Section 3: The Cardiovascular System

Question 1

What are the 3 layers of the heart?

Answer 1

1) Outer epicardium
2) Middle myocardium (75% of hearts mass)
3) Inner endocardium

Question 2

What is the structure and function of the pericardium?

Answer 2

Loose-fitting bag of connective tissue which surrounds the heart and releases pericardial fluid reducing friction during contraction

Question 3

Why is the left ventricle thicker than the right?

Answer 3

Left ventricle must overcome a pressure of 120mmHg compared to 25 mmHg of the right ventricle

Question 4

What is the role of the AVN and SAN and how does the heart differ from typical skeletal muscle in how it conducts an electrical impulse?

Answer 4

• SAN initiates the electrical impulse
• AVN conducts the impulse through the atria to the ventricles
• Cells of the myocardium are all connected to one another and consequently contraction occurs as a single unit

Question 5

How is blood circled around the heart itself and what are the arteries involved?

Answer 5

Supply blood to left ventricle:
- Left main stem artery
- Left anterior descending artery 
- Circumflex artery 
Supplies blood to right ventricle:
- Right coronary artery 
Deoxygenated blood is collected in coronary sinus where it drains back into right atrium

Question 6

What are the three layers which make up arteries and veins?

Answer 6

Outer layer: Tunica adventitia
Middle layer: Tunica media
Inner layer: Tunica intima

Question 7

What is the function of endothelial cells?

Answer 7

• Lining prevents blood cells sticking (normally)
• Secretes agents to increase vasodilation and vasoconstriction
• Releases anti-clotting molecules and platelet inhibitors that reduce thrombosis
• Inhibition of smooth muscle cell proliferation and migration

Question 8

What is blood composed of?

Answer 8

Plasma (55%)
- 90% Water
- 7% plasma proteins 
- 3% Other
Formed elements (45%)
- >99% red blood cells 
- <1% White blood cells and platelets

Question 9

What is the ratio distribution of water and how is it transferred within the body?

Answer 9

• 2/3 within cells (intracellular)
• 1/3 outside cells between tissues and in blood plasma (extracellular)
• Blood moves down a pressure gradient (and it’s constituents such as glucose)
• Consequently, blood moves into cells at arterial end and back into the veins

Question 10

Outline the steps in systemic circulation including the valves involved

Answer 10

Left ventricle—> Aortic Valve—-> Aorta—->Vena Cava (S/I)—–> Right atrium—–> Tricuspid valve—–> Right ventricle—-> Pulmonary valve—-> Pulmonary artery—-> Pulmonary vein—–> Left atrium—–> Mitral valve—–> Left ventricle

Question 11

What are the factors contributing to venous return?

Answer 11

Skeletal muscle: Contraction producing squeezing aciton on veins
Valves: Prevent backflow and consequent pooling of blood in lower extremities
Inhalation: Increases pressure in abdomen and decreases in thoracic cavity creating a ‘suck’ type action

Question 12

Outline the Cardiac cycle

Answer 12

1) Ventricle contract causing aortic and pulmonary valves
2) Ventricles and atria both relaxed allowing atria to fill
3) Increase in pressure opens the atrioventricular valve
4) 80% of the blood passively flows into the ventricle and the remaining 20% occurs after contraction
5) Ventricular contraction then begins from the Apex of the heart upwards
6) Pressure builds within the ventricles causing tricuspid and mitral valves to shut
7) Pressure builds in the ventricles causing the pulmonary and aortic valves to open ejecting blood in the systemic circulation

Question 13

What are general guidelines for healthy heart rate/BP

Answer 13

Heart rate: 60-80 BPM

Blood pressure : 120/70

Question 14

Outline the impulse through the cardiac cycle

Answer 14

1) Electrical activity start in SAN
2) Delay of 0.1 seconds then results in atrial depolarisation
3) During the delay atria contract
4) Wave of electrical activity is conducted through bundle of HIS and Purkinje fibres
5) Following contraction the heart muscle cannot be stimulated until it has relaxed from it’s previous ‘all-or-none contraction’ a period referred to as the refractory periods

Question 15

What are the variables contributing to blood pressure?

Answer 15

BP = CO X TPR

• Cardiac output: Amount of blood pumped by the ventricles each minute (CO = HR X SV)
• Total peripheral resistance: Sum of all the vascular resistance within systemic circulation

Question 16

How is heart rate controlled?

Answer 16

• Neurons innervate the sinoatrial node
  1) Parasympathetic system - acts on the heart through vagus nerve - secretes acetylcholine
  2) Sympathetic system - noradrenaline (sympathetic) adrenaline (adrenal medulla) - acts on beta 1 receptors increasing HR

Question 17

What are the mechanisms responsible for increasing stroke volume?

Answer 17

• End diastolic volume: Increased in EDV increase distension of arterial wall causing more forceful contraction
• Increased sympathetic activity results in more forceful contraction increase ejection fraction (66% in a healthy adult)

Question 18

Summarise the typical ‘flight or fight response’ contributing to the redistribution of blood flow

Answer 18

• Noradrenaline and adrenaline act on Beta-1 adrenergic receptors in the heart increasing HR and contractility (SV) and cardiac output (CO=HR X SV)
• Noradrenaline and adrenaline act on Beta-2 adrenergic receptors in the arterioles of the skeletal muscle increasing vasodilation and consequent blood flow
• Noradrenaline and adrenaline act on alpha-adrenergic receptors in arterioles of less active tissue thereby diverting blood flow away

Question 19

How is blood pressure detected/changed and in what capacity can this contribute to preventing dizziness during postural hypotension ?

Answer 19

• Baroreceptors in the carotid sinus and aortic arch - BP fall - HR increase and Vasoconstriction occurs (BP = CO X TPR)
• Postural hypotension: Patients stands - 0.5-0.7 liters of blood into the lower vein - reduced venous return and therefore preload - baroreceptor reflexes decreases this
• This effect takes a few seconds so initial dizziness will occur

Question 20

Outline the flow of blood through the coronary arteries

Answer 20

1) Open cusps of aortic valve block blood flow into ventricles during ventricular contraction
2) Ventricular contraction constrict coronary arteries preventing blood flow
3) Diastole results in aortic valve closing but ventricle pressure remaining high leads to flow of blood into coronary arteries (80% during diastole)

Question 21

What percentage of blood flow is directed to coronary flow and does this change during exercise?

Answer 21

• 4-5%: This value does not change during exercise

Question 22

How does myocardial tissue specialize in its metabolism of energy?

Answer 22

• More mitochondria then any other tissues in the body relying exclusively on oxidative phosphorylation
• Glucose, fatty acids, and lactate formed by skeletal muscles are used by myocardial cells regenerate ATP

Question 23

What do coronary arteries dilate in response to and why is this necessary?

Answer 23

1) Increased metabolic activity
2) Release of nitric oxide from the endothelium
3) Increased sympathetic activity
- O2 Utilisation is already at 70% (not 25%) meaning increases O2 utilization relies on coronary blood flow

Question 24

What are the determinants of myocardial work?

Answer 24

Force generated during contraction:
- Preload - Tnesion exerted on the heart wall
- Afterload - The resistance from systemic circulation which has to be overcome
Heart rate
Myocardial mass
Rate pressure product = HR x SBP (RPP = HR x SBP)

Question 25

Name the four valves of the heart and from which areas they prevent back flow

Answer 25

(Tricuspids)
Mirtal: Left Atria and Left Ventricle
Tricuspid: Right atria and Right ventricle
Pulmonary: Right ventricle and Pulmonary artery
Aortic: Left ventricle and aorta