UNIT 4 Chapter 9: The Endocrine System
Section 9.2
9.2 Hormonal Regulation of Growth,
Development, and Metabolism
Hormones secreted from the pituitary gland are mainly
involved in growth and development.
Hormones secreted from the thyroid gland are mainly
involved in regulating metabolic rate.
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Pituitary Gland
The pituitary gland has two lobes (posterior pituitary and
anterior pituitary) and is about the size of a pea (1 cm). It
is located below the hypothalamus at the base of the brain.
The pituitary gland secretes
hormones involved in the body’s
growth, development, metabolism,
reproduction, and other essential
life functions.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Pituitary Gland
The posterior pituitary
gland is part of the
nervous system. It
stores and secretes the
hormones antidiuretic
hormone (ADH) and
oxytocin, which are
produced in the
hypothalamus.
Continued…
UNIT 4 Chapter 9: The Endocrine System
The Pituitary Gland
The anterior pituitary
gland produces and
secretes six major
hormones.
Section 9.2
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
Human Growth Hormone
The anterior pituitary gland regulates growth, development,
and metabolism through the production and secretion of
human growth hormone (hGH). This hormone affects almost
every body tissue.
Growth factors from the liver and hGH
increase the following processes:
•
•
•
protein synthesis
cell division and growth
breakdown and release
of fats in adipose tissue
The targets of hGH include the liver, muscle
cells, and bone cells.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
Human Growth Hormone
Human growth hormone stimulates the growth of muscles,
connective tissue, and bones.
If the pituitary gland secretes
excess amounts of hGH
during childhood, it can result
in gigantism. Insufficient
hGH production results in
pituitary dwarfism.
(A) The world’s tallest man stands 2.36 m in
height. His wife is 1.68 m tall. (B) People with
pituitary dwarfism have typical body proportions.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
Human Growth Hormone
Overproduction of hGH in adulthood can lead to acromegaly.
Since skeletal growth has been completed in adulthood, hGH
can no longer cause an increase in height. Instead, there is
widening of the bones and soft tissues of the body.
Acromegaly results from
excessive production of
hGH during adulthood. It
may be difficult to diagnose
the condition in the early
stages before a person’s
appearance noticeably
changes.
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Thyroid Gland
The thyroid gland is known as a “metabolic thermostat”
because the hormones it secretes regulate metabolic rate.
The thyroid gland lies below the
larynx and has two lobes. It
produces and secretes thyroxine
(T4), a hormone that increases the
rate at which the body metabolizes
fats, proteins, and carbohydrates for
energy. Thyroxine stimulates cells
in the heart, skeletal muscles, liver,
and kidneys to increase cellular
respiration.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Thyroid Gland
Low production of thyroxine is called hypothyroidism and
can result in cretinism. Individuals with cretinism are stocky
and shorter than average. Hormonal injections are required in
childhood so that mental development delays do not occur.
Adults with hypothyroidism experience fatigue and weight
gain due to a slow metabolism.
Overproduction of thyroxine is called hyperthyroidism.
Symptoms include anxiety, insomnia, and weight loss. It can
result in Graves’ disease, where the immune system attacks
the thyroid gland. Hyperthyroidism can be treated with
medication or removal of part of the thyroid gland.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Thyroid Gland
Thyroxine secretion is controlled by negative feedback.
(1) The hypothalamus
secretes a releasing
hormone that stimulates the
anterior pituitary gland.
(2) The anterior pituitary
releases TSH into the
bloodstream. (3) TSH
targets the thyroid gland.
(4) TSH causes the thyroid
to secrete thyroxine into the
bloodstream. Thyroxine
stimulates increased
cellular respiration in target
cells throughout the body.
(5) High levels of thyroxine
cause negative feedback
on the pituitary and
hypothalamus, shutting
down production of TSH.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.2
The Thyroid Gland
The thyroid gland requires iodine to make thyroid
hormones. If there is insufficient iodine in the diet,
thyroxine cannot be made, and there will be no signal to
stop TSH secretion. Constant stimulation of the thyroid
gland by TSH causes a goitre, which is an enlargement of
the thyroid gland.
In Canada, it is uncommon for people to have goitres
because iodine is added to table salt. Other dietary sources
of iodine include seafood and dairy products.
UNIT 4 Chapter 9: The Endocrine System
The Parathyroid Gland and
Calcium Homeostasis
Calcium is an essential mineral for
nerve conduction, muscle
contraction, skeletal development,
and healthy teeth. Calcium levels in
the blood are regulated in a negative
feedback system by two hormones:
calcitonin and parathyroid hormone
(PTH).
When blood calcium levels are too
high, the thyroid gland secretes
calcitonin to promote uptake of
calcium by the bones.
Section 9.2
UNIT 4 Chapter 9: The Endocrine System
Calcium Homeostasis
When blood calcium levels are low, the
parathyroid glands release PTH. PTH
stimulates bones to break down bone
material and secrete calcium into the
blood.
PTH also stimulates the kidneys to
reabsorb calcium from the urine. This
activates vitamin D, which stimulates
the absorption of calcium from the
digestive tract.
Section 9.2
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
9.3 Hormonal Regulation of the Stress
Response and Blood Sugar
What happens to your body when
you experience stress?
The endocrine system helps you
cope with stressful situations. The
stress response involves many
interacting hormone pathways,
including those that regulate
metabolism, heart rate, and
breathing.
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
The Adrenal Glands
The adrenal glands are a pair of organs involved in regulating
the stress response and blood sugar levels.
Each adrenal gland is composed of two layers:
• the adrenal medulla (inner layer)
• the adrenal cortex (outer layer)
Each layer produces different
hormones and functions as an
independent organ.
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
The Adrenal Medulla: Regulating the
Short-Term Stress Response
The adrenal medulla secretes two hormones: epinephrine and
norepinephrine.
These hormones regulate a short-term stress response that is
also known as the fight-or-flight response. In response to a
stressor, the following events occur in the short-term stress
response:
• Neurons in the sympathetic nervous system carry a signal
from the hypothalamus to the adrenal medulla.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
The Hormones of the Pancreas
The pancreas functions in both the digestive and endocrine
systems. There are over 2000 clusters of endocrine cells,
called the islets of Langerhans, scattered throughout the
pancreas. These cells secrete the following hormones:
•
•
insulin (secreted by beta cells) lowers blood glucose
by making target cells more permeable to glucose
glucagon (secreted by alpha cells) increases blood
glucose by stimulating the liver to convert glycogen to
glucose
Both hormones are regulated by negative feedback loops.
Continued…
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
The Hormones of the Pancreas
(A) The silhouette shows the location of the pancreas in the human body. (B) A close-up view of the
pancreas shows one of the many islets of Langerhans on the surface of the pancreas.
Continued…
UNIT 4 Chapter 9: The Endocrine System
The Hormones of
the Pancreas
Negative feedback regulates blood
glucose levels within a very narrow range.
Section 9.3
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
The Effects of Glucose Imbalance
Diabetes mellitus is a condition that results when the body
does not produce enough insulin or does not respond properly
to insulin. Glucose stays in the blood after meals instead of
entering the cells; as blood glucose levels rise after meals and
stay high, the result is high blood sugar (hyperglycemia).
Without glucose inside the cells, an individual becomes
fatigued and begins using fat and protein for metabolic
energy. The kidneys cannot reabsorb the excess glucose, so
glucose is excreted in the urine. Over the long term,
permanent damage occurs to the eyes, nerves, and kidneys.
Severe infection (gangrene) can occur in the limbs.
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
Causes of Diabetes
There are two major types of diabetes:
• Type 1: The immune system attacks and
destroys the insulin-producing beta cells
in the pancreas. People with type 1
diabetes are diagnosed in childhood and
need daily insulin injections.
• Type 2: Insulin receptors on the body’s
cells stop responding to insulin. People
who are overweight have a greater
chance of developing this condition. It is
usually diagnosed in adulthood and can
be controlled with diet, exercise, and
oral medications.
A light micrograph of
pancreatic beta cells
from someone with
type 1 diabetes. Many
of the beta cells have
been destroyed,
leaving behind only
non-beta cells
(stained purple), and
so the islet is
malformed.
UNIT 4 Chapter 9: The Endocrine System
Section 9.3
Toward a Cure for Diabetes
In 1921, Canadian scientists Frederick Banting and Charles
Best were the first to isolate insulin and use it successfully
to treat a person with diabetes.
Today, transgenic bacteria are used to produce synthetic
insulin in large quantities for diabetes treatment. Successful
islet cells transplants have also been performed to restore
beta cell function.
A continuous blood glucose monitor and
insulin pump. The pump releases small
amounts of insulin throughout the day, which
minimizes the need for insulin injections.