Chapter 49 Hormonal Regulations

-      hormones derived from tyrosine:

o  Cetecholamines: (neurohormones) epinephrine, norepinephrine, and dopamine

o  Thyroid hormones: “doube” tyrosine plus iodine: T3; T4

-      Hormones derived from Tryptophan

o  Serotonin and melatonin (pineal gland)

-      peptide hormones:

o  regulated secretion (common): hormone stored in secretory granules; released when stimulated e.g. neurohormones

o  constitutive secretion: hormone is not stored, but secreted as needed e.. cortisol during stress

-      Protein hormones:

o  Synthesized as prohormones proteolytically cleaved to generate mature, active form e.g. insulin

1.    diffuse into cell from blood

2.    bind to nuclear receptors in target cell

3.    act as transcriptional factors (regulate gene sequences)

4.    results in alteration of gene expression e.g. estrogens

1.    Hormone binds receptor

2.    Associated G-protein activated

1.    Hormone binds to R

2.    G-protein activated; stimulates (Gs); inhibits (Gi); phospholipase C

3.    Phospholipase C splits membrane bound phospholipid into:

4.    IP3; initiates release of Ca2+ from storage sites in ER

5.    DAG; activates PKC leading to protein phosphorylation: DE phosphorylation

6.    Characteristics of hormones in question

-      Activate intrinsic R kinase; if enough ATP around; phosphorylation of tyrosine residues in receptor (auto phosphorylation)

-      causes specific signaling cascade of other proteins inside cell

1.    endocrine; JH is released from the corpus allatum into blood (JH maintains larval stage)

2.    Neuroendocrine; BH (brain neurohormone) is stored and then released from corpus cardiacum into blood

3.    Stimulates prothoracic glands to release MH (ecdysone)

4.    JH slowly reduced (metamorphosis)

5.    Full adult form only occurs in absence of JH, and presence of MH

1.    nuclei in hypothalamus release oxytocin and ADH (regulated secretion of stored neuropeptides) at axon terminals

2.    upon stimulation; oxytocin, ADH enters capillaries of PP (neuroendocrine)

3.    carried via blood to targe gland for end organ stimulation

1.    releasing hormones secreted by hypothalamic nuclei

2.    released directly into portal circulation

3.    carried via portal vein to AP lobe cells

4.    bind to AP cell receptors

5.    stimulate hormone production by AP cells (endocrine)

-      GH hyposecretion abnormally low levels

o  In childhood; pituitary dwarfism; treatment= injections of GH before longbones ossigy

o  In adults: reduced muscle and bone mass

-      GH hypersecretion: abnormally high levels

o  In childhood: gigantism

o  In adults: acromegaly; no effect on height but connective tissue thickens; and finer, foot, face bones, increase in girth

-      Follicular cells secrete thyroid hormones T3, T4, which stimulate body’s rate of metabolism

-      Parafollicular cells secrete calcitonin, a polypeptide hormone that helps lower Ca2+ levels when blood levels are HIGH (hypocalcemic)