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ENDOCRINE SYSTEMANATOMY AND PHYSIOLOGY OVERVIEW

IRIL I. PANES, RN, MAN

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OVERVIEW OF ANATOMY ANDPHYSIOLOGY

The Endocrine system is composed of aninterrelated complex of glands that secrete avariety of hormones directly into thebloodstream

Its major function; together with the nervoussystem; is to regulate body functions and

processes.

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Endocrine Vs. Nervous

The endocrine systemcoordinates slowerand longer response

to stimulus. Regulates growth and

homeostatic

processes.

The nervous systemcoordinates responseto sudden

environmentalchanges throughhigh-speed electricalsignals.

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HORMONEREGULATION

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HORMONES

Are chemical substances that act asmessengers to specific cells and organs(target organs), stimulating and inhibitingvarious processes.

Derived from the Greek term hormon which

means to set in motion, arouse, or excite.

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It has two major categories:

1. LOCAL: hormones with specific effect in the

area of secretion2. GENERAL: hormones transported in the

blood to distant sites where they exert theireffect

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CHARACTERISTICS

1. Hormones are secreted in one of threepatterns:

a. DIURNAL SECRETION is a pattern thatrises and falls within a 24-hour period; e.g.Cortisol a hormone that increases in themorning and drops in the evening.

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b. PULSATILE AND CYCLIC PATTERNS ofhormonal secretion rise and fall alonganother time frame, such as monthly; e.g.Estrogen

c. Variable type depends on levels of othersubstrates; e.g. Parathyroid hormone is

secreted in response to serum calcium levels

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CHARACTERISTICS

2. Hormones operate within a feedback system.Feedback loops can be positive or negativeand allow the body to be maintained in anoptimum environment

3, Hormones control the rate of cellular activity.They do not initiate biochemical changes

4. Hormones affect only cells that containappropriate receptors, which initiate a specificfunction

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CHARACTERISTICS

5. Hormones have independent andinterdependent functions. The release ofhormones from one gland often triggers the

release of hormones from the other glands

6. Hormones are constantly deactivated by theliver or other cellular mechanisms and are

excreted by the kidneys

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REGULATION

ROLE OF THE HYPOTHALAMUS ANDPITUITARY GLAND: The two MAJORENDOCRINE GLANDS

Endocrine activity is controlled directly or indirectly by

the hypothalamus, which links the nervous system to theendocrine system. In response to input from other areasof the brain and from other hormones in the blood,neurons in the hypothalamus secrete several releasingand inhibiting hormones. These hormones act onspecific cells in the pituitary gland that regulate theproduction and secretion of the pituitary hormone

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The Pituitary hormones that govern thesecretion of hormones from other glands arecalled TROPIC hormones

Glands influenced by the hormones arecalled TARGET glands

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FEEDBACK SYSTEMS

Blood levels of hormones are also controlledby NEGATIVE FEEDBACK. Once a hormonelevel is sufficient to produce its intended

effect, further elevations in the hormone levelare prevented by negative feedback. Risinglevels of hormone negate the initial change

that triggered that hormone release

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Negative and Positive Feedback

Negative Feedback:the response fromthe effector reducesthe initial stimulus.

Positive Feedback:the response triggersamplification of the

stimulus, leading to agreater response

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THE ENDOCRINEGLANDS

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Hypothalamus

Secretes hormones that make otherendocrine glands secrete their hormones.

Considered the control center of the

endocrine system. Produces two types of hormones:

1)Releasing hormones-switch onhormone production.

2)Inhibiting hormones-switch off hormoneproduction.

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Hypothalamus

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Pituitary Gland

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PITUITARY GLANDSTRUCTURE AND FUNCTION

The pituitary gland lies securely cradledwithin a small recess in the sphenoid bonecalled sella turcica

Master gland of the body

About 70% of the gland is the anterior lobe(adenohypophysis)

30% of the gland is the posterior lobe(neurohypophysis)

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Pituitary Gland

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PITUITARY GLAND( Hypophysis)

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HORMONES OF THEANTERIOR LOBE

a. Secretes tropic hormones (hormones thatstimulate target glands to produce theirhormone)

1. Adrenocorticotropic Hormone (ACTH)

2. Thyroid-stimulating Hormone (TSH)

3. Follicle-stimulating Hormone (FSH)

4. Luteinizing hormone (LH)

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b. Also secretes hormones that have directeffect on tissues

1. Somatotropic or Growth hormone

2. Prolactin

c. Regulated by hypothalamic releasing andinhibiting factors and by negative feedbacksystem

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HORMONE FUNCTIONS Pituitary Anterior lobe

Thyroid stimulating Hormone (TSH) :stimulates thyroid gland to release thyroidhormones

Adrenocorticotropic Hormone (ACTH):stimulates adrenal cortex to produce and

release adrenocorticoids

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HORMONE FUNCTIONS Pituitary Anterior lobe

Follicle Stimulating Hormone (FSH), andLuteinizing Hormone (LH): stimulate growth,maturation, and function of primary and

secondary sex organs

Growth hormone (GH) or somatotropin:stimulates growth of body tissues and bones

Prolactin: stimulates development ofmammary glands and lactation

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HORMONES OF THEPOSTERIOR LOBE

Does not produce hormones but stores thehormones produced by the hypothalamus

1. Antidiuretic Hormone (ADH)

2. Oxytocin

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HORMONE FUNCTIONS Pituitary Posterior lobe

Antidiuretic hormone (ADH): regulates watermetabolism; released during stress or inresponse to an increase in plasma osmolality

to stimulate reabsorption of water anddecrease urine output

Oxytocin: stimulates uterine contractions

during delivery and the release of milk inlactation

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HORMONES OF THEINTERMEDIATE LOBE

Secretes Melanocyte stimulating hormone(MSH)

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HORMONE FUNCTIONS Pituitary Intermediate lobe

Melanocyte stimulating hormone (MSH):affect skin pigmentation

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ADRENAL GLANDS

Two small glands, one above each kidney

Consists of two sections

1. Adrenal cortex (outer portion): producesmineralocorticoids, glucocorticoids, sexhormones (androgens); ESSENTIAL FORSURVIVAL

2. Adrenal medulla (Inner portion): producesepinephrine, norepinephrine

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Adrenal Glands

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HORMONE FUNCTIONS ADRENAL CORTEX

Mineralocorticoids (e.g. Aldosterone):regulate fluid and electrolyte balance;stimulate reabsorption of sodium, chloride

and water; stimulate potassium excretion Sex hormones (androgens, estrogen,

progesterone) : influence development of

secondary sex characteristics

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HORMONE FUNCTIONS ADRENAL CORTEX

Glucocorticoids (e.g. Cortisol, corticosterone):increase blood glucose levels by increasingrate of glyconeogenesis; increase protein

catabolism, increase mobilization of fattyacids; promote sodium and water retention;anti-inflammatory effect; aid body in copingwith stress

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HORMONE FUNCTIONS ADRENAL MEDULLA

Epinephrine, Norepinephrine: function inacute stress; increase heart rate, bloodpressure; dilate bronchioles; convert

glycogen to glucose when needed bymuscles for energy

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THYROID GLAND

Located in anterior portionof the neck

Consists of two lobesconnected by a narrowisthmus

Produces:

1. Thyroxine (T4)

2. Triiodothyronine (T3)

3. Thyrocalcitonin

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HORMONE FUNCTIONS

Thyroxine (T4) andTriiodothyronine (T3):regulate metabolic rate;

carbohydrate, fat and proteinmetabolism; aid in regulatingphysical and mental growth

and development Thyrocalcitonin: lowers serum

calcium by increasing bonedeposition

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PARATHYROID GLANDS

Four small glandslocated in pairs behind

the thyroid gland Produce

Parathormone (PTH)

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FUNCTIONS

Regulate serum calcium and phosphatelevels

Increase resorption of bone, therebymaintaining normal serum calcium levels; and

Maintain an inverse relationship betweenserum calcium and phosphate levels, thereby

fostering normal excitability of nerves andmuscles

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PANCREAS

Located behind the stomach

Has both endocrine and exocrinefunctions

Islets of Langerhans involved inendocrine function

1. BETA CELLS: produce insulin

2. ALPHA CELLS: produce glucagon

P

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Pancreas

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FUNCTIONS

BETA CELLS INSULIN:allows glucose to diffuseacross cell membrane;

converts glucose to glycogen

ALPHA CELLS GLUCAGON:increases blood glucose by

causing gluconeogenesis andglycogenolysis in the liver;secreted in response to lowblood sugar

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GONADS

A. OVARIES : located in the pelvic cavity,produce estrogen and progesterone

B. TESTES : located in scrotum, producetestosterone

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FUNCTIONS

OVARIES: Estrogen and Progesteronedevelopment of secondary sex characteristicsin the female, maturation of sex organs,

sexual functioning, maintenance ofpregnancy

TESTES: Testosterone- development of

secondary sex characteristics in the male,maturation of sex organs, sexual functioning

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ASSESSMENT

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HEALTH HISTORY

A. Presenting problem: symptoms may include

1. Change in appearance, hair, nails, skin(change in texture and pigmentation);change in size, shape or symmetry of head,neck, face, eyes or tongue

2. Change in energy level

3. Temperature intolerance

4. Development of abnormal secondary sexualcharacteristics; change in sexual function

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HEALTH HISTORY

5. Change in emotional state, thought pattern,or intellectual functioning

6. Signs of increased activity of sympatheticnervous system (e.g. nervousness,palpitations, tremors, sweating)

7. Change in bowel habits, appetite or weight;

excessive hunger or thirst8. Change in urinary pattern

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B. Lifestyle: any increased stress

C. Past medical history: growth anddevelopment (any delayed or excessivegrowth); diabetes, thyroid disease,hypertension, obesity, infertility

D. Family history: endocrine diseases, growth

problems, obesity, mental illness

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PHYSICAL EXAMINATION

A. Check height, weight, body stature and bodyproportions

B. Observe distribution of muscle mass, fatdistribution, any muscle wasting

C. Inspect for hair growth and distribution

D. Check condition and pigmentation of skin;

presence of striae

E. Inspect eyes for any bulging

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F. Observe for enlargement in neck area andquality of voice

G. Observe development of secondary sexcharacteristics

H. Palpate thyroid gland (normally cannot bepalpated): note size, shape, symmetry, any

tenderness, presence of any lumps andnodules

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LABORATORY/DIAGNOSTIC TEST

A variety of test may be performed tomeasure the amount of hormones

present in the serum or urine inassessing pituitary, adrenal, and

parathyroid functions; these tests willbe referred to when appropriate under

specific disorders of the endocrinesystem

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THYROID FUNCTION

A. SERUM STUDIES: nonfasting blood studies(no special preparation is necessary)

1. Serum T4 level: measures total serum levelof thyroxine

2. Serum T3 level: measures serumtriiodothyronine level

3. TSH: measurement differentiates primaryfrom secondary hypothyroidism

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B. RADIOACTIVE IODINE UPTAKE (RAIU)

1. Iodine administration orally; measurementby a counter of the amount of radioactiveiodine taken up by the gland after 24 hours

2. Performed to determine thyroid function;increased uptake indicates hyperactivity;

minimal uptake may indicate hypothyroidism

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Nursing Care:

Take thorough history; thyroid medication must bediscontinued 7-10 days prior to test; medications

containing iodine, cough preparations, excessintake of iodine-rich foods, and tests using iodine(IVP) can invalidate this test.

Assure client that no radiation precautions are

necessary

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THYROID SCAN

1. Administration of radioactive isotope (orallyor IV) and visualization by a scanner of the

distribution of radioactivity in the gland

2. Performed to determine location, size,shape and anatomic function of thyroid

gland; identifies areas of increased ordecreased uptake; valuable in evaluatingthyroid nodules

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PANCREATIC FUNCTION

A. FASTING BLOOD SUGAR: measuresserum glucose levels; client fasts frommidnight before the test

B. TWO-HOUR POSTPRANDIAL BLOODSUGAR: measurement of blood glucose 2hours after a meal is ingested

Fast from midnight before the test Client eats a meal consisting of at least 75g

carbohydrate or ingests 100g glucose

Blood drawn 2 hours after the meal

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C. ORAL GLUCOSE TOLERANCE TEST: mostspecific and sensitive test for diabetesmellitus

Fast from midnight before the test

Client ingests 100g glucose; blood sugars aredrawn 30-60 minutes and then hourly for 3-5hours; urine specimens may also be collected

Diet for 3 days prior to test should include 200g

carbohydrate and at least 1500kcal/day

During test, assess the client for reactions such

as dizziness, sweating and weakness

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D. GLYCOSYLATED HEMOGLOBIN(HEMOGLOBIN A) reflects the average ofblood sugar level for the previous 100-120

days. Glucose attaches to a minorhemoglobin (A). This attachment isirreversible

Fasting is not necessary Excellent method to evaluate long term control of

blood sugar

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ANALYSIS

ALTERED NUTRITION: MORE/LESS THAN BODYREQUIREMENT

HIGH RISK FOR INFECTION

ALTERED URINARY ELIMINATION FLUID VOLUME EXCESS OR DEFICIT

HIGH RISK FOR IMPAIRED SKIN INTEGRITY

SEXUAL DYSFUNCTION

KNOWLEDGE DEFICIT INEFFECTIVE INDIVIDUAL COPING

SLEEP PATTERN DISTURBANCE

BODY IMAGE DISTURBANCE