Download Hormones and the Endocrine System

Chemical Coordination
Erick Santizo
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 highspeed 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, enzymesecreting 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.
Invertebrate Hormones

Ecdysone
regulates
molting in
insects.
 Juvenile
hormone
favors the
retention of
juvenile
characteristics.
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.
Diabetes

Diabetes mellitus, perhaps the bestknown endocrine disorder, is caused by
a deficiency of insulin or a decreased
response to insulin in target tissues.

Marked by elevated blood glucose levels.
Diabetes

Type I diabetes mellitus (insulin-dependent
diabetes) is an autoimmune disorder in which
the immune system destroys the beta cells of
the pancreas.
 Type II diabetes mellitus (non-insulindependent diabetes) is characterized either by
a deficiency of insulin or, more commonly, by
reduced responsiveness of target cells due to
some change in insulin receptors.