The Cardiovascular System: Heart Structure and Function

Question 1

Functions of the Heart

Answer 1

1. Generating blood pressure
2. Routing blood: separates pulmonary and systemic circulations
3. Ensuring one-way blood flow: valves
4. Coupling of peripheral and central blood
   circulations

Question 2

The Heart

Answer 2

~300g in a person

Question 3

Pericardium

Answer 3

Protective fluid filled sac that surrounds the heart

Question 4

The Heart Wall – 3 Layers

Answer 4

1. Endocardium
2. Myocardium
3. Epicardium

Question 5

Right Side of the Heart

Answer 5

Receives deoxygenated blood from the body (via veins).

Pumps it to the lungs through the pulmonary artery.

Main parts: Right atrium and right ventricle.

Function: Pulmonary circulation – gets oxygen from lungs.

Question 6

Left Side of the Heart

Answer 6

Receives oxygenated blood from the lungs (via pulmonary veins).

Pumps it to the entire body through the aorta.

Main parts: Left atrium and left ventricle.

Function: Systemic circulation – delivers oxygen to tissues

Question 7

Systemic Circuit

Answer 7

Path: Heart → Body → Heart

Function: Delivers oxygenated blood from the left side of the heart to the body and returns deoxygenated blood back to the heart

Main vessel: Aorta (out), vena cava (back in)

Question 8

Pulmonary Circuit

Answer 8

Path: Heart → Lungs → Heart

Function: Sends deoxygenated blood from the right side of the heart to the lungs to get oxygen, then returns oxygenated blood to the heart

Main vessels: Pulmonary arteries (to lungs), pulmonary veins (back to heart)

Question 9

The Electrocardiograph (ECG)

Answer 9

• Atrial contraction depolarisation = systole
• ventricular contraction = depolarisation systole
• ventricular relaxation = diastole

Question 10

Changes in Pressure During the Cardiac Cycle

Answer 10

Systole = contraction
Diastole = relaxation

Question 11

Events During the Cardiac Cycle

Answer 11

Systole:
1) Isovolumetric contraction period
2) Ejection period

Diastole:
3) Isovolumetric relaxation period
4) Passive ventricular filling
5) Active ventricular filling

Question 12

Baroreflex & the SA/AV Nodes (via Autonomic NS)

Answer 12

When Blood Pressure Rises:
- Baroreceptors (in carotid sinus/aortic arch) detect increase.
- ↑ Parasympathetic, ↓ Sympathetic.
- SA Node: Slows firing → ↓ heart rate.
- AV Node: Slows conduction → delayed ventricular contraction.
- Goal: Lower BP.

When Blood Pressure Falls:
- ↓ Baroreceptor firing.
- ↑ Sympathetic, ↓ Parasympathetic.
- SA Node: Fires faster → ↑ heart rate.
- AV Node: Faster conduction → quicker ventricular contraction.
- Goal: Raise BP.

Question 13

Measurement of Blood Pressure – Principle

Answer 13

Presssure = Flow x Resistance

Question 14

Pulse Pressure

Answer 14

• Superficial temporal artery
• Common carotid artery
• Facial artery
• Axillary artery
• Brachial artery
• Radial artery
• Femoral artery
• Politeal artery (behind knee)
• Dorsalis pedis artery
• Posterior tibialis artery

Question 15

Law Governing the Cardiovascular System:
Darcy’s Law of Flow

Answer 15

Flow = Conductance* x Pressure
CO = SVC x MAP
(Cardiac Output)
(Systemic Vascular Conductance*)
(Mean Arterial Pressure)

At rest:
5 L/min = 0.05 L/min/mmHg x 100 mmHg

Maximal aerobic exercise:
25 L/min = 0.17 L/min/mmHg x 150 mmHg

Question 16

Regulation of Heart
Function

Answer 16

Intrinsic regulation:
- Preload
- Afterload

Extrinsic regulation:
- Parasympathetic stimulation
- Sympathetic stimulation
- Hormonal control

Question 17

Hormonal Control

Answer 17

• Increased stimulation (medulla oblongata down the spinal cord)
• (Adrenal oblongata in the spinal cord)
• Epinephrine (adrenaline) and norepinephrine (noradrenaline)

Question 18

Oxygen Supply to Tissues

Answer 18

• Forearm O2 delivery (mL/min) = Brachial artery blood flow (mL/min) x arterial O2 content (mL/mL)
• Artery blood flow (mL/min) = V (mean) x artery cross-sectional area

Question 19

Summary

Answer 19

• The heart has 2 atria and 2 ventricles
• These chambers expel blood to the systemic and pulmonary circulations
• The heart own circulation happens through the coronary arteries and cardiac veins
• The contraction of the heart (systole) is mediated by action potentials generated in the SA node and conducted through the AV node, the left and right bundle branches and the Purkinje fibers
• The cardiac cycle involves 5 events where changes in intracardiac pressures
  and volumes occur
• The baroreceptors in the heart and carotid bodies control arterial blood pressure
• Darcy’s law of flow explains an important physical principle governing blood circulation
• The intrinsic and extrinsic factors regulating cardiac function are preload,
  afterload, parasympathetic and sympathetic stimulation & circulating hormones