The fastest way to lose marks in PHS 220 endocrine physiology is to memorise each gland as a separate list and miss the one pattern that ties them together. Almost every hormone in the course is controlled by a feedback loop, acts through a specific receptor class, and causes predictable disease when it is either too high, too low, or ignored by its target. Once you read the endocrine system as a set of control loops rather than a pile of facts, the thyroid, the parathyroids, the pancreas and the adrenal glands all start to follow the same logic, and the exam questions that used to feel random become answerable from first principles. This page is a student-written study companion for the endocrine block of PHS 220 Physiology, the compulsory second-semester course for ABUAD 200 Level Pharmacy students.
This guide brings together everything the endocrine block covers in one place: the general principles of hormone signalling, the thyroid gland, calcium and the parathyroids, the endocrine pancreas, and the adrenal glands. The summaries below turn the syllabus into plain-English notes, with original practice questions and worked answers so you can check that each idea has stuck, and callout boxes for the high-yield clinical traps examiners like to set. The full illustrated workbook, with every comparison table and labelled diagram, sits in the reader at the end of this page as a free bonus to the notes here.
- Course: PHS 220 – Physiology (Endocrine block)
- College / Department: College of Medicine and Health Sciences – Department of Physiology
- Level / Semester: 200 Level, Second Semester
- Topics covered: General principles of endocrine physiology (signalling, hormone classes, receptors, feedback, rhythms, the hypothalamo-pituitary axis, disease patterns), thyroid physiology and disorders, parathyroid, calcium and bone homeostasis, pancreatic endocrine physiology, and adrenal physiology and disorders
- Best for: Continuous assessment + second-semester exam revision
Topics Covered in the PHS 220 Endocrine Block
1. General Principles of Endocrine Physiology
Endocrine physiology is the study of how the body keeps a stable internal environment using chemical messengers called hormones, which are released into the blood and act on distant tissues that carry the matching receptor. Hormones work in tiny concentrations yet reach almost everything: metabolism, growth, reproduction, fluid and electrolyte balance, and the stress response. They also never act alone, because the endocrine system is woven into the nervous and immune systems through links such as the hypothalamo-pituitary axis and the way cortisol suppresses inflammation. Chemical signalling itself comes in several ranges: endocrine (through the bloodstream), paracrine (onto neighbouring cells), autocrine (back onto the same cell), neurocrine (along a neuron), and juxtacrine (by direct cell contact).
Hormones fall into three chemical classes, and the chemistry decides everything else about them. Peptide and protein hormones (insulin, glucagon, GH, ACTH, PTH) are water soluble, act on surface receptors, and signal fast through second messengers such as cAMP. Steroid hormones (cortisol, aldosterone, the sex steroids, calcitriol) are made from cholesterol, are lipid soluble, cross the membrane to bind intracellular receptors, and act slowly but for a long time by changing gene transcription. Amine hormones sit in between: the catecholamines behave like water-soluble hormones, while the thyroid hormones behave like steroids. Receptors match this split, from the GPCR families (Gs raising cAMP, Gi lowering it, Gq using IP3 and calcium) and receptor tyrosine kinases for insulin, through to the nuclear receptors that lipophilic hormones use. Receptor number is not fixed either: prolonged exposure down-regulates receptors (the basis of tachyphylaxis), while low hormone levels up-regulate them. Exam tip: tie each hormone to its class, its receptor type and its speed of action, because a single line such as "insulin uses a receptor tyrosine kinase and acts within minutes" answers several question styles at once.
Control comes from feedback. Negative feedback dominates, so the end-product of a cascade shuts off the steps above it, as when cortisol suppresses both CRH and ACTH. Positive feedback is rarer but decisive, the classic example being the mid-cycle LH surge, where high oestrogen flips the pituitary from suppression to amplification and triggers ovulation. Many hormones are also released in pulses or on a circadian rhythm set by the suprachiasmatic nucleus, which is why cortisol peaks in the early morning and why continuous rather than pulsatile GnRH paradoxically switches the axis off. The command centre for all of this is the hypothalamo-pituitary axis: the hypothalamus sends releasing and inhibiting hormones down a private portal blood supply to the anterior pituitary, which in turn sends trophic hormones (TSH, ACTH, GH, FSH, LH, prolactin) to the peripheral glands, while the posterior pituitary simply stores and releases hypothalamic ADH and oxytocin. Exam tip: learn the ratio of trophic hormone to end-hormone, because it localises any endocrine lesion. Primary gland failure raises the trophic hormone, while secondary (pituitary) failure lowers it, and the same rule reads the HPT, HPA and HPG axes.
2. Thyroid Physiology and Disorders
The thyroid is a butterfly-shaped gland in the anterior neck whose job is to set the pace of basal metabolism in almost every cell. Its functional unit is the follicle, a sphere of thyrocytes surrounding a store of colloid (thyroglobulin), with parafollicular C-cells scattered between follicles making calcitonin. Hormone synthesis is a multi-step assembly line that depends on dietary iodine: iodide is trapped by the sodium-iodide symporter, moved into colloid by pendrin, oxidised by thyroid peroxidase, added to tyrosine residues on thyroglobulin (organification), and then coupled, so that MIT plus DIT gives T3 and DIT plus DIT gives T4. The gland stores two to three months of hormone on thyroglobulin, which is why antithyroid drugs take weeks to work. This pathway is also a drug map: propylthiouracil and carbimazole block thyroid peroxidase, radioiodine is taken up by the symporter and destroys follicular cells, and a large iodine load transiently shuts synthesis down through the protective Wolff-Chaikoff effect.
Most thyroid hormone circulates bound to plasma proteins, chiefly thyroxine-binding globulin, and only the free fraction is active. T4 is the main secreted form and acts as a prohormone, while T3 is three to four times more potent and is the true active hormone at the nuclear receptor. This matters clinically: pregnancy and oestrogen raise binding globulin, so total T4 rises while free T4 and the patient stay normal, which is why you interpret total hormone against binding proteins or measure free hormone directly. Thyroid hormone raises the basal metabolic rate and acts on nearly every system, increasing heart rate and cardiac output, sharpening the nervous system, speeding the gut, and being essential for brain development in the fetus. Secretion runs on a negative-feedback loop: hypothalamic TRH drives pituitary TSH, TSH drives the thyroid, and rising T3 and T4 suppress both. Exam tip: read every thyroid disorder as a mismatch between TSH and free T4. Primary hypothyroidism (Hashimoto) shows high TSH with low free T4, Graves disease shows suppressed TSH with high hormone and eye signs, and secondary disease shows both moving the same way. Thyroid storm, a life-threatening flare with fever, severe tachycardia and agitation, is the one emergency to recognise on sight.
3. Parathyroid, Calcium and Bone Homeostasis
The four parathyroid glands are tiny but essential, because complete loss causes fatal hypocalcaemic tetany within days. Calcium itself is kept in a very narrow range, since it drives muscle contraction, neurotransmitter release, the cardiac action potential, clotting and hormone secretion. Only the ionised (free) fraction, about half of total calcium, is physiologically active, and it shifts with pH, so acidosis raises ionised calcium and alkalosis lowers it. Because much of the rest is bound to albumin, a low albumin makes total calcium look falsely low, and you correct for it before acting on a result. Three hormones acting on three organs (bone, kidney and gut) set the serum level: parathyroid hormone and calcitriol raise calcium, while calcitonin lowers it.
Parathyroid hormone is the main minute-to-minute regulator. The chief cells sense a fall in ionised calcium through the calcium-sensing receptor and release PTH, which raises calcium by three routes: it drives bone resorption (indirectly, because osteoblasts carry the receptor and release RANKL to activate osteoclasts), it makes the kidney retain calcium while wasting phosphate, and it stimulates renal 1-alpha-hydroxylase to make active vitamin D. A subtle but heavily tested point is that intermittent PTH is anabolic to bone (the basis of teriparatide for osteoporosis) whereas continuous PTH is catabolic (as in primary hyperparathyroidism). Vitamin D is activated in three steps across skin, liver and kidney to become calcitriol, which mainly boosts calcium and phosphate absorption from the gut. Calcitonin, from thyroid C-cells, is the physiological brake that inhibits osteoclasts, though it plays only a minor role in adult humans. Exam tip: to read a calcium disorder, look at PTH, calcium and phosphate together. Primary hyperparathyroidism gives high calcium with high PTH and low phosphate, while malignancy gives high calcium with a suppressed PTH. Learn the two bedside signs of hypocalcaemia, Chvostek and Trousseau, and the "bones, stones, groans and psychic moans" summary of hypercalcaemia.
4. Pancreatic Endocrine Physiology
The pancreas is mostly an exocrine digestive gland, but the 1 to 2% that is endocrine, the islets of Langerhans, controls blood glucose. The islets hold beta cells (insulin), alpha cells (glucagon), delta cells (somatostatin, which inhibits both), and smaller populations making pancreatic polypeptide and ghrelin. Insulin is the hormone of the fed state. A rise in blood glucose is the primary trigger: glucose enters the beta cell through GLUT-2, raises the ATP-to-ADP ratio, closes potassium channels, depolarises the cell, and lets calcium in to drive insulin release. Because insulin and C-peptide are secreted in equal amounts, C-peptide is measured clinically to judge how much insulin a patient is making themselves. Insulin acts through a receptor tyrosine kinase to promote storage everywhere: the liver makes glycogen and stops gluconeogenesis, muscle takes up glucose through GLUT4 and builds protein, and fat stores lipid and stops breaking it down.
Glucagon is the mirror image, the main counter-regulatory hormone of the fasting state. It is released when glucose is low and acts almost entirely on the liver to raise blood glucose through glycogenolysis and gluconeogenesis, and to make ketones as an alternative fuel. Defending blood glucose is so important that several other hormones back glucagon up: adrenaline acts fast, while cortisol and growth hormone act over hours to raise glucose and reduce insulin sensitivity. This counter-regulatory system is exactly what fails in diabetic hypoglycaemia, which is why the topic matters clinically. Exam tip: memorise the glucose-sensing sequence in the beta cell (GLUT-2, ATP rise, potassium channel closes, depolarisation, calcium entry, exocytosis), because it is a favourite short-answer chain and it also explains how sulfonylurea drugs work by closing the same channel.
5. Adrenal Physiology and Disorders
Each adrenal gland is really two organs in one. The cortex has three zones, and a simple memory aid runs from outside in: the glomerulosa makes the mineralocorticoid aldosterone (salt), the fasciculata makes the glucocorticoid cortisol (sugar), and the reticularis makes androgens (sex). The medulla at the core is a modified sympathetic ganglion that makes the catecholamines adrenaline and noradrenaline. Cortisol, which supplies most glucocorticoid activity, is controlled by the HPA axis (CRH drives ACTH drives cortisol, with early-morning peaks) and does a great deal: it raises blood glucose, breaks down protein and fat stores, is strongly anti-inflammatory and immunosuppressive, and is permissive for vascular tone and catecholamine action. Its disorders bookend each other, with Cushing syndrome from cortisol excess (central obesity, moon face, striae, hypertension, high glucose) and Addison disease from cortisol and aldosterone deficiency (fatigue, weight loss, low sodium, high potassium, pigmentation).
Aldosterone, made only in the glomerulosa, is the main regulator of sodium, extracellular volume and blood pressure. Its strongest driver is angiotensin II through the renin-angiotensin system, with a rise in potassium as a second potent stimulus, while ACTH is only permissive. Acting on the distal nephron it reabsorbs sodium and water and secretes potassium and hydrogen ions, so its excess (Conn syndrome) causes hypertension with a low potassium and suppressed renin. The adrenal androgens are weak but matter in women as a source of libido-supporting hormone, and congenital adrenal hyperplasia links the whole cortex together, because a 21-hydroxylase block starves cortisol and aldosterone while diverting the pathway into androgen excess. Finally, a catecholamine-secreting medullary tumour, the phaeochromocytoma, produces episodic hypertension, headache and sweating, and is treated with alpha-blockade before beta-blockade to avoid a hypertensive crisis. Exam tip: anchor the cortex with the "salt, sugar, sex, deeper you go the sweeter it gets" aid, and always pair each cortical hormone with both its excess and its deficiency, because adrenal questions almost always test the two ends of one axis.
Sample Practice Questions (With Answers)
Here are a few representative questions across the endocrine block, written in our own words, with the reasoning explained so you understand the why, not just the result:
Q1. A patient has a low serum thyroxine. Explain how a single TSH result tells you whether the problem is in the thyroid gland or in the pituitary.
Answer: Use the trophic-to-end-hormone rule. TSH is the trophic hormone and thyroxine is the end-hormone. If the thyroid gland itself has failed (primary hypothyroidism), it can no longer feed back to suppress the pituitary, so TSH rises: low T4 with high TSH. If the pituitary has failed (secondary hypothyroidism), it cannot drive the thyroid in the first place, so TSH is low or inappropriately normal: low T4 with low TSH. The direction TSH moves relative to T4 localises the lesion, and the same logic reads the HPA and HPG axes.
Q2. Teriparatide is a form of parathyroid hormone used to strengthen bone, yet the same hormone in primary hyperparathyroidism weakens it. How can one hormone do both?
Answer: The difference is the pattern of exposure, not the molecule. Given intermittently, as a once-daily injection, PTH favours osteoblast activity and is a net anabolic (bone-building) signal, which is how teriparatide works. When PTH is continuously elevated, as in an autonomous parathyroid adenoma, it drives sustained osteoclastic resorption through the RANKL pathway and a net loss of bone, seen in severe cases as osteitis fibrosa cystica. Intermittent builds, continuous breaks down.
Q3. Why is C-peptide, rather than insulin itself, measured to judge how much insulin a patient is producing?
Answer: Insulin and C-peptide are cleaved from the same precursor (proinsulin) inside the secretory granule and are released into the blood in equal amounts, so C-peptide is a faithful marker of the beta cell's own output. The advantage is that manufactured insulin used for treatment contains no C-peptide. In a patient who is injecting insulin, a high measured insulin with a low C-peptide points to an external source, while a high C-peptide confirms the pancreas is genuinely over-secreting, for example from an insulinoma.
Q4. A patient with Conn syndrome has high blood pressure and a low serum potassium. Link both findings to the action of a single hormone.
Answer: Both come from excess aldosterone acting on the principal cells of the distal nephron. Aldosterone increases sodium reabsorption, and water follows the sodium, expanding extracellular volume and raising blood pressure. At the same time it drives potassium secretion into the urine, which lowers serum potassium. Because the high aldosterone is autonomous, it also suppresses renin, so the classic pattern is hypertension with hypokalaemia and a low renin.
Q5. A pregnant woman has a raised total T4 but is clinically euthyroid with a normal free T4. Explain the discrepancy.
Answer: Only the free fraction of thyroid hormone is active, and it is the free fraction that feedback keeps normal. Pregnancy and oestrogen raise thyroxine-binding globulin, so more hormone is carried bound in the plasma and the total T4 rises. The thyroid simply adjusts to keep the free T4 in range, so the woman remains euthyroid. This is why total T3 and T4 must be interpreted against binding proteins, and why measuring free hormone avoids the trap.
How to Study the Endocrine Block Effectively
- Learn the three hormone classes first (peptide, steroid, amine) and hang every hormone off the right one, because the class predicts its receptor, its speed and where it is made.
- Draw each axis as a three-level loop (hypothalamus, pituitary, gland) and mark the negative-feedback arrows, then use the trophic-to-end-hormone ratio to localise any lesion.
- For calcium, keep a single table of PTH, calcitriol and calcitonin against their effect on bone, kidney and gut, and always read calcium, PTH and phosphate together rather than one at a time.
- Memorise the beta-cell glucose-sensing chain as one sequence, since it recurs in questions and explains sulfonylurea drugs.
- Anchor the adrenal cortex with the salt, sugar, sex memory aid and pair every hormone with both its excess and its deficiency.
- Read the topic summaries here to build the framework, then work through the full illustrated workbook in the reader below and attempt the practice questions from memory before your class test.
Download the Full PHS 220 Endocrine Study Guide
The notes above stand on their own, but if you want the complete endocrine block in one place, the full PHS 220 Endocrine Physiology illustrated study guide is loaded in the reader just below, with the comparison tables for hormone classes, receptors and feedback, the step-by-step thyroid synthesis pathway, the calcium-regulating hormones side by side, and the labelled callout boxes for clinical pearls, drug targets and emergencies. Read it right here on the page, or save a copy so you can keep drilling the axes, tables and disorders offline in the days before your test.
Frequently Asked Questions
Is this PHS 220 endocrine material free?
Yes, completely. There is no fee, sign-up, or paywall anywhere on this page. The endocrine notes, practice questions, and the downloadable study guide are open to any student who needs a hand with the physiology of the thyroid, parathyroids, pancreas and adrenal glands.
Does this guide cover the whole endocrine block or just one gland?
It covers the whole block in one place. This single guide brings together general endocrine principles, the thyroid, calcium and the parathyroids, the endocrine pancreas, and the adrenal glands, which is why it replaces several shorter topic pages that used to be separate.
What is the fastest way to revise the endocrine block before a test?
Work from the axes and the comparison tables. Sketch each hypothalamo-pituitary loop from memory, then cover one column of a table and recall it from the other, focusing on the feedback rules, the calcium-regulating hormones, and the paired excess-and-deficiency disorders. Then attempt the practice questions above from memory, because active recall is close to how the course is examined.
Will these exact questions appear in my exam?
No. This is an original revision set written from scratch to rehearse the reasoning and the phrasing, not a forecast of what your lecturer will set. Use it to practise, then sit your test on the specimens, diagrams and outline your own course actually covers.
About this resource: All summaries, explanations, study tips, and practice questions on this page were written, paraphrased, and adapted by the EverythingABUAD student team to support exam revision. This is an original study aid, not an official ABUAD document, and it is not a prediction of any future exam. Always cross-check with your lecturer's current course outline.
Written by the Everything ABUAD Team
Current students at Afe Babalola University, Ado-Ekiti. Guides are checked against the official ABUAD portal and campus notices, and confirmed with department and course reps before publishing.
