8) Transport in animals

• Circulatory systems:

  • carry gases such as oxygen and carbon dioxide
  • they have a liquid transport medium that circulates around the system
  • they have vessels that carry the transport medium
• Open circulatory systems:

  • blood flows freely through the body cavity
  • returns through valves
  • blood doesn't just transport oxygen
  • body cavity called haemocoel
• Closed circulatory systems: vertebras

  • blood enclosed in blood vessels
• Single circulatory systems are found in fish and worms.
• In single closed circulatory systems, blood flows through the heart and is pumped out to travel all around the body and back to the heart.
• Double closed circulatory system:

  • most efficient system for transporting substances around the body
  • passes through the heart twice per circuit
• Different components in blood vessels:

  elastic fibres - these are composed of elastin and can stretch and recoil, providing vessel walls with flexibility

  smooth muscle - contracts or relaxes, which changes the size of the lumen

  collagen - provides structural support to maintain the shape and volume of the vessel
• Arteries

  • carry blood away from the heart under high pressure
  • walls contain elastin fibres, smooth muscle and collagen.
  • thick walls
  • small lumen
• Arterioles:

  • link the arteries and capillaries
  • the smooth muscle contracts it constricts the vessel and prevents blood flowing into the capillary bed
• Capillaries:

  • large surface area for diffusion
  • One cell thick for thin layer for diffusion
  • highly branched
• Veins:

  • carry deoxygenated blood back to the heart under low pressure
  • valves
  • large lumen
  • thin walls
  • walls made up of lots collagen and little muscle and elastin fibres
• Venules:

  • connect capillaries and veins
  • very thin walls with little amount of smooth muscle
  • Prone to rupture
• 1. electrical impulse generated at sino atrial node
  2. impulse travels across right and left atria
  3. impulse received and delayed at atrio ventricular node until atria has finished contracting
  4. Impulse travels down a bundle of his and is split in two bundle branches
  5. impulse travels up the walls of the ventricles via the purkyne fibres
• Normal ECG = 60-100 bpm
• Bradycardia = <60bpm
• Tachycardia = >100 bpm
• ectopic = altered heart beat, extra beat followed by longer than normal gap before next
• Atrial fibrillation = abnormal rapid an ineffective contraction of the atria
• Transport of oxygen:

  haemoglobin transports oxygen

  haemoglobin - 4x polypeptide chains, 2x alpha chains and 2x beta chains and 1 ion containing haem prosthetic group per polypeptide

  can carry 4 oxygen molecules, has an affinity for oxygen
• Erythrocytes (red blood cells):

  • biconcave shape maxamising surface area for gas exchange
  • small and flexible to pass through narrow capillaries
  • no nucleus
  • packed with haemoglobin
• oxygen dissociation curve:

  haemoglobin binds cooperatively

  each subunit combines with one molecules of oxygen

  haemoglobin binds sequentially with each combination facilitating the next one

  this explains the sigmoid shape
• oxygen dissociation curve steps:

  1. after the first oxygen molecule associates, the combination of the haemoglobin changes
  2. conformational change makes it easier for the second and third oxygen molecules to associate
  3. it is difficult to associate the fourth oxygen molecule, this is because the haemoglobin becomes full
• Transport of carbon dioxide in the blood:

  carried in 3 ways

  dissolved in plasma - 5%

  carbamino-haemoglobin - 10-20%

  hydrogen-carbonate Ions - 75-85%
• Dissolved in plasma

  • carbon dioxide is more soluble in water than oxygen, but this is not sufficient to carry all of the CO2 produced as a result of aerbobic respiration
• Carbamino-haemoglobin

  • co2 combined with the amino acid chain in the polypeptide chains of haemoglobin
• Hydrogen carbonate ions

  co2 +h20 = h2co3 = h+ + hco3-

  catalysed by carbonic anhydrase
• Bohr shift

  • as the concentration of carbon dioxide increases, the affinity of haemoglobin for oxygen decreases
  • curve moves to the right
• Foetal haemoglobin

  • The fetus needs to obtain oxygen from the mother's blood.
  • The fetal haemoglobin therefore has a higher oxygen affinity than the adult haemoglobin found in the mother's blood.
  • This allows the oxygen to dissociate from the mother's haemoglobin, and bind with haemoglobin in the fetal blood.
  • This ensures that the fetus gets enough oxygen to survive while it develops.
• At the lungs:

  1. low partial pressure of carbon dioxide causes carbonic acid and hydrogen ions to reform carbon dioxide
  2. carbon dioxide diffuses out during expiration
• At the tissue

  1. Some of the CO2 dissolves directly into the plasma

  2. Some of the CO2 diffuses directly into the erythrocyte

  3. 10-20% of the CO2 combines with haemoglobin to make carbamino-haemoglobin

  4. 75-85% of CO2 molecules react with H2O to form carbonic acid, reaction catalysed by carbonic anhydrase

  5. Carbonic acid then dissociates into hydrogencarbonate ions and hydrogen ions

  6. Hydrogencarbonate ions actively transported out of RBC by a transporter protein

  7. Chloride ions transported into the cell to maintain electrical balance
• Tissue fluid:

  fills spaces between cells. It is the site of diffusion between blood and body cells, providing cells with nutrients and oxygen while removing waste products. It also helps fight infection as it forms part of the immune response.

  • no red blood cells
  • fewer proteins than plasma
  • fewer white blood cells than plasma
• At the arteriole end of capillary:

  1. A high hydrostatic pressure, exerted by the force of the heart pumping, forces fluid out of capillaries.
  2. This forms tissue fluid surrounding body cells.

  At the venule end of the capillary:

  1. The hydrostatic pressure is lower.
  2. Proteins in blood exert a high oncotic pressure, a type of osmotic pressure, in capillaries.
  3. The water potential is lower in capillaries than in tissue fluid due to fluid loss.
  4. Some tissue fluid moves back into capillaries by osmosis.
• Lymph is the fluid that flows around the lymphatic system via lymph vessels.
• Lymph has a similar composition to tissue fluid, except:

  • Lymph has less oxygen and nutrients.
  • Lymph has more fatty acids.
  • Lymph has more white blood cells
• Circulatory systems are needed because;

  • multicellular organisms are larger, so distance across surface would be too large
  • multicellular organisms have a higher metabolic rate
  • multicellular organisms need to supply nutrients and oxygen rapidly to large number of active cells
• Lymph formation:

  1. some tissue fluid does not re-enter the capillary
  2. fluid instead drains into the lymph vessels forming lymph
  3. lymph transported through lymph vessels by muscular contractions
  4. lymph passed through lymph nodes to filter pathogens
  5. lymph eventually is filtered back into the blood