Question

Assignment: Explain the role of the hypothalamus, pituitary gland and thyroid gland in development of a goiter. Make sure to discuss each gland/organ. Your answer should be a minimum of 100 words, be specific and detailed.

Answer 1

The most common cause of goiters worldwide is a lack of iodine in the diet. In the United States, where the use of iodized salt is common, a goiter is more often due to the over- or underproduction of thyroid hormones or to nodules that develop in the gland itself

Role of hypothalamus,pituitory gland and thyroid gland in development of a goiter:

it depends upon the hypothalamus, the pituitary gland, and the thyroid gland.

The hypothalamus senses low circulating levels of thyroid hormone (Triiodothyronine (T3) and Thyroxine (T4)) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland.^[2]

The HPA, HPG, and HPT axes are three pathways in which the hypothalamus and pituitary direct neuroendocrine function.

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Short overview of thyroid homeostasis.

HYPOTHALAMUS:

The hypothalamus is a small region of the brain. It’s located at the base of the brain, near the pituitary gland.

While it’s very small, the hypothalamus plays a crucial role in many important functions, including:

• releasing hormones
• regulating body temperature
• maintaining daily physiological cycles
• controlling appetite
• managing of sexual behavior
• regulating emotional responses

Anatomy and function

The hypothalamus has three main regions. Each one contains different nuclei. These are clusters of neurons that perform vital functions, such as releasing hormones.

Anterior region

This area is also called the supraoptic region. Its major nuclei include the supraoptic and paraventricular nuclei. There are several other smaller nuclei in the anterior region as well.

The nuclei in the anterior region are largely involved in the secretion of various hormones. Many of these hormones interact with the nearby pituitary gland to produce additional hormones.

Some of the most important hormones produced in the anterior region include:

• Corticotropin-releasing hormone (CRH). CRH is involved in the body’s response to both physical and emotional stress. It signals the pituitary gland to produce a hormone called adrenocorticotropic hormone (ACTH). ACTH triggers the production of cortisol, an important stress hormone.
• Thyrotropin-releasing hormone (TRH). TRH production stimulates the pituitary gland to produce thyroid-stimulating hormone (TSH). TSH plays an important role in the function of many body parts, such as the heart, gastrointestinal tract, and muscles.
• Gonadotropin-releasing hormone (GnRH). GnRH production causes the pituitary gland to produce important reproductive hormones, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Oxytocin. This hormone controls many important behaviors and emotions, such as sexual arousal, trust, recognition, and maternal behavior. It’s also involved in some functions of the reproductive system, such as childbirth and lactation.
• Vasopressin. Also called antidiuretic hormone (ADH), this hormone regulates water levels in the body. When vasopressin is released, it signals the kidneys to absorb water.
• Somatostatin. Somatostatin works to stop the pituitary gland from releasing certain hormones, including growth hormones and thyroid-stimulating hormones.

The anterior region of the hypothalamus also helps regulate body temperature through sweat. It also maintains circadian rhythms. These are physical and behavioral changes that occur on a daily cycle. For example, being awake during the day and sleeping at nighttime is a circadian rhythm related to the presence or absence of light.

Middle region

This area is also called the tuberal region. Its major nuclei are the ventromedial and arcuate nuclei.

The ventromedial nucleus helps control appetite, while the arcuate nucleus is involved in releasing growth hormone-releasing hormone (GHRH). GHRH stimulates the pituitary gland to produce growth hormone. This is responsible for the growth and development of the body.

Posterior region

This area is also called the mammillary region. The posterior hypothalamic nucleus and mammillary nuclei are its main nuclei.

The posterior hypothalamic nucleus helps regulate body temperature by causing shivering and blocking sweat production.

The role of the mammillary nuclei is less clear. Doctors believe it’s involved in memory function.

PITUITARY GLAND:

The pituitary gland is a part of your endocrine system. Its main function is to secrete hormones into your bloodstream. These hormones can affect other organs and glands, especially your:

• thyroid
• reproductive organs
• adrenal glands

The pituitary gland is sometimes called the master gland because it’s involved in so many processes.

Pituitary gland anatomy and function

The pituitary gland is small and oval-shaped. It’s located behind your nose, near the underside of your brain. It’s attached to the hypothalamus by a stalklike structure.

The hypothalamus is a small area of your brain. It’s very important in controlling the balance of your bodily functions. It controls the release of hormones from the pituitary gland.

The pituitary gland can be divided into two different parts: the anterior and posterior lobes.

Anterior lobe

The anterior lobe of your pituitary gland is made up of several different types of cells that produce and release different types of hormones, including:

• Growth hormone. Growth hormone regulates growth and physical development. It can stimulate growth in almost all of your tissues. Its primary targets are bones and muscles.
• Thyroid-stimulating hormone. This hormone activates your thyroid to release thyroid hormones. Your thyroid gland and the hormones it produces are crucial for metabolism.
• Adrenocorticotropic hormone. This hormone stimulates your adrenal glands to produce cortisol and other hormones.
• Follicle-stimulating hormone. Follicle-stimulating hormone is involved with estrogen secretion and the growth of egg cells in women. It’s also important for sperm cell production in men.
• Luteinizing hormone. Luteinizing hormone is involved in the production of estrogen in women and testosterone in men.
• Prolactin. Prolactin helps women who are breastfeeding produce milk.
• Endorphins. Endorphins have pain-relieving properties and are thought to be connected to the “pleasure centers” of the brain.
• Enkephalins. Enkephalins are closely related to endorphins and have similar pain-relieving effects.
• Beta-melanocyte-stimulating hormone. This hormone helps to stimulate increased pigmentation of your skin in response to exposure to ultraviolet radiation.

Posterior lobe

The posterior lobe of the pituitary gland also secretes hormones. These hormones are usually produced in your hypothalamus and stored in the posterior lobe until they’re released.

Hormones stored in the posterior lobe include:

• Vasopressin. This is also called antidiuretic hormone. It helps your body conserve water and prevent dehydration.
• Oxytocin. This hormone stimulates the release of breast milk. It also stimulates contractions of the uterus during labor.

• Several conditions can affect your pituitary gland. Most are caused by a tumor in or around the pituitary gland. This can impact the release of hormones.

  Examples of pituitary gland disorders include:

• Pituitary tumors. Pituitary tumors are usually noncancerous. However, they often interfere with the release of hormones. They can also press against other areas of your brain, leading to vision problems or headaches.
• Hypopituitarism. This condition causes your pituitary gland to produce very little or none of one or more of its hormones. This can affect things like growth or reproductive system function.
• Acromegaly. In this condition, your pituitary gland produces too much growth hormone. This can lead to excessive growth, especially of your hands and feet. It’s often associated with pituitary tumors.
• Diabetes insipidus. This can be caused by a problem with the release of vasopressin. It’s usually due to a head injury, surgery, or a tumor. As a result, people with this condition pass large amounts of heavily diluted urine. They may also feel like they need to drink a lot of water or other fluids.
• Cushing’s disease. The pituitary gland releases too much adrenocorticotropic hormone in people with this condition. This can lead to easy bruising, high blood pressure, weakness, and weight gain. It’s often caused by a tumor near or in the pituitary gland.
• Hyperprolactinemia. In this condition, your blood contains an unusually high amount of prolactin. This can lead to infertility and a decreased sex drive.
• Traumatic brain injury. This involves a sudden blow to your brain. Depending on the injury, it can sometimes damage your pituitary gland and cause problems with memory, communication, or behavior.
• Symptoms of a pituitary gland condition

• Your pituitary gland is involved in a range of things, so any condition involving it can produce a diverse set of symptoms

• headaches

• weakness or fatigue
• high blood pressure
• unexplained weight gain
• trouble sleeping
• changes in psychological state, including mood swings or depression
• memory loss
• reproductive issues, including infertility, erectile dysfunction, and irregular periods
• excessive or unusual hair growth
• lactating when you’re not nursing

• Most of the conditions that cause these symptoms are easy to treat and manage once you determine the underlying cause.

• THYROID GLAND:

• The thyroid is a small gland, measuring about 2 inches (5 centimeters) across, that lies just under the skin below the Adam’s apple in the neck. The two halves (lobes) of the gland are connected in the middle (called the isthmus), giving the thyroid gland the shape of a bow tie. Normally, the thyroid gland cannot be seen and can barely be felt. If it becomes enlarged, doctors can feel it easily, and a prominent bulge (goiter) may appear below or to the sides of the Adam’s apple.

  The thyroid gland secretes thyroid hormones, which control the speed at which the body’s chemical functions proceed (metabolic rate). Thyroid hormones influence the metabolic rate in two ways:

• By stimulating almost every tissue in the body to produce proteins

• By increasing the amount of oxygen that cells use

• Thyroid hormones affect many vital body functions, such as the heart rate, the rate at which calories are burned, skin maintenance, growth, heat production, fertility, and digestion.

• Thyroid hormones

  The two thyroid hormones are

• T4: Thyroxine (also called tetraiodothyronine)

• T3: Triiodothyronine

• The thyroid gland also produces the hormone calcitonin, which may contribute to bone strength by helping calcium to be incorporated into bone.

  T4, the major hormone produced by the thyroid gland, has only a slight, if any, effect on speeding up the body’s metabolic rate. Instead, T4 is converted into T3, the more active hormone. The conversion of T4 to T3 occurs in the liver and other tissues. Many factors control the conversion of T4 to T3, including the body’s needs from moment to moment and the presence or absence of illnesses.

  Most of the T4 and T3 in the bloodstream is carried bound to a protein called thyroxine-binding globulin. Only a little of the T4 and T3 are circulating free in the blood. However, it is this free hormone that is active. When the free hormone is used by the body, some of the bound hormone is released from the binding protein.

  To produce thyroid hormones, the thyroid gland needs iodine, an element contained in food and water. The thyroid gland traps iodine and processes it into thyroid hormones. As thyroid hormones are used, some of the iodine contained in the hormones is released, returns to the thyroid gland, and is recycled to produce more thyroid hormones. Oddly, the thyroid gland releases slightly less of the thyroid hormones if it is exposed to high levels of iodine transported to it in the blood.