Mass transport in animals

• Importance of mass transport systems in multi-cellular organisms

  • Low/small surface area to volume ratio
  • Need a specialised exchange surfaces - like the circulatory system to carry raw materials to their body cells
• Pulmonary circulation


  1. Deoxygenated blood in right side of heart pumped to lungs

  2. Oxygenated blood returns to left side of heart
• Systemic circulation


  1. Oxygenated blood in left side of heart pumped to tissues/ organs

  2. Deoxygenated blood returns to the right side of heart
• Closed double circulatory system

  • Closed - blood stays in blood vessels
  • Double - blood passes through the heart twice
• Blood transports


  • Respiratory gases - carbon dioxide and oxygen
  • Products of digestion - monosaccharides and amino acids
  • Metabolic wastes
  • Hormones
• Coronary arteries


  Deliver oxygenated blood to the cardiac muscle
• Blood vessels entering the heart

  • Vena cava - deoxygenated blood from respiring tissues to heart
  • Pulmonary vein - oxygenated blood from lungs to heart
• Blood vessels leaving the heart

  • Aorta - oxygenated blood from heart to rest of body
  • Pulmonary artery - deoxygenated blood from heart to lungs
• Blood vessel entering lungs

  • Pulmonary artery - deoxygenated blood from heart to lungs
• Blood vessel leaving lungs

  • Pulmonary vein - oxygenated blood from lungs to heart
• Blood vessel entering kidney

  • Renal artery - oxygenated blood from heart/aorta to kidney
• Blood vessel leaving kidney

  • Renal vein - deoxygenated blood from kidney to vena cava/ heart
• Opening of valves


  1. Valves open when pressure behind is greater than the pressure in front

  2. Blood frow is unidirectional - only in one direction
• Atrioventricular valves names


  • Mitral valve - left atrium and left ventricle
  • Tricuspid valve - right atrium and right ventricle
• Atrioventricular valve function


  Prevent backflow of blood from the ventricles into the atria during ventricular systole
• Semilunar valves names


  • Aortic valve - left ventricle and aorta
  • Pulmonary valve - Right ventricle and pulmonary artery
• Semilunar valve function


  Precents backflow of blood from arteries into ventricles
• Right ventricle


  • Has thinner muscular wall
  • Generate a lower blood pressure
  • For deoxygenated blood to travel a shorter distance to lungs
  • Where high blood pressure would damage alveoli
• Systole


  Cardiac contraction
• Diastole


  Cardiac relaxation
• Atrial systole


  1. Atria contract

  2. Ventricles relax - ventricular distole

  3. Blood pushed into ventricles
• Volume and pressure during atrial systole

  • Decreasing volume in atria
  • Increasing pressure in atria
• Valves during atrial systole

  1. Atrioventricular valves forced open

  2. Pressure inside atria greater than pressure in ventricles
• Ventricular systole


  1. Ventricles contract bottom up

  2. Atria relax - Atria diastole

  3. Blood pushed out of heart through arteries
• Volume and pressure during ventricular systole

  • Decreasing volume in ventricle
  • Increasing pressure in ventricle
• Valves during ventricular systole


  1. Semilunar valves open

  2. Pressure inside ventricles greater than pressure inside arteries (pulmonary artery and aorta)

  3. Atrioventricular valves closed

  4. Pressure inside ventricles greater than pressure atria
• Cardiac diastole


  Atria and ventricles both relaxed
• Volume and pressure during diastole

  • Increasing volume
  • Decreasing pressure
• Atrioventricular valves during diastole


  1. Open

  2. Blood from veins (pulmonary and vena cava) fills atria - increasing pressure in atria

  3. Pressure inside atria greater than pressure inside ventricles

  4. Blood flows passively into ventricles
• Semilunar valves during diastole

  1. Shut

  2. Pressure in arteries grater than pressure in ventricles
• Capillaries


  • Form capillary beds which act as exchange surfaces
  • One cell thick
  • Short diffusion distance
  • For exchanging materials between blood and cells
• Red blood cells in the capillary

  • Can only just fit through the lumen
  • Blood flows slower
  • Allows more time for diffusion
• Capillaries highlighted in

  • Alveoli
  • Villi
  • Nephron
  • All places where diffusion occurs
• Pores in walls between cells

  • Allows substance to enter and leave
  • E.g white blood cells
• Capillaries permeate tissues

  • No cell is far away from capillary
  • Short diffusion distance
• Tissue fluid


  • The fluid which surrounds cells
  • Contains water, ions, oxygen, glucose, amino acids and fatty acids
• Purpose of tissue fluid

  • Enables the delivery of useful molecules to cells
  • Moves waste from cells into the blood stream so it can be removed from the body
• Why is there no red blood cells, platelets or large proteins in tissue fluid?

  • Too large to be forced out the pores/ tiny capillaries by ultrafiltration
• Formation of tissue fluid

  1. Substances move out of capillaries though pores in their walls - known as pressure filtration

  2. As blood enters the capillaries from arterioles - the smaller diameter results in a higher hydrostatic pressure

  3. Water, glucose, amino acids, fatty acids, ions and oxygen are forced our - know as ultrafiltration

  4. The red blood cells, large proteins and platelets are too big to fit through the tiny gaps/pores so they remain within the capillary
• Reabsorption of tissue fluid back into the blood

  1. Large molecules remain the capillaries and create a lowered water potential

  2. Towards the venule end the hydrostatic pressure is powered due to the loss of liquid

  3. The water potential is low creating a water potential gradient

  4. Water is reabsorbed back into the capillaries by osmosis