LBYZOOL Activity 06: Early Embryonic Development (Lab Exam 2)

Lab Exam 2 also includes Animal Histology & Organology (no flashcards for that)

2 Types of Development of organisms

Phylogenetic Development and Ontogenetic Development

Phylogenetic Development

type of development:

- evolutionary history of the species
- relationship of organisms to each other & species to each other
- characters similar to a particular group of organisms
- ex. phylogenetic tree (genes, morphological characters, or both)

Ontogenetic Development

type of development:

- entire life history of an organism
- fertilization of egg → embryonic development → adult

Animal embryology

study of specific stage on the ontogenetic development of an animal, the embryo

Embryo

developing young from a fertilized egg to a form that is structurally similar to but does not precisely resemble the adult

Stages of Embryonic Development

- process of change occurring in a developing embryo is a dynamic & continuous one
- fertilization → cleavage → blastulation → gastrulation → neuralation → organogenesis

Segmented or Unfertilized Egg

spherical cells with well-defined nucleus in the center

cytoplasm of an unfertilized egg

organelle:

granular appearance filled with yolky material which is concentrated in one area of the egg

Vegetal pole

pole:

the area where the yolky material is concentrated

animal pole

pole:

area opposite the vegetal pole

telolecithal type

type of egg based on uneven yolk distribution

alecithal type

- type of egg mammals have
- no yolk

Fertilization

stage of embryonic development:

- union of sperm and egg nuclei
- restores chromosome/diploid number of the organism
- can happen externally or internally

Zygote

- embryo as a result of fertilization
- aka fertilized oocyte

Cleavage

stage of embryonic development:

- transforming the single-celled zygote into a multicellular entity
- involves a series of mitotic division
- transforms the zygote to blastomeres
- geometric increase in number of blastomeres
- divisions occur asynchronously during latter stages
- rate of cell division is hampered by the presence of the yolk

morula

- embryo as a result of cleavage
- ball of cells formed as a result of the series of cell divisions

Micromeres

blastomeres that are smaller & situated at animal pole

Macromeres

- blastomeres larger & situated at the vegetal pole
- size due to slower rate of cell divisions during latter stages of cleavage

Blastulation

stage of embryonic development:

- involves an internal secretion of fluid by the blastomeres of the morula
- results in the formation of the blastocoel
- emergence of 2 germ layers: endoderm & ectoderm
- didermic (2 layers)

endoderm

- inner germ layer of cells surrounding blastocoel
- forms into lining of the intestinal tract & lungs

ectoderm

- the outer germ layer of embryo
- forms into CNS, sense organs, epidermis

blastocoel

- aka segmentation cavity
- the fluid-filled cavity inside a blastula

blastula

embryo formed from Blastulation

Gastrulation

stage of embryonic development:

- involves morphogenetic movements
- laying out of primitive gut in endoderm
- formation of blastopore
- formation of 3 germ layers: ectoderm, mesoderm, & endoderm

morphogenetic movements

name of phenomena of the major cell movements & rearrangements to form the body plan characteristic of a species

archenteron

- aka primitive gut / gastrocoel
- forms during gastrulation
- serves as future digestive tract

blastopore

- the opening leading to the gastrocoel
- filled with yolk plug
- bounded by dorsal & ventral lips

anal or cloacal opening

organ formed from blastopore for deuterostomes

deuterostomes

echinoderms & vertebrates

mouth

organ formed from blastopore for protostomes

protostomes

nematodes, mollusks, & arthropods

mesoderm

- middle germ layer
- forms into heart, muscles, urogenital system, vertebral column, dermis of skin, blood

gastrula

embryo formed from Gastrulation

Neurulation

stage of embryonic development:

- contains formation of neural plate, fold, groove, tube, & notochord
- forms CNS

neural plate stage

stage in neurulation:

- dorsal situated ectodermal thickening
- where CNS of vertebrates develop

neural fold stage

stage in neurulation:

- neural plate invaginates

neural groove

the depression formed when neural plate invaginates

neural tube

- neural fold develops into a hollow tube
- future brain & spinal cord
- will be autonomous to the neural plate
- formation of somites in mesoderm

types of somites

epimere
mesomere
hypomere/lateral plate mesoderm

epimere

type of somite:

- most dorsal somite at level of notochord

mesomere

type of somite:

- the middle of mesoderm

hypomere

type of somite:

- lateral plate mesoderm
- in the ventral most portion of mesoderm
- subdivided to inner splanchnic layer & outer somatic layer
- forms coelom

coelom

- aka body cavity
- formed from the cavity between the inner splanchnic layer & outer somatic layer

notochord

- formed from mesoderm
- round structure below the neural tube
- serves as main axial support of vertebrate embryos

neurula

embryo formed from Neurulation

Organogenesis

- formation of organs after germ layers are established
- process wherein the nourishment is from the stored yolk or food material from the egg’s cytoplasm

mesolecithal type

type of egg that contains moderate amount of yolk

tadpole

- swimming larva emerged after frog embryonic development
- undergoes further organogenesis & histogenesis
- gets nourishment from plankton & other microscopic organisms
- transforms into an adult frog within 2.5-3 months through metamorphosis