A morphometric analysis of the lung of a species of bat.

The lungs of five adult Epauleted Fruit-bats (Epomophorus wahlbergi) of mean body weight 96 g were analysed morphometrically. The lung volume per unit body weight was 0.043 cm3/g, the surface area of the tissue barrier (i.e., the effective alveolar surface area) component of the blood-gas pathway per unit body weight was 138 cm2/g, and the surface density of the tissue barrier (surface area of the tissue barrier per unit volume of parenchyma) was 121 mm2/mm3. The harmonic mean thickness of the tissue barrier was between 0.267 and 0.349 micron. The morphometric pulmonary diffusing capacity per unit body weight (DLO2/W) was 0.02 ml O2 per min per mm Hg per g. These values are compared with those of shrews and birds. It is suggested that in bats enlargement of the lungs, small subdivisions of the air spaces, and a thin blood-gas barrier, could be linked with previously reported circulatory adaptations to account for the high oxygen consumption during flight.

Morphometrics of the avian lung. 1. The domestic fowl (Gallus gallus variant domesticus).

The lungs of 5 domestic fowls have been analysed electron microscopically by standard morphometric methods. The anatomical diffusing capacity has been calculated from the relevant parameters. The blood-gas barrier consisted essentially of endothelium, basal lamina, and a very thin squamous epithelial cell. Granular cells are absent and interstitial tissue is minimal. The following measurements are mean values applying to both lungs together, in the fixed state: lung volume, 25.0 cm3; total intrapulmonary blood volume, 6.9 cm3; volume of the exchange tissue, 11.6 cm3; pulmonary capillary blood volume, 3.51 cm3; pulmonary capillary haematocrit, 62.7%; total intrapulmonary air volume, 16.61 cm3; air capillary volume, 6.68 cm3; surface area of the blood-gas barrier, 2.08 m2; surface area of the barrier per unit volume of exchange tissue, 179.5 mm2/mm3; arithmetic mean thickness of the tissue barrier, 1.20 micrometers; harmonic mean thickness of the tissue barrier, 0.314 micrometers; harmonic mean thickness of the plasma layer, 0.342 micrometers. The values of the maximum and minimum morphometric diffusing capacities for the lung (DL02 m) were respectively 3.55 and 1.50 ml O2/min/mm Hg; those for the membrane (Dmo2 m) were 13.61 and 12.01 ml O2/min/mm Hg.

Synaptic morphology of the carotid body of the domestic fowl.

Efferent and reciprocal synapses have been demonstrated in the carotid body of the domestic fowl (Gallus gallus domesticus). Synapses were also found with purely afferent morphology, but were probably components of reciprocal synapses. The general morphology of the endings suggested the presence of two types of axon, afferent axons making reciprocal and perhaps afferent synapses with Type I cells, and efferent axons making efferent synapses with Type I cells. A few axo-dendritic synapses were also found. The dense-cored vesicles associated with the afferent components of reciprocal synapses and with the possible true afferent synapses varied in diameter and core but could belong to one population of pre-synaptic vesicles. These observations are consistent wtih a new theory for the carotid body receptor mechanism. This proposes a spontaneously discharging afferent axon inhibited by an inhibitory transmitter substance released by the Type I cell via the "afferent" component of its reciprocal synapse, the "efferent" component inhibiting this release. Besides this chemoreceptor modulation of its afferent axon, the Type I cell may also have a general secretory function.

The general ultrastructure of the carotid body of the domestic fowl.

Electron microscopic studies of the carotid body of the domestic fowl (Gallus gallus domesticus) have shown Type I and Type II cells combined with axons into compact groups. The many Type I cells in the depths of the organ had a body, containing the nucleus, and an elongated, flared process. Some of the Type I cells in the superficial regions tended to be spindle-shaped. Type I cells were characterised by membrane-bound, dense-cored vesicles about 120 nm in diameter. Type II cells invested the Type I cells and had axons embedded in them as in Schwann cells. The fine structure of the carotid body in the domestic fowl resembles that of the Lovebird (Uroloncha domestica) and of various amphibia and mammals. The possibility is discussed that the Type I cells may have a chemoreceptor or a general secretory function, or even both of these axons leading to or from Type I cells. The main role of the Type II cells seems to be to provide a pathway for functions together.