1. Formation and differentiation of mesoderm, derivates of the germinal layers
Dr Gallatz Katalin

2. What happened until now?
Gametogenesis, fertilization, cleavage.
Blastulation, implantation. The embryonic disc. Formation of ectoderm and endoderm.
Formation and differentiation of mesoderm. Derivatives of the germinal layers.
Neurulation. Folding of the embryo
FROM DR. MARK KOZSUREK

3. Cleavage of the zygote Blastomeres Morula from 12-16 cell stage
Consist of repeating mitotic divisions
of the zygote,
Resulting in a rapid incease of number of cells
In this stage the dividing cells are called
Blastomeres
become smaller with each division.
After 9-cell-stage: compaction mediated
by adhesion glycoproteins.
Morula from cell stage
inner and outer cell mass
embryoblasts trophoblasts

4. 3. Formation of the blastocyst
Zona pellucida degenerates,
fluid flows in, cavity appears
between the cells
blastocystic cavity

5. EPIBLAST/HYPOBLAST SEGREGATION

6. Summary of first week of the human development
Stage 1.
fertilization
formation of the zygote
Stage 2.
2-3. days
early stage of cleavage
morula
Stage 3.
4-5. days
free (unattached ) blastocyst
Stage 4.
5-6. days
attachment of the blastocyst
IMPLANTATION

7. 9-10 day

8. 2. week (end)

9. A TRILAMINARIS Stage – 3. week
1. The hypoblasts induce the epiblasts,
2. The epiblasts proliferate,
3. From the caudal side of the embrionic
disc develops the primitive streak, at the
end of it appears the primitive node and pit
4. Dividing cells migrate under the epiblast
layer along the primitive streak ,
5. Mesoderm is formed
TRILAMINAR EMBRIO:
Ectoderm , mesoderm , endoderm

10. 16th day

11. Gastrulation – formation of the germ layers11

12. Formation of mesoderm
( week)

13. Formation of the notochord
1. Prenotochordal cells invaginating in the primitive pit move forward to the prechordal plate
2. Notochord fuses with the underlying visceral hypoblasts, and its inferior wall
degenerates and disappear.
3. Neuroenteric canal is formed between the amnion and yolk sac for a short time.
4. Definitív notochord develops from the cells of notochordal process between the
prechordal plate and cloacal membrane
Neuroenteric canal

14. DEVELOPMENT OF THE DEFINITIVE NOTOCHORD

15. - Induces the development of neural tube

16. Differentiation of the intraembryonic mesoderm

17. MESODERM Paraxial mesoderma - somite Intermediate mesoderma
gononephrotom
Parietal mesoderm
somatopleura
splanchnopleura

18. DIFFERENTIATION OF THE MESODERM
17th day
paraxial mesoderm
lateral mesoderm .
intermediate mesoderm (gononephrotom).
Lateral mesoderm divides into 2 layers
somatopleura and splanchnopleura.
The cavity between them: intraembryonal coeloma. It is continouos
with extraembryonal coeloma.

19. FROM DR. MARK KOZSUREK

20. FORMATION OF THE SOMITES
At the beginning of the 3rd week somites (or somitomeres) appear both side of
the notochord and developing neural tube
Somites appear first cranially (around the 20th day), than develop caudally
(3 pair/day).
- 4 OCC, 7 CERV, 12 THOR, 5 LUMB, 5 SACR, 8-10 COCC
- In the head region neuromers (mesenchyma of the head) develop.

21. SOMITOGENESIS AND DIFFERENTIATION 4th week
dermatomyotom
SCLEROTOM
Ventromedial cells of the somites migrate and surround
the neural tube and notochord sclerotom vertebra
The remaining part is called dermatomyotom
myotom (muscles develop from it)
dermatom, the dermis and
subcutis develops from it

23. Somites are segmented in the whole length of the embryo,
intermediate mesoderm is segmented rostrally only,
while the lateral plate mesoderm is not segmented at all.

24. DERIVATES OF THE INTERMEDIATE MESODERM
- The intermediate mesoderma or gononephrotom gives the kidneys and
gonads
In the cervical and upper thoracic region it is segmentated , lower it
forms a continuos nephrogen cord

25. Derivates of the lateral mesoderm
From the somatopleura develops the body wall (PARIETAL LAYER OF THE SEROUS MEMBRANES).
From the splanchnopleura mesothelial or serous membranes develop
(pleura, pericardium, peritoneum).

26. intermediate mesoderm kidney, ureter, male genital tract notochord
neural tube
somite
intermediate mesoderm
kidney, ureter,
male genital tract
notochord
splanchnic mesoderm
visceral layer of serous membranes
gut
lateral plate mesoderm
somatic mesoderm
parietal layer of serous membranes
intraembryonic coelom →
body cavities (pericardium, pleura, peritoneum)
FROM DR. MARK KOZSUREK

27. intraembryonic mesoderm extraaembryonic mesoderm
ectoderm
epiblasts
primitive streak
intraembryonic mesoderm
yolk sac endoderm
hypoblasts ?
endoderm
In fact all the tissues and cells of the human are derived from the epiblasts!
extraaembryonic mesoderm
FROM DR. MARK KOZSUREK

28. EMBRYOGENESIS 1. Separation of the embrional-extraembrional tissues
2. Gastrulation: formation of the germ layers – EKTO-, ENDO-, MESODERM
3. Neurulation: formation of the neural tube and crest (CNS AND PNS)
4. Differentiation of the mesoderm

29. Germ layer derivatives

30. ECTODERM Neuroectoderm neural plate neural crest placodes
2. Surface ectoderm
FROM DR. MARK KOZSUREK

31. NEURAL PLATE – NEURAL TUBE
Neurons and glial cells of the central nervous system CNS
(except the microglia)
Retina, dilator and constrictor of pupil muscles of the eye
NEURAL CREST
Peripheral nervous system PNS
medulla of the adrenal gland
melanocytes (which contain melanin pigment)
aorticopulmonary septum of the heart
odontoblasts

32. PLACODS SURFACE ECTODERM
otic placode: epithelial and neural elements of the vestibulocochlear system (organs of hearing and equilibrium)
olphactory (nasal) placode: primary neuroepithelial cells of the nasal cavity
optic (lens) placode: lens of the eye
adenohypophyseal placode: hormone secreting cells of the adenohypophysis
trigeminal placode: gives rise to the cells of the trigeminal ganglion
epibranchial placode: taste buds of the tongue, soft palate and laryngeal inlet, neurons and supporting cells of taste-sensing ganglia of the facial glossopharyngeal and vagus nerves.
SURFACE ECTODERM
Epidermis, hair, nails, sebaceous and sweat glands of the skin
Epithelium of the corne and conjunctiva, epithelium of the lacrimal apparatus
Epithelium and glands of the oral and nasal cavity, enamel of the teeth, salivary glands
Mammary glands
Epithelium and glands of the anus, epithelium of the spongy part of the male urethra

33. MESODERM EPITHELIAL TYPE (densly packed cells)
Intermediate mesoderm → epithelium of the kidney, ureter and the male genital tract (epididymis, ductus deferens, seminal vesicle)
Somato-splanchnopleural junction → cortical cells of the suprarenal gland, gonadal epithelia (not including the germ cells!), epithelium of the uterine tube, uterus and the upper vagina
Somato- and splanchnopleura → mesothelium (simple squamous epithelium)
MESENCHYMAL TYPE
Circulatory system, including the endothelium of blood and lymph vessels, cardiac muscle, formed elements of blood and lymphatic cells
Connective and supportive tissues – all of them!!!
Smooth muscles (not including those in the eyeball!)
Microglia

34. ENDODERM
Epithelium and glands of the GI tract (including liver, gallbladder and pancreas)
Epithelium of the urinary bladder, the prostate, the prostatic part of the male urethtra and the whole length of the female urethra
Epithelium and glands of the airways (trachea, bronchi and alveoli of the lungs)
Epithelium of the tympanic cavity and auditory tube
Thyroid, parathyroid glands
Thymus, tonsills

35. SUMMARY

36. Thank you for your attention!