Endocrine System

Chapter 14

Lisa Ochs RN, BSN 2008

Endocrine System

Regulates most organ systems throughout the body

Communicates through chemical signals called hormones

Actions are usually slower and longer lasting

Composed of endocrine glands

Glands of the

endocrine system

Endocrine glands

Endocrinology is the study of the endocrine system and its functions

Secrete chemical substances called hormones

Hormones are secreted directly into the blood stream (no ducts)

Hormones

Chemical messengers that influence or control the activities of other tissues or organs

Generally effect metabolic processes involving carbohydrates, lipids and fats

Also participate in growth and reproduction and water/ electrolyte balance

Hormones

Classification Proteins

Or protein- related substancesAlmost all hormones are proteins

SteroidsHormones secreted from the adrenal cortex

and sex glands

Targets

Target tissues or target organs are the specific sites where hormones bind

Targets may be close to or far from endocrine gland

Each endocrine gland may have many targets (more targets, more widespread or generalized effects)

Hormone Receptors

Hormones interact with receptor sites on their target tissues

The receptors are either located on the cell membrane (membrane receptors) or within the cell (intracellular receptors)

Each hormones binds with a specific receptor- lock and key theory (so that each hormone affects only certain cells); ensures specificity

Hormone Receptors

Protein hormonesUse membrane receptorsWhen the hormone binds with its receptor, a

second messenger is producedThis second messenger activates enzymes

within the cell

Hormone Receptors

Steroid hormonesUse intracellular receptorsSteroid hormones are lipid soluble (pass

through the cell membrane) Bind to receptors in the nucleus to create a

steroid-receptor complexThis complex stimulates protein synthesis and

alters cellular function

Figure 14-2 What hormones do. A, Hormones are aimed at target tissues or target organs. B, Protein hormones and membrane receptors. C, Steroid hormones and intracellular receptors.

Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.

Control of Hormone Secretions

Negative FeedbackBiorhythmsCentral Nervous System

Negative Feedback

Information about the hormone or its effects is sent back to the gland that secretes that hormone

Ex. Insulin secretion Blood glucose increases… insulin released

from pancreas… glucose moves into the cells, blood glucose falls… less insulin is released

Figure 14-3 Negative feedback control. A, Increased blood glucose levels trigger the release of insulin from the pancreas. B, Decreased blood glucose levels cause the pancreas to decrease its secretion of insulin.

Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.

Insulin is released in response to elevations in

plasma glucose. requires iodine for its synthesis. increases the concentration of glucose

in the blood. is classified as a catecholamine.

Biorhythms

A rhythmic (patterned) secretion of a hormone

Some hormones follow a circadian rhythm (24 hour cycle) or monthly cycle (female reproductive hormones)

May be disturbed by alterations in sleep-wake patterns (shift work, travel)

CNS Control

Activation of the hypothalamus Stimulation of the sympathetic nervous

system (fight or flight) A person’s emotional state may also affect

hormone secretion (especially stress)

Glands

Pituitary gland

Also called the hypophysis About the size of a pea; “Master Gland” Divided into lobes- anterior and posterior Secretions from the anterior lobe is controlled

by the hypothalamus (considered a gland because it secretes several hormones); releasing hormones and release-inhibiting hormones

Pituitary Gland

Anterior Pituitary Gland Also called the adenohypophysis (adeno-

means glandular) Secretes six major hormones; control many

other glands and affect many organ systems Prolactin, ACTH, growth hormone,

gonadotropins, TSH

Growth Hormone Also called somatotropin or somatotrophic

hormone Primarily affects skeletal muscle and long bones;

determines a persons size and height Also affects protein synthesis and use of fats for

energy; causes glucose levels to rise (stimulates conversion of proteins to glucose)

Secreted during periods of exercise, sleep and hypoglycemia

Pituitary Gland

Gigantism- caused by

hypersecretion of growth hormone

Acromegaly is a syndrome that results when the pituitary gland produces excess growth hormone (hGH) after epiphyseal plate closure at puberty.

Dwarfism- caused by

hyposecretion of growth hormone

Here- primordial dwarfism, a rare condition

Prolactin (PRL) Also called lactogenic hormone Promotes milk production in women Stimulates growth of mammary glands and

stimulates milk production after childbirth

Pituitary Gland

Tropic hormones Tropic hormones control or affect other glands Usually in end in –tropin or –tropic

Thyrotropin also called thyroid stimulating hormone (TSH); stimulates the thyroid gland to release hormones

Pituitary Gland

Tropic hormones Adrenocorticotropic hormone (ACTH)

causes the adrenal glands to secrete steroids

Gonadotropic hormones target the sex glands (gonads); include follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Pituitary Gland

Posterior pituitary gland An extension of the hypothalamus Composed of nervous tissue, also called the

neurohypophysis Two hormones are produced in the

hypothalamus and stored in the posterior pituitary until needed; antidiuretic hormone and oxytocin

Pituitary Gland

Posterior pituitary gland Antidiuretic Hormone (ADH)

Released by the body to conserve waterCauses the kidney to reabsorb water from the

urine and return it to the bloodReleased in response to increased blood

concentration (dehydration, decreased volume, trauma, some drugs); alcohol inhibits ADH

Also called vasopressin, causes blood vessels to constrict (and therefore elevate BP)

Pituitary Gland

Posterior pituitary gland Antidiuretic Hormone (ADH)

If ADH is absent, profound diuresis will occur (diuresis means urine production); person may excrete up to 25 liters of urine per day; called diabetes insipidus

Excessive amounts of ADH will cause the body to retain water and certain electrolytes may be “washed out”- especially sodium (dilutional hyponatremia); called syndrome of inappropriate ADH (SIADH)

Pituitary Gland

Posterior pituitary gland Oxytocin

Targets the uterus and mammary glandsStimulates the uterine muscles to contract

during laborBreastfeeding stimulates the release of

oxytocin; causes contraction of the smooth muscles around the mammary ducts and releases breast milk; termed milk let-down reflex

Pituitary Gland

Pituitary Gland

New research has discovered a third hormone released from the posterior pituitary gland- secretin Already known to be secreted by the intestines Released in response to increased concentration of

solutes in the blood (think dehydration) Promotes secretion of ADH “and appears to have

direct water-conserving effects in the kidney as well”

From Jessica Y. S. Chu, et al. (2009) Proceedings of the National Academy of Science September 15, 2009 vol. 106 no. 37 15961-15966

Third lobe Tiny third lobe secretes melanocyte

stimulating hormone Stimulates the melanocytes in the skin and

causes darkening of the skin

Pituitary Gland

Thyroid Gland

Largest endocrine gland Located on the anterior neck; butterfly

shaped- two lobes connected by the isthmus

Composed of follicles that secrete triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine)

Thyroid hormones regulate all phases of metabolism and are necessary for the proper functioning of other hormones

Necessary for the maturation of the nervous system and normal growth and development

Thyroid Gland

Hypothyroidism Results in a condition called myxedemaSlowed metabolic state- slow heart rate, slowed

peristalsis (constipation), low body temperature, low energy, hair loss, weight gain, thickened skin

Cretinism is a congenital absence of thyroid gland; infant will fail to develop physically and mentally

Thyroid Gland

Typical patient with hypothyroidism. Note the puffiness in the face, coarse, thin hair and obesity

Cretinism- congenital lack of thyroid

hormone. Treatment includes replacement of

thyroid hormone and must be started within the first 6 weeks of life or permanent disability

will occur

Hyperthyroidism Excessive secretion of thyroid hormone

results in increased metabolic state; increased heart rate, increased peristalsis (diarrhea), elevated body temp (heat intolerance), hyperactivity, weight loss

Graves’ disease is a common type of hyperthyroidism; characterized by exophthalmia (caused by increased pressure behind the eyeball, which causes it to protrude out of the socket )

Thyroid Gland

Patient with exophthalmia, commonly seen in Graves’ disease. May also be seen in patients with normal functioning thyroid

gland (called euthyroid Graves’ disease)

Regulation of Secretion

Hypothalamus secretes a releasing hormone… stimulates the anterior pituitary to secrete TSH… TSH stimulates the thyroid gland to secrete T3 and T4… when blood levels of thyroid hormones are adequate, negative feedback prevents further secretion

Negative feedback loop

controlling thyroid

hormone secretion

Thyroid and Iodine

Iodine is required by the thyroid gland to synthesize T3 and T4

The iodine comes from dietary sources Tetraiodthyronine (thyroxine) contains 4

iodine atoms, triiodothyronine contains 3 iodine atoms

Iodine Deficiency

When there is a deficiency in the amount of iodine in the diet, the thyroid gland will enlarge

Iodine is needed to produce T3 and T4; without it, the negative feedback loop will not function to stop the secretion of TSH; persistent stimulation by TSH causes the thyroid gland to enlarge, called a goiter

Endemic goiter,

resulting from lack of iodine

in the diet

Parathyroid Glands

Situated along the posterior surface of the thyroid gland

Secrete parathyroid hormone (PTH); stimulated by low blood calcium levels

PTH target organs- bone, intestine, kidneys

Function is to elevate blood calcium levels

Parathyroid Glands

PTH elevates blood calcium three ways: Increases the release of calcium from bone

tissue; stimulates osteoclasis so calcium moves from the bone into the blood

Stimulates the kidneys to reabsorb calcium from the urine; causes the kidneys to increase excretion of phosphate (inverse relationship)

Increases absorption of calcium from the digestive tract; requires vitamin D

Figure 14-6 Parathyroid glands and the three target organs of PTH.

Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.

Parathyroid hormone (PTH)

stimulates osteoclastic activity. is released in response to decreasing

amounts of plasma calcium. increases plasma calcium. All of the above

Blood Calcium Blood calcium levels are also influenced by

calcitonin Secreted by the thyroid gland in response

to elevated blood calcium levels; calcitonin lowers calcium levels

Stimulates osteoblastic activity so calcium moves from the blood and into the bone and increases excretion of calcium in the urine.

Antagonistic to PTH

So…

High blood calcium levels stimulate secretion of ____________ and inhibit secretion of ____________.

Low blood calcium levels stimulate secretion of ____________ and inhibit secretion of ____________.

Hypocalcemia

Lack of calcium causes nerve and muscle membranes to become unstable and continuously fire electrical impulses; causes tetany

Hypocalcemic tetany that involves the muscles of respiration can be fatal; usually affects extremities

Hypocalcemic carpal spasm

Hypercalcemia

Patient develops hyperparathyroidism in response to injury to the parathyroid (usually a tumor)

PTH stimulates osteoclasis (Ca++ moves from bone to blood); excess Ca++ is excreted in the urine (can lead to kidney stones); can also affect CNS, cause slow heart rate, digestive problems (anorexia and constipation)

Adrenal Glands

Two small glands located above the kidneys

Consist of two regions- inner medulla and outer cortex; each secrete different hormones

Figure 14-8A A, The adrenal glands: adrenal medulla and the adrenal cortex.

Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.

Adrenal medulla

Inner region of the adrenal gland- part of the sympathetic nervous system (“fight or flight”)

Secrete epinepherine (adrenaline) and norepinepherine

Classified as catecholamines- help the body respond to stress

Catecholamines

Elevate BP; increase HR Convert glycogen to glucose (more available

to the cells) Increase metabolic rate (create more energy) Cause bronchodilation (more air to lungs) Dilate blood vessels to heart and muscles;

constrict to digestive tract

Adrenal Cortex

Outer region of the adrenal gland Secretes steroids (lipid soluble hormones) Three types:

Glucocorticoids (sugar)Mineralocorticoids (salt)Sex hormones (sex)

Adrenal cortical hormones are essential to life- must be replaced if adrenal cortex is not functioning

Glucocorticoids

Affect carbohydrates- convert amino acids into glucose (gluconeogenesis); helps to maintain blood glucose levels

Also affect protein and fat metabolism when needed for energy

Primary glucocorticoid is cortisol

Cortisol

Cortisol is released in response to stress (physiological stress- disease, injury, infection, pregnancy, as well as emotional stress)

Has an antiinflammatory effects; can be used to treat inflammation (allergic responses, arthritis); drugs like prednisone mimic cortisol’s effects

Cortisol Secretion

Hypothalamus secretes a releasing hormone… stimulates anterior pituitary gland to secrete ACTH (adrenocorticotropic hormone)… stimulates the adrenal cortex to secrete cortisol.

Elevated cortisol levels inhibit further secretion of ACTH (negative feedback)

Which of the following is least descriptive of the adrenal cortex?

Synthesizes iodine-containing hormones

Is a steroid-secreting gland Is responsive to ACTH Secretes cortisol, aldosterone, and

testosterone

Mineralocorticoids

Primary mineralocorticoid is aldosterone Very important for regulating blood volume and

blood pressure, and in regulating the concentration of electrolytes

Often called the salt-retaining hormone Reabsorbs sodium and water and eliminates

potassium in the urine Discussed in Chapter 24

Sex Hormones

Female hormones- estrogens Male homones- androgens (testosterone)

Discussed in Chapter 26

Adrenal Hyposecretion

Adrenal cortical insufficency, Addison’s disease

Characterized by: generalized weakness, muscle atrophy, bronzing of skin, severe loss of fluids and electrolytes. Can lead to hypovolemia, shock and death

Treatment: steroids, fluid and electrolyte replacement

Addison’s DiseaseDeficiency in the secretion of adrenal cortex hormones (cortisone and aldosterone). Symptoms include fatigue, weakness, weight loss, depression and hyperpigmentation (as seen above)

President John F. Kennedy had Addison’s disease.

Cushing’s syndrome Caused by: hypersecretion of ACTH or

cortisol, or by administration of steroids like prednisone

Characterized by: truncal obesity, moon face, buffalo hump, hirsutism, thin skin that bruises easily, bone loss & muscle weakness

Adrenal Hypersecretion

Cushing’s syndromeCushing’s is caused by increased level of cortisol. Symptoms include weight gain, fatigue, headache and the “moon face” appearance of the patient. (Clinically, to distinguish moon face from an obese face is the distribution of fat- in moon face, the fat distribution is higher and the ears are not visible when viewed from the front)

Cushing’s Syndrome

Typical patient with Cushing’s syndrome.

Note truncal obesity, thinner extremities,

buffalo hump, moon face, and striae

Pancreas

Located in the abdomen Both an exocrine gland (involved in

digestion) and an endocrine gland Secretes insulin and glucagon (PIG) to

control blood glucose levels Islets of Langerhans are hormone

secreting cells of the pancreas

Insulin

Released in response to increased blood glucose levels

Helps transport glucose into most cells (liver and brain do not require insulin); facilitated diffusion

Controls carbohydrate, protein and fat metabolism; stimulates glycolysis for energy and helps liver and muscle to store glucose; stimulates building of proteins from amino acids and promotes building of fats from fatty acids

Insulin

Decreases blood glucose levelsTransports glucose from blood into cellsStimulates cells to burn glucose for energy

The only hormone that lowers blood glucose levels!

Diabetes Mellitus

Insulin deficiency Type I, juvenile or IDDM Severe metabolic disturbances Include the three “polys”

PolyuriaPolydipsia Polyphagia

Hyperglycemia Inability of glucose to enter the cellsBody produces additional glucose

(gluconeogenesis) which also cannot be used by the cells

Excess glucose accumulates in the blood

Diabetes Mellitus

Glucosuria or glycosuriaGlucose in the urine

Polyuria Excretion of large volumes of urine, caused by

glucosuria Polydipsia

Excessive thirst caused by polyuria body’s attempt to replace lost volume)

Diabetes Mellitus

Polyphagia Glucose cannot be utilized so the body takes in more

food for fuel

Acidosis Cells cannot burn glucose, so they burn fatty acids

instead; rapid, incomplete breakdown of these results in formation of ketoacids (ketone bodies)

Ketoacidosis Results from accumulation of ketone bodies from fat

breakdown; gives fruity odor to breath; medical emergency

Diabetes Mellitus

Type II diabetes, adult onset diabetes or NIDDM

May have excessive amounts of insulin (hyperinsulinemia), but it cannot function effectively (resulting in hyperglycemia)

Diabetes Mellitus

Damaged insulin receptorsCannot respond to insulin, resulting in

hyperglycemia (which triggers more insulin to be released)

Diminished number of receptorsNumber of receptors can change; lack of

exercise and obesity can decrease number Excess adipose tissue

Secrete hormones that cause a state of insulin resistance

Diabetes Mellitus

Glucagon

Secreted by the pancreas Stimulated by low blood glucose levels Raises blood glucose levels

Converts glycogen stored in the liver into glucose

Stimulates gluconeogenesis

In practice… Diabetic patients are prone to infections Infection increases glucagon secretion, along

with stress hormone secretion (cortisol, epinepherine, growth hormone)

All of these elevate blood glucose levels Patients receiving steroids for other problems

(like prednisone) will also have elevated glucose levels (prednisone mimics cortisol)

So if your diabetic patient has an infection or is on long term steroid therapy- expect them to require higher than normal doses of insulin

NCLEX Question

After several diagnostic tests, a client is diagnosed with diabetes insipidus. The nurse understands that which symptom is indicative of this disorder?

1. diarrhea2. polydipsia3. weight gain4. blurred vision

Rationale

2. Polydipsia, increased thirst, is a common symptom of diabetes insipidus. The patient experiences increased thirst because of the increased fluid loss.

NCLEX Question

Which clinical manifestation should the nurse expect to note when assessing a client with Addison’s disease?

1. Edema

2. Obesity

3. Hirsutism

4. Hypotension

Rationale

4. Hypotension (especially postural) may result from loss of fluids

NCLEX Question

The hypothalamus responds to a decrease in blood pressure by secreting which substance?

1. angiotensin

2. antidiuretic hormone

3. epinepherine

4. renin

Rationale

2. Antidiuretic hormone (ADH)is released in response to declining blood pressure. ADH causes the kidneys to retain water, which increases blood volume and therefore raises blood pressure

NCLEX Question

After a client is admitted with an adrenal malfunction, the nurse demonstrates understanding of the function of the adrenal gland by identifying which hormones as being released by the adrenal medulla?

1. epinepherine and norepinepherine2. glucocorticoids, mineralocorticoids, and androgens3. thryroxinen(T4), triiodothyronine (T3) and calcitonin 4. insulin, glucagon and somatostatin

Rationale

Epinepherine and norepinepherine are both released from the adrenal medulla.

NCLEX Question

Diabetes insipidus is a disorder of which gland?

1. adrenal gland

2. parathyroid gland

3. pituitary gland

4. thryoid gland

Rationale

Diabetes insipidus occurs as a result of the absence of ADH. ADH is secreted by the posterior pituitary gland

NCLEX Question

Which disease is caused by a deficiency of cortical hormones?

1. Addison’s disease

2. Cushing’s syndrome

3. diabetes mellitus

4. diabetic ketoacidosis

Rationale

Addison’s disease results from a lack of cortical hormones