89 9.4 Pituitary Gland

Created by CK-12 Foundation/Adapted by Christine Miller

Figure 9.4.1 Breastfeeding
Figure 9.4.1 Mother’s milk is best for infants.

Milk on Demand

This adorable nursing infant (Figure 9.4.1) is part of a . When he suckles on the , it sends nerve impulses to his mother’s . Those nerve impulses “tell” her to release the hormone into her bloodstream. Prolactin travels to the in the breasts and stimulates milk production, which motivates the infant to keep suckling.

What Is the Pituitary Gland?

The  is the master gland of the , which is the system of glands that secrete into the bloodstream. Endocrine hormones control virtually all physiological processes. They control growth, sexual maturation, reproduction, body temperature, blood pressure, and metabolism. The pituitary gland is considered the master gland of the endocrine system, because it controls the rest of the endocrine system. Many pituitary hormones either promote or inhibit hormone secretion by other endocrine glands.

Structure and Function of the Pituitary Gland

The pituitary gland is about the size of a pea. It protrudes from the bottom of the hypothalamus at the base of the inner brain (see Figure 9.4.2). The pituitary is connected to the hypothalamus by a thin stalk (called the infundibulum). Blood vessels and nerves in the stalk allow direct connections between the hypothalamus and pituitary gland.

Hypothalamus and Pituitary Gland
Figure 9.4.2 The pituitary gland in the endocrine system is closely connected to the hypothalamus in the brain. Both anterior and posterior lobes of the pituitary gland are directly connected to the hypothalamus by capillaries (anterior lobe) and nerve axons (posterior lobe).

Anterior Lobe

The  is the lobe is at the front of the pituitary gland. It synthesizes and releases hormones into the blood. Table 9.4.1 shows some of the endocrine hormones released by the anterior pituitary, including their targets and effects.

Table 9.4.1

Endocrine Hormones Released by the Anterior Pituitary, and Their Targets and Effects.

Anterior Pituitary Hormone Target Effect
Adrenocorticotropic hormone (ACTH) Adrenal glands Stimulates the cortex of each adrenal gland to secrete its hormones.
Thyroid-stimulating hormone (TSH) Thyroid gland Stimulates the thyroid gland to secrete thyroid hormone.
Growth hormone (GH) Body cells Stimulates body cells to synthesize proteins and grow.
Follicle-stimulating hormone (FSH) Ovaries, testes Stimulates the ovaries to develop mature eggs.  stimulates the testes to produce sperm.
Luteinizing hormone (LH) Ovaries, testes Stimulates the ovaries and testes to secrete sex hormones; stimulates the ovaries to release eggs.
Prolactin (PRL) Mammary glands Stimulates the mammary glands to produce milk.

The is regulated mainly by from the . The hypothalamus secretes hormones (called releasing hormones and inhibiting hormones) that travel through capillaries directly to the anterior lobe of the pituitary gland. The hormones stimulate the anterior pituitary to either release or stop releasing particular pituitary hormones. Several of these hypothalamic hormones and their effects on the anterior pituitary are shown in the table below.

Table 9.4.2

Hypothalamic Hormones and Their Effects on the Anterior Pituitary

Hypothalamic Hormone Effect on Anterior Pituitary
Thyrotropin releasing hormone (TRH) Release of thyroid stimulating hormone (TSH)
Corticotropin releasing hormone (CRH) Release of adrenocorticotropic hormone (ACTH)
Gonadotropin releasing hormone (GnRH) Release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Growth hormone releasing hormone (GHRH) Release of growth hormone (GH)
Growth hormone inhibiting hormone (GHIH) (Somatostatin) Stopping of growth hormone release
Prolactin releasing hormone (PRH) Release of prolactin
Prolactin inhibiting hormone (PIH) (Dopamine) Stopping of prolactin release

Posterior Lobe

The  is the lobe is at the back of the pituitary gland. This lobe does not synthesize any hormones. Instead, the posterior lobe stores hormones that come from the hypothalamus along the axons of nerves connecting the two structures (also shown in Figure 9.4.2). The posterior pituitary then secretes the hormones into the bloodstream as needed. Hypothalamic hormones secreted by the posterior pituitary include vasopressin and oxytocin.

  •  (also called antidiuretic hormone, or ADH) helps maintain homeostasis in body water. It stimulates the kidneys to conserve water by producing more concentrated urine. Specifically, vasopressin targets ducts in the kidneys and makes them more permeable to water. This allows more water to be resorbed by the body, rather than excreted in urine.
  •  (OXY) targets cells in the uterus to stimulate uterine contractions, as in childbirth. It also targets cells in the breasts of a nursing mother to stimulate the letdown of milk.

9.4 Summary

  • The is the master gland of the , because most of its control other endocrine glands.
  • The pituitary gland is at the base of the brain, where it is connected to the by nerves and capillaries. It has an (front) lobe that synthesizes and secretes pituitary hormones and a (back) lobe that stores and secretes hormones from the hypothalamus.
  • Hormones synthesized and secreted by the anterior pituitary include , which stimulates cell growth throughout the body, and (TSH), which stimulates the thyroid gland to secrete its hormones.
  • Hypothalamic hormones stored and secreted by the posterior pituitary gland include , which helps maintain homeostasis in body water, and , which stimulates uterine contractions during birth, as well as the letdown of milk during lactation.

9.4 Review Questions

  1. Explain why the pituitary gland is called the master gland of the endocrine system.
  2. Compare and contrast the two lobes of the pituitary gland and their general functions.
  3. Identify two hormones released by the anterior pituitary, their targets, and their effects.
  4. Explain how the hypothalamus influences the output of hormones by the anterior lobe of the pituitary gland.
  5. Name and give the function of two hypothalamic hormones released by the posterior pituitary gland.
  6. Answer the following questions about prolactin releasing hormone (PRH) and prolactin inhibiting hormone (PIH).
    1. Where are these hormones produced?
    2. Where are their target cells located?
    3. What are their effects on their target cells?
    4. What are their ultimate effects on milk production? Explain your answer.
    5. When a baby nurses, which of these hormones is most likely released in the mother? Explain your answer.
  7. For each of the following hormones, state whether it is synthesized in the pituitary or the hypothalamus.
    1. gonadotropin releasing hormone (GnRH)
    2. growth hormone (GH)
    3. oxytocin
    4. adrenocorticotropic hormone (ACTH)

9.4 Explore More

Common Pituitary Diseases, Swedish, 2012.

Diagnosing and Treating Pituitary Tumors – California Center for Pituitary Disorders at UCSF, UCSF Neurosurgery, 2015.

 

Attributions

Figure 9.4.1

Breastfeeding by Petr Kratochvil  on Wikimedia Commons is used under a CC0 1.0 Universal
Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.

Figure 9.4.2

The_Hypothalamus-Pituitary_Complex by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

References

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 17.7 Hypothalamus–pituitary complex [digital image]. In Anatomy and Physiology (Section 17.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/17-3-the-pituitary-gland-and-hypothalamus

Swedish. (2012, April 19). Common pituitary diseases. YouTube. https://www.youtube.com/watch?v=jUKQFkmBuww&feature=youtu.be

UCSF Neurosurgery. (2015, May 13). Diagnosing and treating pituitary tumors – California Center for Pituitary Disorders at UCSF. YouTube. https://www.youtube.com/watch?v=v41AJGP-XmI&feature=youtu.be

License

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Human Biology by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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