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Endocrine System
CHAPTER 31
WHAT WILL YOU LEARN?
The endocrine system produces hormones, chemicals that act on cells to produce a response.
The word “hormone” comes from the Greek word hormaein, “to set in motion.” This is, in fact,
exactly what hormones do—set things in motion. Sometimes, the effects of the hormone occur
over a long period of time. For example, hormones allow us to grow to our adult height, and
they cause the physical changes that turn boys and girls into men and women. Other times, the
effects of hormones are more immediate. Hormones with short-term effects help the body to
maintain homeostasis. For example, insulin is a hormone that regulates blood sugar levels.
The hormones produced by the endocrine system control many of the body’s functions. In this
chapter, you will learn about the glands of the endocrine system, some of the hormones they
produce, and how these hormones act to “set things in motion.” You will also learn about some
of the disorders that occur when the body produces too much or too little of a certain hormone.
When you are finished with this chapter,
you will be able to:
1.
State the main function of the endocrine system.
2.
List the glands that make up the endocrine system.
3.
Describe the feedback mechanism that controls the endocrine system.
4.
List the hormones produced by the different glands of the endocrine system.
5.
Explain how the aging process affects the endocrine system.
6.
Discuss various disorders that affect the endocrine system.
7.
Discuss the special care needs of people who have endocrine system disorders.
Endocrine System: Endocrine / Exocrine Glands
Endocrine glands produce hormones and release them directly into the bloodstream
Exocrine glands produce substances that are released into a hollow organ or onto a surface
Examples of exocrine glands include:
The salivary glands in the mouth, which produce saliva
The sweat glands in the skin, which produce sweat
Exocrine glands are not part of the endocrine system
Endocrine glands include:
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Thymus gland
Adrenal glands
Pancreas
Sex glands (gonads)
Location of Endocrine Glands
Endocrine glands are found in specific places throughout the body
The pituitary gland
◦ Is about the size of a cherry
◦ Lies underneath the brain
◦ Is connected by a stalk, called the infundibulum, to the hypothalamus
The pineal gland
◦ Is located underneath the brain
The thyroid gland
◦ Is located in the neck
◦ Is butterfly-shaped, with two oval lobes located on either side of the larynx; connected by a narrow
band of tissue called the isthmus
Function of the Endocrine Glands
The endocrine system controls many of the body’s processes, such as:
◦ Growth and development
◦ Reproduction
◦ Metabolism
How the Endocrine System works
•Endocrine glands produce hormones, chemicals that act on cells to produce a response
•The hormones are released into the bloodstream
•The hormone travels in the blood until it reaches its target cell
•Once there, it attaches to a special receptor in the cell wall
•Attaching a hormone to a receptor causes a specific reaction in the cell
Negative Feedback System of Endocrine
System
•The secretion of many hormones is initiated by feedback system
•Some change in the internal environment causes the gland to begin producing its hormone
•The gland continues to produce the hormone until the amount of hormone (or some other
related substance) reaches a certain level in the body
• At that point, the gland stops producing the hormone
•The feedback system works very much like a central heating unit in a house
Pituitary Gland
Pituitary Gland: Posterior Lobe
•Antidiuretic hormone (ADH) secreted by the posterior lobe; acts on the kidneys
•ADH limits the amount of water lost from the body in the form of urine
•ADH causes the kidneys to save body fluid by decreasing the amount of urine produced
•The lack of ADH causes the kidneys to produce more urine, eliminating excess fluid from the
body
•Oxytocin is a hormone that:
◦ Causes labor to begin
◦ Lets down milk in the breasts of a nursing mother
Pituitary Gland: Anterior Lobe
•Growth hormone is what causes our bodies to get bigger and taller as we move from infancy
into adulthood
•Growth hormone is usually released in greater amounts during short periods of time, resulting
in a child’s “growth spurts”
•The anterior lobe continues to release growth hormone long after the growing phase of
development is finished because cells continue to need to be replaced throughout a person’s
lifetime
•Thyroid-stimulating hormone (TSH) stimulates the thyroid gland
◦ Produces thyroid hormones
◦ Affects the rate of metabolism in the body’s tissues
Adrenocorticotropic hormone (ACTH) stimulates the adrenal glands
◦ Produces hormones
◦ Helps the body to cope with stress
Pituitary Gland: Anterior Lobe
•Prolactin stimulates the milk glands of the breasts to produce milk when a baby is born
•Gonadotropins regulate the functioning of the sex glands (gonads) in both males and females
◦ Two types of gonadotropins:
◦ Follicle-stimulating hormone (FSH)
◦ Luteinizing hormone (LH)
Thyroid Gland
•The thyroid gland produces the following two hormones:
◦ Thyroxine
◦ Calcitonin
Thyroxine
•The hormone thyroxine sets the rate of metabolism for the cells of the body
•If the thyroid gland releases more thyroxine, the metabolic rate of the cells increases
•If the thyroid gland releases less thyroxine, the metabolic rate of the cells decreases
• The thyroid gland needs iodine to produce thyroxine
•Iodine is found in:
◦ Fish and shellfish
◦ Added to salt and other commercial products
•Goiter can occur when a person is deficient of iodine
Calcitonin
•Calcitonin regulates the level of calcium in the bloodstream
•Calcitonin transports the extra calcium to the bones
•Tetany (cramping of the skeletal muscles and an irregular heart beat) may result if the calcium
level drops too low
•Too much calcium in the bloodstream causes muscles to become weak and slow to respond
Parathyroid Glands
•The parathyroid glands produce parathyroid hormone (PTH)
•PTH increases the amount of calcium in the blood:
◦ Causes calcium to be released from the bones into the bloodstream
◦ Helps the kidneys to keep calcium, instead of excrete it in the urine
◦ Allows us to draw on stored calcium later in life
•The actions of calcitonin and PTH balance each other and help to keep the levels of calcium in
the bloodstream constant
Parathyroid Glands
•If parathyroid glands are surgically removed or become damaged by disease:
◦ PTH is not produced in adequate amounts
◦ The calcium levels may drop, causing tetany
•Tumors of the parathyroid gland can cause an overproduction of PTH that results in:
◦ Excess calcium being removed from the bones
◦ Fragile bones
◦ Formation of kidney stones
Thymus Gland
•The thymus gland secretes thymosin
•Thymosin helps infection-fighting T cells to mature
•An increase in the secretion of thymosin stimulates the body to produce more T cells during an
infection or illness
Adrenal Glands
•Each adrenal gland has two separate parts:
◦ The medulla, or inner portion
◦ The cortex, or outer portion
•Each part secretes distinct hormones
Adrenal Glands: Medullary Hormones
•The medulla of the adrenal glands secretes two hormones:
◦ Epinephrine
◦ Norepinephrine
•Responsible for the “fight-or-flight” response of the body in emergency situations
•Help the heart and lungs deliver more oxygen and nutrients to the muscles, preparing the body to “stand
up and fight or turn tail and run”
◦ Dry mouth
◦ Pounding heart
Adrenal Glands: Cortical Hormones
•Glucocorticoids:
◦ Help to metabolize fats and proteins
◦ Help to maintain a reserve of glucose that can be used in times of stress
◦ Suppress the body’s inflammatory response
•Glucocorticoids are given in the form of drugs for severe inflammatory disorders such as:
◦ Asthma
◦ Rheumatoid arthritis
◦ Severe allergic reactions
•Hydrocortisone is a common medication that is a glucocorticoid
Adrenal Glands: Cortical Hormones
•Mineralocorticoids help to regulate the level of certain minerals in the body, particularly sodium and
potassium
•Aldosterone is the primary hormone in this group
•Aldosterone helps the kidneys to reabsorb sodium and secrete potassium
•Androgens are secreted in small amounts by the adrenal cortex
•Androgens are converted by the body into the sex hormones
◦ Testosterone (in men)
◦ Estradiol (in women)
Pancreas
•The pancreas is both an exocrine gland and an endocrine gland
•It functions as an exocrine gland by producing and secreting enzymes into the small intestine
that help to digest food
•It functions as an endocrine gland by producing two hormones, insulin and glucagon
Pancreas: action of Insulin
•Special cells within the pancreas, called the islets of Langerhans, produce and secrete the
hormone insulin
•Insulin affects all of the body’s cells
•Insulin allows glucose (sugar) to be transported from the bloodstream into the individual cells,
where it is used for energy
•Insulin lowers the blood glucose level
Pancreas: Action of Glucagon
•Glucagon is responsible for raising the blood glucose level
•When the glucose levels in the bloodstream drop, when a person has not eaten for some time,
the pancreas secretes glucagon
•Glucagon stimulates the liver to release the glucose that has been stored as glycogen into the
bloodstream, to supply the cells of the body with fuel for energy
Sex Glands
•The sex glands (or gonads) secrete hormones that:
◦ Cause the onset of puberty
◦ Regulate reproduction
The Effects of Aging on Endocrine System
•The normal processes of aging:
◦ decrease the amount of hormones produced
◦ slow the secretion by the endocrine glands
•Decrease in thyroid hormone levels slows the body’s metabolism
•In women, menopause occurs as a result of decreased hormone production by the ovaries
•In men, secretion of hormones by the testes decreases, affecting sexual drive and function
Disorders of the Endocrine System
•Disorders of the endocrine system can be caused:
◦ When the body produces too much or too little of a certain hormone
◦ By disorders of the hypothalamus, the pituitary gland, or the specific endocrine gland responsible
for the hormone
◦ As a result of poor nutrition
•Corrective measures may be needed to restore the body’s homeostasis and prevent the
imbalances from causing health problems
Pituitary Dwarfism
•A deficiency in the amount of growth hormone secreted during the growing years results in a
condition known as pituitary dwarfism
•A person with pituitary dwarfism is much smaller than average, but still well proportioned
•If the condition is diagnosed while the person is still a child, growth hormone may be given to
help stimulate growth
Pituitary Gigantism
•An excess in the amount of growth hormone secreted during the growing years results in a
condition known as pituitary gigantism
•A person with pituitary gigantism is much larger than average, but still well proportioned
Acromegaly
•The secretion of too much growth hormone after a person has reached adulthood causing
excessive growth of the bones of the hands, feet, and face
•Causes disproportioned appearance, especially in the face and hands
•Person does not grow taller
Thyroid Disorders
•Secretion of thyroid hormones is controlled by the pituitary gland
•Thyroid disorders can be caused by:
◦ Pituitary gland abnormalities
◦ Thyroid gland abnormalities
◦ Nutrient deficiencies, such as a lack of iodine
•A simple blood test can be used to detect imbalances in thyroid hormones
•Once detected, these imbalances can usually be treated
Hyperthyroidism
•Hyperthyroidism or Graves’ disease is caused by the excessive secretion of thyroxine
•In a person with hyperthyroidism, the metabolic rate of the body’s cells is increased
•Signs and symptoms of hyperthyroidism:
◦ Increased hunger accompanied by weight loss
◦ Irregular heartbeat
◦ Inability to sleep
◦ Irritability
◦ Confusion
◦ Increased perspiration, and intolerance to heat
•Hyperthyroidism may be treated by:
◦ Surgically removing part of the thyroid gland
◦ Destroying part of the gland with radiation
Hypothyroidim
•Hypothyroidism results when thyroxine secretion is too low
•In children, hypothyroidism, if left untreated, can result in a condition known as cretinism
◦ Cretinism is characterized by a lack of physical growth and mental development
•Most cases of hypothyroidism develop later in life, as a result of a disorder of the:
◦ Hypothalamus
◦ Pituitary gland, or
◦ Thyroid gland
•Hypothyroidism is more common among women and the elderly
•Hypothyroidism is treated by administering thyroxine in the form of a pill
Hypothyroidism: Signs / Symptoms
•Most cases of hypothyroidism develop later in life, as a result of a disorder of the:
◦ Hypothalamus
◦ Pituitary gland, or
◦ Thyroid gland
•Hypothyroidism is more common among women and the elderly
•Hypothyroidism is treated by administering thyroxine in the form of a pill
Adrenal Gland Disorders
•Two of the most common adrenal gland disorders are:
◦ Addison’s disease
◦ Cushing’s syndrome
•Result from imbalances of the adrenal cortical hormones
Addison’s Disease
•In Addison’s disease, the adrenal cortex is destroyed, resulting in low levels of the adrenal
cortical hormones
•A person with Addison’s disease experiences:
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Muscle weakness and atrophy
Dark discoloration of the skin
Disturbances in the body’s salt and water balance
Hypertension
•A person with Addison’s disease may need assistance with walking and range-of-motion
exercises
Cushing’s Syndrome
•Cushing’s syndrome results from:
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Excessive secretion of glucocorticoids
Disorders of the pituitary gland that affect ACTH secretion
Disorders of the adrenal gland itself
Administering high doses of steroid medications, such as hydrocortisone, for a long period of time
•Signs / Symptoms
• Pockets of fat in the abdomen, on the back, and in the face
• Increased facial hair
• High blood glucose levels, since one of the effects of glucocorticoids is to decrease the use of glucose by
the tissues
Diabetes Mellitus (DM)
•Diabetes mellitus results when the pancreas is unable to produce enough insulin
•Diabetes mellitus can occur in people of all ages and races
•People between the ages of 65 and 74 years and people of African descent are affected most
often
•Diabetes mellitus is the most common of all endocrine gland disorders and is the seventh
leading cause of death among the elderly
•There are two types of diabetes mellitus, type I and type II
Juvenile Diabetes (Type I)
•Caused by destruction of the insulin-producing cells of the pancreas
•Form of diabetes that most often affects children
•Most people who have type I diabetes are diagnosed while they are children or young adults
Insulin
•A person with type I diabetes mellitus must receive daily
injections of insulin
•The insulin is injected into the subcutaneous layer of the
skin, where it is absorbed by the bloodstream
•Several types of insulin are available
•The types of insulin differ in the speed at which they start
working and how long they last in the body
•Some patients or residents receive only one injection of
insulin each day, while others may receive two or three
•Insulin can also be delivered continuously by a pump device
Hypoglycemia / Hyperglycemia
•People who are receiving insulin injections need to have their blood glucose levels monitored closely
◦ Nursing assistants may help with glucose monitoring if properly trained
•Too much insulin causes hypoglycemia, a dangerous drop in blood glucose
◦ Hypoglycemia robs the brain of the glucose that is essential for it to function
•Too little insulin results in hyperglycemia, or too much glucose in the bloodstream
◦ If a person’s blood glucose level increases too much, he can enter a state called diabetic coma
◦ If not treated, diabetic coma can lead to death
Diabetic Diet
•People who are receiving insulin injections must eat an adequate amount of nutritious food at
regular intervals
◦ Meals
◦ Snacks
•A person with type I diabetes must eat a diet with specific amounts of:
◦ Carbohydrates
◦ Sugars
◦ Fats
◦ Proteins to react with the amount of injected insulin
Diabetic Diet
If a person does not eat at the recommended time after receiving her insulin, her blood
glucose level can drop too low, resulting in a condition known as insulin shock
If one of your patients or residents with diabetes refuses to eat, only partially finishes his
meal or snack, or vomits after eating report this to the nurse immediately
Type II Diabetes Mellitus (DM)
•Type II diabetes mellitus: most common in overweight adults
•In people with type II diabetes mellitus:
◦ The pancreas still produces some insulin but the cells of the body are unable to respond
to the insulin
◦ The body is unable to transport the glucose into the cells
◦ This results in higher blood glucose levels
•Symptoms of type II diabetes mellitus may occur gradually and go undetected for a long time
Type II Diabetes Mellitus (DM)
•Type II diabetes is treated through:
◦ Diet
◦ Exercise
◦ Use of oral medications to increase the effectiveness of insulin
•People with severe type II diabetes may need to be treated with insulin injections, especially
during times of illness or stress
•When caring for a person with type II diabetes, be sure to watch closely the amounts and types
of food the person eats
Hypoglycemia / Hyperglycemia: Symptoms
•Signs and symptoms of hyperglycemia and hypoglycemia are often very similar and should be
reported to the nurse immediately. These signs include:
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Excessive hunger
Excessive thirst
Weakness, dizziness, or both
Drowsiness and confusion
Shaking and increased perspiration
Complications of DM
•Many organ systems can be affected by uncontrolled diabetes mellitus of either type
•Low insulin levels increase the release of lipids (fats) into the bloodstream
•The lipids then build up in the linings of the arteries, damaging the blood vessels and possibly leading to:
◦ Atherosclerosis
◦ High blood pressure
◦ Heart disease
◦ Kidney disease
◦ Blindness (diabetic retinopathy)
Preventing Complications
•Early detection of diabetes mellitus is essential for preventing complications
•Once diabetes mellitus is diagnosed, measures can be taken to keep the disease under control
and minimize the risk of developing complications:
◦ Weight loss (if applicable)
◦ Regular exercise
◦ Close attention to recommended diet
◦ Proper use of prescribed medications