Functions and Structure of the Endocrine System
  • Lesson Menu
    • Study Guide
       Study Guide
      Would you like to create a study guide ?
    • Glossary
    • Notes
    • Help
  • Keyboard-only View
  • Alternate View
Open in a new window/tab

TOPIC 02: Structure and Function of the Endocrine Glands

Skip Navigation
Hypothalamic-Pituitary Axis
Previous PageNext Page
Lesson Splash, Page 1
Splash
Lesson Overview, Page 2
Overview
Topic 01: Introduction, Page 3
Mechanisms of Hormonal Regulation
Topic 01: General Functions, Page 4
Mechanisms of Hormonal Regulation
Topic 01: Mechanisms of Hormonal Regulation, Page 5
Mechanisms of Hormonal Regulation
Topic 01: Regulation of Hormone Release, Page 6
Mechanisms of Hormonal Regulation
Topic 01: Hormone Receptors, Page 7
Mechanisms of Hormonal Regulation
Topic 01: Check Your Understanding, Page 8
Mechanisms of Hormonal Regulation
Topic 01: Review, Page 9
Mechanisms of Hormonal Regulation
Topic 02: Introduction, Page 10
Structure and Function of the Endocrine Glands
Topic 02: Hypothalamic-Pituitary Axis, Page 11
Structure and Function of the Endocrine Glands
Topic 02: Thyroid and Parathyroid Glands, Page 12
Structure and Function of the Endocrine Glands
Topic 02: Check Your Understanding, Page 13
Structure and Function of the Endocrine Glands
Topic 02: Review, Page 14
Structure and Function of the Endocrine Glands
Lesson Summary, Page 15
Lesson Summary
11 of 15

Hypothalamic-Pituitary Axis

The hypothalamic-pituitary axis (HPA) forms the structural and functional basis for central integration of the neurologic and endocrine systems, creating what is called the neuroendocrine system.

Select each item to learn more.
HypothalamusThe Anterior PituitaryThe Posterior Pituitary

The hypothalamus is located at the base of the brain. It is connected to the pituitary gland by the infundibulum (pituitary stalk), to the anterior pituitary through hypophysial portal blood vessels, and to the posterior pituitary through a nerve tract referred to as the hypothalamohypophysial tract. These connections are vital to the functioning of the hypothalamic-pituitary system.

The anterior pituitary is composed of two main cell types: (a) the chromophobes, which appear to be nonsecretory, and (b) the chromophils, which are considered the secretory cells of adenohypophysis.

The tropic hormones secreted by the chromophils affect the physiologic function of specific target organs. These hormones can be grouped into three categories:

  • Corticotropin-related hormones (adrenocorticotropic hormone [ACTH] and melanocyte-stimulating hormone [MSH])
  • Glycoproteins (luteinizing hormone [LH], follicle-stimulating hormone [FSH], and thyroid-stimulating hormone [TSH])
  • Somatotropins (growth hormone [GH] and prolactin)

The glycoprotein hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH) influence reproductive function. Adrenocorticotropic hormone (ACTH) regulates the release of cortisol from the adrenal cortex. Thyroid-stimulating hormone (TSH) regulates the activity of the thyroid gland.

Growth hormone (GH) and prolactin are called the somatotropic hormones and have diverse effects on body tissues. GH secretion is controlled by two hormones from the hypothalamus: growth hormone–releasing hormone (GHRH), which increases GH secretion; and somatostatin, which inhibits GH secretion. GH is essential to normal tissue growth and maturation and peaks during adolescence.

Prolactin primarily functions to induce milk production during pregnancy and lactation. It has immune-stimulatory effects and modulates immune and inflammatory responses with both physiologic and pathologic reactions.

The posterior pituitary secretes two polypeptide hormones: (a) ADH, also called arginine-vasopressin, and (b) oxytocin. The major homeostatic function of the posterior pituitary is the control of plasma osmolality, as regulated by ADH. Oxytocin is responsible for contraction of the uterus and milk ejection in lactating women and may affect sperm motility in men.