Circulation and Respiration

• Physiological processes


  • food, water intake
  • oxygen intake
  • elimination of carbon dioxide
  • nutrients, water, salts
  • oxygen
  • carbon dioxide
  • elimination of food residues
  • rapid transport to and from all living cells
  • elimination of excess water, salts, wastes
• Digestive system


  Processes food, water, nutrients, and eliminates food residues
• Respiratory system


  Processes oxygen intake and carbon dioxide elimination
• Circulatory system


  Rapidly transports substances to and from all living cells
• Urinary system

  Eliminates excess water, salts, and wastes
• Aerobic respiration


  Oxygen is needed, carbon dioxide is produced
• Human respiratory system


  • Trachea is lined by ciliated, pseudostratified columnar epithelium
  • Epithelium rests on connective tissue which may include blood vessels, that provide heat-exchange to help condition the air
  • Incomplete rings of hyaline cartilage encircle the trachea
• Concentration gradients for gases

  Gases diffuse down their pressure gradients
• Pressure

  • Pressure exerted by the weight of the air on objects on Earth's surface
  • At sea level = 760 mm Hg
  • Oxygen is 21% of air; its partial pressure is about 160 mm Hg
• Boyle's law


  Pressure of a gas in a closed container is inversely proportional to the volume of the container
• Inspiration and expiration


  1. Diaphragm flattens

  2. External intercostal muscles contract

  3. Volume of thoracic cavity increases

  4. Lungs expand

  5. Air flows down pressure gradient into lungs
• Boyle's law is important because it helps us understand the relation between pressure and volume in the lungs when breathing
• Alveolus


  • Air space inside
  • Pore for airflow between alveoli
  • Red blood cell
  • Alveolar epithelium
  • Capillary endothelium
  • Fused basement membranes of both epithelial tissues
• Alveoli


  Lung air sacs made of simple squamous epithelial cells for easy diffusion of gases
• Respiratory membrane


  Capillaries and alveoli form the respiratory membrane for the exchange of gases between the blood and the lungs
• Exchange of respiratory gases (external and internal respiration)

  1. O2: alveolus -> blood -> cell

  2. CO2: cell -> blood -> alveolus
• Partial pressures involved in respiration

  • External
  • Internal
• The PO2 of blood pumped into systemic capillaries is higher (105 mmHg) than the PO2 in tissue cells (40 mmHg at rest) because the cells constantly use O2 to produce ATP
• Due to the pressure difference, oxygen diffuses out of the capillaries into tissue cells and blood PO2 drops to 40 mmHg by the time the blood exits systemic capillaries
• While O2 diffuses from the capillaries into tissue cells, CO2 diffuses in the opposite direction
• Because tissue cells are constantly producing CO2, the PCO2 of cells (45 mmHg at rest) is higher than that of capillary blood (40 mmHg)
• As a result, CO2 diffuses from tissue cells through interstitial fluid into capillaries until the PCO2 in the blood increases to 45 mmHg
• Transportation of respiratory gases in respiration


  • External
  • Internal
• Role of erythrocytes in the transportation of oxygen and carbon dioxide


  • 97% of O2 is bound to hemoglobin in RBCs, only 3% is dissolved
  • Higher PO2 means more O2 binds to Hb, lower PO2 means less O2 binds to Hb
• Carbon dioxide transport


  • Most CO2 is transported as bicarbonate
  • Some binds to hemoglobin
  • Small amount dissolves in blood
• Lung volumes


  Tidal Volume (VT), Expiratory Reserve Volume (ERV), Inspiratory Reserve Volume (IRV), Residual Volume (RV)
• Lung capacities


  Inspiratory Capacity (IC), Functional Residual Capacity (FRC), Vital Capacity (VC), Total Lung Capacity (TLC)
• Tidal volume


  Amount of air that moves in and out of the lungs during normal quiet breathing
• Expiratory Reserve Volume (ERV)


  Amount of air that is in the lungs after normal quiet breathing
• Inspiratory Reserve Volume (IRV)


  Amount of air that can still be brought into the lungs after normal quiet breathing
• Residual Volume (RV)


  Amount of volume that cannot be exhaled and is always trapped in the lungs
• Fick's 1st Law of Diffusion

  Rate of diffusion across a membrane is proportional to the surface area, difference in partial pressures, and inversely proportional to the distance
• The enormous number of alveoli (approx 300 million in per lung), increases the amount of gas that can diffuse into and out of the lungs
• Respiratory surfaces are extremely thin
• Concentration gradients allow gas exchange during respiration (↑ PO2 at lungs and ↓ at tissues, ↑ CO2 at tissues and ↓ at lungs)
• Surface area to volume ratio


  All animal body plans promote favourable rates of inward diffusion of O2 and outward diffusion of CO2
• Ventilation

  Large-bodied, active animals have huge demands for gas exchange, more than diffusion alone can satisfy. Diverse adaptations make exchange rate more efficient
• Transport pigments

  Rates of gas exchange get a boost with transport pigments (Hb transports oxygen from lungs to cells, Mb has oxygen storing capacity)
• Advantages and disadvantages of water and air as a medium for gaseous exchange


  • Air contains more oxygen than water
  • Water has a higher viscosity than air, increasing the work required to pump the fluid
  • High rate of diffusion of oxygen in air - 10 000 times as rapid as in water
• Gills

  Thin tissue filaments that are highly branched and folded, allow rapid diffusion of dissolved oxygen in water into the bloodstream