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Transcript
PITUTARY GLAND page 1 AC Brown A6k INTRODUCTION A. Hormones/Endocrines Hormones are substances secreted into the blood by specialized glands (endocrine glands) or specialized cells in other tissue. Note: there are two types of glands: endocrine glands (described above) and exocrine glands. Exocrine gland secrete their products either onto the surface of the body (e.g. sweat glands) or into the alimentary tract (e.g. salivary glands of the oral cavity, acid-secreting glands of the stomach). Note: There are several types of cell-to-cell chemical communication: gap junctions, synaptic transmission, paracrine/autocrine, and endocrine Gap Junctions Synaptic Chemical transmission Site of action Direct from cellto-cell Adjacent cells Diffuse across synaptic cleft Postsynaptic cell Specificity due to Anatomic location Anatomic location & receptors Paracrine & Autocrine Diffusion through interstitial fluid Nearby cells (P) or same cell (A) Receptors B. Characteristics of Hormones 1. Hormones circulate in the blood either in free form (dissolved) or bound to carrier proteins 2. Hormones have their effect by binding to receptors on their target organs or tissues. Note: Trophic hormones are hormones whose target is another endocrine gland 3. Hormones are either peptides, proteins, steroids, or amines C. Major Endocrine Glands 1. 2. 3. 4. 5. 6. 7. Pituitary gland: multiple hormones Thyroid gland: thyroxine and triiodothyronine, calcitonin Parathyroid gland: parathyroid hormone Pancreas: insulin and glucagon Adrenal medulla: epinephrine and norepinephrine Adrenal cortex: aldosterone, cortisol Gonads (testis and ovary): androgens (testosterone), estrogens Endocrine Transport by the circulation General (target tissue) Receptors PITUTARY GLAND page 2 INTRODUCTION (continued) D. Other Endocrine Secreting Structures include 1. Kidney: Renin and Erythropoietin (control of red cell production) 2. Heart: Natriuretic Peptide 3. Pineal Gland: Melatonin (entrainment of circadian rhythms, sleep-wake cycle) PITUITARY(also called the "Hypophysis") A. Structure 1. Small gland at the base of the brain 2. Divided into the anterior pituitary (also called the adenohypophysis) and posterior pituitary (also called the neurohypophyssis); there also is an intermediate region (intermediate lobe) 3. Attached to the hypothalamus by the infundibulum or hypothalamo-hypophyseal stalk, which contains a. nerve axons of neurons originating in the hypothalamus and terminating in the posterior pituitary b. blood vessels originating in capillary beds in the hypothalamus and terminating in capillary beds in the anterior pituitary (portal system) AC Brown A6k PITUTARY GLAND page 3 AC Brown A6k PITUITARY(continued) B. Pituitary Hormones Hormone Anterior Pituitary Growth hormone (GH, GRH, somatotropin, STH) Adrenocorticotropic hormone (ACTH, corticotrophin) Thyroid-stimulating hormone (TSH, thyrotropin) Luteinizing hormone (LH) (gonadotropin) Follicle-stimulating hormone (FSH) (gonadotropin) Prolactin (PRL) Posterior Pituitary Antidiuretic hormone (ADH, Vasopressin) Oxytocin Actions Promotes body growth Promotes secretion of cortisol and related glucocoricoids from the adrenal cortex Promotes synthesis and release of thyroid hormones and growth of the thyroid Females: promotes ovulation and luteinization of ovarian follicles Males: promotes testosterone secretion Females: promotes follicle growth Males: promotes spermatogenesis Females: stimulates milk secretion Promotes water retention in the kidney Causes uterine contraction in pregnancy; promotes milk ejection C. Control of Anterior Pituitary Secretion 1. Hypothalamic releasing and inhibiting hormones a. synthesized in the hypothalamus b. released into capillaries in the hypothalamus c. transported by hypothalamo-hypophyseal blood vessels to the anterior pituitary capillary bed (portal system) d. diffuse from the anterior pituitary capillaries to the pituitary secretory cells e. either stimulate (releasing hormones) or inhibit secretion of specific anterior pituitary hormones 2. Feedback a. short loop feedback: feedback from the pituitary hormone to the hypothalamus b. long-loop feedback: feedback from target tissue secretions to the hypothalamus and/or the pituitary PITUTARY GLAND page 4 AC Brown A6k GROWTH HORMONE AND BONE GROWTH A. Bone Structure of Growing Bone 1. Diaphysis: bone shaft 2. Epiphysis: bone ends 3. Epiphyseal plate: plate of cartilage between the diaphysis and epiphysis B. Bone Growth Bone growth occurs as the epiphyseal plate lays down new bone at the end of the shaft. During development, the epiphyseal plate narrows and eventually disappears; this occurs in an orderly sequence at different times for different bones and permits determination of "bone age". When the plate disappears, bone elongation is no longer possible. C. Effect on Bone Development of Growth Hormone 1. Before epiphyseal closure: elongation of long bones either by the direct effect of GH on bone or by GH's stimulation of release of somatomedin medators from the liver 2. After epiphyseal closure: thickening of bone D. Pathophysiology 1. Inadequate GH secretion or defective GH receptors during bone development: Dwarfism 2. Excess GH during bone development: Giantism 3. Excess GH after epiphyseal closure: Acromegaly, enlargement of the hands and feet, growth of facial bones, protrusion of the jaw Acromegaly