Below is information about the structure and function of the feline endocrine system. We will tell you about the general structure of the endocrine system works in cats, how it works, common diseases that affect the endocrine system, and common diagnostic tests performed in cats to evaluate the endocrine system.
What Is the Endocrine System?
A cat’s endocrine system is composed of several different types of glands and organs that produce the hormones of the body. A hormone is a chemical that is secreted by a gland in one area of the body and is carried by the bloodstream to other organs in the body, where it exerts some effect. Most hormones regulate the activity or structure of their target organs. The overall effect of the endocrine system is to regulate, coordinate and control many different bodily functions. The endocrine system includes the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, part of the gastrointestinal tract, pancreas, kidneys, liver, ovaries and testes.
Where Is a Cat’s Endocrine System Located?
The endocrine system is scattered through out the body, as follows:
What Is the General Structure of the Feline Endocrine System?
The endocrine system is made up of a collection of glands distributed throughout the body. The endocrine glands produce hormones, and secrete them directly into the internal environment where they are transmitted via the bloodstream. Hormones produce certain effects at different points in the body. Some endocrine glands are directly under the control of the pituitary gland. For example, the adrenal gland is controlled by the pituitary hormone, adrenocorticotropic hormone (ACTH). ACTH causes the adrenal glands to produce cortisone (cortisol), which is also a hormone. Other endocrine glands respond directly or indirectly to concentrations of substances in the blood, such as the insulin secreting cells of the pancreas responding to the sugar concentration in the blood.
What Are the Functions of the Feline Endocrine System?
The major function of the endocrine system is to regulate numerous bodily functions, using specific hormones as messengers. Some hormones affect nearly all cells, while others regulate and affect only a single organ. Hormones act by regulating cell metabolism, by changing or maintaining enzyme activity in receptor cells, and by controlling growth and development, metabolic rate, sexual rhythms and reproduction.
The amount of hormone produced at any one time is controlled by feedback mechanisms. These feedback mechanisms are interactions between the endocrine glands, the blood levels of the various hormones, and certain activities of the target organ. For example, when the pituitary gland increases the secretion of ACTH, the increased levels are detected by the adrenal gland, and the end result is more production of cortisone hormone by the adrenal glands. As the cortisol levels rise in the bloodstream, the hypothalamus eventually detects these higher levels and sends a message to the pituitary gland. The pituitary gland then turns down its own production of ACTH. As the ACTH levels in the bloodstream subsequently fall, the adrenal gland decreases its production of cortisol to a normal level again. This is called a negative feedback loop.
What Are Common Diseases of the Cat’s Endocrine System?
Diseases of the endocrine system can arise with either overproduction or underproduction of hormones. There are numerous diseases of the endocrine system in dogs.
Diseases of the hypothalamus usually result in decreased function of the pituitary gland. The end result is less secretion of several pituitary hormones such as growth hormone, ACTH, or thyroid stimulating hormone.
Diabetes insipidus is a disease where the kidneys are unable to retain water because of a lack of antidiuretic hormone. Animals with diabetes insipidus, also known as water diabetes, are profoundly thirsty and urinate excessive amounts. Diabetes insipidus is extremely rare in the cat.
Undersecretion of pituitary growth hormone (GH) in young kittens is theoretically possible, but has not been well documented. Insufficient production of growth hormone in puppies results in dwarfism, but a comparable disorder is not known to occur in kittens.
Overproduction of growth hormone causes a disorder called acromegaly. Acromegaly in the cat usually develops from a pituitary tumor. Affected cats are usually severely ill with signs that reflect poorly controlled diabetes mellitus, heart disease and kidney failure.
Hyperthyroidism arises when the thyroid gland becomes overactive and excessive amounts of the hormone thyroxine (T4) are released. Too much thyroxine in the body causes multiple clinical signs, including weight loss, increased appetite, vomiting, diarrhea, high blood pressure, and sometimes excessive activity and excessive vocalization. Hyperthyroidism is common in older cats and may be related to nutritional or environmental factors.
Hypothyroidism is a rare disorder of cats. It arises most often after the thyroid glands have been surgically removed to treat hyperthyroidism. With hypothyroidism the thyroid gland does not produces normal amounts of T4. Hypothyroid cats often become sluggish, gain weight, and may become constipated. They have poorly groomed hair coats, with dry and flaky skin.
Undersecretion of parathyroid hormone is called hypoparathyroidism. This condition may develop in young or adult cats, and may be due to immune destruction of the glands. Hypoparathyroidism may also develop in the cat if these glands were inadvertently removed at the same time the thyroid glands were removed (to treat hyperthyroidism). Because parathyroid hormone is needed to maintain normal calcium levels in the body, hypoparathyroid cats exhibit signs associated with low calcium. Signs include seizures, muscle twitching and tremors, trouble walking and weakness.
Oversecretion of parathyroid hormone, or hyperparathyroidism, also results in abnormal calcium levels in the body. This condition may arise with either benign or cancerous tumors of the gland, and is most often seen in older cats. Calcium levels in the body become very elevated and may result in kidney damage with increased urination, vomiting, loss of appetite, lethargy and muscle weakness.
Diabetes mellitus (or sugar diabetes) is an important disease of the endocrine portion of the pancreas. This common disorder of cats arises with underproduction or inappropriately low secretion (release) of insulin. Insulin is the hormone that controls blood sugar and the usage of blood sugar by various organs in the body. Inadequate production of insulin causes the blood sugar to increase. Signs associated with elevated blood sugar include increased thirst and urination, weight loss despite a normal appetite, and muscle weakness.
Insulinomas are insulin-secreting tumors of the pancreas. Excessive amounts of insulin cause profound hypoglycemia (low blood sugar), and this often results in weakness, disorientation and seizures. These tumors are extremely rare in the cat.
The most common disease of the adrenal gland involves the overproduction of cortisol, also known as hyperadrenocorticism (hypercortisolism) or Cushing’s disease. The disease does not occur in the cat as often as it does in dogs. Cushing’s disease is usually seen in middle aged to older cats and often arises secondary to an overproduction of the hormone ACTH by the pituitary gland. A tumor of the adrenal gland may also result in too much cortisol secretion. Affected cats may have very nonspecific signs, such as lethargy, decreased appetite, weight loss, dehydration, weakness and vomiting.
A less common disease of the adrenal gland is hypoadrenocorticism or Addison’s disease. Addison’s disease is seen more commonly in dogs than cats and is caused by a deficiency of two hormones, cortisone and aldosterone. Aldosterone regulates sodium and potassium levels in the body. Cats with Addison’s disease are often young, and have nonspecific clinical signs, such as weakness, lethargy, vomiting, diarrhea and blood in the bowel movements.
A tumor of the adrenal gland, called a pheochromocytoma, is an extremely rare cause of high blood pressure in the cat. This tumor causes the over production of norepinephrine hormone in the cat. It occurs primarily in older cats.
What Types of Diagnostic Tests Are Used to Evaluate the Endocrine System?
There are several tests that are helpful in evaluating the endocrine system.