ENDOCRINOLOGY | Adult

SYSTEM | CORE REFERENCE

1. Introduction to the Endocrine System

The endocrine system is a network of glands that secrete hormones into the bloodstream. Hormones act as chemical messengers that regulate metabolism, growth, reproduction, fluid balance, and the stress response.

Main Functions

Metabolism: Regulates energy use and nutrient processing.
Growth and development: Supports physical growth and tissue maintenance.
Reproduction: Regulates sexual development, fertility, and pregnancy.
Homeostasis: Maintains glucose, calcium, sodium, and water balance.
Stress response: Coordinates cardiovascular and metabolic responses to illness or injury.

2. Major Endocrine Glands

Gland	Primary Role
Hypothalamus	Coordinates endocrine signaling and pituitary control.
Pituitary	Releases hormones affecting growth, reproduction, thyroid, adrenal function, and water balance.
Thyroid	Regulates metabolic rate and thermogenesis.
Parathyroids	Maintain calcium and phosphate balance.
Adrenal glands	Regulate stress response, blood pressure, and electrolyte balance.
Pancreatic islets	Control blood glucose through insulin and glucagon.
Ovaries and testes	Produce reproductive hormones.
Pineal gland	Secretes melatonin involved in circadian rhythms.

3. Hormonal Feedback

Negative Feedback

Negative feedback limits hormone secretion once the desired physiological effect has occurred.

Example: Thyroid hormones suppress further TRH and TSH secretion through the hypothalamic-pituitary-thyroid axis.

Positive Feedback

Positive feedback amplifies an initial stimulus. During labor, cervical stretching promotes oxytocin release, which strengthens uterine contractions until delivery.

4. Major Endocrine Axes

HPA: CRH → ACTH → cortisol.
HPT: TRH → TSH → T3/T4.
HPG: GnRH → LH/FSH → gonadal hormones.

5. Hormone Receptors

Peptide hormones such as insulin generally bind cell-surface receptors.
Catecholamines such as epinephrine act through membrane receptors.
Steroid hormones such as cortisol bind intracellular receptors and influence gene transcription.

NCLEX KEY POINT High TSH with low free T4 suggests primary hypothyroidism. Low TSH with high free T4 commonly suggests primary hyperthyroidism. Central thyroid disorders may produce different patterns.

6. Nursing Priorities

Recognize changes in temperature, heart rate, blood pressure, and mental status.
Assess urine output and hydration when ADH disorders are suspected.
Monitor blood glucose and electrolytes.
Teach correct hormone replacement and medication timing.
Identify endocrine emergencies promptly.

HORMONES | CORE REFERENCE

1. Hypothalamic Hormones

CRH: Stimulates ACTH release.
TRH: Stimulates TSH release.
GHRH: Stimulates growth hormone release.
GnRH: Stimulates LH and FSH release.
Somatostatin: Inhibits growth hormone and TSH secretion.

2. Anterior Pituitary Hormones

Hormone	Function
GH	Supports growth and tissue metabolism.
TSH	Stimulates thyroid hormone production.
ACTH	Stimulates adrenal cortisol secretion.
LH	Triggers ovulation and stimulates testosterone production.
FSH	Supports follicular development and spermatogenesis.
Prolactin	Stimulates milk production.

3. Posterior Pituitary Hormones

Antidiuretic Hormone (ADH)

Synthesized in the hypothalamus and released by the posterior pituitary.
Promotes renal water reabsorption.
Increases urine concentration.
ADH deficiency or resistance causes diabetes insipidus.
Excessive ADH activity can produce SIADH.

Oxytocin

Stimulates uterine contractions.
Promotes milk ejection during breastfeeding.

4. Thyroid Hormones

T3: Biologically active thyroid hormone.
T4: Major hormone released by the thyroid; converted to T3 in tissues.
Calcitonin: Can reduce calcium through effects on bone resorption, but has a relatively minor role in normal adult calcium homeostasis.

5. Parathyroid Hormone

PTH increases serum calcium through effects on bone, kidneys, and activation of vitamin D, which increases intestinal calcium absorption.

6. Pancreatic Hormones

Insulin: Lowers blood glucose and promotes nutrient storage.
Glucagon: Raises blood glucose by stimulating hepatic glucose production.
Somatostatin: Inhibits secretion of several hormones, including insulin and glucagon.

7. Adrenal Cortex

Cortisol: Stress response, glucose regulation, and anti-inflammatory effects.
Aldosterone: Promotes sodium retention and potassium excretion.
Adrenal androgens: Contribute to androgen activity, particularly in females.

8. Adrenal Medulla

Epinephrine: Increases heart rate and supports fight-or-flight responses.
Norepinephrine: Promotes vasoconstriction and blood pressure support.

9. Gonadal Hormones

Estrogen: Reproductive development, menstrual regulation, and bone health.
Progesterone: Supports the endometrium and pregnancy.
Testosterone: Supports male sexual development and reproductive function.

10. Pineal Hormone

Melatonin helps regulate the circadian sleep-wake cycle.

NCLEX QUICK CONNECTION ADH controls water balance. Aldosterone primarily regulates sodium retention and potassium excretion. PTH raises calcium. Insulin lowers glucose. Glucagon raises glucose.

LABORATORIES | CORE REFERENCE

1. Thyroid Laboratory Studies

Test	Interpretation
TSH	Common adult reference range approximately 0.4–4.0 mIU/L; laboratory dependent.
Free T4	Common range approximately 0.8–1.8 ng/dL; assay dependent.
Free T3	May help evaluate selected cases of hyperthyroidism.
Anti-TPO antibodies	Support autoimmune thyroid disease, especially Hashimoto thyroiditis.
TSH receptor antibodies	Support Graves disease.

Primary Hypothyroidism

High TSH with low free T4.

Primary Hyperthyroidism

Usually suppressed TSH with elevated free T4 and/or T3.

Central Hypothyroidism

Low free T4 with an inappropriately low or normal TSH.

2. Glucose and Diabetes Studies

Test	Clinical Interpretation
Fasting glucose	Normal below 100 mg/dL; prediabetes 100–125; diabetes at least 126 mg/dL when confirmed appropriately.
HbA1c	Normal below 5.7%; prediabetes 5.7–6.4%; diabetes at least 6.5% when diagnostic criteria are met.
Random glucose	At least 200 mg/dL with classic symptoms or hyperglycemic crisis can establish diabetes.
C-peptide	Helps assess endogenous insulin secretion; interpretation depends on concurrent glucose and clinical context.

NCLEX KEY POINT HbA1c reflects glycemic exposure over approximately 2–3 months. Conditions affecting red blood cell turnover may make HbA1c less reliable.

3. Adrenal Studies

Cortisol: Interpretation depends on collection time and clinical circumstances.
ACTH: Helps distinguish primary from central adrenal insufficiency.
Primary adrenal insufficiency: Low cortisol with elevated ACTH.
Central adrenal insufficiency: Low cortisol with low or inappropriately normal ACTH.

4. Electrolytes and Hormones

Primary adrenal insufficiency may cause hyponatremia and hyperkalemia.
Excess mineralocorticoid activity may cause hypertension and hypokalemia.
SIADH commonly causes hypotonic hyponatremia.
Diabetes insipidus may cause hypernatremia when water intake is inadequate.

5. Reproductive Hormones

FSH and LH must be interpreted with age, sex, menstrual phase, and clinical findings.
High LH/FSH with low gonadal hormones suggests primary gonadal failure.
Low or inappropriately normal gonadotropins with low sex hormones suggests hypothalamic-pituitary dysfunction.

6. Nursing Laboratory Priorities

Confirm fasting status when required.
Assess symptoms of hypoglycemia immediately.
Review laboratory-specific reference ranges.
Recognize critical electrolyte abnormalities.
Interpret results in relation to medications and clinical presentation.

NCLEX RED FLAG Severe hyponatremia with confusion, seizures, or altered consciousness requires urgent evaluation.

DISORDERS | CORE REFERENCE

1. Diabetes Insipidus (DI)

DI results from insufficient ADH activity or renal resistance to ADH.

Large volumes of dilute urine.
Intense thirst.
Dehydration and possible hypernatremia.
Low urine specific gravity.

Management

Monitor intake, output, weight, sodium, and hydration.
Replace fluids as clinically indicated.
Central DI: desmopressin may be prescribed.
Nephrogenic DI: address the cause and use condition-specific therapies.

2. SIADH

Excessive antidiuretic activity causes water retention and dilutional hyponatremia.

Concentrated urine.
Low serum sodium.
Low serum osmolality.
Headache, confusion, and seizures in severe cases.

Nursing Management

Fluid restriction when prescribed.
Strict intake and output.
Daily weight.
Neurological monitoring.
Hypertonic saline for selected severe symptomatic cases under close monitoring.

NCLEX SAFETY Correct severe hyponatremia according to an individualized protocol. Excessively rapid correction of chronic hyponatremia can cause osmotic demyelination.

3. Hyperthyroidism

Heat intolerance.
Weight loss.
Tachycardia and tremor.
Anxiety and frequent stools.
Graves disease is a common cause.

Management

Beta-blockers for adrenergic symptoms when appropriate.
Antithyroid medications.
Radioactive iodine or surgery in selected patients.
Monitor for thyroid storm.

4. Hypothyroidism

Cold intolerance.
Fatigue and weight gain.
Bradycardia.
Constipation and dry skin.

Levothyroxine Teaching

Take consistently, commonly in the morning on an empty stomach.
Separate from calcium and iron supplements by approximately four hours.
Do not double missed doses without individualized instructions.
Report palpitations, chest pain, or symptoms of excessive replacement.

5. Hyperparathyroidism

Excess PTH activity can produce hypercalcemia, nephrolithiasis, and reduced bone strength.

Bone pain or fractures.
Kidney stones.
Constipation.
Weakness and cognitive changes.

6. Hypoparathyroidism

Low PTH can cause hypocalcemia.

Perioral tingling.
Muscle cramps and tetany.
Seizures.
Possible laryngospasm.

NCLEX RED FLAG Stridor after thyroid or parathyroid surgery is an airway emergency. Consider postoperative hematoma, laryngeal injury, and hypocalcemia.

7. Cushing Syndrome

Cushing syndrome results from chronic exposure to excess glucocorticoids.

Central adiposity and rounded face.
Proximal muscle weakness.
Thin skin and purple striae.
Hyperglycemia and hypertension.
Increased infection risk.

8. Addison Disease

Primary adrenal insufficiency involves deficient cortisol and often deficient aldosterone.

Hypotension.
Fatigue and weight loss.
Hyponatremia.
Hyperkalemia.
Hyperpigmentation in primary disease.

Teaching

Take prescribed steroid replacement consistently.
Follow individualized sick-day dosing instructions.
Never abruptly discontinue long-term corticosteroids.
Carry medical identification and emergency medication when prescribed.

EMERGENCIES | CORE REFERENCE

1. Thyroid Storm

Thyroid storm is a life-threatening decompensation of thyrotoxicosis.

Clinical Findings

Marked tachycardia.
Hyperthermia.
Agitation, delirium, or altered mental status.
Possible arrhythmias and heart failure.

Priority Management

Assess and support airway, breathing, and circulation.
Provide oxygen when indicated.
Initiate cooling and cardiac monitoring.
Administer prescribed beta-blocker when appropriate.
Give antithyroid medication as ordered.
Administer iodine after antithyroid therapy according to protocol.
Administer glucocorticoids when ordered.
Identify and treat the precipitating cause.

NCLEX RED FLAG Avoid aspirin for fever management in thyroid storm because salicylates can increase circulating free thyroid hormone.

2. Myxedema Coma

Myxedema coma is severe decompensated hypothyroidism. The patient may have altered consciousness without being completely comatose.

Clinical Findings

Hypothermia.
Bradycardia.
Hypotension.
Hypoventilation.
Hyponatremia and possible hypoglycemia.

Priority Management

Support airway and ventilation.
Use passive rewarming.
Administer prescribed IV thyroid hormone.
Give stress-dose glucocorticoids until adrenal insufficiency is excluded.
Treat precipitating illness.

3. Addisonian Crisis

Acute adrenal insufficiency can cause severe hypotension and shock.

Clinical Findings

Profound hypotension.
Dehydration.
Weakness and altered mental status.
Abdominal pain, nausea, or vomiting.
Hyponatremia, hyperkalemia, and hypoglycemia may occur.

Immediate Management

Rapid IV isotonic fluids as clinically indicated.
Immediate parenteral hydrocortisone.
Monitor glucose and electrolytes.
Treat hypoglycemia and significant hyperkalemia.
Address the precipitating cause.

NCLEX PRIORITY Do not delay emergency hydrocortisone in a hemodynamically unstable patient with suspected adrenal crisis while waiting for laboratory confirmation.

4. Severe Hypoglycemia

Common Manifestations

Diaphoresis.
Tremor and tachycardia.
Hunger.
Confusion and behavioral changes.
Seizures or unconsciousness.

Awake and Able to Swallow

Check glucose promptly.
Give approximately 15 g of fast-acting carbohydrate for glucose below 70 mg/dL.
Recheck glucose after 15 minutes.
Repeat treatment if still low.
Provide a meal or snack when appropriate to prevent recurrence.

Unable to Swallow Safely

Do not give oral food or liquids.
Administer IV dextrose when access is available.
Give glucagon when appropriate if IV access is unavailable.
Protect airway and monitor for recurrence.

ENDOCRINOLOGY + METABOLIC DISORDER | DIABETES MELLITUS

1. Diabetes Mellitus

Diabetes mellitus is a metabolic disorder characterized by hyperglycemia resulting from impaired insulin secretion, insulin action, or both.

2. Type 1 Diabetes

Usually results from autoimmune destruction of pancreatic beta cells.
Requires ongoing insulin replacement.
May present at any age.
Diabetic ketoacidosis is a major acute risk.

3. Type 2 Diabetes

Characterized by insulin resistance and progressive beta-cell dysfunction.
May be managed with nutrition, activity, and medications.
Insulin may be needed depending on clinical circumstances.
Hyperosmolar hyperglycemic state is a major acute complication.

4. Common Manifestations

Polyuria.
Polydipsia.
Polyphagia.
Fatigue.
Blurred vision.
Slow wound healing.
Recurrent infections.

5. Hypoglycemia vs. Hyperglycemia

Hypoglycemia	Hyperglycemia
Sweating, tremor, hunger, tachycardia, confusion.	Thirst, frequent urination, dehydration, fatigue, blurred vision.
Immediate glucose assessment and treatment.	Assess glucose, hydration, ketones when indicated, and precipitating illness.

6. Diabetic Ketoacidosis (DKA)

Insulin deficiency leads to lipolysis, ketone production, metabolic acidosis, and dehydration.

Clinical Findings

Nausea, vomiting, and abdominal pain.
Dehydration and tachycardia.
Kussmaul respirations.
Possible fruity breath.
Altered mental status in severe cases.

Nursing Management

Assess ABCs and hemodynamic status.
Begin prescribed isotonic IV fluid resuscitation.
Check serum potassium before insulin administration.
Replace potassium when indicated.
Administer insulin according to protocol once potassium safety is established.
Monitor glucose, ketones, acid-base status, and electrolytes.
Identify the precipitating cause.

NCLEX RED FLAG — DKA Insulin moves potassium into cells. If serum potassium is severely low, insulin must be delayed while potassium is replaced according to protocol.

7. Hyperosmolar Hyperglycemic State (HHS)

Marked hyperglycemia.
Severe dehydration and hyperosmolality.
Neurological changes, including confusion or lethargy.
Usually little or no significant ketoacidosis.

Management

IV fluids and careful correction of volume depletion.
Electrolyte monitoring and replacement.
Insulin according to the treatment protocol.
Close neurological and hemodynamic monitoring.

8. Sick-Day Management

Continue basal insulin in type 1 diabetes; never stop it solely because of poor appetite.
Monitor glucose more frequently.
Check ketones when indicated.
Maintain hydration.
Follow individualized instructions for non-insulin medications, some of which may need temporary withholding during dehydration or acute illness.
Seek urgent care for persistent vomiting, significant ketones, or symptoms of DKA.

9. Long-Term Complications

Coronary artery disease and stroke.
Diabetic kidney disease.
Retinopathy.
Peripheral and autonomic neuropathy.
Foot ulcers and infections.

10. Foot Care

Inspect feet daily.
Wear properly fitting shoes.
Avoid walking barefoot.
Avoid heating pads on areas with reduced sensation.
Report wounds, redness, or signs of infection.

11. Metformin and Iodinated Contrast

Metformin does not require automatic discontinuation for every contrast study. Management depends on kidney function, acute kidney injury, the type of contrast procedure, and institutional policy.

NCLEX SAFETY For patients with acute kidney injury, eGFR below 30 mL/min/1.73 m², or selected arterial catheter procedures, metformin may need to be withheld and renal function reassessed before restarting. Follow the current protocol.