Mass Transport in Animals

• Haemoglobin is a quaternary protein made up of 4 polypeptide chains. At the centre of each is the prosthetic group - iron ions. Each polypeptide chain can bind with an oxygen molecule. Haemoglobin, can be either fully saturated with oxygen, totally unsaturated or anywhere in between.
• • At high oxygen concentrations haemoglobin has a high affinity for oxygen which means it loads with oxygen more readily.
  • At low oxygen concentrations haemoglobin has a low affinity for oxygen which means it unload more readily to respiring tissues.
• Binding of oxygen to haemoglobin-

  • initially, the first oxygen struggles to bind and the flattened part at the bottom of the 'S' shaped curve illustrates this.
  • once the first molecule of O2 has bound, it changes shape of the haemoglobin making it more easy for the next 2 molecules to bind. Cooperative binding.
  • the fourth O2 only has a single binding site to attach to as all the others are already bound to O2. This results in the flattening of the curve at the top.
• The Bohr effect:

  • Carbon dioxide concentration increases during exercise. It dissolves in the blood and the resulting acidity changes the shape of the haemoglobin and decreases its affinity.
• An animal whose curve is shifted to the left has a higher affinity for oxygen at a low partial pressure and so its haemoglobin will load more readily with oxygen
• An animal whose curve is shifted to the right has lower affinity for oxygen at the same partial pressure and so its haemoglobin will unload more readily to the respiring tissues.
• Artial Systole:

  The ventricles are relaxed and the atria contract. This increases the pressure and decreases the volume in the atria, pushing the blood into the ventricles. The atrioventricular valves are opened.
• Ventricular Systole:

  The atria relax and the ventricles contract. There is now more pressure in the ventricles so the atrioventricular valves close to prevent backflow. The pressure is also higher in the ventricle than in the artery which forces the semi lunar valves to open as blood is forced into the arteries.
• Atrial and Ventricular Diastole:

  The atria and the ventricles both relax. The higher pressure in both the aorta and the pulmonary artery (from elastic tissue recoil) force the semi lunar valves closed. Blood returns to the heart as the pressure in the vena cava and pulmonary vein is greater than in the atria. As ventricles continue to relax, there is a higher pressure in the atria so the atrioventricular valves open and blood trickles into the ventricles.
• Aorta - carries blood away from the heart to the rest of the body
• Vena Cava - vein carrying deoxygenated blood from the body back to the heart.
• pulmonary artery - carries deoxygenated blood from the lungs back to the heart.
• pulmonary vein - carries oxygenated blood from the lungs to the left atrium
• renal artery - carries blood to the kidneys and the renal vein removes it
• coronary artery - carries oxygenated blood to the heart and the coronary vein removes it.
• cardiac output = stroke volume x heart rate
• Artery:

  • collagen fibres
  • thick layer of smooth muscle to withstand high hydrostatic pressure
  • elastic tissue for elastic recoil
  • endothelium cell membrane
  • small lumen
• Capillary:

  • basement membrane (collagen)
  • fenestrations
  • Lumen (small)
• Vein:

  • collagen & connective tissue
  • thin layer of smooth muscle & elastic tissue
  • endothelium
  • semi lunar valves
  • lumen large so less friction
• Tissue Fluid:

  1. High hydrostatic pressure at the arteriole end due to contraction of the left ventricle
  2. Small substances are forced through the endothelial, capillary walls
  3. tissue fluid forms
  4. large, soluble proteins retained in the blood lower the water potential.
  5. The hydrostatic pressure decreases in the blood due to: water being lost, friction due to the cross sectional area of the capillary bed.
  6. There is a water potential gradient between the tissue fluid and the blood, so water is lost down its water potential gradient by osmosis.
  7. any excess water drains into the lymphatic system.