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Hypothalamus and Pituitary Gland

Hypothalamus and Pituitary Gland

Author: Sophia Tutorial
Description:

Identify the hypothalamus and pituitary glands and the role they play in homeostasis.

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Tutorial
what's covered
Welcome to this lesson on the hypothalamus and pituitary gland. Today, you are going to be learning about the role of the hypothalamus and pituitary gland in the endocrine system. Specifically, you will learn about:
  1. Hypothalamus & Pituitary Gland Overview
  2. Posterior Lobe of the Pituitary Gland
  3. Anterior Lobe of the Pituitary Gland
  4. Growth Hormone Disorders

1. Hypothalamus & Pituitary Gland Overview

The hypothalamus and pituitary gland interact to control activities of various body organs and to help regulate the homeostasis of the body. The hypothalamus and pituitary gland regulate homeostasis by producing, storing, and secreting various hormones. The hypothalamus and pituitary gland can be found in the brain.

The pituitary gland consists of two separate lobes, each of which secretes different hormones. The posterior lobe stores and releases hormones from the hypothalamus, while the anterior lobe of the pituitary gland makes and releases hormones.

terms to know
Hypothalamus
A part of the forebrain that works closely with the pituitary gland to monitor the body's organs and their functioning.

Pituitary Gland
Called the “master gland” because of its effects on other glands, the endocrine hormones increase activity/secretion of many major glands of the endocrine system.

2. Posterior Lobe of the Pituitary Gland

The hypothalamus works closely with the pituitary gland, which is composed of the anterior and posterior lobes. Within the hypothalamus, there are neurons that synthesize antidiuretic hormone (ADH) and oxytocin.

Posterior Pituitary Hormones
Oxytocin Oxytocin plays a couple of different roles. One of its targets are mammary glands, which causes milk to move into the ducts during breastfeeding.

Oxytocin also acts on muscles within uterine walls causing contractions during childbirth. Essentially, oxytocin levels rise when a woman needs to give birth and is what causes labor contractions and pains. In summary, oxytocin acts on mammary glands to move milk into ducts and to help with contractions during childbirth.
Antidiuretic Hormone (ADH) Antidiuretic hormone causes water to be conserved within kidney nephrons, lowering someone's urine output.

These hormones will move down the axons of neurons and build up in their axon endings, which are located in the posterior lobe of the pituitary gland. When an action potential triggers a hormone release, the hormones will enter capillaries and then travel through the bloodstream to their target cell.

File:7393-Pituitary_Lobe.png

term to know

Posterior Lobe of Pituitary Gland
Also called the neurohypophysis, the posterior lobe of the pituitary gland developed from brain tissue during embryonic development and therefore is directly innervated by the hypothalamus; the two hormones the posterior pituitary secretes are antidiuretic hormone (ADH) and oxytocin.

3. Anterior Lobe of the Pituitary Gland

If we take a look at our anterior lobe of the pituitary gland, hormone secretion works a little bit differently. Neurons within the hypothalamus will secrete certain hormones into capillaries at the base of the hypothalamus. From there, blood will flow from capillaries on the hypothalamus to the capillaries on the anterior lobe. The hormones secreted from the anterior pituitary will then enter the bloodstream and circulate to their targets.

File:7391-Anterior_Lobe.png

The following hormones are released by the anterior lobe of the pituitary gland:

Anterior Pituitary Hormones
Prolactin (PRL) A hormone that plays a role in milk production in mammary glands.
Luteinizing hormone (LH) A hormone that plays a role in the reproductive system. It also helps with the secretion of other hormones and targets mostly in the ovaries and testes.
Follicle stimulating hormone (FSH) Another hormone that plays a role in the reproductive system; it targets the ovaries and testes, and it plays a role in egg and sperm.
Thyroid stimulating hormone (TSH) A hormone that controls the release of thyroid hormone.
Adrenocorticotropic hormone (ACTH) A hormone that stimulates the release of cortisol from the adrenal glands.
Growth hormone (GH) A hormone that regulates a person's growth that is secreted by this anterior lobe.

term to know

Anterior Lobe of Pituitary Gland
Also called the adenohypophysis, the anterior lobe of the pituitary gland started developing in the nasopharynx and migrated up into the skull to join with the posterior lobe of the pituitary gland; since the anterior pituitary didn’t originate in the brain there are no direct neural connections to it; the anterior pituitary gland secretes six hormones: Growth hormone (GH), adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH), prolactin, luteinizing hormone (LH) and follicle stimulating hormone (FSH).

4. Growth Hormone Disorders

Growth hormone regulates our height at epiphyseal plates within the ends of bones. Excess growth hormone secretion makes epiphyseal plates more active, which in turn causes bones to grow too much making a child taller than normal. If too much growth hormone is secreted by the anterior lobe of the pituitary gland, it can lead to a disorder called gigantism. Gigantism is a condition in which too much hormone is released during childhood, resulting in a much larger body than average. A person with gigantism has normal body proportions; however, they will be much taller and much larger than the average person because of the excess in growth hormone.

Growth hormone overproduction can also affect adults. However, the person will be unable to grow any taller because epiphyseal plates have calcified over. Instead, tissues, especially bone, increase in thickness but not in length. Tissues like bone, skin, cartilage, tissues of the face, hands, and feet are all going to become abnormally thick; this condition is called acromegaly.

Sometimes too little growth hormone can be secreted, which can lead to pituitary dwarfism. This is caused either by an underproduction or lack of secretion of growth hormone. A pituitary dwarf will be very short but with normal proportions. Pituitary dwarfism can be a genetic condition that can be passed down through generations.

Injuries or tumors that affect the pituitary gland can affect the amount of growth hormone being released. Sometimes if this is detected in children while they're still growing, they can receive shots of artificial growth hormone, which will then increase the growth hormone levels and help them grow to an average height. However, this is very expensive and also a big ethical debate.

terms to know
Gigantism
A condition in which growth hormone levels are too high at an age before growth plates ossify; this causes bones and other tissues to grow proportionally larger than average.
Acromegaly
A condition in which growth hormone levels are too high after growth plates ossify; this causes bones to thicken and extremities to enlarge but bones cannot grow in length; the most prominent signs are enlarged facial features, hands, and feet.

Pituitary Dwarfism
A condition in which growth hormones levels are too low at a young age and the person is proportionally smaller than normal.

summary
This lesson has been an overview of the role of the hypothalamus and pituitary gland in the endocrine system. Specifically, this lesson focused on the pituitary gland's posterior lobe (which produces and secretes oxytocin and ADH), the pituitary gland's anterior lobe (which stores and secretes prolactin, luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, and growth hormone). You also learned that growth hormone disorders can be a result of overproduction or underproduction of growth hormones being secreted into the body. Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

Attributions
Terms to Know
Acromegaly

A condition in which growth hormone levels are too high after growth plates ossify; this causes bones to thicken and extremities to enlarge but bones cannot grow in length. The most prominent signs are enlarged facial features, hands and feet.

Anterior Lobe of Pituitary Gland

Also called the adenohypophysis, the anterior lobe of the pituitary gland started developing in the nasopharynx and migrated up into the skull to join with the posterior lobe of the pituitary gland. Since the anterior pituitary didn’t originate in the brain there are no direct neural connections to it. The anterior pituitary gland secretes six hormones: growth hormone (GH), adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH), prolactin, luteinizing hormone (LH), and follicle stimulating hormone (FSH).

Gigantism

A condition in which growth hormone levels are too high at an age before growth plates ossify; this causes bones and other tissues to grow proportionally larger than average.

Hypothalamus

A part of the forebrain that works closely with the pituitary gland to monitor the body's organs and their functioning.

Pituitary Dwarfism

A condition in which growth hormone levels are too low at a young age and the person is proportionally smaller than normal.

Pituitary Gland

Called the “master gland” because of its effects on other glands; endocrine hormones increase activity/secretion of many major glands of the endocrine system.

Posterior Lobe of Pituitary Gland

Also called the neurohypophysis, the posterior lobe of the pituitary gland developed from brain tissue during embryonic development and therefore is directly innervated by the hypothalamus. The two hormones the posterior pituitary secretes are anitdiuretic hormone (ADH) and oxytocin.