General

• Digestive system


  To digest food and absorb the nutrients obtained from digestion
• Pancreas and salivary gland


  Glands which produce digestive juices containing enzymes
• Stomach

  Produces hydrochloric acid - which kills any bacteria present and provides the optimum acidic pH for the protease enzyme to function
• Small intestine


  The site where soluble food molecules are absorbed into the bloodstream
• Liver


  Produces bile (stored in the gallbladder) which emulsifies lipids and allows the lipase enzyme to work more efficiently
• Large intestine


  Absorbs water from undigested food, producing faeces
• Enzymes

  Act as biological catalysts which speed up the rate of biological reactions without being used up
• Enzyme shape

  Enzymes have a specific active site which is complementary to their substrate
• Metabolism


  The sum of all the reactions in a cell or an organism
• Types of metabolic reactions catalysed by enzymes

  • Building larger molecules from smaller molecules
  • Changing one molecule to another
  • Breaking down larger molecules into smaller molecules
• Lock and key hypothesis

  The shape of the enzyme active site and the substrate are complementary, so can bind together to form an enzyme-substrate complex
• Temperature effect on enzymes

  Up to a certain point, increasing temperature increases enzyme action, as molecules have a higher kinetic energy. Above a certain temperature, the shape of the active site is altered and the enzyme becomes denatured, so it can no longer catalyse the reaction. The optimum temperature is around 37°
• Locations of enzyme production

  • Carbohydrases: amylase - salivary gland and pancreas; maltase - small intestine
  • Proteases: pepsin - stomach; others - pancreas and small intestine
  • Lipases: pancreas and small intestine
• Role of proteases


  Break down proteins into amino acids
• Role of lipases

  Break down lipids into fatty acids and glycerol
• Bile production and storage

  Bile is made by the liver and stored in the gallbladder
• Circulatory system

  Carries oxygen and other useful substances to bodily tissues, and removes waste substances
• Double circulatory system


  One pathway carries blood from the heart to the lungs - where the gaseous exchange of oxygen and carbon dioxide takes place. One pathway carries blood from the heart to the tissues
• Destination of blood from right ventricle

  The lungs
• Destination of blood from left ventricle

  Body tissues
• Importance of double circulatory system

  It makes the circulatory system more efficient - for example, oxygenated blood can be pumped around the body at a higher pressure by the left ventricle
• Heart chambers

  4 - right atrium, right ventricle, left atrium, left ventricle
• Thicker left ventricle wall

  The left ventricle has to pump blood at a higher pressure around the whole body
• Main blood vessels associated with the heart

  • Aorta (left) - carries oxygenated blood from the heart to the body
  • Pulmonary vein (left) - carries oxygenated blood from the lungs to the heart
  • Vena cava (right) - carries deoxygenated blood from the body to the heart
  • Pulmonary artery (right) - carries deoxygenated blood from the heart to the lungs
• Purpose of heart valves

  Prevent the backflow of blood
• Blood flow through the heart

  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle is pumped to the lungs, and blood in the left ventricle is pumped to the body
• Valves in the heart

  Prevent the backflow of blood
• Coronary arteries


  Supply the heart muscle with oxygenated blood
• Blood flow through the heart

  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle enters the pulmonary artery and blood in the left ventricle enters the aorta
• The approximate value of the natural resting heart rate is 70 beats per minute
• Heart rate control

  Heart rate is controlled by a group of cells in the right atrium which act as a pacemaker. They release waves of electrical activity which cause the heart muscle to contract.
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries

  • Thick muscle layer - adds strength to resist high pressure
  • Thick elastic layer - allows arteries to stretch and recoil - in order to withstand high pressure
• Veins

  • Wide lumen - enables low pressure
  • Valves - prevent backflow of blood
• Capillaries


  • Walls are one cell thick - short diffusion path
  • Permeable walls - substances can diffuse across
  • Narrow lumen - blood moves slowly - more time for diffusion
• Blood flow rate calculation

  Volume of blood / number of minutes
• Location of lungs

  The lungs are located in the thorax. They are protected by the ribcage and separated from the rest of the abdomen by the diaphragm.
• Tissues and organs of the gas exchange system

  • Trachea
  • Intercostal muscles
  • Bronchi
  • Bronchioles
  • Alveoli
  • Diaphragm
• Lung ventilation by intercostal muscles

  1. Intercostal muscles contract

  2. Ribcage moves upwards and outwards

  3. Diaphragm flattens and volume of the chest increases

  4. Increased volume results in decreased pressure

  5. Air is drawn into lungs down pressure gradient
• Gas exchange at the alveoli

  1. Oxygen diffuses from the alveoli into the capillary bloodstream down its concentration gradient

  2. Carbon dioxide diffuses from the capillary into the alveoli down its concentration gradient