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The Endocrine System (Regulation of Hormone Release (Three types of…

- - - - provides reserve of hormone in blood
      - increases solubility of lipid-soluble hormones
      - increases half-life
- - - - produce calcitonin
    - - Thyroid hormone has 2 parts
        
        triiodothyronine (T3)
        
        thyroxine (T4)
      - thyroid hormone derived from the amino acid - tyrosine
  - - - 2) Iodide trapping - NA/I symporter shuttles iodine into cell
        
        3) oxidation of iodide as it passes into colloid - catalyzed by pendrin
        
        4) iodination of tyrosine (iodine attached to tyrosine) forming MIT or DIT, catalyzed by pendrin, occurs at follicle cell-colloid junction
        
        5) coupling of T1 and T2 molecules in the colloid - produces T3 and T4
        
        6) pinocytosis and cleavage of thyroid hormones
        
        7) release of thyroid hormones to the bloodstrem
  - - - inceased HR, contractility and cardiac output
      - increased respiration
      - enhanced substrate mobilization
- - - - oxytocin
        
        Stimulated by: cervical/uterine stretching, suckling of infant at breast
        
        Inhibited by: lack of appropriate neural stimuli
        
        Target organs and effects: uterus - stimulates uterine contractions, initiates labor
        Breast - initiates milk ejection
      - antidiuretic hormone (ADH)
        
        Stimulated by: increased blood solute concentration or decreased blood volume, pain, some drugs, low BP
        
        Inhibited by: adequate hydration of the body and by alcohol
        
        Target organs and effects: stimulate kidney tubule cells to reabsorb water
  - - - thyroid stimulating hormone
        
        Stimulated by: Thyrotropin releasing hormone, and in infants cold temp
        
        Inhibited by: feedback inhibition exerted by thyroid hormones on ant. pituitary and hypothalamus, and by GH inhibiting hormone
        
        stimulates normal development and secretory action of the thyroid
      - adrenocorticotropic hormone (ACTH)
        
        promotes release of glucocorticoids and androgens
        
        stimulated by: corticotrophin releasing hormone, stimuli that increase CRH release include fever, hypoglycemia, and other stressors
        
        Inhibited by: feedback inhibition exerted by glucocorticoids
      - Gondatropins
        
        follicle stimulating hormone
        
        stimulates production of gametes, F - stimulates ovarian follicle maturation and production of estrogen, M - promotes testosterone production
        
        luteinizing hormones
        
        regulate function of gonads, F - triggers ovulation and prod. of estrogen, M - promotes testosterone production
        
        Inhibited by: feedback inhibition of estrogen/proestrogen and testosterone
        
        Stimulated by: GnRH release
    - - growth hormone
        
        Target organs: liver, muscle, bone, cartilage, and other tissues
        
        anabolic hormone, stimulates somatic growth, mobilizes fat, spares glucose
        
        Growth promoting effects mediated indirectly by IGFs
        
        1) uptake of nutrients from the blood and their incorporation into protein and DNA, allowing growth by cell division
        
        2) formation of collagen and bone matrix
        
        Stimulated by: GHRH, triggered by low GHRH levels as well as secondary triggers like hypoglycemia, low levels of fatty acids, exercise, other stressors
        
        Inhibited by: GH and IGF feedback inhibition
        
        Over secretion in children = gigantism / Under secretion in children = pituitary dwarfism
        
        acromegaly = over secretion of GH in adults, overgrowth of bones of the hands, feet, and face "enlarged extremities"
        
        GH has a diabetogenic (anti-insulin effect)
        
        decreases the rate of glucose and metabolism --> conserves glucose uptake and metabolism = raises blood glucose level ~ opp. effect of insulin
      - prolactin
        
        breast secretory tissue, promotes lactation
        
        Inhibited by: PIH (dopamine)
        
        Stimulated by: decreased PIH, enhanced by estrogen, birth control pills, breast feeding
- - - - receive direct innervation from preganglionic fibers of the sympathetic division of the ANS, synapse with postganglionic fibers(modified sympathetic ganglion)
    - - epinephrine (80%) - more powerful regulator of the heart
      - norepinephrine - more powerful effect on peripheral vasoconstriciton
      - Effects depnd on the type of receptor present at target cells - either alpha or beta
        
        norepi binds only a receptors
        
        epi binds both a and B receptors
  - - - secretes glucocorticoids
        
        1) cortisol 2) cortisone 3) corticosterone
        
        cortisol only one secreted in significant amounts, regulates metabolism of major fuel sources in the body
      - general actions
        
        effect on fuel metabolism: glucose sparing diabetogenic effect, increases lipolysis (breakdown of fats) and inhibits glucose uptake by skeletal muscles
        
        enhance epinephrine's effect on BP
        
        inhibit collagen synthesis (most important structural protein in the body)
        
        strong, anti-inflammatory effect
    - - secretes mineralocorticoids
        
        aldosterone
        
        enhances Na reabsorption (and K excretion) in the kidney
        
        as Na is reabsorbed, creates an osmotic gradient and can reabsorb more water
        
        4 mechanisms through which aldosterone secretion is regulated
        
        atrial natriuretic peptide (ANP), increased blood pressure/blood volume
        
        inhibits RAAS and aldosterone secretion
        
        plasma concentrations of Na and K (increased K)
        
        ACTH (adrenocorticotropic hormone) - only during periods of severe stress
        
        renin-angiotensin mechanism (RAAS)
        
        renin is released from specialized cells in the juxtaglomerular apparatus of the kidney in response to: decreased BP or BV, dec. plasma osmolarity
        
        renin catalyzes the reactions
        
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    - - secretes gonadocorticoids, esp. androgens (converted to testosterone or estrogen)
        
        may trigger puberty's onset and appearance of secondary sex characteristics
        
        miniscule amount compared to the gonads
- - - - thyroid hormones
      - steroid hormones
    - - the cAMP cascasde
        
        hormone receptor binding activates G proteins
        
        G stimulatory alpha subunit (Gs-a) --> activation of adenylate cyclase (enzyme, not the 2nd messenger)
        
        ATP + adenylate cyclase = cAMP
        
        cAMP activates protein kinase A
        
        phosphorylates proteins that produce a physiologic effect
        
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        can induce effects at very low concentrations because initiate an amplifying cascade of reactions
      - some hormones bind to receptors with inhibitory G proteins
        
        activation of an inhibitory a-subunit (Gi-a)
        
        activates PDE
        
        results in greater than normal rate of cAMP breakdown
        
        lower cellular cAMP levels --> reduced enzyme activity
      - PIP-calcium signal mechanism
        
        hormone receptor binding --> G protein activation (GDP --> GTP)
        
        act. G proteins dissociates an a subunit, which activates phospholipase C
        
        phospholipase C activates hydrolysis of PIP2
        
        DAG
        
        activates protein kinase C
        
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        IP3 (can move through the cytoplasm)
        
        causes release of Ca from the ER and mitochondria
        
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