Human Embryogenesis (Pinhal-Enfield)

Question 1

When is the embryogenic period & hallmarks

Answer 1

1-8 weeks

Organogenesis & high teratogen susceptibility

Question 2

When is the fetal period and what are hallmarks

Answer 2

9-38 weeks

Differentiation, growth, weight gain

Lower teratogen susceptibility

Question 3

What happens during ovulation?

Answer 3

Oocyte discharges from ovary & migrates into uterine tube during ovulation

Ovulated oocyte is surrounded by shell with layers (follicle)

Question 4

Capacitation

Answer 4

Spermatozoa conditions in female tract to fertilize oocyte, but need to undergo Capacitation to fertilize

(It’s a biochemical step that allows sperm to fertilize)

Question 5

Where does fertilization occur

Answer 5

Ampulla of the uterine tube (this is where the oocyte & capacitated sperm meet)

Sperm can live in female tract for several days; an oocyte that’s not fertilized degenerates within 24 hours of ovulation

Question 6

Implantation of early embryo is during _____

Answer 6

Endometrial secretory phase

Question 7

If pregnancy occurs, the corpus lute up is maintenance by ______ which is secreted by trophoblast a of placenta

Answer 7

Human chorionic gonadotropin (hCG)

**if pregnancy doesn’t occur, corpus lute up degerates & decline of progesterone leads to endometrium shedding & beginning of new cycle

Question 8

3 oocyte shell layers from inside to out

Answer 8

Plasma membrane

Zona pellucida

Plasma membrane

Question 9

Corona radiata

Answer 9

Outer crown of follicular cells around oocyte

Protection, energy, support for oocyte

Chemoattractant for sperm

Aka cumulus oophorus

Question 10

Zona pellucida

Answer 10

Intermediate glycoprotein layer

Made up of “zone proteins” (ZP)

ZP3 binds sperm

Question 11

Plasma membrane is the ____ layer that a sperm needs to penetrate during fertilization

Answer 11

Last

Question 12

How and when are sperm modified?

Answer 12

• sperm modified by secretions in female tract
• modifications can take several hours; mandatory ripening process (Capacitation)

-modifications in sperm intracellular signaling & sperm tails become hyper-activated & more motile

Question 13

What is removed from sperm during Capacitation

Answer 13

Glycoproteins & plasma proteins removed from tip of sperm head

Now, membrane overlying acrosome more fluid for enzyme release during fertilization

Question 14

3 phases of fertilization

Answer 14

1. Penetration of corona radiata
2. Penetration of zonal pellucida
3. Plasma membrane fusion

Question 15

Phase 1 of fertilization

Answer 15

-capacitated sperm penetrate the corona radiata via whipping sperm tail

***only 300 of 300 million ejaculated sperm penetrate the corona radiata

Question 16

Phase 2 of fertilization

Answer 16

Sperm heads bind to ZP3 sperm receptors in zone pellucida and release acrosome like enzymes that dissolve the zone pellucida & allow sperm to penetrate the zone pellucida

Question 17

Phase 3 of fertilization

Answer 17

Oocyte & sperm plasma membranes fuse

• sperm nucleus enters oocyte while its plasma membrane melds with oocyte plasma membrane
• oocyte meiosis II completion & formation of haploid definitive oocyte (& polar body)
• female gamete (ovum) and male gamete (sperm) fuse their haploid (n) pro nuclei & form a diploid (2n) zygote

Question 18

How does oocyte block polyspermy in order to stop fertilization by more than one sperm?

Answer 18

Upon sperm contact with oocyte plasma membrane
–> oocyte plasma membrane depolarizes & there is an intracellular Ca 2+ tsunami that induces cortical reaction

Zone pellucida is impermeable to other sperm

Question 19

Dizygotic twins

Answer 19

• aka fraternal
• toe oocyte said are simultaneously ovulated & each fertilized by separate sperm
• 70% of twin pregnancies (1%)
• genetic content different
• separate amniotic cavity

Question 20

Monozygotic twins

Answer 20

• identical
• 30% of pregnancies
• single oocyte fertilized by single sperm; splits into 2 within first week
• timing or split determines if twins have shared or split amniotic cavities
• earlier the split: more independent their support structures will be
• genetic contact same

Question 21

What is cleavage and what does it result in?

Answer 21

• cleavage is a series of symmetrical mitotic cell divisions during week 1
• cleavage divisions occur ~20 hours apart and result in BLASTOMERES

Question 22

BLASTOMERES

Answer 22

• result of cleavage

- daughter cells that are smaller with each successive division, encased by the zone pellucida in the early embryo

Question 23

BLASTOMERES up through the 8 cell stage are _____

Answer 23

Totipotent; they can give rise to all embryonic & extraembryonic tissues

**beyond the 8 cell stage, the cells become more differentiated and committed to becoming a particular cell type (no longer Totipotent)

Question 24

Morula

Answer 24

By day 4, 32 cell

-solid ball of compacted cells migrating in the uterine tube toward the uterus

Question 25

How do the cells of the morula segregate & begin to establish polarity?

Answer 25

Inner cell mass (ICM)/embryo last --> fetus Outer cell mass (OCM)/trophoblast -->placenta

Question 26

How does blastocyst form

Answer 26

Fluid from uterine cavity penetrates zona pellucida to surround cells of the morula's ICM By 4.5 days after fertilization, penetrating fluid pools and forms blastocyst cavity of the blastocyst

Question 27

Embryoblast/ICM cells are _____

Answer 27

Pluripotent (give rise to any/all embryonic cells but not placenta) Pluripotent embryoblast/ICM cells have potential as embryonic stem cells (ES cells) **totipotent up until 8 cell stage, then becomes morula -->blastocyst (pluripotent here....as becomes fetus becomes multi potent and unipotent

Question 28

When does implantation occur?

Answer 28

~6 days after fertilization during the secretory phase of the endometrium. (Day 20 of 28 day cycle)

Question 29

_______ drive blastocyst implantation

Answer 29

Trophoblasts

Question 30

How do Trophoblasts drive blastocyst implantation?

Answer 30

Trophoblasts @ embryonic pole of blastocyst secrete enzymes that degrade the zona pellucida -->blastocyst "hatches" thru the zona pellucida on day 5 & implants into endometrium Trophoblasts @ embryonic pole embed into uterine wall, eventually form fetal components of placenta & secrete hCG which induces corpus luteum to continue secretion of progresterone for endometrium maintenance

Question 31

With implantation, pregnant uterine endometrium undergoes _______ reaction with increased glandular activity

Answer 31

Decided reaction

Question 32

Ectopic pregnancy

Answer 32

Blastocyst normally implants into anterior or posterior uterine body wall ---> ectopic is occurs outside this region 95% occur in uterine tube (in ampulla, where fertilization taking place)

Question 33

In week 2, embryoblast of the blastocyst forms ____

Answer 33

2-layered/bilaminar disc *busy time for Trophoblasts, hypoblast, aminoblasts, in forming extraembryonic support

Question 34

Embryoblast different ion forms the

Answer 34

Bilaminar embryonic disc

Question 35

Epiblasts differentiate into ________

Answer 35

Cells of the embryo proper and amnioblasts (Amniotic cavity) Amniotic fluid: fetal urine, oligohydramnios (not enough), polyhyrdaminios (too much)

Question 36

Hypoblasts proliferate & migrate to line inner trophoblast surface of blastocyst cavity This becomes the ......

Answer 36

Yolk sac - ventral to bilaminar disc and eventually regresses - early exchange/hematopoiesis/germ cells to gonads

Question 37

Hypoblasts give rise to tissue that makes up ____

Answer 37

Connecting stalk -->becomes umbilical cord & connects the embryo/fetus to the placenta

Question 38

Trophoblasts invade uterine endometrium (and along with hypoblast derived tissue) contribute to formation of _____

Answer 38

Fetal part of placenta ***maternal part of placenta develops from trophoblast altered endometrium

Question 39

Chorion frondosum What is it and what makes it up

Answer 39

Fetal part of placenta made up of Trophoblasts and hypoblasts

Question 40

Decidua basalis

Answer 40

Maternal part of placenta Made up of uterine endometrium

Question 41

What does fetal blood carry

Answer 41

Waste to placenta from umbilical arteries (2) Nutrients from placenta to umbilical vein (1)

Question 42

What does maternal blood carry

Answer 42

Nutrients to placenta from spiral arteries Waste from placenta to uterine veins *waste-nutrient exchange and separation of fetal and maternal blood @ placental barrier

Question 43

What are Trophoblasts, hypoblasts, amnioblasts, doing during week 2?

Answer 43

Forming extraembryonic support

Question 44

During week 3, the epic last of the bilaminar embryo forms trial minor sic in process called

Answer 44

GASTRULATION

Question 45

Week 3 is a busy time for epic lasts in formation of

Answer 45

Intraembryonic germ layers

Question 46

GASTRULATION occurs with ____ formation

Answer 46

GASTRULATION occurs with primitive streak formation in the epic last of the bilaminar desk

Question 47

3 primary germ layers of the trial minor embryo: These originate from ____

Answer 47

Ectoderm, mesoderm, endoderm These layers originate from epic last

Question 48

Epiblast cells migrate to the ______ where they detach and invaginate through it during ____

Answer 48

Epiblast cells migrate to the primitive streak where they detach and invaginate through the primitive streak during GASTRULATION Invaginated epic lasts migrate & form a flat disc-like embryo with 3 layers (trilaminar)

Question 49

Epiblast cells that intercalated among hypoblast cells displace & replace hypoblast cells to form

Answer 49

Endoderm

Question 50

Epiblast cells settle between the endoderm and epiblast to form

Answer 50

Mesoderm (these cells migrate laterally and carnially)

Question 51

Epiblast cells that remain behind are

Answer 51

Ectoderms

Question 52

Ectoderm does what

Answer 52

Communication w external environment Nervous system, epidermis, sensory receptors, some glands

Question 53

Mesoderm does what

Answer 53

Support through muscles and connective tissues Skeletal, muscular, urogenital, cardiovascular systems

Question 54

Endoderm does what

Answer 54

Digesting, breathing, secreting (many hands) Epithelial of urinary bladder, GI-respiratory, some glands

Question 55

2 sites in embryo where ectoderm and endoderm adhere tightly together without migration of intervening mesoderm

Answer 55

1. Buccopharyngeal membrane | 1. Cloacal membrane

Question 56

Buccopharyngeal membrane

Answer 56

Lies at cranial end of embryo & future location of oral cavity

Question 57

Cloacal membrane

Answer 57

Lies at caudal end of embryo as future location of anus

Question 58

What happens when primitive streak doesn't regress

Answer 58

Primitive streak regresses by end of the 3rd week as the notochord mesoderm forms Teratomas form when primitive streak fails to regress & contain multiple tissue types derived from pluripotent epiblast cells

Question 59

Week 1 of prenatal development beings/ ends with:

Answer 59

Begins with fertilization & ends with blastocyst implantation

Question 60

Week 2 of prenatal development forms

Answer 60

Bilaminar disc & supportive extraembryonic structures (including placenta)

Question 61

Week 3 of prenatal development results in

Answer 61

GASTRULATION of epiblast Forms trilaminar embryo with 3 primary germ layers