Fertilization And Implantation

Question 1

How many sperm enter the vagina near the uterus?

Answer 1

~300 with ~200 reaching the ampulla of oviduct

Many barriers to overcome including distance, immune system, secretions and timing

Question 2

If a male secretes <20 million sperm/ejaculate what is this considered as?

Answer 2

Infertility

Question 3

What action helps to move sperm through the uterus/cervix?

Answer 3

Myometrium contractions as a result of estrogen near the ovulation period

Question 4

What are the 3 barriers that must be breached in order for fertilization to occur?

Answer 4

The expanded cumulus (corona radiata), ZP and plasma membrane of the oocyte

Question 5

What is the cumulus cell matrix?

Answer 5

Predominantly hyaluronic acid and is digested by sperm via membrane bound hyaluronidase

Question 6

What occurs during week 1 of embryonic development?

Answer 6

Cleavage (cell division without growth)
Embryo reaches 16 cell stage morula on day 3
Early blastocyst on day 4
Implantation occurs day 6-8

Question 7

What is cleavage?

Answer 7

Individual cells = blastomeres which are totipotent
Mitotic divisions maintain 2N diploid complement
Cells become smaller

Question 8

Describe human chorionic gonadotropin (hCG)

Answer 8

Secreted by trophoblast and syncytiotrophoblasts
Measurable in blood ~8 days post ovulation
Structure closely related to LH

Question 9

What are the functions of hCG?

Answer 9

Prevents involution of the corpus luteum
Prevents menstruation
Leads to increased secretion of progesterone and estrogen

Question 10

How does hCG function as an autocrine growth factor?

Answer 10

Stimulates trophoblast growth and development + stimulates placental growth

Question 11

What is ectopic implantation?

Answer 11

Implantation somewhere other than the uterine fundus
Most commonly in the oviduct (tubal pregnancy; MC in ampulla)
No decidualization
Invasion is not controlled and can rupture the tissues and cause hemorrhage

Question 12

Describe placentation

Answer 12

Spaces (lacunae) appear within syncytiotrophoblasts ~day 9 which break maternal capillaries and are filled with endometrial secretions, maternal blood, and digested matrix for nutrient transfer
Includes the formation of primary, secondary and tertiary villi

Question 13

How are primary villi formed?

Answer 13

Proliferation of syncytiotrophoblast and cytotrophoblast to lacunae

Question 14

How are secondary villi formed?

Answer 14

Mesenchyme cells form extraembryonic mesoderm invade villi and is now called the chorionic membrane

Question 15

How are tertiary villi formed?

Answer 15

Eventually mesenchymal cells form fetal blood vessels de novo