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On this page
  • Hypothalamus-Pituitary System
  • CRH
  • GnRH
  • Somatostatin
  • TRH
  • Dopamine
  • Melanocyte Inhibiting Factor
  • Anterior Pituitary
  • FSH and LH
  • ACTH
  • TSH
  • GH
  • HCG
  • MSH
  • POMC
  • Basophils and Acidophils
  • Feedback
  • Posterior Pituitary
  • ADH

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  1. 01 Step 1
  2. Endocrinology

07 Pituitary Secretions

Previous06 Pituitary AnatomyNext08 Pituitary Pathology

Last updated 5 years ago

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Hypothalamus-Pituitary System

The anterior lobe of the pituitary gland communicates with the hypothalamus by the hypothalamic–hypophysial portal system:

  1. The hypothalamus is supplied by blood coming from the superior hypophyseal artery.

  2. Hypothalamic hormones enter the capillary plexus near the median eminence, and travel via long portal veins to the anterior pituitary.

  3. In the anterior pituitary, hormones exit a secondary capillary plexus to stimulate or inhibit hormone release from their specific endocrine target cells.

  4. Endocrine cells respond by increasing or decreasing their output of tropic hormones into systemic circulation.

Hypothalamus outlined on MRI: ..

In contrast, the posterior lobe of the pituitary gland contains the axons of neurons whose cell bodies are located in hypothalamic nuclei.

  1. Hormones are synthesized in the hypothalamus, packaged in secretory granules and transported down the nerve axons for secretion.

  2. Upon stimulation of the hypothalamic cell bodies, hormone-containing granules are released by exocytosis into peripheral circulation, via the capillary plexus of the inferior hypophyseal artery.

..

..

CRH

GnRH

Somatostatin

TRH

Dopamine

Melanocyte Inhibiting Factor

Anterior Pituitary

  • Follicle stimulating hormone (FSH)

  • Luteinizing hormone (LH)

  • Adrenocorticotropic hormone (ACTH)

  • Thyroid stimulating hormone (TSH; thyrotropin)

  • Prolactin

  • Growth hormone (GH)

FSH and LH

LH

FSH

Male

Leydig cell:

Sertoli Cell:

testosterone synthesis

sperm maturation

Female

Theca Cell:

Granulosa Cell:

testosterone synthesis, ovulation, corpus luteum formation

follicle growth, estrogen secretion

..

ACTH

TSH

GH

Also increased by

  • Exercise

  • Sleep (very high just after onset of sleep)

  • Starvation (hypoglycemia)

.,

  • Glucose

  • Somatostatin (released in response to IGF-1; GH)

  • IGF-1 (direct and indirect).,

Growth Hormone Receptor

IGF-1

  • Stimulates chondrocytes, increase linear growth

  • Stimulates muscles, increase lean muscle mass

  • Stimulates organs, increase organ size

.,

GH Effects

  • Increased insulin resistance and blood sugar

  • Increased lipolysis by activating hormone sensitive lipase

  • Increased IGF-1 that results in bone, muscle, and organ growths.,

  • increased blood sugar (diabetogenic)

  • increased insulin resistance in peripheral tissues

  • hyperinsulinemia.,

GH Deficiency

  • Children: failure to grow

  • Adults: increased fat, low lean body mass, low energy..

HCG

MSH

[_](MSH and Cushing's disease)In Cushing's disease, the ACTH adenoma produces both excess ACTH and MSH, causing the characteristic darkened skin...

POMC

Basophils and Acidophils

  • “GPA”: Growth hormone and Prolactin are secreted by Acidophils

  • “B FLAT”: Basophils secrete Follicle stimulating hormone, Lutenizing hormone, Adrenocorticotropic hormone, and Thyroid stimulating hormone...

Feedback

Posterior Pituitary

  • Paraventricular nuclei: Oxytocin

  • Supraoptic nuclei: ADH..

The hypothalamus directly synthesizes hormones, which are complexed with neurophysins and shipped into the posterior pituitary for storage and secretion. The hypothalamic-pituitary hormones that utilize this non-capillary secretion mechanism include arginine vasopressin (aka antidiuretic hormone) and oxytocin...

ADH

[_](ADH's 2 main effects)Vasopressin has an antidiuretic effect (reabsorbs water) and is also a moderate vasoconstrictor. ..

  • Pain/stress

  • Hypoglycemia

  • Nausea

  • Volume contraction

  • Nicotine and opiates

  • Angiotensin II..

  • Alpha-agonists

  • Ethanol

  • Atrial natriuretic peptide

  • Cold..

  • Regulate serum osmolarity

  • Maintain (increase) blood pressure..

  • ADH binding activates adenylyl cyclase, which increases cAMP and activates protein kinase A.

  • Activated protein kinase A phosphorylates aquaporin-2-containing vesicles, stimulating their transport and fusion with the luminal plasma membrane

  • The insertion of more aquaporin channels allows water to move rapidly from the tubular lumen into the collecting duct cell, reclaiming more water.

  • The result is an increase in blood volume and a decrease in plasma osmolarity.

Note: this function can be remembered by the latter half of the hormones name -pressin (remember, a pressor is any agent that increases blood pressure by stimulating constriction of blood vessels)...

Stimulates ACTH secretion, as well as the release of other peptides derived from proopiomelanocortin (e.g. MSH, β-endorphin).,

Stimulates the secretion of LH, FSH.,

Inhibits the secretion of GH and TSH.,

Pharm uses:

..

Stimulates the secretion of TSH and prolactin. Prolactin is under tonal dopamine inhibition, and excess TRH levels suppress dopamine. Thus, prolactin levels will increase as dopamine decreases.,

Inhibits the release of prolactin.,

Inhibits the release of MSH.,

There are 6 major hormones secreted by the anterior pituitary (mnemonic: FLAT PiG):

..

Secreted by gonadotropes of the anterior pituitary.,

Secreted by corticotrophs of the anterior pituitary and stimulates adrenal growth and steroidogenesis.,

Secreted by thyrotrophs of the anterior pituitary and stimulates thyroid hormone synthesis and release.,

Secreted by somatotropes of the anterior pituitary and is counter-regulatory to insulin. It stimulates linear height growth via insulin-like growth factor (IGF-1), which is released by the liver in response to stimulation by GH.,

Growth hormone-releasing hormone (GHRH, somatocrinin) stimulates the secretion in pulsatile fashion.

Is decreased by:

Protein hormone and binds to surface receptors, uses JAK2-STAT pathway.,

..

aka Somatomedin.,

Many growth hormone receptors are found in the liver, and they secrete IGF-1, which mediates many of GH effects. IGF-1 is also produced in peripheral tissues and mediates its effect in paracrine fashion...

Has following effects:

IGF-1 is measured in serum as indicator of GH function, as GH is difficult to measure with its pulsatile fashion...

Has following effects:

GH decreases blood glucose intake in to cells and will cause anti-insulin effects:

Most common caues is pituitary tumor from masses or as result of surgery/radiation...

Symptoms are different for children and adults:

Treatment is synthetic growth hormone and IGF-1 level monitoring..

TSH, LH, FSH and human chorionic gonadotropin (hCG) share a common α-subunit, while the β-subunit of these hormones determines hormone specificity.

..

aka melanotropin.,

MSH, or melanotropin, stimulates melanin synthesis and is secreted from the intermediate lobe of the pituitary...

Derived from pro-opiomelanocortin (POMC).,

Cells of the anterior pituitary are categorized into two groups, basophils and acidophils, based on whether they stain readily with acidic or basic dyes. To remember which type of hormone-secreting cells fall into which category, use the mnemonics “GPA” and “B FLAT”:

Anterior pituitary hormones enter the systemic circulation and exert their effects at target glands. Eventually, the target gland response is limited by its hormonal product exerting negative feedback inhibition at the level of the pituitary gland or hypothalamus...

:

Vasopressin and oxytocin are two hormones that are secreted from the posterior pituitary. Note that vasopressin is also called antidiuretic hormone (ADH) and arginine vasopressin (AVP).

A nonapeptide that is synthesized predominately in the supraoptic nucleus of the hypothalamus, and secreted from the posterior pituitary upon stimulation of these cell bodies. .,

Travels down the nerve axon in neurosecretory granules to be stored in the nerve terminals, lying in the posterior pituitary gland. Neurophysins are the carrier proteins which make this transport possible.,

The primary stimulus for antidiuretic hormone (ADH) secretion is an increase in serum osmolarity. A loss of intracellular water from hypothalamic osmoreceptor neurons bathed by hyperosmolar blood will stimulate ADH release. Other factors that increase ADH secretion include:

The primary inhibitor of ADH secretion is a decrease in serum osmolarity. Other factors that decrease ADH secretion include:

Antidiuretic hormone (ADH) has two primary functions:

ADH increases water reabsorption by binding to V2 receptors on the capillary (basal) side of principal cells in the renal collecting duct:

..

Vasopressin also causes vasoconstriction of arterioles through binding to V1 receptors, stimulating a IP3/Ca2+-mediated response. This vasoconstriction leads to a direct increase in arterial pressure.

Antidiuretic hormone also increases the permeability of the inner medullary collecting duct to urea. This increases the osmotic gradient created by the countercurrent multiplier, facilitating the production of concentrated urine (i.e. increasing urine osmolarity)..

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