module 3 (transport in animals)

• Open circulatory system


  • The transport medium is usually pumped directly to the open body cavity
  • There are very few transport vessels
• Closed circulatory system


  The transport medium remains inside of the vessels
• Single closed circulatory system


  • The blood only passes through the heart once per cycle
  • e.g. fish

  
• Double closed circulatory system

  • The blood passes through the heart twice per cycle
  • e.g. most mammals

  
• Tissue fluid


  • Liquid bathing all cells
  • Contains water, glucose, amino acids, fatty acids, ions and oxygen
  • Enables delivery of useful molecules to cells and removal of waste
• Tissue fluid formation


  1. At the arteriole end, the smaller diameter results in high hydrostatic pressure

  2. Small molecules forced out (ultrafiltration)

  3. Red blood cells/large proteins too big to fit through capillary gaps so remain
• Capillaries


  • Form capillary beds
  • Narrow diameter (1 cell thick) to slow blood flow
  • Red blood cells squashed against walls shortens diffusion pathway
  • Small gaps for liquid/ small molecules to be forced out
• Arterioles


  • Branch off from arteries
  • Thickest muscular layer to restrict blood flow
  • Thinner elastic layer and outer layer than arteries as pressure is lower
• Structure of arteries


  • Thick muscular layer
  • Thick elastic layer
  • Thick outer layer
  • Small lumen
  • No valves
• Capillary endothelium


  • Flat (squamous) cells
  • One cell thick
  • Contains small gaps for small molecules to pass through (e.g. glucose, oxygen)
• Different types of blood vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins

  
• Reabsorption of tissue fluid

  1. Large molecules remaining in capillary lower its water potential

  2. Towards venule end there is a lower hydrostatic pressure due to a loss of liquid

  3. Water is reabsorbed back into capillaries by osmosis

  4. Not all liquid will be reabsorbed by osmosis as equilibrium will be reached
• Role of the lymph in tissue fluid reabsorption

  Excess tissue fluid is absorbed into the lymphatic system to form lymph and drains back into the bloodstream and deposited near the heart

  
• Structure of the heart

  • Cardiac muscle
  • Walls of heart have a thick muscular layer
  • Unique because it is: myogenic- can contract and relax without nervous or hormonal stimulation, never fatigues- so long as adequate oxygen supply
• Coronary arteries


  • Blood vessels supplying cardiac muscle with oxygenated blood
  • Branch off from aorta
  • If blocked, cardiac muscle will not be able to respire, leading to myocardial infarction (heart attack)
• Pericardial membranes


  • Inelastic membranes surrounding the heart
  • Prevent the heart from filling and swelling with blood

  
• Adaptation of the left ventricle

  • Has a thicker muscular wall in comparison to right ventricle
  • Enables larger contractions of muscle to create higher pressure
  • Ensures blood reaches all body cells

  
• Veins connected to the heart

  • Vena cava- carries deoxygenated blood from body to right atrium
  • Pulmonary vein- carries oxygenated blood from lungs to left atrium

  
• Arteries connected to the heart

  • Pulmonary artery- carries deoxygenated blood from right ventricle to lungs
  • Aorta- carries oxygenated blood from left ventricle to the rest of the body

  
• Valves within the heart

  • Semilunar valves are located in aorta and pulmonary artery near the ventricles
  • Atrioventricular valves between atria and ventricles
• Opening and closing of valves

  Valves open if the pressure is higher behind them compared to infront of them
• Cardiac output


  • Volume of blood which leaves one ventricle in one minute
  • cardiac output=heart rate x stroke volume

  
• Stroke volume


  Volume of blood that leaves the heart each beat
• Cardiac cycle


  Consists of diastole, atrial systole and ventricular systole

  
• Diastole


  1. Atria and ventricular muscles are relaxed

  2. Blood enters the atria via the vena cava and pulmonary vein

  3. This increases pressure in the atria

  
• Atrial systole


  1. Atria muscular walls contract, increasing pressure

  2. The pressure in the atria becomes greater than the pressure in the ventricles

  3. The atrioventricular valves open and blood flows into the ventricles

  4. Ventricular muscle relaxed

  
• Ventricular systole


  1. Ventricular muscular walls contract

  2. Pressure in the ventricle becomes greater than the atria pressure

  3. Atrioventricular valves close and semi-lunar valves open

  4. Blood is pumped into the artery

  
• Tachycardia


  • When the heart is beating over 100bpm
  • This is normal during exercise but would be abnormal during rest
• Bradycardia


  • When the heart is beating at less than 60 bpm
  • If the heart rate drops too low, an artificial pacemaker is needed to regulate the heart rate
• Fibrillation


  This is when there is an irregular rhythm of the heart
• Ectopic heartbeat


  Additional heartbeats that are not in rhythm
• ECG


  • An ECG measures the waves of depolarisation
  • Can be used to diagnose irregularities in heart rhythm
  • Electrodes are stuck onto the skin to detect electrical activity

  
• Sinoatrial node (SAN)


  • Located in right atrium and is known as the pacemaker
  • Releases wave of depolarisation across the atria, causing muscles to contract
• Atrioventricular node (AVN)


  • Located near the border of the right/ left ventricle within atria
  • Releases another wave of depolarisation after a short delay when it detects the first wave from the SAN
• Bundle of His


  • Runs through septum
  • Can conduct and pass the wave of depolarisation down the septum
• Purkyne fibres


  • In walls of ventricles
  • Spread wave of depolarisation through ventricle walls
  • The muscular walls of ventricles contract from the bottom up

  
• Role of non-conductive tissue

  • Located between atria and ventricles
  • Prevents wave of depolarisation travelling down to ventricles
  • Causes slight delay in ventricle contraction

  
• Irregular rhythm of the heart


  Additional heartbeats that are not in rhythm
• ECG


  Measures the waves of depolarisation
• ECG


  Can be used to diagnose irregularities in heart rhythm