transport in animals

• in a single circulatory system, blood flows through the heart once for each circuit of the body
• in a double circulatory system blood passes through the heart twice for each circuit of the body
• in single circulatory system:

  • blood pressure drops
  • limits efficiency of exchange process
  • fish use it as they have lower needs that are supported but gaseous exchange
• in a double circulatory system:

  • pulmonary circulation is movement of blood to lungs
  • systematic circulation is movent of blood which carries oxygen and nutrients to tissues
  • high pressure maintained
  • effective movement of nutrients
  • two separate pressures, a lower one for pulmonary in order to not damage lungs delicate capillarys
• in an open circulatory system - blood is not held in vessels
• open circulatory system:

  • transport medium passes through the haemocoel (body cavity)
  • directly bathes tissues and cells in blood
  • transport system has low pressure
  • returns to heart through open-ended vessel
• • insect blood is called hemolymph
  • does not carry dissolved gasses
  • transports food and nitrogenous waste
  • enters heart through Ostia
  • pumps towards head through peristalsis
  • pours out into the body cavity
• disadvantages of an open circulatory system:

  • low blood pressure
  • slow blood flow
  • circulation affected by body movement or lack of
• in a closed circulatory system blood is held in vessels
• closed circulatory system:

  • tissue fluid bathes tissues and cells
  • heart pumps blood under pressure
  • substances transported by blood enter and leave by diffusion
  • contain blood pigment that carry respiratory gases
• advantages of a closed circulatory system:

  • high pressure
  • fast blood flow
  • rapid delivery of nutrients
  • rapid removal of waste
  • transport is independent of body movements
• arteries:

  • carry blood away from the heart
  • blood is at high pressure
  • artery wall is thick
  • lumen is relatively small
• wall in arteries:

  • inner layer, thin layer of elastic tissue (for stretch & recoil to maintain blood pressure)
  • middle layer, thick layer of smooth muscle
  • outer layer, thick layer of collagen & elastic tissue (provides strength to withstand high pressure & recoil to maintain pressure)
• arterioles:

  • small blood vessels
  • distribute blood from arteries to capillaries
  • walls contain a layer of smooth muscle
  • contraction constricts diameter, this increases resistance to flow & reduces rate of flow
  • constriction diverts flow of blood to regions demanding more oxygen
• capillaries:

  • very thin walls
  • exchange between blood & tissue fluid
  • narrow lumen, red blood cells squeezed against walls helping transfer of oxygen by reducing diffusion path
  • walls have single layer of flattened endothelial cells
  • walls are leaky, allowing blood plasma to leave
• venules:

  • collect blood from capillary bed, leading into veins
  • walls have thin layer of collagen, muscle & elastic tissue outside endothelium
• veins:

  • carry blood to heart
  • blood is at low pressure
  • thin walls
  • lumen is large to ease blood flow
  • walls have collagen, smooth muscle & elastic tissue (less than arteries)
  • walls do not need to stretch & recoil, not actively constricted
  • contain valves to prevent backflow
  • can be flattened by surrounding skeletal muscle that applies pressure
• hydrostatic pressure is the pressure that a fluid exerts on walls of a blood vessel
• oncotic pressure is the pressure exerted by the fluid in the capillarys
• tissue fluid is the fluid surrounding cells and tissues containing blood plasma and dissolved substances it is formed by plasma leaking from capillaries
• formation & return of tissue fluid:

  • at arterial end, blood has high hydrostatic pressure, pushing blood out of capillarys
  • at venous end, hydrostatic pressure is lower so oncotic pressure allows some of tissue fluid to re-enter the blood
• lymph system:

  • some tissue fluid is redirected into the lymphatic system
  • drains excess tissue fluid returning it to blood system in subclavian vein in chest
  • fluid is called lymph, it contains more lymphocytes produced in the lymph nodes
• haemoglobin: a red protein/pigment responsible for transporting oxygen in the blood. Its molecule comprises four subunits, each containing an iron ion bound to a haem group.
• partial pressure is the pressure exerted by a specific gas
• the higher the PO2, the greater the affinity between Hb and O2
• oxygen dissociation curve shows how much oxyen is carried at different partial pressures of oxygen (PO2)
• Valves:

  • prevent blood backflow.
  • only open one way.

  high pressure behind of valve - valve forced open.

  High pressure in front of valve - valve forced shut.
• Atria are thin walled chambers that receive blood from veins. They contract first so they can fill ventricles with blood. Atrial contraction is not strong enough to pump blood out on its own.
• Ventricles are thicker-walled chambers which pump blood out of heart. Ventrical walls have muscle fibres arranged in layers around the chamber. This allows them to contract strongly when stimulated together as a unit.
• The right side of the heart pumps deoxygenated blood to lungs where CO2 diffuses out and O2 diffuses in. The left side of the heart receives oxygenated blood from lungs and pumps it round body tissues.
• Ventricles have thicker walls than atria as they need to be able to push blood out into arteries. Ventricals contract second because it takes longer for them to fill up with blood compared to atria.
• atrial systole:

  • Atria contract
  • decrease in atrial volume in and increase in atrial pressure.
  • Causes blood to be pushed into ventricles via atrioventricular valves.
  • Slight increase in ventricular volume and pressure as ventricles receive ejected blood from contracting atria.
• ventricular systole:

  • ventricles contract, pushing blood out of the heart
  • decreases ventricular volume and increases ventricular pressure.
  • atrioventricular valves shut to prevent backflow due to higher pressure in ventricles and atria.
  • High pressure in ventricles opens semi lunar valves
  • blood forced into pulmonary artery and aorta.