During birth, an infant is normally stimulated to breathe by_________________.
surfactant
CO2 accumulating in the infant's blood
prostaglandins
an increased O2 level in the infant's new environment
The Correct Answer is B
A. Surfactant reduces surface tension in the alveoli, aiding in lung expansion, but it does not directly stimulate breathing.
B. CO2 accumulating in the infant's blood: The accumulation of CO2 in the infant's blood is a significant stimulus for the first breath after birth. High levels of CO2 trigger the infant's respiratory centers to start breathing.
C. Prostaglandins are involved in labor and delivery but do not directly stimulate breathing in the newborn.
D. An increased O2 level in the infant's new environment: Increased O2 levels do not directly stimulate breathing; rather, the accumulation of CO2 is the primary stimulus.
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Correct Answer is B
Explanation
A. Ductus venosus and ductus arteriosus: The ductus venosus bypasses the liver, not the lungs. The ductus arteriosus does allow blood to bypass the lungs by connecting the pulmonary artery to the aorta. However, this option is not entirely correct since the ductus venosus is not involved in bypassing the lungs.
B. Foramen ovale and ductus arteriosus: The foramen ovale allows blood to pass directly from the right atrium to the left atrium, bypassing the lungs. The ductus arteriosus connects the pulmonary artery to the aorta, also bypassing the lungs.
C. Fossa ovalis and umbilical arteries and vein: The fossa ovalis is a remnant of the foramen ovale in adults and does not function in fetal circulation. The umbilical arteries and vein are involved in exchanging oxygenated and deoxygenated blood between the fetus and placenta, not bypassing the lungs.
D. Ligamentum venosum and ligamentum arteriosum: These are the adult remnants of the ductus venosus and ductus arteriosus, respectively. They do not play a role in fetal circulat
Correct Answer is C
Explanation
A. Trypsin functions in the small intestine, where the environment is slightly alkaline. Therefore, this enzyme does not function at a low pH.
B. Pancreatic amylase also functions in the small intestine, where the pH is neutral to slightly alkaline.
C. Pepsin functions in the stomach, where the environment is highly acidic (pH 1.5 to 2). Pepsin is the correct answer because it works optimally at this low pH.
D. Salivary amylase functions in the mouth, where the pH is neutral or slightly alkaline.