Human Biology (Fertilisation) Flashcards
What is the usual method of fertilisation and how does it work?
The usual method is sexual intercourse. Male sperm need to be brought into contact with an ovum produced by the female
What is a fertilised egg called?
A zygote.
Where does fertilisation normally occur?
Fertilisation normally occurs in the uterine tubes when the ovum is about one-third of the way down the tube.
What occurs to the nuclei of the sperm and ovum?
The nucleus of the oocyte develops into a female pronucleus (a haploid nucleus of the oocyte), which fuses with the male pronucleus to form a single nucleus that now has the diploid number of chromosomes.
What occurs to the secondary oocyte once the sperm has entered?
The secondary oocyte completes the second meiotic division
what are the components of semen?
Semen contains the secretions of the seminal vesicles, bulbo-urethral glands and prostate gland. The greatest contribution comes from the seminal vesicles, which produce a thick fluid containing nourishment for the sperm
What needs to occur to the male for sexual intercourse to take place efficiently?
For sexual intercourse to take place, and for sperm to be deposited in the vagina, the penis must become become erect. An erection results from blood rushing into the spaces of the erectile tissue of the penis.
What occurs to the sperm once it has entered the oocyte?
- The tail is absorbed
- The head begins to move through the cytoplasm in the form of a male pronucleus – the haploid nucleus of the sperm.
What two layers are the secondary oocyte made of?
The outer corona radiata consists of follicle cells held together by cementing materials that contain acid.
The inner zona pellucida is a glycoprotein matrix surrounding the plasma membrane of the oocyte.
What is insemination?
The sperm are released in the vagina at the entrance to the uterus.
What is ejaculation?
Rhythmic contractions of the epididymis, vasa deferentia, seminal vesicles and prostate gland propel the contents of the ducts and glands into the urethra and then out of the body. The ejaculated material consists of semen, which contains around 250 to 300 million sperm.
What does the fertilisation membrane inhibit?
More sperm from entering the oocyte.
What occurs when the plasma membranes of the oocyte and spermatozoa fuse?
When the plasma membranes of the oocyte and spermatozoa fuse, the nucleus of the sperm enters the ovum, stimulating the formation of a fertilisation membrane around the oocyte.
What does an acrosomal reaction do, and how does it affect the zona pellucida?
This causes digestive enzymes from the acrosome to be released. These enzymes break down the glycoprotein matrix of the zona pellucida, giving the sperm access to the plasma membrane of the oocyte.
In relation to the corona radiata, why is it necessary to have a large number of sperm?
Because the more there is, the easier it will be for them to release enzymes to loosen the cells of the corona radiata, allowing a cell to penetrate the corona radiata.
