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Part 2 book "Avian anatomy - Textbook and colour atlas" includes content: Immune system and lymphatic organs (organa lymphopoetica); nervous system (systema nervosum); endocrine glands (glandulae endocrinae); the eye (organum visus); the ear (organum vestibulocochleare); common integument (integumentum commune); clinical examination; imaging techniques, handling, restraint and anaesthesia, medication and blood collection techniques, endoscopy, surgical fracture management, falconry and raptor medicine.
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Ebook Avian anatomy - Textbook and colour atlas (2/E): Part 2
12
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Immune system and
lymphatic organs
(organa lymphopoetica)
K.-D. Budras, H. E. König and R. Korbel
The lymphatic system of the class Aves includes the follow- organs (thymus, cloacal bursa, spleen and bone marrow) and
ing distinguishing features: the tonsils (tonsillae pharyngis, oesophagi and caeci).
In phylogenetic terms, the avian lymphatic system can
• lymphatic hearts (cor lymphaticum), be considered a transitional stage between that of reptiles
• mural lymphatic formations in the lymphatic vessels, and mammals, exhibiting characteristics of both.
• the cloacal bursa (bursa of Fabricius, bursa Fabricii). A multidirectional system, incorporating anastomosing
lymphatic vessels and lymph hearts, is seen in amphibians
The primary function of the lymphatic system and its cells, and reptiles. In mammals, on the other hand, the flow of
particularly lymphocytes and macrophages, is to provide the lymph through the lymphatic system has become exclu-
protective response referred to as immunity. Anatomically, sively unidirectional.
the lymphatic system includes the lymphatic vessels (includ- Embryonically, birds have both a unidirectional sys-
ing the lymph hearts) and lymphatic tissue. The main tem, in which lymph drains into veins at the paired venous
components of the lymphatic tissue are the lymph nodes, angle, and an ‘alternative route’, by which lymph passes
diffuse lymphoreticular formations (with or without a through paired lymph hearts (located either side of the
germinal centre) found predominantly in parenchymatous first caudal vertebrae) to enter the dorsal pelvic veins. The
organs such as endocrine glands and the liver (formatio- persistence of lymph hearts post-hatching varies according
nes lymphoreticulares parenchymatosae), the lymphatic to species.
12.1 Histological section of the cloacal bursa (bursa Fabricii) of a chicken.
Avian Anatomy.indb 179 05/10/2016 12:15
180 Avian Anatomy
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12.2 Wall of the initial segment of a collector vessel (vas 12.3 Wall of the terminal segment of a collector ves-
lymphaticum myotypicum) with external lymphoreticu- sel (vas lymphaticum myotypicum) with internal mural
lar formations (schematic; left – longitudinal section, reticular formations (schematic: left – longitudinal sec-
right – transverse section). Adapted from Berens von tion; right – transverse section). Adapted from Berens
Rautenfeld et al. 1983. von Rautenfeld et al. 1983.
Other features peculiar to the avian lymphatic system of the lymphatic tissue found in reptiles, and are widely
are the cloacal bursa, a primary lymphatic organ for the distributed in the lymphatic vessels of birds.
differentiation of B-lymphocytes (Figure 12.1), and a spe-
cialised system of lymphatic chambers in the cloaca and Lymphatic vessels
phallus that brings about erection (see Chapter 9 ‘Male (systema lymphovasculare)
genital organs’). The lymphatic vascular system drains fluid from most of
Birds also appear to represent an intermediate phylo- the tissues of the body. As in mammals, lymphatic capil-
genetic stage with respect to the development of lymph laries (and thus lymphatic drainage) are absent in epithelial
nodes. These are present only in water and marsh species, tissue, cartilage, bone marrow, the thymus and in much of
as paired cervicothoracic and lumbar nodes. While avian the central nervous system.
lymph nodes can reach substantial lengths (up to 40mm in The lymphatic capillaries (rete lymphocapillare) are
the goose), their structure differs significantly from those blind-ended. These structures are also referred to as ‘initial
of mammals, bearing greater resemblance to mural lym- lymph sinuses’, a term that better reflects their variable
phoreticular formations (Figures 12.2 and 12.3). Only just calibre. Fluid travels through pre-formed fissures within
visible to the naked eye, these latter structures are typical the tissue towards the capillaries (sinuses). This phenom-
12.4 Lymp ...