Chapter 28 Flashcards
Gonads
Testes in males and ovaries in females; produce gametes and secrete sex hormones.
Ducts
Store and transport gametes.
Accessory sex glands
Produce substances that protect the gametes and facilitate their movement.
Supporting structures
Assist in the delivery of gametes (Eg. The penis in males and the uterus in females).
Male reproductive system
Include the testes, a system of ducts (epididymis, ductus deferens, ejaculatory ducts, and urethra), accessory sex glands (seminal vesicles, prostate, and bulbourethral glands), and several supporting structures, including the scrotum and the penis.
Scrotum
The supporting structure for the testes. Consists of loose skin and underlying subcutaneous layer that hangs from the root (attached portion) of the penis.
Raphe
A median ridge that separates the scrotum into lateral portions.
Scrotal septum
Divides the scrotum into two compartments, each containing a single testis. Made up of a subcutaneous layer and the dartos muscle.
Dartos muscle
Muscle tissue that is composed of bundles of smooth muscle fibers. Found in the scrotal septum and the subcutaneous layer of the scrotum.
Cremaster muscle
A series of small bands of skeletal muscle that descend as an extension of the internal oblique muscle through the spermatic cord to surround the testes.
Why is the location of the scrotum and the constriction of its muscle fibers relevant?
The location of the scrotum and the contraction of its muscle fibers regulate the temperature of the testes. Normal sperm production requires a temperature about 2–3°C below core body temperature. This lowered temperature is maintained within the scrotum because it is outside the pelvic cavity. In response to cold temperatures, the cremaster and dartos muscles contract. Contraction of the cremaster muscles moves the testes closer to the body, where they can absorb body heat. Contraction of the dartos muscle causes the scrotum to become tight (wrinkled in appearance), which reduces heat loss.
Exposure to warmth reverses these actions.
Testes (testicles)
Paired oval glands in the scrotum measuring about 5 cm (2 in.) long and 2.5 cm (1 in.) in diameter. Each testis (singular) has a mass of 10–15 grams. The testes develop near the kidneys, in the posterior portion of the abdomen, and they usually begin their descent into the scrotum through the inguinal canals (passageways in the lower anterior abdominal wall) during the latter half of the seventh month of fetal development.
Tunica vaginalis
A serous membrane that is derived from the peritoneum and forms during the descent of the testes. Partially covers the testes.
Hydrocele
A collection of serous fluid in the tunica vaginalis. May be caused by injury to the testes or inflammation of the epididymis
Tunica albuginea
A white fibrous capsule composed of dense irregular connective tissue, that is internal to the tunica vaginalis and surrounds the testis. Extends inwards and forms septa that divides the testis into lobules.
Lobules
Internal compartments.
Seminiferous tubules
Tightly coiled tubules where sperm are produced. Each of the 200-300 lobules contain one to three of these.
Spermatogenesis
The process by which the seminiferous tubules of the testes produce sperm.
Spermatogenic cells
Sperm-forming cells. One of two types of cells found in the seminiferous tubules.
Spermatogonia
Stem cells that develop from primordial germ cells.
Primordial germ cells
Arise from the yolk sac and enter the testes during the fifth week of development. Differentiate into spermatogonia.
Sperm cell (spermatozoon)
The most mature spermatogenic cell. Is released into the lumen of the seminiferous tubule.
Sustentacular cells (Sertoli cells)
Large cells embedded among the spermatogenic cells in the seminiferous tubules. Extend from the basement membrane to the lumen of the tubule.
Blood-testis barrier
Tight junctions that are internal to the basement membrane and spermatogonia. Join neighboring sustentacular cells to one another. Form an obstruction. Substances must first pass through the sustentacular cells before they can reach the developing sperm. By isolating the developing gametes from the blood, this prevents an immune response against the spermatogenic cell’s surface antigens, which are recognized as “foreign” by the immune system. The blood–testis barrier does not include spermatogonia.
Interstitial cells (Leydig cells)
Clusters of cells in the spaces between adjacent seminiferous tubules. Secrete testosterone (promotes a man’s libido (sexual drive)).
Androgen
A hormone that promotes the development of masculine characteristics.
Describe the order of spermatogenesis
Spermatogonia -> some of the spermatogonia differentiate into primary spermatocytes ->secondary spermatocytes -> spermatids -> spermatoza (sperm cell)
Primary spermatocyte
A singular primary spermatocyte is produced from a singular spermatogonium. Are diploid (2n) and have 46 chromosomes.
Secondary spermatocyte
Two secondary spermatocytes are produced from a singular primary spermatocyte. Are haploid (n) and have 23 chromosomes. Formed by meiosis I.
Spermatids
Four spermatids are produced from two secondary spermatocytes. Are haploid (n) and have 23 chromosomes. Formed by meiosis II.
Spermiogenesis
Final stage of spermatogenesis. Is the development of haploid spermatids into sperm. No cell division occurs. Each spermatids becomes a single sperm cell.
Sperm cell
Four spermatoza are produced from four spermatids.
Spermiation
The release of sperm from their connections to sustentacular cells.
Sperm
Each day about 300 million sperm complete the process of spermatogenesis. A sperm is about 60 μm long and contains several structures that are highly adapted for reaching and penetrating a secondary oocyte.
What are the two major parts of a sperm? Describe them:
- Head: flattened and pointed; about 4-5 μm long. Contains a nucleus and acrosome.
- Tail: subdivides into the neck, middle piece, principal piece, and end piece.
Nucleus (of head)
Contains 23 highly condensed chromosomes.
Acrosome (of head)
Covers anterior two-thirds of nucleus. Is a caplike vesicle filled with enzymes that help sperm to penetrate a secondary oocyte to bring about fertilization. Among the enzymes are hyaluronidase and proteases.
Neck (of tail)
The constricted region just behind the head that contains centrioles. The centrioles form the microtubules that comprise the remainder of the tail.
Middle piece (of tail)
Contains mitochondria arranged in a spiral, which provide the energy (ATP) for locomotion of sperm to the site of fertilization and for sperm metabolism.
Principal piece (of tail)
The longest portion of the tail.
End piece (of tail)
The terminal, tapering portion of the tail.
Gonadotropinreleasing hormone (GnRH)
Hormone that stimulates gonadotrophs in the anterior pituitary to increase their secretion of the two gonadotropins - lutenizing hormone (LH) and follicle-stimulating hormone (FSH).
Lutenizing hormone (LH)
Stimulates interstitial cells, which are located between seminiferous tubules, to secrete the testosterone.
Testosterone
Hormone that is synthesized from cholesterol in the testes and is the principal androgen. Is lipid-soluble and readily diffuses out of interstitial cells into the interstitial fluid and then into blood. Via negative feedback, testosterone suppresses secretion of LH by anterior pituitary gonadotrophs and suppresses secretion of GnRH by hypothalamic neurosecretory cells.
Dihydrotestosterone (DHT)
An androgen which testosterone gets converted into by the enzyme 5 alpha-reductase. Happens in some target cells, such as those in the external genitals and prostate.
Follicle-stimulating hormone (FSH)
Acts indirectly to stimulate spermatogenesis.
Androgen-binding protein (ABP)
Binds to testosterone, keeping its concentration high. FSH and testosterone act synergistically on the sustentacular cells to stimulate secretion of ABP into the lumen of the seminiferous tubules and into the interstitial fluid around the spermatogenic cells.
Inhibin
Released by sustentacular cells. A protein hormone which inhibits FSH secretion by the anterior pituitary. If spermatogenesis is proceeding too slowly, less inhibin is released, which permits more FSH secretion and an increased rate of spermatogenesis.
Secondary sex characteristics
Traits that distinguish males and females but do not have a direct role in reproduction. These include muscular and skeletal growth that results in wide shoulders and narrow hips; facial and chest hair (within hereditary limits) and more hair on other parts of the body; thickening of the skin; increased sebaceous (oil) gland secretion; and enlargement of the larynx and consequent deepening of the voice.
What are the four effects of the androgens?
- Prenatal development
- Development of male sexual characteristics
- Development of sexual function
- Stimulation of anabolism
Straight tubules
A series of short ducts that sperm and fluid empties into from the lumen of the seminiferous tubules. These straight tubules lead to the rete testis.
Rete testis
A network of ducts that sperm empties into from the straight tubules. These rete testeis lead to the efferent ducts.
Efferent ducts
Coiled ducts in the epididymis which sperm empties into from the rete testis. These efferent ducts lead to the ductus epididymis.
Ductus epididymis
A single tube which sperm empties into from the efferent ducts. Is lined with pseudostratified columnar epithelium and encircled by layers of smooth muscle. The free surfaces of the columnar cells contain stereocilia. Connective tissue around the muscular layer attaches the loops of the ductus epididymis and carries blood vessels and nerves.
Epididymis
Is an organ about 4 cm (1.5 in.) long that curves along the superior and posterior border of each testis having a comma shape in profile. Each epididymis consists mostly of the ductus epididymis. Site of sperm maturation and helps propel sperm into the ductus (vas) deferens during sexual arousal by peristalic contraction of its smooth muscle. Also stores sperm.
What are the three components of the epididymis? Describe them:
- Head: superior portion.
- Body: narrow mid portion.
- Tail: smaller, inferior portion. At its distal end, the tail continues as the ductus (vas) deferens.
Stereocilia (in ductus epididymis)
Are long, branching microvilli (not cilia) that increase the surface area for the reabsorption of degenerated sperm.
Sperm maturation
The process by which sperm acquire motility and the ability to fertilize an ovum. This occurs over a period of about 14 days.
Ductus deferens (vas deferens)
Is about 45 cm (18 in.) long, and ascends along the posterior border of the epididymis through the spermatic cord and then enters the pelvic cavity. There it loops over the ureter and passes over the side and down the posterior surface of the urinary bladder. The mucosa of the ductus deferens consists of pseudostratified columnar epithelium and lamina propria (areolar connective tissue). The muscularis is composed of three layers of smooth muscle; the inner and outer layers are longitudinal, and the middle layer is circular. Conveys sperm during sexual arousal from the epididymis toward the urethra by peristaltic contractions of its muscular coat. Like the epididymis, the ductus deferens also can store sperm.
Ampulla
The dilated terminal portion of the ductus deferens.
Spermatic cord
A supporting structure of the male reproductive system that ascends out of the scrotum. Each spermatic cord consists of a ductus (vas) deferens as it ascends through the scrotum, the testicular artery, veins that drain the testis and carry testosterone into circulation (the pampiniform plexus), autonomic nerves, lymphatic vessels, and the cremaster muscle.
Inguinal canal
An oblique passageway in the anterior abdominal wall just superior and parallel to the medial half of the inguinal ligament. The spermatic cord and the ilioinguinal nerve pass through here.
Where does the inguinal canal begin and where does it end?
Originates at the deep (abdominal) inguinal ring (a slitlike opening in the aponeurosis of the transversus abdominis muscle) and ends at the superficial (subcutaneous) inguinal ring (a somewhat triangular opening in the aponeurosis of the external oblique muscle).
Varicocele
A swelling in the scrotum due to a dilation of the veins that drain the testes.
Ejaculatory duct
Formed by the union of the duct from the seminal vesicle and the ampulla of the ductus (vas) deferens. Are just superior to the base (superior portion) of the prostate and pass inferiorly and anteriorly through the prostate. They terminate in the prostatic urethra, where they eject sperm and seminal vesicle secretions just before the release of semen from the urethra to the exterior.
Urethra
The shared terminal duct of the reproductive and urinary systems. Serves as a passageway for both semen and urine. Passes through the prostate and the penis.
What three parts does the urethra get subdivided into?
- Prostatic urethra
- Intermediate (membranous) urethra
- Spongy urethra
External urethral orifice
The opening of the urethra to the exterior.
Seminal vesicles (seminal glands)
Secrete an alkaline, viscous fluid that helps neutralize acid in the female reproductive tract, provides fructose for ATP production by sperm, contributes to sperm motility and viability, and helps semen coagulate after ejaculation.
Prostate
Secretes a milky, slightly acidic fluid that contains enzymes that break down clotting proteins from the seminal vesicles.
What four substances does the fluid that the prostate secretes contain?
- Citric acid
- Several proteolytic enzymes, such as prostate-specific antigen (PSA)
- Acid phosphate
- Seminalplasmin
Bulbourethral glands (Cowper’s glands)
Secrete an alkaline fluid that neutralizes the acidic environment of the urethra and mucus that lubricates the lining of the urethra and the tip of the penis during sexual intercourse.
Semen
A mixture of sperm and seminal fluid.
Seminal fluid
A liquid that consists of the secretions of the seminiferous tubules, seminal vesicles, prostate, and bulbourethral glands. Provides sperm with a transportation medium, nutrients, and protection from the hostile acidic environment of the male’s urethra and the female’s vagina.
Capacitation
A series of functional changes that sperm undergo in the female reproductive tract before they are able to fertilize a secondary oocyte. Capacitation causes a sperm cell’s tail to beat even more vigorously, and it prepares the sperm cell’s plasma membrane to fuse with the oocyte’s plasma membrane.
Hemospermia
The presence of blood in semen.
Penis
Contains the urethra and is a passageway for the ejaculation of semen and the excretion of urine. Cylindrical in shape.
What three components does the penis consist of?
- Body
- Glans penis
- Root
What are the two cylindrical masses of the body of the penis? Describe them:
- Corpora cavernosa penis: two dorsal masses
- Corpus spongiosum penis: smaller midventral masses; contains the spongy urethra and keeps it open during ejaculation.
Tunica albuginea cavernosa penis
Fibrous tissue that surrounds the two cylindrical masses.
Erectile tissue
Composed of numerous blood sinuses (vascular spaces) lined by endothelial cells and surrounded by smooth muscle and elastic connective tissue. Encloses the three cylindrical masses of the body of the penis.
Corona
Margin of the glans penis.
What are the two components of the root of the penis? Describe them:
- Bulb of the penis: the expanded posterior continuation of the base of the corpus spongiosum penis.
- Crura of the penis: two separated and tapered portions of the corpora cavernosa penis.
What two ligaments support the weight of the penis?
- Fundiform ligament
- Suspensory ligament of the penis
Female reproductive system
Include the ovaries (female gonads); the uterine (fallopian) tubes, or oviducts; the uterus; the vagina; and external organs, which are collectively called the vulva, or pudendum. The mammary glands are considered part of both the integumentary system and the female reproductive system.
Ovaries
Produce secondary oocytes and hormones, including progesterone and estrogens (female sex hormones), inhibin, and relaxin.
Identify where the broad ligament, mesovarium, ovarian ligament, and suspensatory ligament is:
Hilum
Found in each ovary. The point of entrance and exit for blood vessels and nerves along which the mesovarium is attached.
What seven parts does each ovary consist of? Describe them:
- Ovarian mesothelium (surface epithelium): a layer of simple epithelium (low cuboidal or squamous) that covers the surface of the ovary.
- Tunica albuginea: a whitish capsule of dense irregular connective tissue located immediately deep to the ovarian mesothelium.
- Ovarian cortex: a region just deep to the tunica albuginea. It consists of ovarian follicles surrounded by dense irregular connective tissue that contains collagen fibers and stromal cells.
- Ovarian medulla: deep to the ovarian cortex. Similar to the ovarian cortex, but consists of more loosely arranged connective tissue and contains blood vessels, lymphatic vessels, and nerves.
- Ovarian follicles: in the cortex and consist of oocytes and the cells surrounding them. When these surrounding cells form a single layer, they are follicular cells. When these surrounding cells form several layers, later on in development, they are granulosa cells. The surrounding cells nourish the developing oocyte and begin to secrete estrogens as the follicle grows larger.
- Mature (graafian) follicle: a large, fluid-filled follicle that is ready to rupture and expel its secondary oocyte.
- Corpus luteum: contains the remnants of a mature follicle after ovulation. Produces progesterone, estrogens, relaxin, and inhibin until it degenerates into the corpus albicans.
Corpus albicans
Fibrous scar tissue.
Oogenesis
The formation of gametes in the ovaries. Begins in females before they are even born.
Oogonia
Diploid (2n) stem cells that divide mitotically to produce germ cells.
Primary oocytes
Larger cells that some oogonia develop into. Enter prophose of meiosis I during fetal development but don’t complete this stage until after puberty.
Primordial follicle
Primary oocyte and single layer of flat follicular cells that surround it.
Stromal cells
Fibroblast-like cells.
Primary follicles
What primordial follicles develop into. Consist of a primary oocyte that is surrounded by granulosa cells in a later stage of development.
Zona pellucida
A clear glycoprotein layer between the primary oocyte and the granulosa cells.
Theca folliculi
Organized layer formed by stromal cells that surround the basement membrane.
Secondary follicle
What a primary follicle develops into.
What are the two layers that the theca folliculi differentiates into in a secondary follicle? Describe them:
- Theca interna: highly vascularized internal layer of cuboidal secretory cells that secrete androgens.
- Theca externa: an outer layer of stromal cells and collagen fibers.
Antrum
Cavity in the center of the secondary follicle.
Corona radiata
What the innermost layer of the granulosa becomes when it firmly attaches to the zona pellucida.
First polar body
Smaller haploid (n) cell produced by meiosis I that essentially is a packet of discarded nuclear material.
Secondary oocyte
Larger haploid (n) cell produced by meiosis I. Once formed, it begins meiosis II but then stops in metaphase.
Ovum
Or mature egg; the larger haploid (n) cell that the secondary oocyte splits into.
Second polar body
The smaller haploid (n) cell that the secondary oocyte splits into.
Zygote
A diploid (2n) cell that is the product of the nuclei of the sperm cell and the ovum uniting.
Uterine tubes (fallopian tubes or oviducts)
Two tubes that extend laterally from the uterus. Lie within the folds of the broad ligaments of the uterus. Provide a route for sperm to reach an ovum and transport secondary oocytes and fertilized ova from the ovaries to the uterus.
Infundibulum (of uterine tube)
Funnel-shaped portion of each tube.
Fimbriae
A fringe of fingerlike projections.
Ampulla (of uterine tube)
The widest, longest portion of the uterine tube. Makes up two-thirds of its length.
Isthmus (of uterine tube)
The medial, short, narrow, thick-walled portion of the uterine tube that joins the uterus.
Peg cells
Non-ciliated cells that have microvilli and secrete a fluid that provides nutrition for the ovum. Found in the mucosa of the uterine tubes.
Uterus
The womb; serves as part of the pathway for sperm deposited in the vagina to reach the uterine tubes. It is also the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor. During reproductive cycles when implantation does not occur, the uterus is the source of menstrual flow.
What are the three subdivisions of the uterus?
- Fundus
- Body
- Cervix
Isthmus (of uterus)
A constricted region between the body of the uterus and the cervix.
Uterine cavity
The interior of the body of the uterus.
Cervical canal
The interior of the cervix.
Internal os
Where the cervical canal opens into the uterine cavity.
External os
Where the cervical canal opens into the vagina.
Identify where the broad ligament, uterosacral ligament, cardinal (lateral cervical) ligament, and round ligament is:
What three layers does the uterus consist of? Describe them:
- Perimetrium: the outer layer. Composed of simple squamous epithelium and areolar connective tissue.
- Myometrium: the middle layer. Composed of three layers of smooth muscle fibers that are thickest in the fundus and thinnest in the cervix. The thicker middle layer is circular; the inner and outer layers are longitudinal or oblique.
- Endometrium: the inner layer.
Vesicouterine pouch
A shallow pouch formed by the perimetrium.
Retrouterine pouch (pouch of Douglas)
A deep pouch formed by the perimetrium. It is the most inferior point in the pelvic cavity.
What are the three components of the uterus?
- An innermost layer composed of simple columnar epithelium (ciliated and secretory cells) lines the lumen.
- An underlying endometrial stroma is a very thick region of lamina propria (areolar connective tissue).
- Endometrial (uterine) glands develop as invaginations of the luminal epithelium and extend almost to the myometrium.
What are the two layers that the endometrium gets divided into?
- Stratum functionalis (functional layer): lines the uterine cavity and sloughs off during menstruation.
- Stratum basalis (basal layer): the deepest layer; is permanent and gives rise to a new stratum functionalis after each menstruation.
Uterine arteries
Branches of the internal iliac artery and supplies blood to the uterus.
Identify where the arcuate arteries, radial arteries, straight arterioles, and spiral arterioles are:
Vagina
A long fibromuscular canal lined with mucous membrane that extends from the exterior of the body to the uterine cervix. It is the receptacle for the penis during sexual intercourse, the outlet for menstrual flow, and the passageway for childbirth.
Fornix
Surrounds the vaginal attachment to the cervix.
Mucosa
Is continuous with that of the uterus. Consists of nonkeratinized stratified squamous epithelium and areolar connective tissue that lies in the rugae.
Rugae
A series of transverse folds.
Muscularis
Is composed of an inner circular layer and an outer longitudinal layer of smooth muscle that can stretch considerably to accommodate the penis during sexual intercourse and a child during birth.
Adventitia
The superficial layer of the vagina. Consists of areolar connective tissue. Anchors the vagina to adjacent organs such as the urethra and urinary bladder anteriorly and the rectum and anal canal posteriorly.
Hymen
A thin fold of vascularized mucous membrane. Forms a border around and partially closes the vaginal orifice.
Vaginal orifice
The opening of the vagina to the exterior.
What are the five components of the vulva? Describe them:
- Labia majora: two longitudinal folds of skin that extend inferiorly and posteriorly. Are covered by pubic hair and contain an abundance of adipose tissue, sebaceous (oil) glands, and apocrine sudoriferous (sweat) glands.
- Labia minora: two smaller folds of skin. Are devoid of pubic hair and fat and have few sudoriferous glands, but they do contain many sebaceous glands which produce antimicrobial substances and provide some lubrication during sexual intercourse.
- Clitoris: a small cylindrical mass. Is capable of enlargement on tactile stimulation and has a role in sexual excitement in the female.
- Vestibule: contains the hymen (if still present), the vaginal orifice, the external urethral orifice, and the openings of the ducts of several glands.
- Bulb of the vestibule: consists of two elongated masses of erectile tissue just deep to the labia on either side of the vaginal orifice. The bulb of the vestibule becomes engorged with blood during sexual arousal, narrowing the vaginal orifice and placing pressure on the penis during intercourse.
Prepuce of the clitoris
A layer of skin that is formed at the point where the labia minora unite and covers the body of the clitoris.
Perineum
The diamond-shaped area medial to the thighs and buttocks of both males and females. It contains the external genitals and anus.
What two componenets can the perineum be divided into? Describe them:
- Urogenital triangle: anterior; contains the external genitals.
- Anal triangle: posterior; contains the anus.
Breast
Hemispheric projection of variable size anterior to the pectoralis major and serratus anterior muscles and attached to them by a layer of fascia composed of dense irregular connective tissue.
Nipple
Pigmented projection that has a series of lactiferous ducts.
Lactiferous ducts
Ducts where milk emerges.
Areola
Circular pigmented area of skin surrounding the nipple. Contains modified sebaceous (oil) glands.
Suspensory ligaments of the breast (Cooper’s ligaments)
Strands of connective tissue that run between the skin and fascia and support the breast.
Mammary gland
A modified sudoriferous (sweat) gland that produces milk.
Lobules
Smaller compartments within a mammary gland.
Alveoli
Grape-like clusters of milk-secreting glands that are embedded in connective tissue.
What is the flow of milk from the alveoli?
Alveoli -> secondary tubules -> mammary ducts -> lactiferous sinuses -> lactiferous duct
What are the five important functions of estrogens secreted by ovarian follicles?
- Promote the development and maintenance of female reproductive structures, secondary sex characteristics, and the breasts. The secondary sex characteristics include distribution of adipose tissue in the breasts, abdomen, mons pubis, and hips; voice pitch; a broad pelvis; and pattern of hair growth on the head and body.
- Increase protein anabolism, including the building of strong bones. In this regard, estrogens are synergistic with human growth hormone (hGH).
- Lower blood cholesterol level, which is probably the reason that women under age 50 have a much lower risk of coronary artery disease than do men of comparable age.
- Every month, after menstruation occurs, estrogens stimulate proliferation of the stratum basalis to form a new stratum functionalis that replaces the one that has sloughed off.
- Moderate levels in the blood inhibit both the release of GnRH by the hypothalamus and secretion of LH and FSH by the anterior pituitary.
Progesterone
Secreted mainly by cells of the corpus luteum, cooperates with estrogens to prepare and maintain the endometrium for implantation of a fertilized ovum and to prepare the mammary glands for milk secretion. High levels of progesterone also inhibit secretion of GnRH and LH.
Relaxin
Produced by the corpus luteum during each monthly cycle relaxes the uterus by inhibiting contractions of the myometrium. Presumably, implantation of a fertilized ovum occurs more readily in a “quiet” uterus. During pregnancy, the placenta produces much more relaxin, and it continues to relax uterine smooth muscle. At the end of pregnancy, relaxin also increases the flexibility of the pubic symphysis and may help dilate the uterine cervix, both of which ease delivery of the baby.
Inhibin
Secreted by granulosa cells of growing follicles and by the corpus luteum after ovulation. It inhibits secretion of FSH and, to a lesser extent, LH.
What are the four phases of the female reproductive cycle? Describe them:
- Menstrual phase (menstrualtion or menses): lasts for roughly the first 5 days of the cycle.
- Preovulatory phase (proliferative phase): the time between the end of menstruation and ovulation. Is more variable in length than the other phases and accounts for most of the differences in length of the cycle. It lasts from days 6 to 13 in a 28-day cycle.
- Ovulation: the rupture of the mature (graafian) follicle and the release of the secondary oocyte into the pelvic cavity, usually occurs on day 14 in a 28-day cycle. During ovulation, the secondary oocyte remains surrounded by its zona pellucida and corona radiata.
- Postovulatory phase (luteal phase and secretory phase): the time between ovulation and onset of the next menses. In duration, it is the most constant part of the female reproductive cycle. It lasts for 14 days in a 28-day cycle, from day 15 to day 28.
What are the three steps in the positive feedback effect on the cells that secrete LH and gonadotropin-releasing hormone (GnRH) and cause ovulation?
- A high concentration of estrogens stimulates more frequent release of GnRH from the hypothalamus. It also directly stimulates gonadotrophs in the anterior pituitary to secrete LH.
- GnRH promotes the release of FSH and additional LH by the anterior pituitary.
- LH causes rupture of the mature (graafian) follicle and expulsion of a secondary oocyte about 9 hours after the peak of the LH surge. The ovulated oocyte and its corona radiata cells are usually swept into the uterine tube.
