Hypothalamic and Pituitary Hormones

Overview

Overview/Background

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  • Feedback Relationships:

    • Feedback between anterior pituitary and its three target glands:

      • gonads

        • if gonads fail or removed then LH & FSH increased ­ (primary hypogonadism)

      • adrenal cortex

        • with adrenal cortex destruction/removal, primary adrenal-insufficiency occurs (Addison's disease) with increased­ serum ACTH concentration

      • thyroid

        • thyroid failure  leads to  primary hypothyroidism resulting in increased ­ TSH

    • With removal/destruction of the pituitary gland, trophic hormone is lost:

      • Secondary hypogonadism

      • Adrenal-insufficiency

      • Hypothyroidism

    • With removal/destruction of the pituitary gland: no effect on vasopressin (AVP) and oxytocin provided intact hypothalamus

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  • Pituitary Control:Hypothalamus- chemical mediation (hormones)

    • Hypothalamic hormonal synthesis through portal vascular system to the pituitary stalk to the pituitary anterior lobe

    • Pituitary stalk interruption causes:

      • decreased release from the anterior pituitary of: GH, LH, FSH, TSH, & ACTH

      • increased prolactin (hypothalamic influence is normally inhibitory for prolactin secretion)

    • Hypothalamic ablation:

      • decreased levels of GH, LH, FSH, TSH, ACTH, AVP & oxytocin

      • increased prolactin

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  • growth hormone-releasing hormone (GHRH) dominant GH release influence (+)

  • Somatostatin: inhibitory hormone for GH release (-)

  • Luteinizing hormone-releasing hormone (LHRH) -- also called gonadotropin-releasing hormone (GnRH): controls LH & FSH

  • Thyrotropin-releasing hormone (TRH) controls TSH release; influences prolactin release

  • Corticotropin-releasing hormone (CRH) & other factors control ACTH release

  • Dopamine: major prolactin inhibitory influence (PIF)

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Pituitary and Hypothalamic Hormones
Pituitary Hormone

Hypophysiotropic Hormone
Thyrotropin (TSH) Thyrotropin-releasing hormone (TRH) -- tripeptide
Adrenocorticotropin (ACTH)
  • Corticotropin-releasing hormone (CRH) -- 41 amino acids
  • Vasopressin (AVP); and other peptides
Luteinizing hormone (LH) Leutinizing hormone-releasing hormone (LHRH) -- decapeptide
Follicle-stimulating hormone (FSH) LHRH -- decapeptide
Growth hormone (GH)
  • Growth hormone-releasing hormone (GHRH) -- 44 amino acids
  • Growth hormone release-inhibiting hormone (somatostatin, GIH) -- 14 amino acids; somatostatin: also inhibits TRH-stimulated TSH release
Prolactin
  • Prolactin release-inhibiting factor (PIF) -- dopamine
  • Prolactin-releasing factor (PRL) -- peptide; TRH stimulates prolactin release

{adapted from Table 328-1: Biller, Beverly, M. K. and Daniels, Gilbert, H. Neuroendocrine Regulation and Diseases of the Anterior Pituitary and Hypothalamus, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, p. 1973

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Flashcard Practice: Neuroendocrine Acronyms

 

  • Physiological Consequences of Pituitary Tumors:

    • hormonal over production/under production

    • Pituitary tumors: most common syndromes due to:

      • growth hormone excess

        • gigantism, acromegaly

      • prolactin excess

        • galactorrhea and/or hypogonadism

    • ACTH-secreting tumors: Cushing's disease

    • TSH-secreting tumors: hyperthyroidism (rare)

    • Gonadotropin-secreting tumors: hypogonadism (paradoxical)

    • Large pituitary tumors:

      • hypopituitarism (due to gland compression; or pituitary stalk compression) ® visual field disturbances {optic chiasm compression}

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  • Hypothalamic disease:

    • Hypopituitarism

    • Prolactin secretion increased

    • Significant Diagnostic Indication:

      • Diabetes insipidus (due to vasopressin {AVP} deficiency)

Anatomy : Pituitary

  • Pituitary gland (hypophysis) resides within sella turcica of the sphenoid bone at the skull base (weight = between 0.4 and 0.8 grams)

  • Midsagittal section through human pituitary

  • Sagittal section of a human pituitary, showing the relationship of its blood supply to the hypothalamic neurosecretory cells in the adenohypophysis

  • Sagittal section of a human pituitary, showing the relationship of its blood supply to the neurosecretory cells of the supraoptic and paraventricular nuclei of the hypothalamus

  • Pituitary gland components:

    • anterior lobe (adenohypophysis)

    • posterior lobe (neurohypophysis)

  • Separated from brain by diaphragma sella (dura mater extension) and by thin bone layers from the sphenoid sinus anteriorly and inferiorly

  • Sella lateral walls abut on the cavernous sinuses (containing internal carotid arteries & cranial nerves III, IV, V, and VI. Recurrent

  •  Optic chiasm located slightly anterior to pituitary stalk -- just above diaphragma sella.

    • Reason why pituitary tumors result in visual field effects, cranial nerves palsies, sphenoid sinus invasion

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Anatomy: Hypothalamus

1. cerebral peduncle 
2. mamillary body 
3. floor of hypothalamus 
4. optic nerve 
5. olfactory tract

image source attribution:  University of Manitoba Anatomy (http://www.umanitoba.ca/faculties/medicine/units/anatomy/bmr/graphics/hypothalamus.html)

 

  • Hypothalamus:

    • anterior extension to optic chiasm margin

    • posterior extension including mammillary bodies

    • Separated from pituitary by:

      • hypothalamic sulcus of the third ventricle

    • Rounded inferior hypothalamic base: tuber cinereum

      • Base central portion (median eminence or infundibulum) formed by third ventricle floor, continuing inferiorly to form the pituitary stalk

        • Hypothalamic releasing factors synthesized in neurons located along third ventricular margins

          • Fibers from these neurons terminate in the median eminence adjacent to portal capillaries

    • Neuronal cell bodies of supraoptic and periventricular hypothalamic nuclei produce vasopressin and oxytocin which are transported  along nerve axons (supraopticohypophyseal and paraventriculohypophyseal tracts) to the posterior lobe

    • Hypothalamic-anterior pituitary communication: chemical

      •  Hypothalamic neuronal releasing factors flow through the portal system to stimulate or inhibit anterior pituitary hormone production

      •  Anterior pituitary blood supply: (highest blood flow of any tissue --{0.8mL/g/min})

        • Blood supplied by way of the hypothalamus

          • Two derivatives of the internal carotid arteries (superior hypophyseal arteries {SHA} terminate in median eminence {which resides outside the blood-brain barrier} capillary network.

          •  These capillaries exhibit a fenestrated endothelium which results in easy access to hypothalamic releasing hormones (regulation: vasoactive intestinal peptide)

          • Capillaries form 6-10 straight veins: the hypothalamic pituitary portal circulation -- main blood supply to anterior lobe (supply nutrients and hypothalamic factors)

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Primary Reference: Fizgerald, P.A. and Klonoff, D.C. Hypothalamic and Pituitary Hormones, in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 603-618.
Primary Reference:Biller, Beverly, M. K. and Daniels, Gilbert, H. Neuroendocrine Regulation and Diseases of the Anterior Pituitary and Hypothalamus, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp 1972-1998