Respiratory System

Normal inspiration is achieved by contraction of the external intercostal muscles and the diaphragm. The neck and abdominal muscles are used for deep inspiration and forced exhalation, respectively.

Bands of cartilage shaped like a “C” keep the trachea rigid and open.

Tidal volume is the volume of air that is inhaled and exhaled while “at rest”.

The amount of gas that will dissolve in water is proportional to its partial pressure (Henry’s law). Hence, if the partial pressure in the atmosphere halves, the partial pressure in the alveoli will be approximately half, so the amount that will dissolve will also approximately halve.

Henry’s law states “the amount of gas that will dissolve in water is proportional to its partial pressure”. The ppO₂ in an atmosphere of 100% oxygen is about five times normal. In addition, air at three times normal atmospheric pressure has ppO₂ about three times normal. Hence, the blood oxygen concentration will be 5 × 3 = 15 times normal. 15 × 100 mmHg = 1500 mmHg.

Deep inspiration is helped by contracting the neck muscles (scalene, sternocleidomastoid), but this increases and not decreases lung volume.

Choice C refers to cellular respiration, choice D to external respiration.

The concentration of a gas dissolved in water is expressed in terms of the partial pressure of that gas in the mixture of gases that were in contact with the water. Gas will continue to dissolve until the water is saturated. At this point we say that the concentration of dissolved gas is the same as the partial pressure of that gas in the atmosphere in contact with the water. The same units, mmHg are used.

Oxygen in alveolar air will diffuse down its concentration gradient into capillary blood until blood in the capillary is also at 100 mmHg. After this there is no concentration gradient to effect a net diffusion.

Adrenaline and noradrenaline cause bronchioles to dilate which allows for greater ventilation.