transport in animals

• arteries carry blood away from the heart under high blood pressure and possess a pulse

  veins carry blood towards the heart under low blood pressure and doesn't have a pulse so it doesn’t have an elastic recoil
• the right side of the heart pumps deoxygenated blood to the lungs where it picks up oxygen and gets rid of carbon dioxide
• the left side of the heart pumps oxygenated blood to the body
• Structure of arteries


  • Tunica intima - endothelial layer made of connective tissue and elastic fibres
  • Endothelium is one cell thick and reduces friction between blood and vessels
  • Thick tunica media - smooth muscle cells and layer of elastic tissue
  • Smooth muscle cells provide strength so the arteries can withstand high pressure and it allows the lumen to contract and narrow
  • Elastic tissue maintains blood pressure by stretching and recoiling out any fluctuations
  • Tunica externa - mostly collagen - a strong protein that protects blood vessels from damage from over stretching
  • Narrow lumen - maintains high blood pressure
• arterioles carry blood to capillaries

  blood pressure is lower than arteries’ and effect of pulse is weaker

  elastic layer is thinner but smooth muscle layer is thicker so they can contract and cut off blood to specific organs and cam control amount of blood flow passing through capillaries
• structure of veins

  • tunica intima - endothelial layer
  • thinner tunica media - smooth muscle and elastic layers are thinner as they don’t have to withstand a high blood pressure
  • tunica externa - collagen
  • larger lumen - carry large volumes of blood, helps to ensure blood returns to heart at adequate speed
  • valves - prevent backflow, helps blood return to heart
• venules connect capillaries to veins

  • large lumen
  • little/no elastic fibres
  • no muscular layer due to low blood pressure
• capillaries are branched between cells and form networks called capillary beds

  they’re the site of where substances are exchanged between blood and cells
• structure of capillaries

  • small lumen - blood travels slowly so there‘s more oppurtunity for diffusion
  • walls made of single layer of endothelial cells which makes the walls one cell thick - short diffusion distance
  • pores - allow blood plasma to leak and forms tissue fluid + white blood cells squueze through to fight infected tissues
• tissue fluid is formed by blood leaking out of capillaries, its composition is very similar to plasma’s

  plasma is mostly made up of water and makes up roughly half of blood
• exvhange of substances between blood and cells occur via tissue fluid e.g CO2 will dissolve into tissue fluid and it’s moved into capillaries + it transfers glucose and water to tissue cells
• hydrostatic pressure - the pressure exerted in a fluid (the blood pressure generated by heart contractions)
• oncotic pressure - pressure exerted by plasma proteins within a blood vessels

  plasma proteins are hydrophilic and lower water potential within the blood vessel which causes water to move into the blood vessel via osmosis
• arterial end

  hydrostatic pressure is greater than osmotic pressure so the net movement of water is out of the capillaries and into tissue fluid

  proteins remain in the capillaries as they‘re too large so the increased protein content creates a water potential gradient between capillary and tissue fluid
• venous end

  • osmotic pressure is greater than than hydrostatic pressure so water flows back into the capillaries via osmosis
  • hydrostatic pressure is reduced due to increased distance from heart and the slow blood flow in capillaries
  • the water potential gradient is the same as the arterial end’s
  • 90% of water lost at the arterial end is reabsorbed at venous end, 10% is collected by lymph vessels
• if blood pressure is high, pressure at the arterial end is greater so more fluid is pushed out and fluid accumulates around tissue - fluid is called oedema
• formation of lymph

  • some tissue fluid will enter the lymph vessels - they are separate from circulatory system, have closed ends and large pores which allow large molecules to pass through
  • the larger molecules that were unable to pass through capillary walls enter the lymphatic system through valves in vessel walls as lymph
• once lymph is formed:

  • liquid moves along vessels by compression from body movement (valves prevent back flow of fluid)
  • the lymph will re-enter the bloodstream through veins close to the heart
  • plasma proteins that have escaped will return to capillaries, if they didn’t then water potential of tissue fluid would lower which prevents reabsorption of water into blood in capillaries
  • lipids are also transported from intestines to bloodstream via the lymph system
• differences between plasma and tissue fluid

  plasma: higher conc of glucose, amino acids, plasma proteins

  lower water potential

  higher O2 conc

  lower CO2 conc

  tissue fluid:higher conc of substances secreted e.g insulin
• pathway of blood

  1. deoxygenated blood enters heart through vena cava (superior from upper body, inferior from lower)
  2. right atrium
  3. right ventrincle
  4. pulmonary artery
  5. lungs
  6. oxygenated blood re enters through pulmonaryvein
  7. left atrium
  8. left ventricle
  9. pumped out of aorta to rest of body
• the coronary arteries

  supply heart with oxygen and nutrients by receiving its own blood supply
• cardiac cycle

  • definition: series of events taken in one heart beat
  • systole - contraction
  • diastole - relaxation
  • contraction causes decrease in volume of blood in corresponding chamber, increases when relaxed
  • valves open when blood pressure is greater behind them in front vice versa for when close