Fertilization & Implantation

DING DONG

It is a physiologic process where there is a rupture of the dominant follicle of the ovary

Ovulation

T/F: In ovulation, the immature egg comes out on the follicle

F → mature egg

Phases of Ovulation

Ovary → ______ & ______

Follicular & Luteal phase

Phases of Ovulation

Endometrium → _______ & ______

• Menstrual & Proliferative phase

• Secretory Phase

Follicular Phase (Ovary)

Which hormone stimulates the development of 3 to 30 primordial follicles into primary follicles?

Follicle stimulating Hormone (Stimulates follicle growth)

Follicular Phase (Ovary)

FSH is produced by your ______ gland

Pituitary Gland

Follicular Phase (Ovary)

T/F: Estrogen rise causes all stimulated follicles to mature equally.

False – estrogen rise inhibits FSH, leading most follicles to degenerate; only 1 becomes dominant.

Follicular Phase (Ovary)

What is the process called when non-dominant follicles degenerate?

Follicular atresia ( ↑ Estrogen inhibits FSH = degeneration)

Follicular Phase (Ovary)

T/F: 2 follicles becomes dominant & continues to mature after follicular atresia

False → 1 only ( survival of the fittest)

Which phase of the uterine cycle corresponds to the follicular phase?

Proliferative phase

Follicular Phase (Ovary)

T/F: Endometrial proliferation in the proliferative phase is primarily stimulated by progesterone.

False → estrogen (thickens uterine lining)

Follicular Phase (Ovary)

What happens to the uterine lining during the proliferative phase?

It thickens due to ______ stimulation (endometrial proliferation). 😜

What is released after the follicular phase?

Follicle

Which hormone surge triggers ovulation?

Luteinizing hormone (LH)

Ovulation

T/F: Ovulation occurs at the end of the luteal phase.

False → it occurs before the luteal phase, around day 14.

What happens to the dominant follicle during ovulation?

It ruptures and releases the egg.

The corpus luteum is formed before the egg is released.

False → the follicle ruptures first, then transforms into the corpus luteum.

Which hormone is dominant in the luteal phase?

Progesterone

T/F: The corpus luteum is responsible for producing progesterone during the luteal phase.

True

Around what day of a typical 28-day cycle does ovulation occur?

Day 14

What is released from the ovarian follicle during ovulation?

A mature secondary oocyte

T/F: The FSH surge triggers the release of a secondary oocyte during ovulation.

F → LH surge

Name the 2 protective structures that surround the ovulated oocyte

Zona pellucida and corona radiata

T/F: The ovulated oocyte can remain viable for fertilization for about 48–72 hours.

F → 12-24 hours

Through which structure does the ovulated oocyte travel for potential fertilization?

The fallopian tube

T/F: Without the FSH surge, ovulation will not occur.

False → LH

Fertilization: Egg as Oocyte

T/F: The oocyte is a motile cell that can move toward the sperm.

False → its nonmotile

Fertilization: Egg as Oocyte

In which stage of meiosis is the secondary oocyte arrested before fertilization?

Metaphase II

Fertilization: Egg as Oocyte

What surface feature of the oocyte increases its contact area?

Microvilli

Fertilization: Egg as Oocyte

T/F: The zona pellucida has a glycoprotein coat which promotes sperm entry.

False → it acts as a barrier to sperm.

Fertilization: Egg as Oocyte

How many layers cover the oocyte?

3

Egg → Graafian follicle

Which structure is the innermost layer of cumulus that provides vital proteins to the oocyte?

Corona Radiata

Egg → Graafian follicle

It is found between oocyte and follicular cell thin glycoproteins which surrounds the oocyte to prevent polyspermy

Zona pellucida

Egg → Graafian follicle

It has glycoproteins which bind to sperm preventing them to penetrate too deeply into the oocyte

Zona Pellucida

Egg → Graafian follicle

What is the cluster of cells directly surrounding the oocyte called?

Cumulus

Egg → Graafian follicle

The antrum is a hormone-producing layer of follicular cells.

False → it is a fluid-filled space that develops among follicle cells.

Which theca layer produces estrogen?

Theca interna

T/F: Theca externa is primarily connective tissue, not hormone-producing.

True

T/F: A sperm is small , asymmetrical and non-motile cell

False → Motile

• Its head contains hydrolases

Sperm

Which part of the sperm contains the father’s genetic material?

Head (with nucleus, 5–6 μm)

Sperm

T/F: The acrosome cap contains mitochondria for sperm movement.

False – it contains enzymes to break down the egg’s outer membrane.

Sperm

What is the narrow connecting region between the head and tail?

neck

Sperm

The sperm midpiece contains mitochondria that supply energy for movement.

True

Sperm

Which sperm structure acts as a whip-like flagellum (40–50 μm) to propel it forward?

tail

Sperm

Which structure at the tip of the sperm head contains enzymes essential for fertilization?

Acrosome

What is the process called when a secondary spermatocyte fuses with a secondary oocyte?

Fertilization

T/F: Fertilization usually occurs in the uterus.

False → it occurs in the ampullary region of the uterine tube.

How many spermatozoa are typically deposited in the vagina during intercourse?

2-5 Million

T/F: The average lifespan of sperm inside the female reproductive tract is only 24 hours.

False – it is 3–7 days (average 5 days).

Physical Stressors of Sperm (READ)

• A. ejaculation

• B. contractions in female tract

• C. change in pH environment

• D. mucous secretions

• E. defenses of female immune system

• F. anatomy of the fallopian tube (double tract fallopian tube)

Which two processes must sperm undergo to gain the ability to fertilize an oocyte?

Capacitation and the acrosome reaction

T/F: Spermatozoa are capable of fertilization as soon as they enter the female genital tract.

False → they must undergo capacitation and acrosome reaction first.

What cells may produce chemoattractants that guide sperm toward the oocyte at ovulation?

Cumulus cells surrounding the egg

T/F: Multiple sperm can successfully penetrate and fertilize the oocyte.

False – only one sperm enters; the rest help break down barriers.

What enzyme do sperm release to help disintegrate barriers around the secondary oocyte?

hyaluronidase

The barriers that sperm must overcome include the

• corona radiata

• zona pellucida

• Cortical reaction.

List the pathway of sperm through the female reproductive tract.

Vagina → Cervix → Uterus → Fallopian Tube

Most of the millions of sperm released will reach the egg.

False – only a few hundred reach the egg.

What process allows sperm to become capable of fertilization inside the female reproductive tract?

Sperm Capacitation

T/F: Capacitation is completed in the testes before ejaculation

False – it occurs in the female reproductive tract.

Which change during capacitation removes the glycoprotein layer from the sperm head, enabling egg binding?

Glycoprotein removal

T/F: Membrane fluidity decreases during capacitation to stabilize the sperm.

False – membrane fluidity increases, improving mobility.

What term describes enhanced sperm movement that helps them reach the egg faster?

Hyperactivation

Release of enzymes that allow sperm to penetrate the egg’s outer layer

Acrosome Reaction

What structure/s moves the oocyte into the fallopian tube?

Fimbriae and cilia

After being drawn into the fallopian tube, where does the oocyte move next?

Uterus

Egg Defense

What is the outermost layer of the egg, composed of follicular cells which facilitates the interaction between sperm and egg?

Corona Radiata

T/F: The corona radiata only provides a physical barrier and does not nourish the ovum.

False → it provides protection and nourishment.

T/F: Sperm can reach the inner layers of the egg without penetrating the corona radiata.

False – sperm must penetrate the corona radiata using enzymes like hyaluronidase.

T/F: The zona pellucida allows multiple sperm to penetrate the egg.

False → 1 only pero may instances na 2 nagsasabay

What is the primary function of the zona pellucida?

Protective barrier and sperm-binding

What is the primary function of the cortical reaction?

Prevent polyspermy ( fertilization of an egg by multiple sperm)

T/F: The cortical reaction occurs before any sperm fuses with the egg.

False → it occurs after a sperm fuses with the egg.

T/F: The cortical reaction alters the glycoproteins of the zona pellucida to prevent other sperm from binding.

True

What is the outcome of the cortical reaction on the zona pellucida?

It “zips up” the zona pellucida, creating a barrier to further sperm entry

How does sperm penetrate the corona radiata?

Flagellar movement pushes through, and hyaluronidase breaks down hyaluronic acid

T/F: Hyaluronic acid is a major component of the zona pellucida

False → it is a major component of the extracellular matrix of the corona radiata

Which receptor on the zona pellucida does sperm bind to for penetration?

ZP3 Receptors

T/F: The acrosome reaction occurs before sperm binds to ZP3 receptors.

False – binding to ZP3 triggers the acrosome reaction

T/F: Multiple sperm successfully penetrate the zona pellucida during fertilization.

False → only one sperm successfully penetrates

• enzyme reaction weakens/digests the barrier to allow sperm entry

T/F: Only the sperm head enters the oocyte during membrane fusion.

False → both head and tail enter the cytoplasm.

What happens to the plasma membranes during sperm entry?

The sperm plasma membrane fuses with the oocyte membrane

T/F: Entry of the sperm head and tail into the oocyte prevents competing fertilization.

False → completes fertilization

Zygote Formation (read)

• Sperm penetrates the zona pellucida

• Sperm and egg membranes fuse

• Sperm nucleus enters the egg

• Male and female pronuclei fuse → Zygote (diploid cell)

Preventing Polyspermy

What is the fast block to polyspermy?

Immediate, temporary change in oocyte membrane potential upon first sperm fusion (less significant in mammals)

Preventing Polyspermy

What triggers the slow block to polyspermy?

Calcium wave released within the oocyte

Preventing Polyspermy

T/F: Enzymes from cortical granules modify the zona pellucida and remove sperm receptors, permanently preventing other sperm from entering.

True ( Slow Block)

T/F: Zona pellucida hardens and sperm receptors are removed, permanently blocking polyspermy during Slow Block

True

What percentage of spermatozoa actually enter the uterus after ejaculation?

1%

T/F: Sperm reach the uterus immediately, within seconds.

False → trip from cervix to uterus takes 30 minutes to 6 days

Where do both sperm and oocyte meet for fertilization?

Ampulla of FT

T/F: Sperm use uterine contractions to help them reach the oocyte

True

• oocyte moves via ciliary beat and rhythmic contraction of the fallopian tube muscles too

What happens to the chromosome number after fertilization?

Restoration of the diploid number (half from father, half from mother)

T/F: Fertilization does not determine the sex of the embryo.

F → it determines sex depending on whether the sperm carries X or Y.

Which sperm chromosome combination produces a female embryo?

X-carrying sperm (XX)

Which sperm chromosome combination produces a male embryo?

Y-carrying sperm (XY)

T/F:Fertilization initiates cleavage of the zygote.

True

Clinical Correlates: Contraceptives

• Barrier Method

  • Condoms containing spermicides

  • Female condom lining vagina

• Hormonal Method

  • Estrogen and/or progestin - inhibits ovulating by preventing release of FSH and LH form pituitary gland, changing the lining of the uterus and thickening cervical mucus making it difficult for sperm to enter uterus

• IUD

  • hormonal – releases progestin that causes thickening of cervical mucus, make sperm less active

  • copper – release copper to uterus preventing fertilization or inhibits attachment of fertilized egg to the uterine wall, prevent sperm from entering uterine tubes

• Emergency contraceptive pill (ECP)

  • prevents pregnancy if taken 120 hours after sexual intercourse; high dose of progestin

• Sterilization

  • Vasectomy

  • Tubal Ligation

Congrats

→» nextset