Pituitary Gland Hypothalamus Hypothalamus and Pituitary Gland The

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

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 nonendocrine tissue • Located outside the blood-brain barrier

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. 1. Oxytocin 2. Vasopressin/ADH 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 Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Anterior Pituitary - Trophic Hormones 1. 2. 3. 4. 5. 6. 7. Human Growth Hormone - h. GH Thyroid-Stimulating Hormone - TSH Follicle-Stimulating Hormone - FSH Luteinizing Hormone - LH Prolactin - PRL Adrenocorticotropic Hormone - ACTH Melanocyte-Stimulating Hormone - MSH

Human Growth Hormone (h. GH/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

h. GH Feedback Loops Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Thyroid-Stimulating Hormone (TSH) a. k. a. Thyrotopin • Produced by thyrotrophs • 1°- acts on thyroid (T 3/T 4). 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 Gn. RH

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 Gn. RH

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

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

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

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.

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 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.

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 letdown/ejection Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.