🫀Biology Unit 4 Transport

• Components of the heart

  • Sinoatrial node (SAN)
  • Atrioventricular node (AVN)
  • Bundle of His

  
• Components of blood

  • Plasma
  • Erythrocytes
  • Leucocytes (neutrophils, eosinophils, monocytes and lymphocytes)
• Functions of blood

  • Transport
  • Defence
  • Formation of lymph and tissue fluid
• Tissue fluid

  • Transfer of materials between the circulatory system and cells
  • Interchange of substances through the formation and reabsorption of tissue fluid, including the effects of hydrostatic pressure and oncotic pressure
  • Tissue fluid that is not reabsorbed is returned to the blood via the lymph system
• Roles of inorganic ions in plants

  • Nitrate ions - to make DNA and amino acids
  • Phosphate ions - to make ADP and ATP
  • Calcium ions - to form calcium pectate for the middle lamellae
  • Magnesium ions - to produce chlorophyll
• Alveoli

  • many alveoli increase surface area
  • folded to increase surface area
• Ventilation in humans

  1. Muscle contractions increase the volume of the thorax

  2. Decreases the pressure in the lungs (by Boyle's law)

  3. Causes air to move in

  4. Air flows in and out by the same route
• Air always flows from a high pressure to a low pressure

  
• Inspiration

  1. Diaphragm contracts and flattens downwards

  2. External intercostal muscles contract, pulling the ribs up and out

  3. Increases the volume of the thorax and the lungs, and stretches the elastic-walled alveoli

  4. Decreases the pressure of air in the alveoli below atmospheric

  5. Air flows in from high pressure to low pressure

  
• Normal expiration

  1. Diaphragm relaxes and curves upwards

  2. External intercostal muscles relax, allowing the ribs to fall

  3. Decreases the volume of the thorax and the lungs, and allows the alveoli and bronchioles to shrink by elastic recoil

  4. Increases the pressure of air in the alveoli above atmospheric

  5. Air flows out from high pressure to low pressure
• Forced expiration

  1. Abdominal muscles contract, pushing the diaphragm upwards

  2. Internal intercostal muscles contract, pulling the ribs downward

  3. Gives a larger and faster expiration, used in exercise
• Pulmonary ventilation

  The volume of air ventilating the lungs each minute
• Ventilation rate

  Calculated from the pressure graph by measuring the time taken for one ventilation cycle
• Tidal volume


  The normal volume of air breathed in each breath

  
• Gas exchange

  • Passive, uses diffusion, gases move down their own concentration gradients, slow
• Ventilation

  • Active, uses mass flow, all gases in air move together in one direction, quick
• Fish gills

  • Composed of thousands of filaments covered in feathery lamellae, each only a few cells thick containing blood capillaries, giving a large surface area and short distance for gas exchange

  
• Ventilation in fish

  Water enters through the mouth but exits through the opercula valves, a one-way ventilation necessary because water is denser and more viscous than air
• Inspiration in fish

  Mouth opens, muscles in the mouth and opercula contract, increasing the volume of the buccal and opercular cavities, decreasing the pressure of water, causing water to flow in through the open mouth and over the gills from high pressure to low pressure
• Expiration in fish

  Mouth closes, mouth and opercular muscles relax, decreasing the volume of the buccal cavity, increasing the pressure of water, forcing the opercula valves open and water to flow out over the gills and through the opercula valve from high pressure to low pressure
• Water always flows from a high pressure to a low pressure in fish ventilation
• Counter-current exchange in fish gills

  • Blood flows towards the front of the fish while water flows towards the back, maintaining a higher concentration of oxygen in the water than in the blood, allowing 80% of the dissolved oxygen to be extracted
• Insect gas exchange

  • Insects have openings called spiracles that lead to a network of tubes called tracheae and tracheoles that carry air directly to the cells, with the smallest tracheoles penetrating the cells

  
• Insect ventilation

  • Small insects rely on diffusion, larger insects use muscles to squeeze their abdomen and suck air in and out of the spiracles
• Insects can close their spiracles using a muscular valve to counteract water loss
• Plant gas exchange

  • Main gas exchange surfaces are the spongy mesophyll cells in the leaves, which have a huge surface area and short diffusion distance, and are ventilated by exposure to the air
• Stomata

  Pores in the leaf surface that allow gases to enter and leave the leaf
• Opening of stomata

  K+ ions are actively pumped into the guard cells, lowering the solute potential, causing water to diffuse in by osmosis, making the guard cells turgid and forcing the stomata open
• Lenticels

  • Loosely-packed cells with air spaces between them in woody plant stems, serving the same function as stomata in leaves
• Mass transport

  A fluid (liquid or gas) moves in a particular direction due to a force, with the fluid and everything dissolved or suspended in it moving in the same direction at the same speed, requiring energy but being fast
• Diffusion

  Solutes move in random directions due to their thermal energy, with a concentration difference resulting in the substance diffusing down its concentration gradient, being very slow and only useful over small distances
• Evolution of circulatory systems

  • Small invertebrates rely on diffusion
  • Many invertebrates have an open circulatory system with haemolymph
  • Vertebrates have a closed circulatory system, with fish having a simple single circulatory system, amphibians and reptiles having a double circulatory system with a three-chambered heart, and mammals and birds having an efficient double circulatory system with a four-chambered heart
• Amphibians and reptiles

  • Have lungs instead of gills
  • Have a double circulatory system that pumps blood separately to the lungs and the rest of the body
  • Only have a three-chambered heart, so the oxygenated and deoxygenated blood mix in the single ventricle, so gas exchange is not very efficient
• Mammals and birds

  • Have a double circulatory system, with a four-chambered heart
  • One side of the heart pumps blood to the lungs only and is called the pulmonary circulation
  • The other side of the heart pumps blood to the rest of the body – the systemic circulation
  • This double circulatory system is more efficient as the oxygenated and deoxygenated blood don't mix
  • The blood in the systemic circulation is pumped to the body's cells at high pressure, allowing for fast gas exchange
  • This in turn permits fast respiration and a more active, warm-blooded lifestyle
  • Mammals and birds evolved from different reptile ancestors, so their four-chambered hearts evolved independently – an example of convergent evolution
• Human circulatory system

  • Double circulatory system with a 4-chambered heart
  • Right side of the heart pumps blood to the lungs only (pulmonary circulation)
  • Left side of the heart pumps blood to the rest of the body (systemic circulation)

  
• Heart

  • Four chambers: two thin-walled atria on top which receive blood, and two thick-walled ventricles underneath which pump blood
  • Veins carry blood into the atria and arteries carry blood away from the ventricles
  • Between the atria and the ventricles are atrioventricular valves which prevent back-flow of blood
  • Left valve has two flaps and is called the bicuspid (or mitral) valve, right valve has 3 flaps and is called the tricuspid valve
  • Valves are held in place by valve tendons ("heart strings") attached to papillary muscles
  • There are also two semi-lunar valves in the arteries called the pulmonary and aortic valves
  • Left and right halves of the heart are separated by the inter-ventricular septum
  • Walls of the right ventricle are 3 times thinner than on the left and it produces less force and pressure in the blood
• Cardiac muscle

  • Composed of cells called myocytes
  • When myocytes receive an electrical impulse they contract together, causing a heartbeat
  • Myocytes are constantly active so have a great requirement for oxygen, fed by numerous capillaries from two coronary arteries
• Cardiac cycle

  1. Atrial systole: SAN contracts and transmits electrical impulses throughout the atria, which both contract, pumping blood into the ventricles

  2. Ventricular systole: Electrical impulse passes from the atrioventricular node (AVN) to the Purkinje fibres, with a short delay, then the ventricles contract from the bottom up, squeezing blood upwards into the arteries

  3. Diastole: Atria and ventricles relax, while the atria fill with blood

  
• Electrocardiogram (ECG)

  • Recording of the electrical activity of the heart
  • Characteristic pattern of peaks and troughs each cycle, labelled PQRST, caused by specific events in the cardiac cycle
  • Changes in these ECG waves can be used to help diagnose problems with the heart
• Cardiac output

  • Amount of blood flowing through the heart each minute
  • Calculated as the product of the heart rate and the stroke volume