1. Chapter 3 Embryology

2. Human development in brief

3. Mitosis Meiosis One cell duplicates
2 “daughter” cells are genetically identical to first cell (both diploid)
Happens all over body
One cell creates 4 daughter cells
Each daughter cell has half the number of chromosomes of the germ cell (each is haploid)
Happens in testes and ovaries only

4. Table 3.1a
Sister chromatids
Centromere

5. sperm or eggs

6. Prophase I Fig. 3.2a Meiosis I Replicated chromosome Sister chromatids
Tetrad
Prophase I
Maternal (“mom”) chromosomes
Paternal (“dad”) chromosomes
Homologous chromosomes (each composed of sister chromatids) pair up (synapsis), and the pair forms a tetrad.
Crossing over occurs between homologous maternal and paternal chromosomes, ensuring genetic diversity.

7. attached to centromere
Fig. 3.2a Meiosis I
Spindle fiber
attached to centromere
Metaphase I
Maternal (“mom”) chromosomes
Paternal (“dad”) chromosomes
Centromere
Homologous replicated chromosomes line up above and below the equator of the cell, forming a double line of chromosomes.
Spindle fibers attach to the centromeres.
Equator

8. Homologous replicated
Fig. 3.2a Meiosis I
Anaphase I
Homologous replicated
chromosomes separate
Maternal (“mom”) chromosomes
Paternal (“dad”) chromosomes
Maternal and paternal pairs of replicated chromosomes are separated and pulled to the opposite ends of the cell, a process called reduction division.
Note that the sister chromatids remain attached in each replicated chromosome.

9. Fig. 3.2a Meiosis I Telophase I and Cytokinesis Replicated chromosome
Maternal (“mom”) chromosomes
Paternal (“dad”) chromosomes
Nuclear division finishes and nuclear envelopes re-form.
The cytoplasm divides and two new cells are produced, each containing 23 replicated chromosomes only.
The replicated chromosomes are still composed of sister chromatids.
Cleavage
furrow

10. Fig. 3.2b Meiosis II Prophase II
Nuclear envelope breaks down, and replicated chromosomes cluster together. (There is no crossing over in prophase II.)

11. Fig. 3.2b Meiosis II Metaphase II
Spindle fibers extend from the centrioles to each sister chromatid in each chromosome and align the replicated chromosomes along the equator of the cell.

12. Fig. 3.2b Meiosis II Anaphase II Sister chromatids separate
Sister chromatids of each replicated chromosome are pulled apart at the centromere.
Sister chromatids (now called single chromosomes) migrate to opposite ends of the cell.
Sister chromatids
separate

13. Fig. 3.2b Meiosis II Telophase II and Cytokinesis
Nuclear division finishes, and the nuclear envelopes re-form.
The four new daughter cells that are produced each contain 23 single chromosomes only.
Single
chromosomes
Cells separate into four
haploid daughter cells

15. Nondisjunction Chromosomes don’t separate in meiosis II
Gametes
23 chromosomes
(normal)
22 chromosomes
(monosomy)
24 chromosomes
(trisomy)
Nondisjunction Chromosomes don’t separate in meiosis II
Nondisjunction of chromosome 21 leads to Down Syndrome

16. © David M. Phillips/Visuals Unlimited
Fig. 3.3
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
Acrosome
Head
Nucleus
Secondary oocyte
in metaphase II
Midpiece
Sperm pronucleus
Polar bodies
First polar body
Zona pellucida
Oocyte
plasma
membrane
Flagellum
Corona radiata
Ovum pronucleus
Phase 1:
Sperm penetrates corona radiata.
Phase 2:
Sperm undergoes acrosome
reaction and penetrates
zona pellucida.
Phase 3:
Sperm and oocyte
plasma membranes fuse.
(a) Sperm
(b) Three phases of fertilization
-Haploid egg and haploid sperm fuse
-Create diploid zygote
Sperm
Oocyte
SEM 4700x
(c) Phase 1 of fertilization
© David M. Phillips/Visuals Unlimited

17. (c) Phase 1 of fertilization
Fig. 3.3
Flagellum
Midpiece
Nucleus
(a) Sperm
Head
Acrosome
Sperm
Oocyte
SEM 4700x
(c) Phase 1 of fertilization

18. Table 3.2a Fertilization Haploid egg and haploid sperm fuse
Create diploid zygote
Nucleus
Oocyte plasma
membrane
120 µm
Ovum pronucleus
Sperm pronucleus
120 µm

19. 120 µm 120 µm 4-cell stage 8-cell stage Table 3.2c
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120 µm
120 µm
4-cell stage
8-cell stage

20. Table 3.2d
Morula
120 µm

21. Table 3.2e
Embryoblast
Blastocyst
Trophoblast
120 µm

22. Table 3.2f Cytotrophoblast Embryoblast Syncytiotrophoblast
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Cytotrophoblast
Embryoblast
Syncytiotrophoblast

23. video of blastulation Fig. 3.4 Zona pellucida Zygote 2-cell stage
Morula
Embryoblast
Blastocyst cavity
Degenerating
zona pellucida
Trophoblast
Early blastocyst
Late blastocyst

24. Fig. 3.5 Ovum pronucleus Sperm pronucleus Zygote Blastocyst
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Fertilization
Sperm
Ovum pronucleus
Sperm pronucleus
Secondary oocyte
Zygote
Ovulation
Ovary
2-cell
stage
4-cell
stage
Blastocyst
Endometrium
Cleavage
8-cell
stage
Uterus
Morula = Ball
Implantation
Embryoblast = Frisbee
Trophoblast

25. Fig. 3.6 Blastocyst Trophoblast Embryoblast Amniotic cavity Amnion
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Functional layer
of endometrium
Lumen of uterus
Day 5
Blastocyst
Day 6
Trophoblast
Embryoblast
Day 7
Trophoblast
Embryoblast
Cytotrophoblast
Syncytiotrophoblast
Yolk sac
Day 8
Hypoblast
Bilaminar
germinal disc
Epiblast
Cytotrophoblast
Syncytiotrophoblast
Day 9
Yolk sac
Cytotrophoblast
Hypoblast
Syncytiotrophoblast
Epiblast
Bilaminar germinal disc
Amniotic cavity
Uterine gland
Amnion

26. Amniotic cavity Amnion Fig. 3.7 Yolk sac Connecting stalk
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Yolk sac
Amniotic cavity
Connecting stalk
Amnion
Amniotic cavity
Connecting stalk
(future umbilical cord)
Amnion
Amniotic cavity
Embryo
Amnion
Embryo
Yolk sac
Chorion
Chorion
Functional
layer of
uterus
Functional
layer of
uterus
Placenta
Yolk sac
(a) Week 3
(b) Early week 4
Placenta
Maternal artery
Maternal vein
Maternal blood
Chorionic villus
(in placenta)
Amniotic cavity
Umbilical cord
Amnion
Trophoblast cells
Umbilical vein
Umbilical arteries
Embryo
Umbilical vein (carries oxygenated blood to embryo)
Yolk sac
Umbilical artery (carries deoxygenated blood to placenta)
Fig. 3.7
(c) Late week 4

27. Table 3.3

28. Gut tube lined by endoderm
Fig. 3.10
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Cephalocaudal folding
Transverse folding
Ectoderm
Ectoderm
Mesoderm
Mesoderm
Neural tube (forming)
Connecting
stalk
Amniotic cavity
Amniotic cavity
Amnion
Paraxial
mesoderm
(somite)
Endoderm
Endoderm
Notochord
Intermediate
mesoderm
Yolk sac
Yolk sac
Lateral plate
mesoderm
Cephalic
Allantois
Caudal
Right side
Left side
Late week 3
Week 3
Ectoderm
Mesoderm
Neural tube
Ectoderm
Mesoderm
Amniotic cavity
Amnion
Notochord
Paraxial mesoderm
(somite)
Heart tube
Endoderm
Vitelline duct
Intermediate mesoderm
Yolk sac
Lateral plate mesoderm
Gut tube lined by endoderm
Early week 4
Midweek 4
Mesoderm
Ectoderm
Ectoderm
Mesoderm
Amnion
Somite
Heart
Intermediate
mesoderm
Endoderm
Peritoneal
cavity
Gut tube
Allantois
Mesentery
Yolk sac
Gut tube
Endoderm
Abdominal wall
(lateral plate mesoderm)
Late week 4
Late week 4
(a)
(b)

29. -Nervous tissue and sense organs -Pituitary gland -Adrenal medulla
Fig. 3.12
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Ectoderm
Endoderm
Mesoderm
Ectoderm
-Epidermis of skin and epidermal derivatives (hair, nails, sweat glands, mammary glands)
-Nervous tissue and sense organs
-Pituitary gland
-Adrenal medulla
-Enamel of teeth
-Lens of eye
Endoderm
-Epithelial lining of respiratory tract,
GI tract, urinary tract, reproductive
tract, tympanic cavity, auditory tube
-Liver (most of)
-Gallbladder
-Pancreas
-Palatine tonsils (portion of)
-Thyroid gland
-Parathyroid glands
-Thymus
Ectoderm
Endoderm
Mesoderm
-Dermis of skin
-Adrenal cortex
-Epithelial lining of blood vessels, lymph vessels, serous membranes
-Heart
-Kidneys and ureters
-Internal reproductive organs
-Muscle tissue
-Spleen
-Connective tissue

30. Inside vs. Outside the body
Inside = not exposed to outside world
Blood vessels
Heart
Liver
Bones
Outside = anything exposed to outside world
Lumen (food side) of digestive
Lungs
Reproductive tract
Urinary tract
Material has to cross epithelium to go from outside to inside the body
lining of stomach and intestine
alveoli (air sacs) in lungs