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The Endocrine System. Endocrine System. Function: Regulates Coordinates Integrates Works cooperatively with the nervous system No ducts: Reactions not immediate -last longer than N.S. responses. Hormones. - PowerPoint PPT Presentation
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The Endocrine System
Endocrine System
Function:RegulatesCoordinatesIntegratesWorks cooperatively with the nervous systemNo ducts: Reactions not immediate -last longer than
N.S. responses
Hormones
Substances secreted by cells that regulate the activity of another tissue or organ
Most produced by glandsSome produced by clusters of cellsSome produced by neurons (neurohormones)
Hormones
Types of HormonesAmino Acid DerivativesSimple amines, thyroxin, peptides and proteins Examples:
Thyroid hormones, epinephrine and NE, insulin, glucagon
Most hormones this type
Hormones
Types of hormonesSteroid hormonesDerived from cholesterol Includes gonadal hormones (sex hormones) and
adrenal hormones (cortex only)Examples:
Progesterone, testosterone, cortisol, aldosterone
Hormones
Types of hormonesEicosanoidsAre paracrine hormones (local hormone = produced by
cells and released to effect cells in the same area)Examples:
Prostaglandins, leukotrines
Intracellular Receptors
Receptors
On the target cell -bind hormone Determine the effect the hormone will have on the
target cellBinding may cause:
Change in membrane permeability or potentialSynthesis of substances such as proteins or enzymesActivation or deactivation of enzymesSecretion of substancesStimulation of mitosis
Hormone Actions
Alter the activity of target cellsDecrease or increase cellular activity in target cellsOnly affect cells with receptors for that hormone
Hormone action: What happens when a hormone binds with a receptor?
1. Channels
2. 2nd messenger
3. Genes
HORMONE ACTION
Where are the receptors?1. On the cell membrane (AA hormones)
intracellular second messenger2. In the nucleus (steroid hormones & thyroxine)
direct gene activation
HORMONE ACTION- Second Messenger
Intracellular second messengerHormoneReceptorG proteinAdenylate cyclase systemCyclic AMPProtein kinases
Hormone Mechanisms
Second MessengersHormone binds to a
receptor on plasma membrane
Series of reactions initiated within the cell
Example: Cyclic AMP
Second MessengersCyclic AMP (cAMP)
Formed from ATP when a hormone binds to receptor
Hormone/receptor binding ‘G’ protein activates or inhibits
adenyl cyclase ATP converted to cAMP May activate protein kinases Initiates cascade of enzymes
within the cell Effect depends upon target cell
Second Messenger System
Second MessengersPIP Mechanism
PIP2 split into diacylglycerol and IP3
Both act as second messengers
IP3 triggers the release of calcium from the ER
Ca2+ acts as a third messenger
Diacylglycerol may activate protein kinases
Second messenger system
Direct Activation of GenesSteroid hormones can pass through the plasma membraneBind to receptors inside cellHormone/receptor binding stimulates genes on the DNA to begin
protein production
Gene Activation
Hormone Regulation
Nervous SystemUltimate control of hormone mechanisms belongs to the nervous systemMainly hypothalamus and sympathetic nervous system
Endocrine Gland Stimuli
Hormone Regulation
Stimulation or inhibition of endocrine glands comes from THREE sources:
Other hormones
Humoral stimuli
Neural stimuli
Hormone RegulationHormonal Regulation (by
other Hormones)Hormones may stimulate or
inhibit the release of other hormonesHypothalamus-
Regulates anterior pituitary gland
Pituitary hormones- Stimulate release of
hormones from other glands
Hormone Regulation
Regulation by Humoral Stimuli Changing ion or nutrient levels in
the blood may inhibit or stimulate the release of hormones
Example: Low blood calcium (Ca2+) PTH released from the parathyroid
glands Ca2+ released from bone Increase in blood Ca2+
Hormone Regulation
Regulation by Neural StimuliNerve impulses may stimulate
the release of hormonesExample:Sympathetic neurons
stimulate release of epinephrine and norepinephrine from the adrenal medulla
Feedback Mechanisms
Negative Feedback System Rising hormone or ion levels
inhibit further hormone release from the gland
Positive Feedback System Rising hormone levels cause
an increase in the hormone being secreted
Hypo or HypersecretionMay result in a disorderExamples:
Diabetes
Grave’s disease
Addison’s disease
Cushing’s disease
Major Endocrine GlandsPituitary Gland (Hypophysis)
Posterior lobe (Neurohypophysis)Releases 2 hormones
produced in the hypothalamus
anterior lobe
posterior lobe
Posterior Pituitary Gland
Posterior LobeDerived from hypothalamusPosterior lobe +
infundibulum = neurohypophysis
Neuron axons to pituitary = hypothalamic hypophyseal tract
hypothalamic hypophyseal tract
Posterior Pituitary Gland
Two hormones released hereBoth produced in nuclei of the
hypothalamusBoth secreted into capillaries in
posterior pituitary for distribution to the body
Oxytocin & ADH
Hypothalamus
SON/PVN – produce ADH & oxytocin
Released from posterior pituitary
Pituitary
Posterior lobe:• Pituicytes
ADH
Oxytocin
Posterior Pituitary Gland Supraoptic Nucleus
ADH (Vasopressin) Stimulates increased
reabsorption of water by kidney tubules
Decreases urine volume Increases blood volume React to Osmoreceptors
ADH & oxytocin
Paraventricular Nucleus Oxytocin Uterine contractions Milk release (Contraction
of mammary gland smooth muscle
Supraoptic nuclei
Paraventricular nuclei
Ventral Hypothalamus
Releasing and inhibiting hormonesThru portal systemTarget = anterior pituitary
Anterior Pituitary Gland
Hypophyseal Portal System
primary capillary plexus
neurons in ventral hypothalamus
hypophyseal portal veins
secondary capillary plexus
secretory cells
Anterior Pituitary Gland
Anterior Lobe = AdenohypophysisDerived from roof of mouthProduces hormonesRelease of hormones is controlled
by hormones from neurons of the ventral hypothalamus = releasing or inhibiting hormones
anterior lobe
Ventral hypothalamu
s
Pituitary (Hypophysis) Location and relationships Densely packed cells (anterior)
Anterior lobe: TSH
ACTH
FSH
LH GnRH
Growth h.
Prolactin
MSH
Anterior Pituitary Gland
The following four anterior pituitary hormones are tropic hormones
Tropic Hormones:
TSH
ACTH
FSH
LH
Tropic Hormones
Hormones SecretedThyroid Stimulating Hormone (TSH)Stimulates production and release of thyroid hormones by
the thyroid gland
Release stimulated by TRH Inhibited by rising blood levels of thyroid hormone
Tropic Hormones
Hormones SecretedAdrenocorticotropic Hormone (ACTH or Corticotropin)Stimulates secretion of corticosteroid hormones (esp.
cortisol) from the adrenal cortexRelease stimulated by CRH, fever, hypoglycemia and stress Inhibited by rising cortisol levels
Tropic Hormones
Hormones SecretedFollicle Stimulating Hormone (FSH)Not present until pubertyStimulates gamete production and maturation in both males
and femalesRelease stimulated by GnRH Inhibited by rising gonadal hormones
Anterior Pituitary Gland
Hormones SecretedLuteinizing Hormone (LH)Promotes production of gonadal hormonesControlled by the same hormones as FSHTriggers ovulation in females
Non-tropic HormonesHormones Secreted
Growth Hormone (GH) or SomatotropinProduced in response to growth hormone releasing hormone
(GHRH from hypothalamus)Also secreted in response to hypoglycemia or decreased
blood GH or Increased amino acid levels Inhibited by GHIH (somatostatin from hypothalamus)Stimulates cell growth and division in most cells (esp. bone
and muscle)Mobilizes fat to conserve glucoseHyposecretion results in pituitary dwarfismHypersecretion results in gigantism or acromegaly
Non-tropic Hormones
Hormones Secreted Prolactin (PRL)
Release stimulated by PRH
Inhibited by PIH (dopamine)
Both are influenced by estrogen
Stimulates milk production by breasts
Thyroid Gland - Anatomy
The Thyroid Gland
Two lateral lobes Composed of follicles Cuboidal follicle cells produce thyroglobulin
Thyroglobulin stored in lumen of follicle Iodine attaches Molecule is split into T3 and T4 (mostly T4) Hormones enter circulation, more T3 formed
thyroid gland
Thyroid Gland - histology Follicular cells
follicles colloidthyroglobulin
T3 – triiodothyronine
T4 – thyroxine
Parafollicular cellsCalcitonin
Thyroid Gland - hormones Follicular cells
thyroglobulinT3 – triiodothyronineT4 – thyroxine
• + BMR (glucose oxidation)• maintains bp• tissue growth & development
Parafollicular cellsCalcitonin
• decreases blood calcium• + osteoblasts
Thyroid Gland – T3/T4 production
Follicles – colloid, follicular cells Cells make thyroglobulin Thyroglobulin moves into follicle Iodine pumped into follicle Iodine used to make subunits
• 1 OR 2 IODINE
Subunits moved into follicle cells Subunits join to make T3 or T4 T3/T4 released from follicle cells
Thyroid Hormone Production
Thyroid HormoneT4 converted to T3 once in tissuesSecreted in response to TSH Inhibited by rising blood thyroid hormone levelsEffects:
Increases metabolic rate Increases heat productionPromotes protein synthesis and enhances the affect of GHPromotes uptake of glucose by cellsPromotes lipid metabolismSpeeds up actions of nervous system
Thyroid HormoneHyposecretion
Can result in cretinism in children
Myxedema in adults
HypersecretionGrave’s Disease
Thyroglobulin
Thyroid Gland - pathology
Myxedema – adult hypothyroid
Goiter – enlarged thyroid due to lack of iodine
Cretinism – infantile hypothyroid
Grave’s disease – hyperthyroid exophthalmos
Calcitonin
Secreted by parafollicular or C cells by the thyroid
Released in response high blood calcium
Stimulates uptake of calcium by bone
parafollicular cells
Parathyroid Glands4 to 8 on posterior thyroid
glandSecrete Parathyroid Hormone
(PTH)Secreted in response to low
blood calciumStimulates bone resorptionReleased calcium enters blood Increases absorption of calcium
by intestines and reabsorption by kidneys
parathyroid glands
Parathyroid Hormone
Hypersecretion Depletes calcium from bones Depresses nervous system
activity Skeletal muscle weakness
Hyposecretion Over excitability of neurons Muscle spasms Convulsions
Chief cells
Adrenal (Suprarenal) Glands
Two glands--one on top of each kidney
Outer cortex, inner medullaCortex
Produces over 2 dozen corticosteroids from cholesterol
Increased hormone output in response to ACTH or stress
adrenal gland
cortex
medulla
Adrenal Cortex
Three Regions:Zona GlomerulosaOuter regionProduction of
mineralocorticoids (aldosterone)
Regulation of electrolyte & fluid balance
Aldosterone
95% of mineralocorticoidsSodium reabsorption (and water) by kidney
tubulesIncreases blood volume and pressureStimulated by angiotensin
Renin secreted by kidneysActivates angiotensin hormones in bloodStimulates release of aldosterone
Inhibited by Atrial Natriuretic Factor (ANF)Secreted by heart cells when B.P. risesBlocks secretion of renin and aldosterone
Adrenal Cortex
Zona Fasciculata Middle region Secretes glucocorticoids
(cortisol)
Cortisol Released in response to ACTH Inhibited by increased cortisol Promotes gluconeogenesis
(production of glucose from non-carbohydrate sources)
Causes a rise in B.P. Anti-inflammatory if given in
higher doses
CortisolHypersecretion
Cushing’s SyndromeDepressed bone and cartilage formationDepressed inflammatory response and immune
systemEdema, hypertension, loss of muscle and bone,
‘moon face’Hyposecretion
Addison’s diseaseDrop in blood plasma volumeInability to cope with stress or regulate blood sugar
levelsIncreased skin pigmentation
Adrenal Cortex
Zona ReticularisInner regionProduces
glucocorticoids & gonadocorticoids (androgens and estrogen)
ADRENAL MEDULLA
Chromaffin CellsSecrete epinephrine and
norepinephrine (Catecholamines)
Release stimulated by sympathetic neurons
Prolongs the fight or flight response
The PancreasMixed endocrine and
exocrine functionAcinar Cells
Secrete digestive enzymes into small intestine
Islets of LangerhansContain alpha cells Glucagon
Contain beta cells Insulin
Pancreas
endocrine and exocrine Islets of LangerhansCell Types:
Alpha Glucagon Increases blood sugar
Beta Insulin Decreases blood sugar
Delta Somatostatin Inhibit glucagon/insulin releaseInhibit digestive tract activity
PP Pancreatic Polypeptide
Regulates exocrine functionInhibits bile release
InsulinStimulated by high blood
sugar Inhibited by decrease in
blood sugar or somatostatin (GHIH)
Lowers blood sugarEnhances glucose transport
into cells (esp. muscle)Stimulates glycogen
formation Promotes conversion of
glucose to fatStimulates protein
synthesis in muscle Islet of Langerhans
Glucagon Released in response to low
blood sugar Mobilizes fatty acids, glucose
and amino acids from storage Promotes release of fat from
adipose tissue Promotes:
Gluconeogenesis (production of glucose from non-carb. sources)
Glycogenolysis (breakdown of glycogen into glucose)
Raises blood sugar levels
Diabetes
Diabetes InsipidusCaused by ADH deficiency Large quantities of urineDehydration No blood sugar accumulation
Diabetes MellitusResults from Hyposecretion of insulin or hypoactivity of insulin
DiabetesDiabetes Mellitus
Two types:Type 1 (Juvenile Onset)
Usually before age 20 Decreased amount of beta cells in pancreas Possibly autoimmune cause Long term vascular and neural problems
Type 2 (Adult Onset) Insulin is produced but receptors are resistant to it Family tendencies Influenced by weight, diet and exercise
Diabetes
Lack of insulin or response to itInability of glucose to enter body cellsHigh blood sugarFat stores are mobilized for fuelBlood sugar and fatty acid levels rise higherKetone bodies build up from breakdown of fatty acidsKetosis or acidosis results (lowered blood pH)Crisis, coma or death
DiabetesSymptoms
PolyuriaLarge urine output
PolydipsiaExcessive thirst
PolyphagiaExcessive hunger caused by the inability to use glucose as
an energy source
The Pineal Gland
Secretes melatoninMay affect responses to
light cyclesMay inhibit gonad activity
in humans until puberty
“brain sand”
The Thymus GlandShrinks with ageProduces thymopoietin and
thymosinAids in development of the
immune response (development of T- lymphocytes)
THE GONADSProduce gametes and reproductive hormones
Testosterone in malesMaturation of reproductive organsSecondary sex characteristicsSex drive
Estrogens and progesterone in femalesEstrogens cause maturation of reproductive organs and
appearance of secondary sex characteristicsWith progesterone, promote breast development and cyclic
changes in uterine lining