Embryology Flashcards
4 stages of embryonic development in ALL animals
1) Fertilization
2) Cleavage
3) Gastrulation
4) Organogenesis
Homologues of this drosophila gene are important in embryonic development
Tinman gene - regulates heart position in drosophila
3 key events in fertilization
1) Contact
2) Acrosomal reaction
3) Cortical reaction
Contact
1st stage of fertilization
- Sperm makes contact with protective egg coating (Zona pelludica)
Acrosomal reaction
2nd stage of fertilization
- enzymes dissolve jelly coat
- molecules on sperm bind to receptors on egg
- species specific binding process (not in all mammals)
Cortical reaction
Changes at surface of egg prevent further sperm from entering - Polyspermy
Zona Pellucida
Outer jelly coating of the females egg while still in the ovary
What occurs when the head of the sperm contacts an egg
Spermatozoon touches Zona pellucida
- triggers acrosomal process
- spermatozoon release hydrolytic enzymes
from the acrosome (head)
What is the significant process within the acrosomal process within fertilization?
Release of actin filaments
- pierce the jelly coat
- Proteins on the tip of the acrosomal process bind to receptors and act as lock and key
Acrosomal process - Non-Mammals
Quick-Block Process
- Binding of proteins on acrosomal process causes fusion of spermatozoon and egg
- Fusion triggers Na release
- Na influx causes depolarization
- Depolarization blocks other sperm from fusing
Cortical Reaction
All Mammals Longer lasting - block polyspermy - Cortical granules beneath egg membrane released into perivitelline space - Hardens - Receptors clipped off - No further binding of other sperm
What is is called when rapid cell division occurs and a single egg (zygote) forms many smaller cells?
Blastomeres
What are the first 5-7 divisions called?
Blastula
Blastocyst (in mammals)
What is it called when many small cells surround a fluid filled space?
Blastocoel
What are the two main types of cleavage systems?
1) Holoblastic
2) Meroblastic
Holoblastic cleavage
- yolk concentrated at vegetal pole
- indentation causes “cleavage furrow”
- 1st cleavage: furrow crosses over both vegetal and animal pole
- 2nd cleavage: 90deg. to 1st cleavage
- 3rd cleavage: produces 8 distinct cells
Meroblastic
Furrow cannot pass through vegetal pole
Cleavage only occurs in animal pole
- Results in blastula (blastocyst) which contains a fluid filled blastocoel
What types of animals undergo Meroblastic cleavage? (5)
1) Monotremes
2) Birds
3) Reptiles
4) Fish
5) Insects
What types of animals undergo Meroblastic cleavage? (5)
1) Monotremes
2) Birds
3) Reptiles
4) Fish
5) Insects
Which pole of the zygote is and which type of systematic cleavage impedes furrow formation
Vegetal pole / Meroblastic cleavage
- vegetal pole is more dense and impedes cleavage in certain directions
- difference in pole density is feature of systematic cleavage
Embryoblast
Inner collection (mass) of cells which is attached to the trophoblast - Trophoblast: outermost layer of cells before zona pellucida
Gastrulation results in which 3 layers in the embryo?
1) Endoderm
2) Mesoderm
3) Ectoderm
Endoderm forms: (3)
1) Epithelial lining of respiratory, excretory, reproductive tracts
2) Epithelial lining of digestive tract and liver/pancreas
3) Thymus, thyroid, and parathyroid
Mesoderm forms: (5)
1) Musculo-skeletal system
2) Circulatory/lymphatic systems
3) Excretory/reproductive systems (not germ cells)
4) Dermis of skin
5) Adrenal cortex
Ectoderm forms:
1) Epidermis of skin (and sweat glands, hair follicles)
2) Nervous/sensory systems
3) Pituitary gland, adrenal medulla
4) Jaws and teeth
5) Germ cells
If the first “hole” in the zygote is called the blastocoel, the second one is called?
Archenteron
Archenteron eventually displaces blastocoel and is the only “hole”
Frog Gastrulation
- Hollow ball of cells
- Blastocoel eventually displaced by Archenteron
- Endoderm forms yolk plug surrounded by blastopore
- Blastopore develops into anus
- Mouth/digestive cavity develops form archenteron
Bird Gastrulation
Frog: Hollow ball of cells
Bird: Disc of cells
Contain 2 layers: Epiblast, Hypoblast
EMBRYO DEVELOPS FROM EPIBLAST
The “disc” gastrulation process found in birds is called?
Blastoderm
Primitive streak
Occurs during gastrulation in birds
- Outer epiblast layer innervates towards yolk
- Downward cell movement: Endoderm
- Lateral cell movement: Mesoderm
- Cells left on surface: Ectoderm
What embryonic development changes occur in the zygote before implantation into endometrium of uterus?
Inner cell mass (embryoblast) further divides into
1) Epiblast
2) Hypoblast
Cells of epiblast move inward via the primitive streak and form mesoderm and endoderm
Totipotent:
- Stem cells which can for all cells of the body
- First few divisions after fertilization: 8-cell stage
Pluripotent:
- Can form all cell types of the body but NOT the extraembryonic tissue
Multipotent:
Adult stem cells
Found in bone marrow/adipose tissue
Limited differentiation ability
- Mesenchymal stem cells (MSCs) - cartilage, bone, adipose, [good at forming cells originating from the mesoderm]
Induced pluripotent stem cells
iPSC’s
Produced from adult cells via ‘reprogramming’
Induced pluripotent stem cells
iPSC’s
Produced from adult cells via ‘reprogramming’
Neurulation
Process of forming the notochord
Neurulation (process)
Ectoderm above the notochord becomes the neural plate
Neural folds: Adjacent tissue comes together to form top of neural tube
Neural tube: Formed by neural ectoderm
What are the two types of cells which form near the neural tube?
1) Neural crest cells
2) Somites
Neural crest cells
- Form from neural folds
- Migrate to many parts of the embryo
- Neurons, bone, pigment cells
Somite Cells
- Form from mesoderm
- Play major role in organizing and segmentation of body (ex, vertebrae and associated muscles)
