Fertilization, Implantation and Gastrulation (first 2 weeks) of Human Development

The first sperm reach the fallopian tube within HOW MANY minutes of ejaculation thanks to a combination of their WHAT, ejaculatory WHAT, uterine and oviduct WHAT

The first sperm reach the fallopian tube within 30 minutes of ejaculation thanks to a combination of their MOTILITY, ejaculatory FORCE, uterine and oviduct CONTRATIONS

HOW MANY million of sperm are ejaculated, about HOW MANY sperm reach the fallopian tubes, but only HOW MANY will fertilize the egg

150-300 million of sperm are ejaculated, about 400 sperm reach the fallopian tubes, but only 1 will fertilize the egg

When the first sperm manages to WHAT through the outside of the egg, the WHAT changes so no other sperm are able to enter

When the first sperm manages to DIG through the outside of the egg, the CELL MEMBRANE changes so no other sperm are able to enter

The fused egg and sperm is now a WHAT egg and is called a WHAT ( with HOW MANY chromosomes)

The fused egg and sperm is now a FERTILIZED egg and is called a ZYGOTE ( with 46 chromosomes)

If two eggs are fertilized by two different sperm - called WHAT

Fraternal twins (dizygotic twins)

If one egg is fertilized by one sperm, but during development splits into two - called WHAT

Identical twins (mono-zygotic twins)

If there is incomplete separation, WHAT develop

Siamese twins

Biological sex is determined by the WHAT carried by the WHAT

Biological sex is determined by the SEX CHROMOSOME carried by the SPERM

Within HOW MANY hours of fertilization the WHAT divides by WHAT forming HOW MANY new cells. These cells also divide, forming HOW MANY cells, which divide to form HOW MANY cell. This cell division without enlargement of the cells is called WHAT

Within 30 hours of fertilization the ZYGOTE divides by MITOSIS forming 2 new cells. These cells also divide, forming 4 cells, which divide to form 8 cell. This cell division without enlargement of the cells is called CLEAVAGE

At the 16 cell stage, the zygote is called a WHAT

Morula

The morula reached the WHAT in HOW MANY days after fertilization and forms a WHAT from which new cellular structures can form and is then called a WHAT

The morula reached the UTERUS in 3-5 days after fertilization and forms a HALLOW FLUID POUCH from which new cellular structures can form and is then called a BLASTOCYST

The blastocyst has HOW MANY distinct germ layers

4

The blastocyst layers:

The outer layer called the WHAT (WHAT) implants into the WHAT and will develop into part of the WHAT, the inner membrane (the WHAT), the fluid filled cavity (the WHAT) and the yolk sac, which attaches to the WHAT of the developing embryo

The outer layer called the TROPHOBLAST (CHORION) implants into the ENDOMETRIUM and will develop into part of the PLACENTA, the inner membrane (the ALLANTOIS), the fluid filled cavity (the AMNION) and the yolk sac, which attaches to the ALIMENTARY CANAL of the developing embryo

By the WHICH day after fertilization, the WHAT attaches to the WHAT (about the WHAT day in the menstrual cycle) and is called WHAT

By the 5-7th day after fertilization, the BLASTOCYST attaches to the ENDOMETRIUM (about the 20th day in the menstrual cycle) and is called IMPLANTATION

What are the extra-embryonic membranes

• Chorion

• Allantois

• Amnion

• Yolk sac

The chorion

It secretes the HUMAN CHORIONIC GONADOTROPIC hormone (HCG) which maintains the CORPUS LUTEUM production of ESTROGEN and PROGESTERONE (otherwise it would degenerate and menstruation would occur) (pituitary also secretes HCG); forms the FETAL portion of the PLACENTA

The allantois

Provides BLOOD VESSELS in the PLACENTA (forms the foundation for the UMBILICAL CORD)

The amnion

Forms the AMNIOTIC SAC which will protect the developing embryo/fetus from impact, temperature changes, infection and dehydration

The yolk sac

Is a small sac suspended from the abdominal area, forms the DIGESTIVE TRACT and produces the first BLOOD CELLS, serves NO NUTRITIVE function

The inner cell mass will differentiate into the developing WHAT which becomes the developing WHAT

The inner cell mass will differentiate into the developing EMBRYONIC DISC which becomes the developing EMBRYO

What is gastrulation

The formation of the three primary GERM LAYERS - is a PIVOTAL event in embryonic development. All future tissues, organs and organ systems of the body will develop from the cells of the germ layer.

During the “gastrula“ stage, the embryo (the innermost layer) itself differentiates into 3 layers called WHAT, WHAT and WHAT, each developing into different WHAT

During the “gastrula“ stage, the embryo (the innermost layer) itself differentiates into 3 layers called ECTODERM, MESODERM and ENDODERM, each developing into different ORGAN SYSTEMS

Ectoderm (top layer)

• NERVOUS SYSTEM (brain, spinal cord, sense organs)

• EPIDERMIS (SKIN)

• Outer skin

• nervous tissue and sense organs

• pituitary gland

• tooth enamel

• eye lens

Mesoderm (middle layer)

• SKELETON, MUSCLES

• CIRCULATORY SYSTEM

• REPRODUCTIVE SYSTEMS

• dermis of skin

• cellular lining of blood vessels, lymph vessels, body cavities

• connective tissue

• heart

• kidneys

• spleen

Endoderm (bottom layer)

• cellular lining of respiratory tract, digestive tract, urinary bladder, urethra

• ENDOCRINE GLANDS

• liver

• gallbladder

• pancreas

• thymus

• thyroid glands

• parathyroid glands

The mucous of the cervix will WHAT and WHAT the cervix with a WHAT (preventing the fetus from being WHAT)

The mucous of the cervix will THICKEN and BLOCK the cervix with a PLUG (preventing the fetus from being EXPELLED)