Thursday, April 9, 2009



1. Explain the voluntary control of respiration

Voluntary control of respiratory muscles by the motor cortex can override the medullary respiratory centre. This allows us either to speed up ventilation or to hold our breath at will. However, voluntary control is only partial, because if we stop breathing for more than a minute or so, arterial pco2 rises and po2 falls providing a chemoreceptor –driven stimulus to ventilation.

2. What is air hunger?

Increased activity in the vasomotor centre is primarily responsible for cardiovascular adjustments to low blood pressure but also stimulates ventilation. This explains the increased breathing, known as air hunger, which is seen in surgically shocked patients.

3. What is smokers cough?

Individuals who smoke create a constant irritation to the trachea. Overtime, the irritation from smoke can cause the epithelium of trachea to change from a pseudo stratified ciliated columnar to stratified, squamous epithelium. Without cilia, the epithelium cannot clear the mucus and debris. This provides an environment for the growth of microorganism leading to respiratory infections. This trigger the cough reflex commonly called smokers cough.

4. What are the effects of ageing on the respiratory system?

With advancing age, the airways and tissues of the respiratory tract, including the alveoli, become less elastic and more rigid; the chest wall also becomes more rigid. the result is a decrease in lungcapacity.moreover ,a decrease in blood level of o2,decreased activity of alveolar macrophages and diminished ciliary action of the epithelial lining .owing to all these age related factors ,elderly people are more susceptible to pneumonia, bronchitis and other pulmonary disorders.

5. What is the significance of residual volume?

Some amount of air is always present in the lung because of RV or FRC, and therefore continuous exchange of gases is made possible and thereby concentrations of o2 and co2 in blood are maintained constant.

6. Why are venous RBCs more fragile than arterial RBCs?

When blood passes through tissue capillaries, co2 enters into blood and causes chloride shift. (Chloride ions diffuse from plasma into the RBCs).as a result, osmotic pressure inside the RBCs becomes higher than that of plasma. this causes osmotic absorption of fluid into the RBCs.venous RBCs contain therefore the greater quantity of fluid as compared to arterial RBCs .when placed in hypotonic solutions they can take lesser amount of fluid and hence more fragile than arterial RBCs.

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