Flashcards in Fetal development and Embryology Deck (69)
Describe the process of sperm production.
The process starts with the mitotic division (duplication) of the stem cell located inside the basement membrane of the tubules inside the testes. Then, each of the duplicated stem cells (46 chromosomes) will undergo meiosis division to become the sperm cells that have 23 chromosomes.
How come men have unlimited sperm cells?
Because their stem cells duplicate themselves before developing so they never run out of copies. However the fact that they duplicate then divide mean that there is more of a chance of genetic errors.
How long does the maturation process of sperm take?
around 24 days. This means that if the father uses any toxic substances like smoking or drugs then it can effect the sperm for almost a month
What is the acrosome?
like a crown or helmet which contains enzymes that help the sperm to cross the ovum wall. The acrosome will open the ovum wall and only the head of the sperm, containing the make DNA will enter the ovum. The rest of the cellular structures will stay outside.
What is capacitation?
The maduration that the sperm have to go through in order for fertilisation to happen. This happens inside the female genital tract. The female body sends chemical substances that will unlock certain receptors in the sperm. Which make it capable of reacting to the environment of the female body.
Where does capacitation happen?
Inside the cervical crypts
What happens if the women is in a fertile period?
The cervical music will form channels where the sperm can 'slide' through. Sperm is then stored in cervical crypts, where the capacitation process finishes. These crypts act as a reservoir releasing sperm over several hours Maximising the chances of fertilisation.
What is triggered by an orgasm?
Strong uterine contractions then suction up the sperm into the uterine cavity.
Describe the two walls of the egg.
These walls allow or block the entrance of sperm. The outer one is called the Corona radiata: once sperm gets here the enzyme in the acrosome are released to trigger the zona pellucida to allow the sperm head to penetrate the ovum.
5 steps of fertilisation
1. penetration of corona radiata
2. Species recognition Acrosome reaction
3. Penetration of zona pellucida. Cortical reaction.
4. Gamete fusion
5. Meiosis completion
What triggers the sperm to penetrate the corona radiata?
chemicals produced by the oocyte
What is the cortical reaction?
It happens once a sperm has entered the zona pellucida and it means that no other sperm will be able to enter
What are the 3 stages of fetal development?
Pre embryonic: until implantation
Embryonic: 2-8 weeks
Fetal: week 9 to birth
What happens to the zygote within 24 hours?
The zygote undergoes mitosis and splits into smaller cells. This is called cleavage. Day 2 embryo
By day 4 what is it called?
Morula and has 16-20 cells
What is it called at day 10?
What happens of the 5th day?
Fluid accumulates in the space between the peripheral and central cells of the morula and becomes the hollow blastocyst
What happens when the fluid penetrates the morula?
It divides the cell into 2 main areas: the inner cells becomes the embryoblast and the flattened outer cells
What will the embryoblast become?
What will the flattened outer cells become?
What is the layer of flattened outer cells called?
What happens to the zona pellucida after fertilisation?
It hardens after the cortical reaction and it aims to keep the ball of cells together until they develop into more complex structures. this will disappear with implantation. When the trophoblast will develop further.
What happens after the blastocyst has implanted into the endometrium?
The embryoblast will have divided into 2 layers of different cells: the epiblast (closer to the trophoblast and hypoblast
After it has divided into the epiblast and hypoblast what is it called?
The bilaminar disc
What is the process that puts an end to the pre embryonic stage and starts the embryonic one called?
It develops 3 layers of tissue while the embryo grows in size and fluid fills up 2 cavities in the embryo. This will create the amniotic cavity from the epiblast/ectoderm and the yolk sac from the hypoblast/endoderm.
What has the epiblast become?
What has the hypoblast become?
What was the ectoderm form?
skin, hair and nervous system