Nursing Field Notes / Endocrine · Hormone Hall of Fame 2 of 3 · Med-Surg: Endocrine

🩸 ENDOCRINE SET NG-278 Hormones I NG-279 Hormones II NG-280 Hormones III NG-281 Pituitary Disorders NG-282 SIADH vs DI (1) NG-283 SIADH vs DI (2)

Hormone Hall of Fame II 🦋

Posterior pituitary · thyroid · parathyroid · pineal · thymus

NG-279 ENDOCRINE · PART 2 OF 3 ADHD-friendly visual edition

Part 1 covered the front of the pituitary and the pancreas. Part 2 covers the back of the pituitary and the neck-and-chest glands: the two water-and-uterus hormones stored in the posterior lobe, the thyroid that sets your metabolic speed, the four rice-grain parathyroids that guard calcium, the pineal that reads darkness, and the thymus that trains your immune system and then quietly disappears.

💧 Only TWO come out the backADH (water) and oxytocin (squeeze). Both made in the hypothalamus.

🦋 Thyroid = the thermostatT3/T4 set metabolic rate, temperature, energy, growth. Needs iodine.

🦴 PTH ↑ calciumBone + kidney + gut. Calcitonin (C cells) puts Calcium back in the bone.

🌙 Dark → melatoninPineal. Light shuts it off. Hospital lights = broken sleep = delirium risk.

💧

THE POSTERIOR PITUITARY

STEP 1 · TWO HORMONES

A storage locker at the end of a nerve — it manufactures nothing at all.

🔬 How the back lobe really works

supraoptic neuron → ADH paraventricular neuron → oxytocin posterior lobe (nerve endings)

🧠 "The posterior pituitary is a warehouse, not a factory." That is why a stalk injury or head trauma causes diabetes insipidus — the delivery road is cut, so the ADH never arrives.

💧 ADH — antidiuretic hormone (vasopressin)

Source: Made in the hypothalamus, released from the posterior pituitary
Target: Kidney — the collecting duct
Effect: Makes the kidney reabsorb more water. Result: a small volume of concentrated urine and more water kept in the blood. At high concentrations it also constricts vessels — hence the other name, vasopressin
Trigger: High serum osmolality (blood too concentrated) · falling blood volume or blood pressure · pain, nausea, stress, surgery, opioids, nicotine

ADH controls WATER, not sodium. Everything confusing about SIADH and DI resolves once you hold on to that.

🧠 "ADH Adds DA H₂O." Anti-diuretic = anti-peeing.

GOES DEEPER Too much ADH and too little ADH each get their own page — see NG-282 SIADH vs DI (1) and NG-283 (2).

🤱 Oxytocin

Source: Made in the hypothalamus, released from the posterior pituitary
Target: Uterine smooth muscle · myoepithelial cells around the breast alveoli
Effect: Uterine contractions in labor and after delivery (it clamps the bleeding placental site), and milk let-down — ejecting milk that prolactin already made
Trigger: Stretch of the uterus or cervix · the infant suckling at the breast

🧠 "OXytocin = the OX that pushes." It squeezes: baby out, blood loss down, milk down.

♻️ Positive feedback, drawn twice

Both loops end in an event, not in a shut-off signal: delivery of the baby, or the infant coming off the breast. That is the defining feature of positive feedback.

💊 Where you will meet these two as drugs

Desmopressin (DDAVP) — a synthetic ADH analog used to replace missing ADH in central diabetes insipidus. It is not a vasopressor — it is a water-conserving hormone, and the thing you watch for is water retention and a falling sodium, not blood pressure.
Oxytocin infusion — used to induce or augment labor and to control postpartum bleeding. Because it is chemically close to ADH, prolonged high-dose infusion can cause water intoxication with hyponatremia.

🧠 Both of these drugs can drop the sodium. Any patient on either one gets sodium checks and neuro checks.

⭐ Cut the stalk — what happens to each hormone?

Hormone	After stalk damage
ADH	Falls → diabetes insipidus, huge dilute urine output
TSH · ACTH · GH · FSH · LH	Fall → hypopituitarism
Prolactin	RISES — dopamine was the brake and the brake line is cut

🧠 Everything down except prolactin. That single oddity is a favorite exam item.

🦋

THE THYROID

STEP 2 · THE THERMOSTAT

One butterfly gland that decides how fast every cell in your body runs.

🔬 Thyroid anatomy — front and back

🧠 "Four rice grains hide behind the butterfly." The parathyroids share the address but have nothing to do with metabolism.

🔬 Inside the gland — follicles, colloid and C cells

outside the cells, in a pool of colloid COLLOID stored thyroglobulin 🟢 = parafollicular C cell → CALCITONIN 🔴 = capillary carrying T3/T4 away COLLOID thyroglobulin + iodine IODINE (I⁻) trapped from the diet T3 + T4 → blood ~90% T4, ~10% T3 TSH the order arrives ONE FOLLICLE, MAGNIFIED

Each follicle is a ring of cells around a stored pool of colloid. The thyroid is unique in the body: it banks 2–3 months of hormone outside its cells. That is why antithyroid drugs take weeks to work and why the gland can flood the body all at once in thyroid storm.

🔥 T3 & T4 — thyroid hormone

Source: Thyroid follicular cells
Target: Essentially every cell in the body
Effect: Increases metabolic rate and heat production, raises energy use and oxygen consumption, speeds heart rate and gut motility, and regulates growth and brain development — critical in the fetus and infant
Trigger: TSH from the anterior pituitary (which is triggered by TRH). Requires dietary iodine as a raw material

T4 (thyroxine) is ~90% of what is released but is relatively inactive — it is the storage form. Peripheral tissues convert it to T3, which is the potent, fast-acting one.

🧠 "T4 = the Fuel tank. T3 = the Trigger." Four is stored, three does the work.

🧪 Calcitonin — the forgettable one, mostly

Source: Thyroid parafollicular (C) cells — not the follicles
Target: Bone and kidney
Effect: Lowers blood calcium — blocks osteoclasts and increases urinary calcium loss
Trigger: Excessively high blood calcium

In adult humans calcitonin has no essential day-to-day role — people with no thyroid at all keep normal calcium. As a drug, salmon calcitonin is used in Paget disease of bone, in some cases of hypercalcemia, and occasionally in osteoporosis.

🧠 "CalciTONIN TONES calcium DOWN — and puts it back in the bone."

🚨 The two directions the thermostat can break

🔥 HYPERthyroid — too fast	🧊 HYPOthyroid — too slow
Weight loss despite eating more	Weight gain despite eating less
Heat intolerance, sweating	Cold intolerance, dry skin, hair loss
Tachycardia, palpitations, atrial fibrillation	Bradycardia, low cardiac output
Diarrhea, hyperactive bowel	Constipation
Anxious, restless, tremor, insomnia	Fatigue, slowed thinking, depression
TSH LOW, free T4 high	TSH HIGH, free T4 low (primary)

🧠 "Hyper = everything up but weight. Hypo = everything down but weight." Weight always moves the opposite way to the metabolic rate.

🚨 After a thyroidectomy — the neighbors

Airway first. Keep the head and neck supported and in neutral alignment. Check behind the neck for pooled blood — a hematoma compresses the trachea.
Hoarseness or a weak voice may signal recurrent laryngeal nerve injury. Assess the voice on a schedule.
Tetany — tingling around the mouth, numb fingertips, twitching, carpopedal spasm — means the parathyroids were bruised or removed and calcium is falling. Calcium gluconate must be immediately available.
Thyroid storm — very high fever, tachycardia, agitation — is the emergency in the first 24 hours after surgery on an untreated hyperthyroid patient.

🧠 "Bleed, Breathe, Buzz, Burn." Hematoma · airway · tetany tingling · storm.

🦴

THE PARATHYROIDS & CALCIUM

STEP 3 · THE MINERAL

Four glands the size of rice grains that quietly keep your heart and nerves firing correctly.

🔬 The calcium circuit, drawn through real organs

PTH — raises calcium calcitonin — lowers calcium calcium ion

🦴 PTH — parathyroid hormone

Source: The four parathyroid glands
Target: Bone · kidney · (indirectly) small intestine
Effect: RAISES blood calcium. Pulls calcium out of bone, makes the kidney hold calcium and excrete phosphate, and activates vitamin D so the gut absorbs more calcium from food
Trigger: LOW blood calcium

Calcium and phosphate move in opposite directions. PTH raises calcium and lowers phosphate.

🧠 "PTH = Pulls The calcium Higher." And remember it needs vitamin D to work on the gut — no vitamin D, no absorption, no matter how much PTH you make.

🚨 Low calcium — the nerves get twitchy

Calcium stabilizes nerve membranes. Take it away and nerves fire on their own.

Numbness and tingling around the mouth and in the fingertips — often the first complaint.
Trousseau sign — inflate a BP cuff above systolic; the hand goes into carpal spasm.
Chvostek sign — tap over the facial nerve in front of the ear; the cheek and lip twitch.
Severe: laryngospasm, seizures, prolonged QT.

Total serum calcium — a typical adult reference range is 9.0–10.5 mg/dL, but ranges vary by laboratory, so read the range printed beside the result. Check the albumin — a low albumin lowers the total calcium without lowering the active ionized calcium.

🧠 "CATS go numb" — Convulsions, Arrhythmias, Tetany, Spasms/Stridor. Low calcium = twitchy everything.

📉 High calcium — everything goes limp

Too much calcium and nerves stop firing.

Muscle weakness, deep tendon reflexes reduced, fatigue.
Constipation, nausea, anorexia, abdominal pain.
Confusion, lethargy, and in severe cases coma.
Polyuria and thirst; kidney stones over time; bone pain and fractures.

🧠 "Stones, bones, abdominal groans, and psychiatric overtones." Classic hyperparathyroidism in one line.

🧪 Reading a calcium panel

Pattern	What it usually means
Ca high + PTH high	Primary hyperparathyroidism — a parathyroid adenoma making PTH regardless of the calcium
Ca low + PTH high	Secondary hyperparathyroidism — the glands are working correctly but calcium stays low (classic in chronic kidney disease)
Ca low + PTH low	Hypoparathyroidism — most often accidental damage during thyroid surgery
Ca high + PTH low	Calcium is coming from somewhere else — malignancy, excess vitamin D

🧠 Same two-move rule as page 1: read the hormone, then read the boss above it.

🌙

THE CLOCK & THE SCHOOL

STEP 4 · PINEAL + THYMUS

Two small glands that are easy to skip — and easy marks if you do not.

🌙 The pineal gland and melatonin

🌙 Melatonin

Source: Pineal gland
Target: Brain — sleep and circadian centers
Effect: Causes sleepiness at night and sets the day–night rhythm
Trigger: Darkness / absence of bright light. Bright light shuts it off

🧠 "MELatonin comes out when the lights are MELlow."

🛡️ The thymus and thymosin

🛡️ Thymosin

Source: Thymus, in the upper chest behind the sternum
Target: Immature T lymphocytes
Effect: Drives the development and maturation of T cells — the backbone of cell-mediated immunity
Trigger: Not well established. Activity is highest in childhood and falls after puberty

🧠 "THYmus trains T cells." Both start with T. It is largest in a child and mostly fat by middle age.

📋 Part 2 at a glance

Hormone	Source	Effect on tissue	Stimulus for release
ADH	Posterior pituitary (made in hypothalamus)	Kidney reabsorbs water → small amount of concentrated urine	High osmolality · falling BP/volume · pain
Oxytocin	Posterior pituitary (made in hypothalamus)	Uterine contraction · milk let-down	Stretch of uterus/cervix · infant suckling
T3 / T4	Thyroid follicles	↑ metabolism, temperature, energy; regulates growth & development	TSH (needs dietary iodine)
Calcitonin	Thyroid C cells	Lowers blood calcium; no essential role in adults; used in Paget disease	Excessively high blood calcium
PTH	Parathyroid ×4	Raises blood calcium via bone, kidney and gut	Low blood calcium
Melatonin	Pineal gland	Sleepiness at night	Darkness / lack of bright light
Thymosin	Thymus	T-lymphocyte development; most active in childhood	Not well established

⚡

QUICK RECALL

SAY IT OUT LOUD

💧 ADH Adds DA H₂OLess urine, more concentrated. It controls water, not salt.

🦋 T4 stores, T3 worksThyroid needs iodine. TSH moves the opposite way to the thyroid.

🦴 PTH Pulls it HigherLow Ca → PTH ↑. Post-thyroidectomy tingling = watch for tetany.

🧠 Prolactin makes, oxytocin pushesTwo hormones, two lobes, two jobs.

⚠️ Five traps from this page

Desmopressin is not a vasopressor. It is a synthetic ADH analog given to replace missing ADH. Watch sodium and fluid status, not blood pressure.
Calcitonin is not the mirror of PTH in real life. PTH is essential; calcitonin is largely dispensable in adults.
The parathyroids are separate glands. They only live on the thyroid — they have no role in metabolism.
The thymus shrinks with age. It is the one endocrine organ that is supposed to disappear.
Tetany after a thyroidectomy is a calcium problem, not a thyroid one. Assess with Trousseau and Chvostek, and check that calcium gluconate is on hand.

🔗 Where this goes next

NG-278 · Hall of Fame I — hypothalamus, anterior pituitary, pancreas.
NG-280 · Hall of Fame III — adrenal cortex and medulla, ovaries, testes.
NG-281 · Pituitary Disorders — anterior lobe excess and deficiency.
NG-282 · SIADH vs DI (1) — the ADH page, in full.

🎯 Cover & check — 10 rapid-fire questions

Q1: Which two hormones come out of the posterior pituitary, and where are they made?

ADH and oxytocin. Both are manufactured in the hypothalamus (supraoptic and paraventricular nuclei) and travel down inside nerve axons to be stored in the posterior lobe.

Q2: What happens to urine volume and concentration when ADH rises?

Volume falls and concentration rises — a small amount of dark, concentrated urine with a high specific gravity, because water is being pulled back into the blood.

Q3: A postpartum patient is on a prolonged oxytocin infusion and becomes confused with a sodium of 126. What happened?

Water intoxication. Oxytocin is chemically similar to ADH, so a long high-dose infusion can cause water retention and dilutional hyponatremia. Report it, expect the infusion to be reassessed, and institute seizure precautions.

Q4: Why does the thyroid store hormone outside its cells?

It banks 2–3 months' worth of thyroid hormone bound to thyroglobulin in the colloid. Practically, that means antithyroid medication takes weeks to show an effect, and a stressed gland can release a huge stored load at once in thyroid storm.

Q5: Which cells make calcitonin, and what does it do?

Parafollicular C cells of the thyroid — not the follicular cells. It lowers blood calcium by inhibiting osteoclasts and increasing urinary calcium loss. It is released when calcium is excessively high.

Q6: Name PTH's three routes for raising calcium.

Bone (release stored calcium via osteoclasts), kidney (reabsorb calcium, excrete phosphate, activate vitamin D), and gut (absorb more dietary calcium — but only via activated vitamin D).

Q7: Your patient is 6 hours post-thyroidectomy and reports tingling around the mouth. What do you do?

Suspect hypocalcemia from parathyroid injury. Assess for Trousseau and Chvostek signs, check the airway and voice, notify the provider, obtain a calcium level as ordered, institute seizure precautions and confirm calcium gluconate is available at the bedside.

Q8: A patient has a calcium of 7.4 and a PTH that is high. Is the parathyroid the problem?

No — this is secondary hyperparathyroidism. The glands are responding appropriately to a low calcium. The commonest cause is chronic kidney disease, where the kidney cannot activate vitamin D or excrete phosphate.

Q9: Why do older hospitalized patients so often lose their sleep–wake cycle?

Melatonin is released only in darkness. Continuous light, night-time vitals, alarms and no daylight exposure flatten the melatonin curve, disrupting the circadian rhythm and contributing to hospital delirium. Cluster care, dim lights at night, open blinds in the morning.

Q10: Which endocrine gland is largest in childhood and mostly fat by middle age, and why?

The thymus. Its job — training T lymphocytes under the influence of thymosin — is done mostly before puberty, after which it involutes and is replaced by fat.