Download ENDOCRINE: Endocrine glands Ductless Act with nervous system to

ENDOCRINE:
 Endocrine glands
o Ductless
o Act with nervous system to coordinate and integrate activity of body cells
o Influence metabolic activities by means of hormones transported in blood
o Responses occur more slowly but they last longer than CNS/PNS
 Depends on size: bigger ones last longer because take longer to break
down
 Hormones: long-distance chemical signals that travel in blood or lymph
o Amino acid-based hormones: amines, thyroxine, peptides, and proteins
 Interact with receptor right on cell membrane
o Steroids: synthesized from cholesterol
 Gonadal and adrenocortical hormones
o Circulate in the blood either free or bound
 Steroid and thyroid hormones are attached to plasma proteins (ex:
albumin)
 All other circulate without carriers
 Concentration of a circulating hormone reflects how fast they are
made, how fast they are released, how fast they are inactivated and
removed from body
o Water-soluble hormones: all amino acid-based except thyroid
 Act on receptors in the plasma membrane, usually coupled via G
proteins to secondary messengers
o Lipid-soluble hormones: steroid and thyroid hormones
 Act on receptors in the cell, which directly activate genes
o Blood levels of hormones are controlled by negative feedback systems
 Humoral Stimuli
o Some glands secrete their hormones in direct response to changing blood
levels of certain critical ions and nutrients
o Ex: Ca2+ in the blood
o Falling blood Ca2+ levels parathyroid glands release parathyroid hormone
(PTH)PTH increasesstimulates osteoclasts to degrade bone matrix and
release Ca2+ in the bloodBALANCE
o Rising blood Ca2+ levelsparafollicular cells of thyroid release
calcitoninosteoblasts deposit calcium slatsblood Ca2+ levels fall
 Neural stimuli
o Nerve fibers stimulate hormone release
o Under stress, sympathetic nervous system stimulates adrenal medulla to
release epinephrine and norepinephrine
 Hormonal stimuli
o Many endocrine glands release their hormones in response to hormones
produced by other endocrine glands
o Hypothalamic hormones stimulate the release of most anterior pituitary
hormones
o Anterior pituitary hormones stimulate targets to secrete more hormones
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o Hypothalamic-pituitary feedback loop: hormones from final target organs
inhibit the release of anterior pituitary hormones
Pituitary Gland
o Two lobes: posterior (pituicytes and nerve fibers), and anterior (glandular
tissues)
Posterior
o Is just a storage organ, not a true producing hormone gland, receives
hormones from hypothalamus
o Neural connection to hypothalamus
o Neural hormones include oxytocin and ADH (antidiuretic)
o Transported to posterior, stored till neural stimulus
o Portal vein carries releasing and inhibiting hormones made in hypothalamus
to the anterior pituitary to regulate hormone secretion from the AP
o 1. Hypothalamic neurons synthesize oxytocin and ADH; 2. They are
transported along hypothalamic-hypopheseal tract to posterior pituitary; 3.
Are stored in axon terminals in posterior pituitary; 4. Are released into blood
when hypothalamic neurons fire
Anterior
o 1. Stimulated hypothalamic neurons secrete releasing and inhibiting
hormones; 2. These hormones travel through the portal veins to the AP
where they stimulate or inhibit release of hormones from AP; 3. Anterior
pituitary hormones secreted into secondary capillary plexus
o Secretes 6 hormones
o All are proteins
 TSH (thyroid), ACTH (adrenal), FSH, and LH (testis/ovary)
 Regulate secretory action of other endocrine glands(above)
Growth Hormone (GH)
o Hypersecretion: in children results in gigantism, adults in acromegaly (makes
cells in face grow)
o Hyposecretion: in children results in pituitary dwarfism
o Produced by somatotrophs
o Stimulates most cells, especially bone and skeletal muscle
o Promotes protein synthesis and encourages use of fats for fuel
o Most effects are mediated indirectly by insulin-like growth factors (IGFs)
o GH release regulated by:
 Growth hormone-releasing hormone (GHRH)
 Growth hormone-inhibiting hormone (GHIH)
o Direct action of GH
 Stimulates liver, skeletal muscle, bone, and cartilage to produce IGFs
 Mobilizes fat, elevates blood glucose by decreasing glucose uptake and
encouraging glycogen breakdown (glyconeolysis) in liver
Gonadotropins
o Follicle-stimulating hormone (FSH)
 Stimulates gamete (egg or sperm) production
o Lutenizing hormone (LH)
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 Promotes production of gonadal hormones
o Secreted by gonadotrophs of AP
o *Puberty first, hormones second
o Triggered by gonadotrophin-releasing hormone (GnRH) made in
hypothalamus during and after puberty
o Suppressed by gonadal hormones (feedback)
Prolactin
o Secreted by lactotrophs
o Stimulates milk production right before lactation
o Primarily controlled by prolactin-inhibiting hormone (PIH, dopamine)
o Suckling stimulates PRH release and promotes continued milk production
o Rise and fall with estrogen levels
Oxytocin
o Stimulates uterine contractions during childbirth
o Triggers milk ejection (letdown reflex) in women producing milk
o Stretching of the uterus sends signals to hypothalamus, which produces
oxytocin in response
o Positive feedback mechanism
Thyroid-stimulating hormone (thyrotropin)/(TSH)
o Produced by thyrotrophs
o Stimulates normal development and secretory activity of the thyroid
o Stimulated by thyrotropin-releasing hormone (TRH), made in hypothalamus
o Inhibited by rising blood levels of thyroid hormones that act on pituitary and
hypothalamus (negative feedback)
Thyroid Gland
o Two lateral lobes
o Composed of follicles that produce the glycoprotein thyroglobulin
o Colloid (thyroglobulin + iodine) fills the lumen of the follicles
o Parafollicular cells produce calcitonin
o Very vascular
Hypothalamus(TRH)Anterior pituitaryTSHThyroid glandthyroid
hormones (can feeback and inhibit above)target cells
Thyroid hormone (TH)
o Major metabolic hormone
o T4 (thyroxine): has two tyrosine molecules + 4 bound iodine atoms
o T3 (triiodothyronine): has 2 tyrosine + 3 bound iodine atoms
 1. Thryoglobulin synthesized and discharged into follicle lumen
(synthesize in ribosomes of rough ER, transported to Golgi, packaged
in vesicles to go to follicle lumen)
 2. Iodide is actively transported in from the blood
 3. Iodide oxidized to iodine
 4. Iodine is attached to tyrosine in colloid, forming DIT/MIT
 5. Iodinated tyrosines are linked together to form T3/T4
 6. Thyroglobulin colloid is endocytosed and combined with a
lysosome
7. Lysosomal enzymes cleave T4/T3 from thyroglobulin and
hormones diffuse into bloodstream
o T3 is ten times more active than T4
o They both bind to target receptors
o Peripheral tissues convert T4 to T3 if needed
o Increases metabolic rate and heat production/energy release
o Plays a role in: maintenance of blood pressure, regulation of tissue growth,
development of skeletal/nervous system, repro capabilities
o Rising levels of TH provide negative feedback inhibition on release of TSH
o Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the
negative feedback during pregnancy or exposure to cold
o Hyposecretion in adults-myxedema, endemic goiter if lack of iodine
o Hyposecretion in infants- cretinism (mentally retarded, short body)
o Hypersecretion- Graves’ disease (makes antibodies directed at thyroid
follicular cells, continuously stimulate TH release)
Pancreas
o Pancreatic islets contain endocrine cells
 Alpha cells produce glucagon
 Beta cells produce insulin
 Type 1 diabetes- destruction of the beta cells
Glucagon
o Major target is the liver where it promotes:
 Glycogenolysis: breakdown of glycogen to glucose
 Gluconeogenesis: synthesis of glucose from lactic acid and
noncarbohydrates
 Release of glucose to the blood
o Humoral stimulus (low blood glucose)Hormonal release of glucagon
o Low blood glucose levelpancreas secretes glucagon, stimulates glycogen
breakdown in liver to glucoseblood glucose rises to normal range
Insulin
o Activates insulin receptor
o Cascade leads to increased glucose uptake and enzymatic activities that
 Catalyze the oxidation of glucose for ATP production
 Polymerize glucose to form glycogen
 Convert glucose to fat (particularly in adipose tissue)
o High blood glucose levelpancreas secretes insulinstimulates glycogen
formation in liver, and stimulates glucose uptake by cellsblood glucose
lowers to normal range
o Diabetes mellitus (DM)- due to hyposecretion/hypoactivity of insulin
 Three signs: polyuria (huge urine output), polydipsia (excessive
thirst), polyphagia (excessive hunger/food consumption)
o Hyperinsulinism: excessive insulin secretion, results in hypoglycemia,
disorientation, unconsciousness
Hormone Action on Target Cells
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o 1. Alter plasma membrane permeability or membrane potential by opening
or closing ion channels
o 2. Stimulate synthesis of proteins or regulatory molecules
o 3. Activate or deactivate enzyme systems
o 4. Induce secretory activities (prolactin-milk letdown)
o 5. Stimulate mitosis (GH)
Two Mechanisms:
o 1. Water-soluble hormones cannot enter target cells, act on plasma
membrane receptors, coupled by G proteins to intracellular second
messengers that mediate target cell’s response
o 2. Lipid-soluble: can get through plasma membrane, acts on intracellular
receptors that directly activate genes
Cyclic AMP 2nd Messenger System
o 1. Hormone binds to receptor
o 2. Receptor activates G protein
o 3. G Protein activates adenylate cyclase
o 4. Adenylate cyclase converts ATP to cAMP (2nd messenger)
o 5.cAMP activates protein kinases, which triggers response of target cells
Direct gene activation through lipid-soluble hormones
o 1. Steroid hormone diffuses through the plasma membrane and binds an
intracellular receptor
o 2. Receptor-hormone complex enters the nucleus
o 3. The receptor hormone complex binds a specific DNA region
o 4. Binding initiates transcription of the gene to mRNA
o 5. The mRNA directs protein synthesis