1.3 Comparing the anterior pituitary gland with the posterior pituitary gland

Hypothalamic Control of the Pituitary Gland

• The hypothalamus is responsible for controlling the anterior pituitary gland through the release of specific hormones known as releasing factors.

  • The umbrella term for these hormones includes:

    • Releasing hormones: Stimulate hormone release from the anterior pituitary.

    • Inhibiting hormones: Prevent hormone release from the anterior pituitary.

• The anterior pituitary and posterior pituitary differ in both structure and function:

Anterior Pituitary

• Hormones: The hypothalamus secretes releasing factors into the hypophyseal portal system.

  • These factors are transported through the first capillary bed into the hypophyseal portal vein(s).

  • After traveling through the portal vein(s), they reach the second capillary bed, where they influence the five different types of anterior pituitary cells:

    1. Lactotrophs: Produce prolactin.

    2. Somatotrophs: Produce growth hormone (GH).

    3. Corticotrophs: Produce adrenocorticotropic hormone (ACTH).

    4. Thyrotrophs: Produce thyroid-stimulating hormone (TSH).

    5. Gonadotrophs: Produce luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

  • These hormones released by the anterior pituitary are known as tropic hormones because they act on other endocrine glands.

Posterior Pituitary

• The posterior pituitary's function is simpler:

  • Hormone Production: Hormones such as Antidiuretic Hormone (ADH) and Oxytocin are synthesized in the hypothalamus.

  • These hormones are then transported down the axons and stored in the axon terminals of the posterior pituitary.

  • Release Mechanism: ADH and oxytocin are released into the bloodstream in response to an action potential, causing fusion of vesicles containing these hormones with the membrane.

Summary of Control Mechanisms

• The hypothalamus has a dual role:

  • Produces releasing factors transported to the anterior pituitary via the hypophyseal portal circulation.

  • Synthesizes and sends hormones directly to the posterior pituitary for storage and release upon stimulation.

• This highlights the functional differences between the two regions of the pituitary gland:

  • Anterior Pituitary: Controlled by releasing factors and involved in producing various tropic hormones.

  • Posterior Pituitary: Stores and releases hormones produced in the hypothalamus directly into circulation upon neuronal firing.