[The morphology of the thyroid gland in poultry with special regard to seasonal variations]. / Untersuchungen zur Form der Schilddrüse (Glandula thyreoidea) beim Geflügel mit besonderer Berücksichtigung der jahreszeitlichen Schwankungen.

ABSTRACT

The thyroid glands of 31 chickens at the age of 17 to 24 months were investigated. Different methods of anatomical preparation, casts of vessels and scanning electron microscopy were used. The thyroid gland of birds is a paired organ. It is located on the ventral surface of the base of the neck within the thoracic inlet. The left thyroid gland is placed more cranially than the right one. Each thyroid gland is closely connected to the common carotid artery on the medial side, from which it is supplied and to the jugular vein on the lateral side. It is a reddish-brown organ and of lenticular profile. The gland measures on average 10 mm in length, 6 mm in width and 2 mm in thickness, and is covered by a thin connective tissue capsule which holds adipose cells. It seems that each thyroid follicle is surrounded by a net of capillaries. The investigation by scanning electron microscopy proved that the follicles are oval with a pyramidal top on each end. The cuboidal epithelium cells leave impressions in the colloid. Epithelium cells carry microvilli on the follicle side surface. Described seasonal changes of the thyroid gland in size and activity were able to be confirmed by the examination of the organ in July and December. In winter the follicular cells were higher and the follicles had a greater volume.