(Source: Ferenc Husvéth)
Capacitation, generally speaking, is the change sperm undergo in the female reproductive tract that enables them to penetrate and fertilize an egg.
This step is a biochemical event; the sperm moves normally and looks mature prior to capacitation. It is important to note that once the sperm reaches the egg, it does not mean that it is capable of fertilizing it immediately. In order to fertilize the egg, the sperm must undergo the process of capacitation in the reproductive tract where a number of enzymes and signaling molecules are involved. This process can take around 10 hours, which means that the fertilization time is approximately 24 hours.
Capacitation causes a series of changes in sperm’s biochemical composition and structure such that they develop increased motility and are prepared for interactions with the egg (or oocyte) at fertilization. Essentially, the sperm becomes able to break through the membrane (known as the zona pellucida) that surrounds the egg. Once sperm is able to traverse the zona pellucida, it can begin the process of fertilizing the egg.
It is also important to consider the two distinct types of fertilization when thinking about capacitation and how it occurs:
Nuts & Bolts: Capacitation
To learn more about, please visit our series of posts about the male reproductive system:
Albumin - a protein made by your liver that helps keep fluid in your bloodstream so it doesn't leak into other tissues. Albumin also carries various substances throughout your body, including hormones, vitamins, and enzymes.
Biochemical - relating to the chemical processes and substances which occur within living organisms.
Conception - the process of becoming pregnant involving fertilization or implantation or both.
Ejaculation - the action of ejecting semen from the body.
Endocrine System - a chemical messenger system consisting of hormones, the group of glands of an organism that secrete those hormones directly into the circulatory system to regulate the function of distant target organs, and the feedback loops which modulate hormone release so that homeostasis is maintained.
Enzyme - a substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction.
Epididymis - a highly convoluted duct behind the testis, along which sperm passes to the vas deferens.
In vitro fertilization - process of fertilisation where an egg is combined with sperm outside the body.
In vivo fertilization - fusion of sperm with egg occurs within the body of a female.
Lipoprotein - any of a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.
Oocyte - a cell in an ovary which may undergo meiotic division to form an ovum.
Spermatozoa - the mature motile male sex cells of an animal, by which the ovum is fertilized, typically having a compact head and one or more long flagella for swimming.
Zona pellucida - the thick transparent membrane surrounding a mammalian ovum before implantation.
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