Question

Hypopituitarism may result from trauma, such as an automobile accident severing the stalk connecting the hypothalamus and anterior pituitary, or from tumors of the pituitary gland. In trauma, usually all of the releasing hormones from hypothalamus fail to reach the anterior pituitary. With a tumor of the gland, some or all of the pituitary hormones may be shut off. Posterior pituitary hormones may also be lost. Hypopituitarism can be life threatening. Usual therapy is administration of end organ hormones in oral form. If the stalk between the hypothalamus and anterior pituitary is severed, the pituitary would fail to cause the ultimate release of all of the following hormones except A. ACTH. B. estradiol. C. oxytocin. D. testosterone. E. thyroxine.

Short answer

A. ACTH B. Estradiol C. Oxytocin D. Testosterone E. Thyroxine Answer: C. Oxytocin

Step-by-step solution

Understand the functions of the hypothalamus, anterior pituitary, and posterior pituitary

The hypothalamus is a part of the brain that produces and releases various hormones that regulate the release of other hormones from the pituitary gland. The pituitary gland is divided into two parts: the anterior pituitary and the posterior pituitary. The anterior pituitary releases hormones in response to the releasing hormones from the hypothalamus, while the posterior pituitary stores and releases hormones that are produced by the hypothalamus.

Identify the hormones produced by each gland

- Hypothalamus: Produces releasing hormones, including those that regulate the release of hormones from the anterior pituitary, and also produces oxytocin and antidiuretic hormone (ADH), which are stored and released by the posterior pituitary. - Anterior pituitary: Releases various hormones, including adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), thyroid-stimulating hormone (TSH), and prolactin. - Posterior pituitary: Stores and releases oxytocin and antidiuretic hormone (ADH) produced by the hypothalamus.

Determine which hormone on the list is not affected by the severed stalk

Based on the functions of each gland and the hormones they produce: - A. ACTH is released by the anterior pituitary - B. Estradiol is a hormone produced by the ovaries in response to LH and FSH, which are released by the anterior pituitary - C. Oxytocin is produced by the hypothalamus and released by the posterior pituitary - D. Testosterone is a hormone produced by the testes in response to LH and FSH, which are released by the anterior pituitary - E. Thyroxine is a hormone produced by the thyroid gland in response to TSH, which is released by the anterior pituitary From the list, the only hormone that is not affected by the severed stalk between the hypothalamus and anterior pituitary is oxytocin, as it is produced by the hypothalamus and released by the posterior pituitary. The correct answer is C. Oxytocin.

Key concepts

Hypothalamus Function

The hypothalamus plays a pivotal role in the endocrine system, acting as the command center for the pituitary gland, which is often termed the 'master gland'. Situated at the base of the brain, the hypothalamus synthesizes and secretes neurohormones, often called releasing hormones, that control the release of hormones from the anterior pituitary gland.

Functions of the hypothalamus include regulating hunger, sleep, thirst, body temperature, and circadian rhythms, among other vital processes. Hormonally, it directly produces oxytocin and antidiuretic hormone (ADH) which are stored in the posterior pituitary gland. These particular hormones travel down the nerve cells' axons into the posterior pituitary. It's crucial to differentiate between this direct production and the indirect control it has over hormones like ACTH, TSH, LH, FSH, and GH, by means of releasing or inhibiting hormones (like GnRH for gonadotropins, TRH for TSH, or CRH for ACTH) that act on the anterior pituitary.

Anterior Pituitary Hormones

The anterior pituitary gland, also known as the adenohypophysis, is a crucial component of the endocrine system. It responds to signals from the hypothalamus and secretes a diverse array of hormones with wide-ranging effects.

• Adrenocorticotropic Hormone (ACTH) stimulates the adrenal glands to produce cortisol.
• Thyroid Stimulating Hormone (TSH) prompts the thyroid gland to produce thyroid hormones like thyroxine.
• Growth Hormone (GH) drives growth in tissues and bones.
• Prolactin plays a significant role in milk production in mammals.
• Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) govern reproductive processes, including the production of sperm and eggs, and the secretion of sex hormones by the gonads.

These hormones reach their respective target organs through the bloodstream, where they elicit specific cellular responses. It's important to understand that if the connection between the hypothalamus and anterior pituitary is impeded, as stated in the exercise, the release of these hormones would be compromised.

Posterior Pituitary Hormones

Unlike the anterior pituitary, the posterior pituitary, or neurohypophysis, does not produce hormones itself; instead, it stores and releases hormones made by the hypothalamus. Two primary hormones associated with the posterior pituitary are:

• Oxytocin, which is involved in several processes, including childbirth, lactation, and social bonding.
• Antidiuretic Hormone (ADH), also known as vasopressin, regulates water retention by the kidneys and plays a role in maintaining blood pressure.

When the hypothalamus creates these hormones, they are transported to and stored in the posterior pituitary. They are then released into the bloodstream when needed. Notably, if the connection between the posterior pituitary and the hypothalamus is severed, these stored hormones could still potentially be released. Therefore, a traumatic severing of the stalk between the hypothalamus and the anterior pituitary would not affect the release of posterior pituitary hormones such as oxytocin.