Lectures 27-28 Embryology Flashcards
Embryology is
The study of embryonic development
Embryonic development follows a set order:
- Fertilization (fusion of sperm and egg into a zygote)
- Cleavage (cell division of blastula/blastocyst)
- Gastrulation (blastula rearranges layers of cells into gastrula)
- Organogenesis (rudimentary organs form)
The fusion of sperm and egg creates a
Zygote
Rearrangement of blastula into layers of cells is called
Gastrula
Tinman gene
Regulates position of heart
Fertilization involves three steps
- Contact
- Acrosomal Reaction
- Cortical Reaction
The ___ sperm and egg give rise to a ____
Haploid; diploid zygote
In fertilization, contact is when
Spermatozoa makes contact with the protective layer surrounding the egg
The protective layer of the egg is called
Zona pellucida (jelly coat)
Contact with the zona pellucida (jelly coat) triggers
Acrosomal reaction in the spermatozoon
Model species for fertilization is the
Echinodermata (sea urchin)
The Acrosomal of sperm is
Species specific
The Acrosomal of sperm releases
Hydrolytic enzymes to digest a hole in jelly coat
The reason species cannot breed outside their own species is due to
Acrosome on sperm (what breaks down the zona pellucida of the egg)
Acrosomal process contain ___ that ___
Actin filaments; pierces the jelly coat
Proteins on the tip of the Acrosomal process
Bind to receptors on the egg plasma membrane (lock and key)
The “lock and key” occurrence of the acrosome to the egg is especially important in
Species with external fertilization in water
The fusion of proteins on Acrosomal process to receptors on the egg causes
Fusion of plasma membranes of the spermatozoon and egg
Fusion of plasma membranes of the sperm and egg triggers
Opening of Sodium channels
The opening of Na+ channels during the Acrosomal reaction causes (3)
-sodium to rapidly diffuse into the egg
-depolarization
-blocks other sperm from fusing
Cortical reaction of fertilization causes
Changes at surface of the egg to prevent further sperm from entering (ie. blocks polyspermy)
Cortical granules are located
Beneath the plasma membrane of egg
The perivitelline space is
Space between plasma membrane and outer vitelline layer in the egg - enzymes are released here
The fertilization envelope is formed when
Enzymes are released into the perivitelline space causing the vitelline layer to lift and harden
Two types of Cleavage patterns
- Holoblastic (therian mammals, amphibians, echinoderms)
- Meroblastic (monotremes, birds, reptiles, fish, insects)
Cleavage is
The succession of rapid cell divisions —> zygote (large fertilized egg) becomes many smaller cells (blastomeres)
Blastomeres are
Smaller cells of the zygote
Blastocoel
Ball of cells surrounding a fluid-filled space
The first 5-7 divisions during cleavage produce
A hollow ball of cells called Blastula (Blastocyst in mammals)
Meroblastic cleavage results in
Yolk concentrated towards the vegetal pole, with less yolk at opposite animal pole
The difference between holoblastic and meroblastic cleavages is essentially
If the yolk is whole or partial
Cleavage furrow
An indentation that forms during division causing a division of the cells in half
The cleavage furrow in holoblastic division generates
4 blastomeres of equal size
In holoblastic cleavage, the animal hemisphere
Contains smaller blastomeres
During the 3rd division of holoblastic cleavage, _____ are produced
8 cells
Cleavage in meroblastic occurs
ONLY in animal hemisphere
Blastodisc
A small disc at the animal pole where cleavage occurs in meroblastic
The end result of holoblastic cleavage is
A ball of cells called the Blastula (Blastocyst)
The fluid-filled space in the blastula is called
Blastocoel
The inner cell mass (embryoblast) is
A group of cells in the mouse and human that forms the embryo and is a source of embryonic stem cells
What forms the embryo and is a source of embryonic stem cells?
Inner cell mass (embryoblast)
Trophoblast
Outer layer of cells that does not contribute to the embryo but forms the chorion
The chorion forms the
Placenta
Gastrulation involves
Reorganization of cells to form a 3-layered embryo
The embryonic germ layers are (3)
-endoderm (inner)
-mesoderm (middle)
-ectoderm (outer)
Each embryonic germ layer will
Contribute to a distinct set of tissues
A group of cells on the dorsal surface of the blastula invaginate to form a small, indented crease called the
Blastopore
As more cells continue to enter through enlarging blastopore, a new space starts to form called the
Archenteron
The blastopore surrounds a ply of yolk-filled cells that forms
The anus
Archenteron becomes the
Cavity of digestive tract
The avian blastula has a disc of cells atop a yolk mass called
The blastoderm
The bid blastoderm divides to form (2)
-epiblast
-hypoblast
The blastocoeal of birds sits
In between the epiblast and hypoblast
Primitive streak
Cells from the epiblast move to the centre of the blastoderm and inwards towards the yolk producing a thickening
Cells that migrate through the primitive streak and move downward form
The endoderm
Cells that migrate through the primitive streak and migrate laterally form
The mesoderm
Cells left behind on the surface of the primitive streak form
Ectoderm
What forms the embryo in mammals
Inner cell mass (embryoblast)
What forms the chorion in mammals
Trophoblast
Trophoblast cells secrete
Enzymes that facilitate implantation into endometrium of uterus
The inner cell mass in mammals divides into (2)
-epiblast (forms the embryo)
-hypoblast
In mammals, cells of the epiblast move inward via primitive streak to form (2)
-mesoderm
-endoderm
Totipotent (3)
-can form all cell types of the body
-forms extraembryonic (placental) tissue
-first few divisions after fertilization (8-cell stage)
What forms the extraembryonic (placental) tissues
Totipotent
Pluripotent (2)
-can form all cell types of body EXCEPT extraembryonic (placental tissue)
-cells come from the inner cell mass
Embryonic stem cells (ESCs) and Induced pluripotent stem cells (iPSCs) are
Pluripotent
Embryonic stem cells (ESCs)
Are isolated from embryos
Induced Pluripotent Stem Cells (iPSCs)
Are produced from adult cells via “reprogramming”
Adult stem cells are
Multipotent
Multipotent (3)
-adult stem cells
-found in bone marrow, adipose tissue, etc
-limited differentiation ability
Cartilage, bone, adipose tissue contain
Mesenchymal stem cells (MSCs)
The study of the development of CNS
Neurulation
The notochord is formed by
Cells from the dorsal mesoderm
The neural plate is formed from
The ectoderm above the notochord
Neural tube is generated by
The unfolding of the neural folds adjacent to the neural plate
The neural tube includes
Brain and spinal cord
In vertebrates, two cell types develop near the neural tube
-neural crest cells
-somites
Neural crest cells are (2)
-from neural folds
-migrate to many parts of the embryo
Somites are (2)
-from mesoderm
-play a major role in segmentation of body structures
