Structure and Function of the Pituitary Gland in Cats
Dr. Bari Spielman
The anterior (front) lobe is called the adenohypophysis, which is subdivided into three regions that produce a variety of hormones. It is controlled by substances called releasing hormones that are transported from the hypothalamus through tiny blood vessels.
What Is the Pituitary Gland?
The pituitary gland, also referred to as the hypophysis, is a small, oval gland that is attached to the underside or base of the brain. It is an important link between the nervous system and endocrine system and releases many hormones that affect multiple body functions.
Where Is the Pituitary Gland Located?
The pituitary gland is located on the underside of the brain within the skull. The pituitary is attached to the hypothalamus (an important part of the underside of the brain) via a stalk-like structure. The hypothalamus acts as the collecting center for information concerning the internal well being of the body. It uses much of this information to regulate the secretion of the hormones produced by the pituitary.
What Is the General Structure of the Pituitary Gland?
The pituitary gland is smaller than the size of a pea. Physiologically, the pituitary gland is divided into two distinct lobes that arise from different embryological sources.
The posterior (rear) lobe includes the neurohypophysis, which is controlled by nerve fibers from the hypothalamus.
What Are the Functions of the Pituitary Gland?
Although very small, this organ plays a major regulatory role in the entire endocrine system. Each lobe of the pituitary gland produces certain hormones in response to the body's needs. They are then circulated in the blood to a variety of the body's tissues. The close structural positioning of the glandular and nervous segments of this gland is symbolic of its function in interrelating the nervous and endocrine systems.
The functions of the adenohypophysis are to make hormones that turn on other endocrine organs. Examples of these stimulating hormones are as follows:
Growth hormone stimulates growth of multiple cells and tissue types.
Prolactin stimulates milk production after giving birth.
Adrenocorticotropic hormone (ACTH) stimulates the adrenal glands.
Thyroid-stimulating hormone (TSH) stimulates the thyroid gland.
Follicle-stimulating hormone (FSH) stimulates the ovaries and testes.
Luteinizing hormone (LH) stimulates the ovaries and testes.
Melanocyte-stimulating hormone controls skin pigmentation or color.
The neurohypophysis has two major functions, depending upon the hormone produced:
Antidiuretic hormone (ADH) or vasopressin regulates water conservation by the kidney
Oxytocin is a potent stimulus of the muscles of the uterus and induces uterine contractions. It also encourages milk to be expressed from the alveoli into the mammary ducts during suckling.
What Are Common Diseases of the Pituitary Gland and?
There are no common disorders of the pituitary gland in the cat, and pituitary diseases are very rare in the cat. Most result from overproduction or underproduction of one of the pituitary hormones.
Hyperadrenocorticism. The over production of the pituitary hormone, ACTH, produces a disease called hyperadrenocorticism or Cushing's disease. Overproduction of ACTH stimulates the adrenal glands to make excessive amounts of cortisol hormones. Cushing's disease is usually seen in middle aged to older cats. Weakness, lethargy, abnormal hair coat, increased incidence of infections, and a pot-bellied appearance are common signs.
Acromegaly. The overproduction of pituitary growth hormone results in a disease called acromegaly. Acromegaly in the cat usually arises from a functioning tumor of the pituitary gland. It often causes sugar diabetes (diabetes mellitus) and kidney failure. These cats become very ill and often die.
The underproduction of the pituitary hormone, ADH, causes diabetes insipidus or water diabetes. Diabetes insipidus is a disorder in which the kidneys are unable to retain water and affected cats cannot concentrate their urine and urinate excessively. They are also profoundly thirsty. This disease is extremely rare in cats.
Although a deficiency of growth hormone is theoretically possible in the cat, it has not been documented in clinical cases.
Pituitary tumors, both benign and malignant, may occur in cats.
What Types of Diagnostic Tests Are Used to Evaluate the Pituitary Gland?
There are several tests that are particularly helpful in evaluating the pituitary gland.
Blood tests. Most of these tests measure the amount of cortisol in the blood stream and are timed tests that are taken over the course of a day. Examples of these include the ACTH stimulation test, measurement of ACTH in the blood, and the low dose and high dose dexamethasone suppression tests (LDDST, HDDST).
A serum biochemistry profile may reveal the presence of diabetes mellitus, kidney failure, and other disorders in cats with acromegaly.
The diagnosis of acromegaly requires the measurement of somatomedin C (insulin-like growth factor-I) levels in the blood.
Computed tomography (CT scan) and/or magnetic resonance imaging (MRI) are also valuable tools in assessing the shape, size and internal structure of the pituitary gland.