Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chapter 16 The Endocrine System Part B

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Major Endocrine Organs: Pituitary (Hypophysis)  Pituitary gland:  Two-lobed organ  Secretes nine major hormones  Neurohypophysis:  Posterior lobe (neural tissue) & the infundibulum  Receives, stores, & releases hormones (from the hypo- thalamus)  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 (Hypophysis) Figure 16.6

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pituitary-Hypothalamic Relationship: Posterior Lobe:  Is a downgrowth of hypothalamic neural tissue  Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)  Nuclei of the hypothalamus synthesize:  Oxytocin  Antidiuretic hormone (ADH)  These hormones are transported to:  The posterior pituitary

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Anterior lobe:  Is an outpocketing of the oral mucosa  Has no direct neural contact with the hypothalamus, but  Has (with the hypothalamus) a vascular connection called the hypophyseal portal system:  The hypophyseal portal system consists of:  The primary capillary plexus  The hypophyseal portal veins  The secondary capillary plexus PLAY Pituitary-Hypothalamic Relationship

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pituitary-Hypothalamic Relationships: Anterior Lobe Figure 16.6

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Adenophypophyseal Hormones  The six hormones of the adenohypophysis:  GH (Growth hormone)  TSH (Thyroid stimulating hormone)  ACTH (Adrenocorticotropic hormone)  FSH (Follicle stimulating hormone)  LH (Luteinizing hormone)  PRL (Prolactin)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Adenophypophyseal Hormones  Four of the six hormones are tropic (turn on) hormones  They are the TSH, ACTH, FSH, and LH  They regulate the secretory action of other endocrine glands  An additional pituitary hormone has been isolated:  Pro-opiomelanocortin (POMC)  Can be split enzymatically into:  ACTH  Opiates  MSH

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Activity of the Adenophypophysis  The hypothalamus regulates the anterior pituitary through:  Releasing hormones:  Stimulate synthesis & release of hormones  Inhibiting hormones:  Shut off the synthesis & release of hormones

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Growth Hormone (GH)  Stimulates:  Most cells, but targets:  Bone  Skeletal muscle  Promotes:  Protein synthesis  Encourages:  The use of fats for fuel

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Growth Hormone (GH)  Hypothalamic hormones that regulate GH include:  Growth hormone–releasing hormone (GHRH):  Stimulates GH release  Growth hormone–inhibiting hormone (GHIH):  Also called somatostatin  Inhibits GH release

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Metabolic Action of Growth Hormone  GH stimulates the following tissues to produce insulin-like growth factors:  Liver  Skeletal muscle  Bone  Cartilage  GH direct action:  Promotes lipolysis  Inhibits glucose uptake

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Metabolic Action of Growth Hormone (GH) Figure 16.7

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Biol  Wed, 04/24/’13

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Thyroid Stimulating Hormone (Thyrotropin)  Stimulates:  The thyroid secretory activity  Triggered by:  Hypothalamic thyrotropin-releasing hormone (TRH)  Blocked by:  Rising blood levels of thyroid hormones (-ve feedback on pituitary & hypothalamus to block TSH release)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Adrenocorticotropic Hormone (Corticotropin)  ACTH stimulates:  The adrenal cortex to release cortico-steroids  Triggered by:  Hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gonadotropins  Gonadotropins include:  Follicle-stimulating hormone (FSH)  Luteinizing hormone (LH)  FSH stimulates gamete (egg or sperm) production  Absent from the blood in prepubertal boys and girls  Triggered by:  Hypothalamic gonadotropin-releasing 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:  Hypothalamic prolactin-releasing hormone (PRH)  Inhibited by:  Hypothalamic prolactin-inhibiting hormone (PIH)  Its blood levels rise toward the end of pregnancy  Suckling Stimulates:  PRH release  Continued milk production

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Posterior Pituitary & 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

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oxytocin  A strong stimulant of uterine contraction  Regulated by a positive feedback mechanism:  Leads to increased uterine contractions, ending in birth  Triggers milk ejection (“letdown” reflex) in lactating women  Synthetic and natural oxytocic drugs are used to induce or hasten labor  Plays a role in:  Sexual arousal and satisfaction in males and non-lactating females

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Antidiuretic Hormone (ADH)  Helps avoiding dehydration or water overload by:  Preventing urine formation  Osmoreceptors:  Monitor solute concentrations of the blood  With high solutes:  ADH preserves water  With low solutes  ADH is not released, thus causing water loss  Alcohol:  Inhibits ADH release  Causes copious urine output

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Thyroid Gland  The largest endocrine gland  Located in the anterior neck  Consists of two lateral lobes connected by a median tissue mass called the isthmus  Composed of follicles lined with follicle cells  Follicle cells produce the glycoprotein thyroglobulin  Thyroglobulin + iodine form a colloid filling the follicle lumen  The colloid is the precursor of the thyroid hormone  Parafollicular (endocrine) cells, produce the hormone calcitonin

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Thyroid Gland Figure 16.8

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Thyroid hormone:  Major metabolic hormone  Consists of two related iodine-containing compounds  T 4 – thyroxine  T 3 – tri-iodothyronine Thyroid Hormone

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Effects of Thyroid Hormone  TH is concerned with:  Glucose oxidation  Increasing metabolic rate  Heat production  TH plays a role in:  Maturation and reproductive capabilities

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  A peptide hormone  Produced by the parafollicular, or C, cells  Lowers blood calcium levels in children  Antagonist to parathyroid hormone (PTH) Calcitonin

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Calcitonin targets the skeleton, where it:  Inhibits:  Osteoclast activity (and thus bone resorption)  The release of calcium from the bone matrix  Stimulates:  Calcium uptake  Calcium incorporation into the bone matrix  Regulated by:  A humoral (blood Ca 2+ level) negative feedback mechanism Calcitonin

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Parathyroid Glands  Tiny glands  Embedded in the posterior aspect of the thyroid  Contains two types of cells arranged in cords  The Chief (principal) cells secrete PTH  PTH (parathormone):  Regulates calcium balance in the blood

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Parathyroid Glands Figure 16.11

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  PTH release increases Ca 2+ in the blood as it:  Stimulates osteoclasts to digest bone matrix  Enhances the reabsorption of Ca 2+ & the Secretion of phosphate by the kidneys  Increases (indirectly) the absorption of Ca 2+ by intestinal mucosal (thru stimulating vit D activation by the kidneys)  Rising Ca 2+ in the blood inhibits PTH release Effects of Parathyroid Hormone

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Effects of Parathyroid Hormone Figure 16.12

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Break Slide  