Week 1 Hypothalamus and Pituitary Hormones PDF

Week 2 : The Hypothalamus & Pituitary Gland Hypothalamus & Pituitary Gland: Learning Objectives  Describe the anatomic connections between the hypothalamus and the pituitary gland and the functional significance of each connection.  The hypothalamus controls the pituitary gland by both neural and...

Week 2 : The Hypothalamus & Pituitary Gland Hypothalamus & Pituitary Gland: Learning Objectives  Describe the anatomic connections between the hypothalamus and the pituitary gland and the functional significance of each connection.  The hypothalamus controls the pituitary gland by both neural and hormonal mechanisms. Identify the two different pathways used for hypothalamic –pituitary interactions.  Differentiate between the routes of transport of hypothalamic neuropeptides of the posterior and anterior pituitary. The Hypothalamus And Pituitary Gland  The hypothalamus–pituitary complex can be thought of as the “command center” of the endocrine system.  This complex secretes several hormones that: ◦ directly produce responses in target tissues ◦ regulate the synthesis and secretion of hormones of other glands (Releasing hormones / Inhibitory hormones)  Functionally, the hypothalamus controls the pituitary gland by both neural and hormonal mechanisms Hypothalamus  The hypothalamus receives neural inputs from many areas of the brain.  This information, related to the well-being of the body, is integrated in the hypothalamus  “Internal Mileau” ◦ Refers to the extra-cellular fluid environment, interstitial fluid, and its physiological capacity to ensure protective stability for the tissues and organs of multicellular organism Claude Bernard Functions of the Hypothalamus  Maintain the chemical constancy and temperature of the internal environment of the body  Hypothalamus also functions with the limbic system as a unit that regulates emotional and instinctual behavior. ◦ Ex: Increase in Plasma Osmolarity Principal Hypothalamic Regulatory Mechanisms  Temperature Regulation  Osmolarity  “Appetitive” behavior ( Hunger, Thirst, Sex)  ANS / Defensive Reactions (fear, rage)  Control of body rhythms (sleep/wake patterns) Pituitary Gland  Anterior Pituitary ◦ Epithelial component ◦ Adenohypophysis ◦ Vascular connection  Posterior Pituitary ◦ Neural structure ◦ Neurohypophysis ◦ Neural connection Posterior Pituitary (Neurohypophysis)  Posterior pituitary represents a downgrowth of the hypothalamus.  The posterior pituitary is a collection of nerve axons whose cell bodies are located in the hypothalamus  Supraoptic nuclei (SON) ◦ produce antidiuretic hormone (ADH) [vasopressin]  Paraventricular nuclei (PVN) ◦ produce oxytocin  ADH and oxytocin are released into the capillary plexus of the inferior hypophyseal artery Hypothalamohypophyseal tract. Posterior Pituitary - Hormones  Oxytocin ◦ Stimulates contraction of smooth muscle of both the uterus during delivery and the breast to cause ejection of milk ◦ Also interacts with the brain to increase feelings of emotional bonding between individuals. (“Bonding Hormone”)  Antidiuretic Hormone (ADH) [also called vasopressin] ◦ Stimulates kidneys to reabsorb water, decrease urine output, stimulates thirst center to increase fluid intake, and in high doses it causes vasoconstriction. Regulation of the Anterior Pituitary  Neuroendocrine cells within the hypothalamus produce hypophysiotropic (regulatory) hormones which control secretion of the anterior pituitary hormones (RH & RIH) Hypophysiotropic Hormones  Thyrotropin-releasing hormone (TRH)  Gonadotropin-releasing hormone (GnRH)  Corticotropin-releasing hormone (CRH)  Growth hormone–releasing hormone (GHRH)  Growth hormone–inhibiting hormone (somatostatin)  Prolactin releasing hormone (PRH)  Prolactin-inhibiting hormone (PIH) Hypothalamic - Hypophyseal Portal System  Hypothalamic hormones (RH & IH) are transported to the anterior pituitary via the:  hypothalamic-hypophyseal portal blood vessels ◦ direct vascular link between the hypothalamus and the anterior pituitary  The blood from these capillaries (venous blood) drains into the hypophyseal portal vessels and is delivered directly to the anterior lobe of the pituitary Implications Of The Portal Blood Supply to the Anterior Lobe  The hypothalamic hormones can be delivered to the anterior pituitary directly and in high concentration  The hypothalamic hormones do NOT appear in the systemic circulation.  Only the cells of the anterior pituitary receive high concentrations of the hypothalamic hormones. Hormones – Hypothalamic Cell Type Growth hormone (GH) - Somatotrophs  Prolactin (PRL) - Lactotrophs  Follicle-stimulating hormone (FSH) - Gonadotrophs  Luteinizing hormone (LH) - Gonadotrophs  Adrenocorticotropic hormone (ACTH) - Corticotrophs  Thyroid-stimulating hormone (TSH) - Thyrotrophs   Each of the anterior pituitary hormones is a peptide or polypeptide. Structure Mechanism of control Hormones synthesized by hypothalamus Posterior Pituitary Anterior Pituitary ¼ of pituitary gland Composed of nervous tissue ¾ of pituitary gland composed of endocrine tissue Neural Hormonal Supraoptic nuclei (SON) produce antidiuretic hormone (ADH) Synthesized and released into hypothalamo-hypophyseal portal system Paraventricular nuclei (PVN) produce oxytocin Synthesized and transported to posterior pituitary Oxytocin & ADH released into the inferior Hormones released, hypophyseal artery or synthesized and released, by pituitary gland Thyrotropin-releasing hormone (TRH) Prolactin-releasing hormone (PRH) Gonadotropin-releasing hormone (GnRH) Corticotropin-releasing hormone (CRH) Growth hormone–releasing hormone (GHRH) Prolactin-inhibiting hormone (PIH) Growth-inhibiting hormone (GIH) Hormones synthesized and released Thyroid-stimulating hormone (TSH) Prolactin (PRL) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Adrenocorticotropic hormone (ACTH) Growth hormone (GH) Negative Feedback Control  The resultant changes in target gland hormones and metabolic substrates exert negative feedback control