Lecture 6 Cardiovascular System

Question 1

What are the main functions of the circulatory system?

Answer 1

1. Transport and distribute essential substances to the tissues
2. Remove metabolic byproducts
3. Adjustment of oxygen and nutrient supply in different physiologic states
4. Regulation of body temperature
5. ‘Humoral’ communication (helps fight infection)

Question 2

What are the two circuits within the cardiovascular system?

Answer 2

Pulmonary Circuit:
Right ventricle pumps into the pulmonary trunk, blood then travels to pulmonary arteries (branches) then to the lungs. Pulmonary veins return O2 rich blood to the left atrium
Systemic Circuit:
Left ventricle pumps blood into the Aorta carrying oxygen rich blood which branches with an artery to each organ. Arteries divide into arterioles and capillaries which lead to venules.

Question 3

What muscle type is the heart mainly composed of?

Answer 3

Myocardium (muscle cells)

Question 4

What are the valves within the heart?

Answer 4

Bicuspid (mitral) valve
Tricuspid valve
Pulmonary valve
Aortic valve

Question 5

What are the semilunar valves?

Answer 5

Pulmonary valve
Aortic Valve
- Found at ventricular exit points to prevent backflow into the ventricles

Question 6

What are the atrioventricular valves?

Answer 6

Tricuspid valve (3 leaflets)
Bicuspid (mitral) valve (2 leaflets)
- Valves reinforced by chordae tendinae

Question 7

How is deoxygenated blood brought into the heart?

Answer 7

The inferior and superior vena cava
blood enters into the right atrium

Question 8

How is deoxygenated blood sent to the lungs

Answer 8

• Pumped out of the right ventricle
• past the pulmonary semilunar valve
• through the left pulmonary arteries

Question 9

Which ventricle is more muscular and why?

Answer 9

• The left ventricle
• has to pump a much higher pressure to get blood to the rest of the body (120 mm Hg)

Question 10

What is the purpose of the coronary artery circulation?

Answer 10

Feeds heart important oxygen and nutrients

Question 11

How are myocardial muscle cells attached to each other

Answer 11

intercalated disks which contain desmosomes which allow for force transfer and gap junctions which allow for electrical connectivity

Question 12

What is a syncytial network?

Answer 12

Branched myocyte connections (1 cell may be connected to several - amplification)

Question 13

How much space do mitochondria take up in cardiac muscle cells?

Answer 13

They take up 1/3 of the cell volume and help feed oxygen to the tissue

Question 14

Describe the process of excitation-contraction coupling

Answer 14

1. AP enters from adjacent cell
2. Voltage-gated Ca2+ channels open
3. Ca2+ induces Ca2+ release through ryanodine receptor-channels
4. Local release causes Ca2+ spark
5. Summed Ca2+ sparks create a Ca2+ signal
6. Ca2+ ions bind to troponin to initiate contraction
7. Relaxation occurs when Ca2+ unbinds from troponin
8. Ca2+ is pumped back into the sarcoplasmic reticulum for storage
9. Ca2+ is exchanged with Na+ by the NCX antiporter
10. Na+ gradient maintained by Na+ K+ pump

Question 15

How does the acto-myosin interaction work?

Answer 15

• At rest, TnT prevents myosin head groups from cross-bridging with actin
• When active, Ca2+ acts as a switch activating Troponin C, flipping tropomyosin out of the way, allowing for cross-bridging with actin

Question 16

Describe the phases of an AP

Answer 16

Upstroke phase:
- Na+ permeability increases as Na+ channels open
- causes depolarization towards Na+ equilibrium
Downstroke phase: Na+
- Sodium channels inactivate –> decreasing permeability
- Potassium channels open causing hyperpolarization

Question 17

What is the difference between a cardiac AP and a neural and skeletal muscle AP?

Answer 17

Main difference is duration
- Neural AP = 1ms
- Skeletal muscle cell =2-5 ms
- Cardiac action potential ranges from 200-400 ms

Question 18

Steps in a myocardial AP

Answer 18

1. Upstroke phase causes opening of Na+ channels –> depolarization
2. Na+ channels inactivate, K+ channels open for a brief moment
3. K+ channels close and Ca2+ channels open causing a plateau phases where membrane potential doesn’t change
4. K+ channels reopen causing repolarization back to resting potential which is around -90 mV and Ca2+ channels close

Question 19

How long is the refractory period in a cardiac cell?

Answer 19

• Refractory period lasts almost as long as the entire muscle twitch
• ensures that tetanus state cannot occur which keeps a cyclical activation