Hormone Classification and Mechanisms Practice Questions
60 free Hormone Classification and Mechanisms practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which classification best describes insulin based on its chemical nature?
- A Steroid hormone
- B Amino acid derivative
- C Peptide hormone
- D Eicosanoid
Correct answer: Peptide hormone
Insulin is a peptide hormone composed of amino acid chains. Peptide hormones are water-soluble and act via cell surface receptors.
Which hormone class typically binds to intracellular receptors?
- A Peptide hormones
- B Protein hormones
- C Steroid hormones
- D Catecholamines
Correct answer: Steroid hormones
Steroid hormones are lipid-soluble and cross the cell membrane to bind intracellular receptors. These hormone-receptor complexes regulate gene transcription.
Which second messenger is commonly involved in peptide hormone signaling?
- A DNA
- B cAMP
- C mRNA
- D tRNA
Correct answer: cAMP
cAMP is a common second messenger generated after hormone-receptor interaction at the cell surface. It activates protein kinase A to mediate cellular effects.
Which hormone mechanism involves activation of tyrosine kinase receptors?
- A Steroid hormone action
- B Insulin action
- C Thyroid hormone action
- D Cortisol action
Correct answer: Insulin action
Insulin acts via a receptor with intrinsic tyrosine kinase activity. This leads to phosphorylation cascades that regulate glucose metabolism.
Which hormone is derived from cholesterol?
- A Insulin
- B Adrenaline
- C Thyroxine
- D Cortisol
Correct answer: Cortisol
Cortisol is a steroid hormone synthesized from cholesterol. Steroid hormones are lipid-soluble and act through intracellular receptors.
Which feature is characteristic of water-soluble hormones?
- A Bind nuclear receptors
- B Stored in secretory vesicles
- C Act via gene transcription directly
- D Require carrier proteins in plasma
Correct answer: Stored in secretory vesicles
Water-soluble hormones are stored in secretory vesicles and released by exocytosis. They act on membrane-bound receptors using second messengers.
Which hormone uses the IP3-DAG signaling pathway?
- A Glucagon
- B Adrenaline acting on beta receptors
- C Angiotensin II
- D Cortisol
Correct answer: Angiotensin II
Angiotensin II activates the phospholipase C pathway. This produces IP3 and DAG, leading to calcium release and protein kinase C activation.
Which mechanism best explains the delayed but prolonged action of steroid hormones?
- A Second messenger amplification
- B Rapid enzymatic breakdown in plasma
- C Alteration of gene transcription
- D Depolarization of cell membrane
Correct answer: Alteration of gene transcription
Steroid hormones alter gene transcription after binding intracellular receptors. This process takes time but produces long-lasting effects.
Which hormone acts via G protein–coupled receptors?
- A Thyroxine
- B Cortisol
- C Glucagon
- D Aldosterone
Correct answer: Glucagon
Glucagon binds to G protein–coupled receptors on hepatocytes. This activates adenylate cyclase and increases cAMP levels.
Which hormone classification includes epinephrine?
- A Steroid hormone
- B Peptide hormone
- C Amino acid derivative
- D Eicosanoid
Correct answer: Amino acid derivative
Epinephrine is an amino acid derivative synthesized from tyrosine. These hormones are water-soluble and act via membrane receptors.
Which hormone-receptor interaction directly activates gene transcription without second messengers?
- A Insulin-receptor complex
- B Steroid hormone-receptor complex
- C Glucagon-receptor complex
- D Parathyroid hormone-receptor complex
Correct answer: Steroid hormone-receptor complex
Steroid hormone-receptor complexes act as transcription factors. They bind to DNA and directly regulate gene expression.
Compared with peptide hormones, steroid hormones in the circulation are characterized by:
- A High plasma half-life
- B Act via surface receptors
- C Rapid onset of action
- D Stored in vesicles
Correct answer: High plasma half-life
Steroid hormones are bound to carrier proteins, giving them a longer plasma half-life. Peptide hormones circulate freely and are rapidly degraded.
Which second messenger mediates calcium release from the endoplasmic reticulum?
- A cAMP
- B cGMP
- C IP3
- D DAG
Correct answer: IP3
IP3 binds to receptors on the endoplasmic reticulum. This causes release of intracellular calcium stores.
Which hormone mechanism explains signal amplification?
- A Direct DNA binding
- B Carrier protein transport
- C Second messenger cascades
- D Hormone degradation
Correct answer: Second messenger cascades
Second messenger cascades amplify hormonal signals. A single hormone-receptor interaction can generate many intracellular responses.
Which hormone is an example of a protein hormone?
- A Growth hormone
- B Cortisol
- C Aldosterone
- D Thyroxine
Correct answer: Growth hormone
Growth hormone is a protein hormone composed of amino acids. It is water-soluble and acts via membrane receptors.
Which mechanism best describes thyroid hormone action?
- A Activating adenylate cyclase
- B Opening membrane ion channels
- C Binding to nuclear receptors
- D Activating phospholipase C
Correct answer: Binding to nuclear receptors
Thyroid hormones enter cells and bind nuclear receptors. This leads to altered transcription of target genes.
Which hormone does NOT require a cell surface receptor?
- A Insulin
- B Glucagon
- C Aldosterone
- D Parathyroid hormone
Correct answer: Aldosterone
Aldosterone is a steroid hormone that diffuses into cells. It binds intracellular receptors rather than membrane receptors.
Which factor primarily determines hormone specificity?
- A Circulating hormone concentration
- B Receptor presence on target cells
- C Rate of hormone degradation in plasma
- D Extent of plasma protein binding
Correct answer: Receptor presence on target cells
Hormone specificity depends on the presence of appropriate receptors on target cells. Only cells with receptors respond to the hormone.
Which hormone class is synthesized on demand and not stored?
- A Peptide hormones
- B Protein hormones
- C Steroid hormones
- D Glycoprotein hormones
Correct answer: Steroid hormones
Steroid hormones are synthesized on demand from cholesterol. They are not stored in secretory vesicles.
Which intracellular event is a common final pathway for many hormone actions?
- A DNA replication
- B Protein phosphorylation
- C Ribosome formation
- D Membrane depolarization
Correct answer: Protein phosphorylation
Many hormone actions converge on protein phosphorylation. This modifies enzyme activity and cellular function.
Which of the following hormones is synthesized in the rough endoplasmic reticulum and stored in secretory granules until needed?
- A Cortisol
- B Thyroxine
- C Glucagon
- D Estradiol
Correct answer: Glucagon
Glucagon is a peptide hormone, which is synthesized as a preprohormone in the rough ER. Unlike steroid hormones, peptide hormones are stored in vesicles and released via exocytosis upon stimulation.
Although both are classified as amine hormones derived from tyrosine, how do thyroid hormones differ from catecholamines regarding their transport in blood?
- A Thyroid hormones are water-soluble and travel freely.
- B Thyroid hormones are lipid-soluble and require carrier proteins.
- C Catecholamines are lipid-soluble and require carrier proteins.
- D Catecholamines have a much longer half-life than thyroid hormones.
Correct answer: Thyroid hormones are lipid-soluble and require carrier proteins.
Thyroid hormones (T3 and T4) are lipophilic and circulate primarily bound to thyroxine-binding globulin and albumin. In contrast, catecholamines like epinephrine are water-soluble and travel dissolved in the plasma.
In the Phospholipase C (PLC) signaling pathway, which molecule is responsible for directly triggering the release of calcium from the endoplasmic reticulum?
- A Diacylglycerol (DAG)
- B Protein Kinase C (PKC)
- C Inositol trisphosphate (IP3)
- D Cyclic AMP (cAMP)
Correct answer: Inositol trisphosphate (IP3)
PLC cleaves membrane phospholipids into DAG and IP3. While DAG remains in the membrane to activate PKC, IP3 diffuses into the cytosol and binds to ligand-gated calcium channels on the ER.
Which structural feature is characteristic of the intracellular receptors used by steroid hormones to bind to DNA?
- A Leucine zippers
- B Zinc fingers
- C GTPase loops
- D SH2 domains
Correct answer: Zinc fingers
Steroid hormone receptors contain specific DNA-binding domains called zinc fingers. These allow the receptor-hormone complex to bind to Hormone Response Elements (HREs) on the promoter regions of target genes.
The insulin receptor is a classic example of which type of signaling mechanism?
- A G protein-coupled receptor (GPCR)
- B Ligand-gated ion channel
- C Receptor Tyrosine Kinase (RTK)
- D Intracellular nuclear receptor
Correct answer: Receptor Tyrosine Kinase (RTK)
The insulin receptor has intrinsic enzymatic activity. Upon insulin binding, the receptor undergoes autophosphorylation of its tyrosine residues, which then activates downstream signaling proteins like IRS-1.
Which enzyme is responsible for the termination of the second messenger signal produced by Adenylyl Cyclase?
- A Phosphodiesterase (PDE)
- B Protein Kinase A (PKA)
- C Phospholipase A2 (PLA2)
- D GTPase activating protein
Correct answer: Phosphodiesterase (PDE)
Adenylyl cyclase produces cAMP, which activates PKA. Phosphodiesterase breaks down cAMP into 5'-AMP, effectively ending the intracellular signal and preventing overstimulation of the target cell.
Steroid hormones are derived from cholesterol. Which cellular organelle is the primary site for the initial step of steroidogenesis (the conversion of cholesterol to pregnenolone)?
- A Golgi apparatus
- B Mitochondria
- C Rough endoplasmic reticulum
- D Lysosomes
Correct answer: Mitochondria
The rate-limiting step of steroid synthesis occurs when cholesterol is transported into the mitochondria by the StAR protein. Within the mitochondria, the side-chain cleavage enzyme converts cholesterol into pregnenolone.
Which of the following hormones utilizes a mechanism involving the JAK-STAT pathway rather than intrinsic tyrosine kinase activity?
- A Insulin
- B Epinephrine
- C Growth Hormone
- D Aldosterone
Correct answer: Growth Hormone
The Growth Hormone receptor lacks intrinsic kinase activity but instead recruits Janus Kinases (JAKs) upon binding. These kinases then phosphorylate Signal Transducers and Activators of Transcription (STATs) to regulate gene expression.
What determines the 'metabolic clearance rate' of a hormone in the circulation?
- A The rate of hormone secretion into the circulation
- B The affinity of the hormone for its target receptor
- C The degree of protein binding and rate of degradation
- D The number of second messengers activated per hormone
Correct answer: The degree of protein binding and rate of degradation
Hormones that are highly bound to plasma proteins have a lower metabolic clearance rate and a longer half-life. Clearance is primarily achieved through enzymatic degradation in the liver and excretion by the kidneys.
Which hormone is an example of an amine derived from the amino acid tryptophan?
- A Norepinephrine
- B Melatonin
- C Thyroxine
- D Dopamine
Correct answer: Melatonin
While most amine hormones (catecholamines and thyroid hormones) are derived from tyrosine, melatonin is synthesized from tryptophan in the pineal gland. It follows a specific metabolic pathway involving serotonin as an intermediate.
A hormone 'permissive effect' is best described by which of the following scenarios?
- A Hormone A and B work together to produce a sum greater than their individual parts.
- B Hormone A must be present for Hormone B to exert its full effect.
- C Hormone A opposes the action of Hormone B.
- D Hormone A stimulates the release of Hormone B.
Correct answer: Hormone A must be present for Hormone B to exert its full effect.
Permissiveness occurs when one hormone enhances the responsiveness of a target organ to a second hormone, often by increasing the number of receptors for that second hormone. For example, thyroid hormone is permissive to the actions of epinephrine on lipolysis.
Which second messenger system is utilized by Atrial Natriuretic Peptide (ANP)?
- A cAMP
- B IP3/DAG
- C cGMP
- D Calcium-Calmodulin
Correct answer: cGMP
ANP binds to membrane-bound guanylyl cyclase receptors. This directly increases the production of cyclic GMP (cGMP), which activates protein kinase G to mediate vasodilation and natriuresis.
What is the primary reason that steroid hormones have a delayed onset of action (minutes to hours) compared to catecholamines?
- A They are rapidly degraded in the bloodstream.
- B They must be converted from prohormones in the plasma.
- C They act by inducing new protein synthesis via gene transcription.
- D They are hindered by the blood-brain barrier.
Correct answer: They act by inducing new protein synthesis via gene transcription.
Catecholamines bind to surface receptors and activate existing enzymes via second messengers (fast). Steroid hormones must enter the nucleus to alter mRNA transcription and translate new proteins, which is a significantly slower process.
Which of the following is an example of a 'eicosanoid' hormone signaling molecule?
- A Prostaglandin
- B Vasopressin
- C Somatostatin
- D Oxytocin
Correct answer: Prostaglandin
Eicosanoids are a class of polyunsaturated fatty acid derivatives, primarily arachidonic acid. Prostaglandins, leukotrienes, and thromboxanes are key examples that typically act as paracrine or autocrine signals.
The phenomenon of 'down-regulation' of receptors occurs in response to:
- A Chronically low levels of a hormone.
- B Chronically high levels of a hormone.
- C The presence of a permissive hormone.
- D Activation of the cAMP pathway.
Correct answer: Chronically high levels of a hormone.
To prevent overstimulation, cells decrease the number or sensitivity of receptors in response to sustained high hormone concentrations. This is often achieved through receptor internalization and degradation.
Which G-protein subunit is responsible for activating the enzyme Adenylyl Cyclase?
- A Gi alpha
- B Gs alpha
- C Gq alpha
- D Beta-gamma dimer
Correct answer: Gs alpha
The Gs (stimulatory) alpha subunit activates adenylyl cyclase to increase cAMP levels. In contrast, the Gi (inhibitory) alpha subunit inhibits the enzyme, lowering cAMP levels.
Which of the following is true regarding the 'Free Hormone' hypothesis?
- A Only hormones bound to proteins can enter target cells.
- B Only the unbound fraction of a hormone is biologically active.
- C Free hormones are protected from renal excretion.
- D The concentration of free hormone is always higher than bound hormone.
Correct answer: Only the unbound fraction of a hormone is biologically active.
Carrier proteins act as a reservoir, but only the 'free' or unbound hormone can diffuse across membranes or bind to cell surface receptors to exert physiological effects. This free fraction is usually less than 1-10% of the total hormone concentration.
Signal amplification in the endocrine system is primarily achieved by:
- A Binding of hormones to many different receptor types at once
- B The irreversible binding of hormone molecules directly to DNA
- C An enzyme cascade where one molecule activates many targets
- D Storing large amounts of cholesterol precursor in the liver
Correct answer: An enzyme cascade where one molecule activates many targets
Amplification allows a very small amount of hormone to produce a large cellular response. One hormone-receptor complex can activate multiple G-proteins, each of which activates an enzyme that produces thousands of second messenger molecules.
Which of the following hormones is lipophilic but is synthesized and stored in large quantities within an extracellular colloid?
- A Aldosterone
- B Insulin
- C Thyroid Hormone
- D Testosterone
Correct answer: Thyroid Hormone
Thyroid hormones are unique; they are lipophilic amines but are stored as part of the thyroglobulin protein in the follicular colloid of the thyroid gland. This provides a several-month supply of hormone, which is unusual for lipid-soluble signals.
Where are the receptors for water-soluble hormones located?
- A Free within the intracellular cytoplasm
- B On the outer surface of the plasma membrane
- C Attached to histone proteins in the nucleus
- D On the inner mitochondrial membrane surface
Correct answer: On the outer surface of the plasma membrane
Water-soluble hormones (peptides and catecholamines) cannot cross the phospholipid bilayer of the plasma membrane. Therefore, they must bind to integral membrane proteins that face the extracellular fluid.
Which of the following hormones is synthesized as a preprohormone and stored in secretory vesicles before being released via exocytosis?
- A Estrone
- B Thyroxine (T4)
- C Insulin
- D Aldosterone
Correct answer: Insulin
Peptide hormones like insulin are synthesized on ribosomes as large preprohormones, processed in the ER and Golgi, and stored in vesicles until a stimulus triggers their release.
The rate-limiting step in the synthesis of all steroid hormones is the conversion of cholesterol to which precursor?
- A Pregnenolone
- B Progesterone
- C Dehydroepiandrosterone
- D Testosterone
Correct answer: Pregnenolone
The conversion of cholesterol to pregnenolone by the enzyme cholesterol desmolase (P450scc) in the mitochondria is the shared rate-limiting step for steroidogenesis.
Which of the following hormones, despite being lipid-soluble, is unique because it is stored extracellularly in a colloid form?
- A Triiodothyronine (T3)
- B Estradiol
- C Cortisol
- D 1,25-Dihydroxyvitamin D3
Correct answer: Triiodothyronine (T3)
Thyroid hormones (T3 and T4) are amine hormones that are lipid-soluble but are stored for several weeks bound to thyroglobulin within the thyroid follicles.
Which signaling mechanism is utilized by the Growth Hormone (GH) receptor?
- A JAK2-STAT pathway
- B Tyrosine Kinase
- C Adenylyl Cyclase-cAMP
- D Phospholipase C-IP3
Correct answer: JAK2-STAT pathway
The GH receptor belongs to the cytokine receptor family; it lacks intrinsic kinase activity and instead recruits cytosolic JAK2 kinases to phosphorylate STAT proteins.
When one hormone is required for a second hormone to exert its full effect, this interaction is known as:
- A Synergism
- B Antagonism
- C Permissiveness
- D Negative feedback
Correct answer: Permissiveness
Permissiveness occurs when hormone A must be present for hormone B to work effectively (e.g., thyroid hormone is permissive for epinephrine's lipolytic effect).
Which second messenger directly activates Protein Kinase C (PKC) in the Phospholipase C signaling pathway?
- A Inositol trisphosphate (IP3)
- B Cyclic AMP (cAMP)
- C Diacylglycerol (DAG)
- D Cyclic GMP (cGMP)
Correct answer: Diacylglycerol (DAG)
In the PLC pathway, PIP2 is cleaved into IP3 (which releases calcium) and DAG. DAG remains in the membrane to activate Protein Kinase C.
Which of the following properties is characteristic of amine hormones derived from tryptophan, such as Melatonin?
- A They are always stored in the colloid.
- B They behave similarly to steroid hormones in the blood.
- C They are synthesized from the amino acid tyrosine.
- D They are water-soluble and bind to membrane receptors.
Correct answer: They are water-soluble and bind to membrane receptors.
Melatonin is an amine hormone derived from tryptophan. Like most water-soluble hormones, it typically acts through membrane-bound G-protein coupled receptors.
The metabolic clearance rate (MCR) of a hormone is inversely proportional to its:
- A Half-life in circulation
- B Concentration in the blood
- C Rate of secretion
- D Molecular weight
Correct answer: Half-life in circulation
Hormones with a high affinity for binding proteins have a longer half-life and a lower metabolic clearance rate because they are protected from degradation and excretion.
Which enzyme is responsible for converting ATP into the second messenger cAMP?
- A Phosphodiesterase
- B Protein Kinase A
- C Adenylyl Cyclase
- D Guanylyl Cyclase
Correct answer: Adenylyl Cyclase
Adenylyl cyclase is a membrane-bound enzyme that, when activated by a G-protein (Gs), catalyzes the conversion of ATP to cyclic AMP.
Which hormone class is primarily transported in the blood bound to specific carrier proteins like CBG or SHBG?
- A Peptide hormones
- B Catecholamines
- C Protein hormones
- D Steroid hormones
Correct answer: Steroid hormones
Steroid hormones are lipophilic and poorly soluble in plasma; they require transport proteins to remain in solution and to increase their half-life.
The Atrial Natriuretic Peptide (ANP) receptor possesses intrinsic activity of which enzyme?
- A Guanylyl Cyclase
- B Tyrosine Kinase
- C Phospholipase C
- D Adenylate Cyclase
Correct answer: Guanylyl Cyclase
ANP binds to a receptor that has intrinsic guanylyl cyclase activity, which converts GTP to cGMP to mediate vasodilation and natriuresis.
What is the primary cellular location for the receptors of Thyroid Hormones (T3/T4)?
- A Plasma membrane
- B Cytoplasm
- C Cell nucleus
- D Mitochondria
Correct answer: Cell nucleus
Thyroid hormone receptors are nuclear receptors already bound to DNA; when T3 binds, it alters the transcription of specific target genes.
A decrease in the number of receptors on a target cell in response to chronically high hormone levels is called:
- A Up-regulation
- B Down-regulation
- C Homologous desensitization
- D Tachyphylaxis
Correct answer: Down-regulation
Down-regulation is a protective mechanism where cells decrease receptor density to prevent overstimulation in the presence of excess hormone.
Which of the following is an example of an eicosanoid that acts as a local hormone (paracrine)?
- A Prostaglandin E2
- B Somatostatin
- C Norepinephrine
- D Insulin-like Growth Factor
Correct answer: Prostaglandin E2
Prostaglandins are eicosanoids derived from arachidonic acid that primarily act as local signaling molecules near their site of synthesis.
Which G-protein subunit is responsible for inhibiting the enzyme Adenylyl Cyclase?
- A Gs-alpha
- B Gi-alpha
- C Gq-alpha
- D G-beta/gamma
Correct answer: Gi-alpha
The 'i' in Gi stands for inhibitory; this G-protein subunit decreases the activity of adenylyl cyclase, lowering intracellular cAMP levels.
Which of the following hormones exerts its effect through a receptor that undergoes autophosphorylation on tyrosine residues?
- A Leptin
- B Insulin
- C Epinephrine
- D Parathyroid Hormone
Correct answer: Insulin
The insulin receptor is a receptor tyrosine kinase; upon insulin binding, the beta subunits phosphorylate each other to initiate downstream signaling.
According to the 'Free Hormone Hypothesis', which fraction of a hormone is biologically active and able to cross cell membranes?
- A The fraction bound to albumin
- B Globulin-bound hormone
- C The unbound hormone fraction
- D The total hormone concentration
Correct answer: The unbound hormone fraction
Only the free hormone can diffuse out of capillaries and bind to receptors or enter cells; the bound fraction acts as a reservoir.
Which second messenger is used by the majority of hypothalamic-releasing hormones acting on the anterior pituitary?
- A cAMP
- B cGMP
- C Calcium/IP3-DAG
- D Tyrosine Kinase
Correct answer: Calcium/IP3-DAG
Many hypothalamic hormones like GHRH use cAMP, but others like GnRH and TRH primarily utilize the Phospholipase C (Calcium/IP3) pathway.
Which enzyme terminates the action of cAMP by converting it into inactive 5'-AMP?
- A Alkaline Phosphatase
- B Phosphodiesterase
- C ATPase
- D Creatine Kinase
Correct answer: Phosphodiesterase
Phosphodiesterases break the phosphodiester bond in cAMP and cGMP, effectively 'turning off' the second messenger signal.
The 'Hormone Response Element' (HRE) refers to a specific sequence found on:
- A The hormone receptor protein
- B A specific DNA sequence
- C The plasma membrane
- D The messenger RNA
Correct answer: A specific DNA sequence
HREs are specific DNA sequences in the promoter regions of genes that are recognized and bound by activated steroid or thyroid hormone receptors.