Cardiovascular Physiology

Question 1

Characteristics of cardiac muscle tissue

Answer 1

Made up of cardiac cells –> individual cells but work as one unit

Has intercalated discs: connects ends of muscle cells to each other

Question 2

What is found in the intercalated discs?

Answer 2

Desmosomes: type of cell junction that holds fibers together

Gap junctions: allow action potentials to conduct from 1 muscle fibre to its neighbour

Question 3

Importance of the SA node

Answer 3

Natural pacemaker of the heart –> initiates AP 100/min

Nerve impulses from ANS + hormones can modify the speed

APs from SA node go throughout both atria via gap junctions + excite contractile fibers

Question 4

Importance of the AV node

Answer 4

Located in the interatrial septum

AP slows down here (has smaller fibers + less gap junctions)

Question 5

Why is it important that the AP slows down at the AV node?

Answer 5

The delay allows for the atria to empty their blood into the ventricles

Question 6

What happens if the SA node gets damaged?

Answer 6

AV node picks up pace making tasks (at a slower rate)

Question 7

Purpose of AV bundle

Answer 7

So AP can conduct from atria –> ventricles

Question 8

Where are the R + L bundle branches found?

Answer 8

They extend down through the interventricular septum toward the heart apex

Question 9

Purpose of purkinje fibers

Answer 9

APs rapidly conduct from heart apex –> ventricular myocardium

Question 10

How to inotropes work?

Answer 10

A substance that alters the movement of calcium through its channels (affects strength of heart contractions)

Positive inotrope = more calcium (epinephrine)

Negative inotrope = less calcium

Question 11

What does the P wave represent?

Answer 11

Small wave –> atrial depolarization

Question 12

What does the QRS complex represent?

Answer 12

Depolarization of the ventricles (repolarization of the atria also occur; masked)

Question 13

What does the T wave represent?

Answer 13

Ventricular repolarization

Question 14

De/repolarization and heart muscle

Answer 14

Depolarization = contraction of heart muscle

Repolarization = relaxation of heart muscle

Question 15

S1 heart sound

Answer 15

AV valve closure

Question 16

S2 heart sound

Answer 16

SL valve closure

Question 17

S3 heart sound

Answer 17

Ventricular filling

Question 18

S4 heart sound

Answer 18

Atrial systole

Question 19

What are isovolumetric contractions?

Answer 19

Ventricles have started to contract but no change in volume

Question 20

What is isovolumetric contraction?

Answer 20

When all 4 valves are closed

Question 21

What is stroke volume?

Answer 21

Volume of blood ejected from LV/RV into aorta/PT

SV = EDV - ESV

Question 22

Which ventricle expels more volume?

Answer 22

They expel the same BUT L side has to travel farther –> more force

Question 23

What is cardiac output?

Answer 23

Volume of blood ejected from the LV/RV into aorta/PT

CO = HR x SV

Question 24

What is cardiac reserve?

Answer 24

Cardiac output (max) - CO (at rest)

In healthy youth, max is 4x the rest output

Question 25

Factors that regulate stroke volume (x3)

Answer 25

1. Preload = degree of stretch on heart before contraction 2. Contractility = force of contraction on individual muscle fibers 3. Afterload = pressure ventricles must overcome before SL valves open

Question 26

Preload

Answer 26

More blood in ventricles = larger EDV = more stretch = larger output Muscle stretch is proportionate to EDV

Question 27

Changes to preload

Answer 27

Heart rate: slow HR = longer ventricle diastole = more filled = more stretch Venous return = more blood going into heart = more stretch

Question 28

Contractility

Answer 28

Intrinsic ability of myocardium to contact Strength of contraction at any given time

Question 29

What changes heart contractility?

Answer 29

Calcium! Positive inotropes = epinephrine Negative inotropes = hypoxia, acidosis

Question 30

Afterload

Answer 30

Pressure ventricles must overcome before SL valves open

Question 31

Factors that affect after load (x2)

Answer 31

Blood pressure = increased = increased afterload Vessel structure = narrow = increased afterload

Question 32

What does an increased afterload mean?

Answer 32

Decreased in SV and more blood will remain in ventricles

Question 33

Factors that regulate heart rate (x4)

Answer 33

ANS = sympathetic = increase Chemical regulation = epinephrine & calcium = increase Age = young age = increase Increased body temp = increase

Question 34

Nervous system control of the heart

Answer 34

CV center on medulla oblongata Affects rates of spontaneous depolarization in SA and AV nodes Sympathetic stimulation can increase contractility and stroke volume