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Foundations 1 > Embryology > Flashcards

Embryology Flashcards

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1
Q

What is the embryonic period?

A

Weeks 1-8

Development of structues

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2
Q

What is the fetal period?

A

Week 9-38 (birth)

Growth

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3
Q

What are PGCs?

A

Primordial germ cells develop at wk 4

Develop into gonads and gametes
Remain dormant in males until puberty

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4
Q

What are the stages of spermatogenesis?

A

PGCs arrested at wk 4
Begin to differentiate into type A spermatogonia in puberty
A few type A spermatogonia differentiate into type B which form primary spermatocytes. They divide into secondary spermatocytes. They enter meiosis II to form 2 spermatids.

Each B spermatogonia results in 4 spermatids

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5
Q

What are the steps of spermiogenesis?

A

Starts with spermatids
Adds acrosome gap, forms flagella, loose organelles and a majority of cytosol
Final product of spermatocyte

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6
Q

What are the steps in oogenesis?

A

By 5th month maximum number of primary oocytes formed and arrested in prophase of meiosis I until puberty
At puberty one primary oocyte completes meiosis I a month to form a secondary oocyte and polar body
Secondary oocyte enters meiosis II but is arrested at metaphase until fertilization

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7
Q

What is the ovarian cycle?

A

Menstrual phase
Follicular/proliferative phase
–> LH surge
Progestational/secretory phase
Menstrual phase if not fertilized or gravid phase

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8
Q

What is capacitation?

A

Conditioning of sperm in female reproductive tract for 7 hours
Interaction between mucosal surface of fallopian tube and sperm

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9
Q

What are the steps of fertilization?

A

Sperm penetrates the corona radiata, then the zona pellucida
Acrosome reaction occurs
Merges with oocyte cell membrane

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10
Q

What is the acrosome reaction?

A

After sperm binds to zona, zona proteins are released to prevent dispermy (acrosin and trypsin like)

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11
Q

What is oocyte response to fertilization?

A

Completes meiosis II and forms female pronucleus which fuses with male pronucleus to form zygote - diploid again

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12
Q

Where does fertilization take place?

A

Ampulla of fallopian tube

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13
Q

What occurs in the first 72 hours after fertilization?

A

Cleavage begins 30 hours post fertilization into two cells
Once into 8 cells forms blastomere
16 cell morula forms 72 hours after fertilization and enters uterus
There is no cell growth

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14
Q

What is the blastocyst and when does it form

A

Outer cell mass of trophoblasts that will form placenta
Inner cell mass of embryoblasts

From morula on day 5

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15
Q

What does trophoblast differentiate into and when?

A

Cytotrophoblasts
Syncytiotrophoblasts

End of wk 1

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16
Q

When does implantation begin?

A

End of week 1

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17
Q

What are the beginning steps of implantation?

A

During progestational phase of menstrual cycle blastocyst implants into functional layer of endometrium
Into the posterior or anterior uterine wall
Zona pellucida must degenerate first
Embryonic pole of blastocyst implants first

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18
Q

What is an ectopic pregnancy and where does it occur typically?

A

Abnormal site of implantation

Ampulla of fallopian tube
Rectouterine pouch

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19
Q

What are clinical signs of ectopic pregnancy?

A

Abnormal uterine bleeding
Sudden onset abdominal pain with missed period

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20
Q

What is placental previa and its effect?

A

Implantation at internal os of cervix, bridging the opening

Causes severe bleeding in second part of pregnancy and with delivery

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21
Q

What is hCG and when is it produced?

A

Glycoprotein produced by syncytiotrophoblast starting on day 6

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22
Q

What is the function of hCG?

A

Stimulates progesterone production by corpus luteum
Causes uterine endometrium to grow and proliferate
Prevents menstrual cycle

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23
Q

What can abnormal hCG levels cause or indicate?

A

Low may cause spontaneous abortion or indicate ectopic pregnancy

High may indicate multiples, hydatidiform mole, or gestational trophoblastic disease

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24
Q

What is are the two types molar pregnancy (hydatidiform mole)?

A

Partial mole
Complete mole

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25
What is a partial mole and its effects?
One oocyte fertilized by 2 sperm (Triploidy) Trophoblastic elements and some fetal parts Abnormally small placenta Vaginal bleeding in first trimester
26
What is a complete mole and its effects?
Fertilization of enucleate ovum (no female pronucleus) by normal sperm No embryo Sperm will duplicate its chromosome Only trophoblastic elements develop Tissue appear as a cluster of grapes
27
What are the germ layers and when do they form?
Endoderm - hypoblast Ectoderm - epiblast Day 8
28
How does the amniotic cavity form?
Between epiblast and trophoblast Derived from epiblast cells
29
How does the primary yolk sac form and when?
Flattened cells arise from hypoblast line the blastocyst cavity Day 9
30
What is the extraembryonic mesoderm?
2 layers between embryo and the cytotrophoblast
31
What are the layers of the extraembryonic mesoderm and where are they located?
Inner splanchnic lines yolk sac Outer somatic lines the cytotrophoblast
32
What will the outer somatic mesoderm become?
Connecting stalk and chorionic plate
33
What is the function of the primitive streak and when does it appear?
It appears in the week 3 and defines body axis
34
Where is the primitive node?
Cephalic end of primitive streak
35
What is gastrulation?
From epiblast of bilaminar disc Forms 3 germ layers - endoderm, mesoderm, and ectoderm
36
What occurs at the cranial end of embryonic disc during week 3?
Prechordal plate induces forebrain development Oropharyngeal membrane develops Mesoderm spreads except to prechordal plate and cloacal membrane
37
What is the cloacal membrane?
Caudal end of embryonic disc
38
What is the notochord and when does it develop?
Grows forward from primitive node between ectoderm and endoderm until it reaches the prechordal plate Future site of vertebral column Days 16-18
39
How does the notochord form?
Prenotochordal cells migrate through primitive streak. they become intercalated in endoderm to form notochordal plate and then detach to form definitive notochord. Cranial to caudal.
40
What is the role of the notochord?
Defines primordial axis or embryo Acts as primary inductor Induces formation of neural plate
41
What happens to the notochord?
Will degenerate and mostly disappears as vertebrae form Remnants as nucleus pulposus in adults
42
What is neurulation and when does it occur?
Notochord signals ectoderm to begin neurulation Neural plate to neural groove to neural tube Will develop into spinal cord and brain Closure of neural tube begins in the middle End of wk 3 and week 4
43
What arises from neural crest cells?
Sensory and autonomic ganglia
44
What is sirenomelia/caudal dysgenesis?
Insufficient mesoderm formed in caudal most region during gastrulation Legs fused together
45
What is a sacrococcygeal teratoma?
Tumor associated with gastrulation at base of coccyx derived from remnants of primitive streak Contains hair, skin, bone, and liver
46
What is a chordoma?
Tumor associated with notochord - slow-growing
47
What is holoprosencephaly?
Caused by high doses of alcohol during third week Kills anterior midline of germ disc - deficiency in craniofacial structures Small forebrain - no hemispheres eyes are close together
48
What are neural tube defects?
Failure of closure of neural tube
49
What are the two types of NTDs?
Anencephaly - at head region Spina bifida - at lumbosacral region
50
What is the intra-embryonic mesoderm?
Differentiation of mesoderm by week 3 into three parts Paraxial mesoderm Intermediate mesoderm Lateral plate mesoderm
51
What arises from the paraxial mesoderm?
Organized into somites by end of week 4 42-44 somites by end of 5th week
52
What are the differentiations of somites and what do they become?
Sclerotome - cartilage and bone Myotome - segmental muscle component Dermatome - skin
53
What does the intermediate mesoderm become?
Urogenital system
54
What are the two layers of lateral plate mesoderm?
Somatic/parietal layer - covering related to amnion Splanchnic/visceral layer - related to yolk sac
55
What are the major derivatives of the endoderm?
Epithelial lining and glands of GI and respiratory tracts
56
What are the major derivatives of the somatic mesoderm?
Parietal serosa Dermis of ventral body connective tissues of limbs
57
What are the major derivatives of the splanchnic mesoderm?
Wall of GI and respiratory tracts Visceral serosa Heart Blood vessels
58
What are the major derivatives of the ectoderm?
Epidermis, hair, nails, glands of skin Brain and spinal cord Neural crest and its derivatives including adrenal medulla
59
What is the folding of the embryo and when does it occur?
Flat disc becomes cylindrical with head fold, tail fold, and lateral folds Margins bound by primitive umbilical opening End of week 3
60
What causes the folds?
Head and tail by neural tube growth Lateral by somite growth
61
What are ventral body wall defects and some examples?
Failure of body wall to close involving one or both lateral body wall folds Thorax - ectopia cordis Abdomen - gastroschisis Pelvis - bladder exstrophy or cloacal exstrophy
62
What is gastroschisis?
Defective development of anterior abdominal wall with herniated abdominal contents into amniotic fluid
63
What are the components of the placenta?
Maternal portion of endometrium - decidua basalis Fetal portion of tertiary chorionic villi
64
What are the stages of placenta development in week 2?
Trophoblast differentiate into inner cytotrophoblast and outer syncytiotrophoblasts Lacunae develop in syncytiotrophoblasts Maternal sinusoids eroded by syncytiotrophoblasts Maternal blood enters lacunar network Establishes primitive utero-placental circulation Formation of primary chorionic villus
65
What is a primary chorionic villus made of?
Cytotrophoblast core covered by a syncytial layer
66
What are the stages of placenta developments in week 3?
Mesodermal cells penetrate primary villi to make secondary chorionic villus Mesodermal core capillaries arise forming tertiary chorionic villus/definitive placental villus Villous capillaries make contact with capillaries in chorionic plate and connecting stalk Intraembryonic circulatory system
67
What is the structure of a secondary chorionic villus?
mesoderm core, cytotrophoblasts, then syncytial covering
68
When does the heart begin to beat?
Week 4 - intraembryonic circulatory system already formed
69
What changes occur in the tertiary chorionic villi after the fourth month and why?
Cytotrophoblasts begin to degrade - easier diffusion
70
What are the functions of the placenta?
Gas exchange Nutrient exchange Transmission of maternal antibodies Hormone production to maintain pregnancy Detox some drugs
71
What is placenta accretia?
Implantation into myometrium instead of endometrium Possible viable pregnancy, but requires hysterectomy to remove placenta after delivery Vaginal bleeding at second trimester or later Massive maternal hemorrhage during delivery
72
What is the amnion and when is it formed?
Large cavity filled with amniotic fluid At week 2 from epiblast
73
What is the function of amniotic fluid?
Fetus suspended inside by umbilical cord Absorbs jolts Allows for fetal movement Prevents adherence of embryo to surrounding tissues
74
What are normal levels of amniotic fluid throughout pregnancy?
30 mL at 10 weeks 450 mL at 20 weeks 800-1000 mL at 37 weeks
75
What is polyhydramnios/hydramnios and its cause?
Excess amniotic fluid - 1500-2000 mL GI abnormalites
76
What is oligohydramnios and its effects?
Less than 400 mL Renal abnormalities, renal agenesis
77
What is an amniocentesis?
Withdrawal of amniotic fluid to detect alpha fetoproteins
78
What is the length of a full-term umbilical cord and what does it contain?
50 cm Right and left umbilical arteries - from fetus to placenta One umbilical vein - placenta to fetus Wharton's jelly
79
How to dizygotic twins occur and how to relate?
Fertilization of two oocytes by two sperms Diamniotic and dichorionic
80
How to monozygotic twins occur and how do they relate?
Fertilization of oocyte by one sperm that splits into two at blastocyst stage Typically diamniotic and monochorionic, but may be dichorionic as well

Foundations 1 (28 decks)

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