Respiratory

Question 1

What are the two types of respiratory epithelium lining the alveoli?

Answer 1

Type I - flat, large, basically the gas exchange cells

Type II - thick, less abundant than Type I and responsible for alveolar repair, as well as production of surfactant

Question 2

What are the main immunological cells in the alveoli?

Answer 2

1. Pulmonary alveolar macrophages (PAMs) which directly phagocytose particles which manage to evade the mucociliary escalator.
2. Lymphocytes
3. Plasma cells
4. Mast cells

Question 3

How much does movement of the diaphragm account for change intrathoracic volume?

Answer 3

Diaphragmatic movement accounts for 75% of the change in intrathoracic pressure.

Question 4

What is eructation?

Answer 4

Belching

Question 5

What are the parts of the diaphragm?

Answer 5

1. Crural - attached to the vertebral bodies
2. Costal - attached to the internal surface of the ribcage
3. Central tendon

Question 6

What is the approximate volume of intrapleural fluid?

Answer 6

15-20mL only. Main function to serve as a lubricant between parietal and visceral pleura

Question 7

How much air per normal breath?

Answer 7

500mL tidal volume = 6-8L per minute

Question 8

How much dead space is there in the respiratory system?

Answer 8

150mL in the upper conducting zones of the airway

Question 9

What is the average lung volume at rest?

Answer 9

2.5-3L

Question 10

What is the distinguishing feature between respiratory and terminal bronchioles?

Answer 10

Terminal bronchioles are the smallest of the conducting airways. They then transition into respiratory bronchioles which contain aveoli.

Question 11

What is the average resting pressure in the pulmonary artery?

Answer 11

15mmHg

Question 12

What are the main components of the respiratory membrane?

Answer 12

The alveolus has type I epithelium and these are essentially adjacent to capillary epithelium. In total this membrane is only around 0.3micrometres thick!

The capillary itself is only 10micrmetres wide, just enough for RBCs and that’s it

Question 13

How much surface area is available for gas exchange?

Answer 13

70 square metres or 50 square feet

Question 14

What happens to the respiratory membrane when pulmonary pressure is too high?

Answer 14

The blood gas exchange barrier can be damaged and impair ventilation.

Question 15

What are the phases of respiratory in regards to thoracic pressures?

Answer 15

1. Initially, diaphragmatic movement causes a negative intrapleural pressure to fall from -2mmHg to -8mmHg.
2. This is followed by expansion of the lung which causes intrapulmonary pressure to fall to around -2mmHg
3. Air flows in through a path of least resistance (usually the conducting airway system) until atmospheric and lung pressure is the same
4. Venous return also increases as a result of this negative intrathoracic pressure

Question 16

How is the functional residual capacity calculated?

Answer 16

The FRC is a sum of the experiatory residual volume (the amount that normal sits in the lungs on passive respiration but can be pushed out if need be) plus the residual volume (the amount left in the airways even after expired residual volume is gone)

Thus

FRC = ERV + RV

Question 17

What factors decrease the FRC?

Answer 17

1. Sitting in the supine position
2. Being pregnant - decreases the RV and ERV
3. Post-operative atelectasis obviously with lung collapse there is decrease ERV
4. Anything which impinges on lower airways such as chronic bronchitis with sputum retention

Question 18

What is the best way to manage an acute drop in the FRC?

Answer 18

High flow oxygen delivered by mask

Question 19

What pathologies can cause a restrictive lung disease pattern?

Answer 19

Anything which decreases the body capacity for expansion such as:

1. Fractured ribs
2. Splinting due to pain from upper abdominal surgery
3. Spinal cord pathology which impinges on intercostal function

Anything which directly compromises the capacity of the lung such as a lobar pneumonia will also reflect a restrictive lung disease pattern.

Question 20

How long is capillary blood in contact with the respiratory membran in the resting state?

Answer 20

0. 75 seconds

0. 25 seconds in the active state

Question 21

Where are the peripheral chemoreceptors involved in regulating respiration located?

Answer 21

1. Carotid bodies,
   - The peripheral chemoreceptors are the only chemoreceptors in man which are capable of modifying the hypoxic respiratory response.
   - These chemoreceptors are not affected by anaemia
   - They are also minimally active until the Pa02 is down to 50-60mmHg

Question 22

What is the Bohr effect?

Answer 22

The Bohr effect basically describes the effect of pH on oxygen affinity of haemoglobin.

In the exercising state where there is a large amount of CO2, an increased number of H+ ions are formed by virtue of buffer system in making CO2 more soluble.

With increased H+, haemoglobin becomes more likely to be bound by H+ and CO2, in exchange for dumping of oxygen.

Question 23

How is CO2 transported from tissues back to the lung?

Answer 23

In BLOOD PLASMA:

1. Dissolved
2. Forms carbamino compounds with plasma proteins
3. Following buffering of H+ in the RBC, HCO3 lives in the plasma

In RBCs:

1. Dissolved
2. Formation of carbamino-Hb
3. H+ buffered and 70% of the HCO3 produced enters the plasma in exchange for chloride ions
4. Overall there is increase in osmolality intracellularly so water also enters with chloride

Question 24

What layers must gases traverse to enter RBCs?

Answer 24

1. Surfactant
2. respiratory epithelial cell *type I
3. Interstitium
4. Capillary endothelium
5. Plasma
6. RBC membrane

Question 25

How is oxygen carried in blood?

Answer 25

1. With Hb | 2. Freely dissolved

Question 26

What factors affect the affinity of haemoglobin for oxygen?

Answer 26

Hb will have higher affinity for oxygen in the following: 1. Alkalosis 2. Low CO2 3. Low temperature 4. Low 2,3 DPG (biphosphoglyceric acid) Hb has a lower affinity for oxygen in the inverse, think of peripheral tissues! 1. CO2, H+ and temperature are high in exercising muscle to haemoglobin has lower O2 affinity, therefore will more likely offload its oxygen which is good for tissue perfusion

Question 27

How does carbon monoxide affect the haemoglobin-oxygen dissociation curve?

Answer 27

CO has 240x the affinity for Hb than oxygen. I therefore competitively antagonises the oxygen binding site on the Hb molecule. Contrary to logic, CO actually INCREASES oxygen affinity on haemoglobin molecules. So when a single CO is bound, the remaining sites want for more O2 so the dissociation curve is actually shifted to the left initially. Overall however, the dissociation curve will plateau out at an oxygen saturation much lower than normal, despite any changes in the PaO2

Question 28

What are the features of CO poisoning?

Answer 28

Systemically reduced oxygen concentration in both arterial and venous blood. O2 curve shifted to the left Normal partial pressure of oxygen

Question 29

What forms of CO2 exist in VENOUS blood? (i.e from tissues to the lungs)

Answer 29

60% is in the form of BICARBONATE 10% is dissolved 30% is formed with carbamino proteins

Question 30

What forms of CO2 exist in ARTERIAL blood? from lung to tissues?

Answer 30

90% is in the form of BICARB (mostly in RBCs) 5% is dissolved 5% is as carbamino proteins

Question 31

What is the Bohr EQUATION (not to be confused with Bohr Effect)?

Answer 31

The Bohr equation is basically a ratio that can be used to estimate the dead space with the understanding that only alveolar ventilation undergoes gas exchange. THEREFORE: (PalveolarCO2 - PexpiredCO2) / PalveolarCO2 = Vd / Vt where Vd = dead space.

Question 32

How is respiration controlled in the body?

Answer 32

Three components: 1. Affectors (sensors) 2. Central mediator (brain) 3. Effectors: cause change in ventilatory effort

Question 33

What are the central mediators of respiration?

Answer 33

1. Brainstem: - medullary respiratory centre (below the 4th ventricle with two areas, dorsal for inspiration and ventral for expiration) - Apneustic centre - lower part of pons which stimulates the dorsal inspiratory area - Pneumotaxic centre - upper pons which can inhibit inspiration and thus regulates volume and RR 2. Cerebral cortex can override the medulla

Question 34

Where are the central chemoreceptors located?

Answer 34

The are on the ventral surface of the medulla and are bathed in CSF with CO2 imbued. They mainly respond to changes in the pCO2. The chemoreceptors are mainly activated by the change in pH due to an increase in buffered CO2. So with an increase in CO2 diffusing into the CSF, the pH drops relative to that of the blood. Chronically, if the PCO2 is elevated, the pH is buffered eventually by movement of extra bicarbonate ions. Therefore the most important controlled of medullary respiration in the action of pH on central chemoreceptors.

Question 35

Where are the peripheral chemoreceptors located?

Answer 35

Only in carotid bodies. They respond to changes in arterial blood, changes in PO2, pH and PCO2. Normally the response to PO2 is pretty minimal, but response to PCO2 is much quicker, and even more rapid than that of central chemoreceptors.

Question 36

What factors impact on the ventilatory control during exercise?

Answer 36

1, Afferent feedback from limb movement 2. Increase in body temperature Additionally, increase in PCO2 and reduction in arterial pH causes more firing of arterial chemoreceptors whcih in turn leads to increases in activity of medullary respiratory centres - increased RR and ventilation volume.

Question 37

What is the Hering Breuer reflex?

Answer 37

The Hering Breuer reflex is a nerual reflex in response to excessive stretching of pulmonary musculature indicating overinflation of the lungs. It is mediated by pulmonary stretch receptors in airway smooth muscle. These send responses to the medulla and apneustic area of the pons via vagus. This inhibits the dorsal inspiratory area of the medulla which in turn inhibits the apneustic area of the pons.

Question 38

What effects on the ABG would be seen in a young healthy patient hyperventilating leading to the doubling of alveolar ventilation? (prior to activation of renal compensation)

Answer 38

1. Decreased PaCO2 2. Decrease in bicarbonate 3. Decreased ICP (low CO2 leads to vasoconstriction which leads to lowered ICP 4. Increase of PaO2

Question 39

What factors INCREASE pulmonary vascular resistance?

Answer 39

1. Pulmonary artery and venous pressures: - When these pressures are increased, you may think that the vascular resistance should INCREASE. However, when either pressures rises they cause recruitment of dormant vessels normally collapsed in lower pressure systems which overall DECREASES the vascular resistance. Secondly increase in arterial and venous pressures causes capillary dilatation due to poor smooth muscle components which leads again to DECREASE in PVR. 2. Lung volume: - At low lung volumes, PVR is high because the extra-alveolar vessel calibre is LOW thanks to smooth muscle and elasticity - However inversely at high lung volumes, the extra-alveolar vessels are high calibre but resistance remains high because now the capillaries are stretched and their caliber is small.