female reproduction & fertilization development

chapter 50-52

What triggers female reproductive development in the absence of testes and male hormones?

AMH and testosterone aren't produced, so the Müllerian ducts develop into female reproductive structures and the Wolffian ducts degenerate, resulting in typical female development—even without ovaries.

How does the XX chromosome pair influence gonadal development?

required for undifferentiated gonadal tissue to develop into functional ovaries.

What are the main functions of the ovaries in the female reproductive system?

Ovaries produce one ovum each month and secrete key hormones: estrogen, progesterone, inhibin, and relaxin.

What are the structural regions of the ovary and their functions?

Cortex (outer): Site of oogenesis in saclike follicles.
Medulla (inner): Contains blood vessels, lymphatics, and nerves.

How is the ovulated oocyte transported from the ovary to the uterus?

Fimbriae sweep the ovary to catch the oocyte; smooth muscle contractions and cilia in the uterine tube then move it toward the uterus over 3–4 days.

What supports sperm and zygote survival in the uterine tube?

Non-ciliated cells in the uterine tube secrete nutritive substances.

What are the three main regions of the uterus, and what are their roles?

• Body: Main region supports pregnancy.

• Fundus: Rounded top area, superior to uterine tube openings.

• Cervix: Narrow lower neck opens into vagina.

What are the functions of the uterus in reproduction?

provides the site for implantation and supports fetal development; it also serves as the path for sperm to reach the uterine tubes.

What are the layers of the uterine wall and their functions?

• Perimetrium (outer serosa): Protective outer covering.

• Myometrium (middle): Thick smooth muscle that contracts during childbirth.

• Endometrium (inner): Layer where implantation occurs, contains simple columnar epithelium and CT.

What is endometriosis and how does it relate to the endometrium?

occurs when tissue similar to the endometrium grows outside the uterus, causing pain and reproductive issues.

What is oogenesis and where does it occur in the female reproductive system?

is the process of producing female gametes (ova) in the ovaries.

What is the primordial follicle, and what does it contain?

the first follicle formed during fetal development. It contains one primary oocyte surrounded by a single layer of squamous follicular cells.

What happens during the follicular (preovulatory) phase?

During this phase, several primordial follicles are hormonally stimulated by LH and FSH to develop into primary follicles. Oocytes within these follicles begin to mature.

What role do granulosa cells play in follicle maturation?

secrete estrogen as the follicle matures, which stimulates changes in the uterine lining. They also organize into the zona granulosa layer.

What is the zona pellucida, and why is it important?

a thin band of glycoproteins that surrounds the oocyte, regulating sperm-egg interactions and allowing sperm to bind during fertilization.

What happens during the formation of a secondary follicle?

forms from a primary follicle, with fluid-filled pockets developing in the granulosa cell layer. Thecal cells outside the granulosa produce androgens, which are converted to estrogen by granulosa cells.

Describe the antral (tertiary or Graafian) follicle.

has merged fluid-filled pockets and contains a primary oocyte surrounded by granulosa cells, forming the antrum. The primary oocyte completes meiosis I to form a secondary oocyte.

What happens at ovulation?

occurs when the secondary oocyte, surrounded by the zona pellucida and corona radiata, is released from the ovary. This process is triggered by a surge in LH.

What is the role of the corpus luteum in the luteal phase?

After ovulation, the ruptured follicle becomes this; an endocrine gland that secretes progesterone and some estrogen to support the early stages of pregnancy if fertilization occurs.

What is the corpus albicans?

the scar tissue left behind after the corpus luteum degrades, typically when pregnancy does not occur.

How do estrogen and progesterone regulate the menstrual cycle?

promotes the development of the dominant follicle

maintains the uterine lining for pregnancy. Both hormones regulate the secretion of GnRH, FSH, and LH.

What are the phases of the uterine cycle, and what changes occur in the uterus during each phase?

three phases:

• Menstrual phase (Days 1-5): Shedding of the stratum functionalis of the endometrium.

• Proliferative phase (Days 6-14): Endometrial lining thickens in response to estrogen.

• Secretory phase (Days 15-28): Progesterone stimulates the endometrial glands to secrete glycogen-rich fluid to sustain a potential embryo.

What is the function of the stratum functionalis and stratum basalis in the endometrium?

the innermost layer, where implantation occurs and which is shed during menstruation
the deeper layer that replenishes the functionalis after menstruation.

What triggers ovulation?

a sudden surge in LH, which causes the primary oocyte to complete meiosis I and the secondary oocyte to be released from the ovary.

What happens during the secretory phase of the uterine cycle if pregnancy does not occur?

the functionalis layer of the endometrium dies, and menstruation begins as the menstrual phase starts.

How does estrogen affect follicular development?

stimulates the development of the dominant follicle into a vesicular follicle, promoting positive feedback for further estrogen production.

How does progesterone help maintain pregnancy?

maintains the uterine lining for implantation and supports pregnancy once fertilization has occurred, preventing further ovulation.

What is the LH surge, and when does it occur in the cycle?

just before ovulation (~34-48 hours prior) and triggers the completion of meiosis I and the release of the secondary oocyte.

What happens in the luteal phase if fertilization does not occur?

the corpus luteum degrades into the corpus albicans, leading to a decrease in progesterone and estrogen, which triggers the beginning of menstruation.

What is the role of GnRH, FSH, and LH in regulating the ovarian cycle?

GnRH stimulates the release of FSH and LH from the anterior pituitary. FSH promotes follicle development, while LH triggers ovulation and the formation of the corpus luteum.

Where does fertilization typically occur in the human female reproductive system

occurs in the upper third of the uterine tube, also known as the fallopian tube, specifically in the ampulla, which is the widest section of the tube.

What is capacitation in sperm activation?

series of physiological changes sperm undergo after ejaculation. These changes enable sperm to be capable of fertilizing the egg. It involves the removal of protective proteins from the sperm’s head and alterations in the sperm membrane, enhancing its ability to bind to the egg.

What is the acrosomal reaction and what triggers it?

is a process where enzymes are released from the sperm’s acrosome (a cap-like structure on the sperm head) when the sperm makes contact with the zona pellucida of the egg. This reaction is triggered by the binding of sperm to specific glycoproteins in the zona pellucida, enabling sperm to penetrate the egg's outer layers.

What are the enzymes released during the acrosomal reaction, and what do they do?

Hyaluronidase breaks down the corona radiata, allowing sperm to reach the zona pellucida.

What is the corona radiata and why is it important during fertilization?

a layer of granulosa cells around the oocyte, which sperm must penetrate to reach the zona pellucida.

What happens when sperm bind to the zona pellucida?

Triggers the acrosomal reaction, releasing enzymes to help sperm penetrate the egg’s outer layers.

What is the zona pellucida and its role in fertilization?

a protective glycoprotein layer that sperm must penetrate and plays a key role in sperm binding and the acrosomal enzyme release and extension

What is the significance of the acrosomal enzymes released during fertilization?

They help sperm penetrate the corona radiata and zona pellucida, allowing sperm to reach the egg membrane.

What is polyspermy and why is it prevented?

when more than one sperm fertilizes the egg, leading to an abnormal number of chromosomes. It’s prevented to ensure normal development.

How is polyspermy prevented?

After the first sperm enters, the egg’s membrane depolarizes and cortical granules modify the zona pellucida, blocking other sperm.

What happens during the egg’s membrane change after sperm entry?

The egg’s membrane depolarizes, preventing additional sperm from entering.

How do cortical granules contribute to the block to polyspermy?

Cortical granules release enzymes that modify the zona pellucida, making it impermeable to other sperm.

What happens after sperm enters the egg in terms of genetic material?

The sperm’s and egg’s nuclei fuse, forming a diploid zygote.

What happens to the sperm once it successfully fertilizes the egg?

The sperm’s tail disintegrates, and its head merges with the egg’s nucleus.

What is the role of multiple sperm in fertilization?

What is the role of multiple sperm in fertilization?

fertilization events in ovum

Ca2+ rises

polar body formed

corical vesicles bind oocyte membrane

release enzymes causing ZP to harden and receptor breakdown which prevents sperm binding

human fertilization is

monospermic

What is the first stage after fertilization called?

Zygote – a single diploid cell formed when sperm and egg nuclei fuse.

What happens about 30 hours after fertilization?

The zygote begins cleavage—rapid mitotic cell divisions.

What is the morula and when does it form?

A solid ball of cells formed by day 3, still inside the zona pellucida; precursor to the blastocyst.

What causes the transition from morula to blastocyst?

Uterine milk enters the morula, forming a fluid-filled cavity.

What are the two main parts of the blastocyst?

Embryoblast (inner cell mass → embryo) and Trophoblast (outer layer → placenta).

What is hatching and when does it happen?

Around day 5, the blastocyst hatches from the zona pellucida, enabling implantation.

Why is hatching important for the blastocyst?

It allows better access to nutrients and enables the blastocyst to adhere to the uterine lining.

When is the developing human called an embryo?

From implantation to the 8th week of development.

When is it called a fetus?

From the 9th week to birth, when all major organs are formed and developing.

What are the key differences between zygote, blastocyst, embryo, and fetus?

• Zygote: Single cell post-fertilization

• Morula: Solid ball of cells

• Blastocyst: Hollow structure with fluid and cell layers

• Embryo: 2nd to 8th week, organ formation

• Fetus: 9th week to birth, growth and maturation

What is gastrulation?

It's the process where the blastula becomes a three-layered embryo called a gastrula.

What are the three germ layers formed during gastrulation?

Ectoderm, Mesoderm, and Endoderm.

what does the ectoderm form?

Epidermis of skin, nervous system, and parts of eyes and ears.

What does the mesoderm form?

Muscle, bone, kidneys, blood, gonads, and connective tissue.

What does the endoderm form?

Lining of the gut, and parts of the respiratory, urinary tracts, and some internal organs.

Where and how does implantation occur?

The blastocyst implants into the functionalis layer of the endometrium, usually on the posterior wall near the fundus. The syncytiotrophoblast digests its way in.

What hormone is secreted during implantation and what does it do?

hCG is secreted by the syncytiotrophoblast; it maintains the corpus luteum, which keeps estrogen and progesterone levels high to maintain the uterine lining.

What happens to hCG levels after the placenta develops?

hCG decreases once the placenta takes over hormone production.

What is the function of the chorion?

It's the outer membrane that contributes to the fetal part of the placenta.

What is the function of the amnion?

It's the inner membrane that surrounds the embryo and fills with protective amniotic fluid.

What does the allantois become?

It contributes to umbilical blood vessels.

What is the role of the yolk sac?

It helps in early blood cell formation and germ cell migration.

What is the structure of the placenta?

Dual origin: fetal part from chorion (chorionic villi), maternal part from endometrium.

What is the function of the placenta?

Nutrient, gas, and waste exchange between mother and fetus; not a total barrier.

Why is the fetus not rejected by the mother’s immune system?

The placenta acts as a selective barrier and modulates immune responses.

What are the major placental hormones and their functions?

• hCG: Maintains corpus luteum and fetal testosterone production.

• Progesterone: Maintains uterine lining, inhibits contractions and GnRH.

• Estrogen: Stimulates uterine growth and mammary development.

• CRH: May regulate pregnancy length and labor timing.

• hCS: Supports fetal growth, shifts maternal metabolism to spare glucose, supports corpus luteum.

• Relaxin: Loosens pubic symphysis, relaxes uterus, promotes blood vessel growth.

How does the pancreas respond during pregnancy?

Increases insulin to offset maternal insulin resistance (glucose-sparing for fetus).

What changes occur in the adrenal glands?

Aldosterone increases, raising Na⁺ and water retention to boost blood volume.

How do thyroid hormones change?

They increase metabolism, pulse, and O₂ delivery to the fetus.

What is chorionic villus sampling (CVS)?

A prenatal test done ~10–13 weeks, sampling placental tissue for genetic testing.

What is amniocentesis?

A test done ~15–20 weeks, withdrawing amniotic fluid to analyze fetal chromosomes.

When do conjoined twins occur?

When the embryo does not fully split during early development.