Physiology 3120 Lecture Notes - Lecture 51: Steroid Hormone Receptor, Anterior Pituitary, Thyroid

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Lecture 51 Introduction of Endocrinology
Definitions
- Endocrine System
o Tissues and cells capable of secreting and responding to hormones (signaling
molecule)
o Communication system
o The two components (target organs) communicate via chemical messengers called
hormones
o One organ releases a hormone which targets another organ to elicit an endocrine
response (cause a change in physiology)
- NEURAL: functions mediated by electro-chemical conduction along nerves
o Rapid communication between brain and other components of nervous system
- ENDOCRINE: functions are mediated by chemical messengers called hormones
o Goes through the blood to target a tissue
- Hormone
o A chemical substance, formed in one organ or part of the body and carried in the
blood to another organ or part
o Depending on the specificity of their effects, hormones can alter the functional
activity of just one organ or of various numbers of them
GnRH targets pituitary
T3 targets several organs of the body to influence vaso-metabolic rate
- Hormones are:
o Regulators of physiologic events
o Effective in minute quantities (pictograms/nanogram quantities very small
amounts)
o Synthesized by cells/endocrine glands
o Hormone influences physiological response to meet a need of the body (adapt)
o Greek hormon, to rouse or set in motion
Not all hormones are the same!
- ENDOCRINE: chemical mediators produced in one part of the body which act on a distant
part Remote control
o Goes through the blood to get to the target receptor on organ
- PARACRINE: chemical mediators produced in one cell that acts on a neighbouring cell
Neighbourhood watch
o Cells near each other influence each other
- AUTOCRINE: chemical mediator produced in one cell and acts on that same cell
Self control
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Nervous vs. endocrine system
- Physical form of information transfer
o Action potentials (nerve firing) vs chemicals (hormones)
- Speed of information transfer
o Fractions of seconds vs minutes, hours, days
o Nervous system is faster
o E.g. insulin can act in minutes vs. thyroid hormone take days or months to elicit a
long term response
o Endocrine is generally slower than the nervous system
- Mechanism of gradation (stimulate response)
o Frequency (increase firing of AP) vs. amplitude modulation
o To up regulate a response, when hormone gets to target receptor, there is
amplification of the message due to the fact that the receptor upon activation leads
to down stream signalling events in the cell that amplifies the response
E.g. insulin binding receptor influences increases transcription and
translation of multiple copies of a particular gene
- Mechanism to achieve specificity
o "Wiring" (nerves and where they go allow for specificity) vs receptors (how specific
receptor is to hormone that circulates the body)
o Inactivity of receptors of hormone leads to pathological situations rather than the
hormone (e.g. diabetes)
Hormone types
- PEPTIDE/POLYPEPTIDE
o Small monomers e.g. TRH; 3 AA
o Large multimeric proteins e.g. TSH, FSH, LH; 200+ AA
o Water soluble dissolve in blood to travel between tissues
- STEROID
o Derived from cholesterol metabolism, 4 hydrocarbon rings with various side chains
o All start off as cholesterol and due to intracellular enzymes, we can get various
metabolites leading to various forms of steroid hormones
o Water insoluble
o Lipid soluble (requires binding protein in serum) need carrier proteins to travel
between organs
o E.g. testosterone, estrogen, vitamin D
- AMINO ACID DERIVATIVES
o Derived from amino acids
o e.g. epinephrine, thyroxine (T4 derived from tyrosine large aromatic structures)
o Lipid soluble
o Water insoluble
o Requires carrier protein to move from tissue to tissue
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Human endocrine system
- Virtually every tissue in the body produces some sort of hormone
- Endocrine: if it secretes hormones
- The gut secretes its own series of hormones to regulate food intake and digestion (CCK,
ghrelin, gastrin, secretin, NPY….
- The heart secretes ANP, an important factor in regulating vascular tone and volume
- The kidneys secrete EPO which increases erythrocyte formation
- The liver secretes angiotensinogen (angiotensin precursor), IGF-I (involved in growth) and
thrombopoietin  platelets
- Fat produces many adipokines e.g. leptin – influence appetite)
- Most cells produce locally-acting growth factors and cytokines
Regulation of endocrine secretion I: negative feedback
1) Between two hormones
- Organ A produces hormone A and acts on tissue B to make tissue B produce hormone B
- When level of hormone B is too high in the circulation, there is a negative feedback effect to
shut down hormone A from tissue A
- E.g. TSH is produced in anterior pituitary and acts
on thyroid gland to produce T3 when levels of T3
get too high, it shuts down the production of TSH
from anterior pituitary
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Document Summary

Neural: functions mediated by electro-chemical conduction along nerves. Endocrine: functions are mediated by chemical messengers called (cid:498)hormones(cid:499: goes through the blood to target a tissue. Endocrine: chemical mediators produced in one part of the body which act on a distant part (cid:523)(cid:498)remote control(cid:499)(cid:524: goes through the blood to get to the target receptor on organ. Paracrine: chemical mediators produced in one cell that acts on a neighbouring cell (cid:523)(cid:498)neighbourhood watch(cid:499)(cid:524: cells near each other influence each other. Autocrine: chemical mediator produced in one cell and acts on that same cell (cid:523)(cid:498)self control(cid:499)(cid:524) Physical form of information transfer: action potentials (nerve firing) vs chemicals (hormones) Mechanism to achieve specificity: wiring (nerves and where they go allow for specificity) vs receptors (how specific receptor is to hormone that circulates the body) Inactivity of receptors of hormone leads to pathological situations rather than the hormone (e. g. diabetes)

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