Physiology Test 1 — Questions and Answers

Question 1: A hormone is known to activate phospholipase C with subsequent release of calcium from internal stores. The release of calcium most likely occurs as a result of an increase in the concentration of which of the following intracellular second messengers?

Calcium
cAMP
cGMP
Diacylglycerol
Inositol 1,4,5-trisphosphate (Correct answer)

Correct answer: Inositol 1,4,5-trisphosphate

When a hormone activates phospholipase C, this enzyme cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). IP3 then binds to receptors on the endoplasmic reticulum, triggering the release of calcium from these internal stores into the cytoplasm. This increase in intracellular calcium mediates various cellular responses.

Question 2: A 28-year-old man with a history of intravenous drug use comes to the physician because of a 6-week history of fever, nonproductive cough, chills, and progressive shortness of breath. His temperature is 39°C (102.2°F), pulse is 110/min, respirations are 32/min and regular, and blood pressure is 120/80 mm Hg. Physical examination shows a white, patchy, loosely adherent exudate on the buccal mucosa bilaterally. A chest x-ray shows bilateral interstitial infiltrates. After receiving treatment for pneumonia, he agrees to participate in a clinical study of the effects of interleukin-2 (IL-2). After administration of IL-2, which of the following hematologic changes is most likely in this patient?

Decreased CD4+ T lymphocytes
Decreased erythrocytes
Decreased platelet count
Increased CD4+ T lymphocytes (Correct answer)
Increased erythrocytes
Increased platelet count

Correct answer: Increased CD4+ T lymphocytes

The patient's history of HIV and opportunistic infections (Pneumocystis pneumonia, oral candidiasis) indicates significant immunosuppression, typically associated with low CD4+ T lymphocyte counts. Interleukin-2 (IL-2) is a cytokine that stimulates the proliferation, differentiation, and activation of T lymphocytes, particularly CD4+ and CD8+ T cells. Therefore, administration of IL-2 is most likely to lead to an increase in CD4+ T lymphocytes, aiming to bolster the immune response.

Question 3: A 5-year-old girl falls through the ice while skating on an outdoor pond. She is removed from the water within 1 minute, but dry clothing is not available, and she is still cold and wet 20 minutes later. Which of the following mechanisms helps maintain the patient’s core temperature during the period following her rescue?

Cutaneous vasodilation
Diving response
Increased thermoregulatory set point
Release of endogenous pyrogen
Shivering (Correct answer)

Correct answer: Shivering

When the body is exposed to cold, shivering is a primary physiological mechanism to generate heat and maintain core temperature. Shivering involves involuntary, rapid contractions of skeletal muscles, which significantly increases metabolic heat production. This process helps to counteract heat loss and prevent hypothermia in cold environments, as seen in the child after falling into icy water.

Question 4: A 39-year-old woman comes to the physician for a follow-up examination because she recently was diagnosed with hypertension. Her blood pressure is 156/100 mm Hg. Physical examination shows no other abnormalities. Serum studies show normal findings. A 24-hour urine collection shows three times the normal excretion of epinephrine and metanephrine. The excessive epinephrine production in this patient is most likely caused by which of the following cell types?

Chromaffin (Correct answer)
Juxtaglomerular
Zona fasciculata
Zona glomerulosa
Zona reticularis

Correct answer: Chromaffin

The elevated urinary excretion of epinephrine and metanephrine is highly suggestive of a pheochromocytoma, a tumor of the adrenal medulla. Chromaffin cells, located in the adrenal medulla, are specialized neuroendocrine cells that synthesize and secrete catecholamines, including epinephrine and norepinephrine. These cells are the source of excessive catecholamine production in pheochromocytoma, leading to hypertension.

Question 5: The blood flow through an organ is measured while the perfusion pressure is varied experimentally. An abrupt, sustained increase in perfusion pressure increases flow initially, but over the course of 1 minute, the flow returns nearly to the baseline level despite continued elevation of the perfusion pressure. The organ under study is exhibiting which of the following?

Active hyperemia
Autoregulation (Correct answer)
Ischemia
Reactive hyperemia

Correct answer: Autoregulation

This phenomenon describes autoregulation, the intrinsic ability of an organ or tissue to maintain a relatively constant blood flow despite changes in perfusion pressure. When perfusion pressure increases, the blood vessels in an autoregulating organ constrict (myogenic response) or release vasoconstrictors. This increases resistance and returns blood flow towards its baseline level, ensuring stable nutrient and oxygen delivery.

Question 6: After an overnight fast, a 52-year-old man undergoes infusion of acid through a catheter into the upper duodenum. This most likely will increase pancreatic secretion mainly through the action of which of the following substances?

Cholecystokinin
Gastrin
Glucagon
Secretin (Correct answer)
Vasoactive intestinal polypeptide

Correct answer: Secretin

Acidification of the duodenum, as described, is the primary stimulus for the release of secretin from S cells in the duodenal mucosa. Secretin then acts on the pancreatic duct cells to stimulate the secretion of a bicarbonate-rich fluid. This bicarbonate neutralizes the acidic chyme entering the duodenum, creating an optimal pH for the activity of pancreatic digestive enzymes.

Question 7: A 20-year-old woman is brought to the emergency department 20 minutes after being stung by a wasp. She says that she feels a lump in her throat and chest tightness. She has a history of allergy to wasp venom. Her pulse is 120/min, and blood pressure is 80/40 mm Hg. Physical examination shows eruptions that coalesce into giant urticaria. There is audible wheezing. Which of the following best describes the cause of this patient’s reaction?

Activation of macrophages by soluble immune complexes
Binding of antigen to preexisting cell-fixed IgE antibodies (Correct answer)
Formation of IgG antibodies against extracellular matrix antigen
Formation of IgM antibodies against cell surface receptor antigens
Induction of a cytotoxic reaction by CD8+ T lymphocytes

Correct answer: Binding of antigen to preexisting cell-fixed IgE antibodies

This patient is experiencing anaphylaxis, a severe, systemic Type I hypersensitivity reaction. This reaction is mediated by IgE antibodies, which are pre-formed and fixed to the surface of mast cells and basophils. Upon re-exposure to the allergen (wasp venom), the antigen binds to these cell-fixed IgE antibodies, triggering degranulation and the rapid release of inflammatory mediators like histamine, leading to the observed symptoms.

Question 8: A demonstration is performed during a lecture on muscle physiology in which a student is asked to fully extend his right arm with the palm up. Two large textbooks are placed on his palm, one at a time. Which of the following facilitates the maximum amount of tension that allows the student to keep his arm extended in place under the increasing weight of the books?

Amount of Ca 2+ released from the sarcoplasmic reticulum
Amount of muscle phosphocreatine
Amplitude of the action potential
Number of motor units recruited (Correct answer)
Rate of cross-bridge recycling

Correct answer: Number of motor units recruited

To generate increasing amounts of force or tension in a muscle, the nervous system employs a mechanism called motor unit recruitment. As more weight is added, the brain activates a greater number of motor neurons, which in turn activate more motor units and thus more muscle fibers. This allows for a graded increase in muscle tension, enabling the student to counteract the increasing load and keep his arm extended.

Question 9: During an experiment on the cough reflex in humans, a volunteer inhales air containing different amounts of particles that will impact and adhere to mucus primarily in the trachea. Blockade of which of the following receptors would most likely prevent this volunteer’s reflex to initiate a cough?

Chemoreceptors
Irritant receptors (Correct answer)
J receptors
Proprioceptors
Stretch receptors

Correct answer: Irritant receptors

The cough reflex is a protective mechanism initiated by the stimulation of irritant receptors located in the airway epithelium, particularly in the trachea and large bronchi. These receptors detect mechanical or chemical irritants, sending afferent signals via the vagus nerve to the brainstem. Blockade of these specific receptors would prevent the detection of the particles and thus inhibit the initiation of the cough reflex.

Question 10: A 35-year-old man has an adenoma of the parathyroid gland, with increased serum concentrations of parathyroid hormone (PTH) and calcium. In this patient, PTH induces which of the following processes to cause hypercalcemia?

Production of 25-hydroxycholecalciferol
Shift of Ca 2+ from the intracellular to the extracellular fluid compartment
Stimulation of osteoclast activity (Correct answer)
Suppression of renal production of 1,25-dihydroxycholecalciferol

Correct answer: Stimulation of osteoclast activity

Parathyroid hormone (PTH) is the primary regulator of calcium homeostasis. In the context of an adenoma causing increased PTH, the hormone directly stimulates osteoclast activity in the bone. Osteoclasts are responsible for bone resorption, a process that releases calcium and phosphate from the bone matrix into the bloodstream, thereby increasing serum calcium concentrations.

Question 11: A female newborn delivered at 32 weeks’ gestation develops severe respiratory distress within hours of birth. Despite resuscitative efforts, the patient dies. Examination of the lungs at autopsy shows lung alveoli with radii of less than 50 μm (N=100). Which of the following is most likely decreased in the lungs of this newborn?

Airway resistance
Compliance (Correct answer)
Elastic recoil
Surface tension
Vascular resistance

Correct answer: Compliance

This premature newborn's severe respiratory distress is characteristic of neonatal respiratory distress syndrome (NRDS), which is caused by a deficiency in pulmonary surfactant. Surfactant reduces surface tension in the alveoli, preventing their collapse and making the lungs easier to inflate. Without adequate surfactant, the lungs become stiff and difficult to expand, leading to decreased lung compliance.

Question 12: A 55-year-old woman who is obese has a greater risk for endometrial carcinoma than a 55-year-old woman with the same health history and status who is not obese. Which of the following best explains this increased risk?

Accelerated catabolism of antioxidants
Association of obesity with smoking
Carcinogenic effects of dietary fats
Greater average number of pregnancies
Impairment of immune surveillance by T lymphocytes
Increased production of estrogen by adipose tissue (Correct answer)
Later age of menopause
More frequent episodes of vaginitis

Correct answer: Increased production of estrogen by adipose tissue

Obesity is a significant risk factor for endometrial carcinoma due to the increased production of estrogen by adipose tissue. Adipose tissue contains the enzyme aromatase, which converts androgen precursors into estrogens. Higher levels of circulating estrogen, particularly unopposed by progesterone, chronically stimulate the endometrium, promoting hyperplasia and increasing the risk of malignant transformation.

Question 13: A 4-hour-old female newborn delivered at 30 weeks’ gestation has respiratory distress. Her temperature is 36.5°C (97.7°F), pulse is 160/min, respirations are 85/min, and blood pressure is 68/40 mm Hg. Arterial blood gas analysis on room air shows: pH 7.18 PCO2 78 mm Hg PO2 55 mm Hg Endotracheal intubation and mechanical ventilation are required. The primary cause of this patient’s condition is a dysfunction of which of the following cell types?

Alveolar macrophages
Pneumocytes (Correct answer)
Pulmonary chondrocytes
Pulmonary vascular endothelial cells
Smooth muscle cells

Correct answer: Pneumocytes

The patient's presentation is consistent with neonatal respiratory distress syndrome (NRDS), a condition primarily caused by insufficient production of pulmonary surfactant. Surfactant is synthesized and secreted by Type II pneumocytes, which are specialized alveolar cells. Dysfunction or immaturity of these pneumocytes leads to inadequate surfactant, resulting in alveolar collapse and severe respiratory failure.

Question 14: A 22-year-old man is brought to the emergency department because of a 6-hour history of severe, sharp, upper back pain. He has had progressive fatigue during the past 3 weeks. He is 183 cm (6 ft) tall and weighs 79 kg (175 lb); BMI is 24 kg/m2 . His temperature is 36.9°C (98.5°F), pulse is 90/min, and blood pressure is 160/55 mm Hg. Physical examination shows long, thin upper and lower extremities. Fingertip to fingertip with arms outstretched is 189 cm (74 in) wide. A high-pitched midsystolic click is heard predominantly over the apex. Which of the following best describes the primary genetic cause of this patient’s condition?

Expression of genomic duplication within the fibrin gene
Mutation in keratin-14 gene
Nonsense mutation in fibrillin-1 gene (Correct answer)
Overexpression of collagen X gene
Overexpression of fibronectin gene

Correct answer: Nonsense mutation in fibrillin-1 gene

The patient's features, including tall stature, long extremities (arm span greater than height), and cardiovascular findings like a midsystolic click (mitral valve prolapse) and wide pulse pressure (suggesting aortic root dilation), are classic for Marfan syndrome. This is an autosomal dominant disorder caused by mutations in the *FBN1* gene, which encodes fibrillin-1, a crucial component of elastic fibers in connective tissue. A nonsense mutation would lead to a truncated, non-functional protein.

Question 15: A 25-year-old woman comes to the physician because of a 2-day history of muscle cramps and profuse, watery stools. She returned from a trip to Pakistan 3 days ago. Her temperature is 37°C (98.6°F), pulse is 120/min, and blood pressure is 80/50 mm Hg. Stool culture shows numerous curved, gram-negative bacteria; there are no erythrocytes or leukocytes. Oral rehydration is initiated. The blood pressure increases, and the pulse decreases. The oral hydration formula most likely promotes sodium absorption via the gut by allowing cotransport with which of the following?

Albumin
Fatty acid
Glucose (Correct answer)
Magnesium
Potassium

Correct answer: Glucose

Oral rehydration solutions (ORS) are highly effective in treating dehydrating diarrheas, such as cholera, by leveraging the sodium-glucose cotransport system in the small intestine. This system actively absorbs sodium and glucose together, which then creates an osmotic gradient that drives the passive absorption of water. This mechanism allows for efficient rehydration even in the presence of severe secretory diarrhea.

Question 16: A 26-year-old woman is brought to the emergency department because of a 4-day history of flu-like symptoms accompanied by vomiting following each attempt to eat or drink. Her temperature is 38.5°C (101.3°F), pulse is 93/min, respirations are 24/min, and blood pressure is 105/70 mm Hg. Physical examination shows no other abnormalities. Which of the following additional findings is most likely in this patient?

Decreased serum ADH (vasopressin) concentration
Increased serum aldosterone concentration (Correct answer)
Increased serum atrial natriuretic peptide
Increased urine sodium and chloride concentrations
Increased urine volume

Correct answer: Increased serum aldosterone concentration

Profuse vomiting leads to significant fluid loss, resulting in hypovolemia and a compensatory decrease in blood pressure. The body responds by activating the renin-angiotensin-aldosterone system (RAAS). Increased renin leads to increased angiotensin II, which stimulates the adrenal cortex to release aldosterone, promoting sodium and water reabsorption in the kidneys to restore blood volume and blood pressure.

Question 17: A 77-year-old man comes to the physician because of swelling of his legs and feet for 6 months. He has a 40-year history of alcoholism and a 5-year history of hepatic disease. Physical examination shows ascites and a 2+ edema of the lower extremities. A decrease in which of the following most likely promotes edema formation in this patient?

Capillary hydrostatic pressure
Filtration coefficient
Interstitial colloid osmotic pressure
Interstitial fluid hydrostatic pressure (Correct answer)
Plasma colloid oncotic pressure (Correct answer)

Correct answer: Interstitial fluid hydrostatic pressure

Chronic liver disease, often seen in alcoholism, impairs the liver's ability to synthesize albumin, the main plasma protein. A decrease in plasma albumin leads to a significant reduction in plasma colloid oncotic pressure. This reduced oncotic pressure diminishes the force that draws fluid back into the capillaries, causing fluid to leak into the interstitial space and peritoneum (ascites), thereby promoting edema formation.

Question 18: A 30-year-old woman comes to the physician for a routine health maintenance examination. She takes no medications. Physical examination shows no abnormalities. Serum studies show a calcium concentration of 12 mg/dL. An increase in which of the following substances is the most likely cause of the serum finding in this patient?

Bone morphogenic protein
Calcitonin
Integrins
Parathyroid hormone (Correct answer)
Vitamin A

Correct answer: Parathyroid hormone

The most common cause of asymptomatic hypercalcemia is primary hyperparathyroidism, typically due to a parathyroid adenoma. This condition results in excessive secretion of parathyroid hormone (PTH). PTH acts to increase serum calcium by stimulating osteoclast activity (bone resorption), increasing renal calcium reabsorption, and promoting the renal production of 1,25-dihydroxycholecalciferol (calcitriol), which enhances intestinal calcium absorption.

Question 19: A 28-year-old woman comes to the physician because of a 3-month history of shortness of breath with exertion. She takes an oral contraceptive. There are no occupational exposures to birds or grain dusts. Her respirations are 20/min. The lungs are clear to auscultation. Cardiac examination shows a regular rate and rhythm; S2 is slightly louder than S1 . Cardiac catheterization shows a pulmonary artery pressure of 78/31 mm Hg (N=15–30/3–12) with a normal left ventricular end-diastolic pressure. Which of the following is most likely changed in this patient?

Decreased alveolar ventilation
Decreased left ventricular afterload
Increased muscle tone
Increased pulmonary compliance
Increased pulmonary vascular resistance (Correct answer)

Correct answer: Increased pulmonary vascular resistance

The patient's elevated pulmonary artery pressure (78/31 mm Hg) with a normal left ventricular end-diastolic pressure indicates pre-capillary pulmonary hypertension. This condition is characterized by increased resistance within the pulmonary arterial circulation, rather than issues with the left heart. Oral contraceptive use is a known risk factor for developing pulmonary vascular disease and increased pulmonary vascular resistance.

Physiology Test 1

A hormone is known to activate phospholipase C with subsequent release of calcium from internal stores.
The release of calcium most likely occurs as a result of an increase in the concentration of which of the following intracellular second messengers?