JOURNEY OF AN EMBRYO

SPERMATOGENESIS

• A process where male spermatogonia develop into mature spermatozoa.

• Occur in testes and epididymis in mammals and takes approximately 64 days.

• Step 1 – Spermatocytosis• Step 2 – Meiosis in Sertoli cells• Step 3 – Spermiogenesis

STEP IN SPREMATOGENESIS

• Monospermy – fusion of a single sperm and egg nuclei

• Polyspermy – excess of adhesion sites that leads to fusion of a single engg with more than 1 sperms.

MONOSPERMY & POLYSPERMY

OOGENESIS

FERTILIZATION

EVENTS THAT LEADS TO FERTILIZATION

General steps of early embryonic development

Embryology

Morula, 8 cell stage

1 - morula, 2 - blastula

1 - blastula, 2 - gastrula with blastopore; orange - ectoderm, red - endoderm.

There are 4 stages of embryonic development:

Cleavage Patterning Differentiation Growth

CLEAVAGE PRODUCES A BALL OF CELLS FROM ZYGOTE

• cleavage is the division of cells in the early embryo

• The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote.

MEANING

PATTERN OF CLEAVAGE

1. Amount and distribution of yolks in their eggs• Isolechital• Mesolechital• Telolechital• Centrolechital2. Polarity of eggs• Animal pole• Vegetal pole

Types of cleavage:

Cleavage patterns followed by holoblastic and meroblastic eggs

Holoblastic Meroblastic

•Bilateral (tunicates, amphibians)

Discoidal (fish, birds,reptile)

Radial (sea urchin, amphioxus) •Superficial (insects)

Rotational (mammals)

Spiral (annelids, mollusks)

Spiral cleavage

GASTRULATION

- a phase early in the development of most animal embryo, during which the morphology of the embryo is dramatically restructured by cell migration.

GASTRULATION

- a phase early in the development of most animal embryos, during which the morphology of the embryo is dramatically restructured by cell migration.

• The purpose of gastrulation is :- to position the three embryonic germ layers, the endoderm, ectoderm and mesoderm.

• gastrulation occurs after implantation, around days 14-16 after fertilization in human embryogenesis. (in human )

GATRULATION IN SEA URCHINS

GASTRULATION IN FISH

GASTRULATION IN BIRD

EVENTS IN DEVELOPMENT THAT INVOLVED THE MIGRATION OF

CELLS WITHIN THE EMBRYO DEVELOPMENT

About 1th week•After fertilization,embryo reaches two-cell stage•The blastula implants into the uterus

2th week•Within 2 weeks,many thousand of cells formed(embryo)

About 5th week•A gestational sac on ultrasound•Embryo at 4 weeks after fertilization.

6th week•In the beginning of the 6th week,a small ring called yolk sac on ultrasound•At the end of the 6th week the fetal pole and perhaps cardiac activity in the embryo

Embryo at 4 weeks after fertilization.

At 7th weekA well defined fetal pole and deinite cardiac cavity

By 9th weekA baby is called fetus. At this time the heartbeat with a doptone device about 50% of the time can heard

is about five weeks old (or from the seventh week of menstrual age).

Fetus at 8 weeks after fertilization.

Fetus at 8 weeks after fertilization.

This embryo is also from an ectopic pregnancy, this one in the cornu (the part of the uterus to which the Fallopian tube is attached). The features are consistent with a developmental age of seven weeks (reckoned as the ninth week of pregnancy

At end of first trimester(12th week)Placenta formed and supply the baby with oxygen from mother’s blood supply,and ridding wastes tthrough mom’s blood system At 13th weekBaby growing very quickly Week 16th – 20th Mother may feel a fluttering that is baby’s movement(quickening)Fetus at 18 weeks after fertilization 20th week Baby is half-way fully formedBaby is quite active and moving often

21th weekBaby’s eyes still closed,movement is stronger,skin is pinkAs baby and uterus grow,they are displacing organs that reside normally in the lower abdomen and pelvis

Fetus at 18 weeks after fertilization

By 24th weekUterus having intermitent contractionsBaby weights over one and one half poundBaby is consider viable(half babies born is survive at this stage)

26th to 28th weekLungs maturedBaby starting to store part in the subcutaneous layer of skin and hair growingBaby eyes is open

32th to 33th weekBaby weight about 4 ½ pounds and about 16-17 inches along

About 34th weekBaby lung start to work well

From 36th weekBaby consider fully develop Fetus at 38 weeks after

fertilization

NEURULATIONAND

ORGANOGENESIS

PROCESS OF NEURULATION

Neurulation begins with the formation of a neural plate, a thickening of the ectoderm caused when cuboidal epithelial cells become columnar.

Changes in cell shape and cell adhesion cause the edges of the plate fold and rise, meeting in the midline to form a neural tube.

The cells at the tips of the neural folds come to lie between the neural tube and the overlying epidermis. These cells become the neural crest cells.

Both epidermis and neural plate are capable of giving rise to neural crest cells.

Organogeneis is the period of animal development during which the embryo is becoming a fully functional organism capable of independent survivial.Organogenesis is the process by which specific organs and structures are formed, and involves both cell movements and cell differentiation. Organogenesis requires interactions between different tissues. These are often reciprocal interactions between epithelial sheets and mesenchymal.

ORGAN PRODUCED BY THE 3 GERM LAYERS