Endocrine System and Hormones Practice Questions
39 free Endocrine System and Hormones practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which gland is known as the master gland of the endocrine system?
- A Thyroid gland
- B Adrenal gland
- C Pituitary gland
- D Pineal gland (epiphysis)
Correct answer: Pituitary gland
The pituitary gland regulates the activity of most other endocrine glands. It secretes several tropic hormones under the control of the hypothalamus.
Hormones are best described as:
- A Locally acting autocrine molecules
- B Electrochemical nerve impulses
- C Chemical messengers
- D Regulatory structural proteins
Correct answer: Chemical messengers
Hormones are chemical messengers secreted by endocrine glands into the bloodstream. They act on specific target organs to regulate physiological functions.
Which hormone regulates basal metabolic rate in the body?
- A Insulin
- B Adrenaline
- C Thyroxine
- D Growth hormone
Correct answer: Thyroxine
Thyroxine, secreted by the thyroid gland, controls basal metabolic rate. It influences oxygen consumption and energy metabolism.
The hypothalamus connects the endocrine and nervous systems by controlling the:
- A Thyroid gland
- B Adrenal gland
- C Pituitary gland
- D Pancreas (both endo- and exocrine)
Correct answer: Pituitary gland
The hypothalamus secretes releasing and inhibiting hormones that regulate pituitary activity. This forms a functional link between the nervous and endocrine systems.
Which gland secretes melatonin?
- A Pituitary gland
- B Thyroid gland
- C Pineal gland
- D Adrenal gland
Correct answer: Pineal gland
Melatonin is secreted by the pineal gland. It regulates circadian rhythms and sleep-wake cycles.
Insulin is secreted by the:
- A Alpha cells of pancreas
- B Beta cells of pancreas
- C Adrenal medulla
- D Thyroid gland
Correct answer: Beta cells of pancreas
Insulin is produced by the beta cells of the islets of Langerhans in the pancreas. It lowers blood glucose levels by promoting cellular uptake of glucose.
Which hormone increases blood glucose level during stress?
- A Insulin (hypoglycemic hormone)
- B Glucagon (pancreatic alpha cells)
- C Adrenaline
- D Thyroxine (thyroid hormone)
Correct answer: Adrenaline
Adrenaline is released during stress and stimulates glycogen breakdown. This increases blood glucose to meet energy demands.
Steroid hormones exert their action mainly by:
- A Binding to membrane receptors
- B Activating second messengers
- C Altering gene expression
- D Opening ion channels
Correct answer: Altering gene expression
Steroid hormones enter target cells and bind to intracellular receptors. The hormone-receptor complex directly regulates gene transcription.
Which hormone uses cyclic AMP as a second messenger?
- A Thyroxine
- B Insulin
- C Adrenaline
- D Testosterone
Correct answer: Adrenaline
Adrenaline acts through membrane receptors and activates adenylate cyclase. This increases cyclic AMP, which mediates intracellular responses.
The adrenal cortex mainly secretes:
- A Catecholamines (epinephrine and norepinephrine)
- B Mineralocorticoids and glucocorticoids
- C Melatonin (pineal-derived indolamine)
- D Growth hormone (somatotropin)
Correct answer: Mineralocorticoids and glucocorticoids
The adrenal cortex produces steroid hormones including aldosterone and cortisol. These regulate metabolism, stress response, and electrolyte balance.
Which endocrine gland is absent in fish but present in higher vertebrates?
- A Thyroid gland
- B Pituitary gland
- C Parathyroid
- D Pancreas gland
Correct answer: Parathyroid
Parathyroid glands are absent in fish and appear in terrestrial vertebrates. They regulate calcium and phosphate balance.
Growth hormone primarily influences:
- A Calcium metabolism and bone turnover
- B Blood glucose levels and glycogen storage
- C Body growth and protein synthesis
- D Reproductive cycles and gonad function
Correct answer: Body growth and protein synthesis
Growth hormone stimulates growth of bones and muscles. It enhances protein synthesis and cell division.
Which hormone regulates calcium levels by promoting bone resorption?
- A Calcitonin (thyroid C-cells)
- B Parathyroid hormone
- C Vitamin D (calcitriol form)
- D Thyroxine (T4 hormone)
Correct answer: Parathyroid hormone
Parathyroid hormone increases blood calcium levels by promoting bone resorption. It acts antagonistically to calcitonin.
Peptide hormones differ from steroid hormones in that they:
- A Are lipid soluble
- B Bind intracellular receptors
- C Act through membrane receptors
- D Directly regulate gene transcription
Correct answer: Act through membrane receptors
Peptide hormones are water-soluble and cannot cross the cell membrane. They act by binding to membrane receptors and activating second messengers.
Which hormone is known as the emergency hormone?
- A Cortisol (stress glucocorticoid)
- B Insulin (pancreatic beta cells)
- C Adrenaline
- D Glucagon (pancreatic alpha cells)
Correct answer: Adrenaline
Adrenaline prepares the body for fight-or-flight responses. It rapidly increases heart rate, blood pressure, and energy availability.
The hormone responsible for lowering blood calcium levels is:
- A Parathyroid hormone (PTH)
- B Calcitonin (thyroid C-cells)
- C Vitamin D (calcitriol)
- D Aldosterone (mineralocorticoid)
Correct answer: Calcitonin (thyroid C-cells)
Calcitonin reduces blood calcium by inhibiting bone resorption. It is secreted by the thyroid gland.
Negative feedback regulation in the endocrine system ensures:
- A Perpetual maximum hormone secretion
- B Continuous hormone degradation regardless of need
- C Stable hormonal balance within normal physiological limits
- D Uncontrolled gland activity leading to hypersecretion
Correct answer: Stable hormonal balance within normal physiological limits
Negative feedback inhibits hormone secretion once optimal levels are reached. This maintains internal hormonal balance.
Which gland has both endocrine and exocrine functions?
- A Thyroid
- B Adrenal
- C Pancreas
- D Pituitary
Correct answer: Pancreas
The pancreas secretes digestive enzymes (exocrine function) and hormones like insulin and glucagon (endocrine function). It is a dual-function gland.
Which hormone primarily regulates circadian rhythm?
- A Cortisol
- B Melatonin
- C Thyroxine
- D Prolactin
Correct answer: Melatonin
Melatonin controls sleep-wake cycles and circadian rhythms. Its secretion increases during darkness.
Hormone-receptor specificity is determined by:
- A Hormone concentration
- B Size of the hormone
- C Structure of the receptor
- D Rate of hormone secretion
Correct answer: Structure of the receptor
Only cells with specific receptors respond to a hormone. The structural compatibility between hormone and receptor ensures specificity.
Which of the following describes the 'Second Messenger' mechanism typically used by peptide hormones like Glucagon?
- A The hormone binds a surface receptor, activating Adenylate Cyclase
- B The hormone enters the nucleus directly to bind DNA
- C The hormone is transported into the mitochondria to produce ATP
- D The hormone dissolves freely in the lipid bilayer to reach the cytoplasm
Correct answer: The hormone binds a surface receptor, activating Adenylate Cyclase
Peptide hormones are water-soluble and cannot cross the lipid bilayer. They bind to membrane receptors, which often activate G-proteins and secondary messengers like cAMP to propagate the signal.
The 'Hypophyseal Portal System' is a specialized vascular arrangement that allows the Hypothalamus to communicate with the:
- A Anterior Pituitary
- B Posterior Pituitary
- C Adrenal Medulla
- D Thyroid Gland
Correct answer: Anterior Pituitary
Releasing and inhibiting hormones from the hypothalamus travel through the portal veins directly to the anterior pituitary (adenohypophysis) to regulate the secretion of its tropic hormones.
Which hormone is synthesized by the Hypothalamus but stored and released by the Posterior Pituitary?
- A Inhibin
- B Adrenocorticotropic Hormone (ACTH)
- C Oxytocin
- D Luteinizing Hormone (LH)
Correct answer: Oxytocin
Oxytocin and Antidiuretic Hormone (ADH) are produced by neuronal cell bodies in the hypothalamus and transported down axons to be released from the posterior pituitary (neurohypophysis).
Aldosterone, a mineralocorticoid secreted by the Zona Glomerulosa of the adrenal cortex, primarily functions to:
- A Increase blood glucose levels by promoting gluconeogenesis in the liver
- B Promote sodium reabsorption and potassium excretion in the kidneys
- C Stimulate the fight-or-flight response
- D Regulate calcium deposition in bones
Correct answer: Promote sodium reabsorption and potassium excretion in the kidneys
Aldosterone acts on the distal tubules of the kidney to conserve sodium and water, thereby regulating blood pressure and electrolyte balance.
Which of the following is an example of 'Humoral Stimulus' for hormone release?
- A TSH stimulating the Thyroid gland
- B Nerve fibers stimulating the Adrenal Medulla
- C Low blood calcium levels stimulating Parathyroid Hormone (PTH) release
- D Hypothalamic releasing hormones directly stimulating the Anterior Pituitary gland
Correct answer: Low blood calcium levels stimulating Parathyroid Hormone (PTH) release
Humoral stimuli refer to changes in the blood levels of certain ions or nutrients that directly trigger the release of a specific hormone.
The 'Islets of Langerhans' contain Alpha cells that secrete which hormone?
- A Insulin
- B Glucagon
- C Somatostatin
- D Pancreatic Polypeptide
Correct answer: Glucagon
Alpha cells secrete glucagon, which raises blood glucose levels, while Beta cells secrete insulin, which lowers them.
Which hormone is essential for the metamorphosis of an axolotl into a terrestrial salamander if administered artificially?
- A Ecdysone
- B Thyroxine (T4)
- C Growth Hormone (GH)
- D Cortisol
Correct answer: Thyroxine (T4)
Thyroid hormones are the primary drivers of metamorphosis in amphibians. Axolotls are naturally neotenic but can be induced to metamorphose with thyroxine.
The precursor molecule for the synthesis of all steroid hormones, such as Estrogen and Testosterone, is:
- A Amino acids
- B Glucose
- C Cholesterol
- D Fatty acids
Correct answer: Cholesterol
Steroid hormones are lipophilic molecules derived from cholesterol, which allows them to diffuse easily through the plasma membrane of target cells.
Hypersecretion of Growth Hormone (GH) in adults, after the closure of epiphyseal plates, results in a condition known as:
- A Gigantism
- B Acromegaly
- C Cushing's Syndrome
- D Grave's Disease
Correct answer: Acromegaly
Acromegaly involves the overgrowth of bones in the face, hands, and feet in adults. Gigantism occurs if hypersecretion happens during childhood before the bones stop growing.
Which hormone, secreted by the heart's atria, acts as an antagonist to Aldosterone by promoting the excretion of sodium and water?
- A Atrial Natriuretic Peptide (ANP)
- B Erythropoietin
- C Angiotensin-Converting Enzyme (ACE)
- D Angiotensin II
Correct answer: Atrial Natriuretic Peptide (ANP)
ANP is released in response to high blood pressure (stretching of the atria) and helps lower blood volume and pressure by inhibiting sodium reabsorption.
The 'Ultimobranchial bodies' in lower vertebrates (like fish and amphibians) are homologous to which cells in the mammalian thyroid gland?
- A Follicular epithelial cells
- B Parafollicular (C) cells
- C Chief cells
- D Oxyphil cells
Correct answer: Parafollicular (C) cells
Parafollicular cells secrete calcitonin. In lower vertebrates, these cells form separate glands called ultimobranchial bodies before being incorporated into the thyroid in mammals.
Which of the following is a characteristic effect of 'Epinephrine' (Adrenaline)?
- A Constriction of bronchioles and airway passages
- B Stimulation of glycogenolysis in the liver
- C Increased digestive activity
- D Lowering of the heart rate
Correct answer: Stimulation of glycogenolysis in the liver
Epinephrine triggers the 'fight-or-flight' response, which includes breaking down glycogen into glucose to provide immediate energy for muscles.
The 'Pineal Gland' secretes melatonin primarily during which period?
- A During periods of high stress
- B During daylight hours
- C During darkness/nighttime
- D Immediately after a meal
Correct answer: During darkness/nighttime
Melatonin production is inhibited by light reaching the retina and stimulated by darkness, helping to regulate the sleep-wake cycle and circadian rhythms.
Which hormone is responsible for stimulating the contraction of the gallbladder and the release of pancreatic enzymes?
- A Gastrin
- B Secretin
- C Cholecystokinin (CCK)
- D Gastric Inhibitory Peptide (GIP)
Correct answer: Cholecystokinin (CCK)
CCK is produced by the duodenum in response to fats and proteins, signaling the digestive system to release bile and enzymes.
In the 'Lock and Key' model of hormone action, the 'Key' represents the hormone and the 'Lock' represents the:
- A Intracellular second messenger
- B Target organ
- C Blood vessel
- D Specific receptor protein
Correct answer: Specific receptor protein
Hormones circulate throughout the entire body, but they only affect target cells that possess the specific receptor protein configured to bind that hormone.
Which condition is caused by an iodine deficiency, leading to an enlarged thyroid gland?
- A Diabetes Insipidus
- B Addison's Disease
- C Exophthalmos
- D Simple Goiter
Correct answer: Simple Goiter
Without iodine, the thyroid cannot produce T3 and T4. The resulting lack of negative feedback causes the pituitary to overproduce TSH, leading to gland hypertrophy (Goiter).
Which hormone stimulates the 'Sertoli cells' in the testes to support spermatogenesis?
- A Follicle Stimulating Hormone (FSH)
- B Luteinizing Hormone (LH)
- C Inhibin
- D Testosterone secreted by Leydig cells
Correct answer: Follicle Stimulating Hormone (FSH)
FSH acts on the Sertoli cells to promote sperm development, while LH acts on Leydig cells to produce testosterone.
The 'Addison’s Disease' is characterized by the hyposecretion of hormones from the:
- A Adrenal Medulla
- B Thyroid Gland
- C Adrenal Cortex
- D Pancreas
Correct answer: Adrenal Cortex
Addison's disease occurs when the adrenal cortex fails to produce enough cortisol and aldosterone, leading to fatigue, low blood pressure, and skin darkening.
Which hormone exhibits a 'Positive Feedback' loop during the onset of labor in mammals?
- A Oxytocin
- B Progesterone
- C Prolactin
- D Estrogen
Correct answer: Oxytocin
During labor, the stretching of the cervix triggers oxytocin release, which causes more contractions, leading to more stretching and further oxytocin release until birth occurs.