Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Fertilization - Pre-Embryonic Development
Ovulation generally takes place between 9th to 14th day after the end of last menstrual period. Fertilization of oocyte initiates development and should take place within about 24 hours after ovulation; or else the oocyte degenerates. The female reproductive tract plays a very active role in the fertilization process. Newly ejaculated mammalian sperms are not able to undergo acrosomal reaction unless they reside in the female reproductive tract for some time. This need is known as capacitation. During this process the sperm membrane cholesterol is thought to be reduced like some of it is taken up by albumin molecules present in the female reproductive tract. With no these changes in the membrane the acrosomal reaction cannot occur. Except for this, there are coating factors or inhibitors that are to be removed that would otherwise prevent fertilization.
To reach the ovum the sperm has to move upwards by the uterus aided by its tail as well as the secretions of the cervix which contains a protein mucin. This forms threadlike highways all along which the sperm travels. While the sperm reaches the ovum (secondary oocyte) it invades the follicular cells. An enzyme hyaluronidase is released from the acrosome of the sperm head. This enzyme take out the extracellular matrix and disperses the corona radiata cells. Another enzyme acrosin digests a path for the sperm through the zona pellucida. In the acrosome of the sperm this trypsin like enzyme is inactive and requires to be activated by a glycoprotein in the female reproductive tract. Once a sperm passes by the zona pellucida, this covering becomes impenetrable by other sperms. This is termed as the zona reaction. The structure of the membrane changes and lysosomal enzymes are released from the secondary oocyte which prevents other sperms from attaching to the membrane. Usually only one sperm enters the ovum. Two sperms may take part in fertilization under an abnormal process known as dispermy. The resulting embryo consists of 69 chromosomes and may appear normal, but it is always aborted. Occasionally a triploid infant may be born but it dies shortly.
Thus polyspermy does not generate viable embryos. As the sperm head enters the egg it loses its tail. The secondary oocyte completes its second meiotic division making a mature ovum and a second polar body. The nuclei of the sperm and ovum fuse to form the zygote completing the process of fertilization. The offspring's sex is ascertained at fertilization by the type of sperm that enters the ovum. You would recall that all female gametes bear X chromosome while the male gametes may bear either the X or the Y chromosome. If the ovum is fertilized by a sperm bearing X chromosome it will develop into a female; and into a male child if it is fertilized by a chromosome bearing the Y chromosome. Which type of sperm may fertilize the ovum de ends entirely on chance. Therefore, whether the offspring will be a boy or a girl is the genetic responsibility of the father rather than of the mother.
In addition, pregnancy or constipation may worsen GERD by increasing intra-abdominal pressure. Secondary causes of GERD include reflux caused by acid hypersecretory states, connec
After Abutment Connection The patient may complain of pain during screw tightening. Any clinical evidence should be looked into. It is important not to overtighten and overtorq
HOW TO START.
Asexual Reproduction in Animals Reproduction may be referred as production of true copies. Most of the animals that are quite familiar to us generate male and female gametes (
Explain about Mental foramen and nerve Mental foramen is a strategically important landmark during osteotomy procedures. Its location and the possibility that an anterior loop
Fatty acids are a very significant adenosine triphosphate (ATP) and source of energy for various cellular organisms. Over fatty acids, glucose and other nutrients can be stored eff
What is the estimated percentage (in mass) of water in the human body? Is this percentage expected to be larger in the adult or in the old individual? About 65% of the human in
Mechanoreceptors - Receptors Mechanoreceptors involve those receptors involved in perception of touch, pressure, tension, hearing, vibration, gravity, muscle tension etc. Th
Explain the introduction of history of mart disease? Cardio-vascular diseases (CVD) are the leading causes of death and disability both in the developed and the developing na
Neural Basis of Responses to Sex Pheromones The ability of insects to detect and discriminate between a variety of pheromones with great sensitivity depends on the presence of
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +1-415-670-9521
Phone: +1-415-670-9521
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd