Veterinary Endocrine System (VETERINARY ASSISTANT EDUCATION)

Main Ideas

Endocrine System Overview

The endocrine and nervous systems coordinate the body’s functions. The presenter describes the hypothalamus as an important coordinator.

The glands discussed include the pituitary, thyroid, parathyroids, pancreas, adrenal glands, ovaries, and testes. They produce hormones that affect many body processes.

The presenter explains negative feedback as a control mechanism: a gland releases a hormone, hormone levels are monitored in the blood, and production adjusts when levels are too high or too low. A thermostat regulating a furnace is used as an analogy. Hormone regulation often involves multiple glands influencing one another rather than a single gland acting alone.

Pituitary Gland

The pituitary is described as the “master gland” because its hormones regulate other glands and body functions. Hormones and roles discussed include:

• Thyroid-stimulating hormone (TSH): Stimulates the thyroid.
• Growth hormone: Supports bone growth and helps regulate energy use.
• ACTH: Stimulates the adrenal glands.
• Prolactin: Supports mammary-gland development and milk production.
• Follicle-stimulating hormone (FSH): Helps trigger the estrous cycle.
• Luteinizing hormone (LH): Initiates ovulation.
• Antidiuretic hormone (ADH): Helps maintain water balance.
• Oxytocin: Supports milk ejection and uterine contractions.

Pituitary dysfunction can affect thyroid function, blood pressure, ovulation, growth, and energy metabolism.

Thyroid Gland and Thyroid Disease

The thyroid lies on either side of the upper trachea. T3 and T4 help regulate metabolism, while calcitonin is involved in blood-calcium regulation. Thyroid regulation is presented as a negative-feedback loop involving the hypothalamus, pituitary, and thyroid.

• Hypothyroidism is an underactive thyroid. Common signs include lethargy, reduced energy, poor coat condition, and weight gain. It is most commonly seen in dogs and is generally treated with daily thyroid-hormone replacement.
• Hyperthyroidism is an overactive thyroid. Signs include hyperactivity, weight loss, muscle loss, increased vocalization, and a faster heartbeat. It is more commonly seen in cats. Treatment may include daily medication to suppress thyroid activity or radioactive iodine.

Pancreas, Insulin, and Diabetes

The pancreas has both digestive (exocrine) and hormone-related (endocrine) functions. Insulin helps regulate blood glucose and supports glucose entering cells for energy use.

If the pancreas does not produce enough insulin, diabetes can result. Some dogs and cats require daily insulin injections. The presenter also mentions specialized low-carbohydrate veterinary diets, particularly for cats.

When glucose cannot be used by cells, the body may break down fat and protein for energy, producing acidic byproducts. Signs of diabetes include:

• Weight loss
• Increased urination (polyuria)
• Increased thirst (polydipsia)
• Reduced appetite
• Loss of muscle mass

Blood and urine testing may reveal high glucose.

Adrenal Glands and Adrenal Disease

The adrenal glands sit near the kidneys and produce hormones involved in stress responses and in regulating functions such as blood pressure and heart rate.

• Cushing’s disease (hyperadrenocorticism): The presenter describes this as excessive cortisol production. Possible signs include a pot-bellied appearance, hair loss, increased skin pigmentation, polyuria, and polydipsia. Laboratory findings may include lipemic serum and increased glucose and cholesterol. Causes mentioned include adrenal or pituitary tumors, with pituitary tumors described as more common.
• Addison’s disease (hypoadrenocorticism): Insufficient adrenal hormone production, particularly cortisol, can disrupt electrolyte balance and the body’s stress response. Signs can vary widely and may include weakness, depression, poor appetite, vomiting, polyuria, polydipsia, and muscle tremors.

The presenter emphasizes that Addison’s disease can be difficult to recognize because its signs are varied and may be intermittent. They recount their dog Leia’s severe Addisonian crisis, which included tremors, inability to stand, very low blood pressure, and a heart murmur.

Homework

• Identify three functions of testosterone in the body.
• Research two hormones secreted by the ovaries and describe their effects.

Speakers and Sources Featured

• Presenter: An unnamed veterinary educator who explains the endocrine system and shares a personal account of their dog, Leia.
• American Association of Feline Veterinary Practitioners (AAFP): Cited as the source of a cat-hyperthyroidism treatment resource recommended in the presentation.
• Leia: The presenter’s dog, mentioned in an anecdote; she is not a speaker.