Welcome back to the EverythingABUAD study portal! This page is a complete, student-written study companion for PHS 220 – Parathyroid Glands & Calcium Homeostasis, prepared for ABUAD 200 Level Pharmacy students (Second Semester).
Calcium balance is controlled by three hormones acting on three organs, and exam questions almost always test how they pull together. The classic trap is muddling which hormone raises calcium and which lowers it. Below we break the system down in plain language, flag the recurring comparisons, and give you original practice questions with worked answers. The full study guide is available in the interactive reader at the end as a free bonus.
- Course: PHS 220 – Physiology II
- College / Department: College of Pharmacy / Pharmacy
- Level / Semester: 200 Level, Second Semester
- Topics covered: Importance of calcium, calcium homeostasis, PTH, calcitonin, calcitriol (vitamin D), calcium disorders
- Best for: Continuous assessment + final exam revision
Topics Covered in PHS 220: Calcium Homeostasis
1. Why Calcium Matters
Plasma calcium is held in a narrow range because it controls nerve and muscle excitability, blood clotting, and acts as an intracellular signal. Exam tip: link low calcium to increased excitability (tetany) and high calcium to reduced excitability (lethargy, weakness) — it makes the symptoms memorable.
2. The Calcium Homeostasis Overview
Three hormones (PTH, calcitriol, calcitonin) act on three organs (bone, kidney, gut) to keep calcium stable. Exam tip: draw the triangle — hormone, target organ, effect on calcium — before you answer any calcium question; it organises everything.
3. Parathyroid Hormone (PTH)
PTH is the main calcium-raising hormone. It releases calcium from bone, increases reabsorption in the kidney, and activates vitamin D to boost gut absorption. Exam tip: remember PTH also lowers phosphate (by increasing renal phosphate excretion) — calcium up, phosphate down is a recurring pattern.
4. Calcitriol (Active Vitamin D)
Calcitriol is the active form of vitamin D, produced by hydroxylation in the liver then the kidney (the step PTH stimulates). It mainly increases calcium and phosphate absorption from the gut. Exam tip: know the two activation steps and which organ does each — liver first (25-OH), then kidney (1,25-OH).
5. Calcitonin
Calcitonin, from the thyroid C-cells, lowers calcium by inhibiting bone breakdown — the physiological opposite of PTH, though its role in humans is comparatively minor. Exam tip: use calcitonin as the 'calcium-lowering' counterweight to PTH when a question asks you to compare them.
6. Disorders of Calcium Regulation
Hyperparathyroidism raises calcium (stones, bones, groans, psychiatric moans); hypoparathyroidism lowers it (tetany, tingling, Chvostek/Trousseau signs). Exam tip: tie each disorder back to PTH level and to the calcium/phosphate pattern it produces.
Sample Practice Questions (With Answers)
Here are a few representative questions, written in our own words, with the reasoning explained so you understand the why — not just the answer:
Q. Name the three hormones that regulate plasma calcium and state whether each raises or lowers it.
Answer: PTH raises calcium, calcitriol (active vitamin D) raises calcium, and calcitonin lowers calcium. PTH and calcitriol are the dominant players; calcitonin's role in humans is comparatively minor.
Q. How does PTH affect plasma phosphate, and why?
Answer: PTH lowers plasma phosphate. While it mobilises both calcium and phosphate from bone, it strongly increases phosphate excretion in the kidney, so the net effect is a fall in phosphate alongside a rise in calcium.
Q. Which organ performs the final, PTH-stimulated step in activating vitamin D?
Answer: The kidney. Vitamin D is first hydroxylated in the liver to 25-hydroxyvitamin D, then the kidney performs the 1-hydroxylation to form active calcitriol (1,25-dihydroxyvitamin D) — the step PTH stimulates.
How to Study PHS 220 (Calcium Homeostasis) Effectively
- Draw the three-hormone / three-organ triangle before answering any calcium question.
- Anchor the symptoms to excitability: low calcium → tetany, high calcium → lethargy.
- Remember the reciprocal calcium/phosphate movement that PTH produces.
- Understand the concepts here, then self-test with the workbook before your exam.
Download the Full PHS 220 Calcium Homeostasis Study Guide
Ready to revise? Use the interactive reader below to read the full calcium homeostasis study guide with diagrams and worked detail. You can read it directly on the page or download it for offline revision before your exam.
Frequently Asked Questions
Is this PHS 220 material free?
Yes — every resource on EverythingABUAD is completely free for ABUAD students.
Does this cover the full PHS 220 syllabus?
This guide covers the calcium homeostasis portion of the PHS 220 syllabus. Work through it alongside the other PHS 220 topic guides on EverythingABUAD, and always cross-check against your lecturer’s current outline.
Will these exact questions appear in my exam?
No. These are original practice questions written for revision only and are not a prediction of the actual exam.
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.
