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Introduction
- What is embryogenesis? When does it occur in humans?
- What is morphogenesis? When does it occur in humans?
- Elaborate on the phrase “ontogeny recapitulates phylogeny”. Who termed this phrase, and
what prompted him to say it? What are some ways in which it is true? What are some ways in
which it is false? (Bonus: revisit this question once we cover the chapter about comparative
embryology and elaborate on your answer!)
For each of the following processes, give a brief definition. As the class progresses, we will
encounter examples of each. Revisit this question to list examples as we encounter them!
Epiboly
- definition:
- examples:
Invagination
- definition:
- examples:
Evagination
- definition:
- examples:
Involution
- definition:
- examples:
Ingression
- definition:
- examples:
Delamination
- definition:
- examples:
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Gametogenesis
- Compare and contrast mitosis and meiosis.
- Define ploidy:
- Define n-number:
- Compare and contrast spermatogenesis and oogenesis.
Label all stages of gametogenesis below. Indicate ploidy and n-number at each stage.
2
Male
- Where are the primordial germ cells located in the testis? Be as specific as possible.
- What are the support cells in spermatogenesis? What is their function?
- Describe the relationships between spermatogonia and Type Ap, Type Ad, and Type B
primordial germ cells.
Label each region and structure of the mature sperm cell in the following image, and describe
each region or structure’s function.
Label all cells in the following image, and indicate each germ cell’s ploidy and n-number, as
well as all meiotic and/or mitotic divisions.
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Female
Title each stage of oocyte development in the
image to the right. Indicate the ploidy and nnumber of the germ cell in each stage. Also
label everything that can be labeled in each
stage.
- Describe the process of ovulation.
- When in development do the female
chromosomes first replicate from 2n to 4n?
- When does the first meiotic division occur
in females?
- When does the second meiotic division
occur in females?
- What is a polar body?
- What is the structure and function of the
zona pellucida?
- What is the structure and function of the
corona radiata?
- Define yolk:
- Use fancy yolk words to describe the human
yolk distribution and classification.
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Fertilization
- What are some problems with fertilization? How do humans deal with each of these
problems? Why is fertilization worth going through all of those bad things?
List the 5 big steps of fertilization, and describe all sub-parts of each in the following chart.
Big step
Sub-parts
Description
- List all enzymes involved in fertilization, and indicate what structure/layer each enzyme
breaks down.
- Compare and contrast the “Fast block” and “Slow block” oocyte responses. Why are these so
important?
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Early Development
Fill in the blanks:
Fusion of the male and female pronuclei creates a _______________, which undergoes
____________ to create two cells called __________________. These cells continue dividing via
MITOSIS / MEIOSIS (circle one), eventually becoming a ____________ when it reaches 12 cells.
A fluid-filled cavity forms, at which point the ball of cells is called a _________________. The
outer cell mass is called the __________________ and the inner cell mass is called the
________________. Every part of an adult arises from the INNER / OUTER (circle one) cell mass.
Complete the following flow chart, drawing arrows from each word down to the structures in
the next row that it will become. When applicable, indicate the process by which this
transformation occurs.
When you have finished, think of more structures that we’ve learned so far that arise from
ectoderm, mesoderm, and endoderm, and add these structures to the final row.
Blastocyst
Embryoblast
Epiblast
Hypoblast
Ectoderm
Neural tube
Neural crest
Trophoblast
Cytotrophoblast
Mesoderm
Placodal ring
Syncytiotrophoblast
Endoderm
Notochord
Somites
Allantois
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Essay: Describe the process of gastrulation, using simple labeled diagrams and bullet points.
Time yourself – this should take about 10 minutes.
Essay: Describe the process of notochord formation, using simple labeled diagrams and
bullet points. Time yourself – this should take about 10 minutes.
Essay: Describe the process of neurulation, using simple labeled diagrams and bullet points.
Time yourself – this should take about 5 minutes.
Essay: Describe the process of intraembryonic coelom formation, using simple labeled
diagrams and bullet points. Time yourself – this should take about 5 minutes.
What are the “Big Three” processes that occur during the third week?
What is the relationship between the prechordal plate and oropharyngeal membrane? What
is the significance of these structures? Describe their role during gastrulation and notochord
formation. Which germ layer is missing in this region? What does the oropharyngeal
membrane become in an adult?
Define splanchnopleure:
Define somatopleure:
What separates the somatopleure and splanchnopleure?
Describe the formation of the primary and secondary yolk sacs.
Describe the formation of somites from paraxial mesoderm.
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In each of the following diagrams, color ectoderm blue, mesoderm red, and endoderm yellow.
Label everything that you can.
8
Label the following diagrams, and color the ectoderm blue, the endoderm yellow, the
embryonic mesoderm (which arises during gastrulation) red, and the extraembryonic
mesoderm purple. On the left side, draw the choreon (trophoblast) where it belongs on each
image. On the right side, label or color the intraembryonic coelom in each image.
Left
Right
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Placentation
Justify the statement, “The uterus is the mammalian nest”:
Fill in the blanks:
The uterus is made of three layers, the _______________, _______________, and _______________. The
innermost layer can be subdivided further in two ways – structurally into the _______________
and _______________, and functionally into the more stable _____________________ and the more
variable _______________________. Implantation occurs ____________ days after fertilization, when
the _______________ pole of the blastocyst attaches to the _______________ (region) of the uterus.
What prevents the uterus from shedding its lining after implantation?
List all of the contents of the chorionic cavity:
Essay: Describe the development of chorionic villi using simple labeled diagrams and bullet
points. Make sure to include:
- What they form from
- What they push into
- What induces this development
- All intermediate stages of development
- What type of mesoderm they contain
- Their final stage in a “mature” placenta
- How they connect back to the developing embryo
Time yourself – this should take 5-10 minutes.
Essay: Describe the formation and function of the lacunar network and intervillous space.
Make sure to include all structures that are involved in the formation, the contents of the
space formed, and the purpose of forming this space. Time yourself – this should take about 5
minutes.
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In the following image, label the following structures:
- chorion
- chorionic villus
- lacunar network
- connecting stalk
- primary yolk sac
- secondary yolk sac
- prechordal plate
- chorionic cavity
- exocoelomic cavity
Color all of the mother’s tissues red.
Color everything that will develop into an adult structure blue.
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Trace a molecule of oxygen from mom’s uterine spiral artery to the blood vessel carrying
oxygenated blood to the connecting stalk/umbilical cord (which we will later learn is the
umbilical vein). List all structures and vessels that the oxygen will pass through, as well as all
layers which the oxygen will diffuse through.
Uterine spiral artery
Blood vessel in umbilical cord
Is maternal blood ever in direct contact with fetal blood?
Define a cotyledon:
List all of the maternal components of the mature placenta:
List all of the fetal components of the marture placenta:
What are some important functions of the placenta?
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On this image, label or color
the following:
- decidua basalis
- uterine septum
- cotyledon
- extraembryonic mesoderm
- intervillous space
- tertiary stem villus
- chorionic plate
- maternal arteries and veins
- cytotrophoblast
- syncytiotrophoblast
Is this structure a part of the
smooth or villous chorion?
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Comparative
In the following chart, the vertebrates discussed in the comparative chapter are listed across
the top, and various characteristics of their development and structure are listed on the side.
Place an X in the chart to indicate every structure or process which contributes to the
development of each vertebrate.
Amphioxus
Amphibian
Bird
Mammal
Microlecithal
Mesolecithal
Megalecithal
Isolecithal
Centrolecithal
Telolecithal
Blastula
Blastocyst
Spaces in blastula or blastocyst
are intraembryonic
Spaces in blastula or blastocyst
are extraembryonic
All cells of blastula or
blastocyst become embryo
Some cells of blastula or
blastocyst become
extraembryonic tissues
Ball-shaped embryo before
gastrulation
Plate-shaped embryo before
gastrulation
Undergoes gastrulation
Gastrulation via primitive
streak
Gastrulation via blastopore
Ends up with 3 germ layers
Achieves basic vertebrate body
plan
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Summarize Karl Ernst Von Baer’s Four Laws:
1.
2.
3.
4.
Compare and contrast a blastula and blastocyst using this fun Venn Diagram:
blastula
blastocyst
Why was the evolution of extraembryonic tissues in bird/reptile embryos so significant?
Why does the bird/reptile embryo contain so much more yolk than amphioxus or
amphibians?
Why do mammalian embryos not have as much yolk as a bird/reptile?
Essay: Using simple labeled diagrams and bullet points, describe how a ball-shaped embryo
undergoes gastrulation to form 3 germ layers. Time yourself – this should take 5-10 minutes.
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Integument
Next to each pointer on these images of adult anatomy, write the letter corresponding to every
embryonic precursor from which this adult structure arises. Assume this section of
integument is taken from the anterior abdominal wall.
A. lateral plate mesoderm
B. outer enamel epithelium
C. neural crest
D. ameloblasts
E. ectoderm
F. extraembryonic mesoderm
G. neural fold
H. trophoblast
I. paraxial mesoderm
J. epiblast
K. dermatome of somite
L. inner enamel epithelium
M. hyboblast
N. odontoblasts
O. body ectoderm
P. blastula
Q. mesoderm
R. splanchnopleure
S. somatopleure
T. dental sac
U. embryoblast
In blue, circle all letters above
which contribute to the
epidermis. In red, circle all
letters above which contribute
to the dermis. (Hint: review
the definitions of epidermis
and dermis)
If the integument section were taken from the face, which answers would change? What
would they change to? What about if the section was taken from the skin over the spinous
processes of a vertebra? If you have the patience, print two more copies of this page and
answer this question for each of the 3 regions of integument.
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What is the function of the vernix caseosa in the developing embryo? What is it made of?
Essay: Using simple labeled diagrams and bullet points, describe the formation of the
epidermis, beginning with a single layer of cuboidal ectodermal cells, and ending with the
adult stratified epidermis containing 4 cell types. Be sure to indicate the origins of all cell types
Fill in the blanks: The formation of the epidermis begins with a single layer of cuboidal
_________________ cells covering the underlying _________________. This single layer of cells then
produces an overlying layer of _________________, and the original cuboidal cells are now
renamed the _________________ layer. Cells from the ____________________ migrate below the
developing epidermis and differentiate into _________________. Around 11-21 weeks in
development, a third layer of epidermal cells forms, named the _________________ layer, and
_________________ migrate into the epidermis to become melanocytes. As the epidermis grows,
cells on the surface begin to die as they are pushed away from the blood supply, and these
dead cells form the ___________________. In addition to keratinocytes from the _________________,
and melanocytes from the _________________, the epidermis also contains immune cells called
____________________which originate from the _________________(germ layer) and
mechanoreceptors called _________________ which originate from the ___________________.
Describe the basic process of forming structures via epidermal invagination. Name 5 adult
structures which form via epidermal invagination.
Why are teeth considered integumentary structures?
17
Complete the following flow chart to outline the development of a tooth. Draw arrows from
each item in the flow chart down to the structures below which it will become.
ectoderm
mesoderm
body ectoderm
tooth bud
neural crest
dental papilla
dental sac
enamel organ
inner
enamel
epithelium
outer
enamel
epithelium
ameloblasts
enamel
enamel
reticulum
cementoblasts
dentin
cement
odontoblasts
periodontal ligament
For each item in the flow chart above which is visible in a diagram below, choose a color.
Underline the item in the flow chart, and color that structure on every diagram below
where it is visible. Note that 4 of the items in the flow chart are not visible on any of these
diagrams. Also indicate the stage of tooth development for each diagram.
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