endocrinology 2nd major control system in the body
TRANSCRIPT
Endocrinology
• 2nd major control system in the body• “study of chemical messengers (hormones)
secreted by endocrine glands and other tissues”
• major role: to maintain homeostasis• coordinates many processes:
– metabolism, respiration, excretion, reproduction
Homeostasis
• concept of Claude Bernard• individuals live with 2 environments:
– external milieu– internal milieu
• bodies control internal milieu > allows independence from external milieu
Homeostasis
• contents of “fluid environment”:– glucose– amino, fatty acids– Electrolytes
• result: wide distribution of mammals to all types of habitats
Feedback systems
• endocrine and other sensory cells have “setpoint” for monitoring substances in blood
• low levels > hormone released (e.g. Ca2+ and parathyroid hormone)
• some systems shut off due to negative feedback• some are regulated by positive feedback
Other mechanisms of regulation
• Actions of opposing hormones– PTH and calcitonin– glucagon and insulin
• the brain / pituitary connection– time of day– temperature– nutrition
Subcategories of hormones
• Neurohormones: produced by nerve cells– Neuropeptides– Nonpeptidergic
neurohormones– Neuromodulators
• Pheromones:– Released to exterior of animal– Modulates response of another animal
• Lumones: released into lumen of GI tract• Chalones: inhibit mitosis• Growth factors: mitogenic peptides
Subcategories of hormones, cont’d.
Protein and peptide hormones
• Made of amino acids• Variable in size (e.g., TRH=3 amino acids)• Ring structures may be present (e.g., oxytocin,
vasopressin)• Many synthesized in precursor form > modified
prior to secretion (e.g., insulin; Fig. 1.8)• Some consist of two peptide chains (e.g., pituitary
glycoproteins)• Possible glycosylation• Transmembrane receptors
Hormones derived from tyrosine
• Enzymes present in cells determine which catecholamine will be synthesized
• Tyrosine > DOPA > dopamine > norepinephrine > epinephrine (handout)
• Catecholamines can be hormones, neurotransmitters
• Transmembrane receptors• Thyroid hormones (thyroxine, triiodothyronine)
also derived from tyrosine– T3 > 2 tyrosines with 3 iodine atoms (Fig. 5.3)– T4 > 2 tyrosines with 4 iodine atoms
• Nuclear receptors
Steroid hormones
• Derived from cholesterol• Glucocorticoids (e.g., cortisol), mineralocorticoids
(aldosterone)• Gonadal steroids (progesterones, androgens,
estrogens)• “generational” relationships• Enzymes present in cell determine steroids
produced• nuclear receptors• bind to proteins in blood > extends half-life• in liver, conjugated to glucuronic acid or sulfated
> inactivated
Terms to include:
• DNA, gene, codon, structural gene (“coding sequence”), regulatory regions, introns, exons
• Transcription, RNA polymerase, RNA, mRNA
• Translation, ribosomes, tRNA, amino acids, amino terminus, carboxy terminus
Peptide synthesis
• nucleotide sequence of gene dictates amino acid sequence of peptide
• sequence is transcribed into RNA• introns splicing occurs• mRNA leaves nucleus• translation occurs on ribosomes• peptides transported to RER and then Golgi
for modification(s) and packaging
Prohormones
• “precursors” to peptide hormones• often, peptides are spliced from much larger
hormones• examples:
– oxytocin– gonadotropin-releasing hormone (GnRH)
• precursors are packaged with endopeptidases in secretory vesicles