Fertilization to birth Flashcards
1
Q
Describe fertilization:
A
- Occurs in the oviduct
- Egg takes about 4 days to travel down oviduct to uterus
- Fertilization must occur within 12-24 hours of release from ovary
- The successful sperm must therefore navigate the vagina —> cervix —> uterus —> most of the oviduct
2
Q
Describe the process of fertilization:
A
- Multiple sperm reach the egg
- Egg coating consists of outer corona radiata and the thicker zona pellucida
- When sperm hit corona radiata, acrosomes release enzymatic contents
- Enzymes begin to break down the zona pellucida, sperm keep pushing at egg
- Hundreds of sperm may be required to clear one path to egg
3
Q
What happens when one sperm gets into the egg?
A
- Egg membrane changes (depolarizes) (so no more sperm can bind to it)
- Sperm head collapses, and sperm nucleus fuses with egg nucleus (within 12 h)
- Resulting single cell with 46 chromosomes is called a zygote
- Takes several days to get to uterus but begins to divide while in oviduct
4
Q
Describe cleavage:
A
- Zygote begins to divide within 30 hours of fertilization
- Cells division occurs quickly with little time for growth, as a result zygote remains same size, just made of many small cells instead of one big one
- Division without overall growth is cleavage
5
Q
Describe morula:
A
- When zygote is 16 cells, becomes morula
- Morula enters uterus 3-5 days after fertilization
- Begins to fill with fluid from uterus – allows two groups of cells to form
6
Q
What is a blastocyst?
A
- When two groups of cells have formed
- Hollow structure
- Outer layer of cells is trophoblast
- Goes on to form chorion then placenta
- Inner is inner cell mass (embryoblast)
- Goes on to form embryo
7
Q
Describe implantation:
A
- Occurs around 10th to 14th day
- Trophoblast secretes enzyme to break down part of endometrium
- Blastocyst settles in to endometrium
- Woman is now officially pregnant
- Trophoblast starts to secrete hCG (human chorionic gonadotropin)
8
Q
Describe hormone regulation through pregnancy:
A
- hCG secretion continues for two months to maintain CL
- CL remains for pregnancy but placenta secretes most of estrogen and progesterone after first trimester
9
Q
Describe gastrulation:
A
- Process of forming the primary germ layers of the embryo
1. Space forms between inner cell mass and trophoblast – forms amniotic cavity
2. Inner cell mass flattens into disk-like structure – embryonic disk (short stalk connects embryonic disk to endometrium)
3. Two layers form in embryonic disk (ectoderm —> outer layer, endoderm —> inner layer)
4. Third layer forms, mesoderm —> middle layer - Ectoderm is closest to amnion, endoderm is closest to yolk sac
- All future body tissues are derived from these three germ layers
10
Q
When can a fetus be called an embryo?
A
Once the 3 layers are formed by gastrulation, it is now called an embryo
11
Q
How do identical twins happen?
A
Cell mass separates into two separate embryos before undergoing gastrulation
12
Q
How do conjoined twins happen?
A
The inner cells mass did not completely separate
13
Q
What does the ectoderm give rise to?
A
- Epidermis
- Nervous tissue and sense organs
- Pituitary gland
- Adrenal medulla
- Tooth enamel
- Eye lens
14
Q
What does the mesoderm give rise to?
A
- Dermis
- Lining of blood vessels and body cavities
- Muscle
- Connective tissue
- Adrenal cortex
- Heart
- Kidneys
- Internal reproductive organs
- Spleen
15
Q
What does the endoderm give rise to?
A
- Lining of digestive and respiratory tract
- Liver
- Gallbladder
- Pancreas
- Thymus
- Tonsils
- Parathyroid and thyroid
