Exam 2 - Spermatogenesis, Oogenesis, Folliculogenesis, Male + Female Gonads and Reproductive Tract

What is oogenesis?

The production and maturation of eggs; it begins during embryonic development.

How does an oocyte compare with a sperm cell in size and cytoplasm?

The oocyte is much larger and contains abundant cytoplasm; sperm has very little cytoplasm.

Are oocytes motile?

No. Oocytes are generally immobile gametes.

Which gamete generally costs more energy to produce?

The egg; it is larger and contains more cytoplasm and energy reserves.

What does the egg contribute at fertilization?

Nutrients, most cytoplasmic components, and much of the information needed to start and support embryonic development.

What does the sperm contribute at fertilization?

Primarily DNA (the paternal genetic contribution).

What is the oolemma?

The oocyte's plasma membrane; sperm must penetrate it to release DNA into the egg cytoplasm.

What is the ooplasm?

The cytoplasm of the oocyte, containing organelles such as the nucleus, Golgi, and mitochondria.

What is the germinal vesicle?

The oocyte's nucleus, which contains its DNA.

What is the corona radiata?

The layer of follicular cells surrounding the ovulated oocyte.

What is the zona pellucida?

A mammalian extracellular envelope around the oocyte; it is one of the barriers sperm must pass during fertilization.

What is the chorion in the context of egg envelopes?

An accessory egg envelope found in teleost fish.

What is the micropyle?

An opening in an egg envelope through which sperm can enter in some species.

What is yolk and what does it do?

Energy reserves, including lipid droplets and glycogen, that support embryonic development.

Which groups may have yolk rich eggs?

Many animals, including insects, octopuses, fish, reptiles, and marsupial mammals.

When does meiosis begin in female mammals?

During fetal/embryonic development, before birth.

What happens to oogonia during the proliferation phase?

They multiply by mitosis in the developing ovary and give rise to primary oocytes.

When does mammalian oogonial mitosis mostly end?

Around birth; the prenatal divisions establish a finite ovarian reserve.

In what stage are primary oocytes arrested before puberty?

Prophase I, at diplotene (dictyate) after crossing over.

What triggers some primary oocytes to resume meiosis I in a cycle?

The LH surge.

What are the products of meiosis I in oogenesis?

A large secondary oocyte and a small first polar body, produced by asymmetric cytokinesis.

What happens to the secondary oocyte after meiosis I?

It begins meiosis II and arrests at metaphase II; it is the cell that is ovulated.

What triggers completion of meiosis II?

Fertilization.

What are the products of meiosis II?

An ovum and a second polar body.

What happens when sperm and ovum nuclei unite?

They form a diploid (2n) zygote.

Why are polar bodies small?

Asymmetric divisions retain most of the oocyte's cytoplasm and resources in one functional egg.

How many polar bodies can result from oogenesis?

Usually up to three; the first polar body may or may not divide.

What can oocyte anatomy reveal about maturity?

The position or disappearance of the germinal vesicle and the presence of a polar body can indicate meiotic stage; a polar body suggests completion of meiosis I.

What happens to ovarian reserve over a reproductive lifespan?

It declines; most follicles do not ovulate and are lost, primarily through atresia.

Why is the ovarian reserve finite in most mammals?

Most oogonial mitosis occurs before or shortly after birth, so new oocytes are generally not continually produced.

What is the oogamy hypothesis?

A proposed evolutionary process in which selection for more numerous small gametes and larger resource rich gametes drove gametes toward the sperm and egg forms.

What is the ovary's basic internal organization?

An outer cortex and inner medulla; follicles develop in the ovarian stroma, mainly in the cortex.

What is a follicle?

An oocyte together with the surrounding follicular cells that support it and produce hormones.

Can an oocyte develop normally outside its follicle?

No. Follicular cells support oocyte development; some follicular cells remain with the oocyte after ovulation.

What is folliculogenesis?

The development and growth of follicles surrounding oocytes.

What characterizes a primordial follicle?

A primary oocyte arrested in meiosis I, surrounded by a single layer of flattened (squamous) granulosa cells; it is a resting follicle.

What are the three fates of a primordial follicle?

Remain resting, enter growth and become a primary follicle, or undergo atresia; most are eventually depleted by atresia.

What characterizes a primary follicle?

A growing follicle with a single layer of cuboidal granulosa cells; it may become atretic or continue toward the secondary stage.

What characterizes a secondary follicle?

It has several layers of proliferating granulosa cells, a developing zona pellucida in mammals, and theca cells near the basal lamina.

What are the two main fates of a secondary follicle?

Undergo atresia or respond to FSH and continue developing toward a tertiary follicle.

What makes a tertiary (antral) follicle?

Fluid filled spaces between granulosa cells merge to form an antrum.

What are the theca interna and theca externa?

Theca layers that differentiate around a growing follicle; theca interna is steroid secreting, while theca externa is the outer supportive layer.

What are cumulus, antral, and mural granulosa cells?

Granulosa cell groups named by location: cumulus cells surround the oocyte, antral granulosa cells border the antrum, and mural granulosa cells lie near the basement membrane.

What does gonadotropin independent follicle growth mean?

Early follicle recruitment and growth can occur through intraovarian regulation without FSH dependence.

What does gonadotropin dependent follicle growth mean?

Later antral follicle growth depends on gonadotropins, especially FSH, with increasing LH responsiveness as follicles mature.

How is the dominant follicle selected?

Follicles differ in hormone responsiveness; the dominant follicle has advantages such as greater granulosa cell mitosis, more FSH receptors, higher aromatase activity, and stronger ability to keep growing as FSH falls.

How does a growing follicle contribute to its own selection?

It secretes estrogen; estrogen feedback lowers FSH, so follicles with greater FSH responsiveness are more likely to continue growing.

What is follicular atresia?

Degeneration and loss of a follicle, which can occur at any developmental stage and accounts for the loss of most follicles.

What percentage of follicles may become atretic?

The lecture notes that more than 99% of follicles present at birth become atretic; fewer than 1% reach ovulation.

What are the main functions of the ovaries?

They produce ova and steroid hormones, including estrogen and progesterone.

Where are ovaries located across species, according to the lecture?

They are internal; their shape and structure vary among vertebrates.

What supports the ovary in the pelvic cavity?

The mesovarium, a mesentery; in humans the ovarian ligament also helps suspend the ovary.

What is the tunica albuginea of the ovary?

A thin connective tissue covering over the ovary.

What initiates physical rupture of the follicle at ovulation?

Prostaglandins and other changes increase theca interna capillary dilation and permeability; fluid and proteins enter follicular tissue, and proteases weaken the ovarian wall.

What are MMPs in ovulation?

Matrix metalloproteinases, proteases that help weaken the ovarian wall so the follicle can rupture.

What happens to the follicle wall after ovulation?

Remaining follicular cells hypertrophy and proliferate, forming the steroid producing corpus luteum.

What does the corpus luteum secrete?

Progesterone, which rises after ovulation.

When does the primate corpus luteum reach peak mass and progesterone production?

About seven days after ovulation.

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

It begins to degrade around 10 to 12 days after ovulation and becomes a corpus albicans.

What are the two broad phases of a 28 day menstrual cycle?

The follicular phase before ovulation and the luteal phase after ovulation.

What is the relationship between LH and ovulation?

The LH surge triggers ovulation and resumption of meiosis in the selected oocyte.

What is the relationship between FSH and follicle growth?

FSH supports the growth of developing antral follicles; changing FSH levels help select a dominant follicle.

How does estrogen affect oviduct epithelial cells?

It promotes taller ciliated cells, faster ciliary beating, and increased mucus secretion.

How does progesterone affect oviduct activity compared with estrogen?

It generally has effects opposite to estrogen on ciliary activity and mucus secretion.

What is a sperm reservoir in the oviduct?

In some species, sperm bind to oviduct epithelium and can be stored there for extended periods before fertilization.

How long can sperm remain in the human oviduct, according to the lecture?

About five days; humans do not form the long term sperm reservoirs found in some other species.

What is the likely effect of sperm binding to oviduct epithelium?

It can slow sperm activity and prolong sperm survival.

What is the uterus?

The organ where a fertilized zygote implants and the embryo develops.

What are the three main regions of the human uterus?

Fundus, body, and cervix.

What are the uterine wall layers from inner to outer?

Endometrium, myometrium, and perimetrium.

What is the myometrium?

The muscular uterine wall; it contracts during menstruation and childbirth.

What can stimulate uterine contractions around reproduction?

Hormonal signals and prostaglandins, including prostaglandins in semen noted in the lecture.

What is the endometrium?

The uterine lining, which is built up under estrogen and progesterone and shed during a non fertile menstrual cycle.

What is the stratum functionalis?

The superficial endometrial layer with epithelium and uterine glands; it is shed during menstruation.

What is the stratum basalis?

The deeper endometrial layer that remains during menstruation and helps regenerate the lining.

What is the cervix?

The lower part of the uterus that connects the uterus to the vagina and dilates during labor.

What happens to the cervix during labor?

It effaces (thins) and dilates to permit delivery.

What is the role of cervical mucus?

Its consistency changes with hormones; it can form a barrier to microbes and, near ovulation, become thinner and more favorable to sperm movement.

How does cervical mucus change near ovulation?

High estradiol makes it wetter, clearer, more abundant, more alkaline, and stretchier, helping sperm pass through the cervix.

What can dried fertile cervical mucus form?

A fern like crystallization pattern.

What is the vagina's normal structural state and how does it stretch?

It is a normally collapsed tube with folds called rugae that allow expansion during copulation and childbirth.

Why is the vaginal environment acidic?

Some vaginal bacteria metabolize glycogen into lactic acid, which helps limit yeast and other infections.

What can raise vaginal pH?

Semen is less acidic than the vaginal environment; the lecture also notes an association between estrogen changes and vaginal pH.

What is the hymen?

A variable, partial covering at the vaginal opening; its shape and degree of opening vary and it is not a measure of virginity.

What are the labia majora and labia minora?

The labia majora are the outer, typically hair bearing folds; the labia minora are the inner folds around the vaginal and urethral openings.

What do the Bartholin (greater vestibular) glands secrete?

Moistening fluid near the vaginal entrance; secretion can vary with hormonal state.

What is the clitoris notable for?

It contains a high concentration of sensory nerve endings.

What is the perineum?

The region between the vaginal opening and the anus.

What are the main functions of the testes?

Sperm production and testosterone production.

Where are testes located in vertebrates?

They may be internal in the abdominal cavity or external in a scrotum, depending on species.

What are the three connective tissue coverings of the testis discussed in lecture?

Tunica vaginalis (parietal and visceral layers) and tunica albuginea.

What is the tunica albuginea?

A connective tissue covering around the testis that supports and protects it.

What is the spermatic cord?

The structure connecting each testis to the body wall; it contains the vas deferens, blood vessels, nerves, and other tissues.

What does the tunica dartos do?

Its smooth muscle wrinkles or relaxes the scrotal skin to help regulate heat loss.

What does the cremaster muscle do?

It raises or lowers the testes in response to temperature or touch, helping regulate temperature and protect the testes.

What is the cremaster reflex?

A response to touch or temperature that moves the testes via cremaster contraction or relaxation.

Why is the scrotum outside the body cavity in many mammals?

It helps maintain testicular temperature below core body temperature for effective spermatogenesis.

What temperature difference is noted for scrotal testes?

They are maintained about 2 to 3°C below core body temperature (roughly 3°C lower in the lecture).

What is the pampiniform plexus?

A network of veins in the spermatic cord that cools incoming testicular arterial blood by countercurrent heat exchange.

How does the pampiniform plexus cool the testicular artery?

Cooler venous blood absorbs heat from the incoming arterial blood before it reaches the testis.