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Physiology 3120 Lecture Notes - Autocrine Signalling, Paracrine Signalling, Endocrine System

Course Code
Tom Stavraky

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Human Physiology
Friday, February 12, 2010
“Endo I”
Endocrine system
Tissues and cells capable of secreting/responding to hormones
A chemical substance produced in one part of the body that is secreted into the
bloodstream and then circulates throughout the body; but a lot of variability
Can affect one or a number of organs (i.e. GnRH vs. T3)
Regulators of physiological events
Effective in small quantities (i.e. high affinity)
Synthesized by cells or glands
Some hormones can act in different ways (i.e. paracrine signalling; autocrine signalling)
Nervous vs. endocrine system
Two ways that our body exerts control; work together
Physical form of info transfer
Endocrine chemical messenger; nervous AP
Endocrine minutes/hours/days; nervous seconds
Mechanism of gradation (strength)
Endocrine amplitude (concentration) of hormone; nervous frequency of AP
Mechanism for specificity
Endocrine receptors; nervous “wiring”
Endocrine system
Many major glands (i.e. hypothalamus, pituitary [master control system], adrenals, thyroids,
gonads, pancreas, etc.)
Many other cells that aren’t in discrete glands that also produce hormones
Gut cells secrete many hormones (i.e. gastrin, secretin, CCK)
Heart cells secrete ANP
Kidneys secrete EPO
Liver secretes IGF-1 and angiotensinogen
Fat cells produce leptin
Regulation of hormones
Negative feedback
Between 2 hormones (i.e. TSH and T3; T3 inhibits TSH release from pituitary)
Between a hormone and a metabolite (i.e. parathyroid hormone & Ca)
Between antagonistic pairs of hormones (i.e. insulin & glucagon on glucose metabolism)
Positive feed forward
Reproductive cycle; rising level of estrogen stimulates release of LH
Classes of hormones
Peptide hormones
Small monomers, or they can be large multimeric proteins
Water soluble; freely dissolve in blood plasma; can’t cross cell membrane
Cell-surface receptors (i.e. GPCRs, Tyr-kinase receptors, receptor-mediated ion channels)
Largest class of cell-surface receptors (over 800 with known function)
Beta-gamma subunits have physiological function as well as the alpha; many
different G-alphas (see Phys 3140a notes)
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