Microanatomy and Histochemistry of the Salt Glands of the Kentish Plover, Charadrius alexandrines (Aves, Charadriidae)

Abstract

Problem statement: Histological and histochemical investigations on the salt glands of birds are very limited. The present study was performed to characterize the microanatomy and histochemistry of the salt glands of the Kentish plover (Charadrius alexandrines). Approach: Salt glands of the bird under study were fixed, dehydrated, cleared, impregnated and blocked out by paraffin wax. Paraffin sections were utilized in histological and histochemical examinations to characterize the structure and chemical contents of these glands. Results: The Kentish plover had a well developed bilateral seromucous salt glands lie in the supraorbital depression of the frontal bone. Each gland is about 0.18 g and had lobular arrangement consisted of one cell thick secretory tubules enmeshed in tiny blood capillaries. The tubules radiate from central canals that drain in a main duct of 3-4 mm in length and opens into the external nares. The secretory tubules were lined by a single layer of principal cells and opens in intercalated ducts followed by striated ducts. The employed histochemical tests indicated that seretory tubules elaborate proteins and acid mucosubstances but are devoid of glycogen and neutral mucosubstances while the intertubular stroma showed metachromatic, alcianophilic and PAS reactivity. Conclusion/Recommendations: The results of the present study revealed that salt glands of Kentish plover are active adaptive tool of osmoregulation to control the amount of water needed by this bird. More research is needed to understand the adaptation of the seabirds to the physiological stress of the salt load.