Topic 8

• Factors that mean that multicellular animals need transport systems

  Large size, high metabolic rate, low surface area to volume ratio, rate of diffusion is not enough, large distance between where molecules are produced and where they are needed
• Types of circulatory system

  Single, double, open, closed
• Features different circulatory systems have in common

  Liquid transport medium, vessels that carry the transport medium, of pumping mechanism
• Open circulatory system


  Few blood vessels, haemocoel (Open body cavity), low pressure
• Circulatory system in insects

  Open, haemolymph doesn't carry oxygen and carbon dioxide, haemolymph transports nitrogenous waste, body cavity split by membrane, heart extends along length of thorax and abdomen
• Disadvantages of open circulatory systems

  No steep diffusion gradients, amount of fluid flowing to a tissue can't be changed
• Closed circulatory system


  Blood enclosed in vessels, blood returns directly to the heart, substances leave and enter thro ugh walls of blood vessels
• Examples of organisms with closed circulatory systems

  Echinoderms, cephalopod molluscs, mammals
• Single circulatory system


  When the blood travels once through the heart for each complete circulation of the body
• How a single circulatory system works

  Oxygen and carbon dioxide diffuse through set of capillaries, substances exchanged through other capillaries to organ systems
• Disadvantages of single circulatory system

  Low blood pressure, low speed
• Circulatory system in fish

  Single circulatory system, countercurrent gaseous exchange system, body weight supported by water so can be active without efficiency
• Double circulatory system


  The blood travels twice through the heart for each circuit of the body
• Two circuits in the double circulatory system

  Heart to lungs, heart to body
• Advantages of doubl circulatory system

  High pressure, fast flow of blood
• Examples of blood vessels (Types)

  Arteries, arterioles, capillaries, veins, venules
• Function of arteries


  To carry oxygenated blood away from th heart to tissues in the body
• Structure of arteries


  Elastic fibres, smooth muscle, collagen, order of layers from smallest to largest is lumen endothelium elastic muscle tough outer
• Role of elastin fibres in blood vessels

  Stretching and recoiling, flexibility
• Role of smooth muscle in blood vessels

  Contracts or relaxes to change the size of the lumen
• Role of collagen in the blood vessels

  To provide structural support, to maintain the shape and volume of the vessel
• Role of endothelium in the blood vessels


  Smooth so blood flows over it
• Function of arterioles


  To link arteries and capillaries
• Structure of arterioles


  More smooth muscle, less elastin
• Why do arterioles constrict and dilate?

  To control the flow of blood to organs and capillary beds
• Function of capillaries


  To link arterioles to venules
• Structure of capillaries


  Narrow lumen to squeeze oxygen out of red blood cells, gaps between endothelial cells in capillary wall,
• Adaptations of capillaries


  Narrow diameter so short diffusion distance, thin wall for rapid diffusion, smooth endothelium, large surface area to allow more exchange
• Function of veins


  To carry deoxygenated blood from the cells of the body towards the heart
• Structure of veins


  Lots of collagen, little elastic fibre, wide lumen, valves, smooth endothelium, sequence of layers is lumen endothelium elastic muscle tough
• Function of venules


  To link capillaries with veins
• Structure of venules


  Thin walls, little smooth muscle
• Disadvantage to structure of veins

  Low pressure when having to work against gravity
• Adaptations to structure of veins

  Valves, bigger veins run between active muscles, breathing movement during of chest act as a pump
• How tissue fluid is formed

  Plasma proteins in capillaries decrease water potential, water moves into capillaries by oncotic pressure, blood still under pressure due to hydrostatic pressure, hydrostatic pressure greater than oncotic pressure so fluid squeezed out of capillaries at the arterial end, fluid fills spaces between cells
• Oncotic pressure


  Pressure created by the osmotic effect of solutes
• Hydrostatic pressure


  Pressure exerted by a fluid
• Differences between composition of blood and tissue fluid

  No red blood cells, no plasma proteins
• How tissue fluid gets back into blood vessels

  Hydrostatic pressure falls, oncotic pressure is greater than hydrostatic pressure, water moves back into the capillaries by osmosis at the venous end
• Lymph


  Liquid that leaves the blood vessels and drains into the lymph capillaries