Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
ENDOCRINE SYSTEM Corrected by Dr. C.Gerin From Marieb 08/29/16 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Endocrine System Anatomy: “ana” = separate from; “tomy”= cut open => dissection Physiology: “logy” = study; “physio” =related to natural functioning =>study of living organism Copyright © 2006 Pearson Inc., publishing as Benjamin Cummings 8/26/13 Dr. C.Education, Gerin, Anat227 Introduction The nervous system and the endocrine system work together: neuro-endocrine system The nervous system: produces short-term, very specific responses The endocrine system: produces long-lasting, more general responses Copyright © 2006 Pearson Inc., publishing as Benjamin Cummings 8/26/13 Dr. C.Education, Gerin, Anat227 3 Major Endocrine Organs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.1 Autocrines and Paracrines Autocrines – chemicals that exert effects on the same cells that secrete them Paracrines – locally acting chemicals that affect cells other than those that secrete them These are not considered hormones since hormones are long-distance chemical signals Copyright © 2006 Pearson Inc., publishing as Benjamin Cummings 8/26/13 Dr. C.Education, Gerin, Anat227 Introduction The endocrine system releases chemicals called hormones : protein or lipids (steroid) Secreted by a gland or gland-like structure Travel in bloodstream target organ or tissue distant Therefore, response = distant site in the body Copyright © 2006 Inc., Anat227 publishing as Benjamin Cummings 8/26/13 Dr.Pearson C. Education, Gerin, 6 The main endocrine organs are:$$$$$ Epiphysis = Pineal gland (pine cone; melatonine) Hypothalamus Pituitary gland = Hypophysis Thyroid gland Parathyroid glands Thymus gland Suprarenal glands Pancreas Reproductive glands 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 7 An Overview of the Endocrine System Other endocrine tissues are: Heart Kidney Adipose cells Digestive tract 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 8 The Endocrine System$$$$$$ RH Hypothalamus Pineal Gland= epiphysis Production of ADH, oxytocin, and regulatory hormones SRH IRH Melatonin Parathyroid Glands (on posterior surface of thyroid gland) Hypophysis=Pituitary Gland SH Pars distalis (anterior lobe): ACTH, TSH, GH, PRL, FSH, LH, and MSH Neurohypophysis (posterior lobe): Release of oxytocin and ADH Parathyroid hormone (PTH) Heart Natriuretic peptides: Atrial natriuretic peptide (ANP) Brain natriuretic peptide (BNP) Thyroid Gland H Thyroxine (T 4) Triiodothyronine (T 3) Calcitonin (CT) Kidney Erythropoietin (EPO) Calcitriol (Chapters 19 and 26) Thymus (Undergoes atrophy during adulthood) Adipose Tissue Thymosins KEY TO PITUITARY HORMONES ACTH TSH GH PRL FSH LH MSH ADH Leptin Resistin Suprarenal Glands Each suprarenal gland is Adrenocorticotropic hormone subdivided into: Thyroid-stimulating hormone Medulla: Growth hormone Epinephrine (E) Prolactin Norepinephrine (NE) Follicle-stimulating hormone Cortex: Luteinizing hormone Cortisol, corticosterone, Melanocyte-stimulating hor*mone aldosterone, androgens Antidiuretic hormon (= AVP=Vasopressine Digestive Tract Numerous hormones CCK,… (detailed in Chapter 25) Pancreatic Islets Testis Insulin, glucagon Gonads Testes (male): Androgens (especially testosterone), inhibin Ovaries (female): Estrogens, progestins, inhibin Ovary 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 9 Figure Gross Anatomy and Histological Organization of the Pituitary Gland and Its Subdivisions$$$$$ Mamillary body Third Median ventricle eminence HYPOTHALAMUS Optic chiasm Infundibulum Diaphragma sellae Pars tuberalis Adenohypophysis (anterior lobe) Pars distalis Neurohypophysis (posterior lobe) Pars intermedia Sphenoid (sella turcica) Relationship of the pituitary gland to the hypothalamus 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 10 Figure 19.2 Hypothalamic Control over Endocrine Organs HYPOTHALAMUS Secretion of regulatory hormones to control activity of pars distalis (anterior lobe) of pituitary gland Production of ADH and oxytocin Control of (sympathetic) output to suprarenal medullae Preganglionic motor fibers Suprarenal gland Medulla Neurohypophysis (posterior lobe) of pituitary gland Pars distalis (anterior lobe) of pituitary gland Hormones secreted by pars distalis of pituitary gland control other endocrine organs 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Release of ADH and oxytocin* Secretion of epinephrine and norepinephrine 11 An Overview of the Endocrine System The Hypothalamus (RH) Secretes regulatory hormones (RH) Stimulating releasing hormones (SRH) inhibiting releasing hormones (IRH) Acts as an endocrine organ Releases antidiuretic hormone (ADH)= arginine vasopressine (AVP) and oxytocin to the pituitary gland Contains autonomic nervous system centers 8/26/13 Dr. C. Gerin, Anat227 Exerts control over t Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 12 The Pituitary Gland = HYPOPHYSIS The Adenohypophysis = SH Consists of five different cell types Thyrotropes: release thyroid-stimulating hormone (TSH) Corticotropes: release adrenocorticotropic hormone (ACTH) and melanocytestimulating hormone (MSH) Gonadotropes: release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), prolactin* (PRL) 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 13 Insulin-like growth factor 1 (IGF-1), also called somatomedin C => IGH => role in childhood growth and continues to have anabolic effects in adults. 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 14 The Pituitary Gland The Hypophyseal Portal System Within the infundibulum is a plexus of capillaries Capillaries are fenestrated Regulatory hormones leave the hypothalamus and pass through the portal vessels to the adenohypophysis 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 15 Figure The Pituitary Gland and the Hypophyseal Portal System$$$$$$ Supraoptic Paraventricular nuclei nuclei Mamillary body HYPOTHALAMUS Optic chiasm Superior hypophyseal artery Capillary Beds ADENOHYPOPHYSIS OF PITUITARY GLAND Infundibulum Portal veins = BRIDGE between the neural release from the hypothalamic n. AND the anterior hypohysis Inferior hypophyseal artery NEUROHYPOPHYSIS OF PITUITARY GLAND Endocrine cells Hypophyseal veins 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 16 Figure 19.4 Pituitary Hormones and Their Targets$$$$ Hypothalamus Direct Control by Nervous System KEY TO PITUITARY HORMONES Direct Release of Hormones Indirect Control Through Release of Regulatory Hormones Sensory Osmoreceptor stimulation stimulation Regulatory hormones are released into the hypophyseal portal system for delivery to the anterior lobe of the pituitary Medulla Adenohypophysis of pituitary gland ACTH TSH GH PRL FSH LH MSH ADH Adrenocorticotropic hormone Thyroid-stimulating hormone Growth hormone Prolactin Follicle-stimulating hormone Luteinizing hormone Melanocyte-stimulating hormone Antidiuretic hormone Posterior lobe of pituitary gland ADH Suprarenal gland ACTH Cortex TSH Epinephrine and norepinephrine Liver Thyroid gland Kidneys GH Oxytocin MSH PRL FSH Males: Smooth muscle in ductus deferens and prostate gland LH Somatomedins Females: Uterine smooth muscle and mammary glands Glucocorticoids (cortisol, corticosterone) Bone, muscle, other tissues Mammary glands Ovaries of female Testes of male Melanocytes (uncertain significance in healthy adults) Thyroid hormones (T3, T4) Inhibin Testosterone 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Estrogen Progesterone Inhibin 17 CONCLUSION NERVOUS SYSTEM: LOCAL RELEASE and LOCAL ACTION ENDOCRINE SYSTEM: Gland SECRETION , BLOOD TRANSPORT, DISTANT ACTION Epiphyseal Gland= Pineal Gland Hypothalamus =RH (RHLH=GnRH) Anterior Hypophysis = SH (FSH) Target Organ: Gonades 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 18 Figure 17.8 Autonomic Distribution of the Parasympathetic Output Pterygopalatine ganglion N III Lacrimal gland Eye Ciliary ganglion PONS N VII Salivary glands Submandibular ganglion N IX Otic ganglion N X (Vagus) Heart Lungs Autonomic plexuses (see Figure 17.9) Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic nerves Small intestine Rectum Spinal cord S2 Kidney S3 S4 KEY Preganglionic neurons Ganglionic neurons Uterus Ovary Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings 8/26/13 Dr. C.©Gerin, Anat227 Penis Scrotum 19 Urinary bladder Figure 17.4 Anatomical Distribution of Sympathetic Postganglionic Fibers Eye PONS Salivary glands Sympathetic nerves Superior Cervical sympathetic ganglia Middle Heart Inferior Gray rami to spinal nerves T1 T1 T2 T2 T3 T3 T4 T4 T5 T5 T6 T6 T7 T7 T8 T8 T9 T9 T10 T10 T11 Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) Lung Celiac ganglion Superior mesenteric ganglion Liver and gallbladder Stomach T11 T12 L1 L1 L2 L2 Lesser splanchnic nerve L4 L5 S1 S2 S3 S4 S5 Spleen Pancreas Large intestine Lumbar splanchnic nerves L3 L3 L4 Sympathetic chain ganglia Greater splanchnic nerve T12 L5 S1 S2 S3 S4 S5 Cardiac and pulmonary plexuses Small intestine Inferior mesenteric ganglion Suprarenal medulla Sacral splanchnic nerves Kidney Spinal cord KEY Preganglionic neurons Ganglionic neurons Coccygeal ganglia (Co1) fused together (ganglion impar) Uterus Ovary Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 8/26/13 Dr. C. Gerin, Anat227 Penis Scrotum 20 Urinary bladder Figure The Regulation of Thyroid Secretion Hypothalamus releases TRH Homeostasis Disturbed Decreased T3 and T4 concentrations in blood or low body temperature TRH Anterior lobe Pituitary gland HOMEOSTASIS Anterior lobe Normal T3 and T4 concentrations, normal body temperature Adenohypophysis releases TSH TSH Homeostasis Restored Increased T3 and T4 concentrations in blood Thyroid gland Thyroid follicles release T3 and T4 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings 8/26/13 Dr. C.©Gerin, Anat227 21 NOW GROSS ANATOMY DISSECTION MODEL OBSERVATION DESCRIPTION LAB EXERCISES 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 22 Hormones Hormones – chemical substances secreted by cells into the extracellular fluids to the blood stream Regulate the metabolic function of other cells Have lag times ranging from seconds to hours Tend to have prolonged effects Are classified as amino acid-based hormones, or steroids Eicosanoids – biologically active lipids with local hormone–like activity 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormone Action Hormones alter target cell activity by one of two mechanisms Second messengers: Regulatory G proteins Amino acid–based hormones Direct gene activation Steroid hormones The precise response depends on the type of the target cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mechanism of Hormone Action Hormones produce one or more of the following cellular changes in target cells Alter plasma membrane permeability Stimulate protein synthesis Activate or deactivate enzyme systems Induce secretory activity Stimulate mitosis 8/26/13 Dr. C. Gerin, Anat227 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Amino Acid-Based Hormone Action: cAMP Second Messenger Hormone (first messenger) binds to its receptor, which then binds to a G protein The G protein is then activated as it binds GTP, displacing GDP Activated G protein activates the effector enzyme adenylate cyclase Adenylate cyclase generates cAMP (second messenger) from ATP cAMP activates protein kinases, which then cause cellular effects Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 8/26/13 Dr. C. Gerin, Anat227 Amino Acid-Based Hormone Action: cAMP Second Messenger Extracellular fluid Hormone A Adenylate cyclase Hormone B 1 1 2 GTP 3 GTP GTP Receptor Gs GTP GTP 2 Gi GDP GDP ATP Catecholamines ACTH FSH LH Glucagon PTH TSH Calcitonin 3 4 Receptor GTP cAMP 5 Inactive protein kinase A Active protein kinase A Triggers responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channels, etc.) Cytoplasm Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.2 Amino Acid-Based Hormone Action: PIP-Calcium Hormone binds to the receptor and activates G protein G protein binds and activates phospholipase Phospholipase splits the phospholipid PIP2* into diacylglycerol (DAG) and IP3 (both act as second messengers) DAG activates protein kinases; IP3 triggers release of Ca2+ stores Ca2+ (third messenger) alters cellular responses** Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Amino Acid-Based Hormone Action: PIP Mechanism Extracellular fluid Hormone DAG 1 4 2 GTP 3 GTP 5 Receptor Gq GTP Catecholamines TRH ADH GnRH Oxytocin GDP IP3 Phospholipase C 5 Endoplasmic reticulum Cytoplasm Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Active protein kinase C PIP2 Inactive protein kinase C Triggers responses of target cell 6 Ca2+ Ca2+- calmodulin Figure 16.3 Steroid Hormones This interaction prompts DNA transcription to produce mRNA The mRNA is translated into proteins, which bring about a cellular effect Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Steroid hormone Cytoplasm Steroid Receptorhormone chaperonin complex Receptor-hormone complex Molecular chaperones Binding Hormone response elements Chromatin Transcription mRNA mRNA Nucleus Ribosome Translation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings New protein Figure 16.4 Target Cell Specificity Hormones circulate to all tissues but only activate cells referred to as target cells Target cells must have specific receptors to which the hormone binds These receptors may be intracellular or located on the plasma membrane Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Target Cell Specificity Examples of hormone activity ACTH receptors are only found on certain cells of the adrenal cortex Thyroxin receptors are found on nearly all cells of the body Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Target Cell Activation Target cell activation depends on three factors Blood levels of the hormone Relative number of receptors on the target cell The affinity of those receptors for the hormone Up-regulation – target cells form more receptors in response to the hormone Down-regulation – target cells lose receptors in response to the hormone Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormone Concentrations in the Blood Hormones circulate in the blood in two forms – free or bound Steroids and thyroid hormone are attached to plasma proteins* All others are unencumbered Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormone Concentrations in the Blood Concentrations of circulating hormone reflect: Rate of release Speed of inactivation and removal from the body Hormones are removed from the blood by$$$$$: Degrading enzymes The kidneys Liver enzyme systems Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Interaction of Hormones at Target Cells Three types of hormone interaction Permissiveness – one hormone cannot exert its effects without another hormone being present Synergism – more than one hormone produces the same effects on a target cell Antagonism – one or more hormones opposes the action of another hormone Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Control of Hormone Release Blood levels of hormones: Are controlled by negative feedback systems Vary only within a narrow desirable range Hormones are synthesized and released in response to: Humoral stimuli (blood) Neural stimuli Hormonal stimuli Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Humoral Stimuli Humoral stimuli – secretion of hormones in direct response to changing blood levels of ions and nutrients Example: concentration of calcium ions in the blood Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone) PTH causes Ca2+ concentrations to rise and the stimulus is removed Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Humoral Stimuli Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.5a Neural Stimuli Neural stimuli – nerve fibers stimulate hormone release Preganglionic sympathetic nervous system (SNS) fibers stimulate the adrenal medulla to secrete catecholamines* NA, A http://upload.wikimedia.org/wikipedia/commons/8/89/Nor adrenalin_-_Noradrenaline.svg http://upload.wikimedia.org/wikipedia/commons/3/36/Adr enalin_-_Adrenaline.svg Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.5b Hormonal Stimuli Hormonal stimuli – release of hormones in response to hormones produced by other endocrine organs The hypothalamic hormones stimulate the anterior pituitary In turn, pituitary hormones stimulate targets to secrete still more hormones Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Stimuli$$$$ Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.5c Nervous System Modulation The nervous system can override normal endocrine controls For example, control of blood glucose levels Normally the endocrine system maintains blood glucose Under stress, the body needs more glucose The hypothalamus and the sympathetic nervous system are activated to supply ample glucose Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Major Endocrine Organs: Pituitary Gland (Hypophysis) Pituitary gland – two-lobed organ that secretes nine major hormones Neurohypophysis – posterior lobe (neural tissue) and the infundibulum Receives, stores, and releases hormones from the hypothalamus Adenohypophysis – anterior lobe, made up of glandular tissue Synthesizes and secretes a number of hormones Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Major Endocrine Organs: Pituitary Gland (Hypophysis) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.6 Pituitary-Hypothalamic Relationships: Posterior Lobe The posterior lobe is a downgrowth of hypothalamic neural tissue Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract) Nuclei (of what?) of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pituitary-Hypothalamic Relationships: Anterior Lobe The anterior lobe of the pituitary is an outpocketing of the oral mucosa There is no direct neural contact with the hypothalamus Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pituitary-Hypothalamic Relationships: Anterior Lobe There is a vascular connection, the hypophyseal portal system, consisting of: The primary capillary plexus The hypophyseal portal veins The secondary capillary plexus PLAY InterActive Physiology ®: The Hypothalamic Pituitary Axis Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pituitary-Hypothalamic Relationships: Anterior Lobe Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.6 Adenophypophyseal Hormones The six hormones of the adenohypophysis: Abbreviated as GH, TSH, ACTH, FSH, LH, and PRL Regulate the activity of other endocrine glands In addition, pro-opiomelanocortin (POMC): Has been isolated from the pituitary Is split into ACTH, opiates, and MSH Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Activity of the Adenophypophysis The hypothalamus sends a chemical stimulus to the anterior pituitary Releasing hormones stimulate the synthesis and release of hormones Inhibiting hormones shut off the synthesis and release of hormones Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Activity of the Adenophypophysis The tropic hormones that are released are: Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Growth Hormone (GH) Produced by somatotropic cells of the anterior lobe that: Stimulate most cells, but target bone and skeletal muscle Promote protein synthesis and encourage the use of fats for fuel Most effects are mediated indirectly by somatomedins Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Growth Hormone (GH) Antagonistic hypothalamic hormones regulate GH Growth hormone–releasing hormone (GHRH) stimulates GH release Growth hormone–inhibiting hormone (GHIH) inhibits GH release Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Metabolic Action of Growth Hormone GH stimulates liver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors Direct action promotes lipolysis and inhibits glucose uptake Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Metabolic Action of Growth Hormone (GH)$$$$ Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.7 Thyroid Stimulating Hormone (Thyrotropin) Stimulates the normal development and secretory activity of the thyroid Triggered by hypothalamic peptide thyrotropinreleasing hormone (TRH) Rising blood levels of thyroid hormones act on the pituitary and hypothalamus to block the release of TSH Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Adrenocorticotropic Hormone (Corticotropin) Stimulates the adrenal cortex to release corticosteroids Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm Internal and external factors such as fever, hypoglycemia, and stressors can trigger the release of CRH Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gonadotropins Gonadotropins – follicle-stimulating hormone (FSH) and luteinizing hormone (LH) Regulate the function of the ovaries and testes FSH stimulates gamete (egg or sperm) production Absent from the blood in prepubertal boys and girls Triggered by the hypothalamic gonadotropinreleasing hormone (GnRH) during and after puberty Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functions of Gonadotropins In females LH works with FSH to cause maturation of the ovarian follicle LH works alone to trigger ovulation (expulsion of the egg from the follicle) LH promotes synthesis and release of estrogens and progesterone Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functions of Gonadotropins In males LH stimulates interstitial cells of the testes to produce testosterone LH is also referred to as interstitial cell-stimulating hormone (ICSH) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Prolactin (PRL) In females, stimulates milk production by the breasts Triggered by the hypothalamic prolactin-releasing hormone (PRH) Inhibited by prolactin-inhibiting hormone (PIH) Blood levels rise toward the end of pregnancy Suckling stimulates PRH release and encourages continued milk production Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Posterior Pituitary and Hypothalamic Hormones Posterior pituitary – made of axons of hypothalamic neurons, stores antidiuretic hormone (ADH) and oxytocin ADH and oxytocin are synthesized in the hypothalamus ADH influences water balance Oxytocin stimulates smooth muscle contraction in breasts and uterus Both use PIP-calcium second-messenger mechanism Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings