Unit 7 Calcium Homeostasis

Question 1

What are the three major hormones that regulate calcium balance?
a) Insulin, cortisol, glucagon
b) PTH, calcitriol (vitamin D), calcitonin
c) Epinephrine, GH, ACTH
d) Aldosterone, thyroid hormone, estrogen

Answer 1

b) PTH, calcitriol (vitamin D), calcitonin

Explanation: These three hormones regulate calcium levels by acting on bone, kidney, and intestine.

Question 2

What is the main function of parathyroid hormone (PTH)?
a) Promote calcium excretion
b) Stimulate osteoblasts
c) Increase blood calcium by bone resorption and renal reabsorption
d) Decrease vitamin D synthesis

Answer 2

c) Increase blood calcium by bone resorption and renal reabsorption

Explanation: PTH raises plasma Ca²⁺ by stimulating osteoclasts and increasing reabsorption in the kidney.

Question 3

How is calcitriol (active vitamin D) produced?
a) Activated from vitamin D in liver and kidney via PTH stimulation
b) Made in the stomach from dietary calcium
c) Synthesized in the adrenal cortex
d) Made in bone marrow from cholesterol

Answer 3

a) Activated from vitamin D in liver and kidney via PTH stimulation

Explanation: PTH promotes conversion of vitamin D to calcitriol in the kidney, increasing Ca²⁺ absorption in the gut.

Question 4

What does calcitonin do?
a) Raises blood calcium
b) Stimulates bone resorption
c) Lowers blood calcium by inhibiting osteoclasts
d) Promotes calcium absorption in intestines

Answer 4

c) Lowers blood calcium by inhibiting osteoclasts

Explanation: Calcitonin is secreted by the thyroid and acts as a counter-regulatory hormone to PTH.

Question 5

Where is the majority of calcium in the body stored?
a) Blood plasma
b) Liver
c) Intracellular cytosol
d) Bone matrix

Answer 5

d) Bone matrix

Explanation: About 99% of the body’s calcium is stored in the hydroxyapatite crystals of bone.