Transcript Developmental Aspects of Cells and Tissue Development

Developmental Aspects of Cells
and Tissue Development
All cells come from one cell
The fertilized egg or “zygote
Begins mitosis 24 hours post
fertilization
Undergoes mitosis to create the
trillions of cells that make up one
human being
Blastocyst Stage – Day 7
Consists of many cells
Divided into two parts
inner cell mass
trophoblast
Has attached to the
endometrium of the
uterus
Endometrium of Uterus
Blastocyst
Trophoblast
Fluid filled inner
compartment
Inner Cell Mass
Located on side of
blastocyst
Creates the
amniotic sac and
the three primary
tissue germ
layers
Inner Cell Mass = Future Embryo
but also Stem Cells
• http://www.pbs.org/newshour/health/stem_c
ells.swf
New information!
• What if you could reprogram cells back to
stem cells?
• http://www.teachersdomain.org/asset/nsn08
_vid_stemcell2/
Three primary germ layers
Germ means “initial”
Includes the ectoderm, mesoderm and
endoderm
All three are responsible for cell specialization
and tissue formation
Once cells specialize, they lose the ability to
do other functions
Formed during gastrulation
Picture of three germ layers
• Ectoderm
• Mesoderm
• Endoderm
Gastrulation
• "It is not birth, marriage, or death, but gastrulation,
which is truly the most important time in your life."
Lewis Wolpert (1986)
• During gastrulation, cell movements result in a massive
reorganization of the embryo from a simple spherical ball
of cells, the blastula, into a multi-layered organism. During
gastrulation, many of the cells at or near the surface of the
embryo move to a new, more interior location.
• The primary germ layers (endoderm, mesoderm, and
ectoderm) are formed and organized in their proper
locations during gastrulation.
Gastrulation
• Formation of the internal “gastric” system
or gastrointestinal system
• In deuterostomes (animals with backbones
and starfish) the anus forms first (deutero –
second, stome – mouth)
• In protostomes, the mouth forms first
Gastrulation
• Gastrulation occurs after implantation,
around days 14-16 after fertilization in
human embryogenesis
• Occurs prior to neurulation
Gastrulation
• http://bcs.whfreeman.com/thelifewire/conte
nt/chp20/2002001.html
• In addition to forming the internal GI tract,
it also leads to the formation of the three
germ tissue layers
Ectoderm (outer skin)
Forms the
Outer epithelium – skin, hair, lining of
mouth
Tooth enamel
Neural tube – spinal cord and brain
Neural crest – sensory ganglia, skull, gill
arches and dentine
Mesoderm (middle skin)
• Notochord
• Lining of
thoracic and
abdominal cavity
• Circulatory
system
• Skeleton (except
skull)
• Skeletal muscles
• Dermis
• Connective
Tissues
• Urogenital
system
Endoderm (inner skin)
• Gut
• Respiratory
tract
• Liver
• Pancreas
• Epithelium of
urogenital
system
Neurulation
• Formation of the spinal
cord and brain tissue
(neural crest and neural
tube formation)
• Occurs around day 18,
post fertilization
• Not sure what causes
problems
– Genetics?
– Maternal high fever during
neurulation phase
– Maternal use of valproic
acid to control epilepsy
Anencephaly
“without a cephalic region”
• The fetus on the following page was born
without the top of it’s skull or it’s cerebrum.
• Although the fetus maintains a heartbeat
and breathing, it has lost it’s “suck reflex”
and will die from infection due to the open
head
• This is an example of a neural tube defect
occuring as an embryo.
Spina Bifida
• Neurulation stops
along the spinal cord,
forming a
meningomyelocele
(expulsion of
meninges and spinal
cord through unfused
area)
Developmental Fate
• Determined by cell position in the developing
embryo
• Chemical messages given off will determine cell
fate (what it becomes)
• Stem cells divide and give off chemical messages
that tell the other cells what to be determined by
placement of the cell in the growing embryo
• Determined by homeobox genes, which turn
other genes on or off to allow development!
Homeobox genes
• Copy and past the URL into the bar and
view the video
• http://www.pbs.org/wgbh/evolution/library/
03/4/l_034_04.html
Homeobox Genes
• Also called protooncogenes
• Important in
cell/tissue/organ
development in embryos
• Turn genes “off” or “on”
so that enyzmes and
proteins are created for
tissue and organ
development
• Can be affected by alcohol
and drugs taken during the
first months of pregnancy
Thalidomide
• Drug given as a sedative
in Europe during the
1950’s and 1960’s
• Found to cause profound
defects of developing
arms and legs of embryos
during their formation
• Banned in U.S. after
discovery of this problem
by Frances Oldham
Kelsey in 1962.
Animation of Development
Tissues
• Each of the four tissues observed
muscles (movement), connective
(support), covering (epithelial) and
control (nervous) come from these
three germ layers
Cells that become amitotic
•
•
•
•
Liver cells (hepatocytes)
Cardiac cells
Mature nervous cells
Pancreatic tissues, such as the Isles
of Langerhans which produce
insulin
Aging and cell death
• Begins at
physical
maturity
• May be due to
–Toxic
chemicals
–Oxidating
chemicals
– Poor diet
– Genetics
–Xrays/UVA
–Alcohol
Aging
• Epithelial tissue become thinner,
easily damaged, drier due to
decreased sebaceous gland output,
loss of elasticity
• Decreased estrogen, progesterone,
testosterone output
Aging
• Connective tissue aging permits
sagging of skin
• Decreased bone formation leads to
osteoporosis
• Muscles and nerves atrophy – slow
down, slower to react
• Aging circulation = decreased
nutrients/oxygen to tissues
• Hyperplasia – increased tissue
growth or enlargement
– Examples include breast
enlargement during pregnancy;
earlobe enlargement and nose
tissue enlargement as you age
Other tissue
changes