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6.6 HORMONES,
HOMEOSTASIS &
REPRODUCTION
UNDERSTANDING
APPLICATIONS & SKILLS
HOMEOSTASIS
Question:
What is homeostasis?
Answer:
The ability of organisms to maintain a stable internal
environment
PRINCIPLES OF HOMEOSTASIS
• In order for an organism to maintain a stable
internal environment, there are several things that it
needs
Communicators
Communicators
(e.g. brain)
(Sensory Nerves)
PRINCIPLES OF HOMEOSTASIS
• Generally works by using negative feedback
Negative Feedback:
In biology, a system whereby a change elicits a
reaction that elicits a return to the original condition
Most systems in the body are controlled this way.
Examples
• Temperature regulation
• Blood glucose regulation
• Appetite control
HORMONES
What is a Hormone?
A chemical substance produced in the body and
released into the bloodstream. It controls and
regulates the activity of certain cells or organs. A
hormone is released from a specific cell or organ and
only affects its target cell
HORMONES
Some common hormone releasing organs
STUDYING HORMONES
To fully understand a hormone and its effects, you
should know the following information about it
• Organ of release
• Target organ/cells
• Effect on target organ/cells
• What stimulates it
• What inhibits it
STUDY CHART
Hormone
Insulin
Glucagon
Thyroxin
Leptin
Melatonin
Testosterone
Estrogen
Progesterone
Secreted
By
Target
Effect
Stimulated
by
Inhibited
by
BLOOD GLUCOSE REGULATION
• Two hormones are responsible
• Insulin and glucagon
• Both are released from the
pancreas; specifically, they
are released by a section of
the pancreas called the
“Islets of Langerhans”
BLOOD GLUCOSE REGULATION
Insulin
• Released from β cells in the
Islets of Langerhans of the
pancreas
• Released when blood sugar is
high
• Increases glucose uptake into
cells by making the cell
membrane permeable to
glucose
• Also stimulates glylcogen
formation in the liver
• Release is inhibited when
blood glucose decreases to
normal levels
Glucagon
• Released by αlpha cells in the
Islets of Langerhans of the
pancreas
• Released when blood sugar is
low
• Causes glycogen in the liver to
break down and get released
into bloodstream
• Inhibited when blood glucose
returns to normal levels
DIABETES – WHEN BLOOD SUGAR IS
NOT REGULATED
• Diabetes is a condition where glucose cannot enter
the cells. This causes blood glucose to remain high
for a long time after a meal.
• There are several kinds of diabetes but the two most
common are Type I (early onset) and Type II (adult
or late onset)
TYPE I VS TYPE II
TYPE I Diabetes
• Occurs because person cannot
make insulin
• Usually occurs at a young age
and is a lifelong condition
• May be caused by the body’s
own immune system
• attackingand destroying Beta
cells in the pancreas
• Can be treated with insulin
injection or islet cell transplants
TYPE II Diabetes
• Person can make insulin but it is
not effective in getting glucose
into cells
• Usually occurs in overweight
adults
• Often occurs because person
eats too much food that is high
in sugar. This causes insulin
levels to be high all the time.
Eventually, the cells become
insulin resistant and lose their
sensitivity to it
• Can be treated with diet and
exercise
REGULATING METABOLISM
• Thyroxin is released from the thyroid gland in the lower part of the
neck
• It regulates metabolic rate
• It stimulates energy metabolism so you have more energy,
burn more calories and release more body heat
• Its release mechanism is complex but it can be stimulated
by low body temperature
• Many people are unable to properly regulate their metabolism so
they have too much or too little
THYROID DISORDERS
Hyperthyroidism
(too much)
• High energy; hyper
• May find it difficult to
focus
• Rapid heartbeat
• Very thin even though
they may eat a lot
• Feeling hot
• Hair loss
• Increased sweating
Hypothyroidism
(too little)
• Lack of energy;
sluggishness
• Depression and
forgetfulness
• Slow heartbeat
• Gain weight very easily
• Feeling cold
• Puffy face
LEPTIN – THE APPETITE HORMONE
Where is leptin secreted from?
Adipose (fat) cells
What does it do?
Suppresses your appetite.
How does it do this?
Leptin acts on special cells in
the hypothalamus of the
brain and causes apetite
to decrease
HOW DOES LEPTIN WORK
Leptin is often called a “Master Hormone”. That is, it
controls and affects things by stimulating or inhibiting other
hormones.
How Does Leptin Suppress Your Appetite?
Several ways:
1. It counteracts the effects of a feeding stimulant
released in the gut called neuropeptide Y
2. Counteracts the effects of a neurotransmitter called
adandamide which stimulates appetite.
3. Leptin promotes the synthesis of an appetite
suppressant called α-melanocyte-stimulating hormone
LEPTIN
What happens if you don’t produce leptin?
This is actually a leptin deficient mouse (left) that was
treated with leptin
WHAT AFFECTS LEPTIN LEVELS
• Leptin level is
• increased by perceived emotional stress
• decreased by increases in testosterone levels
• increased by increases in estrogen levels
• chronically reduced by physical exercise training
• increased by insulin
• paradoxically increased in obesity
• Some foods are said to affect leptin levels as well
LEPTIN & OBESITY
• Since leptin is secreted from adipose tissue (fat cells), it is not
surprising that obese individuals have more of it.
• But it seems a little surprising that a hormone that supresses
appetite is higher in obese people. Do obese people eat less
than thin people?
• Generally, they do not. While obese people have more leptin,
most have developed a condition known as leptin resistance.
• This is a condition where leptin no
longer affects the hypothalamus to
the same degree that it used to
• This is a common occurrence in
living things; when levels of something remain high for too long, the
body gets used to it and stops
responding (see insulin resistance)
MELATONIN – SLEEP/WAKE CYCLE
CONTROL
• Melatonin is the hormone responsible for Circadian
Rhythms; the daily cycle of sleep and wakefulness
• It is released by the Pineal gland in the brain and
controlled by special cells in the hypothalamus
called the suprachiasmatic nuclei
MELATONIN
What Does Melatonin Do?
• Makes you drowsy
• Lowers your core temperature
When is it Released?
MELATONIN
What Stimulates/Inhibits It?
The SCN seem to have their own timekeeping cycle
that ranges from ~24-26 hours (people kept in the
dark will develop a sleep wake cycle that is usually a
little over 24 hours
Nerves in the retina (back of the eye) that are
stimulated by light will send impulses to the SCN
causing them to inhibit the release of melatonin. So
light will decrease melatonin and drowsiness.