chapter 47 Animal development

model organisms

are used by biologist to study development, chosen for the ease with which they can be studied in the laboratory: sea urchin, frog, chick, nematode

fertilization

is the formation of a diploid zygote from a haploid egg and sperm

Acrosomal reaction

is triggered when the sperm meets the egg

 

the cortical reaction

seconds after the sperm binds to the egg, vesicles just beneath the egg plasma membrane release their contents and form a fertilization envelope which acts as the slow block to prevent polyspermy

the acrosome

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

High concentration of calcium ions

is required to the cortical reaction to take place

Egg Activation

The rise in Ca2+ in the cytosol increases the rates of cellular respiration and protein synthesis by the egg cell

•The proteins and mRNAs needed for activation are already present in the egg

•The sperm nucleus merges with the egg nucleus and cell division begins

zona pellucida

extracellular matrix of the egg

zona pellucida, or extracellular matrix of the egg

sperm must travel through a layer of follicle cells surrounding the egg, before it reaches the ___________

Cleavage

a period of rapid cell division without growth. fertilization is followed by this

blastomeres

are cleavage partitions the cytoplasm of one large cell into many smaller cells

blastula

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

blastocoel

fluid filled cavity in a blastula (a ball of cells)

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

meroblastic cleavage

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

 

morphogenesis

the process by which cells occupy their appropriate locations, involves

–Gastrulation, the movement of cells from the blastula surface to the interior of the embryo

–Organogenesis, the formation of organs

gastrulation

rearranges the cells of a blastula into a three layered embryo called a gastrula

organogenesis

the formation of organs

gastrula

is a three layered embryo

Embryonic Germ layers

The three layers produced by gastrulation

ectoderm

forms the outer layer

endoderm

lines the digestive tract

mesoderm

partly fills the space between the ectoderm and endodermis

ectoderm (outer layer of embryo)

• epidermis if the skin and its derivatives like sweat glands, hair follicles

• nervous and sensory systems

• pituitary gland, adrenal medulla

• jaws and teeth

• germ cells

mesoderm (middle layer of embryo)

skeletal and muscular systems

lymphatic and circulatory systems

excretory and reproductive systems (except germ cells)

dermis of skin

adrenal cortex

endoderm (inner layer of embryo)

epithelial lining of digestive tract and associated organs (liver, pancreas)

epithelial lining of respiratory, excretory and reproductive tracts and ducts

thymus, thyroid, and parathyroid glands

blastocysts

human equivalent of the blastula

inner cell mass

cluster of cells at one end of the blastocyst

trophoblast

is the outer epithelial layer of the blastocyst and does not contribute to the embryo, but instead initiates implantation

organogensis

various regions of the germ layers develop into rudimentary organs

neurulation

begins as cells from the dorsal mesoderm form the notochord, a rod extending along the dorsal side of the embryo

neural crest cells

develop along the neural tube of vertebrates and form various parts of the embryo (nerves, parts of teeth, skull bones, and so on)

somites

Mesoderm lateral to the notochord forms blocks

differentiation

refers to the resulting specialization in structure and function