Understanding the Human Circulatory and Lymphatic Systems

The Internal Environment

• Refers to the fluids that surround the cells.
• Temperature and composition must be stable for the correct working of cells.
• This internal environment is maintained by the organ systems of the body.
• Interstitial fluid (plasma): Surrounds and bathes the cells.
• Blood and lymph: Collect and distribute substances for the cells (O2, nutrients) and remove waste.

The Circulatory System

• Carries nutrients and oxygen throughout the body and collects waste (blood): Blood Circulatory System.
• Returns excess interstitial fluid to the blood.
• Transports fat to the blood.
• Defends the immune system (lymph): Lymphatic System.

The Lymphatic System

• Lymph capillaries:
  • Thin vessels closed at one end.
  • Collect excess interstitial fluid.
• Lymphatic vessels:
  • Large vessels with valves that prevent lymph from flowing backward.

Blood Vessels

There are three types of blood vessels:

• Arteries:
  • Carry blood away from the heart.
  • Large near the heart.
  • Arterioles (small) farther from the heart.
• Veins:
  • Carry blood from organs to the heart.
  • Venules (thin) far from the heart.
  • Thick close to the heart.
  • Vein walls.
  • Valves prevent blood from flowing backward.
• Capillaries:
  • Connect arterioles and venules.
  • Tiny.
  • Capillary walls.

The Heart

• Muscular organ, fist-sized.
• Between the lungs, left of the sternum.
• Heart walls: Cardiac muscle (myocardium) that pumps blood.
  • Four chambers: Two atria at the top and two ventricles below.
  • A partition separates the right and left sides. Chambers on the same side are connected:
  • Tricuspid valve: Connects the right atrium and ventricle.
  • Mitral valve: Connects the left atrium and ventricle.
• Right atrium: Deoxygenated blood enters the right atrium through the superior and inferior vena cava and passes to the right ventricle.
• Right ventricle: Deoxygenated blood leaves the right ventricle and enters the lungs through the pulmonary artery. The pulmonary semilunar valve prevents blood from flowing backward.
• Oxygenated blood leaves the lungs through the pulmonary veins and enters the left atrium.
• Left ventricle: Oxygenated blood leaves the left ventricle through the aorta. The aortic semilunar valve prevents blood from flowing backward. Blood flows to all organs.
• The coronary arteries supply blood to the muscle tissue of the heart.