Endocrine system

ilm1993's version from 2017-07-27 12:22


Question Answer
Endocrine systemInfluences metabolic activity by means of hormones
Endocrine glandspituitary, thyroid, parathyroid, adrenal, pineal, and thymus
The pancreas and gonads produce bothhormones and exocrine products
The hypothalamus has bothneural functions and releases hormones
Other tissues and organs that produce hormones adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart

Autocrines and Paracrines

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Autocrineschemicals 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 sincehormones are long-distance chemical signals


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Eicosanoidsbiologically active lipids with local hormone–like activity
Hormoneschemical substances secreted by cells into the extracellular fluids
Amino acid basedAmines, thyroxine, peptide, and protein hormones
Steroidsgonadal and adrenocortical hormones

Hormone Action- how hormones get into the cell

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Second messengers Regulatory G proteins; Amino acid–based hormones
Direct gene activationSteroid hormones

Amino Acid-Based Hormone Action: cAMP Second Messenger

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1Hormone (first messenger) binds to its receptor, which then binds to a G protein
2The G protein is then activated as it binds GTP, displacing GDP
3 Activated G protein activates the effector enzyme adenylate cyclase
4 Adenylate cyclase generates cAMP (second messenger) from ATP
5 cAMP activates protein kinases, which then cause cellular effects
DAG activates protein kinases; IP3 triggers release ofCa2+ stores
Ca2+ (second messenger)alters cellular responses

Steroid Hormones

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This interaction prompts DNA transcription to producemRNA
The mRNA is translated intoproteins, which bring about a cellular effect

Target Cell Specificity

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Hormones circulate to all tissues but only activate cells referred to astarget cells
Target cells must havespecific receptors to which the hormone binds
These receptors may be intracellular or located on the plasma membrane
Target cell activation depends on three factorsBlood levels of the hormone, Relative number of receptors on the target cell, The affinity of those receptors for the hormone
Up-regulationtarget cells form more receptors in response to the hormone
Down-regulationtarget cells lose receptors in response to the hormone

Hormone Concentrations in the Blood

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Concentrations of circulating hormone reflect Rate of release, Speed of inactivation and removal from the body
Hormones are removed from the blood byDegrading enzymes, The kidneys, Liver enzyme systems

Types of hormone interaction

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Permissivenessone hormone cannot exert its effects without another hormone being present
Synergismmore than one hormone produces the same effects on a target cell
Antagonismone or more hormones opposes the action of another hormone

Humoral Stimuli

Question Answer Column 3
Humoral stimulisecretion of hormones in direct response to changing blood levels of ions and nutrients; Exampleconcentration of calcium ions in the blood
Neural stimulinerve fibers stimulate hormone release. Example: sympathetic response to adrenal medulla
Hormonal stimulirelease of hormones in response to hormones produced by other endocrine organs. Example: The hypothalamis stimulate the anterior pituitary in turn, pituitary hormones stimulate targets to secrete still more hormones


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Example of overrideglucose use under stress
The nervous systemcan override normal endocrine controls


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Pituitary glandtwo-lobed organ that secretes nine major hormones
Neurohypophysisposterior lobe (neural tissue) and the infundibulum (Receives, stores, and releases hormones from the hypothalamus)
Adenohypophysisanterior lobe, made up of glandular tissue (Synthesizes and secretes a number of hormones)

Pituitary-Hypothalamic Relationships: posterior lobe

Question Answer
The posterior lobe is a downgrowth ofhypothalamic neural tissue
Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)
Nuclei of the hypothalamus synthesizeoxytocin and antidiuretic hormone (ADH)
These hormones are transported to theposterior pituitary

Pituitary-Hypothalamic Relationships: Anterior Lobe

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The anterior lobe of the pituitary is an outpocketing of the oral mucosa
There is no direct neural contact with thehypothalamus
There is a vascular connection, the hypophyseal portal system, consisting ofThe primary capillary plexus, The hypophyseal portal veins, The secondary capillary plexus

Adenophypophyseal Hormones

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The six hormones of the adenohypophysisGH, TSH, ACTH, FSH, LH, and PRL
What do the adenohypophysis hormones do?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 (melanocyte-stimulating hormone)
The hypothalamus sends a chemical stimulus to theanterior pituitary
The tropic hormones that are released areThyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH), Follicle-stimulating hormone (FSH) , Luteinizing hormone (LH)


Question Answer
Growth hormonemost cells, but target bone and skeletal muscle, promote protein synthesis and encourage the use of fats for fuel
GH stimulatesliver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors
Rising blood levels of thyroid hormones act on the pituitary and hypothalamus toblock the release of TSH
TSHStimulates the normal development and secretory activity of the thyroid
Adrenocorticotropic Hormone (Corticotropin)Stimulates the adrenal cortex to release corticosteroids
Gonadotropinsfollicle-stimulating hormone (FSH) and luteinizing hormone (LH)
FSH stimulates gamete (egg or sperm) production
Gonadotropin Triggered bythe hypothalamic gonadotropin-releasing hormone (GnRH) during and after puberty
LH works with FSH tocause maturation of the ovarian follicle
LH works alone totrigger ovulation (expulsion of the egg from the follicle)
ProlactinIn females, stimulates milk production by the breasts

The Posterior Pituitary and Hypothalamic Hormones

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Posterior pituitarymade of axons of hypothalamic neurons, stores antidiuretic hormone (ADH) and oxytocin
ADH and oxytocin are synthesized inthe hypothalamus
ADH influenceswater balance
Oxytocin stimulatessmooth muscle contraction in breasts and uterus; Regulated by a positive feedback mechanism
Both use PIP-calcium second-messenger mechanism

Thyroid hormone Hormones (cont)

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T4thyroxine; has two tyrosine molecules plus four bound iodine atoms
T3 triiodothyronine; has two tyrosines with three bound iodine atoms
TH plays a role inMaintaining blood pressure, Regulating tissue growth, Developing skeletal and nervous systems, Maturation and reproductive capabilities


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CalcitoninLowers blood calcium levels in children
Antagonist toparathyroid hormone (PTH)
Regulated bynegative feedback mechanism
Chief (principal) cellssecrete PTH
PTH (parathormone) regulatescalcium balance in the blood
PTH release increases Ca2+ in the blood as itEnhances the reabsorption of Ca2+ and the secretion of phosphate by the kidneys

Adrenal Glands

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Adrenal glandspaired, pyramid-shaped organs atop the kidneys
Aldosteronemost important mineralocorticoid ; Maintains Na+ balance by reducing excretion of sodium from the body
Renin-angiotensin mechanism kidneys release renin, which is converted into angiotensin II that in turn stimulates aldosterone release
ACTHcauses small increases of aldosterone during stress
Atrial natriuretic peptide (ANP)inhibits activity of the zona glomerulosa


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Cortisol provokesGluconeogenesis (formation of glucose from noncarbohydrates); Rises in blood glucose, fatty acids, and amino acids
Excessive levels of glucocorticoidsDepress cartilage and bone formation; Inhibit inflammation
Most gonadocorticoids secreted are _____, and the most important one is _____Androgen, testosterone
Androgens can be converted into estrogens after menopause

Adrenal medulla

Question Answer
Made up of chromaffin cells that secreteepinephrine and norepinephrine
Secretion of these hormones causesBlood glucose levels to rise, Blood vessels to constrict
Epinephrine is the more potent stimulator of theheart and metabolic activities
Norepinephrine is more influential onperipheral vasoconstriction and blood pressure


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Glucagonpromotes Glycogenolysis (the breakdown of glycogen to glucose) and
Gluconeogenesissynthesis of glucose from lactic acid and noncarbohydrates
InsulinLowers blood glucose levels
The three cardinal signs of Diabetes arehuge urine output, excessive thirst, excessive hunger and food consumption


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Paired ovaries in the abdominopelvic cavity produceestrogens and progesterone
TestosteroneInitiates maturation of male reproductive organs

Hormones Cont.

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Thymopoietins and thymosinshormones that are essential for the development of the T lymphocytes (T cells) of the immune system
Heartproduces atrial natriuretic peptide (ANP), which reduces blood pressure, blood volume, and blood sodium concentration
Gastrointestinal tractenteroendocrine cells release local-acting digestive hormones
Placentareleases hormones that influence the course of pregnancy
Kidneyssecrete erythropoietin, which signals the production of red blood cells
Skinproduces cholecalciferol, the precursor of vitamin D
Adipose tissuereleases leptin, which is involved in the sensation of satiety, and stimulates increased energy expenditure