AN ANATOMICAL STUDY OF THE LYMPHOID ORGANS OF THE GUINEA FOWL (NUMIDA MELEAGRIS GALEATA) AT EMBRYONIC AND POSTHATCHING PERIODS
AN ANATOMICAL STUDY OF THE LYMPHOID ORGANS OF THE GUINEA FOWL (NUMIDA MELEAGRIS GALEATA) AT EMBRYONIC AND POSTHATCHING PERIODS
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Date
1997
Authors
ONYEANUSI, Barth Zuchukwu
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Abstract
Guinea fowl lymphoid tissues (the thymus,Bursa of
Fabricius, Harderian gland and the spleen) were examined at
embryonic and post-hatching periods to observe the gross and
histologic features and their growth rate in relation to the
age of birds. Whole embryos from day three to day 17 were
wax-embedded, serially sectioned at 5.0m, stained with
Hematoxylin and Eosin and observed for histological details
using light microscope.
Individual lymphoid tissues obtained by dissecting
embryos from day 18 to day of hatching and from guinea fowls
from day one post-hatch till 32 weeks of age were epon
embedded. Thick sections (0.5 - 1.0m)and thin sections (0.05
- 0.2m) were observed using light and electron-microscopy
respectively.
A total of 100 birds, in groups of five, were euthenized
and their lymphoid tissues used for the study of the growth
rate in relation to the age of the birds.
Five adult birds at the age of 20 weeks post-hatch were
used to study the gross features of the tissues.
Gross Anatomy
The thymus was grossly observed to contain a total of 13
lobes with seven lobes on the right side and six lobes on the
left side of the neck. The third and the sixth lobes were the
largest.
The bursa of Fabricius was an oval blind sac with a
short stalk from its point of origin. Each gland contained 12
to 14 primary folds or plicae internally.
The Harderian gland was a bright pink organ with slight
constriction about its midpoint and had an irregular outline.
It had a mean length of 15.0±0.8 mm and a width of 6.0±0.4 mm
at the broader end.
The spleen was a smooth bean-shaped structure with a
on the ventral surface which formed the entry and exit
of its vessels. The organ was covered by a thin but tough
capsule except at the hilus. Three short arteries entered the
splenic substance at its ventral surface.
Morphometric Values
It is observed that the thymus, bursa,Harderian gland
and spleen had minimal mean weights at day one post hatch.
The maximal mean weights were around 18 - 20 weeks post-hatch
except Harderian gland which had its maximum at 32 weeks.
The bursa and thymus had minimal relative weights at 32
weeks while the Harderian gland and spleen had theirs around
24 - 26 weeks.
The bursa, spleen and thymus had their maximal relative
weights at four weeks while Harderian gland had maximal
relative weight at 10 weeks.
Fig.l revealed a significant decrease in weight and the
commencement of involution of the thymus after 20 weeks and
of bursa after 18 weeks. Harderian gland and spleen had
continous growth throughout the study.
Histology
Thymus
The thymus was first observed on day seven of incubation
as a collection of reticular cells and large lymphocytes.
Individual red blood cells were seen together with the
reticular and lymphoid cells on day 10 and these red blood
cells had appeared in groups on day 12. Small lymphocytes and
the begging of capsular formation were observed on day 14.
By day 16, few blood vessels were seen in the interlobular
spaces.
By day 18, thymic corpuscles appeared within the gland
and there was presence of tiny vacuoles within the reticular
cells. Macrophages were first observed on day 20, the cortex
and medulla became distinguishable by day 21.
On day 24, thymic corpuscles contained few debris at
central region. Distribution of blood vessels was uniform
between the cortex and medulla at five days post-hatch while
plasma cells appeared in the gland at three weeks post-hatch.
Bursa
The bursa was observed day eight of incubation and
bounded by two layers of epithelial cells. Blood capillaries
and few lymphocytes appeared in the mesenchyma on day 12.
Vacuoles were also observed in the epithelial cells.
Capsule, plicae"and epithelial buds had formed on day 18
and macrophages were observed on day 20. Blood vessels had
occurred in the cortex and goblet cells were observed on day
21 while plasma cells were seen on day 22. On day one posthatch
surface epithelium was pseudostratified.
Harderian gland
Harderian gland, bounded by epithelial and mesenchymal
cells, was observed on day 10 of incubation. Blood vessels
and red blood cells were seen on day 12 while large
lymphocytes appeared on day 13. The capsule appeared on day
14 while small granules were seen in the lymphocytes on day
16. Tiny vacuoles appeared in the epithelial cells on day 18,
and tubulo-acinar formation and small tubular ducts were also
seen on this day.
By day 19,pseudostratification of epithelium was
observed. Acinar cells were filled with secretory materials
on day 24. At eight weeks, squamosis of epithelial cells was
evident.
Spleen
This organ was observed on day seven of incubation as a
bean-shaped structure comprising of reticular cells and large
lymphocytes. Red blood cells were noticed in addition on day
eight. Sinusoids appeared on day nine while capsular
formation was seen on day 10.
Small lymphocytes, macrophages and small blood vessels
were observed on day 11. By day 16, granulocytes had
appeared. Red and white pulps were distinguishable on day 21.
On day one post-hatch, granulocytes had disappeared and
capsule was at its greatest thickness. At seven weeks posthatch,
plasma cells and monocytes were observed in the
splenic cords and sinusoids respectively. Two germinal
centres appeared in the gland at 13 weeks post-hatch.
Although the lymphoid organs of birds are based on the
same structural patterns as have been mentioned by several
hors, it has been conclusively shown that at least there
are minor but important differences that exist within these
individual glands amongst the different species of birds.
The study has shown that both the thymus and bursa
undergo involution at different times in different avian
species and in the guinea fowl they do not invariably
disappear altogether. The spleen and Harderian gland did not
even begin to regress as late as 32 weeks of life but
continued to grow.
This study however, provides an opening for further
investigation beyond 32 weeks of life to observe the final
outcome of these lymphoid organs in the guinea fowl. There
would also be the need for thymectomy or splenectomy to
erve its effect on the sizes and cell contents of the
other lymphoid tissues so as to give a better picture of the
interaction between primary and secondary lymphoid organs.
Description
A DISSERTATION SUBMITTED TO THE POSTGRADUATE SCHOOL, AHMADU BELLO
UNIVERSITY, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY (Ph.D).
DEPARTMENT OF ANATOMY
FACULTY OF VETERINARY MEDICINE
AHMADU BELLO UNIVERSITY,
ZARIA.
1997
Keywords
ANATOMICAL STUDY,, LYMPHOID ORGANS,, GUINEA FOWL,, NUMIDA MELEAGRIS GALEATA,, EMBRYONIC AND POSTHATCHING PERIODS