Overview
The hypothalamus and pituitary gland sit at the top of the system. The hypothalamus releases hormones that tell the pituitary what to do; the pituitary then directs the thyroid, adrenal glands and gonads. Most of these loops are controlled by negative feedback: when a hormone level rises, it switches off its own release.
Other glands respond directly to the blood: the pancreas to glucose, the parathyroids to calcium. The ovaries and testes produce sex hormones (see the reproductive system). In this 3D model the thyroid and parathyroid glands are illustrative shapes placed in their correct position.
Main functions
- Metabolism and energy use (thyroid hormones)
- Blood glucose control (insulin and glucagon)
- Calcium balance (PTH and calcitonin)
- Stress response, fluid balance and blood pressure (cortisol, aldosterone, epinephrine)
- Growth, development and reproduction
- Sleep–wake rhythm (melatonin)
Key structures
-
Pituitary gland
The pea-sized "master gland" that directs other endocrine glands.
-
Thyroid gland
A butterfly-shaped gland in the neck that sets the body's metabolic rate.
-
Parathyroid glands
Four tiny glands behind the thyroid that control blood calcium.
-
Adrenal glands
Two glands on top of the kidneys that manage stress, salt and water.
-
Pineal gland
A tiny gland deep in the brain that releases melatonin.
Negative feedback: the thyroid loop
The hypothalamus releases TRH, which makes the pituitary release TSH, which makes the thyroid release T3 and T4. When T3 and T4 are high, they inhibit TRH and TSH, so production slows. When they are low, TSH rises.
This is why TSH is the first test for thyroid disease: high TSH usually means an underactive thyroid (the pituitary is pushing harder), and low TSH usually means an overactive thyroid.
Nursing assessment
- Ask about changes in energy, weight, appetite, temperature tolerance, thirst and urination.
- Inspect and palpate the thyroid from behind while the client swallows; listen for a bruit over an enlarged gland.
- Check blood glucose and look for signs of hypoglycemia (shaky, sweaty, confused) or hyperglycemia (thirst, polyuria).
- Observe for moon face, buffalo hump or hyperpigmentation (adrenal disorders).
- Monitor vital signs, weight and fluid balance in pituitary and adrenal disorders.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Type 1 diabetes | Autoimmune destruction of insulin-producing beta cells | Polyuria, polydipsia, polyphagia, weight loss; risk of diabetic ketoacidosis | Insulin teaching, glucose monitoring, sick-day rules, recognizing DKA (Kussmaul breathing, fruity breath) |
| Type 2 diabetes | Insulin resistance with relative insulin deficiency | Often gradual: fatigue, infections, slow healing, blurred vision | Lifestyle, oral agents or insulin, foot care, yearly eye exam |
| Hypothyroidism | Too little thyroid hormone | Fatigue, cold intolerance, weight gain, constipation, bradycardia, dry skin | Levothyroxine on an empty stomach in the morning, lifelong; monitor for myxedema coma |
| Hyperthyroidism (Graves' disease) | Too much thyroid hormone | Heat intolerance, weight loss, tachycardia, anxiety, exophthalmos | Cool environment, high-calorie diet, eye protection, watch for thyroid storm |
| Addison's disease | Adrenal insufficiency (low cortisol and aldosterone) | Fatigue, weight loss, hypotension, hyperpigmentation, low sodium and high potassium | Lifelong steroid replacement, extra doses during stress, medical ID |
| Cushing's syndrome | Excess cortisol, often from long-term steroid therapy | Moon face, buffalo hump, central obesity, thin skin, high glucose | Infection and fracture prevention, glucose monitoring, never stop steroids abruptly |
| Diabetes insipidus and SIADH | Too little ADH (DI) or too much ADH (SIADH) | DI: large volumes of dilute urine, high sodium. SIADH: low urine output, low sodium, confusion | Strict I&O, daily weights, sodium monitoring, fluid restriction in SIADH |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| Fasting blood glucose | 70–99 mg/dL | 126 mg/dL or higher on two occasions indicates diabetes |
| Hemoglobin A1C | Below 5.7% | 5.7–6.4% prediabetes; 6.5% or higher diabetes; reflects about 3 months |
| TSH | About 0.4–4.0 mIU/L | High in primary hypothyroidism, low in hyperthyroidism |
| Free T4 | About 0.8–1.8 ng/dL | Low in hypothyroidism, high in hyperthyroidism |
| Cortisol (morning) | About 5–25 mcg/dL | Low in Addison's, high in Cushing's |
| Sodium | 135–145 mEq/L | Low in SIADH and Addison's; high in diabetes insipidus |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- Rule of 15 for hypoglycemia: give 15 g of fast-acting carbohydrate, recheck in 15 minutes, repeat if still below 70 mg/dL.
- Levothyroxine: same time every morning, 30–60 minutes before breakfast; effects take weeks.
- After a thyroidectomy, check for tingling around the mouth and positive Chvostek's or Trousseau's signs (low calcium from parathyroid injury).
Practice questions
8 NCLEX-style questions on the endocrine system. Pick an answer to see the rationale.
-
A client with diabetes is shaky and sweaty with a glucose of 58 mg/dL and is alert. What does the nurse give first?
Show the answer and rationale
Answer B: 15 g of fast-acting carbohydrate, such as 4 oz of juice. Rule of 15: give 15 g of simple carbohydrate, recheck in 15 minutes and repeat if below 70 mg/dL.
-
A high TSH with a low free T4 indicates:
Show the answer and rationale
Answer B: Primary hypothyroidism. When the thyroid makes too little hormone, the pituitary raises TSH to stimulate it.
-
After a thyroidectomy, the client reports tingling around the lips. What does the nurse assess next?
Show the answer and rationale
Answer B: Chvostek's and Trousseau's signs. Perioral tingling suggests hypocalcemia from parathyroid injury.
-
Which finding is expected in Addison's disease?
Show the answer and rationale
Answer B: Hypotension, low sodium and high potassium. Low aldosterone causes sodium loss and potassium retention; low cortisol causes hypotension and fatigue.
-
Which instruction is correct for levothyroxine?
Show the answer and rationale
Answer B: Take in the morning on an empty stomach. Food, calcium and iron reduce absorption. Treatment is usually lifelong.
-
Which A1C result indicates diabetes?
Show the answer and rationale
Answer D: 6.8%. An A1C of 6.5% or higher meets the diagnostic criterion for diabetes; 5.7–6.4% is prediabetes.
-
A client with a head injury has a large output of very dilute urine. The nurse suspects:
Show the answer and rationale
Answer B: Diabetes insipidus. Lack of ADH stops water reabsorption, causing polyuria, low urine specific gravity and rising sodium.
-
Which gland releases ADH into the blood?
Show the answer and rationale
Answer B: Posterior pituitary. ADH is made in the hypothalamus and stored and released by the posterior pituitary.