Structure of the Heart

A. Chambers

1. Right Atrium:

   • Receives deoxygenated blood from:
     • Superior vena cava: From the upper body.
     • Inferior vena cava: From the lower body.
     • Coronary sinus: From the heart itself.

2. Right Ventricle:

   • Pumps deoxygenated blood to the lungs via the pulmonary artery for oxygenation.

3. Left Atrium:

   • Receives oxygen-rich blood from the lungs via the pulmonary veins.

4. Left Ventricle:

   • Pumps oxygenated blood to the body through the aorta.

B. Valves

1. Tricuspid Valve:

   • Between the right atrium and right ventricle; prevents backflow during ventricular contraction.

2. Pulmonary Valve:

   • Between the right ventricle and pulmonary artery; prevents backflow after blood is pumped to the lungs.

3. Mitral Valve (Bicuspid):

   • Between the left atrium and left ventricle; prevents backflow during ventricular contraction.

4. Aortic Valve:

   • Between the left ventricle and aorta; prevents backflow after blood is ejected to the body.

C. Blood Vessels Connected to the Heart

1. Vena Cava: Return deoxygenated blood to the right atrium.
2. Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
3. Pulmonary Veins: Transport oxygenated blood from the lungs to the left atrium.
4. Aorta: Delivers oxygenated blood from the left ventricle to the body.
5. Coronary Arteries: Supply oxygenated blood to the heart muscle.

Cardiac Cycle and Conduction System

A. Cardiac Cycle

1. Systole: Contraction phase; blood is ejected from the heart.
2. Diastole: Relaxation phase; the heart refills with blood.
   • Duration: ~0.8 seconds per cycle (~72 beats/min)
   • Normal beats per minute is 60-100

B. Conduction System

1. Sinoatrial (SA) Node:
   • Natural pacemaker; initiates heartbeat.
2. Atrioventricular (AV) Node:
   • Delays impulses from the atria to the ventricles, allowing for complete atrial contraction.
3. Bundle of His:
   • Transmits electrical signals down the interventricular septum.
4. Purkinje Fibres:
   • Spread signals through the ventricles, ensuring coordinated contraction.

Blood Vessels: Types and Roles

A. Arteries

• Carry oxygenated blood away from the heart (except pulmonary arteries).
• Structure: Thick, elastic walls to withstand high pressure.
• Types:
  1. Conducting Arteries: Large arteries like the aorta.
  2. Distributing Arteries: Deliver blood to specific organs.
  3. Arterioles: Control blood flow to capillary beds.

B. Veins

• Return deoxygenated blood to the heart (except pulmonary veins).
• Structure: Thinner walls and lower pressure compared to arteries.
• Valves: Prevent backflow, especially in the limbs.

C. Capillaries

• Microscopic vessels for nutrient, gas, and waste exchange.
• Structure: Single-cell-thick walls for efficient exchange.
• Function:
  • Gas Exchange: Oxygen diffuses into tissues; carbon dioxide diffuses out.
  • Nutrient Delivery and Waste Removal: Transport essential nutrients and remove cellular waste.

Systemic and Pulmonary Circulation

A. Pulmonary Circulation

• Pathway:
  • Deoxygenated blood from the right atrium → right ventricle → pulmonary artery → lungs (oxygenation) → pulmonary veins → left atrium.
• Purpose: Oxygenate blood and remove carbon dioxide.

B. Systemic Circulation

• Pathway:
  • Oxygenated blood from the left atrium → left ventricle → aorta → body tissues (gas and nutrient exchange) → deoxygenated blood returns via veins → vena cava → right atrium.
• Purpose: Deliver oxygen/nutrients and remove waste from body tissues.

Conclusion

The heart and circulatory system work together to sustain life by delivering oxygen and nutrients while removing waste. Understanding this system’s structure and function is vital for comprehending cardiovascular health.

References

1. StatPearls. (2021). Cardiovascular System Anatomy and Function. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK493197/

2. National Cancer Institute. (n.d.). Cardiovascular System. Retrieved from https://training.seer.cancer.gov/anatomy/cardiovascular/

3. Medscape. (2023). Overview of the Cardiovascular System. Retrieved from https://emedicine.medscape.com/article/1948510-overview?form=fpf

4. Cleveland Clinic. (n.d.). Heart: Anatomy and Function. Retrieved from https://my.clevelandclinic.org/health/body/21704-heart

5. Medical News Today. (n.d.). What to Know About the Cardiovascular System. Retrieved from https://www.medicalnewstoday.com/articles/cardiovascular-system#:~=What%20to%20know%20about%20the%20cardiovascular%20system&text=The%20cardiovascular%20system%20consists%20of,blood%20back%20to%20the%20lung