Fertilization

3-30 Primordial Follicles

in the Follicular Phase of Menstruation, how many primordial follicles are stimulated to primary follicles

Estrogen

Follicular Phase: ____ inhibits FSH, causing stimulated follicles to degenerate

Follicular stimulating hormone

Hormone that stimulates primordial follicles into primary follicles within the ovaries

True

True/False: Only one follicle becomes dominant and continues to mature

Estrogen

Hormone that stimulates thickening of uterine lining

Endometrial proliferation (proliferative phase)

Estrogen stimulates thickening of uterine lining

False; thinner and more elastic

True/False: Estrogen causes cervical mucus to be thicker and less elastic to facilitate sperm entry

This LH surge causes the mature dominant follicle to rupture and release the egg (ovulation).

What hormone triggers ovulation?

around day 14 in a typical 28-day cycle

Ovulation occurs when?

Progesterone

What hormone is dominant during the luteal phase?

12-24 hours

The oocyte released during ovulation is viable for fertilization for about ___________

Corpus luteum formation, progesterone dominance

Luteal Phase

Oocyte

• Large (~100 um)

• large and nonmotile gamete

Metaphase 2

Division of oocyte is arrested in __________ and completed upon fertilization

zona pellucida

glycoprotein coat of the eff acting as a barrier to the sperm

corona radiata

inner most layer of cumulus, provides vital proteins to the oocyte

zona pellucida

surrounds the oocyte; found between the oocyte and follicular cell thin glycoproteins that help prevent polyspermy by binding to sperm preventing them to penetrate too deeply into the oocyte

cumulus

cluster of cells surrounding the oocyte

antrum

fluid filled space that develop among follicle cells

Theca interna – produces hormone (estrogen)

Theca externa - more of a connective tissue

Theca Layer of Egg

Sperm

small, asymmetrical and motile cell

1. Tail

2. Midpiece

3. Head with Acrosome

   • contains hydrolases

Components of sperm

Nucleus, hold genetic (DNA) material from father; 5-6 micrometers

head of sperm

cap (acrosome)

– end of head, contains enzymes that break down the outer membrane of the egg cell

neck

narrow region between head and tail of sperm

Midpiece

region between head and tail; contains mitochondria to provide energy for sperm movement

Tail

flagellum; long whip like structure (40-50 micrometers), helps it propel through the reproductive tract

Fertilization

- the process by which the secondary spermatocyte and the secondary oocyte fuse

Ampullary region

SIte of fertilization

2 – 5 million

number spermatozoa deposited in vagina during intercourse

3 to 7 days (average is 5 days)

life span of sperm in female reproductive tract is

1. ejaculation

2. contractions in female tract

3. change in pH environment

4. mucous secretions

5. defenses of female immune system

6. anatomy of the fallopian tube (double tract fallopian tube)

Sperm is subject to physical stress due to:

chemoattractants produced by cumulus cells surrounding the egg, and swim to the ampulla where fertilization usually occurs

At ovulation, sperm again become motile, perhaps because of

1. capacitation

2. the acrosome reaction

◦ Spermatozoa are not able to fertilize the oocyte immediately upon arrival in the female genital tract but must undergo the following to acquire this capability:

hyaluronidase

- Only one sperm enters and the rest engage in disintegration of 3 barriers around secondary oocyte via _______

• Corona radiata

• Zona pellucida

• Cortical Reaction

3 barriers to penetration of the egg

• Vagina → Cervix → Uterus → Fallopian Tube

The Journey of the Sperm

a few hundred

Although millions of sperm are released, only _______ reach the egg.

Sperm undergo maturation to become capable of fertilization.

Sperm Capacitation

1. Glycoprotein removal

2. Membrane fluidity increased

3. Hyperactivation

4. Acrosome Reaction

Sperm capacitation occurs through?

Removes the glycoprotein layer from the sperm head for sperm to bind with egg

(Sperm Capacitation) Glycoprotein removal

sperm membrane is more fluid allowing better mobilit

(Sperm Capacitation) Membrane fluidity increased

Enhances sperm movement enabling them to reach egg faster

(Sperm Capacitation) Hyperactivation

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

(Sperm Capacitation) Acrosome Reaction

• The oocyte is drawn into the fallopian tube by fimbriae and cilia.

• It then moves toward the uterus.

Journey of Sperm - Oocyte

Cortical Reaction

Egg’s Defenses: : Once one sperm enters, the egg changes to prevent other sperm from entering (block to polyspermy).

Zona Pellucida

thick, transparent membrane made of glycoproteins found inside the corona radiata, before the plasma membrane

Function: prevent polyspermy (the fertilization of an egg by multiple sperm)

Function of Cortical Reaction

Sperm's flagellar or whipping action push the cells through corona radiata and hyaluronidase enzyme breaks down hyaluronic acid (major component of extracellular matrix of corona radiata)

Key Stages of Penetration: Penetration of Corona Radiata

1. Binding to ZP3 receptorsAcrosome Reaction: Binding triggers release of digestive enzymes from the head (e.g., acrosin) to digest the zona. Enzyme reaction are released to digest zona pellucida and weakens the barrier Only one sperm successfully penetrates.

Key Stages of Penetration: Penetration of Zona Pellucida

• Sperm penetrates the zona pellucida

• Sperm and egg membranes fus

• Sperm nucleus enters the egg

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

Zygote Formation

Polyspermy

Fertilization by more than one sperm

1. Fast Block

2. Slow Block

Mechanisms of Preventing Polyspermy

• (depolarization)

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

Mechanisms of Preventing Polyspermy: Fast Block

• (Cortical Reaction): Calcium wave released within the oocyte.

• Causes release of cortical granules into the perivitelline space.

• Enzymes from granules modify the zona pellucida (zona reaction), hardening it and removing sperm receptors

• This permanently blocks further sperm entry.

Mechanisms of Preventing Polyspermy: Slow Block

ciliary beat and rhythmical contraction of muscle of tube

Oocyte travel via?

30 min to 6 days

Duration of Trip to uterus from cervix of spermatozoa

1. Restoration of the diploid number of chromosomes (half from the father and half from the mother

2. Determination of the sex of the new individual ◦ An X-carrying sperm produces a female (XX) embryo, and a Y-carrying sperm produces a male (XY) embryo

3. Initiation of Cleavage

Results of Fertilization

1. Condoms containing spermicides

2. Female condom lining vagina

(Contraceptives) Barrier 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

(Contraceptives) Hormonal method

• 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

(Contraceptives) Intrauterine device (IUD)

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

(Contraceptives) Emergency contraceptive pill

• vasectomy

• tubal ligation

(Contraceptives) Sterilziation