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Lecture 2

Lecture 2 Classification of hormones and control of release.docx

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University of Toronto St. George
Michelle French

Lecture 2: Classification of hormones and control of release October-23-12 5:16 PM Features of hormones • Can be made in different parts of the body •Chemicals made by cells in specific endocrine glands or other tissues o Can be single cells that do this •Transported in the blood to distant targets •Bind to specific receptors o Only cells with receptors will be responsive. There may be more than one type of receptor for each hormone •May act on multiple tissues o Can have different effects: insulin also causes glycogen deposition in the liver •Alter the activity of target cells •Action must be terminated (turned off/on) •Maintain homeostasis or precipitate change in many physiological processes Types of hormones •Peptide (3 or more amino acids) o Most hormones o Made in advance in cells o Synthesized like secreted proteins o Stored in secretory vesicles o Release by exocytosis upon a signal o Water soluble (dissolved in plasma) o Short half life in plasma (because they’re not bound to something they don't have protection) o Bind to membrane receptors (hydrophilic so can't get in cells) o Synthesis, packing and release • N- terminal signal sequence sends the protein to the RER  Signal sequence cleaved off as protein is made • Processing occurs in golgi- hormone can get glycosylated, folded, form disulphide bonds etc • Single preprohormone can contain  Several copies of the same hormone • e.g. prepro TRH gives 6 TRH (3 amino acids each), other peptides and signal sequence  More than one type of hormone • Pro-opiomelanocortin gives ACTH, gamma lipotropin, beta enorphin and signal sequence o Procesing • Formation of disulphide bonds, glycosylation, removal of C-peptide (connecting) •Steroid (derived from cholesterol) o Synthesised only from cholestoerol o Made on demand • Not stored, released as soon as made o Released by simple diffusion o Water insoluble • Bound to carriers in blood • Hydrophobic = lipid soluble = can go through plasma membrane o Long half life (as bound to carriers) o Cytoplasmic or nuclear receptors (sometimes plasma membrane receptors) o Biosynthesis occurs in mitochondria and SER o Type of hormone made depends on which enzymes are present in the cell • E.g. Cholesterol converted to aldosterone and cortisol in adrenal cortex, but to estradiol in the ovaries • Amine (derived from single amino acids) o Only synthesized from tryptophan or tyrosine o Trp: melatonin (behaves like peptides/steroids) • Darkness hormone • Secrete at night during sleep • Made in pineal gland (also in GI tract,
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