2IntroductionThe endocrine system assists the nervous system with communication and control of the bodyCharacteristics of endocrine glandsThey are ductlessEndocrine glands secrete hormonesHormones are carried to distant target cells through the bloodstreamHormones only act on cells (target cells) that possess receptors sensitive to the hormone – highly specific action.
3Other signals Exocrine glands Have ducts Secrete chemicals directly onto a surfaceExamples: sweat glands, mucous cellsParacrine signalsChemicals that affect only nearby cellsExample: prostaglandins secreted with semen stimulate muscular contractions within female reproductive organsAutocrine signalsChemicals that affects only the cells that produced it.Example: T-cells secrete interleukins (IL), which stimulate the proliferation of the T-cells (monoclonal population)NeuroendocrineNervous tissue that secretes hormonesExample: hormone secretion from the hypothalamus.
4Endocrine vs. Nervous Tissue The endocrine and nervous systems communicate using chemical signalsNeurons release neurotransmitters into a synapse affecting postsynaptic cellsEndocrine glands release hormones into the bloodstream to specific target cell receptorsFigure 13.2 Chemical communication. (a) neurons release neurotransmitters onto synapses, affecting postsynaptic cells. (b) Glands release hormones into the bloodstream. Blood carries hormone molecules throughout the body, but only target cells respond.
5Endocrine vs. Nervous Tissue Nervous SystemEndocrine SystemCell…………………………………. Neuron Glandular EpitheliumSignal………………………………. neurotransmitter hormoneSpecificity of action…………. receptors on postsynaptic cell receptors on target tissuesSpeed of onset…………… <second seconds to hoursDuration of action……………. usually very brief may be brief or last for days
6Chemistry of Hormones Chemically, hormones are either: Steroid or steroid-like hormonesBiogenic AminesPeptide hormones
7Steroid Hormones Properties Steroid hormones are derived from cholesterolThey are composed of hydrophobic lipids (insoluble in water)IncludeEstrogenTestosteroneAndrogens (weak sex hormones)AldosteroneCorticoids (hormones secreted from the adrenal cortex)
8Biogenic Amines Properties Amines are synthesized from amino acids IncludeNorepinephrineEpinephrineMelatoninThyroid hormones (these are also hydrophobic, or water insoluble)
9Peptide Hormones Properties Composed of long chains of amino acids (polypeptides)IncludeHypothalamic hormonesPituitary hormonesPancreatic hormonesGastrointestinal hormones
10Water Solubility & Membrane Permeability Steroid + Thyroid HormonesAre hydrophobic – transported in the plasma attached to proteinsCell membrane permeable – due to their hydrophobic properties, these hormones readily cross the phospholipid bilayer of the cell membrane.All other HormonesAre hydrophilic– freely dissolved in plasmaCell membrane impermeable – these hormones do not cross the cell membrane, and must rely on 2nd messengers to relay a signal into target cells.2nd messenger – molecule that relays and amplifies a hormone signal into the cell.
11Actions of steroid hormones A steroid hormone crosses the cell membraneHormone combines with a protein receptor in the nucleusThe hormone-receptor complex activates transcription of a specific DNA regionThe mRNA leave the nucleus into the cytoplasmThe mRNA is translated into a protein.
12Actions of Non-steroid hormones A non-steroid hormone reaches the target cell,The hormone binds to a membrane receptorBinding to the receptor activates an enzyme in the cell membrane (adenlyate cyclase)Adenlyate cyclase converts ATP into cyclic adinosine monophosphate (cAMP)cAMP is a second messenger that promotes a series of reactions leading to the cellular changes associated with the hormone’s action.
13Control of Hormonal Secretions Hormone secretion is generally controlled in three ways:Negative FeedbackHormone DeactivationUp/Down Regulation
14Negative FeedbackThe endocrine gland, or system controlling it senses the concentration of the hormone that gland secretes.When the level of a specific hormone drops below needed levels, the endocrine gland is stimulated to secrete more hormone.As the hormone concentration reaches the needed level, stimulation of that endocrine gland is reduced, and production of that hormone is reduced.Figure Hormone secretion is under negative feedback.
15Negative Feedback Indicates negative feedback inhibition. Figure 13.8 Examples of endocrine system control. (a) one way the hypothalamus controls the anterior pituitary, which in turn controls other glands (b) the nervous system controls some glands directly, and (c) some glands respond directly to changes in the internal environment.Figure As a result of negative feedback, hormone concentration s remain relatively stable, although they may fluctuate slightly above and below average concentrations.
16Hormone DeactivationHalf-life: measures the time for half of the hormone molecules to be removed from plasmaTime Hormone Concentration0 minutes 100%10 minutes 50%20 minutes 25%30 minutes 12.5%Example of half-life: a hormone with a half-life of 10 minutes, decreases in concentration by half every 10 minutes.Hormones are continually secreted in the urine, and broken down by enzymes, primarily in the liver.
17Up/Down RegulationUp-regulation increases the number of receptors on the target cellUp regulation increases a cell’s sensitivity to a hormoneDown-regulation decreases the number of receptors on target cells.Down regulation decreases a cell’s sensitivity to a hormone
19Pituitary Gland (Hypophysis) Location: Lies at the base of the brain in the sella turcica, connected to hypothalamus by a pituitary stalk (infundibulum)2 Lobes:Anterior pituitary (adenohypophysis) Posterior pituitary(neurohypophysis)
20Control of Pituitary Gland Anterior Pituitary GlandPosterior Pituitary GlandReleasing hormones secreted from hypothalamus regulates the anterior lobe.Nerve impulses from hypothalamus regulate the posterior lobe.
21Anterior Pituitary Gland Hypophyseal Portal System –Releasing hormones secreted by the hypothalamus are conveyed to the anterior gland through Hypophyseal portal veins.Releasing hormones act on specific target cells within the anterior pituitary glandIn response, the pituitary gland secretes tropic hormones that travel throughout the body acting on distant target cells.Tropic hormone = hormones that have other endocrine glands as their target
22Example of hypophyseal pathway Releasing Hormone:Thyroid releasing Hormone (TRH)secreted from hypothalamusTropic Hormone:Thyroid Stimulating Hormone (TSH)is secreted from the anterior pituitaryTarget Cells:Thyroid Hormone (Thyroxine) is secreted from thyroid glands
23Anterior Pituitary Hormones Growth Hormone (somatotropin)Hypothalamic Control of GH:Growth Hormone Releasing Hormone (GHRH): promotes GH secretionsSomatostatin: inhibits GH secretionTarget Cells:Epithelial and Connective TissueAdipose TissueLiverActions of GH:Promotes cell growth and division, especially in skeletal muscles and chondrocytesPromotes breakdown and use of fat for energyLiver: promotes breakdown of glycogen for energy
24Growth Hormone Disorders GigantismResults from oversecretion of GH in childhoodUsually caused by a tumor of the pituitary glandHypopituitary DwarfismInsufficient GH during developmentGH therapy may treat condition if administered before the epiphyseal plates ossify
25Anterior Pituitary Hormones 2. Thyroid Stimulating Hormone (thyrotropin)Hypothalamic Control of TSH: Thyroid Releasing HormoneTarget Cells: Thyroid GlandActions: TSH promotes secretions of thyroid hormones(T3 & T4)
26Thyroid Hormones and Negative Feedback Under normal conditions, T3 and T4 inhibit further secretions of TRH and TSHIodine obtained from the diet is essential for thyroid hormone (T3 & T4) synthesis
27An Iodine deficiency prevents the formation of Thyroid Hormones. TRH & TSH continually stimulate the thyroid gland without inhibition.Goiter = enlarged thyroid gland
28Anterior Pituitary Hormones 3. Prolactin (mammotropin)Hypothalamic Control of PRL:Prolactin Releasing Factor: promotes secretion of prolactinProlacting Release Inhibiting Hormone: inhibits PRL secretionTarget Cells: Mammary GlandsActions: Prolactin promotes milk production
29Anterior Pituitary Hormones 3. Adrenocorticotropic Hormone (ACTH)Hypothalamic Control of ACTH:Corticotropin Releasing HormoneTarget Cells: Adrenal CortexActions: ACTH promotes secretions of hormones from the adrenal cortex (e.g. cortisol)
30Anterior Pituitary Hormones Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH)4 & 5 = gonadotropesHypothalamic Control:Gonadotropin Releasing Hormone (GRH)Target Cells: GonadsMale: testes Female: OvariesActions of gonadotropes:Follicle Stimulating Hormone:Female = promotes development of ovarian folliclesMale = promotes development of spermLuteinizing Hormone:Female = promotes the secretion of estrogens and progesteroneMale = promotes the production of testosterone
31Figure Hormones released from the hypothalamus, the corresponding hormones released from the anterior lobe of the pituitary gland, and their target organs.
32Posterior Pituitary Gland Structurally consists of neurosecretory cellsHormones are produced by the hypothalamus, then released from the posterior pituitary gland.
33Posterior Pituitary Hormones Antidiuretic Hormone (ADH)(also called vasopressin)Target Cells: Kidneys & Blood VesselsActions of ADH depend the receptors to which it bindsV1 receptorsLocated within blood vesselsADH, in high concentrations promotes vasoconstrictionMay prevent a drop in blood pressure with profuse bleedingV2 receptorsLocated within tubules of kidneysADH promotes water reabsorption at the kidneys, and thus decreases water loss.Alcohol inhibits ADH secretion, which explains its role as a diuretic.
34Posterior Pituitary Hormones 2. OxytocinActions of OxytocinFemales:stimulates smooth muscle contractions in the uterus during deliveryPromotes ejection of milk from mammary glandsMales: Function is unknown
38Thyroid GlandLocation: The thyroid gland is located just inferior to the larynx.Structure:It consists of two lateral lobes connected by an isthmusContains several follicles.
39Thyroid Gland Follicles Follicles consists of simple cuboidal epithelium & a colloid centerFollicular Cells: produce T3 & T4Coloid: contains Thyroglobulin, which is a storage form of thyroid hormones.Extrafollicular Cells: produce CalcitoninFollicular Cells take up thyroglobulin by endocytosis, then release the thyroid hormones into the bloodstream.
40Thyroid HormonesTarget Cells: T3 & T4 affect many cells throughout the body.Actions of T3 & T4: Raise Metabolic RateIncrease rate of carbohydrate catabolismEnhance protein synthesisPromotes the breakdown and use of lipidsT3 & T4 are major factors in determining the basal metabolic rate (BMR)BMR = calories required to sustain life
41Thyroid HormonesFollicular cells require iodine salts (iodide) to produce T3 and T4.T3 & T4 are hydrophobic molecules (insoluble in water)Nearly 75% of thyroid hormones are attached to thyroid binding globulins.Only the small amounts of the unbound hormones act on target cells.
42Transport of Thyroid Hormones T4 accounts for 95% of circulating Thyroid Hormone, But…T3 is physiologically more active.T3 is 5 times as potent as T4T3 also has a 50-fold higher “free” concentration in the plasma (see figure below).
43Thyroid Disorders Hypothyroidism – insufficient T3 & T4 During infancy – results in intellectual disability, stunted growth, abnormal bone formation (cretinism)During adulthood – low metabolic weight, sluggishness, poor appetite, and sensitivity to coldInfantile hypothyroidismHyperthyroidism – excess T3 & T4Results in high metabolic rate, hyperactivity, weight loss, sensitivity to heat, and exophthamia (protruding eyes)Grave’s DiseaseAutoimmune Disorder: Antibodies target the thyroid gland and mimic TSH. Thyroid antibodies overstimulate thyroid gland, resulting in hyperthyroidism.Grave’s disease may cause exophthalmia
44Calcitonin Extrafollicular cells (C-cells) secrete Calcitonin Calcitonin lowers blood calcium concentrations.Actions of CalcitoninStimulates Osteoblast activity – increases bone depositionInhibits osteoclast activity – reduces bone resorptionPromotes the excreting of calcium from the kidneysMajor Source of Control: elevated blood calcium ion concentration
45Parathyroid Glands Location: 4 small parathyroid glands are located on the posterior aspect of the thyroid glandHormone: PTH (parathyroid hormone)One parathyroid gland surrounded by thyroid follicles.
46Parathyroid Hormone (PTH) Parathyroid Hormone elevates blood calcium levels.Actions of PTH:Stimulates Osteoclast activity – increases bone resorptionInhibits osteoblast activity – reduces bone depositionPromotes calcium reabsorption from the kidneys.PTH also promotes the activation of Vitamin D, which enhances calcium absorption from the small intestine.Major Source of Control: Inadequate blood calcium ion concentration
47Figure Parathyroid Hormone (PTH) stimulates bone to release Calcium (Ca2+) and the kidneys to conserve calcium. It indirectly stimulates the intestine to absorb calcium. The resulting increase in blood calcium concentration inhibits secretion of PTH by negative feedback.
48Calcitonin and PTH have opposing effects on the levels of calcium ions in circulation. Both work together to maintain calcium homeostasis.
49Adrenal GlandsLocation: The adrenal glands are located on the superior aspect of the kidneys.Structure:Adrenal glands are pyramid shaped organs that consist of two partsAdrenal Medulla = secretions controlled by sympathetic nerve fibers Adrenal Cortex = Under hormonal control
50Hormones of the Adrenal Medulla Nerve fibers control secretions: Hormones of the adrenal medulla are under control by the sympathetic division (fight or flight) of the ANS.Hormones: Norepinephrine (noradrenalin) & Epinephrine (adrenalin)Both are classified as catecholamines.Actions: Effects are similar to sympathetic nerve fibers, but longer lasting.Increases heart rate and force of contractionIncreases blood pressureIncreases metabolic rateIncreases blood glucose levels (primarily epinephrine)Decreases digestion
51Beta BlockersEpinephrine & Norepinephrine exert their effects by binding to Beta (ß) adrenergic receptors in heart and walls of the blood vessels.Beta blockers bind to ß-receptors, thus obstructing the binding of catecholamines.Hence beta blockers reduce sympathetic influences of the heart and blood vessels.Therefore, beta blockers decrease heart rate, contractility, and reduce blood pressure.
52Hormones of the Adrenal Cortex 3 Layers of the adrenal cortex secrete over 30 types of steroid hormones.HormonesAldosterone – produced in zona glomerulosaCortisol – produced in zona fasciculataAndrogens – produced in zona reticularis
53Hormones of the Adrenal Cortex Aldosterone (mineralocorticoid)regulates Na+ and K+ concentrationsregulates blood pressureActionsAldosterone causes the kidneys to reabsorb Na+ and to excrete K+Aldosterone indirectly raises blood pressure:Increased Na+ reabsorption increases water reabsorption by osmosis.Controls of Aldosterone SecretionLow blood pressure stimulates aldosterone secretion(renin-angiotensin-aldosterone pathway)Elevated blood K+ concentration promotes aldosterone secretionLow Na+ has only a slight effect on aldosterone secretion.
54Renin-Angiontensin-Aldosterone System ACE Inhibitors block the actions of ACE, and thus lower blood pressure.
55Hormones of the Adrenal Cortex 2. Cortisol (glucocorticoid)Its primary effect is to build up and conserve blood glucose suppliesIts actions keep blood glucose levels constant between meals.ActionsPromotes gluconeogenesis in the livergluconeogenesis = glucose synthesis from non-carbohydratesPromotes the release and used of fatty acids from adipose for energy.Using fatty acids for energy allows glucose to be conserved.Inhibits protein synthesis: amino acids used in gluconeogenesis
56Hormones of the Adrenal Cortex 3. AndrogensSupplement the sex hormones secreted from the gonads.Androgens may be converted into testosterone and estrogens.
57The PancreasStructure & Location: The pancreas is located posterior to the stomach, attached to the duodenum.The pancreas has both digestive and endocrine functions.Pancreatic Islets (Islets of Langerhans) = endocrine cellsDigestion cells(we’ll discuss these with the digestive system)
58Cells of the Pancreatic Islets 3 distinct type of cells secrete 3 hormones:Alpha Cells – secrete glucagonBeta Cells – secrete insulinDelta Cells – secrete somatostatinPancreatic hormones regulate the storage, use, and release of fuels (glucose).
59Pancreatic Hormones 1. Glucagon Overall Effect: During fasting, when blood glucose levels drop, glucagon elevates blood glucose levelsActions of Glucagon:Stimulates glycogenolysis in the liver (breakdown of glycogen into glucose)Glucagon also promotes gluconeogenesisGlucagon also stimulates the breakdown of fats into glycerol and fatty acids.Glycerol is used in gluconeogenesisFatty Acids are metabolized for energy
60Liver Gluconeogenesis Glycogenolysis Amino acids glycerol glycogen glucoseglucoseGlucagon secretions elevates blood glucose concentrations.Gluconeogenesis converts noncarbohydrates, such as amino acids and glycerol, into glucose.Glycogenolysis breaks down large glycogen molecules into glucose.
61Pancreatic Hormones 2. Insulin 3. Somatostatin Overall Effect: Following a meal, when blood carbohydrate levels are high, insulin removes excess glucose from the blood.Actions of Insulin:Stimulates glycogenesis in the liver (formation of glycogen from glucose).It inhibits gluconeogenesis.Insulin promotes glucose uptake in adipose tissue, skeletal muscles, and cardiac muscle.3. SomatostatinOverall Effect: Helps regulate glucose metabolism by inhibiting the secretion of glucagon and insulin.
62Hormonal Control of Glucose Insulin and glucagon function together to stabilize blood glucose concentration. Negative feedback responding to blood glucose concentration controls the levels of both hormones.
63Diabetes Mellitus Type I Diabetes Mellitus (juvenile) Autoimmune disease – immune system destroys beta cells, resulting in the loss of insulin production.Without insulin, blood glucose cannot be taken up and used for energy.Glucose accumulates in the blood and urine = hyperglycemia.Type II Diabetes Mellitus (adult onset)Receptors on target cells wear down and become insensitive to insulin.Target cells resist glucose uptake, even in the presence of insulin.Insulin levels must be higher than normal just to maintain normal glucose concentrations.
64Other Endocrine Glands Pineal GlandLocated posterior to thalamus.The pineal gland secretes melatonin, which regulates circadian rhythms (sleep/wake cycle)Melatonin secretions are greatest in dark. Light inhibits secretions.Thymus GlandSecretes thymosinsPromotes development of certain lymphocytesImportant in role of immunity
65Other Endocrine Glands Reproductive OrgansOvaries produce estrogens and progesteroneTestes produce testosteronePlacenta produces estrogens, progesterone, and gonadotropinOther organs: digestive glands, heart, and kidneyEnd of Section 3, Chapter 13