Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 31

The endocrine system resembles that of other vertebrate classes but has some features with no mammalian counterparts such as the urophysis and the corpuscles of Stannius.

The pituitary (hypophysis) has many endocrine functions including the secretion of hormones (GnRH, TSH, vasopressin, etc.). A saccus vasculosus is associated with the hypothalamus and helps detect seasonal changes (Nakane et al. 2013). The pineal organ (epiphysis) is light‐sensitive and lies between the midbrain and dorsal forebrain; it can be seen through the cartilage in young fish. The urophysis is a thickening of the caudal spinal cord and has neurosecretory cells with an osmoregulatory function (Stoskopf 1993; Roberts and Ellis 2012).

The thyroid gland is usually diffuse, with follicles along the ventral aorta, branchial arteries, pharyngeal cavity, and retro‐orbital tissues. Thyroid hyperplasia (goiter) is common in fish and can cause oral or respiratory obstruction.

Pancreatic tissue (exocrine and endocrine) in bony fish is typically diffuse throughout the adipose tissue or along the portal veins (Caruso and Sheridan 2011). It is occasionally seen as white nodules (Brockmann bodies) in the mesentery around the bile ducts and portal veins (Caruso and Sheridan 2011). In some fish, the pancreas is associated with the venous system or capsule of the spleen. It is a discrete organ in the lungfish (Dipnoi) and some catfish (Stoskopf 1993).

In most fish, interrenal tissue is the equivalent of the mammalian adrenal cortex. It is found within the cranial kidney or around the posterior cardinal veins in teleosts. The suprarenal tissue is the equivalent of the mammalian adrenal medulla and consists of scattered chromaffin tissue within the cranial kidney (Stoskopf 1993; Roberts and Ellis 2012). In sculpins (Cottus spp.), the tissues are combined into a distinct adrenal organ.

Corpuscles of Stannius are endocrine cells in the caudal kidney of bony fish. They act like parathyroid glands and secrete teleocalcin (also called hypocalcin) which blocks calcium absorption across the gills (Roberts and Ellis 2012). Ultimobranchial bodies are endocrine cells located ventral to the esophagus or in the septum that separates the heart from the coelom. They also act like parathyroid glands and produce calcitonin for calcium regulation (Stoskopf 1993; Roberts and Ellis 2012)

It is reported that the pseudobranch may have some endocrine functions (see above). The gonads can also be considered part of the endocrine system as they secrete androgens and estrogens.