Fertilization is
the fusion of gametes to produce a new organism
- sperm fusing with an ovum, which eventually leads to the development of an embryo
- can be internal or external
Fertilization process
- Penetration of the zona pellucida by the spermatozoan
- Enzyme hyaluronidase and acrosin (proteolytic enzyme from acrosome)
- Spermatozoon motility (motility stop once contact with the oocyte has been made)
- The zona reaction occurs after penetration of the zona pellucida and protect the oocyte from further penetration by other spermatozoon.
- Pronuclei develop from the nuclei of the spermatozoon and oocyte which followed by fusion of respective pronuclei to form zygote with the diploid number of chromosomes.
- Fertilization is complete after fused pronulei have dissapeared and are replaced by chromosomes groups united in prophase of the first mitotic division.
- Zygote remains in the uterine tube for 3-4 days before being transferred to the uterus
- Uterine motility is unfavourable for zygote survival and estrogen dominance at etrus must be changed to progesterone dominancem which with the formation of the corpus luteum.
- Progesterone influence on the uterus and promotes development of a glandular endometrium that can secrete uterine milk ( a nutrient medium for embryon preceding its implantation)
Upon fertilization
- Estrogen level will be sustained, while progesterone increased
- The cells in cleavage stage embryo is known as blastomeres
- cell division produces a 16-32 cell structure known as morula - A cavity forms within morula by 6 to 8 days of age, and the cell mass is called a blastocyst
- Blastocyst composed of a hollow sphere of trophoblast cells inside of which is a small cluster cells called the inner cell mass.
- Trophoblast goes on to contribute to fetal membrane systems and the inner cell mass is destined to become the embryo and fetus.
- Stretched and softened zona pellucida ruptures on the equitorial plane allowing blastocyst to escape by a process of hatching.
- The blastocyst attaches to the endometrium -end of oocyte period.
Embryonic period
rapid growth, major tissues, organs and system develop and major features of external body form become recognizable
Fetal period
extends from embryonic period until birth and begins at about day 45 of gestation in the cow
Zone hatching
- blastocyst hatch or escape from zona pellucida
to perform implantation - occur in uterus
enzymatic factors produced in uterus
-estrogen in uterus cause softening in zona hatching
-physical factors
-expansion and contraction of blastocyst result in tear in zona hatching
Post hatching
- Blastocyst escape from zona pellucida provides first cell to cell contact between conceptus and maternal uterine epithelium
- Contact essential for nutrient exchange and placental development
- After hatching, blastocyst (conceptus) enters a phase of rapid growth (hyperplasia) and development
- Physically cover large portion of the endometrium to regulate release of PGF2 to prevent luteolysis (intrauterine Migration & Spacing)
Ectoderm forms
external structures
eg: skin, hair, hooves, mammary gland, neural
Mesoderm forms
heart, muscle, bone
Endoderm forms
internal organs, colon, liver, pancrease
