A&P II Chapter 18 Endocrine System PDF

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Biol 2402 with James Armacost...

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Chapter 18, Endocrine system I.

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Endocrine System  coordinates functions of all body systems  works in conjunction with nervous system  responds to environmental stimuli Hormones  Chemical systems of endocrine system  Regulate target cells at another point in body  Transported through bloodstream

Nervous System Releases mediators called neurotransmitters Mediators act close to site of release Actions are rapid and brief

Endocrine System Releases mediators called hormones Mediators usually act far from release Actions are slow and lengthy

Exocrine Glands Secrete products into ducts that carry them into body cavity, lumen of organ, or to body surface

Endocrine Glands Secrete products (Hormones) into interstitial fluid Products transported by circulatory system

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Hormone Activity  Target cell- site of hormone action  Act on target cell by binding to receptor molecules on or in the target cell Local hormones  Paracrines- act on nearby target cells  Autocrines- act on the same cell that secreted them Circulating Hormones  Act on distant target cells  Transported in blood  Inactivated by liver and excreted by kidneys Classes of Hormones A. Lipid Soluble  Steroid hormones & Thyroid hormones  Bind to transport proteins  Nitric oxide (NO)  Passes easiest through a CELL MEMBRANE B. Water Soluble  Amine hormones  Peptide and protein hormones  Eicosanoid hormones  Passes easiest through BLOOD

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Mechanic process of Hormone Action (Lipid-soluble) *Acts on the inside of target cell 1. Hormone diffuses through phospholipid bilayer of cell membrane of target cell 2. Hormone binds to receptor molecule in cytosol or nucleus and gene expression is altered 3. New mRNA is formed during transcription and new proteins are synthesized 4. New protein alters cell activity Mechanic process of Hormone Action (Water-soluble) 1. Hormone (first messenger) binds to receptor molecule on outer surface of plasma membrane of target cell 2. ATP is converted to cAMP (Cyclic AMP) on inner surface of plasma membrane 3. cAMP (second messenger) activates one or more protein kinases in cytosol or on inner surface of plasma membrane 4. Activated protein kinases then actives/inactivates other cellular proteins 5. Cellular proteins alter cell activity 6. cAMP is inactivated Sensitivity of target cell depends on: A. Hormone concentration B. Number of receptor molecules on surface of target cell  controlled by target cell  Down-regulation (decrease in receptors; decrease in sensitivity)  Up-Regulation (increase in receptors; increase in sensitivity) C. Influences of other hormones  Permissive Effect o Action of one hormone requires simultaneous or recent presence of another to produce its effect  Synergistic Effect o Action of one hormone is increased by the presence of another hormone o Additive effects greater than the sum of individual effects  Antagonistic Effect o Action of one hormone is inhibited by the presence of another o

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Each moderates the effect of the other

Hypothalamus  Region of brain below thalamus  Receives input from nervous system and internal organs  Secretes 9 hormones  Physically linked nervous and endocrine systems

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Endocrine Glands A. Pituitary Gland  Attached to and controlled by hypothalamus  Controls other endocrine glands; contains two lobes  Anterior Lobe: synthesizes and secretes seven hormones 1. Human Growth hormone (hGH)  Targets liver, muscle, bone  Causes target cells to secrete insulin-like growth factors (IGFs) o Stimulate cell growth o Stimulates liver cells to release glucose into blood 2. Thyroid-stimulating hormone (TSH) 3. Follicle-stimulating hormone (FSH) 4. Luteinizing hormone (LH) 5. Prolactin (PRL) 6. Adrenocorticotropic (ACTH) 7. Melanocyte-stimulating (MSH)  Posterior Lobe: stores and secretes two hormones; NO synthesis of hormones 1. Oxytocin (OT): regulates childbirth and lactation 2. Antidiuretic (ADH): decrease urine production (inhibited by alcohol) o Targets kidneys (retain more water), sweat glands (decrease activity), smooth muscle in blood vessels (constrict to increase blood pressure) o Release of ADH: 1. High blood osmotic pressure (dehydration) stimulates osmoreceptors in hypothalamus 2. Osmoreceptors cause hypothalamus to secrete ADH 3. Posterior pituitary releases ADH into bloodstream B. Thyroid Gland  Located in throat below larynx  Three hormones 1. Tetraiodidothyronine T4 2. Triiodothronine T3 o T3 & T4 (known as Thyroid hormones) increase basal metabolic rate (BMR) with the help of hypothalamus and anterior pituitary gland o Increase use of ATP, generates heat for homeostasis o Increase protein synthesis o Increase body growth 3. Calcitonin o inhibits osteoclast activity -> calcium decreases

Chapter 18, Endocrine system C. Parathyroid Glands (four)  Located in the posterior surface of the lateral lobes of thyroid glands (back of neck)  Secretes Parathyroid Hormones (PTH) o Primary function of PTH is to regulate calcium in blood, along with calcitonin o Target cells are osteoclasts in skeletal system o Osteoclasts release calcium into blood o PTH promotes osteoclast activity -> calcium in blood increases o Calcitonin inhibits osteoclast activity -> calcium in blood decreases D. Adrenal Glands (two)  Located superior to each kidney  Consist of two regions: a. Adrenal Cortex (Outer) o Secretes three groups of hormones 1.Mineralocorticoids  Primary: Aldosterone  Regulates levels of Na and K in blood  Regulates excretion of H+ in urine 2.Glucocorticoids  Cortisol  Cortisone  Corticosterone  Maintain metabolic rate and resistance to stress 3.Androgens b. Adrenal Medulla (Inner) o A modified sympathetic ganglion of the autonomic nervous system o Physical linkage between nervous and endocrine system o Secretes two hormones 1. Epinephrine (adrenalin) 2. Norepinephrine o Both stimulate fight-or-flight response o Increases heart rate, stroke volume, blood levels of glucose E. Pineal Gland  Within the epithalamus of brain  Secretes: Melatonin o Promotes sleep and regulates biological clock

Chapter 18, Endocrine system

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Other Tissues with endocrine functions A. Pancreatic islets  In the curve of duodenum (first part of small intestine)  Endocrine cells secrete four hormones, including: o Glucagon

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o Released when blood sugar is level to raise it o Target cells: hepatocytes in liver (convert glycogen -> glucose) Insulin o Released to lower blood sugar o Has various target cells

B. Gonads  Secretes several hormones o Estrogens o Progesterone o Both effect  Development of female secondary sex characteristics (breasts)  Regulation of menstrual cycle  Maintenance of pregnancy o Testosterone  Facial hair and sperm production C. Thymus  Located between the lungs  Secretes four hormones, which promote maturation of T cells (lymphocytes involved in immune response)...