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Embryology LC Y1S1 > General Embryology > Flashcards

General Embryology Flashcards

1
Q

Describe 3 main embryological periods.
Define sperm capacitation.
Describe the process of fertilization
Describe development during first 3 weeks.
List the derivatives of the 3 germ layers.

A
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2
Q

What are the three embryologic periods?

A

1) Pre-embryonic period: “Germinal”, (fertilization till 2nd week)
- Rapid cell growth

2) Embryonic period (3 - 8 week)
- Initiation of organ development

3) Fetal period (9th week - Birth)
- Organs become more mature and increase in mass

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3
Q

What is fertilization?

A

It is the process of male and female pronucleus union in the ampulla with an aim to restore the diploid number of chromosomes, determine the sex, and initiate cleavage

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4
Q

On which day does implantation occur?

A

5-6 (by the end of the first week implantation has already occurred)

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5
Q

When does cleavage start to occur?

A
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6
Q

When is a blastocyte formed?

A
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7
Q

When does a blastomere form?

A
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8
Q

How does the sperm move from the cervix to the fallopian tube?

A

1) Muscle contraction of the cervix and uterine tube

2) By its propulsive motion

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9
Q

What changes occur in a sperm before it fertilizes an egg?

A

1) Capacitation
2) Acrosomal reaction

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10
Q

Describe the process of capacitation

A
  • In the female reproductive tract (Uterus and Uterine tube via their interaction with the epithelial lining)
  • The sperm loses its cholesterol membrane to penetrate the corona cells and undergo an acrosomal reaction
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11
Q

Describe the process of acrosomal reaction

A
  • Sperm must be in close proximity to the follicular cells
  • Where sperm loses its acrosomal membrane releasing enzymes to digest its way through the zona pellucida
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12
Q

What are the phases of fertilization?

A

Phase 1) Penetration of corona radiata

Phase 2) Penetration of zonapellucida
- By binding to the ZP3 receptor initiating the zona reaction

Phase 3) Fusion of oocyte and sperm cell membrane

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13
Q

What is the zona reaction?

A

A reaction where small vesicles “cortical granules” release their enzymes makes the zona pellucida impenetrable to other sperms (blocks polyspermy)

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14
Q

What are the events in the development during the first week?

A

1) Cleavage
2) Compaction
3) Formation of a Morula
4) Formation of a blastocyst
5) Implantation

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15
Q

What is cleavage?

A

It is a series of mitotic cell divisions of the zygote in the fallopian tube till the 16-cell stage (morula) all of them are known as a BLASTOMERES

  • 2-Cell stage (30 hrs)
  • 4-Cell-stage (40 hrs)
  • 12-cell stage (72 hrs)
  • 16-cell stage (Morula “96 hrs”)
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16
Q

What is meant by compaction?

A

After the third cleavage, blastomeres maximize their contact with each other by forming strong junctions together, as the zona pellucida has not disappeared yet, causing the inner mass to stay in contact

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17
Q

What is the source of nutrients of the morula?

A

Uterine tube secretions

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17
Q

What is the shape of the morula?

A

Mulberry appearance

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17
Q

Describe the development of the zygote

A

1) Central - Inner cell Mass - Embryo proper

2) Surrounding cells - Outer cell Mass - Trophoblast

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18
Q

What is a blastocyst?

A

As the morula enters the uterine cavity Fluid begins to penetrate through the zona pellucida, forming a blastocoel forming an inner cell mass and an outer cell mass

  • It is enveloped by the cona pellucida which disappears on day 6 when the blastocyst starts to implant
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19
Q

At which day after fertilization does a blastocyst occur?

A

4.5-5 days

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20
Q

From where does the blastocyst get its nutrients?

A

1) Uterine glandular secretions
2) Surrounding BV

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21
Q

About how many days after fertilization does the blastocyst get implanted?

A

6

22
Q

Describe the process of implantation

A
  • The embedding of the Blastocyst into the functional layer of the uterus at the end of the 1st week during the secretory phase of the uterus
  • With the help of proteolytic enzymes the trophoblastic cells over the embryonic pole begin to penetrate uterine epithelial cells
23
Q

On which day does the zona pellucida disappear?

A

at the end of day, 5 before implantation occurs

24
Q

Describe the secretory phase of the uterus during which the blastocyst implants

A
  • 2-3 days after ovulation
  • Day 21-23 of the uterine cycle
  • Occurs due to the release of progesterone, produced by the corpus luteum
  • The endometrial tissue if filled with glycogen and nutritional materials
  • During this phase:
    1) Endometrium increases in thickness
    2) Uterine glands and arteries become coiled
    3) Tissue becomes succulent
  • Forming three distinctive layers:
    1) Superficial compact layer
    2) Intermediate spongy layer
    3) Thin basal layer
25
Q

Between which layers does the blastocyst implant?

A

Between the opening of two glands, between the compact and spongy layer (AKA Functional layer)

26
Q

What is the name of the endometrium after implantation has occurred?

A

Decidua

27
Q

Describe the decidual reaction

A

Where the endometrium becomes polyhedral loaded with glycogen and lipids, and the tissue becomes edematous due to the extravasation of intracellular fluids

28
Q

Which hormone is responsible for the maturation of the follicle in the ovary?

A

FSH, follicle-stimulating hormone

29
Q

Which hormone is responsible for the ovulation?

A

LH, Leutinizing hormone

30
Q

Which hormone is secreted by the trophoblast cells?

A

HCG

31
Q

Which hormone is secreted by the corpus leuteum to maintain pregnancy?

A

progesterone

32
Q

Which hormone prevents the degeneration of the corpus leuteum?

A

Luteinizing hormone

33
Q

What are the sites of ectopic pregnancy due to the implantation in the wrong place?

A

1) Abdominal cavity
2) Ampulla
3) Tubal implantation
4) Interstitial implantation
5) Internal OS of uterus (cervical opening)
6) In the ovary

34
Q

What is placenta previa, what should you do to prevent the death of the baby?

A

It is the development of placenta in the cervical opening of the uterus, has the highest chance of survival from all ectopic pregnancy sites but a C-section must be performed to prevent the death of the baby

35
Q

At which month usually does the embryo of an ectopic pregnancy die?

A

At the second month of gestation, causing severe hemorrhage and abdominal pain

36
Q

What are the major events of the second week of development?

A
37
Q

What happens on day 8 of development?

A
  • Blastocyst is partially embedded into the endometrium

1) Trophoblast starts to proliferate as two distinctive layers:
1) Syncytiotrophoblast (Multinucleated, with no mitosis, erodes the endometrial tissue)
2) Cytotrophoblast (mononucleated, “mitotically active” actively proliferating)

2) The inner cell mass (Embryoblast) is divided into two layers:
1) Epiblast (contains the amniotic cavity inside it)
2) Hypoblast (cuboidal cells)
- On the exterior they are surrounded by the blastocyst cavity (later to be the primitive yolk sac)

38
Q

What is the amnioblast?

A

Epiblastic cells that are adjacent to the cytotrophoblast

39
Q

What happens on day 9 (lacunar stage) of development?

A
  • At the embryonic pole, Vacuoles appear at the embryonic pole, in the syncytium, fusing and forming large lacunas (lacunar stage)
  • At the abembryonic pole, the Hypoblast gives rise to flattened cells, forming the exocoelomic membrane which lines the interior surface of the cytotrophoblast
  • The blastocyst cavity becomes the exocoelomic cavity “primitive yolk sac”, lined by the hypoblast and the exocoelomic membrane
40
Q

What happens on day 11 and 12?

A
  • Blastocyst is completely embedded into the endometrium
  • Communicating networks at the site of the embryonic pole appear as the trophoblastic lacuna gets filled with maternal sinusoidal blood (uteroplacental circulation)
  • New cells appear between the cytotrophoblast and the exocoelomic cavity derived from the yolk sac cells
    1) Extraembryonic somatic mesoderm (covers the yolk sac)
    2) Extraembryonic splanchnic mesoderm (covers the inner surface of the cytotrophoblast)
    They are filled with extraembryonic cavities that will fuse to form a large extraembryonic coelom/chorionic cavity
41
Q

When is the blastocyst completely embedded into the endometrium?

A

On days 11 and 12

42
Q

On which day is the uteroplacental circulation formed?

A

11-12

43
Q

What happens on day 13?

A
  • Formation of a definitive/secondary yolk sac (lined by the mesoderm/hypoblast)
  • Formation of an extraembryonic cavity (chorionic cavity) from their fusion in the mesoderm layer
  • Part of the primitive yolk sac is pinched off named (exocoelomic cyst)
  • Chorionic plate/extraembryonic somatic mesoderm found lining the extraembryonic cavity/chorionic cavity, while the splanchnic surrounds the (hypo, and epiblasts)
    -Chorionic plate plays a part in the fetal portion of placenta formation
  • Formation of a connecting stalk connecting the hypo/epiblast to the mesoderm
44
Q

What is the source of the tissue that forms the umbilical arteries/veins?

A

Extraembryonic mesoderm

45
Q

Why is the second week of development known as the week of 2’s?

A

1) Trophoblast differentiates into two layers (cyto and syncyto)

2) Embryoblast forms two layers (epi and hypo)

3) Extraembryonic mesoderm splits into 2 (somatic and splanchnic)

4) Two “intra-embryonic” cavities are formed (amniotic and yolk sac)

46
Q

What happens in the third week of development?

A

1) Gastrulation
- Primitive streak formation

2) The oropharyngeal membrane is apparent which will form the oral cavity

47
Q

What is gastrulation?

A

It is the process of forming a trilaminar germ disc (ectoderm, mesoderm, and endoderm)

On days 15-16, On the caudal end, a primitive streak appears on the epiblast and has a depressed hole, apparent named the primitive groove

Starts with the formation of a primitive streak on the surface of the epiblast

48
Q

What happens on days 16-18?

A

Formation of the primitive node (elevated region) is formed at the top of the primitive streak close to the oropharyngeal membrane which acts as an organizer its inner depressed area is called a primitive node

49
Q

Describe the process of gastrulation

A

1) Migration/invasion of the epiblast cells to the primitive groove through the primitive streak

After imagination:
1) The first cell to invaginate forms the endoderm
2) Then mesoderm
3) Then Ectoderm
- They all originated from the epiblast

50
Q

What is a sacrococcygeal teratoma?

A
  • A benign tumor that results when the primitive streak is not closed and the epiblast keeps migrating downwards
  • Most common tumor in newborns and affects females mainly
  • It is removable by surgery
51
Q

What structures/organs develop from the endoderm?

A

1) Epithelial lining of the digestive & respiratory tract

2) Linning of the urethra, bladder, and reproductive system

3) Liver and pancreas

52
Q

What structures/organs develop from the mesoderm?

A

1) Musculoskeletal system

2) Circulatory system

53
Q

What structures/organs develop from the ectoderm?

A

1) Epidermis
2) Nail
3) Hair
4) Epithelium of ear, nose, etc
5) Nervous system

Embryology LC Y1S1 (4 decks)

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