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Premedical Biology
Individual development in
humans
Questions, answers on the next slide
• What is the name of the cell after a fusion of sperm and
ovum cell?
• How many chromosomes does the cell have?
• What does the totipotent cell mean?
• What does a proliferation mean?
• What does a differentiation mean?
• Zygote (46 chromosomes) develops into embryo by cell
division (mitosis). Cell differentiate and create a three-
dimensional form = morphogenesis
• Zygote has genetic information for cell functions and the
program of differentiated cells of the whole organism, body.
• Zygote is totipotent cell
• Proliferation is cell division and growth
• Differentiation is a functional and morphological
diversification
Zygote and embryonal development
Questions, answers on the next slide
• What molecules are responsible for the regulation of early
differentiation of and embryo?
• What is the function in details of these molecules?
Responsible of early differentiation and
early development are:
1. Maternal determinants in egg:
protein molecules, RNA, mRNA….= cytoplasmatic
information molecules, cytoplasmatic determinants
Questions, answers on the next slide
• What molecules are also responsible for the regulation of
differentiation of an embryo?
• What is the origin of these molecules?
• What cells are able to react to these molecules ?
• What is the result of the interaction?
• What is the other way of a communication of cells in the
developing embryo?
• What are the general ways of cell communication ?
• What are the general types of cell signaling?
2. Signal molecules/ Induction
Signal molecules are determined by offspring genome.
It is a type of local signaling between cells in early embryo.
Signals (molecules) have target cells, target cell has an
ability to respond to signals by receptors. The interaction is
accomplished by a change of transcription /regulation of
gene expression.
Cell-cell surface interactions results in a change of
transcription /regulation of gene expression.
Induction / signalling / regulation of gene expression
Questions, answers on the next slide
• What does it mean morphogenesis?
• What molecules are responsible for the regulation of
morphogenesis?
• How does the morphogens work?
• What is the result of the interaction?
• What are products of morphogens?
= formation of the structure of an organism or part; differentiation
and growth of tissues and organs during development.
Anteriorposterior and dorsoventral axe
is done by gradients of products = transcription factors
of maternal regulatory genes ……..…morphogenes
= proteins, which interact with DNA. They activate or deactivate
the transcription of other genes.
In the end of regulatory cascade molecules control cellular
behaviors. Transcription factors have positional information,
they determine the location relative to body axes.
Morphogenesis
Question, answer on the next slide
• What is a consequence of morphogenetic different
expression of transcription factors?
Result of different gene expression, different regulation in the
different part of embryo, is a different development of body
parts.
Different types of cells in the body have the same genetic
information, but create different proteins as result of
regulation of transcription.
Results are tissue specific proteins / determinated
/differentiated cells
Morphogenesis
Question, answer on the next slide
• What are the groups of genes responsible of morphogenesis,
segmentation and different development of body parts?
groups of genes
Egg-polarity genes, maternal - bicoid
Segmentation genes, embryonic:
Gap genes – division alongside the axe
Pair-rule genes – segmentation (every second)
Segment polarity genes
Homeotic genes
Positional information
Question, answer on the next slide
• What are homeotic genes, homeobox?
• What is the consequence of mutation of homeotic gene?
• What do the homeotic gens encode?
Homeotic genes / Homeobox
are evolutionarily highly conserved. They are responsible
for a formation of specific anatomical structures of each
body part, for a identity of body parts.
Mutations lead to formation of the same structures at the
wrong parts.
HOX genes:
encode transcription factors with homeodomain, which is
able to bind to DNA / switch on or off
Homeotic genes / Homeobox are evolutionarily highly
conserved.
Question, answer on the next slide
• What are the morphogenetic processes?
• What are the morphogenetic movements?
Morphogenetic processes
Proliferation
Distribution
Integration
Reduction
Morphogenetic movements
Movements of epitelial embryo cells:
- invagination movement of epithelium
- extension movement caused by rearrangement
- locomotive movement (migration)
Question, answer on the next slide
• Assign humans in the animal kingdom according to the basic
developmental morphological differences…
Porifera - sponges
Cnidaria – jellyfish, corals, anemones
Ctenophora – coma jellies
Platyhelminthes – flatworms
Rotifera
Nematoda – roundworms
Nemertea – ribbon worms
Bryozoa
Phoronida
Brachiopoda
Mollusca – clams, snails, octopuses
Annelida – segmented worms
Arthropoda – crustaceans, insects, spiders
Echinodermata – sea stars, sea urchins
Chordata – lancelets, tunicates, vertebrates
two germs layers
Radial
three germs layers
Schizocoelom
Bilateral
Protostomia / mouth from
blastopore
Pseudocoelom
Coelom without segmetation
Coelom with segmentation
Segmentation homonomously
Sedmentation herenomously
Deuterostomia / anus from
blastopore, mouth
secondarily
Animal kingdom
Questions, answers on the next slide
• What are the early embryo stages of human development?
• What is it cleavage and does the cleavage of human embryo
have specific characteristics?
• What are the characteristics of blastomers?
• How does the human embryo look like after first
differentiation?
Development of humans
• Zygote - cleavage = the series of mitotic cell divisions that
produces a blastula from a fertilized ovum. It is the basis of
the multicellularity of complex organisms. I is a slow rate
division - between 12 and 24 hours
• Morula from blastomers, which are totipotent
• Polarization / animal vegetal pole
• Blastocyst (blastula with blastocoel for non-
mammalian) after differentiation, post-morula
stage, consisting of the trophoblast and an inner cell mass.
After 7 days, there is more than 100 cells
Early blastocyst. From Dorland's, 2000.
Questions, answers on the next slide
• What does a gastrula look like?
• What is it a gastrulation?
• What is an epiblast and what does it give rise to?
• What is a hypoblast and what does it give rise to?
Gastrulation
• Gastrula = stage following the blastula stage; the simplest type consists
of two layers of cells, the ectoderm and entoderm, which have invaginated
to form the archenteron and an opening, the blastopore. Thus, gastrulation
is process by which the bilaminar embryonic disk (Epiblast + Hypoblast) is
converted into a trilaminar embryonic disk.
Epiblast = the outer layer of a blastula that gives rise to the
ectoderm after gastrulation.
Hypoblast = cell layer adjacent to the yolk
sac cavity and subjacent to the epiblast of a
bilayered embryo.
Questions, answers on the next slide
• What is it primitive streak?
• What are the germ layers of human embryo?
Primitive streak An ectodermal ridge in the midline at the
caudal end of the embryonic disc from which arises the
intraembryonic mesoderm; achieved by inward and then lateral
migration of cells. The organizer is Hensen node
Germ layers: Ectoderm forms the outer layer of gastrula
Endoderm lines the digestive tract and
Mesoderm fills the space between the ectoderm and endoderm
Cells separate from the central part of the ectoderm and move
into the interior of the embryo, and become endodermal and
mesodermal cells.
Gastrulation in chicken, mammals
Questions, answers on the next slide
• What is it the function of amnion?
• What is the function of allantois?
• What is the function of chorion?
• What is the function of yolk sac?
Amniotic egg / reptiles, birds and mammals
Extraembryonic
membranes:
Amnion / protection
Allantois / wastes and
gas exchange
Chorion / gas
exchange
Yolk sac /nutrients
Questions, answers on the next slide
• What is the organogenesis?
• What are first primitive organs of human embryo and what do
they give rise to?
• What are somites?
Organogenesis - chordata
The formation and development of the organs.
Mechanisms of an origin of primitive organs from germ
layers are folds, clefts, dense clumps.
Neural tube - ectoderm – centre of nerve system, brain
and spinal cord
Notochord – mesoderm – backbone
Somites - mesoderm - a segmental mass of mesoderm,
occurring in pairs along the notochord and developing into
muscles and vertebrae
Illustration from
Anatomy &
Physiology,
Connexions
Web
site. http://cnx.
org/content/col
11496/1.6/, Jun
19, 2013.
Questions, answers on the next slide
• What does ectoderm give rise to?
In vertebrates, the
ectoderm has three parts:
external ectoderm (also
known as surface
ectoderm),
the neural crest, and
neural tube.
The latter two are known
as neuroectoderm.
Questions, answers on the next slide
• What does mesoderm give rise to?
The body organs, tissues and systems derived from the
mesoderm:
• bones
• cartilage
• most of the circulatory system, including the heart and major
blood vessels
• connective tissues of the gut and integuments
• mesenchyme
• mesothelium
• muscles
• peritoneum (lining of the abdominal cavity)
• reproductive system
• spleen
• urinary system, including the kidneys
The following chart shows the products produced by the
endoderm.
Gastrointestinal tract
Respiratory tract
Endocrine glands and organs (liver and pancreas)
The endoderm
forms the epithelial lining of the entire alimentary canal
except part of the mouth, pharynx and the terminal part
of the rectum, the lining cells of all the glands which
open into the digestive tube, including those of the liver
and pancreas, the epithelium of the auditory tube and
tympanic cavity, of the trachea, bronchi, and alveoli of
the lungs, of the urinary bladder and part of the urethra,
and that which lines the follicles of the thyroid gland and
thymus.
Development of Human Embryonic Tissues.
(© 2001 Terese Winslow)
Campbell, Neil A., Reece, Jane
B., Cain Michael L., Jackson,
Robert B., Minorsky, Peter V.,
Biology, Benjamin-Cummings
Publishing Company, 1996 –
2010.
Thank you for your attention