Biology of Sex Quiz 2 (Females)

Default pathway (old view)

In mammals, an embryo develops as female unless chemical signals indicate it should develop as male. Removing the testis results in a female.

COUP-TFII (new view)

A transcription factor that actively removes the male reproductive tract in female embryos. Mouse embryos lacking it keep both Müllerian and Wolffian derivatives, so female development has an active component.

Müllerian ducts

Develop into the fallopian tubes, uterus, and cervix in females and regress in males.

Wolffian ducts

Develop into the epididymis, vas deferens, and seminal vesicle in males and regress in females.

Bipotential (indifferent) tissues

Embryonic organs that can develop as male or female depending on signals. The major signal is testosterone.

Gonad (bipotential)

Becomes an ovary or a testis.

Genital tubercle

Becomes the clitoris or the glans penis.

Urethral fold

Becomes the labia minora or the penis shaft.

Labioscrotal swelling

Becomes the labia majora or the scrotum.

Dosage compensation

Mechanism that keeps XX females from expressing twice as much X-chromosome gene product as XY males, by inactivating one X in females.

Barr body

The extra, inactivated X chromosome.

Incomplete dosage compensation

Explains why Klinefelter, Turner, and extra-X individuals are not perfectly typical. Extra X chromosomes may not be inactivated right away, or Barr bodies may not be completely inactive and so over-express some X-linked genes.

X-inactivation

Occurs randomly (maternal or paternal X) early in embryonic development in female somatic cells. The same X stays inactivated in all daughter cells after mitosis.

Calico cat

Example of X-inactivation in action. Base coat color is X-linked, so a heterozygous female expresses black fur where one X is inactivated and orange where the other is. White patches are controlled by a separate gene.

Tortoiseshell cat

Shows the same black and orange mosaic as a calico but has no white patches.

Calico males

The lecture's quiz asks what sex chromosomes a calico cat with testes would probably have. The answer is XXY, since a male needs two X chromosomes to be calico.

Estrogens (estradiol)

The "female" sex steroids that activate many female-typical physiologies and behaviors.

Progestins (progesterone)

Hormones from the ovaries and placenta whose primary role is maintaining pregnancy.

HPG axis (female)

The hypothalamus, anterior pituitary, and gonad work together to control gametogenesis and steroidogenesis. It is under negative feedback control, with positive feedback through LH for ovulation.

Vaginal cytology

Light-microscope observation of cells from a vaginal lavage. Stockard and Papanicolaou (1917) showed it correlates with ovarian function, allowing cyclicity to be tracked without surgery.

Cornified epithelium

The vaginal cell type seen around behavioral estrus in rodents.

Female cyclicity

Repeating reproductive cycles. They were a research hurdle because female behavior varies over time.

Menstrual cycle (human)

Typically 24-35 days (28 assumed). Its four phases are menstrual, preovulatory, ovulation, and postovulatory.

Menstrual phase (menstruation)

Roughly the first 5 days, with day 1 being the first day of menses. In the ovaries, FSH drives primordial follicles to primary and secondary follicles. In the uterus, declining estrogen and progesterone trigger prostaglandins that constrict spiral arterioles, and oxygen-deprived cells die.

Preovulatory phase

Days 6-13 of a 28-day cycle, and the most variable in length. Secondary follicles secrete estrogens and one dominant follicle outgrows the others. Estrogens repair the endometrium and its thickness doubles.

Dominant follicle

The one follicle that outgrows the others. Its estrogens lower FSH, so the others stop growing.

Fraternal (nonidentical) twins

Result when 2-3 secondary follicles become co-dominant and are ovulated and fertilized together.

Graafian (mature) follicle

The dominant follicle that normally becomes mature and ruptures at ovulation.

Follicular phase

The ovarian-cycle name for the menstrual plus preovulatory phases, when follicles are growing.

Proliferative phase

The uterine-cycle name for the preovulatory phase, when the endometrium is proliferating.

Ovulation

Rupture of the mature follicle and release of the secondary oocyte (day 14 of 28). High estrogen exerts positive feedback on LH- and GnRH-secreting cells, and the resulting LH surge triggers ovulation.

LH surge

Rapid rise of LH (and estrogen) just before ovulation as negative feedback switches to positive feedback.

Corpus hemorrhagicum

The ruptured follicle immediately after ovulation.

Postovulatory phase

Days 15-28, the most constant in duration (14 days). In the ovarian cycle it is called the luteal phase.

Corpus luteum

Formed from the collapsed follicle under LH influence. It secretes progesterone and estrogen, and lasts about 2 weeks if the oocyte is not fertilized.

Corpus albicans

What the corpus luteum degenerates into if there is no fertilization.

Human chorionic gonadotropin (hCG)

Produced by the embryo's chorion about 8 days after fertilization. It sustains the corpus luteum beyond 2 weeks.

Endometrium changes (luteal phase)

Progesterone and estrogen promote endometrial growth, peaking about a week after ovulation. If fertilization does not occur, hormone withdrawal causes menstruation.

Estrous cycle

Cycle in most mammals with proestrus (hormonal changes leading to ovulation), estrus (coincides with ovulation, female receptive), and diestrus (period until the next breeding period). There is no menses and the uterine lining is reabsorbed.

Menstrual cycle (vs. estrous)

Found in primates, bats, and elephant shrews, and characterized by shedding of the uterine lining (menses).

Spontaneous ovulators

Species that ovulate without an external physical cue (rodents, humans).

Induced ovulators

Species that need vaginal stimulation to ovulate (many carnivores, rabbits, voles). Possible reasons are a short life span (rapid transition to reproductive state) and solitary living (reproduce only when social conditions are right).

Interbirth interval

Time between births. There is an optimal human interval for maximizing offspring survival (data from the !Kung, a hunter-gatherer society).

Pregnancy

Evolved independently about 150 times in vertebrates. Progesterone and estrogen keep rising, first from the corpus luteum and then from the placenta, and progesterone maintains the pregnancy (no menstruation).

Parturition

Birth. Fetal placental CRH (a stress hormone) rises, and oxytocin from the posterior pituitary causes uterine smooth muscle contractions and prostaglandin release.

Oxytocin positive feedback (birth)

The fetus presses on the cervix, mechanoreceptors signal the hypothalamus, and more oxytocin is released until birth.

Ovaries

Paired glands homologous to the testes. They produce secondary oocytes (which develop into mature ova) and hormones (progesterone, estrogens).

Theca cells

Triggered by LH to produce androgens.

Granulosa cells

Triggered by FSH to produce aromatase, which converts androgens to estrogens.

Corpus luteum (source of progesterone)

The main source of progesterone in the early days after ovulation.

Uterine (fallopian) tubes / oviducts

Route for sperm to reach the egg and transport for oocytes and fertilized ova to the uterus. They have three layers: mucosa (ciliary conveyor belt, peg cells nourish the ovum), muscularis (peristaltic contractions), and serosa (outer layer).

Uterus

Has a fundus, body, isthmus, and cervix (which opens into the vagina). It is held in place by ligaments.

Perimetrium

The uterus's outer layer, part of the visceral peritoneum.

Myometrium

Three layers of smooth muscle that contract in response to oxytocin.

Endometrium

The highly vascularized inner layer. The stratum functionalis lines the cavity and sloughs off at menstruation, while the stratum basalis is permanent and regenerates it.

Uterine blood supply

Uterine arteries, then arcuate arteries, then radial arteries.

Vagina

Canal from the body's exterior to the uterine cervix. It has a muscularis (two layers of smooth muscle) and an adventitia (anchors it to adjacent organs).

Hymen

Forms a border around and partially closes the vaginal orifice.

Vulva

The external female genitalia.

Mons pubis

Cushions the pubic symphysis.

Labia majora

Homologous to the scrotum.

Labia minora

Homologous to the spongy (penile) urethra.

Clitoris

Erectile structure with many nerves and blood vessels, homologous to the glans penis.

Vestibule

Region between the labia minora containing the external urethral orifice, ducted gland openings, and the vaginal orifice.

Bulb of the vestibule

Two elongated masses of erectile tissue on either side of the vaginal orifice.

Mammary glands (breasts)

A defining character of mammals. They are modified sudoriferous (sweat) glands that produce milk, with 15-20 lobes divided into lobules of alveoli (milk-secreting glands).

Nipple and areola

The nipple has the openings of the lactiferous ducts, and the areola is the pigmented area around it.

Oogenesis

Formation of gametes in the ovary. It begins before birth and follows essentially the same meiosis steps as spermatogenesis.

Atresia

Degeneration of most germ cells before birth.

Primary oocyte

A germ cell that enters meiosis I during fetal development.

Primordial follicle

A primary oocyte covered by a single layer of flat follicular cells. There are about 200,000-2,000,000 at birth, about 40,000 at puberty, and only about 400 mature in a lifetime.

Follicular development

Each month from puberty to menopause, FSH and LH stimulate several primordial follicles, usually only one reaches ovulation. The sequence is primordial, then primary, then secondary follicle.

Implantation

Attachment of the fertilized embryo to the uterine lining.

Altricial

Born or hatched undeveloped and requiring care and feeding.

Precocial

Born or hatched in an advanced state and able to feed itself.

Gestation period

Length of pregnancy, which varies across species.

Pregnancy outcome problems

The lecture asks why many pregnancies end poorly, raising meiosis errors, climate change, and anatomy (e.g., pelvic canal shape varies among populations, a variation the NYT article says is studied mostly in people of European descent).