Transport in Animals

  • Created by: charley
  • Created on: 28-08-18 17:29

Control of the heartbeat and the electrocardiogram

The sino-atrial node is located in the wall of the right artium. Electrical sitmulation arises at the SAN causing the atria to contract. The atrio-ventricular node spreads the stimulation to the bundle of His after causing a delay. Its then passed to the Purkinje fibres in the ventricle walls where its carried through the muscle causing the ventricles to contract from the apex up. 

  • The P wave shows the voltage generated by the SAN
  • The PR interval is the time taken for the excitation to spread through the AVN
  • The QRS complex shows the depolarisation and contraction of the ventricles
  • The ST segment is the interval between ventricular depolarisation and repolarisation
  • The T wave shows the repolarisation of the ventricles
  • The isoelectric line is the baseline of the trace, the line between the T wave and the P wave

A person with atrial fibrillation has a rapid heart rate and may lack a P wave

A person whos had a heart attack may have a wide QRS complex

A person with enlarged ventricle walls may have a QRS complex with greater voltage change

Changes in the height of the ST segment and T wave may be related to insufficient blood being delivered to the heart

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Transportation of carbon dioxide

Carbon dioxide is transported in plasma, as the hydrogen carbonate ion and bound to heamoglobin as carbamino-haemoglobin.

  • Carbon dioxide in the blood diffuses into the red blood cell
  • Carbonic anhydrase catalyses carbon dioxide and water forming carbonic acid
  • Carbonic acid dissociates into H+ and HCO3- ions
  • HCO3- diffuse out of the red blood cell into the plasma
  • Chloride ions diffuse into the cell from the plasma to maintain electrochemical neutrality 
  • H+ ions cause oxyhaemoglobin to dissociate. The H+ ions combine with haemoglobin making haemoglobinic acid
  • Oxygen diffuses out of the red blood cell into the tissues
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Intercellular/Tissue Fluid

Fluid from the plasma is tissue fluid. It bathes the cells supplying them with solutes and removing waste made by the cells.

At the arterial end of the capillary bed:

  • The high hydrostatic pressure pushes liquid out from the capillary to around the cells
  • Plasma has a low solute potential so tends to pull water back into the capillary 
  • The hydrostatic pressure is geater than the solute potential so water and solutes are forced out 
  • Solutes are used up so their concentration is low in and around the cell, favoiuring diffusion from the capillaries

At the venous end of a capillary bed:

  • The hydrostatic pressure is lower becuase much fluid has been lost
  • Plasma proteins are more concentrated so the solute potential is more negative
  • The osmatic force pulling water into the capillary is greater than the hydrostatic pressure so water returns to the capillaries
  • Tissue fluid picks up carbon dioxide and waste which dissuse into the capillaries down a concentration gradient

Some tissue fluid drains into the lymph capillaries of the lymphatic system. The fluid becomes lymph. It then returns to the venous system through the thoracic duct which empties into the left subclavian vein above the heart.

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