV achieved by:
- Sympathetic stimulation squeezing veins
- Skeletal muscle & respiratory pumps
- More filling time due to ↓ HR
Regulation of SV by contractility?
Contractility is the contractile strength at any given muscle
length. ↑ cytoplasmic [Ca2+] = ↑ cross bridge cycling à
myocardium generates more force
↑ contractility achieved by:
• Sympathetic stimulation (adrenalin & noradrenalin) via
cyclic AMP 2nd messenger system
• Other factors: hormone adrenalin, thyroxine (T4),
glucagon, acidosis, high blood Ca2+, certain drugs
What does increased contractility mean?
Increased contractility (most likely due to sympathetic stimulation) shifts Frank-Starling Law curve to the left, cardiac muscles does not normally operate withing the descending limb of the length tension curve.
