the heart

• the heart is a muscular organ that pumps blood around the body

  
• Blood flow through the heart

  1. Blood enters the heart through the atria

  2. Blood from two vena cavae enters the right atrium

  3. Blood from the pulmonary veins enters the left atrium

  4. The atria fill

  5. The ventricles fill
• Heart valves


  • Prevent blood from flowing back into the atria
• Aorta


  The body's main artery, blood leaves the heart through this from the left side
• Pulmonary artery


  Blood leaves the heart through this from the right side
• Circulatory system of humans

  • Double circulatory system
  • Heart pumps blood through two circuits
• Circuits in human circulatory system

  • Pulmonary circulation
  • Systemic circulation
• whats pulmonary circulation?


  The part of the circulatory system that involves the right side of the heart, the lungs, and the blood vessels that connect them together.
• what is systematic circulation?

  The part of the circulatory system that includes the left side of the heart, the rest of the body apart from the lungs, and the blood vessels that connect them together
• Systemic circulation


  1. Transports oxygen and nutrients to the body

  2. Transports carbon dioxide and other wastes away from cells
• Systemic circulation


  • Under high pressure
  • Has to deliver blood to the extremities of the body
• Pulmonary circulation


  • Under lower pressure
  • Blood is delivered to the lungs only, which are very close to the heart
  • In a healthy person, this lower pressure is optimum for the diffusion of gases
• Blood passes through the heart twice in one complete circulation of the body
• Heart contraction sequence


  1. Atria contract in unison

  2. Ventricles contract in unison (when atria are full)

  3. Part of blood delivered to body

  4. Remainder of blood transported to lungs

  5. Oxygen picked up from lungs
• This means that oxygen can be picked up from the lungs, while at the same time, blood is also being delivered to the body
• Ventricles pump blood out of the heart
• Atria receive blood into the heart
• the heart has four chambers - two atria (upper) and two ventricles (lower)