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 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 B
Explanation
A. Mucosa (mucous membrane): The mucosa is the innermost layer of the digestive tract, not the outermost. It includes the epithelium, lamina propria, and muscularis mucosae.
B. Serosa (mesentery): The serosa is the outermost layer of the digestive tract in parts where it is covered by peritoneum. It consists of a thin layer of areolar tissue topped by simple squamous epithelium.
C. Muscularis externa: The muscularis externa is a layer of muscle in the digestive tract, located beneath the serosa. It is not the outermost layer.
D. Submucosa: The submucosa is a layer of connective tissue located between the mucosa and muscularis externa. It is not the outermost layer.