Circulatory Systems

• The heart has four chambers - two atria and two ventricles.
• diffusion is the net movement of molecules or ions from an area of high concentration to an area of low concentration
• the blood vessels are made up of arteries, veins and capillaries
• arteries carry oxygenated blood away from the heart
• veins carry deoxygenated blood towards the heart
• a mass transport system moves substances efficiently over long distances by mass flow
• a mass flow is the movements of fluids down a pressure or temperature gradient
• an open circulatory system is where blood flows freely through cavities since there are no vessels to conduct the blood - allowing substances to diffuse between the blood and cells
• open circulatory systems have high resistance due to the large distance between cells and the heart
• a closed circulatory system has a higher blood pressure than an open circulatory system
• a closed circulatory system in which the blood is enclosed within tubes - blood vessels (high blood pressure)
• a closed circulatory system is more efficient at delivering substances around the body
• a single circulatory system is when the blood passes through the heart once and then returns to the heart
• a double circulatory system is when the blood passes through the heart twice, and the blood passes through the lungs once
• in a double circulatory system,

  • the right ventricle pumps deoxygenated blood to the lungs to receive oxygen
  • oxygenated blood returns to the heart to be pumped a second time out to the rest of the body.
• advantages of a double circulatory system

  • blood can pass slowly through the region where gaseous exchange takes place
  • maximises the transfer of oxygen and co2
  • the organism can be very active thanks to the blood being pumped vigorously around the body
• In very small organisms, substances such as oxygen, carbon dioxide and digestive products move around the organism by diffusion. Diffusion in unicellular organisms is normally fast enough to meet the organisms energy requirements.
• Animals with closed circulatory systems are normally larger in size because a close circulatory system allows efficient transportation of oxygen and nutrients over longer distances than open circulatory systems. They are often more active than small organisms as blood is transported at high pressures at a rapid rate.
• The human circulatory system consists of two circuits; pulmonary circuit (right side) and systemic circuit (left side). The pulmonary circuit carries deoxygenated blood from the right ventricle to the lungs and back again to the left atrium via the pulmonary veins. The systemic circuit carries oxygenated blood from the left ventricle to all parts of the body except the lungs and back to the right atrium via the superior vena cava and inferior vena cava.
• Blood pressure is measured using a sphygmomanometer which measures the force exerted on the walls of an artery during systole and diastole. Blood pressure is recorded as mmHg or millimetres of mercury. It is written as two numbers separated by a slash e.g. 120/80mmHg. The first number represents the highest pressure reached during systole and the second number represents the lowest pressure reached during diastole.