Intro to Embryology

Question 1

Nondisjunction

Answer 1

Process of separation of homologues chromosome pairs fails. It leads to abnormal chromosome numbers (monosomy or trisomy). Can occur during meiosis I or meiosis II.

Question 2

What is the most common disorder that is a result of nondisjuction?

Answer 2

Down’s Syndrome

Question 3

teratogens

Answer 3

external agents (extrinsic to the fetus) that produce developmental malformations.

Question 4

embryology

Answer 4

branch of biology that deals with the development of an embryo from the fertilization of the ovum to the fetus stage.

Question 5

teratology

Answer 5

The study of abnormalities of physical development. It includes developmental and post-developmental stages (e.g. puberty)

Question 6

What are the stages of embryogenesis?

Answer 6

cleavage (division of zygote and formation of blastocyst), gastrulation (formation of germ layers), organogenesis (differentiation of germ layers).

Question 7

What is gametogenesis?

Answer 7

Formation of gametes. They contain half regular DNA content.

Question 8

How many oocytes and sperm are produced in meiosis?

Answer 8

1 oocyte (3 polar bodies), 4 sperm

Question 9

In what stage of meiosis are primary oocytes arrested in?

Answer 9

prophase I in utero; secondary are in metaphase II,

Question 10

What are the protective layers surrounding a secondary oocyte?

Answer 10

corona radiata and zona pellucida

Question 11

What layer of the sec. oocyte prevents implantation before fertilization?

Answer 11

zona pellucida

Question 12

Where does fertilization occur?

Answer 12

lateral third of fallopian tube.

Question 13

What occurs during fertilization?

Answer 13

fusion of gametes, ZP dissolves, diploid chromosomes restored, sex determined, cleavage initiated.

Question 14

What are the major stages of fertilization?

Answer 14

acrosome released in egg, ZP penetrated, cortical reaction inactivates sperm receptors, polyspermy block, fusion of membranes, meiosis II completed and ovum formed, implantation into uterine wall.

Question 15

What is the embryonic period?

Answer 15

3 - 8 weeks of devleope. Pre-embryonic are the first 2 weeks of development; zygote becomes a spherical, multi-cellular structure.

Question 16

What is the fetal period?

Answer 16

Remaining weeks of development (9-38).

Question 17

What occurs during cleavage?

Answer 17

The zygote divides rapidly under a series of mitotic divisions. After 3 divisions, the cells become tightly compacted into a ball called the morula.

Question 18

What is the morula?

Answer 18

A ball of compacted cells that was originally the zygote. The cells differentiate into inner and outer cell masses and eventually becomes a blastocyst.

Question 19

What is a blastocyst?

Answer 19

A ball of cells that has differentiated into the embroyblast (inner cell mass) and trophoblast (outer cell mass). As it implants into the uterus, the ZP dissolves.

Question 20

What occurs during implantation?

Answer 20

The ZP breaks down and the blastocyst invades the endometrium. The trophoblast cells and embryoblast cells differentiate and form two cavities.

Question 21

What is the trophoblast?

Answer 21

A cavity in the BLASTOCYST that eventually becomes the placenta. It differentiates into the cytotrophoblast and the syncytiotrophoblast (releases progesterone to continue pregnancy).

Question 22

What is cleavage?

Answer 22

The division of the zygote and formation of the blastocyst.

Question 23

What do the hypoblast and epiblast form?

Answer 23

The bilaminar disc.