Development
Chapter 21, 46, 47
Mostly Human Development
See pages 636 and 640 for
overview of Phylogenetic tree
Early Development
• Early Development: Developmental Tissue Layers, Sponges-0,
Gridera/Centophores-2, All other Phyla-3
• Hormones released in hypothalamus
– FSH: Follicle Stimulating Hormone
– LH: Luteinizing Hormone
• At menstruation, there are multiple concurrent events
– Estrogen and Progesterone (hormones from the ovaries) gone down its
concentration
– FSH increases in concentration
– Menstruation is occurring. The endometrial lining of the uterus is flushed out.
• When Estrogen levels drop, the brain monitors and produces FSH. The
target of the increased at FSH is in the ovaries.
• A cluster of cells in the back of the ovary. Each contains the germ line cell.
Primary oocye that started meiosis before birth. But this was arrested in
prophase.
• After 2 or 3 days, usually only one Oocyte continues to mature
The maturing of Oocyte
1. The surrounding cells form the Graffarian Follicle.
2. Continues into the first division of meiosis
3. the developing follicle moves down the Ovary and growing in cell number
4. the follicle continues to mature for about 14 days – it enlarges spatially
and more cells
1)
2)
3)
4)
the meiotic dividing primary oocyte is in a cavity with some surrounding
nursing cells.
The nursing cells are adding nutrients and other components to this
meteoric cell to prepare for it to become an egg
fully developed follicle (egg/ovary)
outer follicle cells synthesis and release Estrogen (steroid) Maturing outer
follicle becomes a hormone producer..
5. Increased Estrogen stimulates the rebuilding of the Endometrium of the
uteral wall and the decline of FSH concentration.
6. The brain monitors increased estrogen and as a feedback mechanism, it
decreases the release of FSH.
The maturing of Oocyte
7. The developing follicle also can secrete inhibits, this is also a hormonal message to
the hypothalamus and anterior pituitary to decrease the release of FSH.
– An egg is being formed – both still requires 2nd meiotic division
– the Estrogens and Inhibins decrease with equals FSH increases
– Endometrium is rebuilding. The endometrium is continuing to form under
hormonal direction and or stimulates currently estrogens. Mostly made of mucus,
blood, glycogen. It's being formed in case of the pregnancy. If there is a pregnancy
endometrium is the nutrient, food, 02 etc. source and will maintain the first part of
the pregnancy.
– This is for internal fertilization only not for things like fish as the ovarian follicle
nears maturity, it's:
• estrogenic output decreases
– This is a signal to the brain or hypothalamus to cause anterior pituitary
» release more FSH
» release a very large amount of luteinizing hormone.
• The estrogen decrease is not enough of drop to stop the endometrium from
building
• spike of LH stimulates to events to occur and a concurrent third event
Ovulation
• Ovulation: Oocyte sent to the filopian tubes and ovaduct with nursing cells
(triggers 2nd meiotic division)
• Remaining follicle cells collapse in and forms the Corpus Luteum.
• Two possible concurrent events during ovulation
• the released egg travels down the ovaduct by Cilia on ovaduct cells and
contraction of smooth muscle cells, called peristolsis.
• The Corpus Luteum becomes the new Hormone Factories: prodcues
Estrogen and Progesterone. - causes LH and FSH to decrease, causes
Endometrium to enlarge more
• (possibility) the egg can be fertilized, but the egg is viable (able to
function) for about 24 hours
– to become fertilized
• sperm must be present during fallopion tubes during 24 hours
• sperms must contact, attach and release nucleus into egg
Ovulation
• Situation #1: if no sperm is present:
– corpus luteum will function longer if pregnancy has occurred. There
will be no message with no sperm. 10-11 days if not pregnant, corpus
luteum deteriorates.
– If both estrogen decreases and inhibins decreases, then FSH increases
and LH increases. If estrogen decreases and progesterone decreases,
more FSH increases then LH.
• Situation #2: Sperms (high number of sperms and obstacles to
sperms) meets, attaches and fertilizes egg
– sperm must overcome obstacles (get lost, environment shock, go up
wrong side, get through the nursing cells, Nona Puluza)
– Multiple sperm must work to fertilize sperm, but if multiple sperm
enter the egg (polysperm), then the egg is worthless and discarded.
– Only one sperm fertilize, protection to avoid polysperm. - but its
dependent on species.
Sea Urchins (polysperm)
Sea Urchins (polysperm)
• Sperm releases acrosomes. Acrosomes are hydrolytic digestive enzymes.
That digests the zona peluza up to the vitealie layer. Actin fibers of sperm
attaches to receptors on the egg membrane and pulls it in. Receptors are
very specific
• the membrane of both cells fuse. Consequences:
– sodium pathways open up and let sodium in. The egg becomes positively
charged. No more sperm can attach.
– Cortical vesicles are all around inside the egg. Calcium rugles out of the cell
and cortical vesicles release and pushes the membrane and vitealine layer
apart. Water does the job. Vitealine stiffens and becomes the fertilization.
Envelope plasma membrane returns to normal charge.
• Slow box 3 polysperm takes about .5 – 1 min. but is long lasting the egg
plasma membrane returns to its condition. The texture of the vitalin layer
of egg changes. The plasma membrane re-polarizes.
Sea Urchins (polysperm)
• The cytoplasmic increases in concentration calcium also
initiates the metabolic and functional changes with the egg
cell.
– Increases cellular respiration
– and increases ATP in cell
– increases in protein synthesis
• DAG, intracellular messenger molecule activates its output
of the cell, so the cytosol becomes more basic. When these
two events is occurring the sperm's nuclear starts to swell
and in about 20 min. after entering the egg, the two nuclei
fuse together. Now a to end nuclear's, fertilization, and the
zygote.
– Male and female genetic info come together
Zygote
Mammals
• extra coating around the populated egg. It is a surrounding corona of the
formal nursing cell. They surrounded the egg in the follicle and continue to
surround the related egg.
• Zona Pellucida
– extracellular matrix woven with glycoproteins that cross-link into a 3-D
network.
– One of these three glycoproteins, ZP3 (zona pellucida glycoprotein #3) also
functions as the sperm's receptor
– binding of plasma membranes cause depolorazation of cell membrane (fast
block)
– corticle vesicles, corticle reaction, changes the zona pellucida and rigid (slow
block)
– zona pellucida does not separate from egg
• events change inside the ovum, 2nd meiotic divisions occurs in mammals
Zygote
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the egg doesn't go through second meiotic division unless sperm perpetrates, it
forms a second polar body due to uneven cytokenesis.
The female nucleus and male do not fuse
both separately replicate DNA, still separate as mitosis occurs
both nuclei lose the nuclear envelope
all chromosomes line up in metaphase in one plane, then fertilization. The cell
finishes mitosis including cytokenesis.
This is now:
– 2 cell zygote, each has a 2n nucleus
– the initiation of cleavage
– the genetic identity of the offspring is established,, unique
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sex chromosomes determine sexual determination
the next events are in the mammalian zygote traveling through the ovaducts 4
days to reach the uterus.
Meanwhile, corpus luteum is fully formed, this produces estrogen and
progesterone; endometrium is growing, cleavage happens while traveling in
ovaduct.
Cleavage
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number of cells increases, mitosis with cytokenisis
cells grow in number, not in size.
Cells are genetically identical to each other.
Egg must contain many organelles to fuel all these cells may grow.
the cytosol and all non-nuclear organelles of the egg just one cell
have now become the cytosol and non-nuclear organelles in many
different descendent cells. The organelles especially the
mitochondria of the developing offspring came only from the egg.
Mitochondrial inheritance is from the mother.
• 2 types of cleavage
– Spiral cleavage
• by 8 cells stage, the cells do not align. The upper for cells are shifted upward
from the lower 4 cells.
• A pattern in protesostome, mouth opens first in the digestive tract, very early
cell differentiation
Cleavage
– Spiral cleavage (cont.)
• Organisms with spiral cleavage tend to have early differentiation only certain
cellular identities in the future and possible as development progresses.
• cellular differentiation for multiorganism
• SL's progress through this differentiation of development, the types of cells
they can end up being in the final organism fully developed becomes more
and more limited.
• During this process, various potential genetic info is being turned on and off.
Many that are turned off, stay off and all descendent cells. Consequently,
there are many types of expressions that may make the descendent cells can
never perform.
• Organisms with spiral cleavage have early cell differitiation
– Radio Cleavage
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by the eight cell stage, upper four cells aligned with lower four cells
Deuterostomes. No differentiation yet (cell division starts later)
all cells are still aligned
anus opens first, mouth second
Morula
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we have radio cleavage. At this point the developing offspring is traveling through
ovaduct. Cleavage is occurring. While still in the over duct, one of the cells no
longer has any of its surface in contact with the outer zona pellucida. No cell
differentiation yet. It is in intercell, cells in contact with zona pellucida or outer
surface are outer cells.
Once this occurs, both inner and outer cells have developmental stage is now
called a morula. Still a solid ball of cells. The zygote has become a morula.
In organisms like us:
– still no cell differentiation. The cells aretotspotent:
• intercell can be exchanged with any outer cell and still have all cellular potentials ahead
of it.
• The zona pellucida remains intact through themorula stage. It is still in the cleavage
stage
• it is the morula that enters the uterus. 4-5 days since ovulation. Likewise, it would be in
on fertilized egg entering the uterus at the same time. The morula cells are still
totipotent.
• Totipotent:all cells possible, not differentiated, any inner cells can be exchanged with
any outer cell
Morula
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Upon morula entering the uterus, several events occur relatively simultaneously:
the zona pellucida starts to disappear. Consequently the volumes can now expand
without much restrictions
the zona pellucida stops a tube pregnancy
a forms in this developing offspring. It is no longer a solid ball of cells. The cavity is
the blastocystic cavity.
– This is a new stage in development
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the outer cells form a single layer around the blastula. The cells have become
trophoblasts (protect and support tissues). They were in contact with the zona
pellucida
the inner cells are pushed to one cluster within the cavity at a whole. The inner
cells have become a single embryoblasts (forms the embryo)
those two cells are not exchangeable because it is the first differentiated cells
The location of a cell highly affects its differentiation. Environment for a cell is
important.
Morula
• The trophoblasts that are in contact with the embryo blasts within a
succession of events, do the following:
• release a sticky substance
• form microvili on the plasma membrane outside the blastula.
• Both help with attachment of the endometrium. The two entities try to
assure attachment of blastula to the endometrium has a embryo blast
facing the endometrium.
• The endometrium also form microvilli in its later stages
• These trophoblast in contact with the embryo blasts, once attachment has
occurred, it will release a hormone called human chonionic
Gondotrophin.(hCG). The target for hCG ourselves of the Corpus Lutein in
the mothers ovary. Without this hormonal message between mom and
partially developed offspring the corpus lutein will degenerate within 10
to 11 days. With the hCG, the corpus lutein last several months. Without it
menstruation follows.
Morula
• However, in corpus luteum receiving hCG, the corpus lutein
stays for several more months. Estrogen and progesterone
levels stays high concentration. Consequently:
– the endometrium continues to enlarge instead of demostrating.
– No new cycle starts. No further start of eggs in the follicles. No
at SH is released.
– This is the starter pregnancy. Due to hCG
– the corpus luteum now lasts about 10 to 8 weeks past ovulation.
• HCG is the development and offspring's message to the
mother not to flush out the developing offspring. It is the
support for material, food, nutrients, 02, etc. for the first
part of the pregnancy. This is about 6 to 7 days after
ovulation for the attachment. There is no menstruation.
Second week (7-14 days
since ovulation)
• implantation; shifting of Embryoplast into two cell layers; growth of
trophoblasts.
• Implantation
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the blastula is completely covered with endometrium material
trophoblasts release enzymes that digest into the endometrium
carves a place for the blastula
opens cavities that increase blood flow (pools of internal blood),
lacunae
– to start implantation, trophoblasts next to the endometrium search
release enzymes that digest into the endometrium
– endometrium grows around the blastula – continues all week
• trophoblasts not touching embryoblasts, starts to touch endometrium
• more enzyme release
– fibrin coagulum: “scabs” over the blastula – completing implantation,
blastula is completely covered
Second week (7-14 days
since ovulation)
– meanwhile, the trophoblasts grow and divide into the
endometrium (cellular differentiation, will later
become the placenta) / the support develops faster
than the offspring, take nutrients from mother
– meanwhile, the embryoblasts change location, go
through one major differentiation
– embryoblasts in contact with trophoblasts become
Epiblasts
– Epiblasts move away from the trophoblasts
– embryoblast not in contact with trophoblasts become
hypoblasts
– amniotic cavity forms
Third Week
• formation of Primitive Steak (depression by cells folding in)
• cellular differentiation of Epiblasts into Ectoderm and Endoderm and then
Mesoderm.
• Hypoblasts reproduce and make one cell layer and makes a yolk sac.
• The Blastocistic Cavity has membranes dividing it
• The epiblasts on the aminotic side differentiate into ectoderm but they
are limited by the walls of the blastula.
• The cells that push into the hypoblasts turn into endoerm. Endoerm
begins to divide themselves – lines the yolk sac, one layer think.
• Once Endoderm lines the egg sac and ectoderm on the amniotic side, a
cavity forms between the cell. Mesoderm fills the cavity
• Folded in cells form Endoderm then Mesoderm
• Primitive streak is formed (depression by cells folding in): the crease in the
Ectoderm cell
• Trilaminar disk formed or three developmental layers
Third Week
• the process is now called Gastrulation (Gastrula)
– zygote – morula – blastula – gastrula
• Invagination
– the folding in of cells from an outer surface to an interior. Environment
= invagination
– Mesoderm begins migrating toward the ephalic end (head); it does not
migrate in procordial plate
• Migrating Mesoderm
• it travels from primitive node toward the Prochordial plate. These
cells turn into (differentiate) cells of the Notocord. The Notochord is
the first characteristic that appears for chordata.
• It travels beyond the procordial plate develops into Cardiogenic
tissue, forms the muscles and values of the heart.
Third Week
• The notochord tissue is the first developed tissue that is still
present in an adult. All other cells (mesoderm, ectoderm, etc) do
not stay.
• Toward the end of the 3rd week, the mesoderm next to the
notochord differentiates into somite cells. Somites are structures
made of somitic cells. They form in pairs on either side of the
notochord. The first pair is between the primordial node and the
pricordial plate. Somites continues to form about 3 pairs a day til
the end of the 5th week. Each pair alternates on the cephalic end to
the caudal end.
• The Gastrula continues to grow and the primitive streak gets
shorter. The streak totally disappears by the 4th week.
• Once the somites appear, the Embryo stage begins. Gastrulization
(folding) continues into the Embryo stage.
– Zygote – morula – blatula – gastrula – embryo
Fourth Week
•
42-44 somite pairs have names
– starting from the cephalic end
• 4 Occipital pairs – skull
• 8 cervical pairs
• 12 thoracic pairs – rib cage
• 5 lumbar pairs – lower back
• 5 sacral pairs – lower back
• 8-10 coccygeal paris – only 3 remain after development; tail for 4-5th week of
development (Apoptosis)
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as somites grow, the Neural Crests grow closer and closer, they eventually connect.
The trapped Ectoderm turn into neurons and Glial cells
The neural tube becomes the spinal chord, hollow dorsal nerve tube
organogensis, starting of organ forming
the widest part of the nureral take at the cephalic end becomes the brain
Notochord = axis of symmetry, bilateral symmetrical
– organizational locate for somite formation
– the location of a cell determines what the cell differentiates into.
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Cells around the notochord receive horomones that cause cell differentiation
Somite dispersal 4-5th week
• Somite cells differentiate into other cells; they “fall apart”
• the somites near the notochord proliferate an disperse.
• The migrating cells differentiate into
– osteoblasts – bone forming cells
– chondroblasts – cartilage forming cells
– fibroblasts – connective tissue
• one somitic pair = one vertebra, encases neural tube and notochord
• the other remaining somite cells migrate and differentiate slightly later
– differentiate – myotome (forms skeletal muscle) – follows osteoblasts,
chondroblats
– dermatome – dermis, subcutaneous (form under/inner layer of skin)
• Neural crest cells disperse and differentiate into front face, nose, teeth,
dermis of skin, upper jaw.
– In abdominal region,
• adrenal medulla and some neurons, lots of differentiation (gene regulation)
Somite dispersal 4-5th week
• Meanwhile, growth an folding (ectoderm, mesoderm); endoderm so far has
been a barrier from yolk sac but not much else, get trapped and passively
move around and become internal
• the upper cells (mesoderm) have been pushing the endoderm cells
• 2 major folding types
– longitudinal – head and tail forming (cephalic, caudal)
• ½ of yolk sac is inside the fold
• heart has swung down, cardiogenic cells migrate to below the head
• amniotic cavity eventually surrounds the embryo dragged by growing Mesoderm cells
– transverse/lateral folding – side folding
• side to side folding – contemporary to longitude folding and somatic dispersal
• in the thoray bones wrap around to form rib cage (ostcoblasts, chordroblasts)
• longitudinal folding is complete before lateral folding is complete. Heart must be
captured.
• Some endometrium is captured in a interior environment. This differentiates into
digestive tracts, also lungs, pancreas, liver.
• The amniotic cavity is enlarged as surrounds the embryo. Cellular differentiation occurs
mostly in embryonic cells. Few types of cells become many cells. (organogenesis)
During fourth week
• the heart forms from cardiogenetic material
– begins to contract even before there is blood.
– Cardiac muscles differentiate from gene cardiogenetic
material
– fish – 2 chambers, mammals – 4 chambers
– chambers form in the thorax cavity
• invaginations (folding)
– form various tissue on the outside that are captured on
the inside (otic pit, lens placode, hair follicle)
– intestines form outside of embryo and are folding into our
gut via yolk sac folding
– the yolk sac and connecting stalk twist, umbilical chord.
During fourth week
• Aptoptosis
– planned cell death
– plays port in development and life
• Gradients in the development of Embryos; blood cell and
blood vessel formation – 4 areas
• formation of blood system all over the embryo
• inside the embryo, outside the yolk sac, connecting stalk, in
the stem villi that will become the placenta
• mesoderm – angioblats – form blood vessels –
pluribotential – any type of blood cell
• blood cells connect into the placenta via ambilical chord
and this allows nutrients to be passed from mother to child.
Blood never touches
Eight weeks
• Eight weeks after ovulation the Embryo stage is over, and the fetal stage
begins.
• Zygote – morula – blatula – gastrula – embryo – fetus
• the placenta begins to fully functions
– exchanges with circulatory system (nutrients, food, gases, water)
• Elimination of waste
• maintains the rest of pregnancy by releasing hormones (estogen and
progesterone)
• Corpus Luteum dies and regeneartion hCG when the placenta begins to
function.
• Many outward characteristics are noticable
– ½ of mass and size is in the head
– eyes aren't rotated foreward
• all organs have started to form (organogenesis)
• most of cellular differentiation has already formed, not all
Eight weeks
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Placenta
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develops before the embryo
by the 10th week, the placenta is fully functioning
umbilical cord is transferring nutrients
the fetus is entirely encased in the amniotic cavity
the placenta is as big as the developing offspring mass-wise
lots of folding in placenta – more surface area – more exchange
the circulatory system must not be exchanged – fatal
membranes keep the systems separate
the membranes are semi-permeable
Electrolytes
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neural and muscle function needs these
calcification of bones
osmotic pressure
cellular integrity (co-factors)
enzymatic co-enzymes
The Fetal Stage
• A time of major growth (some cell differentiation)
• embryo stage – cellular differentiation and organogenesis
• sex differentiation occurs at this time (9th -10th week), (Early
fetal stage)
• the Genetulia will develop male characteristics if
testosterone is present (TDF present) ,XY
• if no testosterone female characteristics will form XX (TDF
absent)
• the product of TDF is a regulatory protein that turns on the
genes for making testosterone among others
• ovaries or testes come from the same tissue
What Can Go Wrong?
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Genetic Incompatibility – mother and father don't fit
Chromosomal Abnormalities – trisomy
some can make. Most do not it to birth
most problems happen in the first two weeks after fertilization. 42
% of evolutated eggs and sperms present do not survive in the 2
weeks.
• Teratogens
– begins to have impact after the first 2 weeks
– any outside agent that influences malformations or debilitating
problems
– have a major impact in the embryonic stage (major cellular
differentiation)
– Rubella (German Measles) Virus, Alcohol (heart problems, growth
deficiencies, mental/learning disorders, joint problems
What Can Go Wrong?
• Hormones
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effective at low concentrations
masculinity hormones (testosterone)
estrogen and progesterone imbalance causes termination
endocrine disruptor
carcinoma of vagina.
Alkaloids (Nicotin) – cigarettes, antibiotics (tetracycline, streptomycin)
anticoagulants (causes fetus to hormone) not Heprin – doesn't cross
the placenta
– pathogens (Rubella, Cytomegavirus,HIV)
– Radiation (X-rays, radioacitivy), and cause cancer
– chemicals – murcury, LSD, tranquilizers, agent Orange
• not all effects are immediate, some present themselves over time.