Examples of SEQs on respiration physiology with their answers by Dr Khaled A Abulfadle

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Summerize the mechanism of stimulation of central chemoreceptors?

Mechanism of stimulation of central chemoreceptors:

Carbon dioxide when increased in the arterial blood passes into the CSF through the blood brain barrier (lipid soluble),
Then, binds with water forming bicarbonic acid which dissociates in presence of carbonic anhydrase into bicarbonate and hydrogen ion which stimulates the central chemoreceptors which in turn stimulates the respiratory center to increase ventilation.

Thus, carbon dioxide indirectly (via hydrogen ions formed in CSF) stimulates the central chemoreceptors (although, excess hydrogen ion itself in arterial blood does not stimulate central chemoreceptors, as it doesn't pass through the blood brain barrier)

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Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Outline factors affecting lung volumes

Factors affecting lung volumes: (also, see lab):
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1-Sex: lung volumes are 15% less in females.
2-They are greater in athletes (can be used as a measure for physical fitness).
3-They are less in recumbent position.
4-They decrease in old age.
5-They decrease in pregnancy.
6- Effect of muscular exercise: e.g. it increase RMV (from 8 L/min to upto 100 L/min).
7-Obstructive lung disease (e.g. emphysema) decreases FEV1/FVC ratio to less than 80%, while, in restrictive lung disease (e.g. pulmonary fibrosis), the ratio may be normal or even increased.
8-They are decreased in certain pathological conditions as:
a-Chest wall diseases:
1.Paralysis of respiratory muscles.
2.Fracture ribs or kyphosis.
b- Lung diseases:
1.Obstructive: bronchial asthma.
2.Restrictive: pneumonia & fibrosis
c-Increased blood volume in the lung: as in pulmonary congestion by left side heart failure.
d-Presence of intra-abdominal masses: as tumor and ascitis. So prevent free descend of diaphragm.

NB: Residual volume is increased in obstructive lung diseases as bronchial asthma.

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

State the transit time required for the transportation of the alveolar gas into capillaries

Transit time:

Definition: it is the length of time blood stays in the pulmonary capillaries.

Significance: it is a limiting factor for gas transfer.

Calculation: flow is defined as volume/time. Therefore, time = volume/flow. But, the entire cardiac output of 6 L/min, or 100 ml/second, and, the flows though the lungs and the pulmonary capillaries have a volume of about 75 ml.

Normal values:
At rest, the transit time is volume/flow i.e. 75 ml/100 ml/sec = 0.75 seconds.
During exercise, cardiac output increases much more than pulmonary capillary volume, therefore transit time decreases (0.3 seconds).

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Why Chloride concentration is higher in the venous RBCs

Due to chloride shift phenomenon i.e.

In venous blood, there is a higher concentration of CO2 some of which enter RBCs and react with H2O to form H2CO3 which dissociates into H+ and HCO3-. Then, HCO3- passes into plasma in exchange with chloride i.e. chloride shifting into RBCs i.e. higher concentration of chloride in the venous RBCs.

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Biosynthesis of surfactant:

The major components of pulmonary surfactant include phospholipids (80%), neutral lipids (mainly cholesterol, 10%), and the two hydrophobic peptides (1–2%) surfactant protein B (SP-B) and SP-C.

Type II epithelial cells synthesize and assemble the lipid and protein components into complexes that are stored as tightly packed membranes in lamellar bodies until secreted into the alveolar airspaces.

Formation of surfactant in infant lung starts from the 24th week of intrauterine life and completes at the 35th week.
Surfactant formation needs cortisol and thyroxin hormones and Ca++.

Surfactant formation is inhibited by insulin and smoking.

Surfactant forms a layer between air and fluid lining alveoli decreasing its surface tension.

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Q: Why acidosis increases 2,3 DPG while, alkalosis decreases it

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A:
Acidosis increases 2,3 DPG (with shifting of oxygen hmoglobin curve to the right) while, alkalosis decreases it as 2,3-DPG, the most concentrated organophosphate in the erythrocyte, forms 3-PG by the action of diphosphoglycerate phosphatase. The concentration of 2,3-DPG varies proportionately to the [H+], which is inhibitory to catalytic action of diphosphoglycerate phosphatase.

Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Q:Why CO is a toxic gas?
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A:CO strongly increases the affinity of hemoglobin for O2, which forces the curve left. But while doing so, it occupies O2 binding sites, so despite carboxyHb having high O2 affinity, each tetramer will carry less O2. Plus, even if it could carry the same number of O2 molecules, the increased affinity would make oxygen delivery to tissues impossible.
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Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Q: What is the mechanism of developing wheezing in asthmatic patients?
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A:
Wheezing may result from localized or diffuse airway narrowing or obstruction from the level of the larynx to the small bronchi. The airway narrowing may be caused by bronchoconstriction, mucosal edema, external compression, or partial obstruction by a tumor, foreign body, or tenacious secretions.

Wheezes are believed to be generated by oscillations or vibrations of nearly closed airway walls.

Air passing through a narrowed portion of an airway at high velocity produces decreased gas pressure and flow in the constricted region (according to Bernoulli's principle).

The internal airway pressure ultimately begins to increase and barely reopens the airway lumen.

The alternation of the airway(s) between nearly closed and nearly open produces a "fluttering" of the airway walls and a musical, "continuous" sound. The flow rate and mechanical properties of the adjacent tissues that are set into oscillation determine the intensity, pitch, composition (monophonic or polyphonic notes), duration (long or short), and timing (inspiratory or expiratory, early or late) of this dynamic symptom and sign.

Wheezes are heard more commonly during expiration because the airways normally narrow during this phase of respiration. Wheezing during expiration alone is generally indicative of milder obstruction than if present during both inspiration and expiration, which suggests more severe airway narrowing.
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Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Q: Discuss Bohr's Equation for measuring dead space

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Answer

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Clinical use of FEV1/FVC
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Admin عدد المساهمات : 9481 تاريخ التسجيل : 06/08/2009

Question

?What is the pressure gradient for pulmonary ventilation
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Answer

It is the trans-thoracic pressure gradient which is the difference between the pressure in the pleural space and the pressure at the body surface (atmospheric pressure), and it represents the total pressure required to expand or contract the lungs and chest wall

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