Animal transport

• Why do multicellular animals need transport systems?

  Have a small SA:V ratio

  Animals have a high metabolic rate so substances need to to be supplied and removed efficiently in order to carry out activities effectively
• Structure of arteries -

  
  

  1. fibrous collagen - strengthen against bp
  2. smooth muscle layer - contracts changing diameter of artery to control blood flow
  3. elastic fibres - elastin stretches when bp passes down and recoils - resist pulse surges
  4. lumen - lined with endothelial cells for smooth surface, reducing friction as blood flows through
• Structure of an artery

  A) Fibrous collagen

  B) smooth muscle cell

  C) Elastin fibres

  D) smooth endothelial cells

  
• Artery walls are relatively thick to withstand high blood pressure.
• Arteries carry blood away from heart at a high pressure.
• Arterioles deliver blood to capillaries in organs and tissues.
• In arterioles, blood pressure is lower than that in arteries.
• Structure of arterioles -

  1. contain thin layers of collagen and elastin
  2. smooth muscle layer is thicker
• Why is the smooth muscle layer thicker in arterioles than in arteries?

  • they control amount of blood passing through capillaries
  • via vasoconstriction and vasodilation
  • which occurs when an organ requires an increased amount of o2
• Structure of capillaries -

  1. extensive branching - large SA for exchanging materials
  2. thin wall (1 endothelial cell thick) - short diffusion distance between blood and cells increasing efficiency
  3. narrow lumen to push RBCs against wall, reducing diffusion distance for o2
  4. leaky walls - allows tissue fluid and WBCs to pass out bloodstream
• What does tissue fluid contain?

  nutrients, hormones, waste, glucose, amino acids, urea
• Veins carry blood towards the heart at a lower blood pressure.
• Venules - small veins that carry blood from the capillaries to the heart.
• Capillary bed - network of capillaries that connects arterioles to venules.
• Structure of veins -

  1. thinner collagen walls - do not have to withstand high blood pressure
  2. thinner elastic layer and smooth muscle layer - blood does not travel in pulses (so no elastic recoil)
  3. larger lumen with endothelial cells - carry greater volume of blood
  4. contain valves - keeps blood moving in one direction towards the heart
• Why do vessels contain endothelial cells in the lumen?

  reduce friction between blood and vessel walls.
• why do veins have a thinner elastic layer?

  blood does not travel in pulses so there is no elastic recoil
• Valves in veins -

  when muscles contract veins are squeezed

  this forces blood forward, then valves remain open

  if blood starts to move backwards, valves shut
• When inhaling, pressure in chest cavity decreases, helping blood in chest veins move towards the heart.
• Structure of a vein -

  A) muscle

  B) elastic

  C) lumen

  D) wall

  
• Lumen and artery

  A) artery

  B) Vein

  
• Oncotic pressure - tendency of water to move from tissue fluid to capillaries
• Hydrostatic pressure - pressure exerted by the fluid on the walls of blood vessels
• Where is tissue fluid formed?

  arteriole end of the capillaries
• Blood plasma - liquid part of blood that contains dissolved substances, WBCs, RBCs and platelets
• Tissue fluid - fluid that surrounds cells exchanging dissolved substances and nutrients from blood across plasma membranes.
• tissue fluid forced out of capillary through gaps between endothelial cells is an example of ultrafiltration (proteins too large to leave)
• At the arterial end of the capillaries:

  Hydrostatic pressure > oncotic pressure

  which contributes to mass flow
• At the venous end of the capillaries:

  Hydrostatic pressure < oncotic pressure
• Tissue fluid at the venule end of capillaries -

  • Hydrostatic pressure is lower as large amounts of water have left blood
  • Oncotic pressure is high due to presence of plasma proteins, causing water to diffuse down gradient via osmosis into blood
• • Remaining 10% of tissue fluid drains into Lymph capillaries which connect to the lymphatic system
  • lymph fluid moves along when limb vessels are squeezed by skeletal muscles
  • valves keep fluid moving forward and lymph fluid returns to blood stream
• Describe the vessel route taken after oxygenated blood enters the heart

  Pulmonary vein -> Left Atrium -> Left Ventricle -> Aorta -> (body) -> Vena Cava -> Right Atrium -> right ventricle -> Pulmonary artery -> (Lungs)
• The pulmonary artery and aorta both contain valves
• Oxygenated blood enters the left atrium via the pulmonary vein
• Deoxygenated blood enters the right atrium via the pulmonary artery
• Atriums and ventricles are separates by atrioventricular valves
• The right ventricle and pulmonary artery

  &

  The left ventricle and aorta

  are each separated by semi lunar valves
• In the right atrioventricular valve sits the tricuspid valve
• In the left atrioventricular valve sits the biscuspid valve
• Left and right side of the heart are separated by the septum wall