Fertilization

Question 1

Fertilization definition and result

Answer 1

• fusion of nuclear material of 2 haploid cells

- Result is diploid cell and a new organism

Question 2

Fertilization:
when?
where?
steps?

Answer 2

• w/in 24 hrs of ovulation
• in ampulla of uterine tubes

1. Capacitation
2. penetrate corona radiata and zona pellucida (acrosome reactions)
3. Oocyte activation

Question 3

sizes

Answer 3

Oocytes = biggest human cell
sperm = smallest human cell

Question 4

Journey of sperm and required stuff for their survival

Answer 4

male reproductive/urinary tract –> deposition in vagina –> female reproductive tract to oviduct

Need seminal fluid, female factors, and capacitation

Question 5

Seminal fluid components

Answer 5

Water –> to flow
Buffers to neutralize acidity of m/f paths
Nutrients: sugar and enzymes which contribute to availability of nutrients
Zinc = antibacterial activity
Clotting and liquefaction factors
Prostaglandins - contraction of smooth muscle in male path
ATP

Question 6

clotting and liquefaction factors

Answer 6

-Initial coagulation (20 mins) to decrease loss from vagina
(caused by semenogelin)

-then liquefaction to increase movement towards cervix
(caused by prostate specific antigen)

Question 7

female factors helping sperm transport

Answer 7

Orgasm - vaginal contractions increase pressure to push sperm into uterus

uterine contractions: penile mechanical stimulation of cervix activates oxytocin

Cervical mucus

• varies in viscosity
• estrogen has thinning effect –> thinnest at ovulation so sperm has best chance

Question 8

female factors not helping sperm transport

Answer 8

acidity of vagina

cervical folds/crypts

ciliary muscular action by fimbriae and oviducts
-estrogen increases # of cilia and progesterone increases ciliary movements

Leukocytes attack sperm and get rid of dead ones

Question 9

Sperm Stats

Answer 9

• 200 mil deposited
• less than 1 mil enter cervix
• few thousand reach oviducts
• few hudred reach the right oviduct
• 20-200 reach oocyte

live 6 days

Question 10

Capacitation of sperm

Answer 10

• destabilization of sperm membrane
• increases motility
• hyaluronidase enzyme availability

Hyaluronidase enzyme degrades hyaluronic acid which is b/t follicular cells in corona radiata and on their membrane

sperm penetrate through corona radiata cells

Question 11

Acrosome reaction

Answer 11

• sperm binds to ZP3 (glycoprotein) of zona pellucida
• exocytosis of enzymes from sperm used to break through zona pellucida
• sperm makes contact with vitelline membrane (the one that surrounds the oocyte)
• binding to ZP2 maintains connection between sperm and oocyte

Question 12

After zona pellucida

Answer 12

sperm moves through perivitrelline space

• lies down next to egg cell membrane
• fusion of cell membranes
• entry of sperm into egg cytoplasm

Question 13

Egg activation steps

Answer 13

1. cortical reaction
2. complete 2nd meiosis (haploid cell and polar body)
3. Mitotic preparation

Question 14

Cortical reaction

Answer 14

• prevents polyspermy which is lethal
• cortical granules beneath oocyte cell membrane release enzymes when activated by high calcium levels at sperm fusion
• enzymes down regulate receptors on zona pellucida, giving the sperm no access to the egg

Question 15

Meiosis

Answer 15

Completion of 2nd meiotic division

• 2ndary oocyte stuck in Metaphase II at ovulation
• calcium stimulates completion

Ovum pronucleus
-nuclear membrane forms around DNA

Question 16

Sperm entry into egg cytoplasm

Answer 16

• nuclear membrane breaks down
• sperm pronucleus forms (new membrane) –> sperm DNA forms chromosomes
• migration of pronuclei towards each other on microtubules
• pronuclei fuse into diploid zygote = new genetic material = “syngamy”
• Mitotic divisions begin: blastomeres

Question 17

What happens if chromosomal aberrations occur?

Answer 17

90% of the time, embryos spontaneously abort within 1st trimester

Question 18

Twins

Answer 18

Fraternal

• -2 ova are fertilized by dif sperm
• dizygotic

Identical

• 1 ovum is fertilized by one sperm
• early embryo divides
• monozygotic

Question 19

In vitro fertilization

Answer 19

• Treatment with high FSH causes overproduction of eggs/ follicular development
• THen treatment with hGH (human chorionic gonadotropin which is similar to LH)
• Then eggs are removed before ovulation (“aspiration” of up to 12)
• mix eggs with sperm in tume
• Post fertilization embryos are transplanted to uterus via catheter
• Transplant happens of day 3 (8 cells) to 5 (70-100 cells)