101. A non-pregnant adult female has persistently reduced thyroid activity, while pituitary growth-hormone secretion remains normal. A likely reproductive consequence is:
ⓐ. induction of ovulation without follicular development
ⓑ. formation of an abnormally persistent corpus luteum
ⓒ. development of persistent menstrual-cycle irregularity
ⓓ. complete replacement of gonadotrophins by thyroid hormones
Correct Answer: development of persistent menstrual-cycle irregularity
Explanation: Reduced thyroid activity in an adult female may disturb the normal menstrual cycle. The effect reflects the wider influence of thyroid hormones on metabolism and physiological regulation rather than a direct replacement of ovarian or pituitary reproductive hormones. The supplied evidence preserves normal growth-hormone secretion, excluding pituitary growth disorders as the primary explanation. Ovulation and follicular development remain principally associated with LH and FSH, while maintenance of the corpus luteum involves LH and ovarian hormonal activity. Thyroid hypofunction can nevertheless alter the regularity of reproductive cycling. The expected outcome under the stated condition is menstrual irregularity rather than a new hormone source or an isolated gain of ovarian function.
102. A thyroid nodule begins synthesising and secreting abnormally large quantities of \(T_3\) and \(T_4\), despite adequate dietary iodine. The resulting endocrine state is most likely:
ⓐ. hyperthyroidism produced by excessive thyroid-hormone output
ⓑ. hypothyroidism produced by inadequate iodothyronine synthesis
ⓒ. hypoparathyroidism produced by deficient PTH secretion
ⓓ. diabetes insipidus produced by reduced vasopressin release
Correct Answer: hyperthyroidism produced by excessive thyroid-hormone output
Explanation: The nodule is located in the thyroid and releases abnormally high quantities of the principal iodothyronines \(T_3\) and \(T_4\). This establishes an excessive thyroid-hormone state, or hyperthyroidism. Adequate iodine availability rules out iodine deficiency as the cause of reduced synthesis. The condition also does not arise from parathyroid or posterior-pituitary failure, since the altered products are specifically thyroid hormones. Thyroid nodules and thyroid cancer are included among causes that can abnormally increase thyroid-hormone synthesis and secretion. Identifying the gland, the hormones and the direction of secretion leads to hyperthyroidism rather than a deficiency disorder. This interpretation links the named structure with the direction of hormonal action and the response of its target tissue.
103. Assess the statements given for exophthalmic goitre or Graves’ disease.
I. The thyroid gland is enlarged.
II. The eyeballs may protrude.
III. Basal metabolic rate is increased.
IV. Progressive weight gain is a characteristic result of the elevated metabolic state.
ⓐ. I and IV only
ⓑ. II and III only
ⓒ. I, III and IV only
ⓓ. I, II and III only
Correct Answer: I, II and III only
Explanation: Graves’ disease is a hyperthyroid condition characterised by enlargement of the thyroid gland, protruding eyeballs and an increased basal metabolic rate. Statements I, II and III are valid. Statement IV conflicts with the metabolic pattern: increased thyroid activity raises energy expenditure and is associated with weight loss rather than characteristic progressive weight gain. The valid combination must include both the structural manifestation and the systemic metabolic effects. Ordinary thyroid enlargement alone is insufficient to establish Graves’ disease; the presence of exophthalmos and a hypermetabolic state provides the important distinction from iodine-deficiency goitre. Evaluating the statements separately prevents one valid relation from making an adjacent but different relation appear valid. After each claim is checked, anatomical region, direction of action and physiological condition must remain mutually consistent.
104. A graph plots basal metabolic rate and body mass against time after the onset of excessive thyroid-hormone secretion. Basal metabolic rate rises steadily, while body mass declines despite adequate food intake. This pattern is most consistent with:
ⓐ. pituitary dwarfism
ⓑ. Graves’ disease
ⓒ. diabetes insipidus
ⓓ. simple goitre
Correct Answer: Graves’ disease
Explanation: The graph shows two linked trends following excessive thyroid-hormone secretion: basal metabolic rate increases and body mass falls. Elevated \(T_3\) and \(T_4\) accelerate metabolic activity, increasing energy expenditure and contributing to weight loss. This combination is characteristic of hyperthyroidism and is included among the major manifestations of Graves’ disease. Pituitary dwarfism involves inadequate growth hormone during development, while diabetes insipidus produces excessive urinary water loss through deficient ADH activity. Simple goitre may enlarge the thyroid without producing the sustained hypermetabolic pattern shown. Interpreting both plotted variables together identifies a hypermetabolic thyroid disorder rather than a growth or water-balance abnormality. The axes and direction of change define the biological interpretation of the curve. The curve is read by following how the measured target variable changes as the hormonal condition changes. The graph supports a qualitative relation and does not supply an unreported numerical threshold.
105. Assertion: Weight loss may occur in Graves’ disease even though the thyroid gland is enlarged.
Reason: Excess thyroid-hormone activity raises basal metabolic rate and increases energy expenditure.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not explain the Assertion
ⓒ. Assertion is true, but Reason is false
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion
Explanation: The assertion is true. Graves’ disease includes thyroid enlargement, but enlargement of the gland does not imply increased body mass. The disorder is hyperthyroid, and elevated thyroid-hormone action raises basal metabolic rate. Greater metabolic activity increases energy expenditure and contributes to loss of body weight. The reason is also true and provides the physiological basis for the weight-loss component of the assertion. It explains how an enlarged endocrine gland can coexist with a decline in body mass. Both statements describe different levels of the same disorder: one gives the observed manifestation, while the other supplies the metabolic mechanism that produces it. A shared topic alone is insufficient; the Reason must account for the event stated in the Assertion.
106. Match each thyroid-related factor with its principal relation. A Column II entry is used once.
| Column I | Column II |
|---|
| P. \(T_3\) and \(T_4\) | 1. Required dietary element for normal iodothyronine synthesis |
| Q. Thyrocalcitonin | 2. Stimulation of thyroid-hormone synthesis and secretion |
| R. TSH | 3. Regulation of metabolism and developmental functions |
| S. Iodine | 4. Reduction of blood \(\mathrm{Ca^{2+}}\) concentration |
ⓐ. P-2, Q-4, R-3, S-1
ⓑ. P-3, Q-2, R-1, S-4
ⓒ. P-3, Q-4, R-2, S-1
ⓓ. P-4, Q-1, R-2, S-3
Correct Answer: P-3, Q-4, R-2, S-1
Explanation: The iodothyronines \(T_3\) and \(T_4\) regulate basal metabolism, nutrient metabolism, development and several other physiological functions, giving P-3. Thyrocalcitonin is a thyroid-derived protein hormone that lowers or regulates blood \(\mathrm{Ca^{2+}}\), giving Q-4. TSH originates from pars distalis and stimulates the thyroid to synthesise and secrete its hormones, so R-2 is appropriate. Iodine is the dietary element required for normal iodothyronine synthesis, completing S-1. The mappings separate a final thyroid product, a calcium-regulating thyroid hormone, an upstream pituitary regulator and a required nutritional component. The final arrangement integrates all pairings and preserves the stated rule about whether entries may be reused. In the completed relation set, checking the defining property of each entry prevents one correct pair from being used to guess the others.
107. Two comparable groups receive identical diets. Group P is given thyroid hormones, while Group Q receives no thyroid-hormone treatment. P shows coordinated changes in carbohydrate, protein and fat metabolism that are absent in Q. The strongest supported conclusion is:
ⓐ. thyroid hormones regulate only carbohydrate digestion in the intestine
ⓑ. thyroid hormones influence the metabolism of all three nutrient classes
ⓒ. thyroid hormones influence carbohydrate and fat metabolism but not protein metabolism
ⓓ. thyroid hormones act only by increasing renal water reabsorption
Correct Answer: thyroid hormones influence the metabolism of all three nutrient classes
Explanation: The treated and untreated groups have the same dietary conditions, while thyroid-hormone exposure is the experimental difference. Coordinated changes in carbohydrate, protein and fat metabolism appear only in the treated group. This observation supports a regulatory role for thyroid hormones across all three nutrient classes. The evidence does not restrict their action to intestinal digestion, nor does it indicate conversion of nutrients into glandular structures. Renal water conservation is primarily associated with ADH, although thyroid hormones also influence broader water and electrolyte balance. The experiment links thyroid-hormone treatment with systemic metabolic changes and supports the conclusion that iodothyronines regulate carbohydrate, protein and fat metabolism. The supplied condition is decisive because it identifies the particular endocrine link responsible for the observed response.
108. Consider the following functions of thyroid hormones.
I. Regulation of basal metabolic rate
II. Support of central neural-system maturation
III. Promotion of erythropoiesis
IV. Influence on water and electrolyte balance
ⓐ. I and III only
ⓑ. II and IV only
ⓒ. I, II and III only
ⓓ. I, II, III and IV
Correct Answer: I, II, III and IV
Explanation: Thyroid hormones have several coordinated physiological roles. They regulate basal metabolic rate and participate in the metabolism of carbohydrates, proteins and fats. During development, they support growth and maturation of the central neural system. They also promote erythropoiesis, contributing to red-blood-cell formation, and influence water and electrolyte balance. Each listed function is consequently valid. The combination illustrates why thyroid-hormone abnormalities can produce widespread effects rather than one isolated symptom. Their actions extend across metabolism, development, blood-cell production and internal fluid regulation, so all four statements belong to the normal functional profile of the iodothyronines. The final combination reflects complete biological consistency across the listed statements rather than recognition of one familiar term.
109. A developing individual has low thyroid-hormone activity. Tests indicate impaired central neural-system maturation, reduced support for red-blood-cell formation and disturbed fluid regulation. The lost hormone functions are best described as:
ⓐ. neural development, erythropoiesis and water-electrolyte balance
ⓑ. milk ejection, uterine contraction and renal water conservation
ⓒ. androgen secretion, ovulation and corpus-luteum maintenance
ⓓ. skin pigmentation, diurnal rhythm and glucocorticoid secretion
Correct Answer: neural development, erythropoiesis and water-electrolyte balance
Explanation: The three observations correspond directly to recognised thyroid-hormone functions. Iodothyronines support development and maturation of the central neural system, promote erythropoiesis and influence water and electrolyte balance. A reduction in thyroid activity can accordingly disturb all three processes. The supplied evidence combines developmental, haematological and fluid-regulatory evidence, requiring identification of one hormone group with broad physiological influence. Oxytocin and ADH account for specific reproductive contractions and renal water conservation, while gonadotrophins regulate gonadal functions. Melatonin, MSH and ACTH belong to different source-target pathways. The complete pattern points to loss of normal thyroid-hormone actions.
110. Determine the proper order for the events in a pituitary-thyroid pathway.
P. \(T_3\) and \(T_4\) are synthesised and secreted.
Q. TSH is released from pars distalis.
R. Thyroid follicular cells are stimulated.
S. Metabolic and developmental processes are regulated.
ⓐ. \(R\rightarrow Q\rightarrow P\rightarrow S\)
ⓑ. \(Q\rightarrow P\rightarrow R\rightarrow S\)
ⓒ. \(Q\rightarrow R\rightarrow P\rightarrow S\)
ⓓ. \(P\rightarrow Q\rightarrow S\rightarrow R\)
Correct Answer: \(Q\rightarrow R\rightarrow P\rightarrow S\)
Explanation: The pathway starts in pars distalis, which secretes TSH. Circulating TSH then reaches the thyroid and stimulates its follicular cells. These cells synthesise and release the iodothyronines \(T_3\) and \(T_4\). The thyroid hormones subsequently act on responsive tissues and regulate metabolism, development and other physiological processes. Each event creates the condition required for the next: follicular stimulation follows TSH release, iodothyronine secretion follows thyroid activation, and systemic responses follow delivery of the final hormones. The valid dependency order is \(Q\rightarrow R\rightarrow P\rightarrow S\), representing an upstream pituitary signal followed by peripheral-gland output and target-tissue effects. Reversing dependent events would place an effect before the signal or process required to produce it. Following the chain step by step prevents an upstream signal from being placed after its downstream response.
111. Compare the following endocrine cases.
| Case | Primary change | Thyroid-hormone output | Basal metabolic rate |
|---|
| P | Loss of TSH-secreting pars-distalis cells | Reduced | Reduced |
| Q | Hormone-secreting thyroid nodule | Increased | Increased |
The best interpretation is:
ⓐ. P and Q both represent deficient ADH action
ⓑ. P represents hyperthyroidism, while Q represents hypothyroidism
ⓒ. P and Q both represent reduced thyroid response to TSH
ⓓ. P shows low pituitary drive while Q shows thyroid hyperactivity
Correct Answer: P shows low pituitary drive while Q shows thyroid hyperactivity
Explanation: Case P begins with destruction of TSH-producing pituitary cells. Reduced TSH removes an important stimulatory input to the thyroid, so thyroid-hormone output and basal metabolic rate fall. Case Q begins within the thyroid itself: a hormone-secreting nodule increases \(T_3\) and \(T_4\) output, producing a rise in basal metabolic rate. The two profiles represent opposite endocrine states created at different levels of the pathway. P is an upstream pituitary-stimulation failure, whereas Q is excessive activity of the peripheral endocrine gland. Interpreting the causal starting point in each row distinguishes the mechanisms more accurately than simply labelling both as thyroid disorders. Cross-row comparison separates a selective endocrine defect from a general failure of the tissue or organ. The inference depends on synthesis across the columns rather than direct retrieval of one visible entry.
112. A protein hormone is secreted by the thyroid gland and acts to lower blood \(\mathrm{Ca^{2+}}\) concentration. The hormone is:
ⓐ. parathyroid hormone
ⓑ. thyrocalcitonin
ⓒ. thyrotropin
ⓓ. tetraiodothyronine
Correct Answer: thyrocalcitonin
Explanation: Thyrocalcitonin, abbreviated TCT, is a protein hormone secreted by the thyroid gland. Its defining physiological relation in this context is reduction or regulation of blood \(\mathrm{Ca^{2+}}\) concentration. Parathyroid hormone has the opposing hypercalcaemic effect and raises blood calcium through actions involving bone, kidneys and the intestine. TSH is a pituitary hormone that stimulates thyroid secretion, while tetraiodothyronine or \(T_4\) regulates metabolism and development. The combination of thyroid origin, protein nature and calcium-lowering action uniquely identifies thyrocalcitonin and separates it from both iodothyronines and the opposing parathyroid hormone. The decisive feature is the complete relation among the named source, messenger, target and physiological effect.
113. A graph plots relative blood \(\mathrm{Ca^{2+}}\) concentration against time after the same calcium-raising challenge in two animals. Animal P has a normal thyrocalcitonin response, whereas Animal Q cannot secrete thyrocalcitonin. P returns toward its initial level, but Q remains elevated. The graph indicates that:
ⓐ. PTH secretion is absent in P but excessive in Q
ⓑ. thyrocalcitonin raises blood calcium only in Q
ⓒ. thyrocalcitonin provides a calcium-lowering influence present in P but missing in Q
ⓓ. \(T_3\) and \(T_4\) directly replace thyrocalcitonin in Q
Correct Answer: thyrocalcitonin provides a calcium-lowering influence present in P but missing in Q
Explanation: The vertical axis represents blood-calcium concentration, and the two curves differ in whether thyrocalcitonin can be secreted after the same calcium-raising challenge. Animal P shows a decline toward its starting level, which is consistent with the blood-calcium-lowering action of thyrocalcitonin. Animal Q remains at a higher concentration because that corrective influence is absent. The graph does not establish the detailed cellular route by which calcium falls, so the justified conclusion remains that thyroid-derived thyrocalcitonin contributes to lowering or regulating blood \(\mathrm{Ca^{2+}}\). The comparison is stronger than reading one curve alone because both animals begin with the same disturbance and differ in one relevant hormonal response. The persistent elevation in Q identifies the missing thyrocalcitonin influence rather than a change in iodothyronine action.
114. Identical experimental animals are divided into two groups. Group P receives thyrocalcitonin, while Group Q receives no hormone. Blood \(\mathrm{Ca^{2+}}\) falls in P but remains near its initial level in Q. The strongest inference is:
ⓐ. thyrocalcitonin produces a blood-calcium-lowering effect
ⓑ. thyrocalcitonin is synthesised by the parathyroid glands
ⓒ. thyrocalcitonin stimulates secretion of growth hormone
ⓓ. thyrocalcitonin raises calcium by demineralising bone
Correct Answer: thyrocalcitonin produces a blood-calcium-lowering effect
Explanation: The treated and untreated groups provide a direct comparison. Only the group receiving thyrocalcitonin shows a fall in blood \(\mathrm{Ca^{2+}}\), linking the hormonal treatment with the observed reduction. The experiment supports a calcium-lowering action but does not identify every tissue mechanism involved. Thyrocalcitonin originates from the thyroid rather than the parathyroid glands, and its effect opposes the blood-calcium-raising action of PTH. Growth-hormone secretion is not the measured outcome. The conclusion should remain limited to what the treatment and observation establish: under the supplied conditions, TCT administration decreases the regulated blood-calcium variable. The relevant mechanism explains both the observed effect and the selectivity of that effect within the endocrine system.
115. Use the arrangement described below. A thyroid lobe is viewed from its posterior surface. Two small endocrine bodies are attached to that lobe, and an equivalent pair occurs on the posterior surface of the opposite lobe. These bodies are:
ⓐ. thyroid follicles
ⓑ. adrenal cortices
ⓒ. pancreatic islets
ⓓ. parathyroid glands
Correct Answer: parathyroid glands
Explanation: Humans generally possess four parathyroid glands arranged as two pairs on the posterior surface of the thyroid. One pair is associated with each thyroid lobe. The described position distinguishes them from thyroid follicles, which are microscopic units within thyroid tissue rather than separate bodies on its posterior surface. Adrenal cortices occur above the kidneys, and pancreatic islets are distributed within the pancreas. Both the number and the spatial relation are required: two small glands behind each of two thyroid lobes give the typical parathyroid arrangement. The figure description therefore identifies the posteriorly placed parathyroid glands rather than a component of the thyroid itself.
116. During an operation, the pair of parathyroid glands on the posterior surface of one thyroid lobe is removed. The other thyroid lobe retains its normal parathyroid pair, and thyroid follicular tissue remains functional. Which immediate interpretation is best supported?
ⓐ. Two parathyroids remain; losing two PTH sources directly increases blood calcium while thyroid hormones continue
ⓑ. Two parathyroids remain; PTH-dependent calcium support may fall while thyroid-hormone synthesis can continue
ⓒ. Two parathyroids remain; PTH-dependent calcium support may fall and thyroid hormones must fall in parallel
ⓓ. Four parathyroids remain; PTH action is unchanged while thyroid hormones fall
Correct Answer: Two parathyroids remain; PTH-dependent calcium support may fall while thyroid-hormone synthesis can continue
Explanation: A usual thyroid has two lobes, each associated with a pair of small parathyroid glands on its posterior surface. Removing the pair on one side leaves the two glands associated with the other lobe. Parathyroid hormone is a calcium-raising hormone: its actions on bone, kidney and intestine help maintain circulating \(\mathrm{Ca^{2+}}\). Losing two glands can reduce that hormonal contribution, although the stem does not establish the exact degree of compensation by the remaining pair. PTH secretion is regulated in relation to circulating calcium, so a precise postoperative concentration cannot be calculated from gland number alone. The thyroid follicular cells are a separate hormone-producing tissue. Since those cells remain functional, their synthesis of \(T_3\) and \(T_4\) need not stop solely because nearby parathyroids were removed. The answer combines anatomical counting with the distinct sources and effects of parathyroid and thyroid hormones.
117. Read the statements on parathyroid hormone.
I. It is a peptide hormone.
II. Its secretion is regulated by circulating \(\mathrm{Ca^{2+}}\) concentration.
III. Its combined actions increase blood \(\mathrm{Ca^{2+}}\).
IV. It is secreted by thyroid follicular cells.
ⓐ. I, II and III only
ⓑ. I and IV only
ⓒ. II, III and IV only
ⓓ. I, II, III and IV
Correct Answer: I, II and III only
Explanation: Parathyroid hormone is a peptide hormone released from the parathyroid glands. Its secretion responds to the concentration of circulating \(\mathrm{Ca^{2+}}\), connecting hormone output with the regulated variable. PTH raises blood calcium through several coordinated actions, so it is described as a hypercalcaemic hormone. Statements I, II and III are valid. Statement IV assigns PTH to thyroid follicular cells, which instead synthesise the iodothyronines \(T_3\) and \(T_4\). The close physical association of parathyroid glands with the thyroid can create source confusion, but posterior location does not make them thyroid follicles. The valid set preserves the hormone’s chemical class, regulator and net physiological effect. When the listed claims are evaluated, the set is established by checking every claim against the relevant source–target–effect pathway.
118. Place the events expected when circulating \(\mathrm{Ca^{2+}}\) falls below the regulated level in the correct sequence.
P. Blood \(\mathrm{Ca^{2+}}\) rises toward its previous level.
Q. PTH secretion increases.
R. Calcium release from bone and recovery through kidney and intestine increase.
S. Parathyroid glands detect the altered circulating calcium condition.
ⓐ. \(Q\rightarrow S\rightarrow P\rightarrow R\)
ⓑ. \(R\rightarrow Q\rightarrow S\rightarrow P\)
ⓒ. \(S\rightarrow R\rightarrow Q\rightarrow P\)
ⓓ. \(S\rightarrow Q\rightarrow R\rightarrow P\)
Correct Answer: \(S\rightarrow Q\rightarrow R\rightarrow P\)
Explanation: The pathway starts with an alteration in the regulated variable: circulating \(\mathrm{Ca^{2+}}\) falls. The parathyroid glands respond to this condition and increase PTH secretion. PTH then promotes processes that add calcium to the blood or reduce its loss, including bone demineralisation, greater renal tubular calcium reabsorption and increased intestinal calcium absorption. These coordinated target effects raise blood calcium toward its earlier level. The order must move from detection to endocrine output, then to target-organ actions and finally to correction of the regulated variable. The dependency sequence is \(S\rightarrow Q\rightarrow R\rightarrow P\). Reversing dependent events would place an effect before the signal or process required to produce it. Following the chain step by step prevents an upstream signal from being placed after its downstream response. The pathway can be checked by tracing the direction of information flow through successive structures or events.
119. An animal receives PTH, and the following changes are recorded.
| Site or variable | Observed change |
|---|
| Bone mineral | Demineralisation increases |
| Renal tubules | \(\mathrm{Ca^{2+}}\) reabsorption increases |
| Intestine | \(\mathrm{Ca^{2+}}\) absorption increases |
| Blood | \(\mathrm{Ca^{2+}}\) concentration rises |
The data support the classification of PTH as:
ⓐ. a hypocalcaemic thyroid hormone
ⓑ. a hypercalcaemic parathyroid hormone
ⓒ. a mineralocorticoid that conserves sodium
ⓓ. an antidiuretic hormone that conserves water
Correct Answer: a hypercalcaemic parathyroid hormone
Explanation: Parathyroid hormone raises the concentration of calcium in blood through effects at several sites. Increased bone demineralisation releases calcium from skeletal mineral stores. Greater renal tubular reabsorption returns more filtered calcium to the blood instead of allowing it to leave in urine. Increased intestinal absorption brings more calcium from digested food into the body. All three processes support the rise in blood \(\mathrm{Ca^{2+}}\) shown in the final table row. A hormone that raises this regulated variable is described as hypercalcaemic, and PTH is secreted by the parathyroid glands. The data link source, several target actions and their integrated blood response. Bone mobilisation contributes calcium, while kidney and intestine influence how much calcium is retained or enters from food. Focusing on only one site would miss why the recorded responses reinforce one another.
120. Two animals start with the same low blood \(\mathrm{Ca^{2+}}\). Both show an equal PTH response, with bone, kidney and intestinal PTH targets functioning normally. Animal Q additionally receives thyrocalcitonin, while Animal P does not. In graphs plotting blood \(\mathrm{Ca^{2+}}\) against time, which comparison is most justified after both treatments have acted?
ⓐ. Q has a larger calcium rise because thyrocalcitonin reinforces PTH at its targets
ⓑ. P and Q must show identical rises because their PTH responses are the same
ⓒ. Q has a lower calcium trajectory than P because thyrocalcitonin opposes PTH's calcium-raising effect
ⓓ. Q must fall below its starting level because thyrocalcitonin always dominates PTH
Correct Answer: Q has a lower calcium trajectory than P because thyrocalcitonin opposes PTH's calcium-raising effect
Explanation: The two animals have the same starting calcium level and the same effective PTH response. PTH acts on bone, renal tubules and intestine in ways that raise circulating calcium, so its calcium-raising contribution is shared by both animals. Q alone receives an additional signal: thyrocalcitonin, whose chapter-level effect is to lower blood \(\mathrm{Ca^{2+}}\). Relative to P, this added opposing influence makes Q's net calcium change smaller, placing its expected trajectory below P's under the stated equal conditions. The comparison does not fix the final numerical concentration in either animal, and it does not prove that Q must finish below its starting value. Equal PTH action cannot guarantee equal graph curves when another hormone differs between the animals. This prediction requires following both the common calcium-raising action and the additional calcium-lowering action rather than classifying either hormone in isolation.
