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doi:10.2141/ jpsa.011038
Copyright Ⓒ 2012, Japan Poultry Science Association.
Morphological and Histological Studies on the Adrenal Gland
of the Chicken (Gallus domesticus)
Kober A.K.M. Humayun1, 2, Masato Aoyama1 and Shoei Sugita1
1
Department of Animal Science, Faculty of Agriculture, Utsunomiya University,
350 Minemachi, Utsunomiya, Tochigi 321-8505, Japan
2
United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology,
3-5-8 Saiwaichou, Fuchu 183-8509, Japan
Morphological and histological studies of the adrenal gland of the adult White Leghorn chicken (Gallus
domesticus) were performed. Macro- and microscopic observations of azan- or formal-dichromate stained (to observe
the chromaffin reaction of adrenal medulla) sections were conducted. The right and left adrenal glands differed in
shape, position, weight, length, width and thickness. The adrenal glands were encapsulated with a thin connective
tissue containing blood vessels. The adrenal parenchyma was composed of two main tissue types, the cortex and
medulla; these were mixed throughout the organ. The adrenal gland could be divided into a subcapsular layer, peripheral zone, and central zone. The whole subcapsular layer was occupied by medulla, and the proportion of medulla
in the central zone (49.7%) was larger than that in the peripheral zone (24.8%). Approximately 60% of the adrenal
gland was cortex, 39% was medulla, and the remaining 1% was sinusoids. The adrenal cortico-medullary ratio in the
adult chicken was approximately 1.6:1. Cortical cells were arranged in columns with a small, round to slightly oval,
eccentric nucleus approximately 4 μm in diameter. Medullary cells were polygonal in shape with a large, spherical,
centrally placed nucleus approximately 5 μm in diameter.
Key words: adrenal cortex, adrenal gland, adrenal medulla, chicken, cortico-medullary ratio
J. Poult. Sci., 49: 39-45, 2012
Introduction
Adrenal glands are important organs in all animals. They
help to maintain homeostasis as well as play important roles
in all types of stress response (Freeman, 1985; Randall et al.,
2002). They function by producing a variety of hormones
that are needed in many facets of everyday life. Hormone
production within the avian adrenal gland occurs in a divided
cortex that produces glucocorticoids (corticosterone) and
mineralocorticoids (aldosterone) and an adrenal medulla that
produces catecholamines (norepinephrine and epinephrine).
Experimental removal of the adrenal gland in birds leads to
eventual death (Peng et al., 2005). In birds, the right and left
adrenal glands are small and yellowish (Carsia and Harvey,
2000). Müller (1929) reported that the right adrenal gland in
adult chicken is roughly pyramidal in shape with a caudally
pointing apex, while the left adrenal gland is less constant in
shape. The weight, length, width, and thickness of adrenal
Received: April 30, 2011, Accepted: August 29, 2011
Released Online Advance Publication: September 25, 2011
Correspondence: S. Sugita, Department of Animal Science, Faculty of
Agriculture, Utsunomiya University, 350 Mine-machi, Utsunomiya, Tochigi 321-8505, Japan. (E-mail: [email protected])
glands vary depending upon a number of factors, such as
species, breed, age, health, and environment (Wells and
Wight, 1971). The avian adrenal gland is unique in that it
consists of a complete intermingling of cortical (interregnal)
and medullary (chromaffin) tissues with no definite cortex
and medulla (Ghosh et al., 200l). The adrenal gland in the
chicken consists of three regions: subcapsular layer, peripheral zone, and central zone (Hodges, 1974).
Several studies on the avian adrenal gland have provided
basic description of this gland, but none have described them
in detail (e. g., chicken: Hodges, 1974; duck: Holmes and
Cronshaw, 1984; pigeon: Bhattacharyya, 1975; quail: Basha
et al., 2004; and African ostrich: Tang et al., 2009). Little is
currently known about the “normal” structure of the chicken
adrenal gland. Prompted by lack of information on the size
differences between the right and left adrenal glands, the
cortico-medullary ratio in the different adrenal regions as
well as cortico-medullary ratio in the whole adrenal gland
and variation in the diameters of cell nuclei of cortical and
medullary tissues among the different regions and this will
require further study. The cortico-medullary ratio will aid in
understanding the functional significance of the chicken
adrenal gland. Therefore, the present study was undertaken
Journal of Poultry Science, 49 (1)
40
to demonstrate in detail morphological and histological
studies on the adrenal gland of the chicken.
Materials and Methods
Collection of Chickens
Twelve healthy adult White Leghorn chickens (6 males, 6
females) weighing 1.8 to 2.3 kg were used to conduct the
present stud. The chickens were obtained from the Tochigi
Prefectural Livestock Experiment Station in Tochigi, Japan.
All chickens were cared for according to guidelines suggested in the care and use of laboratory animals at Utsunomiya University. All procedures involving animals were
carried out in accordance with the Animal Protection Regulations of Japan.
Tissue Processing and Morphometric Measurements of the
Adrenal Gland
The chickens were sacrifice by an overdose of pentobarbital sodium (30 mg/kg body weight). The chickens were
perfused transcardially with a Ringer’s solution (0.9% NaCl,
0. 042% KC1, and 0. 025% CaCl2 in distilled water) and
Zamboni’s solution (0.1M phosphate buffer, pH 7.4 contain
ing 2. 0% paraformaldehyde and 0. 2% picric acid). After
sacrifice, the adrenal glands were carefully removed, weighed on a balance, and the length, width, and thickness of each
gland was measured using calipers. The length of each
adrenal gland was measured along the longitudinal axis; the
width was measured at the thickest portion of the gland, and
the maximum thickness was measured dorsoventrally. Each
adrenal gland was then immersed in 10% formalin in 0.1 M
phosphate buffer (pH 7.4) for 1 week. Tissue blocks were
subsequently prepared and processed conventionally for
paraffin wax embedment. Serial sections were cut at thickness of 5 μm in the coronal plane using a microtome and
mounted on glass slides. Randomly selected sections were
stained with azan.
Light Microscopy with Formal-dichromate Staining and
Calculation of Adrenal Cortico-medullary Ratio
Six adult chickens (3 males, 3 females) were used to
assess the proportions between cortical and medullary tissue
and to examine patterns of medullary tissue in the adrenal
gland. The adrenal medulla demonstrates the chromaffin
reaction (Hartman et al., 1947) and it has also been suggested (Hartman et al., 1947) that an identical histological
picture can be produced by fixing the adrenal medulla in
formal-dichromate. After collection, the adrenal glands were
incubated with potassium dichromate for 48 hours. Thereafter, the glands were incubated for 24 hours in 10% formalin
and for 24 hours in 30% sucrose. Finally, coronal serial sections were cut at 30 μm thickness with a freezing microtome
and mounted on glass slides. The relative proportions of the
different tissue components (cortical, medullary, and sinusoids) were measured using ImageJ software (National
Institutes of Health, Bethesda, MD) in each selected section
that included the whole adrenal gland. The values for the
proportions of each area (cortical, medullary, and sinusoids)
were averaged from two sections for each chicken and expressed as the mean±standard error (SE).
The proportions between cortical and medullary tissue in
the peripheral and central zones of adrenal gland were obtained by using six chickens (3 males, 3 females). Adrenal
cortico-medullary ratio in the peripheral and central zones
data was obtained from ten photomicrographs taken randomly from the peripheral and central zone of ten cross-sections
of each bird using a photomicroscope. Cortex, medulla, and
sinusoids were measured using ImageJ software and averaged. Values were expressed as the mean±SE.
Measurement of the Diameter of the Cell Nuclei in Cortical
and Medullary Tissues
Six adult chickens (3 males, 3 females) were used to measure the diameters of cell nuclei of cortical and medullary
tissues of the adrenal gland. The diameters of cell nuclei of
cortical and medullary tissues were quantified using 100×
photographs (Olympus BX51) and ImageJ software. The
diameters were calculated from 50 randomly selected nuclei
of cortical and medullary cells from three regions (subcapsular layer, peripheral zone, and central zone) of each chicken
and subsequently averaged. Values were expressed as the
mean±SE.
Data Analysis
Two-way repeated measures analysis of variance and the
paired t-test were used to analyze the differences in weight,
length, width, and thickness between right and left adrenals.
Differences were considered significant if P＜0.05.
Results
Topographic Location and Morphology of the Adrenal
Gland
The two adrenal glands of the chicken were small and
brownish-yellow to creamy-yellow in color. The glands
were situated on each side of the median line just anterior to
the bifurcation of the caudal vena cava, close to the gonads
(Fig. 1a). The right adrenal gland differed from the left one
in the shape and the location. The right adrenal gland was
often roughly pyramidal in shape with a caudally pointing
apex, partly adherent to the anterior cranial region of the right
kidney, and located close to the anterior aspect of the right
testis. The left adrenal gland appeared elongated in outline
and was situated on the medial border of the left kidney,
close to the left testis (Fig. 1a, b).
Morphometry of the Adrenal Gland
Two-way repeated measures analysis of variance shows
that there were no significant differences between males and
females adrenal gland morphometric data (P＞0.05), while
significant variation was observed between sides (P＜0.05).
Hence, data were pooled together and averaged. In addition,
data was also categorized by sexes in Table 1 for better
understanding. The average body weight was 2071±35.2 g
(n＝12) in both sexes. Morphometric data on each adrenal
gland are summarized in Table 1. The mean weights of the
right and left adrenal glands were 97.2±1.2 mg and 104.1±
1.4 mg, respectively, indicating that the right adrenal gland
was significantly (P＜0. 01) lighter than the left adrenal
gland. The left adrenal gland was significantly longer than
the right (0. 9±0. 0 cm vs 0. 8±0. 0 cm, respectively; P＜
Humayun et al.: Chicken Adrenal Gland
Anatomical position and general morphology of
the adrenal gland of the normal chicken (non-perfused).
(a) Glands are shown in situ. The two adrenal glands of the
chicken are situated on each side of the median line just
anterior to the bifurcation of the caudal vena cava, close to
the gonads. Arrowhead and arrow indicate right and left
adrenal gland, respectively; black-and-white and black star
indicate right and left testis, respectively; black arrow indicates vena cava. Scale bar indicates 1 cm.
(b) Shape of the adrenal gland. The right adrenal gland (R)
was often roughly pyramidal in shape with a caudally pointing apex, and the left adrenal gland (L) appeared elongated.
Scale bar indicates 0.5 cm.
Fig. 1.
0.01). The right adrenal gland was significantly wider than
the left one (0.6±0.0 cm vs 0.5±0.0 cm, respectively; P＜
0.01). The right adrenal gland was significantly thicker than
the left one (0.5±0.0 cm vs 0.4±0.0 cm, respectively; P＜
0.01).
Histology of the Adrenal Gland
The adrenal gland of the chicken was encapsulated with
thin connective tissue containing blood vessels (Fig. 2a).
Adrenal glands were composed of two morphologically and
physiologically different endocrine glands: the cortex and
medulla (Fig. 2a). Cortical and medullary tissues were
intimately mixed together throughout the gland (Fig. 2a).
The adrenal gland was divided into a subcapsular layer (SZ),
41
peripheral zone (PZ), and central zone (CZ) (Fig. 2a). The
SZ consisted of medullary cells immediately below the
capsule. The PZ consisted mainly of cortical cells, but the
two cell types were evenly intermingled in the CZ. The
medullary tissue formed an almost complete meshwork of
islets, including some larger irregular islets, some with slight
anastomosis, and some elongated islets (Fig. 3a, b). Medullary cells were polygonal in shape and larger than cortical
cells, with basophilic cytoplasm and spherical, centrally
placed nuclei (Fig. 2b). The diameters of cell nuclei of
medullary cells in the SZ, PZ, and CZ were 5.1±0.0, 5.0±
0.0, and 5.1±0.0 μm, respectively (Table 2). However, on
average, the diameter of the cell nuclei of medullary cells
was 5.1±0.0 μm (Table 2).
Microscopic examination of the chicken adrenal gland
showed that cortical tissue occupied a major part of the
adrenal gland. The adrenal cortex consisted of solid, irregular, cylindrical cords of cells (Fig. 2a). In cross-section, the
cords usually appeared round to oval in shape. The cortical
cords in the peripheral zone were larger; these cords were not
regularly arranged, but intimately intertwined with the
medullary strands (Fig. 2a). The cells of the cortical tissue
were arranged in columnar cells with a small, round to
slightly oval and eccentrically placed nucleus (Fig. 2b). The
diameters of cell nuclei of cortical tissue in the PZ and CZ
were 4. 1±0. 0 and 4. 0±0. 0 μm, respectively (Table 2).
However, on average, the diameter of cell nuclei of cortical
tissue cells was 4.1±0.0 μm (Table 2). These cells stained
eosinophilic. Capillaries as well as sinusoids were present
throughout the adrenal (Fig. 2). Usually, sinusoids were
more frequent inside the glandular tissue and often seemed to
create larger sinus venosi in the center of the gland (Fig. 2).
The Adrenal Cortico-medullary Ratio
Because there was no remarkable difference in the adrenal
cortico-medullary percentages between males and females,
data were pooled together. In addition, data was also categorized by sexes in Table 3 and Table 4 for better understanding. In the PZ, the overall mean percentages of cortical
tissue, medullary tissue, and cortico-medullary ratio were
74.0±0.1%, 24.8±0.1%, and 3:1, respectively (Table 3),
and the remaining 1.1±0.0 was sinusoids. In the CZ, the
overall mean percentages of cortical tissue, medullary tissue,
and cortico-medullary ratio were 48.7±0.0%, 49.7±0.0%,
and 1:1, respectively (Table 3), and the remaining 1.5±0.0
was sinusoids. However, in the whole adrenal gland, the
overall mean percentages of cortical tissue and medullary
tissue were 59.7%±0.1%, 39.1%±0.2%, respectively
(Table 4), and the remaining 1.1%±0.4% was sinusoids.
The cortico-medullary ratio was approximately 1.6:1 in the
whole adrenal gland.
Discussion
In this study, we examined the general morphology and
histology of the chicken (Gallus domesticus) adrenal gland.
We found that the location of the adrenal gland is similar to
that described by Wells and Wight (1971), who reported that
the two adrenal glands of chicken were situated on each side
Journal of Poultry Science, 49 (1)
42
Mean values (±SE) of weight, length, width, and thickness of
the chicken adrenal gland
Table 1.
Sex
Parameters
Side
Overall mean
(n＝12)
Male (n＝6)
Female (n＝6)
Weight (mg)
Right
Left
97 . 2±1 . 2*
104 . 1±1 . 4
98 . 3±1 . 9*
107 . 0±1 . 4
96 . 0±1 . 4*
101 . 3±0 . 4
Length (cm)
Right
Left
0 . 8±0 . 0*
0 . 9±0 . 0
0 . 8±0 . 0*
0 . 9±0 . 0
0 . 8±0 . 0*
0 . 9±0 . 0
Width (cm)
Right
Left
0 . 6±0 . 0*
0 . 5±0 . 0
0 . 6±0 . 0*
0 . 5±0 . 0
0 . 6±0 . 0*
0 . 5±0 . 0
Thickness (cm)
Right
Left
0 . 5±0 . 0*
0 . 4±0 . 0
0 . 5±0 . 0*
0 . 4±0 . 0
0 . 5±0 . 0*
0 . 4±0 . 0
Asterisk (*) indicates significant difference (Paired t-test, * P＜0.05) from the organ
of the left side.
of the median line just anterior to the bifurcation of the
caudal vena cava, close to the gonads and the anterior
division of the kidneys. The shape and color of the adrenal
glands in our study were similar to those in a previous study
of the chicken (Hodges, 1974). Hodges (1974) suggested
that the shape of the right adrenal gland in the adult chicken
is roughly pyramidal in shape with a caudally pointing apex
and that the left adrenal gland is less constant in shape. He
stated that the color of adrenal glands in chicken varies
between grayish-yellow and reddish-yellow.
The present study indicated significant variations in
weight, length, width, and thickness of the right and left
adrenal glands of the chicken. In this study, the weight of the
right adrenal gland was significantly lighter than that of the
left one (P＜0.01). Wells and Wight (1971) reported that the
weight of the adrenal gland was 100 to 200 mg in the chicken
and 0.45±0.04 g in the ostrich chick (Tang et al., 2009).
The weight of adrenal glands varies considerably according
to species, breed, age, health, and various environmental
factors (Wells and Wight, 1971). In terms of length, our
present result indicated that the left adrenal gland was
significantly (P＜0.01) longer than the right one. In relevant
studies in other species, the length was recorded as 2.0 to 3.0
cm in the ostrich (Tang et al., 2009) and 13 mm in the
chicken (Hodges, 1974). Regarding weight, the right adrenal gland was significantly (P＜0.01) wider than the left in
our study. Tang et al. (2009) found the ostrich chick adrenal
gland to be 0.6 cm in width, while Müller (1929) found an
average 8 mm width in the domestic hen. Finally, the right
adrenal gland was, on average, significantly thicker (P＜
0.01) than the left one. Similar studies reported that the
adrenal gland thickness was 4 to 5 mm in the chicken
(Hodges, 1974) and 0.3 cm in the ostrich chick (Tang et al.,
2009). To the best of our knowledge, no publication exists
on this topic in the literature; thus, no comparisons of the
right and left adrenal glands could be made with other
studies. Further studies are needed to clarify the reasons for
the differences in size between the right and left adrenal
glands.
Structurally, chicken adrenal glands appear to be encapsulated with thin connective tissue containing blood vessels;
cortical and medullary tissues are completely intermingled
and consist of three regions: the subcapsular layer, peripheral
zone, and central zone (Hodges, 1974). These results are
consistent with those of our study. In birds, the medullary
tissue forms a pattern that varies from scattered islets to an
interwoven network, depending upon the amount of tissue
present. The pattern of the medullary tissue in our study was
similar to those of Hartman et al. (1947) and Holmes and
Cronshaw (1980). They stated that medullary tissue forms
an attractive meshwork pattern, seeming to take the form of
islets in the Florida bobwhite. Moreover, the present results
correspond with those of Hodges (1974) and Ohmori (1998);
similarly, they suggested that adrenal medulla cells in the
chicken are arranged in a polygonal shape, with a large,
spherical, centrally placed nucleus. The basophilic staining
of the cytoplasm is due to its content of numerous small,
basophilic granules. In this study, we measured, for the first
time, the diameters of cell nuclei of medullary cells in the
three different zones of the chicken adrenal gland. There
were a few variations in the diameters of cell nuclei within
the SZ, PZ, and CZ of the adrenal gland of the chicken. As
far as we know, no data exist on this topic in the literature; no
comparisons could be made with other studies. Further study
is needed to clarify the reasons for the differences in the
diameters of cell nuclei of medullary cells in the three
different zones of the chicken adrenal gland. There is one
possible explanation that the nuclei of cells in the CZ are
more highly developed than those in the SZ and PZ. However, on average, the diameters of cell nuclei of medullary
cells in our study were inconsistent with those of Tang et al.
(2009), who found that the medullary cell nuclei in ostrich
chicks were approximately 8 μm in diameter. Moreover,
Hodges (1974) found the mean diameter of the nuclei in
medullary cells in domestic hens to be 6.7 μm.
The present results correspond with those of Aire (1980)
and Hodges (1974), who suggested that adrenal cortical cells
in the chicken are arranged in columns with a small, round to
Humayun et al.: Chicken Adrenal Gland
Histology of the adrenal gland of the normal
chicken. Sections were stained with azan. (a) Prominent
eosinophilic cortical (light staining) and basophilic medullary tissues (darker staining) are arranged in islets. The
cortical (arrow) and medullary (arrowhead) tissues are intermingled. The adrenal gland could be divided into a peripheral zone (PZ), consisting mainly of cortical cells but with
a subcapsular layer of medullary cells (SZ), and a central
zone (CZ) in which the two cell types were evenly intermingled. C, adrenal capsule; VS, venous sinus. Scale bar
indicates 100 μm.
(b) Characteristics of two different cell types in the adrenal
parenchyma. (N) Strand of cortical cells in which the cells
are columnar in type with a small, round to slightly oval, eccentric nucleus. (M) Group of medullary cells are polygonal
with a large, spherical, centrally placed nucleus. Scale bar
indicates 10 μm.
Fig. 2.
43
Fig. 3. Cross-sections of adrenal gland of the normal
chicken. The adrenal gland was treated with formal-dichromate (to observe the chromaffin reaction of adrenal
medulla). (a and b) Distribution patterns of medullary tissue (arrow) and cortical (arrowhead) tissue. The medullary
tissue formed an almost complete meshwork of islets, including some larger irregular islets, some with slight anastomosis, and some elongated islets. Scale bars indicate 1
mm (a) and 60 μm (b).
slightly oval, eccentrically placed nucleus with eosinophilic
staining. In this study, we measured, for the first time, the
diameters of cell nuclei of cortical cells in the different zones
of the chicken adrenal gland. There were variations in the
diameters of cell nuclei within the PZ and CZ. The PZ cells
were characterized for their larger diameters of cell nuclei
compared to that of the cells nuclei of CZ. However, there
might have certain structural differences between the cortical
cells in PZ and CZ of the chicken adrenal gland. To the best
Journal of Poultry Science, 49 (1)
44
Comparisons of diameters of cell nuclei of cortical and medullary
tissues in the three different regions of the chicken adrenal gland (n＝6)
Table 2.
Regions
Component
SZ
(Mean±SE)
PZ
(Mean±SE)
CZ
(Mean±SE)
Overall mean±SE
Medulla (μm)
Cortex (μm)
5 . 1±0 . 0
─
5 . 0±0 . 0
4 . 1±0 . 0
5 . 1±0 . 0
4 . 0±0 . 0
5 . 1±0 . 0
4 . 1±0 . 0
(−) indicate that SZ was no cortical tissue
Table 3. Mean values (±SE) of cortex, medulla, and cortico-medullary (CM) ratios in the three different
regions of the chicken adrenal gland
Regions
Overall
cortex
mean (%)
(n＝6)
Overall
medulla
mean (%)
(n＝6)
SZ
PZ
CZ
0 . 0±0 . 0
74 . 0±0 . 1
48 . 7±0 . 0
100±0 . 0
24 . 8±0 . 1
49 . 7±0 . 0
Sex
Male (n＝3)
Cortex
Medulla
(%)
(%)
0 . 0±0 . 0
73 . 7±0 . 1
48 . 7±0 . 0
100±0 . 0
25 . 0±0 . 0
49 . 7±0 . 0
Female (n＝3)
Cortex
Medulla
(%)
(%)
0 . 0±0 . 0
74 . 2±0 . 1
48 . 7±0 . 0
100±0 . 0
24 . 5±0 . 0
49 . 7±0 . 0
Overall
CM
ratio
0:1
3:1
1:1
Mean values (±SE) of cortex, medulla, and cortico-medullary ratio
in the chicken whole adrenal gland
Table 4.
Parameters
Overall mean
(n＝6)
Cortex (%)
Medulla (%)
59 . 7±0 . 2
39 . 1±0 . 2
Sex
Male
(n＝3)
Female
(n＝3)
59 . 9±0 . 0
38 . 5±0 . 1
59 . 5±0 . 4
39 . 7±0 . 2
of our knowledge, no data exist on this topic in the literature;
no comparisons could be made with other studies. The functional significance of these few variations in the diameters of
cell nuclei in chicken adrenal glands is currently unknown.
It is possible that adrenal cortical tissue synthesizes and
secretes at least two types of cells. However, on average, the
diameters of cell nuclei of cortical cells in our study were
smaller than those found in ostrich chicks (5-7 μm) (Tang
et al., 2009) and domestic fowl (5 μm) (Hodges, 1974).
Hodges (1974) also reported that the few large venous
sinuses that were found in the middle of the chicken adrenal
gland correspond with our results. Notably, there is no true
central vein as in man. Ultimately, the sinuses lead to an
adrenal vein that joins the caudal vena cava (Wells and
Wight, 1971).
In this study, we report, for the first time, the relative
proportions of cortical and medullary tissues in the different
zones of the chicken adrenal gland. There was a variation in
the relative proportions of cortical and medullary tissues in
the PZ and CZ of the adrenal gland of the chicken. The
cortico-medullary ratios in the PZ and CZ were approximately 3:1 and 1:1, respectively. The highest cortico-medul-
Overall CM ratio
1.6 : 1
lary was found in the PZ of the adrenal gland. The functional
significance of differences in cortico-medullary ratios of PZ
and CZ is not completely understood. However, one possible reason is that the higher ratio (large cortex) in PZ may
be required for more production of corticosteroid. Further
study is needed to clarify the reason for such a difference of
cortico-medullary ratio in the PZ and CZ of the adrenal gland
of the chicken. The results of the current study correspond
with those of Carsia et al. (1985), who described that adrenal
cortical and medullary tissues comprise 60% and 40%,
respectively, of the adrenal gland in the chicken. Similarly,
Aire (1980) indicated that approximately 52% of tissue is
adrenal cortical in the Rhode Island Red chicken. This report
indicates an adrenal cortical percentage lower than that in our
study, which may be attributable to breed differences. Undoubtedly, the most striking variations in the cortex and
medulla percentage are those due to age, sex, breed, health,
and environment (Siller et al., 1975). The contention by
Sivaram (1965) that the proportion of medullary tissue is
consistently higher than that of cortical tissue in the domestic
fowl is not supported by the present findings or by those of
Aire (1980) and Carsia et al. (1985), who stated that cortical
Humayun et al.: Chicken Adrenal Gland
tissue was normally greater in proportion than medullary
tissue. The functional significance of this higher proportion
of cortex is not completely understood, but one possible
explanation could be the increased need to regulate water and
electrolyte balance. It is known that the adrenal cortex produces hormones (glucocorticoids and mineralocorticoids)
that aid in water and electrolyte balance; thus, a larger cortex
may be needed for increased production of these hormones in
the chicken, which lives in areas in which water conservation
is extremely important. In this study, the cortico-medullary
ratio was approximately 1.6:1 in the whole adrenal gland,
which probably relates to the physiological status of the
chickens. For example, as we know, these two cell types are
responsible for hormone secretion (the cortex, which produces glucocorticoids [corticosterone] and mineralocorticoids [aldosterone], and the adrenal medulla, which produces
catecholamines [norepinephrine and epinephrine]). When a
bird is exposed to stress, the adrenal glands release corticosterone and catecholamines into the blood, which helps to
adapt the bird to its new set of environmental conditions.
Consequently, a distinct difference was observed in the relative proportions of cortical and medullary tissues.
Acknowledgments
This research was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology of Japan (No. 083281).
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