Comprehensive Basic Science Test

Question 1

In a steady state, the difference in CO2 content between the venous blood leaving a tissue and the arterial blood entering the tissue is determined by which of the following ratios?

Accepted Answer

Tissue CO2 production to tissue blood flow

Answer

The difference in CO2 content between venous blood leaving a tissue and arterial blood entering it reflects the amount of CO2 added to the blood as it passes through that tissue. This CO2 is produced by the tissue's metabolic activity. According to the Fick principle, this difference is determined by the ratio of the tissue's CO2 production rate to the rate of blood flow through that tissue.

Question 2

A 16-month-old boy is brought to the physician by his mother for a well-child examination. His mother expresses concern that he did not walk until the age of 14 months, whereas his older sister walked at the age of 10 months. Physical examination shows no abnormalities. Which of the following best explains this patient’s condition?

Accepted Answer

Normal development

Answer

The normal range for independent walking is typically between 9 and 18 months of age. Walking at 14 months falls well within this normal developmental window. While his older sister walked earlier, individual variations in developmental milestones are common and do not indicate a problem unless they fall outside established normal ranges or are accompanied by other concerning signs.

Question 3

A 77-year-old woman is visited by the home care nurse who notes that the patient is more lethargic than usual. Her skin and mucous membranes are dry. An increase in the serum concentration or activity of which of the following provides the strongest indication that the patient is dehydrated?

Accepted Answer

Albumin

Answer

Dehydration causes a reduction in plasma volume, leading to hemoconcentration. Albumin is a large protein that remains within the intravascular space. When plasma volume decreases due to dehydration, the concentration of albumin in the serum increases because the same amount of albumin is now dissolved in a smaller volume of fluid, making it a strong indicator of dehydration.

Question 4

A male newborn delivered at 26 weeks’ gestation develops respiratory distress immediately after a spontaneous vaginal delivery. His respirations are 40/min. Physical examination shows cyanosis and lower rib retractions with respiration. Heart sounds are normal. Bilateral breath sounds are heard on auscultation. A chest x-ray shows bilateral lung opacities. The most likely cause of this patient’s breathing difficulties is insufficient production of which of the following substances?

Accepted Answer

Surfactant

Answer

The newborn's prematurity (26 weeks' gestation) is the key factor. Premature infants often have immature lungs and insufficient production of pulmonary surfactant. Surfactant reduces alveolar surface tension, preventing alveolar collapse during expiration and ensuring adequate gas exchange, so its deficiency leads to respiratory distress syndrome (RDS), characterized by the described symptoms and diffuse lung opacities.

Question 5

A 28-year-old woman, gravida 1, para 1, comes to the physician because of progressive fatigue since delivering a male newborn 6 months ago. She is sleeping 8 to 10 hours nightly, but she is still tired during the day. She also has not had a menstrual period since her pregnancy. Pregnancy was complicated during the third trimester by severe bleeding from placenta previa. She required multiple blood transfusions during the cesarean delivery, but she did well after the delivery. She was unable to breast-feed her newborn because of poor milk production. Which of the following is the most likely diagnosis?

Accepted Answer

Postpartum pituitary infarction

Answer

The patient's history of severe postpartum hemorrhage, followed by symptoms of hypopituitarism (progressive fatigue, amenorrhea since pregnancy, poor milk production), is classic for Sheehan syndrome. This condition involves ischemic necrosis of the pituitary gland due to massive blood loss during or after childbirth. The enlarged pituitary gland during pregnancy is particularly vulnerable to ischemia, leading to a deficiency in various pituitary hormones.

NBME Practice Test

NBME Practice Test

Comprehensive Basic Science Test