Hormone and chemical
coordination
Learning outcomes
Structure and function of
endocrine system.
Water and lipid soluble molecules.
Relationship of hypothalamus and
pituitary glands.

Hormones
A hormone is a chemical signal that is
secreted into the circulatory system and
communicates regulatory messages
within the body.
Hormones may reach all parts of the
body, but only certain types of cells,
target cells, are equipped to respond.

Systems of Internal Communication
Animals have two systems of internal
communication and regulation:
The nervous system
The endocrine system

Systems of Internal Communication
The nervous system conveys high-
speed electrical signals along
specialized cells called neurons.
The endocrine system, made up of
endocrine glands, secretes hormones
that coordinate slower but longer-acting
responses to stimuli.

Hormones
Advantages of using chemical
messengers:
Chemical molecules can spread to all
tissues through the blood.
Chemical signals can persist longer than
electrical ones.
Many different kinds of chemicals can act as
hormones; different hormones can target
different tissues.

Glands
Many hormones are secreted by
ductless endocrine glands.
Obtain raw materials from and secrete
hormones directly into the bloodstream.
Exocrine glands have ducts for
discharging secretions onto a free
surface.
Sweat glands, salivary glands, enzyme-
secreting glands in the digestive tract.

Hormones
Hormones convey information via the
bloodstream to target cells throughout
the body.
Pheromones carry messages outside
the body – to other individuals.

Hormones
Three major classes of molecules
function as hormones in vertebrates:
Proteins and peptides
Amines derived from amino acids
Steroids

Hormones
Signaling by any of these molecules
involves three key events:
Reception
Signal transduction
Response

Hormones
The hypothalamus regulates the
neuroendocrine system, maintaining
homeostasis in the body.
The hypothalamus can use motor nerves to
send short-lived electrical messages or
hormones to send chemical messages with
a longer duration.

The Chain of Command
 The hypothalamus produces seven different
“releasing” hormones that travel to the
pituitary gland.
 Each releasing hormone stimulates the
pituitary to release a corresponding hormone
which travels to an endocrine gland and
causes it to start producing a particular
endocrine hormone.

Membrane-Bound Receptors
 Many hormones are too
large, or too polar, to
pass through plasma
membranes.
 Bind to transmembrane
proteins that act as
receptor sites on target
cell membranes.
 Hormone is first
messenger.
 Causes activation of a
second messenger
in the cytoplasm.
 cAMP

Nuclear Receptors
 Steroid hormones are
lipid soluble molecules
that bind to hormone
receptors in the
cytoplasm of the target
cell.
 Site of activity is the
nucleus.
 Steroids are
manufactured from
cholesterol.
 Estrogen, progesterone,
testosterone, cortisol.

Nuclear Receptors
 Thyroid hormones
and insect-molting
hormone (ecdysone)
also act through
nuclear receptors.
 Binds to
transmembrane
protein that uses
ATP to move it into
the cell.

Control Pathways and Feedback
Loops
 A common feature of
control pathways is a
feedback loop
connecting the
response to the
initial stimulus.
 Negative feedback
regulates many
hormonal pathways
involved in
homeostasis.

The Pituitary
 The pituitary gland
is located below the
hypothalamus.
 Nine major
hormones are
produced here.
 These hormones act
primarily to influence
other endocrine
glands.

The Pituitary
The posterior lobe of the pituitary
regulates water conservation, milk
letdown, and uterine contraction in
women.
The anterior lobe regulates the other
endocrine glands.

The Anterior Pituitary
 Thyroid stimulating hormone (TSH) – stimulates the
thyroid gland to produce thyroxine which stimulates
oxidative respiration.
 Luteinizing hormone (LH) plays an important role in
the menstrual cycle. It also stimulates the production
of testosterone in males.

The Anterior Pituitary
 Follicle-stimulating hormone (FSH) – plays
an important role in the menstrual cycle. In
males, it causes the testes to produce a
hormone that regulates sperm production.
 Adrenocorticotropic hormone (ACTH) –
stimulates the adrenal gland to produce
steroid hormones. Some regulate glucose
production, others balance sodium &
potassium in the blood.

The Anterior Pituitary
Growth hormone (GH) – stimulates the
growth of muscle and bone.
Prolactin – stimulates milk production.
Melanocyte-stimulating hormone
(MSH) – in reptiles & amphibians, this
hormone stimulates color change.

The Posterior Pituitary
 Antidiuretic hormone
(ADH) regulates the
kidney’s retention of
water.
 Oxytocin initiates
uterine contraction
during childbirth and
milk release in mothers.
 These hormones are
actually synthesized in
the hypothalamus and
stored in the posterior
pituitary.

Biological Clocks
 The pineal gland is
located in the brain
of most vertebrates.
 Evolved from a light
sensitive “third eye”.
 Primitive fish &
some reptiles still
have a third eye.

Biological Clocks
 In other vertebrates it functions as an
endocrine gland secreting melatonin.
 Melatonin controls color change in amphibians
& reptiles.
 Release of melatonin is controlled by light/dark
cycles.
 The primary functions of melatonin appear to
be related to biological rhythms associated
with reproduction.
 Circadian rhythms – 24 hours long.

The Thyroid
 The thyroid gland, located
in the neck, produces:
 Thyroxine – increases
metabolic rate and
promotes growth.
 Two iodine-containing
hormones, triiodothyronine
(T3) and thyroxine (T4).
 Calcitonin – stimulates
calcium uptake by bones.

The Thyroid
 The hypothalamus
and anterior pituitary
control the secretion
of thyroid hormones
through two negative
feedback loops.

The Thyroid
 The thyroid
hormones play
crucial roles in
stimulating
metabolism and
influencing
development and
maturation.

The Parathyroids
 The parathyroid glands are
four small glands attached
to the thyroid.
 The hormone they produce
is parathyroid hormone
(PTH) which regulates the
level of calcium in the blood.
 Essential that calcium is
kept within narrow limits
for muscle contraction,
including the heart.

Calcium Homeostasis
 Two antagonistic
hormones,
parathyroid
hormone (PTH) and
calcitonin, play the
major role in calcium
(Ca2+
) homeostasis in
mammals.

Calcium Homeostasis
 Calcitonin, secreted by the thyroid gland,
stimulates Ca2+
deposition in the bones and
secretion by the kidneys, thus lowering blood
Ca2+
levels.
 PTH, secreted by the parathyroid glands, has
the opposite effects on the bones and kidneys,
and raises Ca2+
levels.
 Also has an indirect effect, stimulating the kidneys
to activate vitamin D, which promotes intestinal
uptake of Ca2+
from food.

The Adrenals
 Mammals have an adrenal gland above each kidney.
 Adrenal medulla is the inner core which produces
adrenaline (epinephrine) and norepinephrine.
 Adrenal cortex is the outer shell that produces the
steroid hormones cortisol and aldosterone.

Adrenal Medulla
The adrenal medulla releases adrenalin
(epinephrine) and norepinephrine in
times of stress.
Identical to the effects of the sympathetic
nervous system, but longer lasting.
 Accelerated heartbeat, increased blood
pressure, higher levels of blood sugar and
increased blood flow to heart and lungs.

Adrenal Cortex
The adrenal cortex produces the steroid
hormone cortisol (hydrocortisone).
Reduces inflammation.
 Synthetic derivatives such as prednisone are
used as anti-inflammatory agents.
Stimulates carbohydrate metabolism.

Adrenal Cortex
The adrenal cortex also produces
aldosterone.
Aldosterone acts in the kidney to
promote the uptake of sodium & other
salts from the urine.
These salts are important in nerve
conduction.
Aldosterone and PTH are the only two
hormones essential for survival.

The Pancreas
 The pancreas is located
behind the stomach and
is connected to the small
intestine by a small tube.
 It secretes digestive
enzymes into the
digestive tract (exocrine
function).
 Endocrine function –
production of insulin
and glucagon.

Glucose Homeostasis
 The islets of
Langerhans in the
pancreas secrete
insulin and glucagon.
 Insulin removes
glucose from the
blood.
 Glucagon returns
glucose to the
blood.