Mammalian Heart: Structure & Function (Edexcel A (SNAB) A Level Biology)

• Circulatory systems are systems which transport fluids containing materials needed by the organism, as well as waste materials that need to be removed
• Circulatory systems are described as being either open or closed
  • In a closed circulatory system blood is pumped around the body and is always contained within a network of blood vessels
  • In an open circulatory system the blood, or blood equivalent, is inside the body cavity and bathes the organs
• Circulatory systems can also be either double or single
  • Double circulatory systems have two loops; one to the lungs and one to the body
  • Single circulatory systems have one loop that includes the lungs and the body
• Humans have a closed, double circulatory system; in one complete circuit of the body blood passes through the heart twice
  • The right side of the heart pumps blood deoxygenated blood to the lungs for gas exchange; this is the pulmonary circulatory system
  • Blood then returns to the left side of the heart, so that oxygenated blood can be pumped at high pressure around the body; this is the systemic circulatory system

Heart structure

• The human heart has a mass of around 300 g and is roughly the size of a closed fist
• The heart is a hollow, muscular organ located in the chest cavity
• It is protected in the chest cavity by the pericardium, a tough and fibrous sac
• The heart is divided into four chambers
  • The two top chambers are atria
  • The bottom two chambers are ventricles
• The left and right sides of the heart are separated by a wall of muscular tissue called the septum
  • The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart

The human heart is adapted for pumping blood around the body

The heart is a muscular organ; the muscle itself is supplied with blood by the coronary arteries, enabling it to pump blood via a series of major blood vessels

Valves in the heart

• Valves are important for keeping blood flowing forward in the right direction and for maintaining the correct pressure in the chambers of the heart
  • The right atrium and right ventricle are separated by an atrioventricular (AV) valve known as the tricuspid valve
    • Remember; the right side of the heart has a tricuspid valve
  • The left atrium and left ventricle are separated by another AV known as the bicuspid valve
  • The right ventricle and the pulmonary artery are separated by a semilunar (SL) valve known as the pulmonary valve
  • The left ventricle and aorta are separated by another SL valve known as the aortic valve
• Valves in the heart
  • Open when the pressure of blood behind them is greater than the pressure in front of them
  • Close when the pressure of blood in front of them is greater than the pressure behind them
• The valves are attached to the heart walls by valve tendons, or cords; these prevent the valves from flipping inside out under high pressure

Adaptations of the Structures of the Heart Table

Blood vessels and the heart

• There are two blood vessels bringing blood into the heart; the vena cava and pulmonary vein
  • The vena cava brings blood from the body
  • The pulmonary vein brings blood from the lungs
• There are two blood vessels taking blood away from the heart; the pulmonary artery and aorta
  • The pulmonary artery takes blood to the lungs
  • The aorta takes blood to the body
• The muscle of the heart itself is supplied with blood by a series of blood vessels known as the coronary arteries
  • The coronary arteries can be seen running across the surface of the heart