Human Embryology Flashcards by Joseph Coromelas

1st _______ weeks important for cranio-facial development

eight

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Normal gestationDuration: ___ +/- 2 weeks = full term____ days from first day of last menstrualperiod (LMP) or_____ days from ovulation.

40; 280 days; 266 days

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Which trimesters are these?
_______ trimester: growth in weight, preparation for birth
_______ trimester: from single cell to baby-looking
________ trimester: growth in length, organogenesis

third; first; second

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How long are each trimesters (in weeks)?

First trimester (~0-14 wks): from singlecell to baby-looking

Second trimester (~15-27 wks): growth inlength, organogenesis

Third trimester (~28 wks to term): growthin weight, preparation for birth

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Which trimester is the most critical period for normal development?

The first trimester

NOTE: 30% of conceptions end in spontaneous abortions

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Why is the first trimester is the mostcritical period for normal development? (3)

1) chromosomal abnormalities
2) abnormal sperm/ oocyte
3) improper implantation

ALSO; women know they’re pregnant ~2 months, so they may drink and smoke week (everyday)

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T/F: During the first trimester, theembryo (1st 8 weeks) and fetus (8-14 weeks) are most sensitive to teratogens,including: alcohol, drugs (prescription andrecreational), cigarette smoke, elevated body temperature(hot tubs, maternal fever).

True

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T/F: Paternal age is not linked with schizophrenia.

False; father’s age is linked due to increase rate of random mutations

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What’s Down Syndrome? How does it occur?

DS= trisomy of chromosome 21

It occurs due to non-disjunction during meiosis

NOTE- non-disjunction is when apair of chromosomes doesn’t split off, resulting in an unequal # of chromosomes(gametes are supposed to be haploid)

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1) _______: sperm + oocyte = embryo
2) _______: via cell division/cleavage, from singlecell to multicellular hollow ball.
3) _______:separating the embryonic region from the extraembryonic components (e.g.placenta) and making intimate contact with maternal tissue.
4) _______: formation of the 3 germ layers – endoderm, mesoderm and ectoderm via cellmigrations.
5) _______: formation of the brain and spinal cord fromthe ectoderm.
6) _______:from the endoderm, via cranial/caudal and bilateral body folding.
7) _______: migration to form muscle, skeleton, dermis, urogenital tract, circulatorysystem, blood and heart.

Time Zero
1) Fertilization
2) Blastocyst Formation
3) Embryonic Dis and Implantation
4) Gastrulation
5) Neurulation
6) Gut Tube Formation
7) Mesoderm Development
Week 4

Each step (Except Fertilization) takes 1 week

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Blastocyst Formation: What is it? What week?

Week 1; cell division/ cleavagne, from single cell to multicellular hollow ball

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Fertilization: What is it? What week? Where does it occur?

Time Zero; sperm+ oocyte= embryo

Occurs: the ampullary portion of the fallopian tube

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During what trimester stage can embryonic stem cells be deliberately differentiated?

Blastocyst Stage (when embryo hatches)

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T/F: Cleavage is cell division accompanied by cell growth

False; it is not

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Cleavage is the first next important step after fertilization. When and at what rate does it occur?

First cleavage occurs at ~24 hr postfertilization, producing the first 2 blastomeres.
Subsequent cell divisions every 12 hrsproduce the ~30 blastomeres of the morula.

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The blastocyst forms from the______ via a process of compaction and is fluid filled.Then the blastocyst separates into2 sets of cells: ______ and _______.

morula;

trophoblast and inner cell mass

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________: becomes the embryo proper and some extraembryonic tissues derives from the small collection of internal blastocyst cells

________: givesrise to the placenta, but not the embryo. derivesfrom the outer cells which become flat and make tight junctions

Inner cell mass

* Trophoblast

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Hatching of the Blastocyst:

The blastocyst emerges from the __________ 5days after fertilization.

At this time, the inner cell mass is abilaminar disc, comprising the _____ and _______.

zona pellucida

epiblast and hypoblast

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T/F: Hatching is required for implantation of the blastocyst in the endometrial wall in week 2.

True!

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How many days after fertilization does implantation occur?

4-6 days after fertilization, theblastocyst reaches the uterus, which is primed for implantation.

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Embryonic Disc and Implantation: What is is and what week does it occur?

Week 2

separatingthe embryonic region from the extra-embryonic components (e.g. placenta) andmaking intimate contact with maternal tissue.

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Describe the how the bilayered disc forms

Theinner cell mass becomes bilayered,comprising the outer epiblast layer and the inner hypoblast layer, surroundedby the trophoblast epithelium

NOTE: innercell mass= 2 layer structure

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Bilayered Disc Formation:

•The______ and _______ produce extraembryonic tissues, while the ______ gives rise mostly to the embryo proper.

Trophoblast and Hypoblast

epiblast

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The dorsal _________ is the normal zone for implantation.

Theembryo first attaches to, then invades the ___________, with the epiblastalways oriented first toward the uterine wall.

_________ cells (from the trophoblast) secrete proteolytic enzymes, allowing the_________ to enter the endometrial wall

Endometrium

Syncytiotrophoblast; blastocyst

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Theinner cell mass which has formed into the bilaminar embryo (______ and _______) and the large fluid-filled space(_________).

epiblast and hypoblast; blastocoel

What three things happens during implantation?

1) syncytiotrophoblasts generate lacunae (w/in endometrium) which fuses w/ other maternal capillaries (joins maternal/ embryonic cirulation) 2) The amniotic cavity forms around epiblast cells 3) Definitive yolk sac forms the hypoblast

Is the hypoblast considered the extraembryonic mesoderm?

yes

What does the primitive yolk sac (aka embryonic umbilical vesicle) forms?

the umbilical trunk

90% of Ectopic Pregnancies are ________, and danger isfrom rupture and subsequent hemorrhage

tubal

What 3 future germ layers reside in the epiblast before gastrulation? What are they destined to do?

1) Ectoderm- brain/ spinal cord & dermis of skin 2) Mesoderm- muscle, bone, blood, urogenital system & dermis of skin 3) Endoderm- GI & respiratory tract

The gastrulation process transforms the single layer _______ into 3 layers: ectoderm, mesoderm and endoderm.

epiblast

The ______ and _______ move initially from the epiblast through the primitive streak, while _______ stays on the surface.

endoderm and mesoderm; ectoderm

The primitive streak, where the endoderm and mesoderm moves through during gastrulation, contains what 3 components?

streak, pit, and node

The primitive streak and node are essential for what 3 things?

- specifying fates of migrating endoerm and mesoderm - inducing the nervous system (neural plate) - defining the rostrocaudal body axis

T/F: During gastrulation, future ectoderm cells move internally via the primitive streak, node and pit, leaving endoderm and mesoderm on the epiblast surface.

False; During gastrulation, future endoderm and mesoderm cells move internally via the primitive streak, node and pit, leaving ectoderm on the epiblast surface.

During gastrulation, presumptive _________ leaves the epiblast first, and replaces the ________ cells to form the embryonic gut. Then, presumptive ______ leaves the epiblast, and invades the space between the ______ and _____, to form muscle and skeleton.

endoderm; hypoblast cells; mesoderm; epiblast; hypoblast/ endoderm

What are the initial 2 germ layers that exist before gastrulation forms the mesoder, ectoderm, and endoderm?

hypoblast; epiblast

Persistant ________ cells are pluripotent (can generate all cell types) and normally disappear at the end of gastrulation via apoptosis. If they don't, they may result in the individual getting __________.

primitive streak cells; teratomas (i.e. sacrococcygeal teratoma) NOTE- teratomas removed after birth due to risk of malignancy

At the end of gastrulation, the germ layers are properly arranged, both ________ and _________.

rostrocaudally and dorsoventrally

At the end of gastrulation, the germ layers are properly arranged, both rostrocaudally and dorsoventrally: 1) _____- gut tube, internal epithelia of buccopharyngeal and cloacal membranes 2) ____- notorchord (axial), paraxial, intermdediate and lateral plate mesoderm 3) ____- neural plate and general ectoderm on the surface of the epiblast

1) endoderm 2) mesoderm 3) ectoderm NOTE- Each germ layer then goes on to produce specific tissues

Each germ layer then goes on to produce specific tissues..... what does the ectoderm, endoderm, and mesoderm eventually form?

Ectoderm- epiderm epithelium (hair, nails tooth enamel), nervous system (PNS/CNS) and neural creast derivatives (pigment cells, tooth dentine) Endoderm- GI tract epithelium, respiratory tract epitheilium and endocrine glands Mesoderm- muscle, skeleton, CT, urogenital tract/ germ cells and heart/ blood/ blood vessels

The nervous system is formed from the ectoderm during gastrulation. The ectoderm is divided into what 2 territories? What type of epithelium are they and what do they form?

1) neural plate- columnar epithelium; brain/ spinal cord 2) lateral ectoderm- cuboidal epithelium; epidermis of skin NOTE- All of the induction of the node occurs at the end of gastrulation

The neural plate is induced to form from the ectoderm by signals from the _____ and from the underlying _______ during gastrulation. This induction also establishes the ______ axis of the future central nervous system.

node; notochord rostrocaudal axis NOTE- All of the induction of the node occurs at the end of gastrulation

What signal is importnat for establishing left-sideness? The dorsal lip of the blastopore (or the node)?

left side- FGF8 (--> Nodal Lefty --> Pitx2) | Dorsal Lip- BMP inhibitor (i.e. Noggin, Chordin, Follistatin)

Neural induction involves embryonic _______, a population of cells that can induce neural cells to form and create ______ axis.

organizers; secondary Body Axis

Embryonic organizers induces neural plate by secretion of ________. What 2 other signals are involved?

BMP inhibitors; IGF and FGF NOTE- Can get induction of multiple head structures by BMP inhibitors

What signaling induces cranial structures? What loss of function will result in a loss of most cranial head structures?

Wnt Signaling; DKK (a Wnt inhibitor) NOTE- too much or too little may result in the same phenotype (i.e. too much Wnt signaling/ too little Wnt signaling= loss of head structure)

________, which occurs during week __ of the first trimester, results from the endoerm via cranial/ caudal and bilateral body folding.

Gut Tube Formation; week 4

Cephalo(rostro)-caudal folding occurs in the 4th week. What are anterior changes (5) and posterior changes (2)?

Anterior Changes: 1) forebrain folds ventrally 2) buccopharyngeal (bp) membrane moves posteriorly/ ventrally to the oral region 3) Future heart moves dorsally/ posteriorly to thoracic region 4) amniotic cavity becomes a protective sac wrapped around embryo 5) Forgut forms Posterior Changes: 1) cloacal membrane moves ventrally/ anteriorly to form future anus 2) hingut forms

Along with cephalo(rostro)-caudal folding, Lateral folding also occurs during week 4, resulting in what?

- fused endoderm - gut-tube - smooth muscle - skin all at the ventral midline both anterior and posterior to yolk sac. The body wall remains open in the region of the yolk sac until ~week 6

What is gastroschisis and how does it occur?

- occurs when bowel, stomach, and liver are herniated outside the abdominal cavity (closure defects) - Incomplete lateral body wall folding in weeks 4-5

_________: migration to form muscle, skeleton, dermis, urogenital tract, circulatory system, blood and heart.

Mesoderm development (week 4 of first trimester)

During gastrulation and as the neural tube fuses, the mesodermal subdivisions form. What are the subdivisions from medial to lateral? (4)

notochord, paraxial, intermediate and lateral plate mesoderm

During gastrulation and as the neural tube fuses, the mesodermal subdivisions form: 1) _______: provides axial support until vertebral column forms 2) ______: muscle, bone and dermis 3) ______: urogenital system 4) ______: smooth muscle, heart, blood and vessels, ventral dermis

1) notochord 2) paraxial 3) Intermediate 4) lateral plate mesoderm

Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives. How is the intervertebral discs formed (4) and what is it?

neural tube > chorda-mesoderm (axial mesoderm) > notochord (serves as embryonic backbone early) > Intervertebral discs ID- offers structure/ signaling support

Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives What are the kidneys/ gonads made from?

Intermediate mesoderm

Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives What is gut smooth muscle, coelom, hear, blood vessels, blood and ventral dermis made from?

lateral plate mesoderm

Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives What somites do the paraxial mesoderm from into and what do each somite produce?

1) Sclerotome- skeleton 2) myotome- striated/ voluntary muscle 3) dermatome- dorsal dermis of the skin NOTE- paraxial mesoderm also gives rise to the head

T/F: The paraxial mesoderm doesn't give rise to the head, along with somites (what somites, 3).

False, gives rise to head Somites- sclerotome, myotome and dermatome

Anterior mesoderms forms what (2)?

head mesenchyme and prechordal plate

Anterior mesoderm form head mesenchyme and prechordal plate by undergoing _____ together with neural crest cells, which forms craniofacial structures including _______ of the face. The _______ is a midline structure that contributes to the _______ (it is also importnat signaling center for forebrain).

EMT; muscles prechordal plate; oropharyngeal membrane

Beginning at neurulation, somites form in the ________, in an anterior to posterior progression. A bilateral pair of somites is added every ___ hours in humans, commencing on day _____. By the end of somitogenesis (end of week __), human embryos have ___ pairs of somites.

paraxial mesoderm; 8 hours; day 21; week 5; 44 pairs

Each somite is partitioned into sclerotome, dermatome, and myotome, which give rise to the skeleton (vertebrate), the dermis, and striated body muscle, respectively. How does this happen?

This occurs via transformation of epithelial cells to a mesenchymal form, to allow migration.

Human Embryology Flashcards

(63 cards)