Review of the Endocrine System

19.0 Endocrine System 19.1 Review of the Endocrine System The endocrine system consists of glands and hormones. Glands are situated throughout the body and produce “hormones.” A hormone is a chemical substance that, once produced by a gland, enters the blood stream, and travels throughout the body. Hormones act as “chemical messengers” to control the work of different organs. Reproductive hormones are covered in Chapter 10. See page 131. Other hormones control growth, blood pressure, chemical balance in the blood and tissues, as well as coordination of many systems within the body. This chapter is about that part of the endocrine system which affects the work of AHAs.

Posterior Pituitary Gland and Oxytocin Oxytocin is a hormone made by the posterior pituitary gland in the brain. When a baby animal starts to nurse, the mother’s pituitary gland releases oxytocin that affects the uterus and the udder. Oxytocin has two main functions:

1. It causes the muscles of the uterus to contract during delivery (to push the baby and placenta out).

1. It causes milk to be released from the udder into the teats (called “milk letdown”) so that milk will flow easily.

Practical Uses of Oxytocin: Sometimes oxytocin injections are given to pigs during delivery to hasten the birth of all the piglets. Oxytocin is also used to help expel the placenta and other secretions from the uterus or, after treating a prolapsed uterus, to make the uterus contract.

The Thyroid Gland and Goiters The thyroid gland consists of two parts, one on each side of the windpipe, just below the larynx. The function of the thyroid gland is to take iodine from the blood and use it make hormone called “growth hormone.” This hormone is necessary for normal development of the brain and body.

“Goiter” is the term for an enlarged thyroid gland. A goiter results from iodine deficiency. The thyroid gland enlarges in an effort to make enough growth hormone, despite the lack of iodine. Goiter (or iodine deficiency) is more serious for fetuses and young animals resulting in stillbirth (i.e. dead at birth), stunting, weakness, and mental retardation. If baby calves, lambs or kids are born dead, always check for goiter. If you find goiter, give “iodized salt” (i.e. salt treated with iodine) to pregnant mothers. See page 310.

Adrenal Glands and Steroids The adrenal glands are two small glands located near the kidney. The hormones made by the adrenal glands are commonly called: “steroids”, “corticosteroids”, or “cortisone.”

Steroids, Corticosteroids and Cortisone AHAs must understand about these hormones because they are made into injections that are often used and abused in veterinary medicine. They are commonly referred to as “steroid” injections. Dexamethasone is a common type of steroid used in veterinary medicine to reduce inflammation and treat allergic reactions or shock. See page 85.

Caution: Steroids reduce the animal ability to fight infection and can cause an animal to abort. Do not use steroids on an animal that has an infection, or is pregnant.

Systems of the Body and Associated Veterinary Problems