Q1

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

Q2

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


Q3

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

Q4

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

Q5

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

Q6

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

Q7

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

Q8

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

Q9

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

Q10

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

 

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