is a p-adrenergic response. High concentrations of adrenaline increase the rate of
chloride loss from isolated frog skin, an effect that is due to stimulation of the secretory glands present (USSING , 1960). It seems unlikely that the catecholamines
normally influence water and sodium exchanges, except in acute circumstances
when their actions could contribute to the confusion of an investigator who is carryingout a distressing experimental procedure. However, the possibility of interactions with the effects of other hormones, particularly those of the neurohypophysis, should be considered.
b) The Adrenal Cortex and Interrenals
The adrenal cortex of marsupial and placental mammals usually contains three
types of cells arranged in successive layers, or zones. These layers, in succession
from the external capsule of the gland, are the zona glomerulosa, the zona [asciculata and the zona reticularis. The cells in these areas can be distinguished by their
cytological appearance, shape and arrangement. Cells in the zona glomerulosa are
round, not very prominent, rich in mitochondria, but poor in lipid droplets. The
zona fasciculata is the largest of the zones; its cells are arranged in columns, and
they are rich in lipid droplets, but poor in mitochondria. The innermost zona reticularis, is made up of flattened 'compact' cells that contain little lipid and numerous
mitochondria. The various cortical zones and cells-types are not distinguishable
in all mammals; the zona glomerulosa cannot be seen in certain mice, lemurs and
monkeys. Analogous types of cells have not been identified in non-mammalian vertebrates.
The presence of different types of cells in the mammalian adrenal cortex suggests that they may be related to some of the endocrine functions of the gland.
Originally it was thought that they represented a centripetal migration of cells,
from the region of their formation to an area (zona fasciculata) where they produced their secretions, followed by final degeneration in the zona reticularis. However, it is now clear that the various zones represent areas where different steroids
may be principally made and stored. Hypophysectomy greatly reduces the glandular secretions of cortisol and corticosterone, but has only a modest effect on the
secretion of aldosterone. This is correlated morphologically with maintenance of
the zona glomerulosa, and degeneration of the other two groups of cells. The adrenogenital syndrome in man is due to an excessive production of androgenic steroids by the adrenal cortex, and this is associated with hyperplasia of the zona rcticularis. This evidence suggests that the zona glomerulosa is primarily concerned
with the production of aldosterone, the zona reticularis with androgenic steroids,
and the zona fasciculata with the secretion of cortisol and corticosterone. It is
doubtful that such partition of labour is entirely discrete, the zona glomerulosa for
instance seems to be able to secrete corticosterone. Attempts have been made to
identify and measure the levels of the different biogenic enzymes and steroids
present in the various zones, a process that is facilitated in large adrenal glands.
RACE and Wu (1961) dissected out the adrenocortical zones of the sperm whale,
Pbyseter catadon, and their analyses generally support the above relationships.
There is, nevertheless, still a considerable crossover among occurrences
72
chloride loss from isolated frog skin, an effect that is due to stimulation of the secretory glands present (USSING , 1960). It seems unlikely that the catecholamines
normally influence water and sodium exchanges, except in acute circumstances
when their actions could contribute to the confusion of an investigator who is carryingout a distressing experimental procedure. However, the possibility of interactions with the effects of other hormones, particularly those of the neurohypophysis, should be considered.
b) The Adrenal Cortex and Interrenals
The adrenal cortex of marsupial and placental mammals usually contains three
types of cells arranged in successive layers, or zones. These layers, in succession
from the external capsule of the gland, are the zona glomerulosa, the zona [asciculata and the zona reticularis. The cells in these areas can be distinguished by their
cytological appearance, shape and arrangement. Cells in the zona glomerulosa are
round, not very prominent, rich in mitochondria, but poor in lipid droplets. The
zona fasciculata is the largest of the zones; its cells are arranged in columns, and
they are rich in lipid droplets, but poor in mitochondria. The innermost zona reticularis, is made up of flattened 'compact' cells that contain little lipid and numerous
mitochondria. The various cortical zones and cells-types are not distinguishable
in all mammals; the zona glomerulosa cannot be seen in certain mice, lemurs and
monkeys. Analogous types of cells have not been identified in non-mammalian vertebrates.
The presence of different types of cells in the mammalian adrenal cortex suggests that they may be related to some of the endocrine functions of the gland.
Originally it was thought that they represented a centripetal migration of cells,
from the region of their formation to an area (zona fasciculata) where they produced their secretions, followed by final degeneration in the zona reticularis. However, it is now clear that the various zones represent areas where different steroids
may be principally made and stored. Hypophysectomy greatly reduces the glandular secretions of cortisol and corticosterone, but has only a modest effect on the
secretion of aldosterone. This is correlated morphologically with maintenance of
the zona glomerulosa, and degeneration of the other two groups of cells. The adrenogenital syndrome in man is due to an excessive production of androgenic steroids by the adrenal cortex, and this is associated with hyperplasia of the zona rcticularis. This evidence suggests that the zona glomerulosa is primarily concerned
with the production of aldosterone, the zona reticularis with androgenic steroids,
and the zona fasciculata with the secretion of cortisol and corticosterone. It is
doubtful that such partition of labour is entirely discrete, the zona glomerulosa for
instance seems to be able to secrete corticosterone. Attempts have been made to
identify and measure the levels of the different biogenic enzymes and steroids
present in the various zones, a process that is facilitated in large adrenal glands.
RACE and Wu (1961) dissected out the adrenocortical zones of the sperm whale,
Pbyseter catadon, and their analyses generally support the above relationships.
There is, nevertheless, still a considerable crossover among occurrences
72