RAAS — MCQs
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A 63-year-old man comes to the physician because of fatigue and muscle cramps for 6 weeks. He also noticed several episodes of tingling around the mouth and in the fingers and toes. He has osteoarthritis of his knees and hypertension. Current medications include ibuprofen and ramipril. He has smoked one pack of cigarettes daily for 35 years. Tapping over the facial nerve area in front of the ear elicits twitching of the facial muscles on the same side of the face. His serum alkaline phosphatase activity is 66 U/L. An ECG shows sinus rhythm with a prolonged QT interval. Which of the following is the most likely underlying cause of this patient's symptoms?
A 23-year-old woman presents to a medical clinic for a follow-up visit. She initially came with complaints of recurrent headaches and darkening of her knuckles and skin creases, which first began 6 months ago after she underwent bilateral adrenalectomy. Today, she says that she frequently bumps into people and objects while walking. Which of the following mechanisms most likely account for this patient’s symptoms?
A 42-year-old gentleman presents to his primary care physician with complaints of persistent headaches and general weakness. He was recently diagnosed with severe hypertension that has been refractory to anti-hypertensive medications. Based on clinical suspicion, a basic metabolic panel is obtained which demonstrates a sodium level of 153 mg/dl and a potassium level of 2.9 mg/dl. The hormone that is the most likely cause of this patient's presentation is normally secreted by which region of the adrenal gland?
A 40-year-old man comes to the physician because of a 4-week history of generalized weakness. He also reports increased urination and thirst. He has type 2 diabetes mellitus and chronic kidney disease. His only medication is metformin. Serum studies show: Na+ 134 mEq/L Cl- 110 mEq/L K+ 5.6 mEq/L HCO3- 19 mEq/L Glucose 135 mg/dL Creatinine 1.6 mg/dL Urine pH is 5.1. Which of the following is the most likely underlying cause of this patient's symptoms?
A 41-year-old man is brought to the emergency room after a blunt-force injury to the abdomen. His pulse is 130/min and blood pressure is 70/40 mm Hg. Ultrasound of the abdomen shows a large amount of blood in the hepatorenal recess and the pelvis. Which of the following responses by the kidney is most likely?
Two days after vaginal delivery of a healthy newborn at term, a 32-year-old woman, gravida 2, para 2, is unable to breastfeed. Her labor was complicated by antepartum hemorrhage and she received two units of packed red blood cells. Her pulse is 99/min and blood pressure is 90/55 mm Hg. Further evaluation of this patient is most likely to show which of the following sets of serum findings? $$$ ACTH %%% Aldosterone %%% Cortisol $$$
A 51-year-old woman comes to the physician because of a 3-month history of fatigue, increased urinary frequency, and low back pain. She reports frequent passing of hard stools, despite using stool softeners. During this time, she has not been as involved with her weekly book club. Her family is concerned that she is depressed. She has no history of serious illness. She has smoked 1 pack of cigarettes daily for the past 20 years. Her pulse is 71/min and blood pressure is 150/90 mm Hg. Abdominal examination shows right costovertebral angle tenderness. The patient's symptoms are most likely caused by hyperplasia of which of the following?
A 55-year-old man with long-standing diabetes presents with a fragility fracture. He has chronic renal failure secondary to his diabetes. His serum parathyroid hormone concentration is elevated. You measure his serum concentration of 25(OH)-vitamin D and find it to be normal, but his concentration of 1,25(OH)-vitamin D is decreased. Which of the following represents a correct pairing of his clinical condition and serum calcium level?
An investigator is studying patients with acute decompensated congestive heart failure. He takes measurements of a hormone released from atrial myocytes, as well as serial measurements of left atrial and left ventricular pressures. The investigator observes a positive correlation between left atrial pressures and the serum level of this hormone. Which of the following is most likely the mechanism of action of this hormone?
A 64-year-old man presents to the emergency department with the complaints of nausea and muscle weakness for the past 24 hours. He further adds that he is significantly aware of his heartbeat. He was diagnosed with type II diabetes mellitus 20 years ago and hypertension 15 years ago for which he is taking metformin and captopril. He occasionally takes naproxen for his knee pain. He does not smoke but drinks alcohol occasionally. His father and sister also have diabetes. His vitals include a temperature of 37.1°C (98.8°F), blood pressure of 145/92 mm Hg, and a regular pulse of 87/min. His body mass index (BMI) is 32.5 kg/m2. Physical examination is insignificant except for grade 4 weakness in both lower limbs. Fingerstick blood glucose is 200 mg/dL. An ECG is ordered and shows peaked T waves. Lab studies show: Blood pH 7.32 Serum bicarbonate 19 mEq/L Serum sodium 135 mEq/L Serum chloride 107 mEq/L Serum potassium 6.5 mEq/L Urine anion gap 20 meq/L Which of the following is the primary defect responsible for this patient’s condition?
RAAS US Medical PG Practice Questions and MCQs
Question 1: A 63-year-old man comes to the physician because of fatigue and muscle cramps for 6 weeks. He also noticed several episodes of tingling around the mouth and in the fingers and toes. He has osteoarthritis of his knees and hypertension. Current medications include ibuprofen and ramipril. He has smoked one pack of cigarettes daily for 35 years. Tapping over the facial nerve area in front of the ear elicits twitching of the facial muscles on the same side of the face. His serum alkaline phosphatase activity is 66 U/L. An ECG shows sinus rhythm with a prolonged QT interval. Which of the following is the most likely underlying cause of this patient's symptoms?
- A. Medication side effect
- B. Ectopic hormone production
- C. Vitamin D deficiency
- D. Destruction of parathyroid glands (Correct Answer)
- E. Albright hereditary osteodystrophy
Explanation: ***Destruction of parathyroid glands*** - The patient presents with **fatigue**, **muscle cramps**, and **paresthesias** (tingling around the mouth, fingers, and toes), which are classic symptoms of **hypocalcemia**. - The positive **Chvostek's sign** (tapping over the facial nerve leading to facial muscle twitching) further confirms hypocalcemia, and a **prolonged QT interval** on ECG is also a known manifestation of low calcium levels. Destruction of the parathyroid glands (e.g., due to surgery, autoimmune disease, or radiation) leads to primary hypoparathyroidism and subsequent hypocalcemia. *Medication side effect* - While some medications can affect calcium levels, neither **ibuprofen** nor **ramipril** are typically associated with profound hypocalcemia leading to such prominent symptoms. - The constellation of symptoms and signs (Chvostek's sign, prolonged QT) strongly points to an underlying calcium metabolism disorder, not a common drug side effect. *Ectopic hormone production* - **Ectopic hormone production** (e.g., PTHrP from tumors) usually causes **hypercalcemia**, not hypocalcemia, by mimicking parathyroid hormone action. - Tumors that could lead to hypocalcemia are rare and usually involve extensive osteoblastic metastases consuming calcium, which is not suggested by the patient's presentation. *Vitamin D deficiency* - **Vitamin D deficiency** primarily causes osteomalacia in adults and rickets in children and can lead to **secondary hyperparathyroidism** as the body tries to compensate for low calcium. - While severe vitamin D deficiency can cause some hypocalcemia symptoms, it doesn't typically present with the acute, symptomatic hypocalcemia signs like Chvostek's sign and prolonged QT interval in this direct manner without other signs of bone disease. *Albright hereditary osteodystrophy* - **Albright hereditary osteodystrophy** is a genetic disorder causing **pseudohypoparathyroidism**, where the body is resistant to PTH, leading to hypocalcemia. - This condition is often associated with characteristic physical features such as **short stature**, **brachydactyly**, and **obesity**, which are not mentioned in this patient.
Question 2: A 23-year-old woman presents to a medical clinic for a follow-up visit. She initially came with complaints of recurrent headaches and darkening of her knuckles and skin creases, which first began 6 months ago after she underwent bilateral adrenalectomy. Today, she says that she frequently bumps into people and objects while walking. Which of the following mechanisms most likely account for this patient’s symptoms?
- A. Feedback inhibition by an exogenous source
- B. Hormonal receptor downregulation
- C. Dissemination of tumor to distant sites
- D. Ectopic secretion of a trophic hormone
- E. Loss of a regulatory process (Correct Answer)
Explanation: ***Loss of a regulatory process*** - This patient likely has **Nelson's syndrome**, which develops after bilateral adrenalectomy for **Cushing's disease**. The removal of adrenal glands eliminates the **negative feedback** normally exerted by cortisol on the pituitary gland. - This leads to unchecked growth of a pre-existing corticotroph adenoma, causing excessive **ACTH** secretion. The high ACTH levels result in **hyperpigmentation** (darkening knuckles and skin creases) due to its melanocyte-stimulating properties, and the growing tumor can cause **visual field defects** (bumping into objects) due to compression of the optic chiasm. *Feedback inhibition by an exogenous source* - This mechanism involves the suppression of endogenous hormone production by an external agent, such as corticosteroid medication. - In this case, the patient's symptoms are due to a lack of feedback, not an excess. *Hormonal receptor downregulation* - This process involves a decrease in the number or sensitivity of receptors in response to prolonged high hormone levels, making the cells less responsive. - While relevant in some endocrine disorders, it does not explain the pituitary tumor growth or the specific constellation of symptoms seen here. *Dissemination of tumor to distant sites* - This option refers to metastasis, where a cancer spreads from its primary location to other parts of the body. - Although the pituitary adenoma grows, Nelson's syndrome is primarily characterized by local tumor expansion and hormonal effects, not distant metastasis. *Ectopic secretion of a trophic hormone* - Ectopic secretion refers to the production of hormones by tissues that do not normally produce them, often associated with paraneoplastic syndromes. - In this scenario, the ACTH is secreted by an adenoma within the pituitary gland, which is its normal site of production, albeit in an unregulated and excessive manner.
Question 3: A 42-year-old gentleman presents to his primary care physician with complaints of persistent headaches and general weakness. He was recently diagnosed with severe hypertension that has been refractory to anti-hypertensive medications. Based on clinical suspicion, a basic metabolic panel is obtained which demonstrates a sodium level of 153 mg/dl and a potassium level of 2.9 mg/dl. The hormone that is the most likely cause of this patient's presentation is normally secreted by which region of the adrenal gland?
- A. Adrenal Medulla
- B. Adrenal Capsule
- C. Zona Reticularis
- D. Zona Glomerulosa (Correct Answer)
- E. Zona Fasciculata
Explanation: ***Zona Glomerulosa*** - The patient's presentation of **severe hypertension refractory to treatment**, **hypernatremia** (sodium 153 mg/dl), and **hypokalemia** (potassium 2.9 mg/dl) is highly suggestive of **primary hyperaldosteronism**. - **Aldosterone**, the hormone responsible for this clinical picture, is primarily secreted by the **zona glomerulosa** of the adrenal cortex. *Adrenal Medulla* - The adrenal medulla primarily secretes **catecholamines** (**epinephrine** and **norepinephrine**), which are involved in the "fight or flight" response. - While excess catecholamines can cause hypertension, they do not typically lead to the characteristic electrolyte disturbances of hypernatremia and hypokalemia seen in this patient. *Adrenal Capsule* - The adrenal capsule is the **outer protective layer** of the adrenal gland and does not secrete hormones. - Its primary function is structural support and protection for the underlying adrenal cortex and medulla. *Zona Reticularis* - The zona reticularis is the innermost layer of the adrenal cortex and primarily produces **androgens**, such as **dehydroepiandrosterone (DHEA)**. - While androgen excess can have various effects, it does not explain the patient's severe hypertension, hypernatremia, and hypokalemia. *Zona Fasciculata* - The zona fasciculata is the middle and thickest layer of the adrenal cortex, responsible for secreting **glucocorticoids**, primarily **cortisol**. - Excess cortisol (Cushing's syndrome) can cause hypertension and hypokalemia, but hypernatremia is less typical; indeed, **cortisol can have mineralocorticoid effects**, but primary hyperaldosteronism is a more specific fit for this electrolyte profile.
Question 4: A 40-year-old man comes to the physician because of a 4-week history of generalized weakness. He also reports increased urination and thirst. He has type 2 diabetes mellitus and chronic kidney disease. His only medication is metformin. Serum studies show: Na+ 134 mEq/L Cl- 110 mEq/L K+ 5.6 mEq/L HCO3- 19 mEq/L Glucose 135 mg/dL Creatinine 1.6 mg/dL Urine pH is 5.1. Which of the following is the most likely underlying cause of this patient's symptoms?
- A. Impaired HCO3- reabsorption in the proximal tubule
- B. Decreased serum cortisol levels
- C. Impaired H+ secretion in the distal tubule
- D. Increased serum lactate levels
- E. Decreased serum aldosterone levels (Correct Answer)
Explanation: ***Decreased serum aldosterone levels*** - The patient presents with **hyperkalemia** (K+ 5.6 mEq/L) and a **normal anion gap metabolic acidosis** (HCO3- 19 mEq/L, anion gap = Na - (Cl + HCO3) = 134 - (110 + 19) = 5 mEq/L), along with a relatively **acidic urine pH of 5.1**. - **Aldosterone deficiency** (often seen in **hyporeninemic hypoaldosteronism** associated with diabetes and chronic kidney disease) characteristically causes type 4 renal tubular acidosis, leading to impaired potassium and hydrogen excretion, thus presenting with hyperkalemia and a normal anion gap metabolic acidosis with low urine pH. *Impaired HCO3- reabsorption in the proximal tubule* - This describes **proximal (type 2) renal tubular acidosis (RTA)**, which typically presents with a **normal anion gap metabolic acidosis**, but usually causes **hypokalemia** due to increased distal potassium excretion. - While it can cause an acidic urine, the predominant feature of hypokalemia is contrary to the patient's hyperkalemia. *Impaired H+ secretion in the distal tubule* - This describes **distal (type 1) renal tubular acidosis (RTA)**, which is characterized by an inability to acidify urine, resulting in a **urine pH > 5.5** in the presence of systemic acidosis. - This contradicts the patient's **acidic urine pH of 5.1**, making type 1 RTA less likely. *Increased serum lactate levels* - **Lactic acidosis** is an **anion gap metabolic acidosis**, whereas this patient has a **normal anion gap metabolic acidosis**. - While metformin can cause lactic acidosis, the calculated anion gap of 5 mEq/L is normal, ruling out this cause. *Decreased serum cortisol levels* - Decreased serum cortisol levels (e.g., in **adrenal insufficiency**) can lead to hyponatremia, hyperkalemia, and acidosis. - However, the primary cause of the acidosis in adrenal insufficiency is usually due to the lack of mineralocorticoid effects (aldosterone), and the presentation here is more specifically aligned with a renal defect in hydrogen and potassium handling.
Question 5: A 41-year-old man is brought to the emergency room after a blunt-force injury to the abdomen. His pulse is 130/min and blood pressure is 70/40 mm Hg. Ultrasound of the abdomen shows a large amount of blood in the hepatorenal recess and the pelvis. Which of the following responses by the kidney is most likely?
- A. Increased sodium reabsorption (Correct Answer)
- B. Increased creatinine reabsorption
- C. Decreased proton excretion
- D. Decreased potassium excretion
- E. Increased sodium filtration
Explanation: ***Increased sodium reabsorption*** - The patient's **hypotension** (70/40 mm Hg) and **tachycardia** (130/min) indicate **hypovolemic shock** due to significant blood loss. - In response to decreased renal perfusion and activated **renin-angiotensin-aldosterone system** (RAAS) and sympathetic nervous system, the kidneys will **increase sodium and water reabsorption** to restore blood volume and pressure. *Increased creatinine reabsorption* - **Creatinine** is freely filtered by the glomeruli and is primarily **excreted** in the urine with very minimal reabsorption. - An increase in creatinine reabsorption is not a normal physiological response to hypovolemic shock. *Decreased proton excretion* - In hypovolemic shock, there is often **lactic acidosis** due to tissue hypoperfusion, which would lead to an **increase in proton excretion** to compensate for the acidosis, not a decrease. - The kidneys aim to maintain acid-base balance by excreting excess acids. *Decreased potassium excretion* - **Aldosterone**, which is highly activated in hypovolemic shock, promotes **sodium reabsorption** in exchange for **potassium and hydrogen ion excretion**. - Therefore, during hypovolemic shock, potassium excretion is typically **increased**, not decreased. *Increased sodium filtration* - In hypovolemic shock, the **glomerular filtration rate (GFR)** decreases due to reduced renal blood flow and perfusion pressure. - A decreased GFR would lead to **decreased sodium filtration**, not an increase, as less blood is filtered through the glomeruli.
Question 6: Two days after vaginal delivery of a healthy newborn at term, a 32-year-old woman, gravida 2, para 2, is unable to breastfeed. Her labor was complicated by antepartum hemorrhage and she received two units of packed red blood cells. Her pulse is 99/min and blood pressure is 90/55 mm Hg. Further evaluation of this patient is most likely to show which of the following sets of serum findings? $$$ ACTH %%% Aldosterone %%% Cortisol $$$
- A. ↑ ↓ ↓
- B. ↓ ↑ ↓
- C. ↑ normal ↑
- D. ↓ normal ↑
- E. ↓ normal ↓ (Correct Answer)
Explanation: ***↓ normal ↓*** - This scenario describes **Sheehan's syndrome**, caused by **postpartum pituitary necrosis** due to severe hemorrhage and hypotension during delivery. - Decreased **ACTH** (adrenocorticotropic hormone) leads to secondary **adrenal insufficiency**, causing decreased **cortisol**. **Aldosterone** secretion, primarily regulated by the **renin-angiotensin system**, remains largely normal because only the zona glomerulosa of the adrenal cortex, which produces aldosterone, is regulated directly by the renin-angiotensin-aldosterone system (RAAS), whereas the pituitary regulates the zona fasciculata and zona reticularis. *↑ ↓ ↓* - This pattern (high ACTH, low aldosterone, low cortisol) suggests **primary adrenal insufficiency** (Addison's disease), where the adrenal glands themselves are failing, leading to a compensatory increase in ACTH. However, this patient's condition is due to pituitary damage. - In primary adrenal insufficiency, both **cortisol** and **aldosterone** would be low, and **ACTH** would be elevated due to a lack of negative feedback. *↓ ↑ ↓* - This pattern (low ACTH, high aldosterone, low cortisol) is inconsistent with most common adrenal or pituitary pathologies. Low ACTH and low cortisol would suggest secondary adrenal insufficiency, but high aldosterone does not fit. - **Hyperaldosteronism** with secondary adrenal insufficiency is rare and not indicated by the patient's presentation. *↑ normal ↑* - This pattern (high ACTH, normal aldosterone, high cortisol) suggests **Cushing's disease** (pituitary adenoma secreting ACTH), or an ectopic ACTH tumor, or a state of acute stress. - The patient's **hypotension** and inability to breastfeed point away from Cushing's and towards hypopituitarism. *↓ normal ↑* - This pattern (low ACTH, normal aldosterone, high cortisol) could be seen in states of iatrogenic **exogenous corticosteroid use**, leading to suppressed ACTH and endogenous cortisol, or in an adrenal tumor producing cortisol independent of ACTH. - This is inconsistent with the symptoms of postpartum hemorrhage and inability to lactate, which indicate a **deficit** rather than an excess of pituitary hormones.
Question 7: A 51-year-old woman comes to the physician because of a 3-month history of fatigue, increased urinary frequency, and low back pain. She reports frequent passing of hard stools, despite using stool softeners. During this time, she has not been as involved with her weekly book club. Her family is concerned that she is depressed. She has no history of serious illness. She has smoked 1 pack of cigarettes daily for the past 20 years. Her pulse is 71/min and blood pressure is 150/90 mm Hg. Abdominal examination shows right costovertebral angle tenderness. The patient's symptoms are most likely caused by hyperplasia of which of the following?
- A. Spindle cells in the kidney
- B. Chromaffin cells in the adrenal gland
- C. Kulchitsky cells in the lung
- D. Parafollicular cells in the thyroid gland
- E. Chief cells in the parathyroid gland (Correct Answer)
Explanation: ***Chief cells in the parathyroid gland*** - The patient's symptoms (fatigue, constipation despite stool softeners, increased urinary frequency, low back pain, and possible depression) are classic signs of **hypercalcemia**. Hypercalcemia, when persistent, is most commonly caused by **primary hyperparathyroidism**, characterized by hyperplasia or adenoma of the **parathyroid chief cells**. - **Hypercalcemia** can lead to "stones, bones, groans, and psychiatric overtones": **kidney stones** (increased urinary frequency), **bone pain** (low back pain), **abdominal groans** (constipation), and **psychiatric symptoms** (fatigue, depression, lethargy). The costovertebral angle tenderness may indicate nephrolithiasis. *Spindle cells in the kidney* - This description typically refers to cells found in certain renal tumors, such as **renal cell carcinoma**, particularly the sarcomatoid variant. - While renal cell carcinoma can present with flank pain, fatigue, and sometimes palpable masses, it does not directly cause the *constellation of hypercalcemia symptoms* described, unless it is a paraneoplastic syndrome, which is less common than primary hyperparathyroidism as a cause of sustained hypercalcemia. *Chromaffin cells in the adrenal gland* - Hyperplasia of **chromaffin cells** in the adrenal medulla causes **pheochromocytoma**, which presents with episodic hypertension, palpitations, headaches, and sweating due to excessive **catecholamine release**. - These symptoms do not match the patient's presentation of fatigue, constipation, and urinary frequency; nor does pheochromocytoma directly cause hypercalcemia. *Kulchitsky cells in the lung* - **Kulchitsky cells** (neuroendocrine cells) in the lung can undergo hyperplasia or transform into **small cell lung carcinoma (SCLC)** or **carcinoid tumors**. - SCLC can cause **paraneoplastic syndromes**, such as SIADH (hyponatremia) or ectopic ACTH production (Cushing's syndrome), but not typically hypercalcemia due to PTHrP. Carcinoid tumors can cause carcinoid syndrome (flushing, diarrhea). *Parafollicular cells in the thyroid gland* - Hyperplasia or neoplasia of **parafollicular cells** (C cells) in the thyroid gland causes **medullary thyroid carcinoma**, which secretes **calcitonin**. - **Calcitonin** acts to *lower serum calcium levels*, therefore, hyperplasia of these cells would generally lead to **hypocalcemia** or normocalcemia, not hypercalcemia.
Question 8: A 55-year-old man with long-standing diabetes presents with a fragility fracture. He has chronic renal failure secondary to his diabetes. His serum parathyroid hormone concentration is elevated. You measure his serum concentration of 25(OH)-vitamin D and find it to be normal, but his concentration of 1,25(OH)-vitamin D is decreased. Which of the following represents a correct pairing of his clinical condition and serum calcium level?
- A. Secondary hyperparathyroidism with elevated serum calcium
- B. Primary hyperparathyroidism with low serum calcium
- C. Tertiary hyperparathyroidism with low serum calcium
- D. Secondary hyperparathyroidism with low serum calcium (Correct Answer)
- E. Primary hyperparathyroidism with elevated serum calcium
Explanation: ***Secondary hyperparathyroidism with low serum calcium*** - **Chronic renal failure** leads to reduced 1-alpha hydroxylation in the kidneys, decreasing the conversion of 25(OH)-vitamin D to its active form, **1,25(OH)-vitamin D**. - This **decrease in active vitamin D** impairs intestinal calcium absorption and causes resistance to PTH in bone, resulting in **hypocalcemia**, which then stimulates the parathyroid glands to produce more PTH, leading to **secondary hyperparathyroidism**. *Secondary hyperparathyroidism with elevated serum calcium* - In secondary hyperparathyroidism due to chronic renal failure, the aim is to correct **hypocalcemia**, so a persistently elevated serum calcium would suggest a different or progressing pathology, such as tertiary hyperparathyroidism. - While PTH is elevated, it is primarily trying to normalize calcium, which is typically low or low-normal, not elevated, in uncomplicated secondary hyperparathyroidism. *Primary hyperparathyroidism with low serum calcium* - **Primary hyperparathyroidism** is characterized by excessive PTH production from a parathyroid adenoma or hyperplasia and typically results in **hypercalcemia**, not low serum calcium. - The elevated PTH in primary hyperparathyroidism is autonomous, not provoked by hypocalcemia, and would also lead to elevated 1,25(OH)-vitamin D levels. *Tertiary hyperparathyroidism with low serum calcium* - **Tertiary hyperparathyroidism** occurs when prolonged secondary hyperparathyroidism leads to autonomous PTH secretion, often resulting in **hypercalcemia**, not hypocalcemia, despite the underlying renal failure. - This option incorrectly pairs tertiary hyperparathyroidism with low serum calcium; the key feature of tertiary hyperparathyroidism is the emancipation of PTH secretion from calcium regulation. *Primary hyperparathyroidism with elevated serum calcium* - While **primary hyperparathyroidism** typically presents with elevated serum calcium, this patient has **chronic renal failure** and a decreased 1,25(OH)-vitamin D, which points to a renal etiology for the calcium imbalance. - In primary hyperparathyroidism, 1,25(OH)-vitamin D levels would generally be normal or elevated due to PTH stimulation of renal 1-alpha hydroxylase, which contradicts the patient's decreased levels.
Question 9: An investigator is studying patients with acute decompensated congestive heart failure. He takes measurements of a hormone released from atrial myocytes, as well as serial measurements of left atrial and left ventricular pressures. The investigator observes a positive correlation between left atrial pressures and the serum level of this hormone. Which of the following is most likely the mechanism of action of this hormone?
- A. Increases potassium excretion at the collecting ducts
- B. Constricts afferent renal arteriole
- C. Decreases sodium reabsorption at the collecting tubules (Correct Answer)
- D. Decreases reabsorption of bicarbonate in the proximal convoluted tubules
- E. Increases free water reabsorption from the distal tubules
Explanation: ***Decreases sodium reabsorption at the collecting tubules*** - The hormone described, exhibiting a positive correlation with left atrial pressure and released from atrial myocytes, is **Atrial Natriuretic Peptide (ANP)**. - ANP promotes **natriuresis** (sodium excretion) and **diuresis** by directly inhibiting sodium reabsorption in the collecting tubules, thereby reducing blood volume and cardiac preload. *Increases potassium excretion at the collecting ducts* - While ANP does promote fluid and electrolyte excretion, its primary effect is on sodium and water, not a direct increase in **potassium excretion**. **Aldosterone**, not ANP, primarily increases potassium secretion in the collecting ducts. - This option describes a mechanism more consistent with **mineralocorticoid activity**, which is counteracted by ANP. *Constricts afferent renal arteriole* - ANP generally causes **vasodilation** of the afferent arteriole and constriction of the efferent arteriole, increasing glomerular filtration rate (GFR). - **Angiotensin II** is a primary constrictor of the afferent and efferent renal arterioles, which is the opposite effect of ANP. *Decreases reabsorption of bicarbonate in the proximal convoluted tubules* - This mechanism is primarily involved in **acid-base balance** and is influenced by factors like parathyroid hormone or respiratory/metabolic acidosis/alkalosis. - ANP's main action is on **sodium and water balance**, not directly on bicarbonate reabsorption. *Increases free water reabsorption from the distal tubules* - **Vasopressin (Antidiuretic Hormone, ADH)** is responsible for increasing free water reabsorption in the distal tubules and collecting ducts. - ANP's action is to *increase* water excretion, working in opposition to ADH to reduce circulating fluid volume.
Question 10: A 64-year-old man presents to the emergency department with the complaints of nausea and muscle weakness for the past 24 hours. He further adds that he is significantly aware of his heartbeat. He was diagnosed with type II diabetes mellitus 20 years ago and hypertension 15 years ago for which he is taking metformin and captopril. He occasionally takes naproxen for his knee pain. He does not smoke but drinks alcohol occasionally. His father and sister also have diabetes. His vitals include a temperature of 37.1°C (98.8°F), blood pressure of 145/92 mm Hg, and a regular pulse of 87/min. His body mass index (BMI) is 32.5 kg/m2. Physical examination is insignificant except for grade 4 weakness in both lower limbs. Fingerstick blood glucose is 200 mg/dL. An ECG is ordered and shows peaked T waves. Lab studies show: Blood pH 7.32 Serum bicarbonate 19 mEq/L Serum sodium 135 mEq/L Serum chloride 107 mEq/L Serum potassium 6.5 mEq/L Urine anion gap 20 meq/L Which of the following is the primary defect responsible for this patient’s condition?
- A. Decreased aldosterone secretion (Correct Answer)
- B. Metformin overdose
- C. Increased ketogenesis
- D. Impaired distal tubule acidification in the kidneys
- E. Decreased bicarbonate reabsorption in the proximal tubules
Explanation: ***Decreased aldosterone secretion*** - This patient's **hyperkalemia** (serum potassium 6.5 mEq/L), **mild metabolic acidosis** (pH 7.32, bicarbonate 19 mEq/L), and elevated urine anion gap (20 mEq/L) are consistent with **Type 4 renal tubular acidosis (RTA)**, which is primarily caused by **decreased aldosterone secretion** or renal hyporesponsiveness to aldosterone. - **Captopril**, an ACE inhibitor, can cause **hypoaldosteronism** by inhibiting the conversion of angiotensin I to angiotensin II, leading to reduced aldosterone synthesis and secretion. This results in impaired potassium excretion and hydrogen ion secretion. *Metformin overdose* - While metformin can cause **lactic acidosis**, the primary issue here is **hyperkalemia** and metabolic acidosis due to impaired potassium and hydrogen ion excretion, not solely lactate accumulation. - The symptoms (nausea, muscle weakness, palpitations) are more indicative of severe hyperkalemia and are less specific to metformin overdose. *Increased ketogenesis* - **Diabetic ketoacidosis (DKA)** involves increased ketogenesis leading to severe metabolic acidosis with a high anion gap. However, the patient's blood glucose (200 mg/dL) is not typically high enough for DKA, and the symptoms, particularly prominent muscle weakness and peaked T waves, point more strongly to **hyperkalemia** rather than DKA. - The **urine anion gap** would typically be negative or slightly positive in DKA, not highly positive (>10) which indicates impaired ammonium excretion. *Impaired distal tubule acidification in the kidneys* - **Impaired distal tubule acidification** is characteristic of **Type 1 RTA**, which typically presents with **hypokalemia** (due to increased potassium excretion) and a metabolic acidosis, rather than the hyperkalemia seen in this patient. - While it can cause metabolic acidosis, the mechanism and electrolyte derangements are different from those observed here. *Decreased bicarbonate reabsorption in the proximal tubules* - **Decreased bicarbonate reabsorption** in the proximal tubules is characteristic of **Type 2 RTA**, which typically presents with **hypokalemia** and a metabolic acidosis. - The key differentiating factor is the potassium level; this patient has **hyperkalemia**, ruling out Type 2 RTA.
Question 11: A 33-year-old woman presents to her primary care provider for a normal check-up. She reports she has been feeling intermittently fatigued over the past 3 months, but she attributes it to her work as a corporate lawyer and balancing family life. She is otherwise healthy and takes no medications. She was adopted and has no information about her biological family. She has 2 children and has been married for 7 years. She drinks 4-5 glasses of wine per week and does not smoke. Her temperature is 99.2°F (37.3°C), blood pressure is 125/65 mmHg, pulse is 78/min, and respirations are 18/min. On exam, she is well-appearing and in no acute distress. A complete blood count is within normal limits. Additional workup is shown below: Serum: Na+: 139 mEq/L Cl-: 99 mEq/L K+: 3.9 mEq/L HCO3-: 23 mEq/L BUN: 18 mg/dL Glucose: 110 mg/dL Creatinine: 1.1 mg/dL Ca2+: 11.1 mg/dL Parathyroid hormone: 700 pg/mL Urine: Na+: 100 mEq/L/24h Ca2+: 100 mg/24h Osmolality: 400 mOsmol/kg H2O Which of the following is the most likely underlying cause of this patient's condition?
- A. Over-secretion of parathyroid hormone
- B. Decreased sensitivity to parathyroid hormone
- C. Gain-of-function mutation in the parathyroid hormone receptor gene
- D. Impaired tubular calcium reabsorption
- E. Loss-of-function mutation in the calcium-sensing receptor (Correct Answer)
Explanation: ***Loss-of-function mutation in the calcium-sensing receptor*** - The patient presents with **hypercalcemia** (Ca2+ 11.1 mg/dL) and **elevated parathyroid hormone (PTH)** (700 pg/mL), which is inappropriate given the high calcium. This combination is highly suggestive of **familial hypocalciuric hypercalcemia (FHH)**. - FHH is caused by an inactivating mutation in the **calcium-sensing receptor (CaSR)**, leading to a "reset" of the calcium set point. The parathyroid glands and renal tubules perceive normal calcium levels as low, resulting in increased PTH secretion and increased renal tubular calcium reabsorption, despite hypercalcemia. *Over-secretion of parathyroid hormone* - While PTH is elevated, simply stating "over-secretion" doesn't explain why this is occurring in the setting of hypercalcemia, which should normally suppress PTH. - This option would typically describe **primary hyperparathyroidism**, but the urinary calcium excretion in this patient (100 mg/24h) is in the low-normal range for hypercalcemia, making FHH a more likely diagnosis than primary hyperparathyroidism. *Decreased sensitivity to parathyroid hormone* - **Decreased sensitivity to PTH** would typically lead to **hypocalcemia** or normal calcium levels, not the hypercalcemia seen in this patient. - Conditions like **pseudohypoparathyroidism** involve PTH resistance but present with hypocalcemia and hyperphosphatemia. *Gain-of-function mutation in the parathyroid hormone receptor gene* - A **gain-of-function mutation** in the PTH receptor would lead to enhanced sensitivity to PTH, causing **hypercalcemia** and **hypophosphatemia**. - However, the PTH level would typically be **suppressed or low** due to feedback inhibition from hypercalcemia, which is contrary to the elevated PTH seen in this patient. *Impaired tubular calcium reabsorption* - **Impaired tubular calcium reabsorption** would lead to **hypercalciuria** (high urinary calcium) and likely normal or low serum calcium as calcium is excessively excreted. - This patient exhibits relatively **low urinary calcium excretion** (100 mg/24h) despite hypercalcemia, which is characteristic of FHH.
Question 12: A couple brings their 1-year-old child to a medical office for a follow-up evaluation of his small, empty scrotum. The scrotum has been empty since birth and the physician asked them to follow up with a pediatrician. There are no other complaints. The immunization history is up to date and his growth and development have been excellent. On examination, he is a playful, active child with a left, non-reducible, non-tender inguinal mass, an empty and poorly rugated hemiscrotal sac, and a testis within the right hemiscrotal sac. Which of the following hormones would likely be deficient in this patient by puberty if the condition is left untreated?
- A. LH
- B. Testosterone (Correct Answer)
- C. FSH
- D. Inhibin
- E. Prolactin
Explanation: ***Testosterone*** - **Testosterone** is produced by the **Leydig cells** in the testes. In untreated cryptorchidism, the elevated temperature in the inguinal canal causes progressive damage to both Sertoli cells and **Leydig cells** over time. - By **puberty**, if left untreated for 11-13 years, the undescended testis will have significant irreversible Leydig cell dysfunction, leading to **reduced testosterone production**. - While unilateral cryptorchidism may allow the contralateral descended testis to partially compensate, this compensation is often **incomplete during the high testosterone demands of puberty**, resulting in relative testosterone deficiency. - This is the most clinically significant hormonal deficiency that develops with prolonged untreated cryptorchidism. *LH* - **Luteinizing hormone (LH)** is produced by the anterior pituitary and stimulates Leydig cells to produce testosterone. In cryptorchidism with resulting testosterone deficiency, LH levels would be **elevated** (not deficient) as a compensatory response. - The pituitary responds normally to low testosterone with increased LH secretion via loss of negative feedback. *Inhibin* - **Inhibin** is produced by **Sertoli cells** in the seminiferous tubules. While cryptorchidism impairs Sertoli cell function and spermatogenesis, inhibin itself is not typically **deficient**. - The primary consequence is **impaired spermatogenesis**, which leads to reduced negative feedback and **elevated FSH** levels, but inhibin levels may remain normal or only modestly reduced. *FSH* - **Follicle-stimulating hormone (FSH)** is produced by the anterior pituitary. In cryptorchidism, FSH is typically **elevated** (not deficient) due to impaired Sertoli cell function and loss of negative feedback from the seminiferous tubules. - Elevated FSH is a marker of tubular dysfunction but is not itself deficient. *Prolactin* - **Prolactin** is produced by the anterior pituitary and primarily regulates lactation. It has no direct role in testicular function or the pathophysiology of cryptorchidism. - There is no association between cryptorchidism and prolactin deficiency.
Question 13: A 25-year-old woman comes to the physician for a pre-employment examination. Her current medications include an oral contraceptive and a daily multivitamin. Physical examination is unremarkable. Serum studies show calcium of 11.8 mg/dL, phosphorus of 2.3 mg/dL, and parathyroid hormone level of 615 pg/mL. A 24-hour urine collection shows a low urinary calcium level. Which of the following is the most likely underlying cause of this patient’s laboratory findings?
- A. Extrarenal calcitriol production
- B. Impaired phosphate excretion
- C. Hyperplasia of parathyroid chief cells
- D. IL-1-induced osteoclast activation
- E. Defect in calcium-sensing receptors (Correct Answer)
Explanation: ***Defect in calcium-sensing receptors*** - The constellation of **hypercalcemia**, **low urinary calcium**, **elevated PTH**, and **hypophosphatemia** is highly suggestive of **Familial Hypocalciuric Hypercalcemia (FHH)**, which is caused by an inactivating defect in calcium-sensing receptors (CaSR) in the parathyroid glands and renal tubules. - In FHH, the parathyroid glands misinterpret the elevated serum calcium as normal or low, leading to **inappropriately high PTH secretion**, while the kidneys excessively reabsorb calcium due to defective CaSRs, resulting in low urinary calcium excretion. *Extrarenal calcitriol production* - This would cause **hypercalcemia** and **hyperphosphatemia** due to increased intestinal absorption of both calcium and phosphate. - **PTH levels** would typically be suppressed, not elevated, in response to hypercalcemia. *Impaired phosphate excretion* - This would lead to **hyperphosphatemia**, not the **hypophosphatemia** observed in the patient. - While hyperphosphatemia can indirectly affect calcium, it does not directly explain the high PTH in the presence of hypercalcemia and low urinary calcium. *Hyperplasia of parathyroid chief cells* - Parathyroid chief cell hyperplasia leads to **primary hyperparathyroidism**, characterized by **hypercalcemia**, **elevated PTH**, and typically **hypercalciuria** (high urinary calcium) due to PTH's actions on the kidney, unlike the low urinary calcium seen in this patient. - While PTH is elevated and calcium is high, the distinguishing feature here is the **low urinary calcium**, which rules out typical primary hyperparathyroidism. *IL-1-induced osteoclast activation* - This mechanism is seen in the **humoral hypercalcemia of malignancy (HHM)**, often due to parathyroid hormone-related protein (PTHrP) secretion or cytokine release by tumors. - In HHM, **PTH levels** would be suppressed, and **phosphate would be normal or low**, but the hallmark is the absence of elevated PTH and often very high calcium, which doesn't match this patient's profile.
Question 14: Activation of the renin-angiotensin-aldosterone system yields a significant physiological effect on renal blood flow and filtration. Which of the following is most likely to occur in response to increased levels of Angiotensin-II?
- A. Decreased renal plasma flow, decreased filtration fraction
- B. Decreased renal plasma flow, increased glomerular capillary oncotic pressure
- C. Increased renal plasma flow, decreased filtration fraction
- D. Increased renal plasma flow, increased filtration fraction
- E. Decreased renal plasma flow, increased filtration fraction (Correct Answer)
Explanation: ***Decreased renal plasma flow, increased filtration fraction*** - **Angiotensin II** causes **efferent arteriolar constriction**, which reduces blood flow leaving the glomerulus, thereby **decreasing renal plasma flow**. - This efferent constriction also increases **glomerular hydrostatic pressure** and reduces plasma flow distal to the glomerulus, leading to a **higher filtration fraction** (GFR/RPF). *Decreased renal plasma flow, decreased filtration fraction* - While **renal plasma flow decreases**, a **decreased filtration fraction** would imply that either GFR decreases disproportionately more than RPF or GFR does not increase despite the RPF reduction, which is not the typical response to **angiotensin II** due to its predominant effect on the **efferent arteriole**. *Decreased renal plasma flow, increased glomerular capillary oncotic pressure* - **Increased glomerular capillary oncotic pressure** is a consequence of increased filtration fraction, as more fluid is filtered out, leaving behind a more concentrated plasma. This option includes a correct element (decreased RPF) but pairs it with a less direct and defining outcome of acute Angiotensin II action as the primary physiological effect. *Increased renal plasma flow, decreased filtration fraction* - **Angiotensin II** causes **vasoconstriction**, predominantly of the efferent arteriole, which by definition would **decrease renal plasma flow**, not increase it. - A **decreased filtration fraction** would be inconsistent with efferent arteriolar constriction which typically raises GFR relative to RPF. *Increased renal plasma flow, increased filtration fraction* - **Angiotensin II** causes **vasoconstriction**, leading to a **decrease in renal plasma flow**, not an increase. - While **filtration fraction is increased**, the initial premise of increased renal plasma flow is incorrect.
Question 15: A 41-year-old female complains of frequent diarrhea and abdominal pain between meals. Endoscopy reveals a duodenal ulcer distal to the duodenal bulb. CT scan of the abdomen demonstrates a pancreatic mass, and subsequent tissue biopsy of the pancreas reveals a malignant islet cell tumor. Which of the following hormones is likely to be markedly elevated in this patient:
- A. Secretin
- B. Vasoactive intestinal peptide
- C. Cholecystokinin
- D. Gastrin (Correct Answer)
- E. Motilin
Explanation: ***Gastrin*** - A pancreatic mass (likely a **gastrinoma**) producing excess **gastrin** leads to Zollinger-Ellison syndrome, characterized by refractory **peptic ulcers** (especially distal to the duodenal bulb) and **diarrhea** due to increased gastric acid. - The high gastrin levels stimulate parietal cells to secrete an excessive amount of **hydrochloric acid**, overwhelming the neutralizing capacity of the duodenum and causing ulcers. *Secretin* - Secretin is released from S cells in the duodenum in response to acid and fatty acids, stimulating **bicarbonate secretion** from the pancreas and bile ducts. - While secretin can be used diagnostically to confirm gastrinoma (paradoxical increase in gastrin), it is not the primary hormone elevated in this syndrome causing the symptoms. *Vasoactive intestinal peptide* - Elevated vasoactive intestinal peptide (VIP) is characteristic of a **VIPoma**, which causes **profuse watery diarrhea** (pancreatic cholera), hypokalemia, and achlorhydria. - This patient's symptoms include abdominal pain and duodenal ulcers which are not typical for a VIPoma. *Cholecystokinin* - **Cholecystokinin (CCK)** is primarily involved in stimulating gallbladder contraction and pancreatic enzyme secretion in response to fats and proteins. - While it can be produced by some neuroendocrine tumors, it does not typically cause the constellation of symptoms (refractory duodenal ulcers, severe diarrhea) seen in this patient. *Motilin* - Motilin is responsible for initiating the **migrating motor complex** during the interdigestive phase, promoting gut motility. - While altered motility can contribute to diarrhea, motilin is not typically associated with ulcer formation or pancreatic islet cell tumors causing gastric hypersecretion.
Question 16: A 16-year-old male presents to his pediatrician concerned that he is not maturing like his friends. He has a history of cleft palate status-post multiple surgeries and asthma treated with budesonide and albuterol. He is a good student and is very active on his school’s gymnastics team. His mother is also concerned that her son does not understand good personal hygiene. She reports that he always forgets to put on deodorant. When asked about this, he says he does not notice any body odor on himself or others. His temperature is 99.2°F (37.3°C), blood pressure is 105/70 mmHg, pulse is 70/min, and respirations are 18/min. His height and weight are in the 20th and 25th percentiles, respectively. On physical examination, his penis and testicles show no evidence of enlargement. He has no pubic or axillary hair. Which of the following sets of hormone levels is most likely to be found in this patient?
- A. Decreased testosterone, increased FSH, increased LH, increased GnRH
- B. Normal testosterone, normal FSH, normal LH, normal GnRH
- C. Increased testosterone, decreased FSH, decreased LH, decreased GnRH
- D. Decreased testosterone, decreased FSH, decreased LH, decreased GnRH (Correct Answer)
- E. Decreased testosterone, normal FSH, normal LH, normal GnRH
Explanation: ***Decreased testosterone, decreased FSH, decreased LH, decreased GnRH*** - The patient's **lack of secondary sexual characteristics** (no pubic or axillary hair, undeveloped genitals) and reported **anosmia** (cannot notice body odor) are classic signs of **Kallmann syndrome**. - Kallmann syndrome is a form of **hypogonadotropic hypogonadism**, characterized by impaired GnRH production from the hypothalamus, leading to low FSH, LH, and consequently low testosterone. *Decreased testosterone, increased FSH, increased LH, increased GnRH* - This hormonal pattern indicates **primary hypogonadism**, where the testes are failing to produce testosterone, but the pituitary and hypothalamus are working correctly and attempting to stimulate the testes. - This patient's clinical presentation, specifically the absence of secondary sexual characteristics and anosmia, is not consistent with primary testicular failure. *Normal testosterone, normal FSH, normal LH, normal GnRH* - This hormonal profile would indicate **normal pubertal development**, which clearly contradicts the patient's presentation of delayed puberty, undeveloped genitals, and lack of secondary sexual characteristics. - Such levels would be expected in a typical 16-year-old male who has undergone puberty. *Increased testosterone, decreased FSH, decreased LH, decreased GnRH* - This pattern is seen in conditions with **exogenous androgen administration** or **androgen-producing tumors**, leading to negative feedback on the hypothalamus and pituitary. - This is inconsistent with the patient's clinical picture of delayed puberty and undeveloped sexual characteristics. *Decreased testosterone, normal FSH, normal LH, normal GnRH* - This specific combination is unusual and does not fit a typical endocrine disorder causing delayed puberty. If testosterone is low, FSH and LH would typically be elevated in primary hypogonadism or decreased in secondary/tertiary hypogonadism. - It does not explain the patient's complete lack of pubertal development associated with anosmia.
Question 17: A 55-year-old woman with rheumatoid arthritis comes to the physician because of a 3-month history of worsening fatigue and dyspnea. She has felt short-of-breath when walking up the stairs to her apartment. Menopause occurred 5 years ago. Her medications are methotrexate and folic acid supplementation. Physical examination shows conjunctival pallor, tenderness of bilateral wrists and knees, and ulnar deviation of the fingers. Her hematocrit is 27%, mean corpuscular volume is 84 μm3, and serum ferritin is 375 ng/mL. Which of the following has most likely contributed to the patient's current symptoms?
- A. Increased release of iron from macrophages
- B. Increased activity of ferroportin-1 in enterocytes
- C. Increased production of reticulocytes in bone marrow
- D. Increased concentration of transferrin in serum
- E. Increased release of hepcidin by hepatocytes (Correct Answer)
Explanation: ***Increased release of hepcidin by hepatocytes*** - The patient has anemia of chronic disease (ACD) due to rheumatoid arthritis, characterized by fatigue, dyspnea, pallor, a low hematocrit (27%), and normal MCV (84 μm3), with an elevated ferritin (375 ng/mL). - **Hepcidin**, released by the liver in response to inflammation, blocks iron release from macrophages and enterocytes, leading to iron sequestration and reduced iron availability for erythropoiesis. *Increased release of iron from macrophages* - In ACD, **iron is sequestered** within macrophages, and its release is *decreased* due to hepcidin's action on ferroportin. - This leads to reduced circulating iron, despite normal or elevated iron stores. *Increased activity of ferroportin-1 in enterocytes* - **Ferroportin-1** activity in enterocytes is *reduced* by hepcidin in ACD, leading to decreased iron absorption from the diet. - This contributes to the functional iron deficiency seen in chronic inflammation. *Increased production of reticulocytes in bone marrow* - Anemia of chronic disease is characterized by **impaired erythropoiesis**, not increased reticulocyte production. - The bone marrow’s response to anemia is blunted due to decreased iron availability and suppression by inflammatory cytokines. *Increased concentration of transferrin in serum* - In ACD, **transferrin levels are typically decreased** (or normal), which is in contrast to iron deficiency anemia where transferrin is usually elevated to compensate for low iron. - Hepcidin's action reduces the overall iron carrying capacity.
Question 18: A 42-year-old woman presents with fatigue. She says that her symptoms have gradually onset after she recently had a total thyroidectomy due to Graves' disease. Past medical history is otherwise unremarkable. The patient is afebrile, and her vital signs are within normal limits. Physical examination is unremarkable. Laboratory findings are significant for the following: Potassium 4.2 mEq/L Calcium 7.8 mg/dL Chloride 102 mEq/L Vitamin D3 8 ng/mL (ref range: 25–80 ng/mL) A deficiency of which of the following is the most likely cause of this patient's symptoms?
- A. Parathyroid hormone (PTH) (Correct Answer)
- B. Thyroid-stimulating hormone (TSH)
- C. 1-alpha-hydroxylase
- D. Calcitonin
- E. 25-hydroxycholecalciferol
Explanation: **Parathyroid hormone (PTH)** - The patient's **hypocalcemia** (calcium 7.8 mg/dL) combined with a history of recent **total thyroidectomy** suggests accidental removal or damage to the **parathyroid glands**, leading to **hypoparathyroidism**. - Without sufficient PTH, the body cannot effectively raise **serum calcium** by stimulating bone resorption, increasing renal calcium reabsorption, and activating **vitamin D**. *Thyroid-stimulating hormone (TSH)* - While thyroidectomy affects thyroid hormone production, the primary issue indicated by the low calcium is related to **parathyroid function**, not typically TSH. - TSH levels would be relevant for assessing **hypothyroidism** but do not directly explain the acute **hypocalcemia** post-surgery. *1-alpha-hydroxylase* - A deficiency in **1-alpha-hydroxylase** would lead to impaired activation of **vitamin D**, resulting in low levels of **calcitriol** (1,25-dihydroxyvitamin D). - This typically causes malabsorption of calcium from the gut, but the immediate and severe hypocalcemia after thyroidectomy points more directly to issues with PTH secretion. *Calcitonin* - **Calcitonin** is produced by the thyroid gland and acts to lower serum calcium, but a deficiency (e.g., after thyroidectomy) would lead to **hypercalcemia**, not hypocalcemia, and its role in calcium homeostasis is minor compared to PTH and vitamin D. - Thyroidectomy would remove calcitonin-producing *C cells*, which would contribute to **raised calcium levels**, rather than the observed **low calcium levels**. *25-hydroxycholecalciferol* - The patient has low **25-hydroxycholecalciferol** (vitamin D3), but this is a common insufficiency and typically leads to chronic, less severe hypocalcemia. - The acute onset of symptoms and hypocalcemia *immediately after thyroidectomy* makes the loss of PTH the more direct and likely cause, as PTH is essential for activating existing vitamin D and directly regulating calcium.
Question 19: A 57-year-old man is rushed to the emergency department by ambulance after being found on the floor gasping for air with severe shortness of breath by his partner. Past medical history is significant for congestive heart failure, hypertension, and hyperlipidemia. He normally takes chlorthalidone, atorvastatin, metoprolol, and valsartan, but he recently lost his job and insurance and has not been able to afford his medication in 2 months. Upon arrival at the hospital, his blood pressure is 85/50 mm Hg, heart rate is 110/min, respiratory rate is 24/min, oxygen saturation 90% on 100% oxygen, and temperature is 37.7°C (99.9°F). On physical exam, he appears obese and can only answer questions in short gasps as he struggles to breathe. His heart rate is tachycardic with a mildly irregular rhythm and auscultation of his lungs reveal crackles in the lower lobes, bilaterally. Which of the following physiologic changes is currently seen in this patient?
- A. ↑ Plasma renin and angiotensin II activity, ↑ blood pressure, normal renal perfusion pressure, ↓ serum pH
- B. ↓ Plasma renin and angiotensin II activity, ↑ blood pressure, normal renal perfusion pressure, ↑ serum pH
- C. ↑ Plasma renin and angiotensin II activity, ↓ blood pressure, ↓ renal perfusion pressure, ↑ serum pH (Correct Answer)
- D. Normal plasma renin and angiotensin II activity, ↓ blood pressure, ↓ renal perfusion pressure, ↓ serum pH
- E. ↑ Plasma renin and angiotensin II activity, ↑ blood pressure, ↓ renal perfusion pressure, ↑ serum pH
Explanation: ***↑ Plasma renin and angiotensin II activity, ↓ blood pressure, ↓ renal perfusion pressure, ↑ serum pH*** - The patient's **hypotension (85/50 mm Hg)** means a decreased **renal perfusion pressure**, which triggers the **renin-angiotensin-aldosterone system (RAAS)**, leading to **increased renin and angiotensin II activity** to try and raise blood pressure. - The patient's **gasping for air** and **struggle to breathe** indicate significant respiratory distress, leading to **hyperventilation** (increased respiratory rate of 24/min). This causes an **excessive exhalation of CO2**, resulting in **respiratory alkalosis** (↑ serum pH), which is a common compensatory mechanism in acute heart failure. *↑ Plasma renin and angiotensin II activity, ↑ blood pressure, normal renal perfusion pressure, ↓ serum pH* - This option incorrectly states **elevated blood pressure** and **normal renal perfusion pressure**, which contradicts the patient's measured hypotensive state. - The patient's presentation with acute respiratory distress and compensatory hyperventilation is unlikely to result in **acidosis (↓ serum pH)**, but rather alkalosis. *↓ Plasma renin and angiotensin II activity, ↑ blood pressure, normal renal perfusion pressure, ↑ serum pH* - This option incorrectly suggests **decreased renin and angiotensin II activity** despite the patient's low blood pressure, which would typically activate the RAAS. - It also includes **elevated blood pressure** and **normal renal perfusion pressure**, which are inconsistent with the patient's clinical presentation of hypotension and heart failure exacerbation. *↑ Plasma renin and angiotensin II activity, ↑ blood pressure,↓ renal perfusion pressure, ↑ serum pH* - This option correctly identifies **increased plasma renin and angiotensin II activity** and **decreased renal perfusion pressure** but incorrectly suggests an **elevated blood pressure**, which is contradictory to the patient's measured blood pressure of 85/50 mm Hg. - Although the **increased serum pH** is consistent with respiratory alkalosis due to hyperventilation, the incorrect blood pressure makes this option unsuitable. *Normal plasma renin and angiotensin II activity, ↓ blood pressure, ↓ renal perfusion pressure, ↓ serum pH* - This option incorrectly states **normal plasma renin and angiotensin II activity**, which would be highly unlikely in a patient with severe hypotension and struggling to maintain blood pressure. - The patient's **hyperventilation** due to respiratory distress would lead to **respiratory alkalosis (↑ serum pH)**, not a decreased pH (acidosis).
Question 20: A 58-year-old Caucasian woman visits her primary care physician for an annual check-up. She has a history of type 2 diabetes mellitus and stage 3A chronic kidney disease. Her estimated glomerular filtration rate has not changed since her last visit. Today, her parathyroid levels are moderately elevated. She lives at home with her husband and 2 children and works as a bank clerk. Her vitals are normal, and her physical examination is unremarkable. Which of the following explains this new finding?
- A. Uremia
- B. Acidemia
- C. Hyperuricemia
- D. Hypercalcemia
- E. Phosphate retention (Correct Answer)
Explanation: ***Phosphate retention*** - **Chronic kidney disease** often leads to **phosphate retention** because the damaged kidneys cannot effectively excrete phosphate. - This elevated phosphate stimulates the parathyroid glands to secrete more **parathyroid hormone (PTH)** as a compensatory mechanism, leading to secondary hyperparathyroidism. *Uremia* - While uremia (accumulation of nitrogenous waste products) is a feature of chronic kidney disease, it is not the **direct cause** of elevated parathyroid levels. - Uremia primarily causes symptoms like fatigue, nausea, and altered mental status, but it doesn't independently trigger PTH release in the same direct manner as phosphate retention or hypocalcemia. *Acidemia* - **Metabolic acidosis** is common in chronic kidney disease, but it generally **inhibits** PTH secretion, not stimulates it. - While it can worsen bone disease, acidemia itself does not explain the primary elevation of parathyroid hormone. *Hyperuricemia* - **Hyperuricemia** (elevated uric acid levels) is often associated with chronic kidney disease due to decreased renal excretion of uric acid. - However, hyperuricemia does not directly cause or explain elevated parathyroid hormone levels. *Hypercalcemia* - **Hypercalcemia** would typically **suppress** parathyroid hormone secretion, not elevate it. - In chronic kidney disease, **hypocalcemia** (due to impaired vitamin D activation and phosphate retention) is more common and would stimulate PTH.
Question 21: A 32-year-old female presents to her obstetrician 3 weeks postpartum for failure to lactate. Of note, she has been unable to tolerate cold environments since the birth of her child. Review of systems is positive for fatigue, lightheadedness, and a 3-pound weight gain over the last 3 weeks. Her delivery was complicated by placenta accreta with postpartum blood loss. Her newborn infant is doing well on formula. She denies any personal or family history of thyroid disease. Physical exam is overall unremarkable. On a panel of hormone testing, which of the following levels is most likely to be normal in this patient?
- A. Thyroid hormone
- B. Cortisol
- C. Luteinizing hormone
- D. Antidiuretic hormone (Correct Answer)
- E. Aldosterone
Explanation: ***Antidiuretic hormone*** - This patient is presenting with symptoms consistent with **Sheehan syndrome**, which is postpartum pituitary necrosis due to severe hemorrhage and hypovolemic shock. - Sheehan syndrome **primarily affects the anterior pituitary**, where most pituitary hormones are produced. - **Antidiuretic hormone (ADH)** is synthesized by the **hypothalamus** and stored/released by the **posterior pituitary**, which is typically **spared** in Sheehan syndrome due to its separate blood supply. - Therefore, **ADH levels would be normal** in this patient, making this the correct answer. *Aldosterone* - The **renin-angiotensin-aldosterone system (RAAS)** is regulated independently by the kidneys and is preserved in pituitary disorders. - Aldosterone levels would also likely be **normal** in this patient. - However, ADH is the better answer as it specifically demonstrates the anatomical distinction between anterior and posterior pituitary function. *Thyroid hormone* - The **anterior pituitary** fails to produce **thyroid-stimulating hormone (TSH)** in Sheehan syndrome, leading to secondary hypothyroidism. - This results in **low thyroid hormone levels**. - Her symptoms of **cold intolerance**, **fatigue**, and **weight gain** are classic manifestations of hypothyroidism. *Cortisol* - The anterior pituitary produces **adrenocorticotropic hormone (ACTH)**, which stimulates cortisol release from the adrenal glands. - In Sheehan syndrome, failure of ACTH production leads to **secondary adrenal insufficiency** with **low cortisol levels**. - This contributes to her **fatigue** and **lightheadedness**. *Luteinizing hormone* - The anterior pituitary produces **luteinizing hormone (LH)**, which is crucial for ovarian function and ovulation. - The patient's **failure to lactate** is due to **prolactin deficiency** (another anterior pituitary hormone), not LH deficiency. - Lack of LH and other gonadotropins would contribute to amenorrhea and loss of reproductive function that often accompany Sheehan syndrome.
Question 22: A 29-year-old patient presents to her primary care physician with persistent amenorrhea and inability to breastfeed over the last 5 months. She says that she has also been very tired since her baby was born and this fatigue was accompanied by an inability to deal with cold weather despite having no problem with cold prior to becoming pregnant. She has gained an additional 5 pounds since delivery. Review of her hospital records reveals that she had a vaginal delivery that was complicated by severe hemorrhage and episodes of hypotension. Which of the following hormone levels is most likely to be normal in this patient?
- A. Thyroid hormone
- B. Cortisol
- C. Aldosterone (Correct Answer)
- D. Follicle-stimulating hormone (FSH)
- E. Prolactin
Explanation: **Aldosterone** - **Aldosterone** is primarily regulated by the **renin-angiotensin-aldosterone system** (RAAS) and is produced by the adrenal cortex, which is not directly affected by pituitary ischemia in Sheehan's syndrome. - The symptoms described (amenorrhea, inability to breastfeed, fatigue, cold intolerance, weight gain) are classic for **Sheehan's syndrome**, which involves panhypopituitarism due to **ischemic necrosis of the pituitary gland** following severe postpartum hemorrhage. However, aldosterone production generally remains intact. *Thyroid hormone* - The pituitary gland produces **thyroid-stimulating hormone (TSH)**, which is essential for thyroid hormone production. Sheehan's syndrome leads to TSH deficiency, resulting in **secondary hypothyroidism** (low thyroid hormone). - The patient's symptoms of fatigue, cold intolerance, and weight gain are consistent with hypothyroidism. *Cortisol* - The pituitary gland produces **adrenocorticotropic hormone (ACTH)**, which stimulates cortisol production from the adrenal cortex. Sheehan's syndrome causes ACTH deficiency, leading to **secondary adrenal insufficiency** (low cortisol). - Fatigue is a common symptom of cortisol deficiency. *Follicle-stimulating hormone (FSH)* - **FSH** is produced by the pituitary gland and is crucial for ovarian function, including follicular development and estrogen production. - Deficiency of FSH (and LH) due to Sheehan's syndrome results in **secondary amenorrhea** and an inability to ovulate. *Prolactin* - **Prolactin** is produced by the pituitary gland and is necessary for lactation. - In Sheehan's syndrome, prolactin deficiency directly leads to the **inability to breastfeed**.
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Renin production and regulation
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Angiotensinogen to angiotensin I conversion
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Angiotensin converting enzyme function
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Angiotensin II receptors and actions
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Aldosterone synthesis and release
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Aldosterone actions on distal tubule
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Sodium and potassium handling in RAAS
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Negative feedback mechanisms
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RAAS in volume regulation
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RAAS in blood pressure control
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Non-classical RAAS components
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RAAS in pathophysiological states
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Pharmacological targeting of RAAS
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