Chapter 29: Development Study Guide

Question 1

1) The first 16 days after fertilization, is this the embryo or preembryonic stage?
2) What is it called once the age is at least 16 days and consists of the primary germ layers?
3) When does the fetal period start?

Answer 1

1) Preembryonic stage is the first 16 days after fertilization
2) Embryo is at least 16 days old and consists of three primary germ layers.
3) Fetal period starts at week 9 until birth

Question 2

1) What are the names of the three primary germ layers?
2) Define embryogenesis.

Answer 2

1) Ectoderm, mesoderm, and endoderm
2) Embryogenesis: events leading up to the embryonic stage

Question 3

1) How long is the egg viable after ovulation?
2) What part of the uterine tube is used for fertilization?

Answer 3

1) Egg must be fertilized within 12 to 24 hours of ovulation
2) The distal one-third of the uterine tube

Question 4

1) What is capacitation?
2) What is the optimal conception window?
3) What is the purpose of the acrosome?

Answer 4

1) The process that migrating sperm must undergo to make it possible to penetrate an egg. Sperm membrane becomes fragile and permeable to Ca2+ ; influx of calcium causes more powerful lashing of the tail
2) Conception optimal if sperm are deposited a few days before ovulation to 14 hours after
3) When sperm encounters an egg, it undergoes an acrosomal reaction that causes exocytosis of the acrosome, releasing the enzymes needed to penetrate the egg. Penetrates granulosa cells, then zona pellucida

Question 5

1) Define polyspermy
2) How is polyspermy prevented? (2 ways)

Answer 5

1) Fertilization by two or more sperm, which would produce a doomed fertilized egg
2) Polyspermy prevented by two methods: depolarization of membrane and producing a physical barrier outside the cell.

Question 6

Does the male mitochondria get inherited by the offspring?

Answer 6

No; the egg destroys the sperm mitochondria, only maternal mitochondria is passed on to the offspring

Question 7

1) When does meiosis II get completed in females, and what stage was the oocyte arrested in?
2) How does the DNA of the egg and sperm mix?
3) What term is used to describe the fertilized egg?

Answer 7

1) After fertilization meiosis II is completed (after being arrested in metaphase II)
2) Sperm and egg nuclei swell and become pronuclei; each pronucleus ruptures and the chromosomes of the two gametes mix into a single diploid set
3) Zygote: The fertilized egg

Question 8

Define the three trimesters by weeks

Answer 8

1) First trimester: from fertilization through 12 weeks
2) Second trimester: weeks 13 through 24; organs complete most of their development
3) Third trimester: week 25 to birth. At 35 weeks and 5.5 lbs, fetus is considered mature

Question 9

1) What is the difference between dizygotic twins and monozygotic twins?
2) Which type always results in twins of the same sex?
3) What 3 processes happen during the pre-embryonic stage (first 16 days)?

Answer 9

1) Monozygotic twins are the result of 1 egg being fertilized (embryoblast divides into two up to 14 days after fertilization); dizygotic twins are the result of 2 eggs being fertilized.
2) Monozygotic twins are always the same sex
3) Cleavage, implantation, embryogenesis.

Question 10

Define cleavage, morula, and blastocyst.

Answer 10

1) Cleavage: mitotic divisions that occur in first 3 days while conceptus migrates down uterine tube; reduces the size of the daughter cells (blastomeres). Pre-embryonic stage.
2) Morula stage: solid ball of 16 cells that resembles a mulberry that are still no larger than the zygote. The zona pellucida disintegrates and releases the blastocyst. Pre-embryonic stage.
3) Blastocyst: a hollow sphere of two layers; trophoblast is the outer layer that will form the placenta and the embryoblast is the inner cell mass. Pre-embryonic stage.

Question 11

1) What defines implantation?
2) How long does it usually take?

Answer 11

1) Implantation: the process of attachment of the blastocyst to the uterine wall (usually fundus or posterior wall) 6 days after ovulation
2) Implantation takes about 1 week

Question 12

1) What structure secretes human chorionic gonadotropin (hCG)?
2) What is the purpose of hCG? What structure does hCG target?

Answer 12

1) Trophoblast also secretes human chorionic gonadotropin (HCG)
2) HCG levels rise until the end of the second month and stimulate the corpus luteum to secrete estrogen and progesterone (progesterone stops menstruation)

Question 13

Define embryogenesis.

Answer 13

The arrangement of blastomeres into three primary germ layers in the embryoblast (gastrulation): Ectoderm, mesoderm, and endoderm.

Question 14

Define organogenesis. What week are all organs present?

Answer 14

1) Organogenesis: germ layers differentiate into organs and organ systems
2) Organs are all present (but not fully functional) at 8 weeks; the time when the embryo becomes a fetus

Question 15

List some major structures that derive from the three germ layers.

Answer 15

1) Ectoderm: Epidermis, nervous system, lens and cornea, internal ear
2) Mesoderm: Skeleton, muscle, cartilage, blood, lymphoid tissue, gonads and ducts, kidneys and ureters
3) Endoderm: Gut and respiratory epithelium and glands, bladder, and urethra

Question 16

Know location and functions of the accessory organs that develop with the embryo:
1) Placenta
2) Umbilical cord
3) Amnion

Answer 16

1) Placenta: forms over the next 6 weeks (after embryogenesis); becomes embryo’s primary source of nutrition
2) Umbilical cord: 2 umbilical arteries that carry blood to the placenta, 1 umbilical vein that carry blood away from the placenta. (umbilical-placental circuit)
3) Amnion: The transparent sac surrounding embryo that fills with amniotic fluid and protects the embryo from trauma, infections, and temperature fluctuations. It allows freedom of movement important to muscle development.

Question 17

Know location and functions of the accessory organs that develop with the embryo:
1) Yolk sac
2) Allantois
3) Chorion

Answer 17

1) Yolk sac: Small sac suspended from ventral side of embryo that contributes to the formation of the GI tract, blood cells, and future egg or sperm cells
2) Allantois: begins as an outpocketing of the yolk sac and forms the foundation for the umbilical cord, becomes part of the urinary bladder.
3) Chorion: outermost membrane enclosing all the rest of the membranes and the embryo; chorionic villi are filled with fetal blood and surrounded by maternal blood

Question 18

1) What does the foramen ovale become after birth?
2) What does the ductus venosus become after birth?
3) What does the ductus arteriosus become after birth?

Answer 18

1) Foramen ovale: Fossa ovalis
2) Ductus venosus: Ligamentum venosum
3) Ductus arteriosus: Ligamentum arteriosum