ABSTRACT
The endocrine system is comprised of the glands and tissues that release hormones into the bloodstream, usually in response to a signal from the hypothalamus or pituitary gland. Most endocrine systems are tightly controlled by positive and negative feedback, with the target organs releasing a product that inhibits the release of the stimulatory or releasing hormone. Endocrine diseases usually involve problems with overproduction or underproduction of hormones, or with altered tissue responses to them. A complete blood count should be submitted to rule out infectious diseases and may yield subtle changes compatible with an endocrine disorder. Measurement of serum concentrations of hormones and response of these hormones to evocative testing plays an important role in the diagnosis of endocrine diseases. Differential diagnoses for hypothyroidism with goitre in adult horses include a benign thyroid tumour or other causes of swelling in the upper neck such as an enlarged salivary gland or lymph node.
