Download by Mrs. Bailey

Endocrine System
by Mrs. Bailey
The endocrine system is a collection of glands that secretes
chemical messages called hormones. These signals are
passed through the blood to arrive at a target organ, which
has cells possessing the appropriate receptor.
The endocrine system uses cycles and negative feedback
to regulate physiological functions. Negative feedback
regulates the secretion of almost every hormone.
Cycles of secretion maintain physiological and
homeostatic control.
Mechanisms of Hormone Action
The endocrine system acts by releasing hormones that in turn
trigger actions in specific target cells. Receptors on
target cell membranes bind only to one type of hormone.
More than fifty human hormones have been identified; all act
by binding to receptor molecules. The binding hormone
changes the shape of the receptor causing the response to the
hormone.
There are two mechanisms of hormone action on all target
cells:
•  Nonsteroid hormone action – binds to a fixed
receptor on plasma membrane - use of 2nd messenger.
•  Steroid hormone action – diffuses into target cell –
into nucleus – binds to a mobile receptor – transcription .
Nonsteroid hormones (water soluble) do not enter the cell
but bind to plasma membrane receptors, generating a chemical signal
(second messenger) inside the target cell. Five different second
messenger chemicals, including cyclic AMP have been identified.
Second messengers activate other intracellular chemicals to produce the
target cell response.
G protein
Refer to page 491
Kinases are
enzymes that
catalyze the
phosphorylation
of proteins!
Nonsteroid
G protein
PIP2
Refer to
page 492
Refer to p. 490
Diseases of the Endocrine System
Goiter - Enlargement of the thyroid NOT associated with
overproduction of thyroid hormone or malignancy.
Causes: Diet deficient in Iodine (Rare in the US) or an increase in TSH due to
a defect in normal hormone synthesis within the thyroid gland.
Treatment: Only needs to be treated if it is causing symptoms. The enlarged
thyroid can be treated with radioactive iodine to shrink the gland or with
surgical removal of part or all of the gland (thyroidectomy). Small doses of
iodine may help when the goiter is due to iodine deficiency.
Refer to page 504
Hypothyroidism
Most common cause is Hashimoto's thyroiditis body's immune system mistakenly attacks the
thyroid gland (autoimmune).
Common symptoms:
• 
• 
• 
• 
• 
• 
• 
Fatigue
Weight gain
Feeling cold
Dry skin and hair
Heavy menstrual periods
Constipation
Slowed thinking
Cretinism
Congenital hypothyroidism
Cretinism is a congenital deficiency in the secretion of the hormone
thyroxine from the thyroid gland. The brain and skeleton fail to
develop properly, resulting in mental retardation and dwarfism.
Symptoms: gradual development of a characteristic coarse, dry
skin, a slightly swollen face and tongue, umbilical hernia, and an
open mouth that drools. The baby is usually listless, slow-moving,
constipated, and a slow feeder.
Treatment: Thyroid hormone promotes
normal physical and mental development.
It is essential that treatment be started
during the first six weeks of life or
irreversible changes may take place! All
states and U.S. territories test newborns for
hypothyroidism.
Hyperthyroidism
Most common cause is Graves' disease. This occurs
when the body's immune system overstimulates the
thyroid.
Common symptoms:
•  Shaking, increased nervousness,
irritability
•  Rapid heart beat or palpitations
•  Feeling hot
•  Weight loss
•  Fatigue
•  More frequent bowel movements
•  Shorter or lighter menstrual periods
Refer to page 504
Diabetes Mellitus
The body does not produce or properly use insulin. The cause of
diabetes continues to be a mystery, although both genetics and
environmental factors such as obesity and lack of exercise appear
to play roles.
Major Types of Diabetes
Type 1: body's failure to produce insulin.
Type 2: insulin resistance (body fails to properly use insulin), as
well as relative insulin deficiency. Most Americans who are
diagnosed with diabetes have type 2 diabetes.
Gestational diabetes: Pregnant women who have never had
diabetes before but who have high blood sugar (glucose) levels
during pregnancy are said to have gestational diabetes.
Addison Disease
Most cases are caused by the gradual destruction of the
adrenal cortex by the body's own immune system. Often
both cortisol and aldosterone are lacking. Rare.
Common symptoms:
•  Drop in blood sodium and glucose
•  Increase in blood potassium
•  Dehydration
•  Weight loss
Treatment:
•  Replace missing hormones with similar steroids. Since Addison's
disease is a chronic condition, daily replacement medication can
never be stopped.
•  Routine care includes regular physician visits, avoidance of
dehydration, and the use of extra medication during illness.
Cushing Syndrome
The body's tissues are exposed to excessive levels of
cortisol for long periods of time.
Refer to p 508
•  Many people suffer the symptoms of Cushing’s
because they take prednisone for asthma, rheumatoid
arthritis, lupus or other inflammatory diseases.
•  Others develop Cushing syndrome because of
overproduction of cortisol by the body. Benign tumors of
the pituitary gland cause most cases of Cushing
syndrome.
•  The tumor causes increased secretion of ACTH. This
form of the syndrome, known as "Cushing's disease,"
affects women five times more frequently than men.
Cushing
Syndrome
Common
symptoms:
•  Redistribution of
body fat à fatty
“moon face”
•  Thin reddened
skin
Gigantism
Caused by hypersecretion of GH
during the growth years (before
ossification of the epiphyseal
plates).
Robert Wadlow was one of
history's largest humans
standing 8' 11.1". Born and
educated in Alton, Illinois, he
was later buried there at age 22,
weighing 490 pounds at the time
of his passing.
Acromegaly
Caused by hypersecretion of GH after skeletal fusion has
occurred. The cartilage still left in the skeleton continues
to form new bone.
May result in a distorted appearance due to enlargement of hands,
feet, face, jaw (causing separation of the teeth), and other body
parts. The patient’s skin usually thickens and the pores are more
pronounced.
Pituitary Dwarfism
Involves abnormally short stature with normal body
proportions caused by hyposecretion of GH during the
growth years.