1

Fertilization & Embryonic

Development

Words To Know

1. Fertilization

- when sperm nucleus fuses with egg

nucleus to form a zygote.

2. Cleavage

- zygote divides by mitosis

- only an increase in cell number, not size

3. Differentiation

- unspecialized embryonic cells develop into

specialized tissues & organs by using the same

genetic material.

- cells begin to turn on or off different genes

(sections of DNA) to trigger different organs to

form.

4. Cell movement

- cells move to proper locations

Cells

Cells Cells

Muscle

cellsBone

cells

Skin

cells

Blood

cells

Fertilization

2

Fertilization

Draw On The Board

The Process of Mitosis

During Cleavage

Nuclear Stage

Nucleus fuses

Solid Ball Hollow Ball

Embryo Development

Blastula >64 cellsMorula (16-64 cells)

Cells moving

Cleavage

Cleavage

3

Morula (solid ball)

Blastula (hollow ball)

Gastrula (ball of cells push in,

differentiation begins- tissues, organs form)

•Blastula – cells around a hollow ball•Gastrulation- cells move inward

•Produces a 3 layer embryo

Ectoderm

Endoderm

Mesoderm

Gastrula: 3 Germ Layers

(3 tissue layers)

Ectoderm

Mesoderm

Endoderm

Outer layer

Middle layer

Inner layer

Gastrula: 3 Germ Layers

(3 tissue layers)

Ectoderm

Mesoderm

Endoderm

Outer layer: skin & nervous system

In-between-layer: Fills in space (muscle, skeleton,

connective tissue, blood, heart)

Inner layer: lining of the digestive tract tissues

(gut) &internal organs

Animation:

Cleavage & Differentiation

• http://www.sumanasinc.com/webcontent/animations/content/stemcells_scnt.html

(*animation)

• http://student.ttuhsc.edu/JBuchanan/histology.htm (other animations)

Implantation- process where embryo secretes enzymes that digest

into the uterus lining.

4

Review: Label A,B,C,D & E

A) 2- cell stage

B) 4- cell stage

C) 8-cell stageD) & E) Morula stage

Review: Label A,B,C

A)Name this process

Gastrulation

B) C)

Ectoderm Endoderm

Embryo Development

• the time from

fertilization up to 2

months

• the time from fertilization to birth

(9 months)

Embryo Gestation

Placenta

Fetus

Amnion

Umbilical

cord

Uterus

Amniotic

fluid

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2 Membranes

Amnion • This develops into a fluid-filled sac to protect & cushion the embryo.

Chorion • The outer membrane that forms into finger-like projections called

chorionic villi. This forms into the uterus lining.

Embryo Features

Placenta• An organ formed by the chorionic villi & uterus lining that connects

mother & fetus.

• Functions (diffusion)

- supplies nutrients (nourishment)

- exchange gases (O2) (respiration)

- eliminates wastes (CO2) (excretion)

Umbilical

Cord• Connects fetus to the placenta

•Contains 2 arteries & 1 vein

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Dangers A Fetus

May Encounter In The Uterus1. Drugs (medications-OTC)2. Caffeine3. Alcohol

4. Poor diet, lack of nutrients5. X-rays, radiation (microwaves)6. Excessive stress, not enough sleep

7. Risky activities (unprotected sex, IV drug use), accidents

8. Smoking

9. Viral infections10. Toxins (pesticides), chemicals

Fetal Alcohol Syndrome

TwinsIdentical Twins

- splitting of 1

egg

Fraternal Twins

- 2 eggs fertilized by 2

different sperms

http://pennhealth.com/health_info/pregnancy/000199.htm* animation

Identical Twins Fraternal Twins

3D & 4D

Ultrasound

http://www.lifeissues.org/ultrasound/4Dindex.htm

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Abnormalities

Ectopic Pregnancy

(outside the uterus)

Siamese Twins (Conjoined twins)

• Identical twins that fail to

complete separately after

fertilization.

• May share chest, head,

pelvis, or other internal

organs.

• Cause: unknown

Separated 2/07

Testicular Cancer

• Affects 6/100,000 men (1% of all cancers in men)

• Age risk 20- 35 years old