81Embryology:
Early and General
Answers
1.The answer is d.(Sadler, pp 95–100. Moore and Persaud, Developing, pp
47–50.)The placental structures shown in the photomicrograph are chori-
onic villi that are fetal tissues. The mother’s contribution to the placenta
(answers a and e)is the blood that flows past the chorionic villi. A fertil-
ized ovum reaches the uterus about 4 days after fertilization. At that time,
it has developed into a multicellular, hollow sphere referred to as a blasto-
cyst. The blastocyst soon adheres to the secretory endometrium and differ-
entiates into an inner cell mass that will develop into the embryo and a
layer of primitive trophoblast. The expanding trophoblast penetrates the
surface endometrium (answers b and c)and erodes into maternal blood
vessels. Eventually, it develops two layers, an inner cytotrophoblast and an
outer syncytiotrophoblast. Solid cords of trophoblast form the chorionic
villi, which then are invaded by fetal blood vessels.
2.The answer is c.(Alberts, pp 1051–1052. Junqueira, pp 423–426. Moore
and Persaud, Developing, pp 20–21.)The husband in the scenario has sperm,
which lack the acrosome (globozoospermia) and therefore the enzymes nec-
essary for penetration of the ovum are missing. The formation of the acro-
some, a specialized secretory granule, is one of many maturation events
occurring during spermiogenesis (the process by which mature sperm are
formed from the spermatids). Acrosome formation involves lytic enzyme mat-
uration and occurs after division of secondary spermatocytes. It involves no
mitotic or meiotic activity (answers d and e).The acrosome develops from
Golgi vesicles just like any other secretory granules. It contains acrosin, a ser-
ine protease, hyaluronidase, and neuraminidase, responsible for the penetra-
tion ability of the sperm. The developing cells are in contact with Sertoli cells
for all of the stages of spermiogenesis. At the end of spermiogenesis, sper-
matids are released by Sertoli cells in a process called spermiation (answer b).
Decapacitation factors are not involved in acrosomal maturation (answer a).