Lecture 3: CV Physiology

Question 1

The myocardium comprises ____ of the heart and is responsible for _____ action. It is a _____, involuntary muscle. The heart ‘wrings’ blood out of the _______.

Answer 1

95%, pumping, striated, ventricles

Question 1

What are desmosomes?

Answer 1

Intercellular junctions that bind cells together in tissues under mechanical stress, such as the heart.

Question 2

What do myocytes form? Intercalated discs contain what?

Answer 2

A functional syncytium (single cell mass containing several nuclei, formed by fusion of cells). Intercalated discs contain desmosomes, gap junction.

Question 3

Name the 5 structures that are responsible for cardiac conduction and their general location.

Answer 3

1. sinoatrial node (RA)
2. atrioventricular node (RA)
3. atrioventricular bundle (between RA/LA)
4. right and left bundle branches (between RV/LV)
5. purkinje fibers (below RV/LV)

Question 4

What are inotropes? How would a positive inotrope act?

Answer 4

Inotropes are substances that change the strength of heart contractions by altering the movement of Ca2+ through the channels. Positive = increasing contraction by enhancing Ca2+ influx.

Question 5

Describe a refractory period in a cardiac sense.

Answer 5

The time interval during which a second cardiac action potential cannot be triggered.

Question 6

Describe an EKG.

Answer 6

Composite record of action potentials produced by all the heart muscle fibers.

Question 7

Name the 6 steps of ECG waves.

Answer 7

1. atrial dep.
2. atrial sys. (contraction)
3. vent. dep.
4. vent sys. (contraction)
5. rep of vent.
6. vent. diastole (relaxation)

Question 8

After P wave forms, _____ contract. After QRS complex appears, _____ contracts and continues throughout the S-T segment. After T wave begins, _____ relax.

Answer 8

Atria, ventricles, ventricles

Question 9

What is stroke volume? Formula and meaning?

Answer 9

Volume of blood ejected from LV/RV into the aorta/PT per heartbeat.
SV = EDV - ESV.
SV = ml/beat. EDV = end diastolic volume. ESV = end systolic volume.

Question 10

Describe cardiac output and its formula.

Answer 10

Volume of blood ejected from LF/RV into aorta/PT each minute.
CO = HR * SV

Question 11

What is the formula for cardiac reserve?

Answer 11

Cardiac output (max) - cardiac output (rest)

Question 12

What are the three factors that regulate stroke volume?

Answer 12

Preload - degree of stretch on heart before contraction.
Contractility - forcefulness of contraction on ind. vent. muscle fibers
Afterload - pressure vents must overcome before semilunar valves open.

Question 13

What are the four factors that regulate HR?

Answer 13

1. autonomic NS
2. hormones
3. age
4. increased body temp