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Quizzes > Health & Medicine

Which Hormone Opposes Parathyroid Hormone? Quiz

Quick, free quiz on calcitonin vs parathyroid hormone. Instant results.

Editorial: Review CompletedCreated By: Lina MathildeUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper cut style illustration for endocrine quiz question on hormone opposing parathyroid hormone on golden yellow background

This quick quiz helps you identify which hormone opposes parathyroid hormone and check your understanding of calcium control. Use it to spot gaps before a test, then try our endocrine system quiz and compare hormone actions in the hormone type quiz. For more practice on structure and function, see the endocrine system assessment quiz.

Which hormone is the primary physiological antagonist to parathyroid hormone?
Calcitonin
Aldosterone
Calcitriol
Insulin
Calcitonin, produced by the parafollicular C cells of the thyroid gland, lowers blood calcium by inhibiting osteoclast-mediated bone resorption. This effect opposes parathyroid hormone, which increases blood calcium by stimulating osteoclast activity. While calcitriol also influences calcium balance, it works in concert with PTH to raise calcium levels.
Which cells in the thyroid gland secrete the hormone that opposes parathyroid hormone?
Chief cells of parathyroid
Follicular cells
Oxyphil cells
Parafollicular C cells
Parafollicular C cells, also known as C cells, are located adjacent to the thyroid follicles and are responsible for producing calcitonin. This hormone lowers blood calcium by inhibiting osteoclasts, opposing the action of parathyroid hormone. The other cells listed do not secrete calcitonin.
What effect does this hormone have on osteoclast activity?
Inhibits osteoclast activity
Stimulates osteoclast activity
Converts osteoclasts to osteoblasts
Promotes osteoclast differentiation
Calcitonin binds to receptors on osteoclasts and inhibits their bone-resorbing activity, leading to decreased release of calcium into the bloodstream. This inhibition directly opposes parathyroid hormone, which stimulates osteoclast-mediated bone resorption. By reducing osteoclast activity, calcitonin helps lower elevated calcium levels.
Which gland secretes calcitonin?
Adrenal gland
Parathyroid gland
Pituitary gland
Thyroid gland
Calcitonin is produced by the parafollicular C cells of the thyroid gland. This is distinct from the parathyroid glands, which produce parathyroid hormone. The adrenal and pituitary glands do not produce calcitonin.
What is the effect of calcitonin secretion on blood calcium levels?
No change in blood calcium
Fluctuates blood calcium cyclically
Decreases blood calcium
Increases blood calcium
Calcitonin lowers blood calcium levels by inhibiting osteoclasts and promoting calcium deposition in bone. This action opposes that of parathyroid hormone, which raises blood calcium levels. The net result of calcitonin release during hypercalcemia is a decrease in circulating calcium.
Which physiological condition most directly stimulates the release of calcitonin?
Hypophosphatemia
Alkalosis
Hypercalcemia
Hypocalcemia
Elevated blood calcium levels (hypercalcemia) directly stimulate the parafollicular C cells of the thyroid to secrete calcitonin. This provides a negative feedback mechanism to lower calcium and counteract parathyroid hormone. Hypocalcemia and the other conditions do not directly trigger calcitonin release.
How does calcitonin affect renal handling of calcium?
Decreases renal calcium reabsorption
Has no effect on renal calcium
Increases renal calcium reabsorption
Converts calcium to phosphate
Calcitonin decreases renal calcium reabsorption in the kidneys, leading to increased urinary excretion of calcium. This effect complements its inhibition of bone resorption to lower blood calcium. In contrast, parathyroid hormone increases renal calcium reabsorption.
Which process is inhibited by calcitonin but stimulated by parathyroid hormone?
Intestinal calcium absorption
Bone osteoblast activity
Bone resorption
Renal phosphate excretion
Calcitonin inhibits bone resorption by acting on osteoclasts, while parathyroid hormone stimulates this process to increase blood calcium. Renal phosphate excretion and intestinal calcium absorption are more directly influenced by PTH and vitamin D rather than calcitonin.
Which of the following hormones does NOT oppose the action of parathyroid hormone?
Calcitonin
Vitamin D (Calcitriol)
Osteoprotegerin
FGF23
Calcitriol (active vitamin D) works in synergy with parathyroid hormone to raise blood calcium by increasing intestinal absorption and bone resorption. Calcitonin, osteoprotegerin, and FGF23 all counteract aspects of PTH's effects.
Why is calcitonin secretion increased after a calcium-rich meal?
To stimulate vitamin D activation
To decrease urinary calcium excretion
To prevent a rapid rise in blood calcium
To enhance parathyroid hormone release
After ingesting a calcium-rich meal, blood calcium levels rise, triggering calcitonin release. This helps blunt the postprandial hypercalcemia by inhibiting bone resorption and increasing renal calcium excretion. It is part of the short-term regulatory mechanism opposing PTH.
What type of hormone is calcitonin based on its chemical nature?
Peptide hormone
Steroid hormone
Amine hormone
Eicosanoid
Calcitonin is a peptide hormone composed of 32 amino acids. It is produced as a prohormone that is cleaved to its active form. This differentiates it from steroid and amine hormones.
Calcitonin binds to which type of receptor on target cells?
G protein-coupled receptor
Tyrosine kinase receptor
Intracellular nuclear receptor
Ion channel receptor
The calcitonin receptor is a G protein-coupled receptor (GPCR) expressed on osteoclasts and other cells. Upon binding calcitonin, it activates the Gs protein-cAMP signaling pathway to exert its effects.
What is the expected effect of calcitonin on osteoclast differentiation?
Converts osteoclasts into osteoblasts
Stimulates differentiation of osteoclast precursors
Inhibits differentiation of osteoclast precursors
Has no effect on osteoclast differentiation
Calcitonin inhibits not only the activity of mature osteoclasts but also the differentiation of osteoclast precursors, reducing the number of bone-resorbing cells. This action opposes parathyroid hormone, which promotes osteoclast formation.
Which G protein subunit is primarily involved in calcitonin receptor signaling in osteoclasts?
Gs
Gi
Gq
G12/13
Calcitonin receptor activation in osteoclasts couples predominantly through the Gs ?-subunit, leading to increased cyclic AMP levels and downstream inhibition of bone resorption. Gi would decrease cAMP, Gq mobilizes calcium, and G12/13 is less relevant.
In the kidney, calcitonin decreases calcium reabsorption in which nephron segment?
Distal convoluted tubule
Proximal convoluted tubule
Loop of Henle
Collecting duct
Calcitonin reduces calcium reabsorption primarily in the distal convoluted tubule, increasing urinary excretion of calcium. Parathyroid hormone, by contrast, enhances calcium reabsorption in this segment.
Elevated calcitonin levels in the bloodstream serve as a clinical marker for which type of carcinoma?
Papillary thyroid carcinoma
Follicular thyroid carcinoma
Medullary thyroid carcinoma
Anaplastic thyroid carcinoma
Medullary thyroid carcinoma originates from parafollicular C cells, which secrete calcitonin. High levels of calcitonin in the blood can indicate this tumor. The other thyroid cancers do not produce calcitonin.
What is the approximate half-life of calcitonin in human circulation?
1 hour
1 minute
10 minutes
24 hours
Calcitonin has a relatively short plasma half-life of about 10 minutes, which allows for rapid adjustment of its levels in response to changing blood calcium. This is much shorter than many other peptide hormones.
What effect does calcitonin have on phosphate excretion in the kidneys?
Decreases phosphate excretion
No effect on phosphate
Increases phosphate excretion
Converts phosphate to calcium
Calcitonin increases urinary phosphate excretion by reducing phosphate reabsorption in the renal tubules. This contributes to lowering serum phosphate levels alongside its calcium-lowering effects.
Unlike parathyroid hormone, calcitonin does NOT directly influence which of the following enzymes?
Renal 1?-hydroxylase
Adenylyl cyclase
Osteoclast proton pumps
Phospholipase C
Calcitonin does not directly affect renal 1?-hydroxylase, the enzyme responsible for activating vitamin D. In contrast, parathyroid hormone stimulates this enzyme. Calcitonin does interact with adenylyl cyclase via its receptor and impacts osteoclast proton pumps indirectly.
In which of the following scenarios would you expect calcitonin levels to be elevated?
Low dietary calcium intake
Hypercalcemia
Metabolic acidosis
Hypocalcemia
Calcitonin release is triggered by elevated blood calcium (hypercalcemia). Hypocalcemia and low calcium intake would suppress its secretion, while metabolic acidosis does not directly stimulate calcitonin.
The active form of human calcitonin is comprised of how many amino acids?
45
60
32
25
Human calcitonin is a 32-amino acid peptide hormone. It is produced from a larger prohormone and undergoes processing and C-terminal amidation to achieve its active form.
Calcitonin is synthesized as part of a larger precursor molecule. What is its name?
Preproinsulin
Preprogastrin
Preproparathyroid hormone
Preprocalcitonin
Calcitonin is initially synthesized as preprocalcitonin, which is then cleaved to procalcitonin and finally to the active hormone. This processing is typical of peptide hormones.
The calcitonin receptor belongs to which GPCR family subgroup?
Class C (metabotropic glutamate)
Class B (secretin-like)
Class A (rhodopsin-like)
Class F (Frizzled)
The calcitonin receptor is part of class B G protein-coupled receptors, also known as the secretin-like family. Members of this class have large extracellular N-termini and are involved in peptide hormone signaling.
Which second messenger increases in osteoclasts after calcitonin receptor activation?
cGMP
DAG
cAMP
IP3
Calcitonin receptor coupling to Gs proteins stimulates adenylyl cyclase, raising intracellular cyclic AMP (cAMP) levels in osteoclasts. This initiates signaling cascades that inhibit bone resorption.
Calcitonin has an inhibitory effect on which aspect of gastrointestinal function?
Gastric acid secretion
Intestinal motility
Pancreatic enzyme release
Bile secretion
Calcitonin modestly inhibits gastric acid secretion, although this is not its primary function. Its main role is in calcium and bone metabolism.
What role does calcitonin play in controlling postprandial calcium levels?
Enhances postprandial calcium absorption in the gut
Prevents excessive postprandial increase in blood calcium
Stimulates PTH release after meals
Converts calcium to phosphate postprandially
Calcitonin helps prevent a rapid rise in blood calcium following a calcium-rich meal by inhibiting bone resorption and promoting urinary excretion of calcium. This counteracts parathyroid hormone's tendency to elevate calcium.
The human CALC-I gene undergoes alternative splicing to produce calcitonin and which other peptide?
Vasoactive intestinal peptide
Substance P
Thyrotropin-releasing hormone
Calcitonin gene-related peptide (CGRP)
Alternative splicing of the CALC-I gene results in two distinct peptides: calcitonin in thyroid C cells and calcitonin gene-related peptide (CGRP) in neuronal tissue. CGRP has roles in vasodilation and nociception.
Compared to human calcitonin, salmon calcitonin is clinically useful because it has:
Identical potency
Shorter half-life
Lower receptor affinity
Higher receptor affinity and longer half-life
Salmon calcitonin has higher affinity for the human calcitonin receptor and a longer plasma half-life than human calcitonin, making it a more potent therapeutic agent. This underlies its use in certain bone disorders.
Which enzyme is primarily responsible for degrading calcitonin in the circulation?
Monoamine oxidase
Neutral endopeptidase
Pepsin
Angiotensin-converting enzyme
Neutral endopeptidase, also known as neprilysin, degrades calcitonin in the bloodstream. Its activity helps regulate the hormone's short half-life.
Persistently elevated calcitonin levels are characteristic of which genetic syndrome?
MEN2B
MEN1
MEN3
MEN2A
Multiple Endocrine Neoplasia type 2A (MEN2A) includes medullary thyroid carcinoma, which secretes excessive calcitonin. MEN1 involves parathyroid and pituitary issues without high calcitonin.
Calcitonin receptor knockout mice exhibit which bone phenotype?
Reduced bone mass
Increased bone mass
Severe osteoporosis
No change in bone mass
Mice lacking the calcitonin receptor show increased bone mass due to unopposed osteoclast activity regulation and altered bone remodeling dynamics. This surprising phenotype highlights complex bone homeostasis.
Salmon calcitonin is approved for the treatment of which condition?
Rheumatoid arthritis
Postmenopausal osteoporosis
Diabetes mellitus
Hyperthyroidism
Salmon calcitonin is used therapeutically to treat postmenopausal osteoporosis by reducing bone resorption. It has also been used for Paget's disease of bone.
Which structural feature of calcitonin is essential for its receptor binding?
N-terminal disulfide bridge
C-terminal carboxy group
Glycosylation sites
Transmembrane domain
Calcitonin's N-terminal disulfide bridge between two cysteine residues is critical for maintaining its bioactive conformation and receptor binding. Without this bridge, the hormone loses activity.
Receptor activity-modifying proteins (RAMPs) influence calcitonin receptor function by:
Phosphorylating the receptor
Assisting receptor folding and cell surface expression
Inhibiting ligand binding
Degrading the receptor
RAMPs help traffic the calcitonin receptor to the cell surface and modulate its ligand specificity and pharmacology. They are accessory proteins for class B GPCRs.
Which hormone inhibits calcitonin secretion from thyroid C cells?
Growth hormone
Somatostatin
Glucagon
Adrenocorticotropic hormone
Somatostatin acts on thyroid C cells to inhibit calcitonin release, as it does with many other endocrine cells. This adds another layer of regulation to calcium homeostasis.
Ectopic calcitonin secretion can be seen in which malignancy outside the thyroid?
Breast carcinoma
Glioblastoma
Small cell lung carcinoma
Colon adenocarcinoma
Small cell lung carcinoma has neuroendocrine origins and can ectopically secrete calcitonin. This is part of the paraneoplastic syndromes associated with these tumors.
Aside from its disulfide bridge, which post-translational modification is critical for calcitonin activity?
Sulfation
Phosphorylation
N-terminal acetylation
C-terminal amidation
Calcitonin undergoes C-terminal amidation, which is necessary for full biological activity. This modification enhances peptide stability and receptor interaction.
Chronic administration of calcitonin often leads to diminishing responses, a phenomenon known as:
Tachyphylaxis
Sensitization
Synergism
Priming
Tachyphylaxis refers to a rapid decrease in response to a hormone with continuous exposure. Patients on long-term calcitonin may exhibit reduced efficacy over time.
Salmon calcitonin's prolonged action in humans is partly due to:
Resistance to proteolytic degradation
Rapid renal clearance
Low receptor affinity
Increased susceptibility to enzymatic cleavage
Salmon calcitonin is less susceptible to proteolytic enzymes than human calcitonin, which contributes to its longer half-life and higher potency in clinical use.
Calcitonin inhibits osteoclast bone resorption by interfering with which critical enzyme in the osteoclast ruffled border?
Collagenase
Na?/K?-ATPase
Carbonic anhydrase II
Vacuolar H?-ATPase
Calcitonin reduces osteoclast resorptive activity by decreasing the activity of vacuolar H?-ATPase, which is essential for acidifying the resorption lacuna. Without this acidification, bone mineral cannot be dissolved.
Why is procalcitonin a valuable biomarker for severe bacterial infection despite being the precursor of calcitonin?
It is cleaved only in the thyroid
Ectopic procalcitonin production is induced systemically by cytokines
Procalcitonin has a longer half-life than calcitonin
It is unrelated to calcitonin synthesis
During severe bacterial infections, inflammatory cytokines induce ectopic expression and release of procalcitonin from multiple tissues. Elevated systemic procalcitonin levels thereby serve as a marker of sepsis.
In chronic kidney disease, calcitonin metabolism is altered primarily due to:
Enhanced thyroid secretion
Decreased renal clearance
Increased hepatic clearance
Reduced bone resorption
Chronic kidney disease impairs the renal clearance of calcitonin, leading to prolonged half-life and higher circulating levels. Hepatic clearance is less affected.
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Study Outcomes

  1. Identify the Counteracting Hormone -

    Determine which hormone opposes the action of parathyroid hormone and learn its role in calcium regulation.

  2. Understand Parathyroid Hormone Function -

    Describe parathyroid hormone function in maintaining blood calcium levels and its impact on bone health.

  3. Analyze Opposing Hormones -

    Compare opposing hormones parathyroid hormone interactions and feedback loops to appreciate endocrine system balance.

  4. Apply Knowledge with Quiz Questions -

    Engage with endocrine system quiz questions to test your grasp of hormone interactions and retention of key concepts.

  5. Leverage Endocrine Hormones Trivia -

    Recall fascinating endocrine hormones trivia to reinforce your understanding of glandular signaling and regulation.

Cheat Sheet

  1. Calcitonin as the Primary Antagonist -

    Calcitonin, secreted by thyroid parafollicular C-cells, opposes the action of parathyroid hormone by inhibiting osteoclast-mediated bone resorption and enhancing renal calcium excretion. This direct counterbalance helps maintain serum calcium within a narrow physiological range. Mnemonic: "Calcitonin Cuts Calcium" to recall its calcium-lowering effect.

  2. Parathyroid Hormone Function Recap -

    Parathyroid hormone (PTH) raises blood calcium by stimulating osteoclasts, increasing renal calcium reabsorption, and activating vitamin D in the kidney (1α-hydroxylase). Understanding parathyroid hormone function is crucial for recognizing how opposing hormones restore balance. Tip: remember PTH's "3 D's" - Bones (deDuce), Kidneys (reDuce loss), and Gut (absoDption with vitamin D).

  3. Calcium Homeostasis Feedback Loop -

    The feedback loop between PTH and calcitonin ensures tight control of extracellular calcium: low Ca2+ triggers PTH release, while high Ca2+ stimulates calcitonin secretion. This interplay illustrates opposing hormones parathyroid hormone dynamics, preventing hypercalcemia or hypocalcemia. Visualize a thermostat model: PTH "turns up" calcium, calcitonin "turns it down."

  4. Renal vs. Skeletal Effects Contrast -

    PTH enhances renal Ca2+ reabsorption and phosphate excretion, whereas calcitonin decreases renal reabsorption of calcium and phosphate. In bone, PTH promotes osteoclast differentiation via RANKL upregulation, while calcitonin directly inhibits mature osteoclasts. Contrast chart suggestion: list each hormone's actions side by side for quick revision.

  5. Clinical Implications and Disorders -

    Imbalances in PTH or calcitonin can lead to hyperparathyroidism, hypoparathyroidism, or medullary thyroid carcinoma (elevated calcitonin marker). Recognizing which hormone opposes the action of parathyroid hormone aids in diagnosing calcium disorders and guiding treatments such as bisphosphonates or calcimimetics. Example case: high serum Ca2+, low PTH, elevated calcitonin suggests malignancy-driven hypercalcemia.

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