Definition and Process of Embryo Formation

Fertilization and cleavage (source, microsoft encharta)

The fetus or embryo is a creature which is in the growing in the womb. Gynecology is located in or outside the main body of the parent body (the egg). Growing up is a change from simple forms and the young to form a complex or adult (Wildan orphans, 1990).
Meanwhile, in Microsoft Encarta 2006 stated that the fetus is a vertebrate animal that has not been born at a stage where all the structural characteristics of adults can already known, mainly descendants of people who have not born after eight weeks of growth.

The process of embryo formation :
Spermatogenesis, The transition from going to an active sex cells divide into mature sperm, and involve various kinds of structural changes that take place in sequence. Spermatogenesis took place in the seminiferous tubules and regulated by the hormone and testosterone gonadtotropin (Wildan orphans, 1990).
Phase formation of spermatozoa was divided into three phases:

• Spermatocytogenesis, Spermatogonia are undergoing mitosis many times that will be the primary spermatocytes. Spermatogonia are primitive structures and can reproduce (divide) by mitosis. Spermatogonia are getting the nutrients from Sertoli cells and develop into primary spermatocytes. Primary spermatocyte chromosomes contain diploid (2n) in the cell nucleus and the experience of meiosis. One spermatocytes will produce two daughter cells, the secondary spermatocytes.
  
• Stages Meiois, Spermatocytes I (primary) away from the basal lamina, the cytoplasm increased and soon had meiosis I followed by meiosis II.
  Sitokenesis in meiosis I and II did not share the complete germ cells separate, but still connected by a bridge sesame (Interceluler bridge). Compared with the spermatocyte I, spermatocyte II has a dark core.
• Stages of Spermiogenesis, Is the transformation of spermatids into spermatozoa which includes 4 phases of Golgi phase, cap phase, akrosom phase and maturation phase. The final results of the four mature spermatozoa. Two spermatozoa will carry chromosomes determine the sex of her "X". If any of these spermatozoa unite with the ovum, the pattern of human somatic cells that were 23 pairs of chromosomes will be maintained.
  Mature spermatozoon consists of:

1. Head (caput), not only contains the core (nucleus) with the chromosome and its genetic material, but also covered by akrosom hyaluronidase-containing enzyme that facilitates the ovum fertilization.
2. Neck (servix), connecting the head with the body.
3. Body (corpus), responsible for producing the energy needed for motility.
4. Tail (cauda), serves to encourage mature spermatozoa into the vas defern and ductus ejakulotorius.

Oogenesis
Sex Cells Primordial
Sex cells of primordial first seen in the embryonic ectoderm of the saccus vitellinus, and a migration to the epithelium germinativum at about 6 weeks to intrauteri life. Each primordial sex cells (oogonia) is surrounded by pregranulosa cells that protect and provide nutrients oogonia and together form a primordial follicle.
Folikel Primordial
A migration of primordial follicles into the ovarian stroma and follicular cortex was produced as many as 200,000. A number of primordial follicles develop during the life of working intrauteri and during childhood, but none reached the cooking. At the time of puberty one follicle can complete the cooking process and called follicle de Graaf, where inside there are sex cells called primary oocytes.
Oosit Primer
Core (nucleus) primary oocytes contain 23 pairs of chromosomes (2n). One pair of chromosomes are chromosomes that determines sex, and called the XX chromosome. Chromosomes called autosomes other. One chromosome consists of two chromatin. Chromatin carry genes called DNA.

Meiosis First division
Meiosis occurs in the ovaries when the follicles de Graaf had finished cooking and before ovulation occurs. Oocyte or ovum nucleus split to separate chromosomes and form two sets that each contain 23 chromosomes. One set of remains larger than the others because it contains all the cytoplasm, the cell is called the secondary oocyte. Smaller cells called the first polar body. Sometimes this primary polar body may divide and will normally degenerate.
This first meiotic division caused haploid chromosomes in oocytes of secondary and primary polar body, also occurs chromatid exchange and the genetic material. Each chromosome is still carrying a chromatid without exchange, but the other one chromatid exchange experience with one chromatid to another chromosome (partner). Thus the two cells contain the same number of chromosomes, but with the genetic material of different patterns.
Oosit Sekunder
The second meiotic division usually occurs only when the head of spermatozoa through the zona pellucida oocyte (ovum). Secondary oocyte divides to form mature ovum and a polar body again, to form two or three polar bodies and a mature ovum, all contain different genetic material. These three polar bodies are normally degenerate. The mature ova that have undergone fertilization began experiencing embryonic development.
Fertilisasi
According to Sri Sudarwati (1990) fertilization is a process of fusion of two kinds of gametes to form a new individual with genetic characteristics derived from both parentalnya. Meanwhile, according Wildan Orphans (1990) fertilization is the entry of spermatozoa into the ovum. After a spermatozoon comes in, the ovum can grow into new individuals.
Spermatozoa around the ovum will produce the enzyme hyaluronidase, an enzyme which breaks protoplasm ova protective order to penetrate an ovum with a little more easily. Enzyme damaging corona radiata and zona pellucida penetration allows for only one sperm only. Body and tail separated from the sperm head immediately after entry into the ovum. Immediately after the two cells together, the two poles of the coil in the core (nucleus) ova having the second meiotic division and are able to unite with the sperm nucleus, chromosome, forming a diploid (2n).