Features of mammary gland morphology in domestic carnivores

Abstract

The mammary gland is a target organ for hormones in the hypothalamus, pituitary gland, thyroid gland, and ovaries. In the postnatal period of animal ontogenesis, breast growth, and development are determined by the estrous cycle and pregnancy. One of the most pressing problems in morphology, mammology, and reproductology of animals is the study of the structure of the breast at the macro and microscopic levels. However, modern studies on the morphology of animals' breasts are mainly devoted to the features of pathomorphological changes in the breast during carcinogenesis. The work aims to conduct a scientific review of the study of normal breast morphology in domestic carnivores. Electronic publication searches have been conducted in the Web of Science, Scopus, PubMed, and Google Scholar databases over the past 20 years. The principles of objectivity and a comprehensive attitude to studying the chosen problem are used. The authors of the review article review the current scientific literature and summarize current knowledge on the features of dog and cat breast morphology. The anatomical structure of the breast of animals is presented with an emphasis on its topography. According to the description of the microscopic structure of the breast, its main structural components are characterized by secretory parts (alveoli and tubes) and intraparticle excretory ducts. Anatomical characteristics of the nerves, blood, and lymphatic vessels of the mammary glands of dogs and cats are presented. Morphological changes in the mammary gland of dogs and cats at different stages of the estrus cycle and during pregnancy are described; in particular, the mammary gland is at rest (inactive) during proestrus and estrus. According to diestrus, due to an increase in progesterone levels, successive morphological changes occur, in particular, stromal and ductal proliferation; early development of lobules with branching ducts and proliferation of alveoli; the dominance of glandular tissue with large lobules containing secretory material; early regression, an increase in interparticle connective tissue, eosinophilic protein secretion in dilated ducts and alveoli. Complete involution of the alveoli and tubes of the breast is recorded at the end of the anestrus. The described anatomical and microscopic features of the structure of the mammary glands of dogs and cats are relevant for the comparative morphology of carnivores at different stages of the sexual cycle and during pregnancy. Data on blood supply, lymphatic drainage, and innervation of the breast are essential for its functional characteristics in normal and pathological conditions, particularly for developing a reasonable model of breast extirpation in malignant tumors.