Zoo-Lab (Sem-1) Chapter 4: Embryology

embryology

study of the development of an animal from the fertilized egg to birth or hatching

zygote

the fertilized egg; it enters a 2-week period of rapid cell division and develops into an embryo

cytoplasmic determinants

the zygote's genome and molecules in the egg cytoplasm which determines development

cell differentiation

the specialization of cells in structure and function

morphogenesis

a major aspect of development in plants and animals; the process by which an animal takes shape / form; only in animals does it involve the movement of cells

model organisms

species that are representative of a larger group and easily studied; classic embryological studies use the sea urchin, frog, chick, and the nematode C. elegans

Caenorhabditis elegans

nematode worm

cleavage; gastrulation; organogenesis

important events regulating development occur during fertilization and the three stages that build the animal's body

fertilization

sperm + egg = zygote; n + n = 2n; brings the haploid nuclei of sperm and egg together, forming a diploid zygote

acrosomal reaction; cortical reaction

onset of embryonic development triggered by the sperm's contact with the egg's surface which initiates metabolic reactions in the egg

acrosomal reaction

triggered when the sperm meets the egg

acrosome

tip of the sperm; releases hydrolytic enzymes that digest material surrounding the egg

hydrolytic enzymes

enzymes that speed up/aid in the breakdown of chemical bonds through the addition of water (hydrolysis); digest material surrounding the egg

depolarization

change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside

polyspermy

fertilization by more than one sperm

fast block to polyspermy

achieved by changing the electric potential of the egg plasma membrane

contact; acrosomal reaction; contact and fusion of sperm and egg membranes; cortical reaction; entry of sperm nucleus

sea urchin fertilization steps

exocytosis

fusion of secretory vesicles with the plasma membrane and results in the discharge of vesicle content into the extracellular space and the incorporation of new proteins and lipids into the plasma membrane

cortical reaction

a reaction that occurs during fertilization, when the sperm cell unites with the egg's plasma membrane, that prevents entry of a second sperm; rise in Ca2+ that stimulates cortical granules to release their contents outside the egg

slow block to polyspermy

the formation of the fertilization envelope and other changes in the egg's surface that prevent fusion of the egg with more than one sperm

egg plasma membrane

around the cytoplasm of the egg

vitelline layer

a structure formed by the extracellular matrix of the egg; a multilayered structure that protects and gives shape to the egg yolk and separates it from the egg white

cortical granule

secretory vesicles poised at the cortex of an egg that, upon stimulation by sperm contact at fertilization, secrete their contents; these contents modify the extracellular environment and block additional sperm from reaching the egg

perivitelline space

the fluid-filled space between the fertilization membrane and the ovum after the entry of a sperm into the egg; participates in the protection of both the embryo and the yolk nutrients during the early incubation

fertilization envelope

the swelling of the vitelline layer away from the plasma membrane; establishes a physical and biochemical barrier that protects the zygote from supernumerary sperm, as well as environmental and microbial agents

supernumerary sperm

extra sperm which succeed in entering the vitellus
- such ova are said to show polyspermy

Calcium ions (Ca2+)

play an important role in fertilization; increases the rates of cellular respiration and protein synthesis by the egg cell

internal

fertilization in mammals and other terrestrial animals is ________

zona pellucida

extracellular matrix of the egg; modified by the cortical reaction as a slow block to polyspermy

12-36

the first cell division occurs __-__ hours after sperm binding

follicle cell

nourishing cell surrounding an oocyte

cleavage

follows after fertilization; period of rapid cell division without growth; partitions the cytoplasm of one large cell into many smaller cells

blastomeres

smaller cells produced by cleavage during mitotic cell division

blastula

a hollow ball of cells with a fluid-filled cavity called blastocoel

blastocoel

the fluid-filled cavity of a blastula

distribution of yolk

by which standard is polarity defined by

yolk

stored nutrients; slows cell division down; can cause uneven cell division at the poles

vegetal pole

pole with more yolk

animal pole

pole with less yolk

cortical rotation

region of the egg in the animal pole rotates toward site of sperm entry, establishes the dorsal/ventral axis and gray crescent

gray crescent

light-gray region of cytoplasm located near the equator of the egg on the side opposite the sperm entry; from where cells of the dorsal originate and invaginate to create the archenteron

holoblastic cleavage

complete division of the egg; occurs in species whose eggs have little or moderate amounts of yolk, such as sea urchins and frogs

isolecithal; mesolecithal

two types of holoblastic yolk distribution

isolecithal

holoblastic; sparse, evenly distributed yolk

radial; spiral; rotational

cleavages of isolecithal eggs

radial cleavage

holoblastic; isolecithal; Echinoderms

spiral cleavage

holoblastic; isolecithal; Annelids, mollusks, and flatworms

rotational cleavage

holoblastic; isolecithal; mammals; Nematodes

displaced radial cleavage

holoblastic; mesolethical; amphibians

mesolecithal

holoblastic; moderate vegetal yolk diposition

meroblastic cleavage

incomplete division of the egg; occurs in species with yolk-rich eggs, such as reptiles and birds

telolecithal; centrolecithal

two types of meroblastic yolk distribution

telolecithal

meroblastic; dense yolk throughout most of cell

discoidal cleavage

meroblastic; telolecithal; fish, reptiles, and birds

centrolecithal

meroblastic; yolk in center of egg

syncytial cleavage

meroblastic; centrolecithal; most insects

blastocyst

stage of early development in mammals that consists of a hollow ball of cells; term used for blastula in placental mammals

trophoblast

outer cells of the blastocyst that secrete enzymes that allow implantation

gastrulation

rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut

ectoderm; endoderm; mesoderm

three embryonic germ layers produced by gastrulation are called

ectoderm

forms the outer layer of the gastrula

endoderm

lines the digestive tract

mesoderm

partly fills the space between the endoderm and ectoderm

mesenchyme cells

small spindle-shaped cells with large nuclei, prominent nucleoli and fine chromatin; migrate from the vegetal pole into the blastocoel

vegetal plate

forms from the remaining cells of the vegetal pole and buckles inward through invagination

invagination

the local inward movement of cells from a cavity

archenteron

endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal

blastopore

from where the archenteron will open through, which will become the anus

involution

similar to invagination, but more dramatic; inward expansion of epithelial cells around an edge, such as the blastopore

epiboly

spreading movement of an epithelium to a deeper or thinner layer

organogenesis

various regions of the germ layers develop into rudimentary organs

frog

model for organogenesis

notochord

forms from mesoderm

neural plate

forms from ectoderm

neural tube

will become the central nervous system = brain and spinal cord

neural crest cells

develop along the neural tube of vertebrates and form various parts of the embryo: nerves, parts of teeth, skull bones

somites

blocks formed by the mesoderm lateral to the notochord

lateral to the somites

where the mesoderm splits to form the coelom

cytoskeleton

drives cell migration, or cell crawling, the active movement of cells

tissue invagination

caused by changes in cell shape and migration

cell crawling

involved in convergent extension, a morphogenetic movement in which cells of a tissue become narrower and longer

extracellular matrix

substance in which animal tissue cells are embedded, consisting of protein and polysaccharides.

cell adhesion molecules

located on cell surfaces; contribute to cell migration and stable tissue structure

cadherins

a class of cell-to-cell adhesion molecule; important in the formation of the frog blastula

same genome

cells in a multicellular organism share the ____ ______

differential gene expression

differences in cell types is the result of differentiation, the expression of different genes

induction

process by which the presence of one tissue influences the development of others

fate maps

general territorial diagrams of embryonic development

body axes

anterior-posterior, dorsal-ventral, left-right

totipotent

cells that are able to develop into any type of cell found in the body

The Dorsal Lip = "Organizer"

Hans Spemann and Hilde Mangold concluded that the blastopore's dorsal lip is an organizer of the embryo

Spemann organizer

initiates inductions that result in formation of the notochord, neural tube, and other organs