Week 3 & 4: Respiratory physiology

Pulmonary Ventilation (breathing)

  • Inhalation and exhalation of air
  • Exchange of air between the atmosphere and the lungs
  • Air flows between the atmosphere & alveoli because of alternating pressure differences, caused by:
    • contraction/relaxation of respiratory muscles
    • alveolar surface tension
    • compliance of the lungs
    • airway resistance

External Respiration • Exchange of gases between the alveoli and blood • Needs to meet the respiratory demands of tissues and organs

Internal Respiration • Exchange of gases between the blood and cells of tissues • Absorption of O2 and production of CO2 + water + energy

Upper Respiratory System

Nasal Cavity
  • Warms, moistens, filters air
  • Detects olfactory stimuli
  • Modifies speech vibrations
Oral cavity
Pharynx (throat)
  • Nasopharynx
  • Oropharynx
  • Laryngopharynx

Lower respiratory System

Trachea
  • Passageway for air
  • Contains C-shaped rings of cartilage
Bronchi
  • Primary Bronchi
  • Lobar Bronchi
  • Segmental Bronchi
  • Larger Bronchioles
  • Smaller Bronchioles
  • Terminal Bronchioles
Lungs
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveoli

 

Conducting Zone - All structures that provide passageways for air to travel into and out of lungs

Respiratory Zone - Site of O2 and CO2 exchange with the blood

Boyle’s Law - ‘for a fixed mass of enclosed gas at a constant temperature, the product of PRESSURE (P) & VOLUME (V) remains contact (k)’

inverse relationship between PRESSURE and VOLUME

Equation: P1V1=P2V2

Inspiration:

For inhalation to occur the volume in lungs must increase, results in a pressure change in lungs below that in atmosphere.

  • Diaphragm contracts and flattens
  • Pressure reduces
  • Volume increases
  • Inhalation is an active process requiring muscle activity and energy

Expiration:

Passive process, requiring pressure change and tissue elastic recoil.

Elastic recoil of the chest wall and lungs reduces the volume - natural tendency to recoil

To cause the movement of air into the lungs it needs to move down a pressure gradient, therefore lung volume must increase (same amount of air but larger volume of space) to decrease pressure and enable the air to move down a pressure gradient.

Factors affecting ventilation:

  1. surface tension of alveolar fluid
  2. compliance of the lungs
  3. airway resistance

Exchange of O2 and CO2 between alveoli and blood, and blood and tissues occurs by Passive diffusion. This process is governed by 2 gas laws:

  1. Dalton’s Law- Total pressure of a mixture of gases is the sum of the pressures of individual gases
  2. Henry’s Law- quantity of a gas that will dissolve in a liquid is directly proportional to the PP of the gas & its solubility. The ability of a gas to stay in solution is greater when its PP is higher and solubility is higher

Factors that determine the R of Exchange:

  1. surface area of the alveoli,
  2. diffusion distance
  3. molecular weight & solubility

Oxygen transport

  • PP of O2 will determine how much O2 binds- higher the PO2, the more O2 binds

   

Sigmoidal shape because as 1 O2 binds, it becomes progressively easier for more to bind- causing a plateau - cooperative binding.

Factors that affect O2 binding:

  1. Acidity (pH)- The Bohr Effect causes a shift in curve due to a pH change
    • As pH decreases (↑acidity), O2 dissociates from Hb more easily
    • As pH increases(↓acidity), O2 binds more readily with Hb

   Common metabolic acids include:

  • Lactic Acid-↑H+
  • Carbonic Acid-↑H+

   Hb acts as a buffer for H+ → H+ ions bind with Hb molecules to cause a shape Δ - with a less strong ‘grip’ on the O2 molecules.

   ⬇️ pH (↑ H+ ions) causes decreased O2 saturation ∴ shifts dissociation curve to the right

    

  1. Partial pressure of CO2

   CO2 binds to Hb

  • As PCO2 ↑, Hb release more O2
  • CO2 is temporarily converted to carbonic acid (H2CO3)
  • As H+ ↑ the BÕR effect occurs

    

  1. Temperature

   As temperature increases, more O2 is released from Hb

  • Metabolically active tissues require more O2
  • More acids and H+ are created, pH is reduced and O2 is released from Hb

      

  1. BPG

   Metabolite of carbohydrate metabolism in RBCs

  • Acts as an inhibitor that binds to the Hb structure -
  • An increase causes the curve to shift to the right (decreased saturation) under the following conditions:

     • Exercise

     • Drop in blood pH

     • Increase in thyroid hormones & growth hormone

  • Foetal Hb has a poor binding of BPG hence greater affinity for O2 than the mother