Which structure is an important site for early blood cell formation and is the first of the extraembryonic membranes to form?
A. Amnion
B. Yolk sac
C. Chorion
D. Zona pellucida
B
You might also like to view...
Unlike an exocrine gland, an endocrine gland
A. secretes to a surface. B. sheds cells with its secretions. C. is a secretory organ. D. contains goblet cells. E. has no ducts.
Breathing is involuntary
Indicate whether the statement is true or false
The sympathetic division of the ANS causes __________ of airway smooth muscle; therefore, resistance is __________.
relaxation; increased constriction; increased constriction; decreased relaxation; decreased none of the choices are correct
Specific immune responses
a. require helper T-cell activation b. are under control of the adaptive immune system c. could not occur if the thymus gland did not develop d. require recognition of antigens by receptors e. have all of the above characteristics