Female Reproductive System: Functions, Cycle, and Fertilization

What are the four primary functions of the female reproductive system?

Producing ova, receiving sperm to facilitate fertilization, housing and nourishing a developing embryo, and lactating to feed young.

What is the function of the oviducts (fallopian tubes)?

They collect secondary oocytes from the ovary, move them toward the uterus via cilia and contractions, and serve as the site of fertilization.

What are the two layers of the uterus and their functions?

The myometrium, which is a thick wall of smooth muscle, and the endometrium, which lines the lumen and thickens monthly to prepare for potential embryo implantation.

What is the role of the cervix?

It is the lower part of the uterus that closes it off from the vagina; it is also the most common site for cancer, often linked to HPV.

What happens to the endometrium if fertilization does not occur?

It is sloughed off during menstruation.

At what stage of meiosis are primary oocytes arrested before puberty?

Prophase I.

How many primary oocytes are typically present at birth versus sexual maturity?

About 1-2 million at birth, decreasing to about 200,000 by sexual maturity.

What is a follicle in the context of the ovary?

A structure within the ovary that contains a primary oocyte and supports its development.

What occurs during the primary oocyte division just before ovulation?

It completes meiosis I, resulting in one polar body and one secondary oocyte through unequal cytokinesis.

At what stage of meiosis is the secondary oocyte arrested until fertilization?

Metaphase II.

What triggers a secondary oocyte to complete meiosis II?

The entry of a sperm cell.

What are the three phases of the ovarian cycle?

The follicular phase (days 1-13), ovulation (day 14), and the luteal phase (days 15-28).

What are the three phases of the uterine cycle?

The menstrual flow phase (days 1-5), the proliferative phase (days 6-13), and the secretory phase (days 15-28).

Which organ systems are involved in the regulation of the menstrual cycle?

The hypothalamus, anterior pituitary, ovaries, and uterus.

What is the primary form of estrogen in the female body?

Estradiol.

What structures secrete estrogen?

Follicle cells and the corpus luteum.

What are the primary functions of estrogen at puberty?

It stimulates the growth of sex organs and the development of secondary sex characteristics.

What is the main source of progesterone?

The corpus luteum.

What is the specific role of progesterone in the uterine cycle?

It completes the preparation of the endometrium for pregnancy and stimulates endometrial glands to secrete nutrient-rich fluid.

What happens to the secondary oocyte if it is not fertilized?

It disintegrates.

What is the function of the vulva?

It consists of the external genitalia and covers the external openings of the female reproductive system.

What initiates the early follicular phase of the ovarian cycle?

The hypothalamus secretes GnRH, which stimulates the anterior pituitary to secrete FSH and LH.

What is the role of estradiol during the early follicular phase?

It provides negative feedback to the anterior pituitary, slowing the release of FSH and LH.

What triggers the LH surge in the late follicular phase?

High levels of estradiol from the maturing follicle stimulate the hypothalamus to release more GnRH, creating positive feedback.

What event occurs approximately one day after the LH surge?

Ovulation, where the secondary oocyte is released into the oviduct.

What does the remaining follicle tissue become after ovulation?

It becomes the corpus luteum, a temporary endocrine gland.

What hormones are secreted by the corpus luteum during the early luteal phase?

High levels of progesterone and estradiol.

What happens to the corpus luteum if pregnancy does not occur?

Low levels of FSH and LH cause it to disintegrate, leading to a drop in estradiol and progesterone.

How is the proliferative phase of the uterine cycle coordinated with the ovarian cycle?

It is coordinated with the follicular phase; ovarian hormones stimulate the endometrium to thicken.

What characterizes the secretory phase of the uterine cycle?

It is coordinated with the luteal phase, where the endometrium completes development with enlarged arteries and glands.

What triggers the menstrual flow phase?

The breakdown of the corpus luteum causes a drop in hormones, leading to the constriction of endometrial arteries and the shedding of the lining.

What are the three primary results of fertilization?

It restores the diploid (2n) number, often determines sex, and activates the egg to begin development.

What are the layers surrounding a mammalian egg from inside to outside?

Plasma membrane, zona pellucida, and follicle cells.

What is the function of the acrosomal reaction?

The acrosome bursts to release enzymes that help the sperm penetrate the zona pellucida.

What triggers the calcium wave in the egg upon fertilization?

Plasmogamy (fusion of sperm and egg plasma membranes) triggers the release of Ca2+ from the smooth ER.

What is the purpose of the cortical reaction?

It triggers the slow block to polyspermy by hardening the zona pellucida and altering sperm receptors.

What metabolic changes occur during egg activation?

Increased respiration, activation of maternal enzymes/proteins, and initiation of protein synthesis.

What is the state of the secondary oocyte before fertilization?

It is arrested at metaphase II of meiosis.

What triggers the completion of meiosis in the egg?

The calcium wave released upon fertilization.

What is karyogamy?

The fusion of the sperm nucleus and the egg nucleus.

What does it mean for a zygote to be totipotent?

It has the potential to give rise to all cell types in the organism.

When is fertilization considered complete?

When the zygote undergoes its first cell division.

What is the role of the zona pellucida in fertilization?

It serves as a glycoprotein matrix that acts as a barrier to interspecific fertilization and is the site of sperm binding.

What are the four major steps in the fertilization process?

Sperm dissolves protective layers, binds to surface receptors, changes occur on the egg surface to prevent polyspermy, and nuclei fuse.

List the three layers surrounding a mammalian egg from inside to outside.

Plasma membrane, zona pellucida (glycoprotein matrix), and follicle cells.

What triggers the 'calcium wave' in the egg during fertilization?

The release of Ca2+ from the smooth endoplasmic reticulum upon plasmogamy.

What occurs during 'egg activation'?

A series of metabolic reactions accelerate, including increased respiration, activation of maternal enzymes/proteins, and protein synthesis.

At what stage of meiosis is a secondary oocyte arrested before fertilization?

Metaphase II.

When is fertilization considered officially complete?

When the zygote undergoes its first division.

What is cleavage in embryonic development?

The second step of development where the zygote undergoes rapid cell divisions without overall growth to become a multicellular embryo.

What is the primary function of yolk in an embryo?

It serves as a food source consisting of proteins, phospholipids, and fats.

How does the amount of yolk affect the pattern of cleavage?

Little yolk allows for faster, equal divisions, while large amounts of yolk result in slower, unequal divisions.

What is a blastula?

A hollow embryo characterized by a central cavity called the blastocoel.

What characterizes equal holoblastic cleavage?

Complete division resulting in cells of equal size with a central blastocoel; seen in echinoderms, mammals, and annelids.

What is unequal holoblastic cleavage?

Complete but asymmetric cleavage caused by yolk distribution, which slows down cytokinesis; observed in amphibians.

What is meroblastic cleavage?

A pattern where only regions without yolk undergo complete division; typical in reptiles, birds, and many fish.

What is the role of microtubules during fertilization?

They guide the sperm nucleus to the egg nucleus for fusion.

What is the 'slow block' to polyspermy?

A mechanism where enzymes released by cortical granules harden the zona pellucida and remove sperm receptors to prevent multiple sperm from fertilizing the egg.

Are maternal proteins and enzymes synthesized from scratch during egg activation?

No, the mRNA is already present in the egg, and these proteins are activated rather than newly synthesized from DNA.

What are the primary characteristics of asexual reproduction?

It involves a single parent producing genetically identical clones without meiosis or gamete fusion.

List four common types of asexual reproduction.

Budding, fission, fragmentation and regeneration, and parthenogenesis.

What is a primary advantage of asexual reproduction for sessile organisms?

It eliminates the need to find a mate, which is beneficial for organisms with low population density or those that cannot move.

What is the fundamental difference between sperm and egg cells?

Sperm are small, motile, and flagellated, while eggs are large, nonmotile, and contain nutrients for the embryo.

What is the main evolutionary advantage of sexual reproduction?

It promotes genetic diversity through new allele combinations, which helps remove harmful alleles and increases the likelihood of survival during environmental changes.

What is the 'reproductive cost' associated with sexual reproduction?

Only half of the population (females) can produce offspring.

What are the two primary functions of the male reproductive system?

To produce sperm and to deliver sperm into the female reproductive tract.

Where does spermatogenesis occur within the testes?

In the seminiferous tubules.

What is the function of Leydig cells?

They are located between seminiferous tubules and produce testosterone and other male sex hormones.

What are the three main functions of the epididymis?

Transporting sperm, maturation of sperm, and storage of sperm.

Why is the scrotum located externally in most mammals?

Sperm cannot develop at body temperature; the scrotum keeps the testes cooler than the rest of the body.

How does the penis achieve an erection?

Nitrous oxide causes smooth muscle to relax, increasing blood flow into erectile tissue; the swelling compresses veins, trapping blood inside.

What substances are secreted by the seminal vesicles and what are their functions?

Fructose (energy for sperm) and prostaglandins (stimulate uterine contractions).

What is the function of the fluid secreted by the prostate gland?

It contains anticoagulant enzymes and citrate, which serves as an energy source for sperm.

What is the role of the bulbourethral glands?

They secrete mucus during arousal to neutralize acidic urine in the urethra.

Trace the path of sperm from the epididymis to the outside of the body.

Epididymis → vas deferens → ejaculatory duct → urethra.

What is the role of spermatogonial stem cells?

They divide via mitosis to maintain the population of undifferentiated cells and produce primary spermatocytes.

What are the stages of meiosis in spermatogenesis?

Primary spermatocytes (2n) undergo Meiosis 1 to become secondary spermatocytes (n), which then undergo Meiosis 2 to become spermatids.

What are the three parts of a mature sperm cell?

Head, midpiece, and tail.

Which hormone stimulates the Leydig cells to produce testosterone?

Luteinizing Hormone (LH).

What are the effects of testosterone during puberty?

It triggers the adolescent growth spurt, the development of primary sex characteristics, and the appearance of secondary sex characteristics.

What is the function of Follicle-stimulating hormone (FSH) in males?

It stimulates the development of seminiferous tubules and activates Sertoli cells.

What is the function of Androgen Binding Protein (ABP)?

It binds to testosterone to help maintain the high levels required for spermatogenesis within the testes.

What is the function of inhibin in the male reproductive system?

It is a peptide hormone that inhibits the secretion of FSH.