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Nat. Volatiles & Essent. Oils, 2022;9(1):13631-13644
13631
Anatomical, Histometrical, And Histochemical
Comparative Study Between Stomach Of Ring
Necked Parakeet - Psittacula Krameri (Scopoli,
1769) And Black Shouldered Kite - Elanus
Caeruleus (Desfontaines, 1789
Jehan M. Rajab1, Sahar A. H. Al-Sharqi2* and Sabah A. Abdel Rahman3
1,2*,3Department of Biology, College of Sciences, Mustansiriyah University, Baghdad/ Iraq.
*Email: saharalsharqi@uomustansiriyah.edu.iq
*Corresponding Author: Sahar A. H. Al-Sharqi
*Department of Biology, College of Sciences, Mustansiriyah University, Baghdad/ Iraq.
Abstract
The present study aims to investigate the anatomical, histometrical, and histochemical aspects of the stomach
in two species of birds, Psittacula krameri (Ring-necked parakeet) and Elanus caeruleus (Black-shouldered
kite). The stomach tissues in the two species were stained with Hematoxylin and Eosin for general histological
study and Periodic Acid Schiff (PAS)-Alcian blue (AB) pH 2.5 for histochemical study. An automated analysis
system was used for histometrical study. The stomach in two species of birds was divided into proventriculus
and ventriculus (gizzard); in the parakeet, proventriculus appeared as fusiform shape and the isthmus
separated the gizzard from proventriculus, while in the kite, the proventriculus was pear shape, and the
isthmus was absent. In the parakeet, the gizzard was a spherical shape with a thick koilin layer, while the kite
has pear shape gizzard with a thin koilin layer. The mucosa was possessed simple tubular glands which were
larger and more in the kite; the submucosa was rich with compound tubular glands which were longer and
wider in the kite. The histochemical results showed a positive reaction of epithelial cells and simple tubular
glands with PAS-AB stains; the koilin and deep gastric glands showed a positive reaction with the PAS stain
only.
Keywords: Histochemical, Histometrical, Kite, Parakeet, Stomach.
Introduction
In birds, the process of digestion in the digestive system takes place by mechanical and chemical action to
absorption the nutrients from their ingested food; the stomach structure in birds is various in shape, size, and
weight according to the feeding nature (Hassouna, 2001). It is the most important part of the digestive system
in birds; there are two parts of the stomach in birds, the glandular part, proventriculus, and the muscular part
ventriculus or gizzard (Hristov, 2020).
The birds are divided into two types according to the nature of the diet, the first type was soft diet eating
birds in which the main role of the gizzard is the storage of food; the stomach has a big single chamber such
as kestrel and owl (Abumandour, 2013, 2014; Al-Saffar, and Al-Samawy, 2014). The second, hard diet eating
birds in which the main role of the gizzard was the mechanical treatment of the food, the stomach has two
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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chambers with a thick wall of ventriculus such as turkey and sparrow (Hassouna, 2001).
The stomach of birds was divided into three types according to nature of diet as noted by (Hassouna,
2001); first type, soft eating birds as in kestrel and owl in which the main function of the gizzard was
the storage of food. Second type, hard diet eating birds as in turkey and sparrow in which the The stomach
of birds was divided into three types according to nature of diet as noted by (Hassouna, 2001); first type, soft
eating birds as in kestrel and owl in which the main function of the gizzard was the storage of food.
Second type, hard diet eating birds as in turkey and sparrow in which the The stomach of birds was divided
into three types according to nature of diet as noted by (Hassouna, 2001); first type, soft eating birds as in
kestrel and owl in which the main function of the gizzard was the storage of food. Second type, hard
diet eating birds as in turkey and sparrow in which the first type, soft eating birds as in kestrel and owl
in which the main function of the gizzard was the storage of food. Second type, hard diet eating birds
as in turkey and sparrow in which the
The hydrochloric acid and pepsinogen are secreted by the proventriculus; the gizzard mixed the food with
these materials due to the strong muscles and thick koilin layer of the gizzard wall (Svihus, 2014; Al-Juboory
et al., 2016).
The current study investigated the anatomical, histometrical, and histochemical aspects of the stomach in the
Psittacula krameri (Scopoli, 1769) and Elanus caeruleus (des Fontaines, 1789), and its relationship with the
type of food consumed for both species.
Materials And Methods
Twenty adult birds were used (10 Ring-necked Parakeets and 10 Black-shouldered Kite). The birds were
brought from Suq Al-ghazl in Baghdad and checked for their health status. The birds were anesthetized by
using chloroform. Tissue samples of the proventriculus and ventriculus were removed and immersed in
formalin for 24h. After fixation, the specimens were dehydrated with alcohol (80, 90, 95, and 100%), then
cleared with xylene, embedded in paraffin wax. The samples were sections to a thickness (5mm) by using a
rotary microtome, and Stained routinely with Hematoxylin and Eosin stains for general histological study, also
special stains of Periodic Acid Schiff (PAS)-Alcian blue (pH 2.5) were used for the histochemical study (Suvarna
et al., 2019). Later, the sections were examined by an Olympus microscope. Images were taken by the digital
microscopic camera for histometrical analysis. The automated computer-adopted image analysis system
Image J® was used.
Results
Anatomical and Morphological description of stomach
1. Ring necked parakeet - Psittacula krameri (Scopoli, 1769)
The anatomical results showed that the stomach was situated in the left median part of the abdominal cavity.
The stomach in the Ring-necked parakeet consists of two chambers, the glandular stomach or proventriculus,
and the muscular stomach, ventriculus, or gizzard. The Proventriculus appeared as a thin-wall fusiform shape
tube started at the narrow end of the thoracic esophagus in the abdominal cavity. The isthmus separated the
proventriculus from the gizzard (Fig.1). The mean length of proventriculus was (1cm) and width (0.5cm).
The ventriculus or gizzard appeared in a Ring-necked parakeet as a disc or biconvex lens shape. It was a thick
wall and with a smooth inner surface. Also, it was lined by thick keratinized tissues with yellowish-green in
color called koilin (Fig. 2). The mean length of the ventriculus was (1.5 cm) and width (1.5cm).
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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Figure 1. Photographic pictures of the stomach in ring necked parakeet (G: gizzard, IS: isthmus, P:
proventriculus).
Figure 2. Photographic pictures of the stomach inner surface in ring necked parakeet (G: gizzard, K: koilin, P:
proventriculus).
2. Black-winged Kite -Elanus caeruleus (desfontaines, 1789).
In the black winged kite, the proventriculus appeared as pear elongated shape, thick wall with five longitudinal
muscular folds. It was a brown color. There was no isthmus separated proventriculus from the gizzard (Fig .3).
The proventriculus in Black-winged Kite appeared longer and wider than the proventriculus of Ring-necked
parakeet. The mean length of proventriculus was (2 cm) and width (1 cm).
The gizzard in the black-winged kite was pear in shape with inner grooves on its surface; the mean length of
the gizzard was (1.25 cm) and width (1.25 cm). Anatomical results showed that the koilin layer was very thin
with poor yellowish green pigment inside the gizzard (Fig. 4).
Figure 3. Photographic pictures of the stomach in the black shouldered kite (E: esophagus, G: gizzard, P:
proventriculus).
P
IS
G
K
P
G
E
P
G
1
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Figure 4. Photographic pictures of the inner surface to the stomach in the black shouldered kite (IG: gizzard
inner grooves, LF: proventriculus longitudinal folds).
The histological and histochemical description of stomach
The wall of the stomach in two species of birds consisted of mucosa, submucosa, muscularis, and serosa.
1. Ring-necked parakeet -P. krameri-
A. Proventriculus
The mucosa of the glandular stomach or proventriculus appeared as a finger-like shaped structure, the
mucosal epithelium was lined with simple cuboidal epithelial cells with central oval nuclei. The epithelium of
mucosa was rested on loose connective tissue represented by lamina propria with few simple tubular glands.
No muscularis mucosa under the mucosa (Fig. 5). The mean thickness values of mucosa were
(143.05±4.89μm) (Tab. 1).
The submucosa was composed of loose connective tissue with a high supply of blood vessels and large oval
to conical compound tubular glands called deep gastric glands filling most of the proventriculus wall and
separating from each other by connective tissue. The histological examination revealed that the deep gastric
glands consisted of numerous secreted units or tubes with different shapes and diameters and arranged with
two rows, each one was lined with cuboidal epithelial cells with a central nucleus resting on a basement
membrane (Fig. 6).
The results showed that the mean length values of the deep gastric glands were (373.21±37.67μm) and the
width (280.80±24.52μm). The mean thickness values of submucosa were (724.43±22.179μm). The muscularis
externa consisted of two layers, inner thick circular muscle fibers and outer thin longitudinal muscle (Fig. 5).
Mean thickness values of the muscularis layer were (71.74±5.61μm). The outer layer was the serosa, which is
composed of loose connective tissue containing blood and lymph vessels, and nerve ends (Fig. 5). The mean
thickness values of serosa were (95.10±4.79μm).
The epithelium of the proventriculus showed a positive reaction with PAS- AB stains. The simple tubular
glands appeared purple; in the compound tubular glands, the cells lining the ducts and central cavities showed
a positive reaction with PAS- AB stains (Fig. 5).
Figure 5. Cross-section of the proventriculus wall in ring necked parakeet (CM: circular muscle, DGG: deep
gastric glands, LM: longitudinal muscle, M: mucosa, S: serosa, SM: submucosa) (H&E) 100X.
LF
IG
LM
CM
DGG
M
SM
SG
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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Figure 6. Cross-section of the proventriculus deep gastric glands in ring necked parakeet (BM: basement
membrane, CEC: cuboidal epithelial cells, DGG: deep gastric gland, LCT: loose connective tissue) (PAS-Alcian
blue) 400X.
Table 1. Measurement of the Proventriculus layers in the ring necked parakeet -P. krameri and the black
shouldered kite -E. caeruleus.
Proventriculus layers thickness
Ring necked parakeet
(Mean μm ± SE)
Black shouldered Kite
(Mean μm ± SE)
Glands length
373.21±37.67
425.59±18.88
Glands width
280.80±24.52
293.90±17.47
Mucosa
143.05±4.89
171.22±2.81
Submucosa
724.43±22.179
819.09±22.52
Musclaris externa
71.74±5.61
247.18±9.75
Serosa
95.10±4.79
329.62±14.26
B. Ventriculus
The mucosa epithelium of the ventriculus was possessed thin folds, finger-like projection toward the lumen.
The folds were lined with simple cuboidal epithelial cells with central oval nuclei (Fig.7, 9). The histological
examination revealed that there was a layer of koilin in front of the epithelial folds, this layer was stained with
eosin only and appeared with clear pink color (Fig. 7). The mean thickness values of koilin were
(170.99±6.10μm). Lamina propria appeared as a connective tissue rich with lymph cells, blood vessels, and a
few simple tubular glands, these glands were lined with simple cuboidal epithelial cells with a central spherical
nucleus (Fig. 8).
The mean thickness values of gizzard mucosa in the Ring-necked parakeets were (200.88±4.29μm). The
submucosa appeared as dense connective tissue with blood vessels and collagenous fibers. The mean
thickness values of submucosa were (59.40±2.39μm) (Tab. 2). The histological examination revealed that the
muscularis externa consisted of a thick layer of inner circular muscle fibers and a thin layer of outer
longitudinal muscle fiber (Fig. 8). The mean thickness values of muscularis were (1124.1±18.54μm). The
outermost layer in the gizzard was the serosa that was composed of loose connective tissue lined with simple
squamous epithelium rich with arterioles, veins, lymphoid vessels, and nerve ends (Fig. 7) The mean thickness
values of serosa were (135.92±4.65μm). The surface covered the gizzard (koilin) showed a pink-colored
positive reaction with PAS and a negative reaction with Alcian blue. The surface of mucosal epithelial cells
that covered the tubular gland was stained strongly with PAS-AB stain (Fig. 9).
CEC
BM
LCT
DGG
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Figure 7. Cross-section of the ventriculus wall in ring necked parakeet (A: arteriole, K: koilin, M: mucosa,
MU: muscularis, S: serosa, SM: submucosa, V: vein) (H&E) 40X.
Figure 8. Cross-section of the ventriculus wall in ring necked parakeet (M: mucosa, MU: muscularis, SM:
submucosa, S: serosa) (PAS-Alcian blue) 100X.
Figure 9. Cross-section of the ventriculus wall in ring necked parakeet (EF: epithelium fold, GG: gastric gland,
LP: lamina propria, SE: simple cuboidal epithelial cells) (PAS-Alcian blue) 400X.
S
EF
LP
GG
SE
MU
SM
M
S
MU
M
SM
K
A
V
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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Table 2. Measurement of the Ventriculus layers in the ring necked parakeet -P. krameri and the black
shouldered kite -E. caeruleus.
Ventriculus layers thickness
Ring-necked parakeet
(Mean μm ± SE)
Black-shouldered Kite)
(Mean μm ± SE)
koilin
170.99±6.10
Very thin
Mucosa
200.88±4.29
289.3±13.75
Submucosa
59.40±2.39
61.46±3.00
Musclaris externa
1124.1±18.54
279.2 ± 7.20
Serosa
135.92±4.65
181.74 ±6.26
2. Black winged kite -E. caeruleus
A. Proventriculus
The mucosa showed numerous fingers-like shape folds called mucosal folds with flat apexes and their length
measured (171.22±2.81μm) The mucosal epithelium was lined with simple columnar epithelium with clear
cytoplasm cells and an oval dark nucleus (Fig.10, 12).
The lamina propria extended inside folds and contained blood vessels, lymphocytes, and simple tubular glands
in the base of the folds which were lined by low columnar cells with spherical nuclei. The muscularis mucosae
composed of smooth muscle arranged longitudinally in a thin layer extends inside the folds. These muscles
surrounded the surface gastric glands and the deep proventriculus glands located under the muscularis of
mucosa (Fig.10).
The thickness values of submucosa were (819.09±22.52μm). The most space of the proventriculus wall
consisted of dense connective tissue rich in blood vessels and filled with deep gastric glands. Each gland was
surrounded by a thin connective tissue, chief cells, blood vessels, and smooth muscles, each gland consisted
of several secretory tubules that empty their secretions in collecting ducts (Fig.11). The mean length values
of these glands were (425.59±18.88μm) and the width (293.90±17.47μm) (Tab. 1).
The muscularis externa consisted of two layers of smooth muscle each oriented in a different plane: an inner
circular layer and an outer longitudinal layer, the muscle layers separated by the connective tissue containing
blood vessels, and nerves (Fig.10). The mean thickness values of muscularis externa were (247.18±9.75μm)
The serosa consisted of connective tissue with blood vessels and lymphocytes and was covered by simple
squamous cells or mesothelium, the mean thickness of serosa was (329.62±14.26μm).
The surface epithelium of the proventriculus showed a strongly positive reaction with PAS-AB stains. The
superficial gastric glands give red color with PAS- AB stain (Fig. 11).
Figure 10. Cross-section of the proventriculus wall in black shouldered kite (DGG: deep gastric glands, M:
mucosa, MF: mucosal folds, MU: muscularis, SM: submucosa) (H&E) 40X.
DGG
M
MU
SM
MF
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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Figure 11. Cross-section of the proventriculus wall in black shouldered kite (DGG: deep gastric gland, K:
koilin, M: mucosa) (PAS-Alcian blue) 100X.
Figure 12. Cross-section of the proventriculus mucosa in black shouldered kite (LP: laminae propria, SE:
simple columnar epithelium) (H&E) 400X.
B. Ventriculus
The mucosa showed long parallel folds, and gastric pits which occupy more than half of the mucosa (Fig. 13)
The mucosa lined by simple columnar epithelial tissue consists of columnar cells representing surface mucous
cells with oval nuclei located near the bases of the cells (Fig.14). The Lamina propria contained numerous long
simple tubular glands with large cavities. These glands are lined by short columnar cells with oval nuclei called
Chief cells. On the other hand, the glands opened in grooves between the folds. Lamina propria was based on
a layer of connective tissue composed of collagen fibers (Fig.15). The muscularis externa consisted of two
muscular layers, the internal arranged circularly and external arranged longitudinally extended into the cores
of gastric folds (Fig.13). The mean thickness values of mucosa were (289.3±13.75μm). The mean thickness
values of submucosa were (61.46±3.00μm). The mean thickness values of muscularis were (279.2 ± 7.20μm)
(Tab. 2). The serosa consisted of connective tissue with collagen fibers, blood vessels, and lymphocytes
covered from the outside by a single layer of simple squamous cells, the mean thickness values were (181.74
±6.26μm). The mucosal epithelial cells lining the surface of the tubular glands were stained strongly with PAS-
AB stain (Fig.15).
LP
SE
DGG
K
M
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Figure 13. Cross-section of the ventriculus folds in black shouldered kite (GP: gastric pits, LF: long fold, M:
mucosa, MU: muscularis, SM: submucosa) (H&E) 40X.
Figure 14. Cross-section of the ventriculus wall in black shouldered kite (GG: gastric glands, GP: gastric pits,
M: mucosa, MU: muscularis, SM: submucosa) (H&E) 100X.
Figure 15. Cross-section of the ventriculus wall in black shouldered kite (GG: gastric gland, GP: gastric pits,
M: mucosa) (PAS-Alcian blue) 400X.
Discussion
The present study showed clear differences between the stomachs of two species of birds, the ring necked
parakeet proventriculus was a fusiform shape tube separated from the gizzard by an isthmus. This result was
in agreement with the finding of Al-Juboory et al. (2016) in the common wood pigeon, while in the black
shouldered kite, proventriculus was pear in shape, wider and longer than that of the parakeet and no isthmus
SM
M
MU
GP
LF
MU
SM
GG
M
G
P
M
GG
GP
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separated proventriculus from the gizzard (Hamdi et al., 2013). Gizzard in the parakeet appeared with disc or
biconvex lens shape, lined with yellowish-green tissue (koilin). Moreover, this result was in agreement with
the finding of Al-Juboory et al. (2016) in the common wood pigeon. The Kite gizzard appeared pear-shaped
with a vertical and longitudinal pattern of the inner folds and grooves, lined with a very poor yellowish koilin
layer (Abumandour, 2014). The koilin layer was a grinding surface, enabling the muscular ventriculus to
mechanically action for digesting food. Granivorous birds possess a thick cuticle layer with a well-developed
muscular ventriculus. In contrast, Carnivores birds possess a thin-walled ventriculus and soft cuticle (Al-Saffar
and Al-Samawy, 2015). The differences in stomach shape in birds are probably due to the feeding habits or
perhaps the amount of food engulfed by birds (Abd-Elnaeem et al., 2019). The birds feed on relative large soft
items of food, it required a stomach adapting more for storage than digestion as in the stomach of Kite under
investigation, by contrast, in the parakeet which feeds on hard items of food, stomach adapting for more
digestion than storage (Al-Juboory et al., 2016).
The histological study showed that the proventriculus wall of two species of birds consisted of the mucosa,
submucosa, muscularis, and serosa; the same result was observed by Al-Taai and Hasan (2020) however
disagree with the finding of Zhu (2015) in Black-tailed crake who mentioned that the proventriculus is
composed of three layers, mucosa, musculosa, and serosa while submucosa was absent.
The mucosa of the proventriculus in the kite was thrown into numerous finger-like shape folds with flat apex;
the simple columnar epithelial cell was lining the proventriculus folds; this finding is identical with many
previous studies such as El-Shammaa et al. (2019) in Ostrich and Hassan and Moussa (2012) in duck.
The lamina propria of mucosa appeared as connective tissue with blood vessels and lymphocytes. Simple
tubular glands were found in the base of proventriculus folds, this finding is identical with many previous
studies such as Jassem et al. (2016) in Common moorhen and Beheiry (2018) in turkey. The Simple tubular
glands in the Kite were lined by low columnar epithelial, similar observations mentioned by AL Sheshani
(2006) on the carnivorous bird, Accipiter nisus.
The parakeet mucosa glands of the proventriculus were lined by simple cuboidal epithelial tissue. Previous
studies have mentioned the same result such as Taher et al. (2020) in moorhen and Hassan and Moussa (2012)
in pigeon. The histological results showed that these glands were larger and deeper in the kite when
compared with parakeet proventriculus glands; muscularis mucosa was not observed under the mucosa in
the parakeet, while in kite the muscularis mucosae appeared as a smooth muscle layer extending inside the
proventriculus folds; this finding was in agreement with Batah et al. (2012).
The submucosa was composed of connective tissue containing blood vessels in both species of birds.
Submucosa occupied most of the proventriculus wall. It was contained numerous deep proventricular glands.
Submucosal glands were compounded tubular branches lined by cuboidal epithelial cells. The results are by
El-Nahla et al. (2011), who confirmed the presence of this gland in the submucosa layer as in the present
study, while other studies mentioned the presence of glands between the muscularis mucosa of quail (Ahmed
et al., 2011). These results are in disagreement with the present finding. These differences in the location of
the glands may be due to species variation or due to developmental stages differences. Each gland enclosed
by a connective tissue contains blood vessels and nerves (El-Nahla et al., 2011).
The muscularis externa was composed of two layers of muscle as mentioned by Kausar et al. (2019) in
domestic pigeons; these findings were in disagreement with Rodrigues et al. (2012) in blue and yellow
macaws. The inner circular layer in the kite is thicker than the outer longitudinal layer such as in pheasant
(Parisa et al., 2019). The findings were in disagreement with El-Nahla et al. (2011).
The tunica serosa in the present study was composed of connective tissue containing blood and lymph vessels
as agreed with the study of Salih et al. (2019).
From the results above it can be concluded that the kind of food reflects some histological differences in the
proventriculus between two species of birds appear in the thickness of the layers that composed the wall of
the glandular stomach in kite and the distribution of deep submucosal glands.
The histological examination in the present study showed that the gizzard wall of the two species of birds
consisted of four layers (Taher et al., 2020); this finding is in disagreement with Zhu (2015) in Black-tailed
crake who mentioned that the ventriculus is composed of three layers, mucosa, musculosa, and serosa while
submucosa was absent.
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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The mucosa of the kite gizzard had three sub-layers, epithelium, lamina propria, and muscularis mucosa; these
findings are in disagreement with the findings of Wilkinson et al. (2018), while the mucosa of parakeet
consisted of two layers, epithelium and lamina propria. The type of feeding leads to the absence of muscularis
mucosae in the parakeet while the muscularis externa more develop which replace from this layer; this result
was in agreement with Zaher et al. (2012).
The present findings showed that the surface lining of the tunica mucosa in kite studied was simple columnar
epithelium; this finding is in agreement with the results of Hussein et al. (2020). In the parakeet, the surface
lining of the tunica mucosa was simple cuboidal epithelium. This finding is in agreement with the results of
Taher et al. (2020) in Moorhen.
The present histological examination revealed that there was a hardened membrane yellow to green in color
resting on the surface of the epithelium in the parakeet. This cuticle or koilin membrane is made from
carbohydrates and proteins, as mentioned by Zhu (2015). This layer shows great variation and is most
elaborate in granivorous. On the other hand, the cuticle or koilin layer did not found covering the epithelium
of the gizzard in the kite; this finding was in agreement with Al-A'araji (2007) and AL Sheshani (2006) who
mentioned that the koilin layer did not found in kestrel and Accipiter nisus. The presence of the koilin layer in
the gizzard of parakeet, and disappeared in the gizzard of the kite could be related to the kind of food on
which the function of gizzard in these birds depends. The species with well-developed muscle and hard thick
membrane protects the gizzard's epithelium (Das et al., 2018). The main function of the muscular stomach in
granivorous species is to triturate the food in preparation for gastric proteolysis. This is achieved by powerful
asymmetrical contractions of the muscles aided by the tough internal cuticle layer, while in species with thin
sac-like gizzard, the gizzard function mainly as a storage organ where the gastric juice can act.
Lamina propria thickness in parakeet was less than that of the kite, which was loose connective tissues with
many tubular glands also appeared in love birds (Al-A'araji, 2007). The differences found between the lamina
propria of gizzard in parakeet and that in kite might be due to the variation in the number of tubular glands
that present in their lamina propria. Submucosa consisted of connective tissue containing blood vessels and
nerves in both studied birds; this finding was in agreement with the result of Madkour and Mohamed (2019).
The histological studies showed that the muscularis externa of the ventriculus was composed of two muscular
layers in the two studied birds arranged into the inner circular layer and outer longitudinal layer. Also, these
findings showed the difference in thickness of this layer between two species of birds in the current study.
Parakeet gizzard showed the larger thickness in its muscularis externa, while the less thickness in the gizzard
of the kite. The muscular part of the stomach in birds is extremely variable in its muscularity dependent on
the type of diet that the bird consumed (Al-Saffar and Al-Samawy, 2015).
The differences in the thickness of the wall of gizzard that appeared in the present work among the two
species of birds were in agreement with Al-Juboory et al. (2016) that observed in carnivorous birds, that
ingested soft food items, the gizzard sac-like structure with a thin wall; this is a marked contrast to the gizzard
of granivorous birds that ingest harder food items, and therefore it requires a well-developed muscular
gizzard; these results were confirmed by Al-Kinany (2019). The gizzard of granivorous bird play important role
in the physical digestion of food while in carnivorous it functions mainly as a storage organ where the gastric
juice can act.
Histochemically, on applying PAS-AB (pH 2.5) stain, the mucous cells lining the epithelium and pits of the
proventriculus were reacted strongly with PAS-AB (pH 2.5) stains. This reaction indicated the presence of high
content of neutral and acidic mucins, similar to findings of Hamdi et al. (2013) in the proventriculus of the
mallard. The deep gastric glands of the proventriculus in the two studied birds give red color with PAS-AB (pH
2.5) stain due to the presence of neutral mucin secretions. This finding is identical with many studies in many
avian species, such as Vanellus spinosus (Taki-El-Deen, 2017) and common starling (Sayrafi and Aghagolzadeh,
2019)
Nat. Volatiles & Essent. Oils, 2022;9(1): 13631-13644
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In the ventriculus (Gizzard), the cuticle layer in the ventriculus showed a pink-colored reaction for PAS and no
reaction with Alcian blue (pH 2.5), due to the presence of neutral mucin (Taher et al., 2020). The mucosal
epithelial cells lining the surface of the tubular glands in the ventriculus were stained strongly with both PAS-
AB (pH 2.5) stains. This reaction indicated the presence of neutral and acid mucin (Al-Saffar and Al-Samawy
2015, 2016). The neutral and acid mucin may protect the ventriculus mucosal surface and forms a resistant
barrier (Taher et al., 2020).
Conclusion
The stomach of birds is different depending on the diet; in carnivorous birds, the stomach was simple with
single-chamber and thin-walled; in granivorous birds, the stomach is complex with two chambers and a thick
wall in the muscular part covered with a koilin layer. There were a high number of longitudinal folds and
gastric glands in the Carnivorous stomach.
Acknowledgment
We extend our sincere thanks to the Mustansiriyah University, the College of Sciences especially the faculty
of the biology department for their cooperation in accomplishing this research.
Conflict Of Interest Statement
The results of the current study are part of the requirements of Ph.D. in Department of Biology, College of
Sciences, Mustansiriyah University in Zoology, for the first author. Also, we are the authors of this manuscript,
declare and confirm that no significant financial or other relationship with any official institution.
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