Embryology Flashcards
What is embryology
Phase between fertilisation and birth
Embryogenesis - from water to land
Problems + solutions
Problems
Dehydration, food availability
Solution
Formation of extra embryonic layers
- amniotic egg
Extra embryonic layers
Amnion
Yolk
Allantois
Chorion
Amnion
Prevents dehydration and protects embryo
Yolk
Nutrition
Allantois
Sequestering waste products
Chorion
Exchanging respiratory gasses
Characteristics of choradata
Notochord
Dorsal hollow nerve cord
Muscular anal tail
Pharyngeal slits or clefts
What distinguishes vertebrates from other chordates
Development of back bone - vertebral column
Cranium
Endoskeleton
What is the phylotipic stage
Tailbud stage
- Fertilisation
Fusion of the nucleus of a male gamete with the nucleus of a female gamete results in production of a zygote
Sperm
Highly conserved features
Head has a cap called the acrosome which contains hydrolytic enzyme which help the sperm penetrates the egg
Hydrolytic enzymes
Hyaluronidase - penetrates corona radiata
Acrosin - digests the sons pellucida
Reproductive strategies
R selected - large no. Of small young, no parental care, rapid growth, short lived, high mortality risk
K selected - small no. Large young, parental care, long maturity, long lived
Effected by temp
Telolecithal egg
Yolk down one end of the egg
- birds, reptiles, fish
Isolecithal egg
Yolk is dispersed
- mammals -
Amount of yolk
Small
Microlecithal - mammals
Mesolecithal - amphibians
Macrolecithal - fish, reptiles, birds
Large
Egg laying
Oviparous
Viviparous
Give birth to live young
- Cleavage
The series of mitotic divisions that take the zygote to a mass of smaller cells, blastula/blastocyst/blastoderm
Two different forms of cleavage
Holoblastic - complete split of cells
- isolecithal
- microlecithal, mesolecithal
Meroblastic - partial cleavage
- telolecithal
- macrolecithal
Cleavage in amphibians
Mesolecithal egg, radial holoblastic cleavage
Cleavage in birds, fish and reptiles
Macrolecithal, discoidal meroblastic cleavage
Division occurs on top of yolk
Blastoderm
Bilaminar disc - 2 layers of cell formed;
1. Epiblast
2. Hypoblast
Cleavage in mammals
Microlecithal egg, rotational holoblastic cleavage
Also asynchronous - not all blastomeres divide at the same time
Trophoblast - outer layer of cells = develops into placenta
- Gastrulation
Rearrangement of the cells by migration and division resulting in the formation of three embryonic germ layers :
1. Endoderm 2. Mesoderm 3. Ectoderm
- Neurulation
Folding process to form the neural tube which become the spinal chord and central nervous system
Formation of yolk and allantois
Endoderm and mesoderm
Formation of chorion and amnion
Ectoderm and mesoderm
Placenta formation in mice
Formed for the Allantois and chorion
- Organogenesis
The series of organised integrated process that transforms an amorphous mass of cells into a complete organ in the developing embryo
What does the ectoderm go on to form
- nervous system
- skin
- epithelia of eye, ear and nose
Paradise mesoderm forms?
Connective tissue
- vertebrae, ribs
- muscle + limbs
- dermis (skin)
Intermediate mesoderm forms?
Urogenital system
- kidneys, gonads
Lateral plate mesoderm forms?
Circulatory system
- heart, vessels
Archenteron
The primary gut formed during gastrulation
Endoderm forms?
Intestines, lungs, liver, pancreas, thymus
- Differentiation
Embryonic cells specialise into diverse tissue structures
Totipotent cells
each single blastomere contains the information to develop a complete individual
What gene regulates organogenesis
Homeobox gene (hox gene)
Homobox gene
Involved in differential gene expression and morphogenesis
Highly homologous
Master controllers
Homeotic genes
Determine animal structure and they contain DNA sequences called homeoboxes
