Lab 13: Development

Question 1

1) Define gestation
2) What 3 things does it consist of?

Answer 1

1) The 38-week period between fertilization and delivery of the fetus
2) Preembryonic period, embryonic period, fetal period

Question 2

1) What happens on day 1 of the preembryonic period?
2) What happens on day 2 of the preembryonic period?
3) What happens on day 4 of the preembryonic period?
4) What happens on day 5 of the preembryonic period?

Answer 2

1) Day 1: Fertilization occurs; requires capacitation and polyspermy prevention. Zygote forms.
2) Day 2: Cleavage starts when the zygote starts to divide (mitosis)
3) Day 4: A morula is formed.
4) Day 5: A blastocyst is formed and has reached the uterus. Consists of trophoblast and inner cell mass.

Question 3

1) What happens on days 6-14 of the preembryonic period?
2) What happens on days 14-16 of the preembryonic period?

Answer 3

1) 6-14: Implantation of the blastocyst and development occurs
2) 14-16: Preembryo becomes an embryo after gastrulation forms the 3 primary germ layers

Question 4

1) Define capacitation
2) What prevents polyspermy?
3) When does the secondary oocyte finish meiosis 2?
4) What forms the zygote?

Answer 4

1) Capacitation: Changes in the sperm in the female system where the enzymes in the acrosome are released (requires ~10 hours)
2) Sperm enters the secondary oocyte and triggers changes in the oocyte to prevent polyspermy.
3) After the sperm enters the secondary oocyte
4) The fusion of the male and female nuclei

Question 5

When does cleavage start?

Answer 5

When the zygote starts to divide (mitosis) (day 2)

Question 6

Define morula. When is it formed?

Answer 6

A solid ball of cells the same size as the zygote; continues to divide. Day 4.

Question 7

Define blastocyst. When is it formed and how does it stay alive?

Answer 7

A hollow ball of cells formed on day 5; fed with uterine milk (glycogen)

Question 8

What are the two parts of a blastocyst? What does each form?

Answer 8

1) Outer layer of cells: trophoblast, forms the chorion
2) Inner cell mass: embryoblast, forms the embryo, amnion, yolk sac, and allantois

Question 9

1) How is the blastocyst implanted?
2) Define gastrulation and when it happens

Answer 9

1) By digesting and liquifying the endometrial cells of the fundus or body of the uterus
2) The process the preembryo/ embryoblast undergoes to form the 3 primary germ layers (and become an embryo). Happens day 14-16.

Question 10

What are the 3 primary germ layers of the embryo?

Answer 10

Ectoderm, mesoderm, endoderm

Question 11

1) What is the chorion?
2) What does the chorion secrete and when?
3) Define placenta and what it’s formed by
4) Describe the anatomy of the placenta
5) What does the placenta serve as?

Answer 11

1) Chorion: The embryonic membrane that forms the embryonic portion of the placenta
2) Secretes hCG until the placenta is fully established in week 9-10.
3) A highly vascularized disc of tissue formed by fingerlike extensions called villi (that will contain fetal capillaries).
4) The spaces in the endometrium between the villi are filled with maternal blood; normally there’s no mixing of maternal and fetal blood, substances just diffuse between them.
5) A site of exchange for nutrition, respiration, and excretion for the embryo and an endocrine gland for the mother

Question 12

1) Define the amnion. What is it filled with?
2) Define allantois

Answer 12

1) Amnion: Surrounds the embryo (later the fetus) and serves as a protective cushion for it. Filled with amniotic fluid that was originally filtered from maternal blood (and fetus also excretes urine into it).
2) Allantois: The part of the yolk sac that eventually forms the umbilical cord.

Question 13

1) What three things does the umbilical cord consist of?
2) What are the 3 functions of the yolk sac?

Answer 13

1) One umbilical vein and two umbilical arteries.
2) Produces RBCs until the liver takes over in week 6, forms part of the GI tract, and is the source of stem cells for the gonads.

Question 14

1) What does the umbilical vein do?
2) What do the umbilical arteries do?

Answer 14

1) U. vein: Carries nutrients and oxygenated blood from the placenta to the fetus. (red)
2) U. arteries: Carry wastes and deoxygenated blood from the fetus to the placenta (purple)

Question 15

1) When is the embryonic period and what happens during it?
2) When does the heart start to beat?
3) What parts of the body are formed by the end of the embryonic period?

Answer 15

1) Day 16 through week 8; organogenesis (the development of organ systems) occurs.
2) The heart starts forming in week 2 and starts to beat in week 4.
3) The arms and legs are distinct, the major brain regions are present (head is nearly as large as body), and the circulatory system is fully functional.

Question 16

1) When is the fetal period and what occurs during it?
2) When is growth rate the highest in the fetal period?
3) What protects the skin of the fetus from the amniotic fluid during this time?

Answer 16

1) Beginning of week 9 until birth; all organ systems continue to grow and develop. The head and body become more proportionate.
2) 9-16 weeks.
3) The vernix caseosa

Question 17

1) What is the activation of sperm called?
2) What stage of development does a preembryo need to be in to be implanted?

Answer 17

1) Capacitation
2) Blastocyst

Question 18

1) When does cleavage occur on the model?
2) What does a morula look like?
3) What does a blastocyst look like?

Answer 18

1) Between the 2 cell stage and 4 cell stage
2) Has lots of small cells but remains the size of a zygote
3) Has lots of empty space and a blue ring around it (trophoblast) on the model. Has an inner cell mass.

Question 19

1) What do the umbilical arteries connect?
2) What is their purpose?
3) What do they look like on the model?
4) What do they become after birth?

Answer 19

1) Internal iliac artery to placenta
2) Carry CO2 and waste to the placenta from the fetus.
3) Purple and wrapped around umbilical vein.
4) Medial umbilical ligaments

Question 20

1) What does the umbilical vein connect?
2) What is its purpose?
3) What does it look like on the model?
4) What does it become after birth?

Answer 20

1) Placenta to liver
2) Carry O2 and nutrients to the fetus
3) Red and long
4) Round ligament of the liver

Question 21

1) What does the ductus venosus connect?
2) What is its purpose?
3) What does it look like on the model?
4) What does it become after birth?

Answer 21

1) Umbilical vein to inferior vena cava
2) Bypass the liver
3) At the part of the umbilical vein that goes through/ behind the liver
4) Ligamentum venosum

Question 22

1) What does the ductus arteriosus connect?
2) What is its purpose?
3) What does it look like on the model?
4) What does it become after birth?

Answer 22

1) Pulmonary trunk to aorta
2) Bypass the lungs
3) Where the aortic arch meets the trunk.
4) Ligamentum arteriosum

Question 23

1) What does the foramen ovale connect?
2) What is its purpose?
3) What does it look like on the model?
4) What does it become after birth?

Answer 23

1) Right atria to left atria (of the heart)
2) Bypass the pulmonary circuit/ lungs
3) A hole in the medial walls of the atria
4) Fossa ovalis

Question 24

Which side of the placenta is the fetal side? Which side is the maternal side?

Answer 24

The side with the bodies of the veins/ arteries and the umbilical cord is the fetal side; the side with only the tips of the veins/ arteries is the maternal side.

Question 25

Where is the amnion located on the developmental sequence models?

Answer 25

Behind the fetus (clearish sac that contains it)

Question 26

List the flow of fetal circulation beginning with the umbilical arteries (8 steps)

Answer 26

1) Umbilical arteries
2) Placental capillaries
3) Umbilical vein
4) Ductus venosus
5) Inferior vena cava
6) Right atrium
7) Foramen ovale
8) Left atrium

Question 27

What 4 things does the ectoderm of an embryo form?

Answer 27

1) Nervous system
2) Epidermis of the skin
3) Hair and nails
4) Sudoriferous and sebaceous glands

Question 28

What does the mesoderm of an embryo form? (3 categories)

Answer 28

1) Skeletal system
2) Most of the muscular, lymphatic, and cardiovascular systems
3) Serous membranes.

Question 29

What does the endoderm of an embryo form? (3 categories)

Answer 29

1) Inner lining of most of the gastrointestinal tract
2) Inner lining of respiratory tract
3) Epithelium of many glands (thyroid, pancreas, thymus, liver).