3 - Cardiac Physiology

Question 1

Describe functions of the heart

Answer 1

• BP
• routing blood through systemic and pulmonary circulations
• regulating blood supply
• one way flow

Question 2

Describe structures of the heart

Answer 2

Pericardium

• fibrous: tough outer layer (anchor)
• serous: thin transparent inner layer
• parietal:
• visceral:

Heart Wall:

• epicardium
• myocardium
• endocardium

Question 3

Describe the conducting system of the heart

Answer 3

1) SA node: produces action potential
2) signal passes to AV (atrioventricular nodes) a delay of 120 milliseconds occurs - atria contracts and blood moves through ventricles
3) the signal splits down the atrioventricular septum and travels down the 2 sides of the heart (supplying Purkinje fibres).
4) contraction occurs

Question 4

Where are the action potentials of the CARDIAC MUSCLE transmitted?

Answer 4

Action Potentials are conducted from cell to cell.

Question 5

What is the rate of Action Potential propogation in the cardiac muscle

Answer 5

Slow = small diameter of fiber + gap junctions

Question 6

Where are the action potentials of the SKELETAL MUSCLE transmitted?

Answer 6

Action potentials are conducted along length of SINGLE fIber

Question 7

What is the rate of Action Potential propagation in the SKELETAL muscle

Answer 7

Skeletal Muscle is faster due to larger due to larger diameter fibers.

Question 8

Describe the SA node

Answer 8

SA node: Sinoatrial node is what originates the action potential in the right atrium.

Question 9

Describe the AV node

Answer 9

AV node: atrioventricular node is what holds the Action Potenital, passess it down the intraventricular septum to the Purkinje fibers.

Question 10

Define absolute and relative refractory periods

Answer 10

Absolute: Cardiac muscle cell is completely insensitive to further stimulation
Relative; cell exhibits reduced sensitivity to additional stimulation.

Question 11

What are the different waves

Answer 11

P Wave: Atria Depolarisation
QRS Complex: Ventricle Depolarisation and Atria Repokarisation
T Wave: Ventrcile Repolariasation

Question 12

What are the 5 events of the cardiac cycle?

Answer 12

1. Isovolumetric Conteraction (during the compltion of
   the QRS complex)
   
   2. Ventricular Systole: period of isometric contraction
   3. Ventricular Systole: period of ejection
   4. Ventricular Diastole: period of isometric relaxation
   5. Ventricular Diastole: passive ventyricular filling

Question 13

• Define the terms systole and diastole

Answer 13

Systole: Contraction
Diastole: Relaxation

Question 14

• Define mean arterial pressure (MAP)

Answer 14

Is the average blood pressure in the aorta

MAP = Cardiac Output (CO) x Peripheral Resistance

Question 15

What factors effecting MAP

Answer 15

• CO

- peripheral resistance: decreased blood pressure

Question 16

What is CO?

Answer 16

Cardiac Output: the amount of blood pumped by the heart per min (formula = SV x HR)

Question 17

What is SV?

Answer 17

Stroke Volume: Amount of blood pumped out by left ventricle per min (litres per min)

Question 18

What is PR?

Answer 18

Peripheral resistance: Resistance of the arteries to blood flow

Question 19

What is Intrinsic Regulation?

Answer 19

Intrinsic Regulation: Involves Neural Control.

* Parasympathetic Stimulation: supplied by vagus nerve, decreases HR, AcH is secreted and hyperpolarization of the heart. 
* Sympathetic Stimulation: Supplied by cardiac nerves. Innervate the SA and AV nodes, coronary vessels and the atrial and ventricular myocardium. Increases HR and force of contraction. Epinephrine and norepinephrine released. (effects > increase HR, incresaed cardiac output. Increased force of contractin causes a lower end systolic volume, heart empties to a greater extent. Limitations: heart has time to fill.

Question 20

What is Extrinsic Regulation?

Answer 20

Extrinsic Regulation:
> Hormonal control: involves hormonal control: epinephrine (adrenaline) and norepinephrine from the adrenal medulla. Occurs in response to increased physical activity, emotional excitement and stress.

Question 21

How does the heart maintain homeostasis?

Answer 21

• BP (controlled by baroreceptors)
• pH, CO2, O2 (receptors in hypothalamus)
• extracellular concentration (K+ conc. effects HR)
• body temp ( HR increases or decreases body temp)

Question 22

How is BP maintained?

Answer 22

Baroreceptors

Question 23

What are the effects of aging on the heart?

Answer 23

• Max HR decreases
• Arrhythmias are more common
• Hypertrophy of ventricles (thickening)