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Flashcards in Early Development Stages Deck (17)
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What are the stages of early development?

1. fertilization
2. morula formation
3. blastula formation
4. gastrulation
5. neurulation



-sperm and secondary oocyte combine
-male and female pronuclei (nucleus of haploid gamete) unite and undergo meiosis
-cleavage of the embryo occurs (occurs the first 3 days post-fertilization)


How does the embryo change after cleavage?

-same cell differentiation before and after cleavage
-same total cell volume before and after cleavage
-increase in total cell number after cleavage
-zona pellucida surrounds the ovum and prevents an increase in volume during early stages but leads to an increase in surface area to maximize nutrient exchange


Morula Formation

-occurs on days 3-4
-it is a solid mass of 16-20 cells that makes up the embryo
-cell adherence allows tight junctions and cell-cell communication


Blastula Formation

-occurs on days 5-14
-result of the morula undergoing blastulation
-it is a hollow ball of cells with a fluid-filled inner cavity known as a blastocoel/blastocyst; essentially an embryo with a BLASTed-out cavity
-around day 7 the blastula implants into the endometrium which allows for access to maternal blood supply/nutrients


What 2 cell groups make-up the blastula?

1. trophoblast cells: surround the blastocoel and give rise to the chorion and later the placenta
2. inner cell mass: protrudes into blastocoel and give rise to the organism itself



-occurs 3 weeks after fertilization
-inner cell mass caves inward to form a tube which leads to the development of the primary germ layers that differentiate
-tube is made of endodermal cells and forms the lining of the primative gut


What is the archenteron?

-the lining of the primative gut that develops into the digestive tract and associated tissues
-made of endodermal cells


What is the blastopore?

-opening of the tube formed during gastrulation
-becomes the anus in deuterostomes (humans) and the mouth in protostomes


Primary Germ Layer - Endoderm

-forms the internal (endodermal organs)
-liver, pancreas, thyroid, bladder, distal urinary and reproduction tracts, thymus, taste buds
-archenteron -> digestive tract -> stomach, intestines
-archenteron -> offshoots -> liver, pancreas, lungs, bladder


Primary Germ Layer - Mesoderm

-forms the means of transport
-develops into the musculoskeletal system, circulatory system, excretory system (kidney), lymphatic system, gonads, adrenal cortex, muscular and connective tissues, layers of digestive and respiratory tracts


Primary Germ Layer - Ectoderm

-'attract-o-derm' -- forms the things that attract you to a person
-develops into integument (epidermis, hair, nails, epithelia of nose + mouth + anal canal), lens of eye, teeth, nervous system (brain, PNS, inner ear), adrenal medulla



-development of the nervous system
(1) rod of mesodermal cells known as notochord form along dorsal embryo and act as primative spine
(2) notochord induces group of overlaying ectodermal cells to slide inward to form the neural folds which surround a neural groove
(3) neural folds grow toward one another until they fuse into a neural tube which gives rise to the CNS
(4) neural crest cells located at the tip of each neural fold migrate outward to form the PNS and specific cell types in other tissues
(5) ectodermal cells migrate over neural tube and crests to cover nervous system


What gives rise to the CNS?

neural tube


What gives rise to the PNS?

neural crest cells


Dizygotic Twins

-fraternal twins
-form from fertilization of 2 different eggs by two different sperm
-not more genetically similar than any other sibling pair


Monozygotic Twins

-identical twins
-form when a single zygote splits into two
-genetic material is identical