Download chemical signals in animals

Hormones and the Endocrine
System
Chapter 45
ENDOCRINE SYSTEM
• Endocrine system – chemical signaling by
hormones
• Endocrine glands – hormone secreting
organs
• Hormones – chemical signals that are
secreted into body fluids (usually blood)
and communicate regulatory messages
throughout body
– Regulate growth, development,
reproduction, metabolism, and
behavior
Figure 45.2 Hormonal regulation of insect development (Layer 3)
CHEMICAL SIGNALING
• Reception – a receptor detects a
signal (usually signal binds to
receptor)
• Transduction – binding of signal to
receptor changes receptor’s shape
which initiates chemical changes
(often several steps)
• Response – final transduced signal
triggers a specific cell response
Figure 45.3 Mechanisms of chemical signaling: a review
• Different cells will have
different receptors.
• This means that one hormone only
affects cells that have receptors
for that specific hormone.
• However, different cells may
have different receptors for
same hormone which can then
cause different affects.
Figure 45.4 One chemical signal, different effects
HUMAN ENDOCRINE GLANDS
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Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary or testis (gonads)
Figure 45.5 Human endocrine glands surveyed in this chapter
PANCREAS
• Secretes insulin and glucagon from the islets
of Langerhans in pancreas
• Insulin and glucagon are antagonistic
hormones.
• Metabolic balance requires a minimum of
90 mg glucose/100 ml blood.
• When blood glucose rises over 90mg/100ml:
– Insulin lowers blood glucose by stimulating
body cells to take in glucose.
– Insulin also slows glycogen breakdown in
liver.
• Before blood glucose reaches
90mg/100ml:
– Glucagon signals liver cells to
break down glycogen into
glucose and release to blood
– Signals liver cells to convert
amino acids and glycerol into
glucose and release to blood
Figure 45.12 Glucose homeostasis maintained by insulin and glucagon
Diabetes Mellitus
• Caused by a deficiency of insulin or loss
of response in target tissues
• Result is high blood glucose levels – so
high that a diabetic’s urine contains
glucose
• More glucose in urine means more water
needed in urine = thirst
• Cells don’t get the glucose they need so
they break down fat instead, which forms
harmful, acidic metabolites.
• Type I diabetes mellitus
– Insulin dependent
– Autoimmune disease where immune
system attacks pancreas ( cells)
and cannot make insulin
– “Juvenile” (adults too)
– Inheritance may play a minor role
– Potentially caused by infections
• Type II diabetes mellitus
– Non-insulin dependent
– Often inherited (although related to poor
diets and lack of exercise)
– Either insulin deficient or lack of response in
target cells
– Accounts for 90% of all diabetics
– Gastric by-pass surgery (duodenum and
jejunum removal) ends diabetes in most obese
patients
• Gestational diabetes – happens to pregnant
women (may be from hormones from placenta
causing insulin resistance in mom)
Figure 45.14 Stress and the adrenal gland
SHORT TERM STRESS
• Stressful stimuli cause hypothalamus
to activate adrenal gland via a nerve
to secrete epinephrine (adrenaline)
and norepinephrine (noradrenaline).
• Multiple effects:
– Glycogen broken down to glucose;
increases blood glucose
– Increased blood pressure and
stroke volume
– Increased breathing rate (dilates
bronchioles)
– Increased metabolic rate
– Change in blood flow patterns
leading to decreased digestion
and kidney activity
– Increase rate of oxygen
delivery to cells (used to
stimulate heart)
Figure 45.12 The synthesis of catecholamine hormones
LONG TERM STRESS
• Hypothalamus secretes a releasing
hormone that activates the anterior
pituitary to release ACTH
(adrenocorticotropic hormone)
• When ACTH reaches the adrenal
gland via blood it stimulates the gland
to secrete corticosteroids.
• Two main types of corticosteroids
– Glucocorticoids (ex. Cortisol)
– Mineralcorticoids (ex. Aldosterone)
• Glucocorticoids
– Promotes glucose synthesis from
noncarbs like proteins – used for fuel
– Break down skeletal muscle for protein
source
– Suppress some parts of immune system
(ex. Anti-inflammatory)
• Mineralcorticoids
– Aldosterone stimulates kidneys to
reabsorb water and sodium so blood
volume and therefore blood pressure
increases