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  • Organization: There are five parallel endocrine axes in the hypothalamic-anterior pituitary regulatory system (Figure 5.1)

  • Chapter organization: For the remainder of this chapter we will organize anatomy, physiology, pathophysiology, and treatments by endocrine axis


Endocrine axes in the hypothalamic–anterior pituitary regulatory system. There are five parallel endocrine axes in the hypothalamic–anterior pituitary regulatory system that control the biosynthesis and release of 1) thyroid hormone, 2) glucocorticoids, 3) the sex steroids estradiol and testosterone, 4) growth hormone, and 5) prolactin. (⊕) indicates stimulatory action and (⊖) indicates inhibitory action. Abbreviations: TRH, thyrotropin-releasing hormone; TSH, thyroid-stimulating hormone; T4, thyroxine; T3, triiodothyronine; CRH, corticotropin-releasing hormone; VP, vasopressin; ACTH, adrenocorticotropic hormone; GnRH, gonadotropin-releasing hormone; FSH, follicle-stimulating hormone; LH, luteinizing hormone; GHRH, growth hormone-releasing hormone; GH, growth hormone; IGF-1, insulin-like growth factor-1; IGF-BP3, insulin-like growth factor binding protein-3.



Hormones secreted by the pituitary gland and their functions. The pituitary is a small gland that is positioned in the base of the brain. The pituitary controls the function of most other endocrine glands, secreting the hormones shown here, which each act on distinct target organ(s) or tissues. As is shown, certain hormones are secreted by the anterior lobe, whereas other hormones are secreted by the posterior lobe.

Anterior Pituitary


  • Etiologies:

    • - Impaired synthesis or secretion of one or more hormones; can be primary or secondary (process impairs hypothalamic hormones, with resultant pituitary failure)

    • - Primary: Traumatic (e.g., head injury), neoplastic (e.g., adenoma), infiltrative/inflammatory (e.g., sarcoidosis), vascular (e.g., sickle cell disease, pregnancy-related), infections (e.g., histoplasmosis, TB), development/structural (e.g., dysplasia)

    • - Secondary: Hypothalamic dysfunction or stalk interruption due to aforementioned processes

  • Clinical features: Depends on which hormones are lost and the extent and duration of deficiency

  • Hormone deficiencies:

    • - ↓ Growth hormone (GH): Fatigue, increased fat mass, decreased muscle mass, growth retardation (children). Clinically this is measured using GH suppression testing with oral glucose tolerance and finding an elevated IGF-1.

    • - ↓ Luteinizing hormone (LH)/follicle-stimulating hormone (FSH): Hypogonadotropic hypogonadism (infertility, amenorrhea, impotence)

    • - ↓ Thyroid-stimulating hormone (TSH): Hypothyroidism, growth retardation (children)

    • - ↓ Adrenocorticotropic hormone (ACTH): Secondary adrenal insufficiency (hypocortisolism; relative preservation of mineralocorticoid production)

    • - ↓ Prolactin: Inability to lactate

  • Diagnosis: Get pituitary MRI. Typically there are low levels of anterior pituitary hormones and thus low levels of target-organ hormones (e.g., low TSH, low free T4). Pearl: Hormone levels that are within normal lab ranges may be “inappropriately normal” based on the clinical context. For example, if free T4 is very low, then a normal TSH level would be inappropriately normal, since in this setting TSH should be elevated.

  • Treatment: Replace deficient hormones. Adrenal insufficiency and ...

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