Hormones released into blood
stream and act on a different
cell (hemocrine)
Hormone clearance by liver
and kidneys:
half-life in plasma:
Amine 2-3 mins
Peptides 4-40 mins
Steroids 4-120 mins
NET EFFECT of hormones acting
on metabolism
levels of hormones vary - circulate together in different
amount. Specificity brought by distribution of RECEPTORS
on target tissues
Hormone action
Hormone -> receptor -> signalling
pathway -> target enzyme -> cell
response e.g. change in metabolism,
contraction, secretion
hormones act by binding to receptors;
target proteins where hormones have
to bind to elicit an effect
Hormone receptors - 3 classes:
G-protein
coupled
receptors
receptor external - e.g.
adrenaline, glucagon - 2nd
messengers elicit effect within
cell
Peptide
hormone
receptors
autocatalytic activity
- kinase cascades
e.g. insulin, growth
hormones
Steroid
hormone
receptors
receptor internal
-e.g.cortisol
Some receptors open into ion
channels e.g.
neurotransmitters e.g. acetyl
choline on Na+ entry
Metabolic regulation and
integration
Insulin and glucagon - respond to
blood glucose
Adrenaline, glucocorticoids e.g. cortisol
(steroids) - STRESS hormones
longer term response -
fight or flight
why hormones needed
to regulate
metabolism?
rapid, coordinated response of metabolism in
dif. tissues to change in body demands e.g.
FASTING, feeding, EXERCISE, rest, STRESS
(fight/flight response)
allow coordinated regulation of
metabolism between different
organisms
abnormal hormonal action - disease - e.g. diabetes, obesity
metabolism
regulated by
change in activity
of enzymes
INTRINSIC
EXTRINSIC
regulation of enzyme
activity by hormones e.g.
allosteric feedback
inhibition
short term -
COVALENT
modification
minutes/seconds
e.g.
Phosphatase
->
kinase
reversible
phosphorylation of
enzymes
long term - change in
enzyme levels by
regulating GENE
TRANSCRIPTION
Regulation of
glucose
homeostasis
4.5 -5.0Mm.
3.5mM fasting.
6.5mM fed.
HIGH glucose =
insulin release -
glucose removal
(into muscle and
adipose tissue)
osmotic diuresis - loss of fluid and
electrolytes - excessive thirst
protein glycosylation -
vascular disease - cataracts
kidney disfunction -
hypertension, heart
disease
glycosylation - poor
circulation - high blood
pressure
Insulin increases and peaks with
blood sugar after a meal. Glucagon
decreases from a higher level
Insulin/glucagon ratio = at
night, determines net effect
Measurement of
hormone levels
1. ELISA - enzyme linked
immunosorbent assay
used to
detect/quantify
of hormones and
drugs
Uses - measurement/detection of hormone levels
(pregnancy, thyroid hormone), illegal drugs, viral
infections (HIV, hepatitus B)
antibody to hormone of interest
immobilised in plastic well
incubate with
blood/urine sample -
hormone will bind to
antibody
incubate with 2nd
(animal) antibody
attached to an
enzyme
wash unbound 2nd antibodies,
incubate with enzyme-substrate.
Coloured product can be quantified -
using sprectrometer and compare w/
standard curve prepared using
purified hormone
pregnancy test -
humans and
horses!
2. Radioimmunoassays
commonly used to detect and
quantify hormones and drugs
Assays v. sensitive as
circulating hormone levels low
Glucagon and
Adrenaline action
Glucagon/adrenaline -> specific receptor
-> signalling pathway -> 2nd messengers
= cAMP, IP, Ca2+ = activation of protein
kinases