In fetal circulation, blood bypasses the lungs by flowing through the
ductus venosus and ductus arteriosus
foramen ovale and ductus arteriosus
fossa ovalis and umbilical arteries and vein
ligamentum venosum and ligamentum arteriosum
The Correct Answer is B
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
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Correct Answer is A
Explanation
A. The bicarbonate, phosphate, and protein: The major chemical buffer systems in the body are the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system. These buffers help maintain pH balance in the blood and other fluids.
B. The urinary and digestive: The urinary and digestive systems are involved in excretion and digestion, not buffering.
C. The bicarbonate, nucleic acids, and protein: Nucleic acids are not major buffering systems in the body; the bicarbonate, phosphate, and protein systems are the primary ones.
D. The urinary and respiratory systems play roles in regulating acid-base balance through excretion and gas exchange but are not chemical buffer systems themselves.
Correct Answer is C
Explanation
A. Esophageal glands secrete mucus to lubricate the esophagus, but they do not cause acid reflux.
B. Pharyngeal constrictors are muscles that help in the swallowing process, not in preventing acid reflux.
C. The lower esophageal sphincter (LES) is a ring of muscle that controls the passage of food from the esophagus to the stomach. If the LES is weakened or relaxes inappropriately, stomach acid can flow back into the esophagus, causing acid reflux or "heartburn."
D. The upper esophageal sphincter controls the passage of food from the pharynx into the esophagus, but it is not involved in preventing acid reflux.