Exchange and Transport

• Arteries carry oxygenated blood away from the heart to all parts of the body.
• Veins return deoxygenated blood back to the heart.
• Capillaries are tiny vessels where exchange between cells and blood occurs.
• Blood pressure is maintained by the contraction of elastic fibres in artery walls.
• Exchange surfaces are adapted for their role by:

  • high SA:V
  • thin - small diffusion distance
  • large surface area - larger area for diffusion to occur over

  some adaptations that are not directly affecting the membrane itself

  • counter current flow - maintains a steep concentration gradient
• Process of fish breathing

  1. Mouth opens, operculum closes and buccal cavity expands increasing the volume of the mouth which brings in water
  2. mouth closes and buccal cavity constricts decreasing the volume and increasing the pressure which forces the oxygen rich water to pass through gills over the lamellae where gas exchange takes place and out the now open operculum
• The ways the gills of a fish are adapted for gas exchange?

  the gill arch has many gill filaments and lamallae that are wide and thin to maxmise the rate of diffusion, by decreasing diffusion distance, and increasing the area that it can occur over.

  Counter current flow: the blood flows opposite to the direction the oxygenated water enters which ensures a steep concentration gradient and allowing to reach a blood oxygen saturation rate upto 100%
• Types of circulatory systems

  • Open
  • Closed
• Open circulatory systems

  • Very few vessels
  • Blood is pumped straight from the heart to the open body cavity and comes into direct contact with cells where exchange takes place and returns to the heart through an open vessel
  • Found mostly in insects where their blood is called haemolymph and transports food and waste
• Closed circulatory systems

  • Blood is enclosed in vessels and pumped around the body under pressure
  • Substances leave and enter the blood by diffusing though the blood vessels
• Single closed circulatory system

  • Blood travels through the heart once for every circulation
  • Goes through 2 sets of capillaries where in the first is where oxygen and carbon dioxides are exchanged
  • Second, located in a different organ systems, substances are exchanged between the blood and cells
  • Low pressure system due to narrow vessels so animals with this tend to have low activity levels
  • Exception is fish as their system is efficient with the addition of countercurrent flow
• Double closed circulatory systems

  • Blood travels to the heart twice for every circulation
  • High pressure and fast flow of blood can be maintained
• Pumping mechanisms

  To move the fluid around the system
• Vessels

  To carry the blood
• Arteries structure

  • Elastic fibres
  • Collagen
  • Smooth muscles
  • Endothelium
• Purpose of arteries

  Transport of oxygenated blood away from the heart to the body under high pressures
• How is the structure of arteries adapted to their function

  • smooth muscles is to strengthen the structure and allow contraction to push blood
  • Contains collagen which has high mechanical strength which allows the artery to withstand high pressures
  • Contains elastic fibres which allow the artery to stretch and recoil to maintain blood pressure
  • Endothelium is the surface being smooth so blood flows smoothly
• Arteriolescompared to arteries

  • Less elastin and more smooth muscle
  • Connect arteries to capillaries
  • Smaller
• Vein structure

  • little smooth muscle and elastic fibres
  • Large lumen - resulting in low blood pressure
  • Transport of deoxygenated blood back to the heart
  • Valves to prevent backflow
  • Endothelium for smooth blood flow
  • Major veins being located between muscles so when they contract they can push blood up against gravity towards the heart
• Venules

  • Smaller than veins, thin walls with a little amount of smooth muscle
  • Connect veins to capillaries
• structure and purpose of Capillaries?

  • Form a network between all tissues in the body and is responsible for the exchange of substances
  • Link arterioles to venules
  • 1 cell thick so short diffusion distance
  • Blood flows slowly so there is more time for diffusion
  • Large surface area for diffusion to occur over
• Blood

  Consists of a yellow fluid called plasma containing various components like hormones, dissolved glucose, mineral ions, proteins and red blood cells
• Function of the blood

  • Transport of oxygen and carbon dioxide
  • Transporting Hormones
  • Transporting platelets to damaged areas for blood clotting
  • Transporting glucose to cells that need them
  • Transporting waste products to excretory organs
• Tissue fluid

  Substances dissolved in plasma diffuse out through the capillary walls except red blood cells and proteins as they are too large and the fluid between the capillary and cells is the tissue fluid
• Plasma has high water potential

  This is called oncotic pressure which is the tendency of water to enter
• Blood is under pressure from being pumped out near the arteries

  This is called hydrostatic pressure which is greater than the oncotic pressure and causes fluid to leave the plasma to form tissue fluid and exchange takes place between the fluid and cells
• As blood travels away from the arteries and to the capillaries:

  
  

  The hydrostatic pressure drops but the oncotic pressure remains the same so the tissue fluid diffuses back into the blood vessel
• Lymph

  Tissue fluid that does not return to the vessel is known as lymph fluid and drains into lymph capillaries, they also pick up fatty acids from the vili of the intestines, they eventually are transported through one way valves and the squeezing of body muscles back into the blood. along the way there are lymph nodes that contains lymphocytes that produce antibodies that are needed and can intercept and pathogens that happen to be in the lymph.
• Enlarged lymph glands is evidence that the body is fighting against a pathogen
• Erythrocytes:

  • biconcave shape to increase surface area and allows them to pass through narrow gaps
  • Contain no other structures to maximise the amount of haemoglobin(Hb) that can be carried
• Need for specialised transport systems

  • SA:V is too small, increased diffusion distance and less surface area is available
  • metabolic demands are very high and simple diffusion is not fast enough to provide
  • Molecules like hormones may need to travel to different sections of the organism