What are the major factors that effect pulmonary vascular resistance in the normal lung?

  • Increased Art or Ven Pressure (A > V)
  • Lung volume ( U/J shaped curve)
  • Alveolar hypoxia > increased PVR via hypoxic vasoconstriction
  • Vascular Smooth Muscle Tone – response to endogenous/ exogenous factors
  • Area of lung (apex partic < base)
  • Position change

Pass Criteria:

  • Must list 3 properties

Why is pulmonary flow so sensitive to pulmonary vascular pressures?

  • V low Pressure system – few resistance vessels
  • Easily distensible vessels
  • Recruitment
  • Only just enough P for normal gravity/ position to get apical flow

Pass Criteria:

  • 2 out of 4 to pass


Draw the curve demonstrating the relationship between O2 concentration v pO2
Prompt: How does this change in anaemic and polycythaemic individual?

respiratory 1

What is the effect of carbon monoxide on these curves?

respiratory 2


What are the physiological changes that allow survival at high altitude?

  1. Hyperventilation >  decreases CO2, > O2
  2. Increased Hb (> EPO ),
  3. Alkalosis moderated by movement of  bicarbonate from CNS (1-2/7) and renal excretion
  4. Increased  2,3,DPG – R shift,
  5. Pulm hypertension (due to alveolar hypoxia inducing pulm vasoconstriction)  –
  6. RV hypertrophy – not really an “adaptation”
  7. Decreased work of breathing

Pass Criteria:

  • 3 of 7 to pass


Describe the distribution of blood flow in the lung of an upright subject at rest

  • Decreases linearly from base to apex
  • Due to hydrostatic pressure
  • Under normal conditions, flow almost ceases at apex
  • Distribution more uniform with exercise
  • Explanation of West’s zones 1 – 3  +/- zone 4
  • Zone 4 only at very low lung volumes

Pass Criteria:

  • Bold to pass

What are the main determinants of flow in these three zones?

  1. Zone 1  PA>Pa>Pv(not under normal conditions and is  alv. dead space)
  2. Zone 2   Pa>PA>Pv (recruitment)
  3. Zone 3  Pa>Pv>PA (distension + recruitment)

Pass Criteria:

  • Identify 3 pressures and their relationship to pass

How does the distribution of blood change when the subject becomes supine?

  • Blood flow from base to apex is almost uniform but flow in posterior segments exceeds that in anterior segments


How is carbon dioxide transported from the tissues to the lungs?

  • In plasma:
    • Dissolved
    • Carbamino compounds with plasma protein.
    • Hydration – H+ buffered – HCO3 in plasma.
  • In red blood cells:
    • Dissolved.
    • Formation of carbamino–Hb.
    • Hydration – H+ buffered – 70% of HCO3 enters plasma.
  • Of the approximately 49 mL of CO2 in each decilitre of arterial blood, 2.6 mL (5%) is dissolved, 2.6 mL (5%) is in carbamino compounds, and 43.8 mL (90%) is in HCO3
  • In the tissues, 3.7 mL of CO2 per decilitre of blood is added; 0.4 mL (10%) stays in solution, 0.8 mL (20%) forms carbamino compounds, and 2.5 mL (70%) forms HCO3
  • The pH of the blood drops from 7.40 to 7.36.

Pass Criteria:

  • Bolded

What is meant by the term ‘chloride shift’?

  1. About 70% of the HCO3 formed in the red cells enters the plasma in exchange for Cl. The exchange is called the chloride shift.
  2. This process is mediated by Band 3, a major membrane protein and is essentially complete in 1 second.
  3. Note that for each CO2 molecule added to a red cell, there is an increase of one osmotically active particle–either an HCO3 or a Cl–in the red cell. Consequently, the red cells take up water and increase in size.

Pass Criteria:

  • Bolded


What is the role of central chemoreceptors in control of ventilation?

  • Located near ventral surface of medulla
  • Rise in blood CO2 increases CO2 in CSF
  • CSF has poor buffering capacity so pH changes rapidly
  • Liberated Hions stimulate chemoreceptors (increasing pH has reverse effect)
  • Efferents stimulate medullary respiratory centre to increase ventilation and return CO2 to normal
  • Chronic CO2 elevation gives normal CSF pH and insensitivity

Pass Criteria:

  • Bolded to pass

What is the role of the peripheral chemoreceptors?

  • Located in carotid and aortic bodies that have high blood flow
  • Respond mostly to decrease in O2 below 100mmHg
  • Impulses transmitted to respiratory centre to increase ventilation
  • Responsible for all of the ventilatory response to hypoxaemia
  • Also responsible for small but rapid response to rise in CO2 and decrease in pH (carotid bodies)

Pass Criteria:

  • 3 out of 5 to pass


What is thoracic compliance?

Change in lung volume per unit change in airway pressure (DV/DP)

Measure of elastic recoil of lungs and chest wall

Normally 200 mL/mmHg in intact thorax

Pass Criteria: Bolded points

What are the main determinants of compliance of the thorax?

  • Surface tension of the alveoli (2/3rds)
  • Elastin/collagen fibres (1/3rd)
  • Alveolar surface tension depends on alveolar pressure, alveolar radius, surfactant
    • Law of Laplace – P=2(or4) x T/R

Pass Criteria:

  • 2 to pass

How does compliance vary throughout the upright lung?

  • Higher at base than apex because apex is already more distended

Pass Criteria:

  • Must say that base > apex


Explain the difference between alveolar and arterial oxygen concentrations in the healthy adult.

  • Physiological shunt of lung (PAO2>PaO2)
  • Blood enters arterial system without passing through a ventilated area of lung
  • Bronchial arterial blood flows to pulmonary veins
  • Coronary arterial blood flows to coronary veins then thebesian veins in left ventricle
  • Atelectasis in lung

Pass criteria:

  • Bold PLUS 1 other


What sensors are involved in control of ventilation?
Prompt: What senses changes in blood gases?

  • Chemoreceptors and mechanical receptors
  • Central chemo in medulla  respond to H+
  • Peripheral chemo in carotid and aortic bodies respond to O2, CO2, H+
  • Stretch receptors in lungs, muscles, joints
  • Irritant receptors in airways
  • J receptors respond to engorged capillaries

Pass criteria:

  • Need peripheral and central


What are the basic elements of the respiratory control system?

  • Sensors;
  • Central Controller;
  • Effectors.

What inputs are there into the respiratory control system?

  • Cortical
  • Central and peripheral chemoreceptors,
  • Lung and other receptors.

What are the basic elements of the respiratory control system?

  • Respond to changes in HI- concentration.
  • CO2 regulates ventilation by effects on pH


Questions 11 to 20