Module 1 Lecture 2

Question 1

Why is the cardiovascular system

important?

Answer 1

• 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

Question 2

What is the cardiac cycle?

Answer 2

The cardiac cycle is the period between one heartbeat

& the next

Question 3

In each cycle, what happens to the Atria and ventricles?

Answer 3

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

Question 4

What is an ECG?

Answer 4

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

Question 5

Label the eletrical events of the cardiac cycle!

Answer 5

–

Question 6

What occurs in the P wave?

Answer 6

atrial depolarization

Question 7

What is the QRS complex

Answer 7

ventricular depolarization

& atrial repolarization

Question 8

What occurs in the T wave?

Answer 8

ventricular repolarization

Question 9

What occurs in PR interval

Answer 9

AV node delay

Question 10

What occurs in the ST segement?

Answer 10

Entire ventricle is depolarized

Question 11

NOTE

Answer 11

Electrical events alwats precede contraction and relaxation

Question 12

What happens in normal sinus rhythm?

Answer 12

8 beats in 6 seconds = 80bpm

Question 13

What occurs in junctional rhythm

Answer 13

the SA node is non-functional, resulting in P waves being absent and AV node paces heart at 40-60bpm

Question 14

What occurs in a second degree heart block?

Answer 14

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

Question 15

What occurs in ventricular fibrillation?

Answer 15

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

Question 16

What are the mechanical phases of the cardiac cycle?

Answer 16

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)

Question 17

Label the diagram, pressure changes and valve closures/openings during a cardiac cycle

Answer 17

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)

Question 18

Define heart rate

Answer 18

HR) – number of times the heart beats (i.e. completes one cardiac
cycle of systole & diastole) in 1 minute

Question 19

Stroke volume (SV)?

Answer 19

Stroke volume (SV) - volume of blood pumped out by each ventricle with each
beat

Question 20

End diastolic volume (EDV)?

Answer 20

End diastolic volume (EDV) - volume of blood in ventricle when filling is
complete (‘preload’)

Question 21

End systolic volume (ESV)

Answer 21

End systolic volume (ESV) - volume of blood remaining in ventricle when
ejection is complete

Question 22

Cardiac output?

Answer 22

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

Question 23

Cardiac reserve?

Answer 23

• difference between resting and maximal CO (i.e. during

exercise CO ↑ 5-fold)

Question 24

CO diagram !!

Answer 24

–

Question 25

How is heart rate determined?

Answer 25

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

Question 26

How is SV determined?

Answer 26

Determined by:

• EDV (venous return)
• Contractility

Question 27

Regulation of SV by EDV?

Answer 27

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

Question 28

Regulation of SV by contractility?

Answer 28

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

Question 29

What does increased contractility mean?

Answer 29

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.