Embryologie
Embryonic development is very similar in the vertebrates. Animals have a very common
development in body-plan.
Fertilization and cleavage initiate embryonic development.
1. Contact
2. Acrosomal reaction – after contact the hydrolytic enzymes will break down the jelly-coat.
Now the Actin filament can get to the sperm-binding receptors. This gives a signal to the
rest of the coat, that no other sperm-cells can enter the egg-cell.
3. Contact and fusion of the sperm and egg-cell membranes.
4. The Cortical Reaction – the cortical granule gets released into a fertilization envelope, this
makes it impossible for other sperm-cells to enter. It activated the cleavage.
5. Entry of the sperm nucleus.
Egg activation
- The rise of Ca2+ in the cytosol increases the rates of cellular respiration and protein
synthesis by the egg cell.
- these rapid changes in metabolism activated the egg.
- proteins and mRNAs are needed for activation, these are present in the egg.
- sperm nucleus merges with the egg nucleus.
The difference to humans is the thick layer of follicle cells that surrounds the egg’s envelope.
Cleavage
Zygote is one cell on top of yolk (ei geel) these will divide into a Gray crescent (2 cell forming
stage). There is another division to a 4 cell stage and then to a 8 cell stage.
Many cell divisions later the blastula is formed with a blastocoel inside. A blastula has at
least 128 cells.
Holoblastic cleavage – complete division of the egg, little yolk by frogs
Meroblastic cleavage – incomplete division of the egg, much yolk by reptiles and birds
Morphogenesis
The process by which cells occupy their appropriate locations.
- Gastrulation: the movement of cells from the blastula surface to the interior of the embryo.
The three-layered embryo it created is called a gastrula.
- Organogenesis: the formation of organs.
Ectoderm (outer embryo layer) Mesoderm (middle embryo layer)
- epidermis of skin and its derivatives - skeletal and muscular systems
- nervous and sensory systems - circulatory and lymphatic systems
- pituitary gland, adrenal medulla - excretory and reproductive systems
- jaws and teeth (except germ cells)
- germ cells - dermis of skin
- adrenal cortex
Endoderm (inner embryo layer)
- epithelial lining of the digestive tract and associated organs
,- epithelial lining of respiratory, excretory, and reproductive tracts and ducts
- thymus, thyroid and parathyroid glands
Gastrulation in frogs
The blastocoel shrinks and an archenteron appears in the endoderm. The mesoderm starts
to surround the endoderm, but leaves a spots open. This is the yolkplug, the ectoderm isn’t
surrounding fully and on this spot you can see the endoderm.
Gastrulation in chicks
- prior to gastrulation, embryo is composed of an upper layer (epiblast) and a lower layer
(hypoblast)
- during gastrulation, epiblast cells move toward the midline of the blastoderm and then into
the embryo toward the yolk.
All cells that form the embryo are from the epiblast!
Developmental adaptations of amniotes
Creating an eggshell: birds, reptiles and monotremes
Protecting the egg in the uterus: marsupian mammals (buidel) and eutherian mammals
In both adaptations there is a fluid around the egg in a sac (amnion). This protects the egg in
both cases from drying-out and allows dry land reproduction.
Mammals and reptiles incl. birds are called amniotes.
Organogenesis
Various regions of germ layers develop into rudimentary organs.
Neurulation
- ectoderm forms the neural plate and neural fold.
- mesoderm forms the notochord.
- endoderm forms a coelom, the Archenteron.
The neural plate gets folded to the inside and forms a tube, during the neural folds are being
pushed towards each other and combine so the tube closes. Then the ectoderm combines at
the closing point and there are neural crest cells. These neural crest cells lay loose between
the ectoderm and the formed neural tube.
Now you have an ectoderm -> crest cells -> neural tube -> (mesoderm) notochord -> somite
with coelom next to the notochord -> endoderm with archenteron.
Morphogenesis in animals involves cell shape, -position and -survival.
It’s not in plants cause it only appears when there is no thick cell-wall.
Convergent extension movements shape a sheet of cells.
The microtubules stretch the cell and the actin filaments lay at the small end. This causes a
ring form.
Programmed cell death (apoptosis) is very important for normal embryologic development.
2e + 3e college
, Embryo drawing
Slices (CT scan):
- coronal = front to back
- transverse = through the middle – liver on the right, looking up from feet, back down.
- sagittal = left to right
Heart lays on top of the liver.
Uterus drawing
Fimbriae fingers hold the ovary and take the ovum into the uterine tube.
Ampulla is the place of fertilization. The ovum gets pulled to the uterine cavity by peristaltic
muscle movement and cilia.
The ovum dies if it isn’t fertilized within 24 hours and the sperm-cells die if they don’t
fertilize.
Morulla stage has 8-16 cells
Inner cell mass are stem-cells and are used for cloning. These cells are pluripotent and can
become every type of cell. They form the embryo.
Gastrulation forms 3 layers out of the two layers.
Embryonic development is very similar in the vertebrates. Animals have a very common
development in body-plan.
Fertilization and cleavage initiate embryonic development.
1. Contact
2. Acrosomal reaction – after contact the hydrolytic enzymes will break down the jelly-coat.
Now the Actin filament can get to the sperm-binding receptors. This gives a signal to the
rest of the coat, that no other sperm-cells can enter the egg-cell.
3. Contact and fusion of the sperm and egg-cell membranes.
4. The Cortical Reaction – the cortical granule gets released into a fertilization envelope, this
makes it impossible for other sperm-cells to enter. It activated the cleavage.
5. Entry of the sperm nucleus.
Egg activation
- The rise of Ca2+ in the cytosol increases the rates of cellular respiration and protein
synthesis by the egg cell.
- these rapid changes in metabolism activated the egg.
- proteins and mRNAs are needed for activation, these are present in the egg.
- sperm nucleus merges with the egg nucleus.
The difference to humans is the thick layer of follicle cells that surrounds the egg’s envelope.
Cleavage
Zygote is one cell on top of yolk (ei geel) these will divide into a Gray crescent (2 cell forming
stage). There is another division to a 4 cell stage and then to a 8 cell stage.
Many cell divisions later the blastula is formed with a blastocoel inside. A blastula has at
least 128 cells.
Holoblastic cleavage – complete division of the egg, little yolk by frogs
Meroblastic cleavage – incomplete division of the egg, much yolk by reptiles and birds
Morphogenesis
The process by which cells occupy their appropriate locations.
- Gastrulation: the movement of cells from the blastula surface to the interior of the embryo.
The three-layered embryo it created is called a gastrula.
- Organogenesis: the formation of organs.
Ectoderm (outer embryo layer) Mesoderm (middle embryo layer)
- epidermis of skin and its derivatives - skeletal and muscular systems
- nervous and sensory systems - circulatory and lymphatic systems
- pituitary gland, adrenal medulla - excretory and reproductive systems
- jaws and teeth (except germ cells)
- germ cells - dermis of skin
- adrenal cortex
Endoderm (inner embryo layer)
- epithelial lining of the digestive tract and associated organs
,- epithelial lining of respiratory, excretory, and reproductive tracts and ducts
- thymus, thyroid and parathyroid glands
Gastrulation in frogs
The blastocoel shrinks and an archenteron appears in the endoderm. The mesoderm starts
to surround the endoderm, but leaves a spots open. This is the yolkplug, the ectoderm isn’t
surrounding fully and on this spot you can see the endoderm.
Gastrulation in chicks
- prior to gastrulation, embryo is composed of an upper layer (epiblast) and a lower layer
(hypoblast)
- during gastrulation, epiblast cells move toward the midline of the blastoderm and then into
the embryo toward the yolk.
All cells that form the embryo are from the epiblast!
Developmental adaptations of amniotes
Creating an eggshell: birds, reptiles and monotremes
Protecting the egg in the uterus: marsupian mammals (buidel) and eutherian mammals
In both adaptations there is a fluid around the egg in a sac (amnion). This protects the egg in
both cases from drying-out and allows dry land reproduction.
Mammals and reptiles incl. birds are called amniotes.
Organogenesis
Various regions of germ layers develop into rudimentary organs.
Neurulation
- ectoderm forms the neural plate and neural fold.
- mesoderm forms the notochord.
- endoderm forms a coelom, the Archenteron.
The neural plate gets folded to the inside and forms a tube, during the neural folds are being
pushed towards each other and combine so the tube closes. Then the ectoderm combines at
the closing point and there are neural crest cells. These neural crest cells lay loose between
the ectoderm and the formed neural tube.
Now you have an ectoderm -> crest cells -> neural tube -> (mesoderm) notochord -> somite
with coelom next to the notochord -> endoderm with archenteron.
Morphogenesis in animals involves cell shape, -position and -survival.
It’s not in plants cause it only appears when there is no thick cell-wall.
Convergent extension movements shape a sheet of cells.
The microtubules stretch the cell and the actin filaments lay at the small end. This causes a
ring form.
Programmed cell death (apoptosis) is very important for normal embryologic development.
2e + 3e college
, Embryo drawing
Slices (CT scan):
- coronal = front to back
- transverse = through the middle – liver on the right, looking up from feet, back down.
- sagittal = left to right
Heart lays on top of the liver.
Uterus drawing
Fimbriae fingers hold the ovary and take the ovum into the uterine tube.
Ampulla is the place of fertilization. The ovum gets pulled to the uterine cavity by peristaltic
muscle movement and cilia.
The ovum dies if it isn’t fertilized within 24 hours and the sperm-cells die if they don’t
fertilize.
Morulla stage has 8-16 cells
Inner cell mass are stem-cells and are used for cloning. These cells are pluripotent and can
become every type of cell. They form the embryo.
Gastrulation forms 3 layers out of the two layers.
