6.The answer is d.(Sadler, pp 34–37.)On fusion of the first sperm with the
oocyte cell membrane, the contents of secretory granules stored just beneath
the oocyte membrane (cortical granules) are released (the zona reaction).
Enzymes stored in those granules cause biochemical and electrical changes in
the zona pellucida and the oocyte membrane that prevent the binding of addi-
tional sperm. Primitive female germ cells (oogonia) enter the first meiotic divi-
sion during fetal development (answer a).This process becomes arrested in
prophase I until individual primary oocytes are hormonally induced to
resume the first meiotic division during puberty and early adulthood (menar-
che to menopause). Fusion of the sperm and oocyte membranes initiates the
resumption of the second meiotic division, resulting in the formation of a hap-
loid pronucleus in the oocyte and extrusion of the second polar body
(answer b).Capacitation(answer c)is a process by which enzymatic secre-
tions of the uterus and oviducts strip glycoproteins from the sperm cell mem-
brane. This is required for penetration of the layer of cells surrounding the
oocyte (corona radiata). The release of enzymes (answer e)from the sperm
acrosomal cap (an enlarged lysosome) results in digestion of the zona pellu-
cida surrounding the oocyte, allowing penetration by sperm.
7.The answer is a.(Moore and Persaud, Developing, pp 17–21. Sadler, pp
22–25.)The maximum number of oogonia occurs at about the fifth month of
development. Primordial germ cells arrive in the embryonic gonad of a
genetic female during the 7th to 12th week where they differentiate into
oogonia. After undergoing a number of mitotic divisions, those fetal cells
form clusters in the cortical part of the ovary. Some of those oogonia differ-
entiate into the larger primary oocytes (notto be confused with primary fol-
licles). The primary oocytes begin meiosis. At the same time, the number of
oogonia continues to increase to about 6,000,000 by the fifth month. At this
time, most of the surviving oogonia and some of the oocytes become atretic
(answers b and c).However, the surviving primary oocytes (400,000 to
1,000,000) become surrounded by epithelial cells and form the primordial
follicles by the seventh month. During childhood (answers d and e)there is
continued atresia, so that by puberty only about 40,000 primary oocytes
remain.
8.The answer is d.(Moore and Persaud, Developing, pp 16–21.)In man,
the time required for the progression from spermatogonium to motile sper-
matozoon is about 2 months (61 to 64 days). Spermatogenesis, the process
Embryology: Early and General Answers 83