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By the end of this section, you will be able to:
  • Describe the obstacles that sperm must overcome to reach an oocyte
  • Explain capacitation and its importance in fertilization
  • Summarize the events that occur as a sperm fertilizes an oocyte

Fertilization occurs when a sperm and an oocyte (egg) combine and their nuclei fuse. Because each of these reproductive cells is a haploid cell containing half of the genetic material needed to form a human being, their combination forms a diploid cell. This new single cell, called a zygote    , contains all of the genetic material needed to form a human—half from the mother and half from the father.

Transit of sperm

Fertilization is a numbers game. During ejaculation, hundreds of millions of sperm (spermatozoa) are released into the vagina. Almost immediately, millions of these sperm are overcome by the acidity of the vagina (approximately pH 3.8), and millions more may be blocked from entering the uterus by thick cervical mucus. Of those that do enter, thousands are destroyed by phagocytic uterine leukocytes. Thus, the race into the uterine tubes, which is the most typical site for sperm to encounter the oocyte, is reduced to a few thousand contenders. Their journey—thought to be facilitated by uterine contractions—usually takes from 30 minutes to 2 hours. If the sperm do not encounter an oocyte immediately, they can survive in the uterine tubes for another 3–5 days. Thus, fertilization can still occur if intercourse takes place a few days before ovulation. In comparison, an oocyte can survive independently for only approximately 24 hours following ovulation. Intercourse more than a day after ovulation will therefore usually not result in fertilization.

During the journey, fluids in the female reproductive tract prepare the sperm for fertilization through a process called capacitation    , or priming. The fluids improve the motility of the spermatozoa. They also deplete cholesterol molecules embedded in the membrane of the head of the sperm, thinning the membrane in such a way that will help facilitate the release of the lysosomal (digestive) enzymes needed for the sperm to penetrate the oocyte’s exterior once contact is made. Sperm must undergo the process of capacitation in order to have the “capacity” to fertilize an oocyte. If they reach the oocyte before capacitation is complete, they will be unable to penetrate the oocyte’s thick outer layer of cells.

Contact between sperm and oocyte

Upon ovulation, the oocyte released by the ovary is swept into—and along—the uterine tube. Fertilization must occur in the distal uterine tube because an unfertilized oocyte cannot survive the 72-hour journey to the uterus. As you will recall from your study of the oogenesis, this oocyte (specifically a secondary oocyte) is surrounded by two protective layers. The corona radiata    is an outer layer of follicular (granulosa) cells that form around a developing oocyte in the ovary and remain with it upon ovulation. The underlying zona pellucida    (pellucid = “transparent”) is a transparent, but thick, glycoprotein membrane that surrounds the cell’s plasma membrane.

Questions & Answers

why rbc is biconcave?
Sudhakar Reply
to carry oxygen easily
anwaar
What part of the brain controls the body temp
Ridwan
hypothalamus
JAYESH
what are epithelial tissues
Sachibu Reply
epithelial tissue that cover overall parts of the body and it's free from blood and nerves
Bhanu
Epithelial tissues are composed of cells laid out in sheets with strong cell-to-cell attachments.
Duah
Epithelial tissues perform a variety of functions that include; protection, secretion, filtration, diffusion, absorption, etc.
Duah
what control the flow of the blood ?
Donkor Reply
the pumping action of the heart
Holly
what is bony promises on the human body
Kelly Reply
what is the bony promises on human body
Kelly
what are bony prominences on human body
Kelly
support of the body
Bhanu
what are the characteristics of blood
yeboah Reply
they are red in colour
Tawoi
why blood is red in color?
Sudhakar
Me phone no petandi meku doubt vunte nenu phone chesi cheputhanu
Mohan Reply
What is respiratory disease
Rita Reply
emphysema
Sudhakar
What are the importance of homeostasis in human body?
Pablo Reply
homeostasis
Abena
it help to keep our salt and water balance
Husna
Homeostasis regulates and mentain internal equilibrium (ie temperature and pH) of the body.
Edmund
maintain temp and ph so our enzyme works properly
Husna
The inability of the body regulating and maintaining the temp. and pH results in disease affection.
Edmund
formation of the bone
Ali Reply
.
mohamed
عاوز ايه يعني من الفورمايشن
Doctor
notes on cell theory and discovery
Masika Reply
Cell theory are a set of rules for overall knowledge on cells. The most famous set of rules include: All cells arise from other cells. The cell is the functional unit of life. The structure (organelles) and morphology of the cell indicates it's main functions.
Carmelo
Antonie Van L. was the first to actually observe alive microorganisms (such as protist and bacteria) in a microscope in the 1600s.
Carmelo
electro phisiology meand
aparna Reply
rouleaux formation factors
Hridya Reply
can anyone suggest me how to learn forearm and hand topic of anatomy?
Anjali Reply
can anyone suggest me how to learn forearm and hand anatomy topic?
Anjali
can anyone suggest me how to learn forearm and hand topic of anatomy? pls pls tell
Anjali
check out youtube videos for trickss and while learning the boness part keep the bone wid u and learn ..... hope it helps u
Subuhi
ohk
Anjali
formation of the bone
Ali
what is the space between d dura mater and pia mater
Uwakwe Reply
Subdural space
Juveriya
Actually sub dural space is space between dura and arachnoid mater And sub arachnoid space is space between arachnoid and pia mater
Juveriya
the smallest bone in the body
Bahja Reply
stapes is the smallest bone in human Body
dipayan
Yeah
Ridwan
what is cell membrane
Hajara
cell membrane is like a protective cover of a cell and it's cytoplasm
dipayan
thanks
Hajara
list two adpitive mechanism that control homeostasis condition
Hajara
positive and negative feedback Mechanism
dipayan
@Dipayan, a cell membrane encloses and surrounds the cytoplasm of the cell. It's structure varies between species of life (eukaryotes, archaea, bacteria), but it is mostly composed of phospholipid, arachidonic acid, proteins, glycoproteins, glycolipids, and cholesterol.
Carmelo
and the glycoprotein and polysaccharides of the cell membrane forms the glycocalyx which has several functions especially in a bacteria.
Norom

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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