transport in animals

• Circulatory systems can be open (in insects) or closed (in fish and mammals)
• Closed circulatory systems come in two forms:

  • Single form: heart with two chambers, blood passes through the heart once for every circuit of the body
  • Double form: heart with four chambers, blood passes through the heart twice for every circuit of the body
• Important structures and functions in the circulatory system:

  • Arteries: carry blood away from the heart, thick-walled to withstand high blood pressure, contain elastic tissue to stretch and recoil, contain smooth muscle to vary blood flow, lined with smooth endothelium to reduce friction
  • Arterioles: branch off arteries, have thinner and less muscular walls, feed blood into capillaries
  • Capillaries: smallest blood vessels, site of metabolic exchange, one cell thick for fast exchange of substances
  • Venules: larger than capillaries but smaller than veins
• • Veins: carry blood from the body to the heart, contain a wide lumen to maximize blood volume, thin-walled under low pressure, contain valves to prevent backflow of blood
• Tissue fluid:

  • Liquid containing dissolved oxygen and nutrients
  • Enables exchange of substances between blood and cells
• Hydrostatic pressure:

  • Created when blood is pumped along arteries, arterioles, and capillaries
  • Forces blood fluid out of the capillaries
  • Only small enough substances can escape through capillary walls to form tissue fluid
• Lymphatic system:

  • Carries remaining tissue fluid back via lymph fluid
  • Contains lymph nodes to filter out bacteria and foreign material
  • Lymph fluid carries waste products
• Mammalian heart and cardiac cycle:

  • Heart is myogenic
  • Sinoatrial node in the right atrium is the pacemaker
  • Atrial systole, ventricular systole, cardiac diastole are the 3 stages of the cardiac cycle
• Haemoglobin:

  • Water-soluble globular protein with two alpha and two beta polypeptide chains
  • Carries oxygen in the blood, each molecule can carry four oxygen molecules
  • Affinity of oxygen for haemoglobin varies with partial pressure of oxygen
  • Fetal haemoglobin has a higher affinity for oxygen compared to adult haemoglobin
  • Affinity of haemoglobin for oxygen is affected by the partial pressure of carbon dioxide (Bohr effect)
• The heart is made up of four chambers, two atria (upper) and two ventricles (lower).