Animal Growth & Development

Beginnings of the Embryo

Fertilization- union of the gametes • Sperm- very small, mobile, ½ of chromosome

set

• Egg- very large, contains yolk, other half of chromosome set

YOLK: energy-rich, contains lipids, proteins, RNA, many ribosomes, mitochondria

Fertilization process

Sperm head hits surface of egg Enzymes break through egg’s surface Egg puts up barrier to other sperm once

activated Sperm nucleus fuses with egg nucleus and

forms zygote (earliest stage of the embryo

Egg Activation Fertilization turns on egg’s metabolism

Causes an increase in cell respirationSynthesis of new proteins occurs using RNA

molecules already present in cytoplasmPlasma membrane blocks a second fertilization by

another spermZygote cytoplasm is rearranged by movements in

cytoskeleton (produces differences among cells when they begin to divide)

10.2 GROWTH, DIFFERENTION AND FORM

Zygote to complex multicellular individual Cell division of embryo

Increasing number of cells make individual grow

Differentiation As cells divide some become specific cell types (Example:

muscle, skin)

Morphogenesis As cells differentiate they organize into specific tissues to later

form organs

*each cell type has a specialized structure and function

How does differentiation

occur? All cells have same DNA Proteins make each cell

different Each cell type expresses

certain genes making specific proteins by protein synthesis

Example: muscle cells make actin and myosin while red blood cells make hemoglobin

10.3 One cell to many

Cleavage Immediately after fertilization the cell divides into two cells. Cells continue to divide simultaneously increasing cell # 2x

for each division: 2→4→8→16, etc. At 16 cells to 64 cells the embryo is called and Morula At the end of cleavage: mass of many cells called a

Blastula All cells are same in size and appearance Usually hollow (hollow part called blastocoel) Shape depends on structure and arrangement of egg and yolk http://www.youtube.com/watch?v=UgT5rUQ9EmQ

Gastrulation Through differentiation and morphogenesis

Blastula becomes Gastrula Forms primary germ layers (3):

Ectoderm- outer layer, will form skin, nervous system and related structures

Mesoderm- middle layer, will form bone, muscles, heart, blood, etc.

Endoderm- inner layer, “tube-like”, will form lining of digestive system

SummaryFertilization

Morula(16-64 cells)

↓Blastula

(can have various shapes)

↓Gastrula

(3 layers- ectoderm, mesoderm, endoderm)

(Pictures show sea urchin development)

Gastrulation continued... Body Plan

In vertebrates, appears during gastrulation General shape of developing organism Notochord

Forms from first mesoderm Stiff rod that will become backbone Runs through middle of embryo just below dorsal ectoderm Establishes anterior-posterior axis (head to tail)

Neural tube Forms from dorsal ectoderm directly above notochord Will form brain, spinal cord and nerves

Some differences among animals...

Some develop directly into young that are like the adult (birds and mammals)

Other animals form larva (frogs, sea stars, insectsDoes not resemble adult formLater goes through metamorphosis

Examples: maggot→ fly

caterpillar→ butterfly

tadpole → frog

10.5 Human Development

Embryo develops inside motherMother provides warm, protected environmentBlood circulation provides nutrition and oxygen,

removes waste and CO2

Zygote goes through cleavage while moving down oviduct

After 5 days- blastocyst (like blastula in other animals) implants in uterine wall

Early changes in Embryo

Human development continued...

Amnion- surrounds the embryo Chorion-encloses other membranes, forms outer

wall of blastocyst Placenta

Forms in gastrulationChorion forms villi into uterine lining→ placentaExchanges nutrients, wastes, O2, CO2 between

mother and embryo through umbilical cord (arteries and veins)

Eggs versus Embryo 

Chorion: lies just beneath the shell & functions in

gas exchange. Allantois: collects & stores nitrogenous wastes. Yolk sac stores food. Amnion cushions & provides watery environment.

gestation 40 weeks to develop Called “fetus” after

start of 8th week Divided into

trimesters 1st: organs and

skeleton begin to form 2nd: 3rd: rapid growth and

maturation

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__fetal_development_and_risk.html