A few seconds after birth, rising O2 levels stimulate the constriction of the ductus arteriosus, isolating the __________.
a. ligamentum ateriosum and fossa ovalis
b. superior and inferior venae cavae
c. ductus venosus and ligamentum arteriosum
d. pulmonary and aortic trunks
Ans: d. pulmonary and aortic trunks
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Amino acids such as alanine contain hydrocarbons as side groups, and these amino acids engage in hydrophobic interactions with each other. Such amino acids are
A. charged.?B. hydrostatic.?C. polar.?D. nonpolar.?E. polyunsaturated.
In response to respiratory alkalosis,
A) the respiratory rate increases. B) the chemoreceptors in the carotid and aortic bodies are further stimulated. C) the kidneys conserve bicarbonate. D) the kidneys secrete more hydrogen ions. E) the respiratory rate decreases.
Which of the following is not true of hemoglobin?
A. It makes up about 1/3 of a red blood cell. B. Each hemoglobin molecule consists of 4 protein subunits. C. Each hemoglobin molecule can bind to up to 20 oxygen molecules at a time. D. Oxyhemoglobin is bright red, and deoxyhemoglobin is dark red. E. All of these are true of hemoglobin.
Nurse cells are not
A) found in the seminiferous tubules. B) important in forming the blood-testis barrier. C) involved in coordinating spermatogenesis. D) precursors to gametes. E) also called Sertoli cells.