Animal Transport 2

• Cardiac cycle = sequence of events of one heartbeat
• 3 stages of cardiac cycle:

  • atrial systole
  • ventricular systole
  • diastole
• Atrial systole:

  • atrium walls contract and the blood pressure in the atria relaxes
  • pushes the blood through the tricuspid and bicuspid valves down into the ventricles, which are relaxed
• Ventricular systole:

  • ventricle walls contract and increase the blood pressure in the ventricles
  • this forces the blood up through the semi-lunar valve, out of the heart, into the pulmonary artery and the aorta
  • blood cannot flow back from the ventricles into the atria as the tricuspid and bicuspid valves are closed by the rise of pressure in the ventricles
  • Pulmonary artery carries deoxygenated blood to the lungs and aorta carries oxygenated blood to the rest of the body
• Diastole:

  • ventricles and atria relax
  • volume of ventricles and atrium increases -> pressure in the ventricles and atrium falls
  • risks the blood in the pulmonary artery and aorta from falling back into the ventricles
  • tendency to flow backwards causes the semi-lunar valve to shut
  • Atriums also relaxes -> blood from vena cava and pulmonary vein enters the atria and the cycle begins again
• Heartbeat = complete contraction and relaxation of the whole heart
• Two sides of the heart work together

  • atria contract at the same time followed by the ventricles
  • when a chamber contract, it is emptied of blood, relaxes-> filled with blood
• • atria walls have little muscle as they only have to push the blood to the ventricles
  • left ventricles have thicker muscles than the right ventricle
  • this is because the left ventricle have to pump the blood around the entire body whereas the right ventricle has to pump the blood to the lungs
• Flow of blood (left side):

  • left atrium relaxes -> receives oxygenated blood from the pulmonary vein
  • when full, pressure forces open the bicuspid valve
  • relaxation of the left ventricle draws blood from the left atria
  • left atrium contracts -> pushes the remaining blood into the left ventricle through the valve
  • left atrium relaxed and bicuspid valve shut, to prevent back flow to the atria -> left ventricle contracts
  • pressure (from strong muscular walls) pushes blood up out of the heart through the semi-lunar valve into the aorta
• sino-atrial node (SAN) = cluster of specialised cardiac cells in the walls of the right atrium, which acts as a pacemaker
• atrio-ventricular node (AVN) = only conducting area of tissue in the wall of the heart between atria and ventricle (septum)
• Control of heartbeat:

  • Wave of electrical stimulation arises at the sino-atrial node and spreads over both atria so they contract together, causing atrial systole
  • Electrical stimulation only spreads to the ventricle from the atrio-ventricular node, introducing a delay in transmission of the electrical impulse
  • Muscles of the ventricles don’t begin to contract until muscles at the atria have finished contracting
  • Atrio-ventricular node passes the excitation down the nerves of the bundle of His and to the apex of the heart
  • Excitation is transmitted to Purkinje fibres in the ventricle walls, which carry it upwards through the muscles of the ventricle wall
  • Impulses cause the cardiac muscle in each ventricle to contract simultaneously, from the apex upwards, pushing blood up to the aorta and pulmonary artery, emptying the ventricles
• Electrocardiogram (ECG) = trace of the voltage changes produced by the heart, detected by the electrodes on the skin
• Tissue fluid = fluid that surrounds cells in tissues and is a mixture of plasma and fluid
• Blood under pressure from the aorta due to the left ventricle contracting
• Blood has a higher hydrostatic pressure compared to osmotic pressure, causing water and solutes to move out of the capillary down a concentration gradient by osmosis to the tissue surroundings
• Solute, like mineral ions, diffuse into the tissue while waste products, such as carbon dioxide and urea, leave the tissue
• As blood moves through the capillary, pressure decreases, making osmotic pressure greater than hydrostatic pressure, leading to water and waste products moving back into the capillaries through osmosis
• 10% of the fluid drains into the lymph capillaries of the lymphatic system, eventually returning to the venous system through the thoracic duct, which empties into the left subclavian vein above the heart
• In tissue fluid formation, red blood cells and plasma proteins are too big to pass the endothelial cell so they remain in the blood, which increase solute concentration as the blood moves across the capillary -> reason why tissue fluid is yellow instead of red
• Tissue fluid:

  • bathes all cells
  • supply oxygen, glucose, hormones/ions to cell
  • remove waste from cells
  • Helps maintain a constant environment around cell
• Action potential/ wave of depolarisation = when the cardiac muscle receives an electrical impulse-> leads to cardiac muscle contract (systole)