Circulation system

• diffusion is the movement of molecules from a high concentration to a low concentration
• red blood cells contain a pigment known as haemoglobin, which allows them to transport oxygen around the body.
• carbon dioxide is transported in the liquid part of the blood known as the plasma
• the need for a circulatory system

  large multi-cellular organisms need a circulatory system so all the cells receive the materials they require

  single celled organisms such as amoeba do not require a circulatory system they are so small that gases and other molecules will move by diffusion in and out of the cell
• an open blood circulatory system means blood leaves blood vessels and flows around the cells of an animals body before entering the blood vessels again
• open blood system

  blood vessels are open ended

  blood leaves the vessel and passes between the cells

  blood returns into the vessel and back to the heart

  for example: crabs, lobsters, spiders, snails and slugs
• closed blood system

  a closed circulatory system means blood remains in a continuous system of blood vessels
• closed blood system

  blood remains in the vessels

  materials are exchanged between the capillaries (thinnest vessels)and body cells

  for example:humans
• closed system advantages

  • blood can be pumped around the body faster
  • oxygen is transported quickly to the cells
  • organisms are more active due to higher metabolic rate
• the humans circulatory system consists of:

  • blood
  • the heart
  • blood vessels
• there are three types of blood vessels

  1. arteries
  2. veins
  3. capillaries
• 1. arteries

  arteries carry blood away from the heart

  arteries then divide into smaller vessels called arterioles

  structure

  • have a thick muscular wall
  • have a small lumen (blood flows through the lumen in the centre of the vessel)
• 2. veins

  • veins carry blood to the heart
  • small veins are known as venules

  structure

  • have a thin muscular wall
  • have a large lumen
  • have valves
• valves control the direction of blood flow/ valves prevent the backflow of blood
• blood pressure in veins and arteries

  arteries

  • blood pressure is high due to the heart pumping
  • this high pressure causes the artery to expand causing a pulse

  veins

  • blood pressure is slow as blood is being carried back to the heart
  • veins have valves
• pulse is the expansion and contraction of an artery wall due to the pumping of the heart
• describe the movement of blood through veins/arteries

  • the heart beats
  • the muscular wall of the veins and arteries contract which pushes blood through the lumen
  • arteries have thick walls because they are under high pressure
  • veins have valves to prevent the backflow of blood
• capillaries

  • capillaries are tiny vessels that link arteries to veins
  • arteries generally carry oxygenated blood (oxygen rich blood) from heart to the body cells
  • veins carry deoxygenated blood (oxygen poor blood) from the body to the heart
  • gases and other materials diffuse in and out of the blood capillaries i.e walls are one cell thick
  • oxygenated blood becomes deoxgenated in the capillaries i.e oxygen diffuses out of the capillaries into the body cells and carbon dioxide diffuses from the body cells into the capillaries
• differences between arteries and veins

  arteries

  • carry blood away from the heart
  • blood under high pressure
  • thick wall
  • small lumen
  • have no valves
  • generally high in oxygen (oxygenated) (apart from the pulmonary artery)

  veins

  • carries blood to the heart
  • blood under low pressure
  • thin wall
  • large lumen
  • have valves
  • generally low in oxygen (deoxygenated) (apart from pulmonary vein)
• location of the heart: thorax
• aorta: carries oxygenated blood away from the heart around the body
• pulmonary vein: carries oxygenated blood from the lungs to the heart
• atrium: top chambers of the heart
• ventricle: bottom chambers of the heart. left ventricle is thicker than the right as the left side of the heart pushes blood around around the body i.e there is high pressure
• bicuspid valve: separates the left atrium and left ventricles

  prevents the backflow of blood
• tricuspid valve: separates the right atrium and the right ventricle

  prevents the backflow of blood
• septum:separates the left and right side of the heart
• cardiac muscle: muscle that contracts/does not tire
• pericardium: membrane surrounding the heart
• vena cava: carries deoxygenated blood away from the body to the heart
• pulonary artery: carries deoxygenated blood away from the lungs
• semi-lunar valves:found in the aorta and pulomary arteries

  prevents the backflow of blood in the heart
• pacemaker (S.A and A.V node): controls the heartbeat
• blood flow in the heart

  deoxygenated blood

  • oxygen poor blood enters the heart through the vena cava and enters the right atrium
  • the atrium contracts and blood is forced through the tricupid valve and into the right ventricle
  • the right ventricle contracts, the tricuspid valve closes and the blood is forced out of the pulmonary artery
  • the pulmonary artery carries deoxygenated blood to the lungs
• blood flow in the heart

  oxygenated blood

  • oxygen rich blood returns to the heart from the lungs via the pulomary vein
  • the blood enters the left atrium
  • the left atrium contracts and blood is forced through the bicuspid valve into the left ventricle
  • the left ventricle contracts the bicuspid valves close and blood is forced into the aorta
  • the aorta carried oxygenated blood around the body
• double circulation

  the two sides of the heart are separated by the septum

  this ensures that the oxygenated and deoxygenated blood never mixes
• pulmonary circuit and systemic circuit are the two circuits in the circulatory system
• pulmonary circuit

  heart -> lungs -> heart

  the right ventricle and pulmonary artery pumps deoxygenated blood from the heart to the lungs

  gaseous exchange occurs in the alveoli

  the blood gains oxygen and loses carbon dioxide by diffusion

  the right ventricle has thin walls as the blood does not need to travel far

  the oxygenated blood is carried from lungs to the heart via the pulmonary vein
• systemic circuit

  heart -> body -> heart ->

  • the left ventricle and aorta pumps oxygenated blood from the heart to the body
  • blood loses oxygen and gain carbon dioxide by diffusion
  • oxygen diffuses into the body cells (mitochondria) for respiration
  • deoxygenated blood is carried back to the heart via the vena cava
  • the left ventricle has thick walls as blood must be transported around the body so has a higher pressure
• advantages of double circulation

  • allows oxygen rich (oxygenated) and oxygen poor blood to be kept separate
  • ensures blood pressure is high enough so blood can reach all parts of the body