Fertilization and Implantation Flashcards Preview

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Flashcards in Fertilization and Implantation Deck (54)
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1
Q

Both the sperm and the oocyte must travel to where for fertilization?

A

Ampulla of oviduct

2
Q

What must happen in order to expose binding sites of the sperm for the ooctye’s zona pellucida?

A

Sperm Capacitation

3
Q

Epididymal sperm’s plasma membrane is coated with what?

A

Many surface molcules/proteins

4
Q

The sperm that is then ejaculated becomes coated with?

A

Seminal plasma

5
Q

Describe seminal plasma

A

Seminal plasma proteins coat the surface molecules on the sperm that is ejaculated

6
Q

Once the ejaculated sperm reaches the female tract, then what occurs?

A

Capacitation

7
Q

Describe capacitation

A

The seminal plasma coatings and sperm surface molecules are REMOVED to expose portions of the sperm that can bind with the oocyte’s zona pellucida

8
Q

Incapacitated sperm (have yet to undergo capacitation) can bind to?

A

Epithelial cells in the oviductal isthmus

9
Q

What does the binding of incapacitated sperm to the isthmus do?

A

Extends the sperm lifespan

INCREASES the probability that the sperm will be in the oviduct when the egg is ovulated!

10
Q

Once incapacitated sperm are capacitated what happens?

A

They are unbound from the isthmus

11
Q

What creates a hyperactive sperm?

A

Sperm capacitation + Chemical signals from oocyte

12
Q

Hyperactivation of sperm results in what physical change?

A

A change in flagella motion from wave-like to whip-like

13
Q

What 3 things does hyperactivation of sperm help with?

A
  1. Increases sperm mobility
  2. Detaches sperm from the epithelium
  3. Helps propel the sperm through the outer layers of the egg to reach the plasma membrane
14
Q

What 3 barriers must be breached during fertilization?

A
  1. Expanded cumulus (corona radiata)
  2. Zona pellucida
  3. Oocyte plasma membrane
15
Q

What is the cumulus cell matrix of the oocyte made of?

A

Hyaluronic acid

16
Q

What does the sperm use to digest the cumulus cell matrix of hyaluronic acid?

A

Hyaluronidase

17
Q

The zona pellucida of the oocyte contains glycoproteins. Which one does the sperm have a receptor for?

A

ZP3

18
Q

Once the sperm binds ZP3 on the oocyte, what happens next?

A

Acrosome reaction

19
Q

Describe the acrosome reaction

A
  • The sperm’s plasma membrane fuses with its acrosomal membrane
  • This causes release of acrosomal enzymes
  • These enzymes digest the zona pellucida locally
  • The sperm can then push forward toward the plasma membrane of the oocyte
20
Q

What protein does the sperm possess to bind to the oocyte plasma membrane?

A

Izumo protein of the sperm binds to the Izumo receptor on the oocyte plasma membrane

21
Q

Once the sperm Izumo protein binds to its receptor on the oocyte, then what happens?

A

The sperm enters the egg

22
Q

Once the sperm enters the egg, list the main things that occur next

A
  • Sperm DNA de-condenses
  • Pronucleus membrane forms around DNA
  • Cortical reaction
  • Male and female chromosomes replicate as pronuclei move together
  • Fusion of pronuclei = beginning of embryonic development!
23
Q

Describe the cortical reaction

A

Triggered by the fusion of the egg and the sperm

- Release of Ca++ alters zona pellucida proteins that BLOCKS the binding of other sperm to prevent polyspermy

24
Q

What does the cortical reaction prevent?

A

Polyspermy (binding of additional sperm to the oocyte)

25
Q

Cleavage

A

Cell division without growth

26
Q

Main steps in week 1 embryonic development

A

Cleavage
Embryo reaches 16 cell stage morula
Early blastocyst
Implantation

27
Q

Around what day is implantation

A

Day 8

28
Q

What is blastocyst hatching?

A

Hatching of the embryo from the zona pellucida prior to implantation

29
Q

Inability for the blastocyst to hatch can result in?

A

Infertility

30
Q

Premature blastocyst hatching can result in?

A

Abnormal implantation

31
Q

hCG

A

Human Chorionic Gonadotropin

32
Q

What secretes hCG?

A

Trophoblasts and Syncytiotrophoblasts

33
Q

What are the functions of hCG?

A

Prevents menstruation
Increases progesterone and estrogen secretion
Stimulates trophoblast and placental growth

34
Q

What are the main stages of implantation?

A
  1. Apposition
  2. Attachment
  3. Invasion
35
Q

Describe the apposition phase of implantation

A

Contact between the endometrium and trophoblasts

  • Usually in a crypt of endometrium
  • Inner cell mass rotation near endometrial epithelium
36
Q

Describe the attachment phase of implantation

A

Trophoblast cells adhere to endometrial epithelium

- Initiates decidualization

37
Q

Describe the invasion phase of implantation

A

Degradation of endometrial epithelial cells AND

Trophoblast fusion and formation of syncytiotrophoblasts

38
Q

What can the syncytiotrophoblasts do during implantation?

A

Protrude through basement membrane and reach endometrial stromal cells

39
Q

Main attributes of syncytiotrophoblasts?

A
  • Express surface adhesive proteins
  • Breakdown of endometrial extracellular matrix
  • Secrete hCG
  • Phagocytosis and bidirectional transfer of materials
40
Q

What are the things syncytiotrophoblasts can secrete to help break down the endometrial extracellular matrix?

A

Metalloproteinases and Angiogenic factors

41
Q

Decidualization occurs in what phase of implantation?

A

Attachment

42
Q

Decidualization

A

Maternal stromal cell changes in response to invasion and progesterone

43
Q

During decidualization, what do the stromal cells change to?

A

Enlarged, glycogen-filled cells

44
Q

After decidualization, the endometrium is called?

A

Decidua

45
Q

After decidualization, the endometrium is ready for?

A

Implantation

46
Q

What 2 things does the decidua do?

A
  1. Forms sheet with adhesive junctions to inhibit migration of embryo
  2. Production of signals to prevent embryo from invading myometrium
47
Q

If the decidua does not not allow the embryo to invade the myometrium, what can occur?

A

Postpartum hemorrhage

48
Q

Ectopic implantation

A

Implantation anywhere other than the fundus of the uterus

49
Q

With an ectopic implantation, what does not occur?

A

Decidualization

50
Q

Since decidualization does not occur with an ectopic pregnancy, the invasion is NOT controlled. What will this cause?

A

Rupture of tissues = hemorrhage

51
Q

Placentation

A

Spaces appear within syncytiotrophoblasts around day 9

- Formation of primary, secondary and tertiary villi

52
Q

Primary villus

A

Syncytiotrophoblasts and cytotrophoblasts

53
Q

Secondary villus

A

Primary villus + mesenchyme

54
Q

Tertiary villus

A

Secondary villus + fetal blood vessels formed de novo