Endocrine System 1

Homeostasis, hormones and hormone mechanisms (lipid-soluble, water-soluble and G-proteins)

homeostasis

the maintenance of a constant internal environment upon external/internal change

ECF

extra-cellular fluid/internal environment

external environment

opportunities (nutrients, waste disposal) and threats (pathogens, changeable)

regulated variable

what is sensed and needs to be kept stable

set point

target for a variable

reference range

range of regulated variable within ‘normal’ limits - 2SD of mean

feedback loop components

sensors, control centre/integrator, communication pathways (nerves/hormones), effectors

positive feedback loop function

moves regulated variable further away from set point than normal

feed-forward

anticipation of change and preventative actions — can be physiological or behavioural

nervous system vs. endocrine system

NS = fast
ES = slow, widespread, longer-lasting (useful for things like growth)

local hormones

acting close to secretion point

paracrines

acting on immediate cells

autocrines

acting on the same cell that secreted it

chemical classifications of hormones

amino acid derivatives, peptide and protein, lipid derivatives

thyroid hormone amino acid derivative

two tyrosine residues linked together — giving lipid solubility

peptide vs. protein hormones

3-49 and 50-200

synthesise of peptide and protein hormones

intially preprohormones synthesised (ribosomes of rER), cleaved into prohormones (ER) then active hormones (golgi) released

lipid derivative hormone properties

produced from modifying 4-ring structure of cholesterol and require transport protein due to lipid solubility

lipid derivative/lipid soluble hormone movement

diffuse across plasma membrane
bind to receptors in cytoplasm or nucleus
complex attaches to SRE (steroid response elements)
alters gene expression

Thyroid hormone movement

receptors on mitochondria (increase energy production) or nucleus (altered gene activation)

water soluble

G-proteins naming convention

named for ability to swap GDP for GTP

G-protein coupled receptors structural features

made from 7 transmembrane protein (folds through membrane 7 times)
extracellular domain binds with hormone
intrecellular domain binds with G-protein

alpha subunit functions/pathways

moves to swap GDP for GTP — can activate enzyme or alter ion channel activity

SIGNAL AMPLIFICATION of G-protein coupled receptors

one hormone (1st messenger) can produce a lot of 2nd messengers

how to reverse/stop process

some G-proteins can inhibit 2nd messenger by converting it to something else or decreasing enzyme activity