Chapter 42 – Endocrine System
Chemical Signals
Categories of Signals
Chemical signals are used:
(1)between individuals,
(2)between body parts, &
(3)between cells
The Action of Hormones
The Action of Hormones
A hormone does not seek out a
target organ; the organ is
awaiting the arrival of the
hormone.
Steroid hormones
Peptide hormones
Target Cell Concept
Action of Hormones
Chemical signals produced by one cell that
regulate the metabolism of other cells
Steroid Hormones -Can cross cell membranes
Peptide Hormones
 Most bind to receptor in plasma membrane
– First Messenger
 Causes internal release of cAMP
– Second Messenger
See ISP 45.2
HormoneInside a
Steroid
receptor
nucleus,
complex
hormones
hormones
binds
to DNAand
such
as
are lipids
resulting
in
estrogen &
cross
cell
activation
of
progesterone
membranes
genes
bind tothat
a
produce
freely
specific
enzymes
receptor
They are lipids that
cross cell
membranes freely
have the same complex of
four carbon rings but have
different side chains
cAMP sets
Activated
Cyclic
AMP
Peptide
an
enzyme
(cAMP)
is are
enzymes
hormones
cascade
in
made
from
can
be
used
the
first
never
enter
a
ATP;
it has
motion
messenger;
repeatedly,
cell so they
one
cAMP
resulting
bind toand
a in
phosphate
calcium
are
receptor
a
thousandgroup
nd
often
the
2
protein
in
fold
attached
to
messenger
plasma
response
adenosine at
membrane.
two locations
Peptide Hormones.ram
Human Endocrine System
Endocrine Glands
Endocrine glands - ductless glands in
contrast to exocrine glands with ducts.
Endocrine system consists of
endocrine glands that coordinate body
activities through hormones.
Their hormones are secreted directly
into bloodstream.
Human Endocrine System
Principal human endocrine glands:
Hypothalamus, pineal, and pituitary
glands  brain.
Thyroid and parathyroid glands  neck.
Thymus  thoracic cavity
Adrenals & pancreas  abdomen area
Ovaries  pelvic cavity
testes  scrotum
Homeostasis
Endocrine system is especially
involved with homeostasis.
Effect of hormones is controlled in 2
ways:
Negative Feedback
–Stops release of hormone
Antagonistic hormones
–Hormones have opposing (or opposite)
effect
Homeostasis
Negative feedback (ex.)
Pancreas produces insulin when blood
glucose rises; this causes liver to store
glucose.
When glucose is stored, level goes down and
pancreas stops insulin production.
Antagonistic hormones (ex.)
Effect of insulin is offset by glucagon
Thyroid lowers blood calcium level;
parathyroids raise blood calcium level.
Hypothalamus
•Pituitary
regulates the Gland
internal
• environment
Connected tothrough
the
autonomic system.
hypothalamus
•• ItLies
controls
heartbeat,
just below
the
temperature,
water
hypothalamus.
as well
as
• balance,
Two portions:
posterior
glandular
& anteriorsecretions
pituitary of
pituitary gland.
• This portion of
pituitary gland is
connected to
hypothalamus by a
stalk-like structure.
• It contains portions of
neurosecretory
cells that originate in
hypothalamus &
respond to
neurotransmitters
to produce
hormones.
Posterior
Pituitary
Hypothalamus
produces
antidiuretic
hormone (ADH or
vasopressin) and
oxytocin, which
pass through axon
endings in
posterior pituitary
and are stored
until released.
Posterior
Pituitary
Posterior Pituitary
Antidiuretic hormone (ADH) promotes
reabsorption of water from collecting
ducts in kidneys.
Nerve cells in the hypothalamus determine
when blood is too concentrated; ADH is
released and kidneys respond by
reabsorbing water.
As blood becomes dilute, ADH is no longer
released; this is a case of negative
feedback.
Posterior Pituitary
Oxytocin is also made in
hypothalamus & stored in posterior
pituitary.
Oxytocin
 stimulates uterine muscle contraction
 stimulates release of milk from
mammary glands
This positive feedback increases
intensity; positive feedback does not
maintain homeostasis.
Anterior Pituitary
Stimulation by hypothalamus
controls release of anterior pituitary
hormones;
Hypothalamus produces:
hypothalamic-releasing hormones
hypothalamic-inhibiting hormones
These pass to anterior pituitary by
portal system of two capillary beds &
one vein.
Negative Feedback
Thyroid-inhibiting
Thyroid-releasing
hormones (TIH)
hormones (TRH)
Produced in &
Produced & released
released from
from hypothalamus
hypothalamus act on
act
on
cells
in
cells in anterior
anterior
pituitary
to
pituitary to inhibit
produce
Thyroid
production & secretion
Stimulating
Thyroid Stimulating
Hormone (TSH)
(TSH).
Hormone
Anterior Pituitary
AP produces 6 different
hormones (each by a distinct cell
type)
3 affect other glands (Tropic
Hormones)
TSH; ACTH; Gonadotropic
hormones (FSH & LH)
3 directly effects on the body
PRL; MSH; GH
Tropic Hormones affect other Glands
Gonadotropic
(ACTH) -
Thyroidhormones
stimulate
stimulating
(FSH & LH)
hormone
sactthe
on
(TSH) adrenal
gonads
stimulates
(ovaries
&
thyroid toto
cortex
testes) &
produce
release
secrete
sex
secrete
thyroxin
cortisol
hormones
Hormones that directly affect the body
Prolactin (PRL)
is produced
Growthonly
after
childbirth.
hormone
Causes
(GH)
mammary
glands to
promotes
produce
milk.
skeletal
Plays
a role&
in
carbohydrate
muscular
and fat
growth
metabolism
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Thyroid Gland
Thyroid gland is in neck and attached to
trachea just below larynx.
Thyroxine (T4) -4 iodine atoms
Triiodothyronine (T3) - 3 iodine atoms
Thyroid hormones increase metabolic rate;
there is no one target organ, all organs respond
Thyroid gland also produces calcitonin
Calcitonin lowers calcium level in blood and
increases deposit in bone by reducing osteoclasts.
Low calcium levels stimulate release of parathyroid
hormone (PTH)
Video:
Hypothalamus,
pituitary,thyroid
Video:
Parathyroid
glands
Parathyroid Glands
4 parathyroid glands are embedded in
posterior surface of thyroid gland.
Produce parathyroid hormone(PTH)
PTH - Ca2+ level in blood increases &
phosphate level decreases.
PTH stimulates the absorption of Ca2+ by:
activating vitamin D – absorb Ca2+ at intestines
the retention of Ca2+ (and excretion of
phosphate) by the kidneys
demineralization of bone by promoting activity
of osteoclasts
Motor
neurons
can
Divisions
of
the
ANS
be divided
into
2 groups
Sympathetic
2
Nervous
Somatic
System
Nervous
System

Parasympathet
ic
Nervous
Autonomic
System
Nervous
System
Autonomic Nervous System
Sympathetic Division“FIGHT or FLIGHT” response.
Sympathetic system is especially
important during emergency
situations.
Neurotransmitter released is mainly
norepinephrine, (similar to epinephrine
-adrenaline- used as a heart stimulant)
Autonomic Nervous System
Parasympathetic Division
REST & DIGEST
System is “housekeeper system”; it
promotes internal responses resulting in a
relaxed state.
Parasympathetic system causes eye pupil
to constrict, promotes digestion, and
retards heartbeat.
Neurotransmitter released is
acetylcholine
Adrenal Glands
Two adrenal glands sit atop each kidney.
Each gland consists of two parts:
adrenal cortex (outer)
adrenal medulla (inner)
Hypothalamus - control over both portions
Medulla - Nerve impulses travel via sympathetic
nerve fibers
Cortex - Hypothalamus uses ACTH-releasing
hormone to control anterior pituitary’s secretion of
ACTH
Figure 42.11
Adrenal Medulla
Epinephrine & norepinephrine
Both hormones bring about body changes
corresponding to Emergency (Fight or Flight).
Blood glucose level rises and metabolic rate
increases.
Bronchioles dilate and breathing rate increases.
Blood vessels to digestive tract and skin constrict;
those to skeletal muscles dilate.
Cardiac muscle contracts more forcefully and heart
rate increases
Figure 42.11
Adrenal Cortex
Adrenal cortex hormones provide a
sustained response to stress.
Adrenal cortex secretes two types of
hormones:
Glucocorticoids
 help regulate blood glucose levels
Mineralocorticoids
 regulate levels of minerals in blood
It also secretes a small amount of both male
& female sex hormones in both sexes
Figure 42.11
Glucocorticoids
Cortisol is a biologically significant
glucocorticoid
Promotes breakdown of muscle protein to
amino acids taken up by liver from blood.
Breaks down fatty acids rather than
carbohydrates; cortisol raises blood
glucose levels.
Counteracts the inflammatory response; it
helps medicate arthritis and bursitis
RAAS
Reninangotensinaldosterone
system works in
2 ways:
Angiotensin
AldosteroneII
cause
constricts
kidney to
absorb
arterioles
Na+
Mineralocorticoid secretion is
controlled by renin-angiotensinaldosterone system. (RAAS)
enzyme renin converts plasma protein
Angiotensin
I
constricts
When
blood
sodium
rises,
water
is
angiotensinogen
to
angiotensin
I;
this
Angiotensin
II stimulates
adrenal
+ levels
Low
blood
vol.
&
Na
arterioles
directly;
aldosterone
reabsorbed
as
hypothalamus
secretes
becomes
angiotensin
II
by
a
converting
cortex
to
release
aldosterone.
+
kidneys
secrete
renin
causes
kidneys
to
absorb
Na
enzyme
in
lungs.
ADH; blood pressure increases
Pancreas
Pancreas lies transverse in abdomen
between kidneys and near duodenum.
Composed of two types of tissue.
Exocrine tissue - produces & secretes
digestive juices into sm. intestine thru
ducts
Endocrine tissues
 pancreatic islets (islets of Langerhans)
–produce insulin and glucagon
pancreas & insulin.ram
Pancreas
 All body cells utilize glucose;
therefore, its level must be closely
regulated.
 Beta cells secrete Insulin is secreted
when blood glucose level is high after
eating
 Alpha cells secrete Glucagon is
secreted between meals in response to
low blood glucose level.
Diabetes Mellitus
Diabetes mellitus is a common disease
where body cells do not take up or
metabolize sugar.
Liver is not storing glucose as glycogen &
cells are not utilizing glucose for energy.
Type I (insulin-dependent) diabetes - pancreas
does not produce insulin
type II (noninsulin-dependent) diabetes usually occurs in obese & inactive individuals of
any age. Cells do not respond to insulin
Testes & Ovaries
Male testes located in scrotum function as
gonads and produce androgens
Testosterone is male sex hormone.
It stimulates development of male secondary sex
characteristics: large vocal cords, pubic hair, etc
Female sex hormones - estrogen &
progesterone
Estrogens secreted at puberty stimulate maturation
of ovaries and other sexual organs.
Hormones are necessary for oocyte development.
Estrogen and progesterone are required for breast
development and regulation of uterine cycle
Thymus Gland
Thymus is a lobular gland that lies in the
upper thoracic cavity.
It reaches its largest size and is most active
during childhood; with age, it shrinks &
becomes fatty.
Some lymphocytes that originate in bone
marrow pass through thymus and change
into T cells.
Thymus produces thymosin which aid
differentiation of T cells and may stimulate
immune cells.
Pineal Gland
Pineal gland produces melatonin, primarily at
night.
In fishes and amphibians, pineal gland is near
surface and is a “third eye” receiving light directly.
In mammals, it is located in third ventricle and
cannot receive light directly; it receives nerve
impulses from the eyes, by way of the optic tract.
Pineal gland & melatonin help establish circadian
rhythms, daily physiological cycles.
Pineal gland may also be involved in human sexual
development
Melatonin Production
Steroid or Peptide Hormone?
Steroid or
Peptide
Hormone?