Pituitary Gland & Hypothalamus

Hypothalamus and Pituitary Gland The hypothalamus and pituitary gland work together to control other endocrine glands. They are connected by the infundibulum. The pituitary is composed of the: Anterior pituitary (glandular) Posterior pituitary (neural) Alternative names: Anterior pituitary: adenohypophysis, pars distalis, pars anterior Posterior pituitary: neurohypophysis, pars nervosa Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Pars intermedia – separates anterior from posterior PVN – paraventricular hypothalamic nucleus SON – supraoptic hypothalamic nucleus

Pituitary Gland Master Gland Controls growth & activity of the Thyroid Gland, Adrenal Gland, Gonads, & Liver “Middleman” between the brain (CNS) and the peripheral endocrine organs Pituitary hormones act on endocrine and non-endocrine tissue Located outside the blood-brain barrier

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Pituitary Gland Anterior lobe (adenohypophysis) Comprises 75% of the weight of the pituitary gland Secretes 7 hormones. Posterior lobe (neurohypophysis) Made of neural tissue Releases two hormones/neuropeptides made by the hypothalamus. Oxytocin Vasopressin/ADH Hormone secreting cells of the neurohypophysis (posterior pituitary), the adrenal medulla and the pineal gland are regulated by direct neural innervation. Stimulation of hormone secretion by nerves is referred to as neuroendocrine transduction. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Hypothalamus Secretes releasing and inhibiting hormones that control the release of hormones by the pituitary gland. They reach the pituitary gland via the hypophyseal portal system.

Hypophysiotropic Hormones Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Hypophyseal Portal System Hypophyseal arteries come off of the carotid artery The arteries of the pituitary gland arise from the internal carotid arteries as the inferior and superior hypophyseal arteries. The inferior hypophyseal arteries mainly supply the pars nervosa before forming short portal vessels to supply the pars distalis. The superior hypophyseal arteries supply the floor of the hypothalamus, the median eminence. The capillary plexus formed by the superior hypophyseal artery in the median eminence form into long portal vessels which run down in the pituitary stalk to form a capillary plexus in the pars distalis. In the median eminence the capillary plexus receives secretions from releasing factor cells. The blood is drained from the pituitary by inferior hypophyseal veins into the dural venous sinuses. Coming from carotid Superior – anterior pituitary Inferior – posterior pituitary Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Anterior Pituitary - Trophic Hormones Human Growth Hormone - hGH Thyroid-Stimulating Hormone - TSH Follicle-Stimulating Hormone - FSH Luteinizing Hormone - LH Prolactin - PRL Adrenocorticotropic Hormone - ACTH Melanocyte-Stimulating Hormone - MSH Trophic- “nourishing”

Human Growth Hormone (hGH/GH) a.k.a. Somatotropin Most abundant AP hormone Produced by somatotrophs Account for majority of cells present in AP 1° - acts on liver (IGF) GHRH stimulates; SST/GHIH inhibits Somatostatin (SST) Growth Hormone Releasing Hormone (GHRH) SST: decreases GH secretion at AP and by decreasing GHRH If you have high IGF-I it will feedback to increase SST and then decrease GH and GHRH

Long Loop Feedback – target tissue secretes hormone that affect the pituitary and the hypothalamus Short Loop Feedback– pituitary (hypophyseal) hormone feeds back to the hypothalamus to shut it down Ultrashort Feedback – Hormone released from the pituitary shuts itself off.

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. hGH Feedback Loops growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH). Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Thyroid-Stimulating Hormone (TSH) a.k.a. Thyrotopin Produced by thyrotrophs 1°- acts on thyroid (T3/T4). In mammals  thermogenesis Stimulated by TRH

Follicle-Stimulating Hormone (FSH) a.k.a Follitropin Produced by gonadotrophs Specifically, FSH-gonadotroph 1°- in men: promotes spematogenesis; in women: follicular growth (estrogen/progesterone) Stimulated by GnRH Increases LH receptors in Leydig cells (sperm production)

Luteinizing Hormone (LH) a.k.a. Lutropin Produced by gonadotrophs Specifically, LH-gonadotroph 1° - in men: acts on testes (testosterone); in women: acts on ovaries (ovulation/CL) Stimulated by GnRH Corpus lutem

Prolactin (PRL) Produced by lactotrophs A.k.a. mammotrophs PRL increases during pregnancy and reaches maximal values at parturition Milk production in post-partum women Stimulated by nursing infant Prolactin-inhibiting factor- a.k.a. dopamine via tonic inhibition

Adrenocorticotropic Hormone (ACTH) a.k.a. Corticotropin Produced by corticotrophs 1° action- stimulates steroid biosynthesis within the adrenal cortex; cortisol Stimulated by CRH High cortisol = Cushings Disease Low cortisol = Addisons Disease Primary Cushings- high cortisol/ Secondary Cushings – high ACTH Primary Addisons- low cortisol / Secondary Addisons- low ACTH Cushings Disease Excessive secretion of ACTH Characterized by excess cortisol and alterations of glucose metabolism Hyperpigmentation, wasting of muscle, puffiness (water retention) Pituitary or hypothalamus tumor Addison’s Disease Absence of ACTH secretion Characterized by decreased cortisol secretion

Melanocyte-Stimulating Hormone (MSH) a.k.a. Melanotropin Produced by corticotrophs Disperse melanin pigment in melanocytes in the skin Not secreted in large amounts by AP

Credit: Dr. Michael Ormsbee, Florida State University

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Hypothalamus and A.P. Negative feedback loops control the secretions of: Thyrotrophs TSH Gonadotrophs LH, FSH Corticotrophs ACTH, MSH Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Posterior Pituitary The posterior pituitary gland does not synthesize any hormones. It stores and releases from axon terminals two hormones: oxytocin (OT) anti-diuretic hormone (ADH)/vasopressin Axons from the neurosecretory cells form the hypothalamohypophyseal tract. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Hypothalamus and Post. Pituitary The PP contains only neuronal axonal endings. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Posterior Pituitary - ADH Antidiuretic hormone (ADH)/vasopressin Amount secreted varies with blood osmotic pressure. Its function is to decrease urine output. Osmoreceptors (neurons) in the hypothalamus monitor blood osmotic pressure. ↑ blood volume causes ↓ ADH secretion ↓ blood volume causes ↑ ADH secretion Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. ADH Feedback Loop Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Posterior Pituitary - Oxytocin The “cuddle” or “love” hormone Active during parturition and post-partum Stretching of cervix = ↑↑ oxytocin release Results in ↑ smooth muscle contractions of uterus After birth – responsible for milk let-down/ejection Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.