Lecture #12: Gas Exchange in Animals

1. General problems of gas exchange (not the same as cellular respiration). (Fig. 42.18)

a. it must allow a continuous supply of O₂ for respiration.

b. it must have an adequate sized surface area for exchange (pulmonary membrane).

c. it must be a moist surface area for adequate diffusion.

2. Tracheal system of insects (and some terrestrial arthropods like spiders). (Fig. 42.22)

3. Countercurrent exchange system in fish gills. (Fig. 42.20) (Fig. 42.21)

4. Ventilation is any process that increases exposure of exchange surface to medium. (Fig. 42.24)

(Mammals ventilate lungs by negative pressure breathing.)

II. ANATOMY OF MAMMALIAN RESPIRATORY SYSTEM

1. Larynx, trachea, bronchi, bronchioles, alveoli. (Fig 42.23)

2. The problem of emphysema, caused by heredity, smoking, and air pollution).

3. Tidal volume (500 ml), vital capacity (4000-5000 mL), residual volume.

4. Breathing center in medulla sends impulses to ribs and diaphragm (10-14/min). (Fig. 42.24)

(A rise in CO₂, or a rise in hydrogen ion concentration, or excitement stimulates medulla.)

III. LOADING AND UNLOADING OXYGEN AND CARBON DIOXIDE (Fig. 42.25)

1. Explain partial pressures of atmospheric pressure of 760 mm Hg.

a. O₂ is 21% (0.21) of atmospheric pressure. (= 160 mm Hg)

b. CO₂ is .03% (0.0003) of atmospheric pressure. (= 0.23 mm Hg)

2. Transport of oxygen: (it is not soluble in water)

a. transported almost entirely by hemoglobin.

b. hemoglobin has four subunits, each with a heme group that binds one O₂.

c. binding of one O₂ causes configurational change that promotes 3 more to bind.

d. unloading one O₂ causes configurational change that unloads the other three.

e. examine the dissociation curve for hemoglobin. (Fig. 42.28a)

f. a drop in pH (CO₂) causes Bohr shift and lowers hemoglobin O₂ affinity (Fig. 42.28b)

g. CO has 200X the affinity of O₂ for hemoglobin gas sites.

3. Transport of carbon dioxide: (Fig. 42.29)

a. 7% is transported as dissolved gas in blood plasma.

b. 23% is transported by binding to amino groups on hemoglobin molecule.

c. 70% is transported by entering RBC and being converted to HCO₃ (carbonic anhydrase)