Module 27: The Reproductive System

Lesson 4: The Ovarian Cycle

Chu Kỳ Buồng Trứng

Nội dung bài học:
Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module The Reproductive System.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Reproductive System

alveoli
(of the breast) milk-secreting cells in the mammary gland
ampulla
(of the uterine tube) middle portion of the uterine tube in which fertilization often occurs
antrum
fluid-filled chamber that characterizes a mature tertiary (antral) follicle
areola
highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling
Bartholin’s glands
(also, greater vestibular glands) glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands
blood–testis barrier
tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm
body of uterus
middle section of the uterus
broad ligament
wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall
bulbourethral glands
(also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation
cervix
elongate inferior end of the uterus where it connects to the vagina
clitoris
(also, glans clitoris) nerve-rich area of the vulva that contributes to sexual sensation during intercourse
corpus albicans
nonfunctional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum
corpus cavernosum
(plural = corpora cavernosa) either of two columns of erectile tissue in the penis that fill with blood during an erection
corpus luteum
transformed follicle after ovulation that secretes progesterone
corpus spongiosum
column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis
ductus deferens
(also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens
ejaculatory duct
duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra
endometrium
inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses
epididymis
(plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation
fimbriae
fingerlike projections on the distal uterine tubes
follicle
ovarian structure of one oocyte and surrounding granulosa (and later theca) cells
folliculogenesis
development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins
fundus
(of the uterus) domed portion of the uterus that is superior to the uterine tubes
gamete
haploid reproductive cell that contributes genetic material to form an offspring
glans penis
bulbous end of the penis that contains a large number of nerve endings
gonadotropin-releasing hormone (GnRH)
hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland
gonads
reproductive organs (testes and ovaries) that produce gametes and reproductive hormones
granulosa cells
supportive cells in the ovarian follicle that produce estrogen
hymen
membrane that covers part of the opening of the vagina
infundibulum
(of the uterine tube) wide, distal portion of the uterine tube terminating in fimbriae
inguinal canal
opening in abdominal wall that connects the testes to the abdominal cavity
isthmus
narrow, medial portion of the uterine tube that joins the uterus
labia majora
hair-covered folds of skin located behind the mons pubis
labia minora
thin, pigmented, hairless flaps of skin located medial and deep to the labia majora
lactiferous ducts
ducts that connect the mammary glands to the nipple and allow for the transport of milk
lactiferous sinus
area of milk collection between alveoli and lactiferous duct
Leydig cells
cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell
mammary glands
glands inside the breast that secrete milk
menarche
first menstruation in a pubertal female
menses
shedding of the inner portion of the endometrium out though the vagina; also referred to as menstruation
menses phase
phase of the menstrual cycle in which the endometrial lining is shed
menstrual cycle
approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase
mons pubis
mound of fatty tissue located at the front of the vulva
Müllerian duct
duct system present in the embryo that will eventually form the internal female reproductive structures
myometrium
smooth muscle layer of uterus that allows for uterine contractions during labor and expulsion of menstrual blood
oocyte
cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilization to become a haploid ovum
oogenesis
process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilization, the ovum
oogonia
ovarian stem cells that undergo mitosis during female fetal development to form primary oocytes
ovarian cycle
approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase
ovaries
female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone)
ovulation
release of a secondary oocyte and associated granulosa cells from an ovary
ovum
haploid female gamete resulting from completion of meiosis II at fertilization
penis
male organ of copulation
perimetrium
outer epithelial layer of uterine wall
polar body
smaller cell produced during the process of meiosis in oogenesis
prepuce
(also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin
primary follicles
ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells
primordial follicles
least developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells
proliferative phase
phase of the menstrual cycle in which the endometrium proliferates
prostate gland
doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation
puberty
life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction
rugae
(of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth
scrotum
external pouch of skin and muscle that houses the testes
secondary follicles
ovarian follicles with a primary oocyte and multiple layers of granulosa cells
secondary sex characteristics
physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function
secretory phase
phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo
semen
ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands
seminal vesicle
gland that produces seminal fluid, which contributes to semen
seminiferous tubules
tube structures within the testes where spermatogenesis occurs
Sertoli cells
cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell
sperm
(also, spermatozoon) male gamete
spermatic cord
bundle of nerves and blood vessels that supplies the testes; contains ductus deferens
spermatid
immature sperm cells produced by meiosis II of secondary spermatocytes
spermatocyte
cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids
spermatogenesis
formation of new sperm, occurs in the seminiferous tubules of the testes
spermatogonia
(singular = spermatogonium) diploid precursor cells that become sperm
spermiogenesis
transformation of spermatids to spermatozoa during spermatogenesis
suspensory ligaments
bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis
tertiary follicles
(also, antral follicles) ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum
testes
(singular = testis) male gonads
theca cells
estrogen-producing cells in a maturing ovarian follicle
uterine tubes
(also, fallopian tubes or oviducts) ducts that facilitate transport of an ovulated oocyte to the uterus
uterus
muscular hollow organ in which a fertilized egg develops into a fetus
vagina
tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby
vulva
external female genitalia
Wolffian duct
duct system present in the embryo that will eventually form the internal male reproductive structures
Nội dung này đang được cập nhật.
Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
The ovarian cycle is a set of predictable changes in oocytes and ovarian follicles. During the reproductive years, it is a roughly 28-day cycle that can be correlated with, but is not the same as, the menstrual cycle. The cycle includes two interrelated processes: oogenesis (the production of gametes) and folliculogenesis (the growth and development of ovarian follicles).
Gametogenesis in females is called oogenesis. The process begins with the ovarian stem cells, or oogonia (Figure 1). Oogonia are formed during fetal development, and divide via mitosis, much like spermatogonia in the testis. Unlike spermatogonia, however, oogonia form primary oocytes in the fetal ovary prior to birth. These primary oocytes are then arrested in this stage of meiosis I, only to resume it years later, beginning at puberty and continuing until the person is near menopause (the cessation of a female’s reproductive functions). The number of primary oocytes present in the ovaries declines from one to two million in an infant, to approximately 400,000 at puberty, to zero by the end of menopause.

The initiation of ovulation—the release of an oocyte from the ovary—marks the transition from puberty into reproductive maturity. From then on, throughout a the reproductive years, ovulation occurs approximately once every 28 days. Just prior to ovulation, a surge of luteinizing hormone triggers the resumption of meiosis in a primary oocyte. This initiates the transition from primary to secondary oocyte. However, as you can see in Figure 1, this cell division does not result in two identical cells. Instead, the cytoplasm is divided unequally, and one daughter cell is much larger than the other. This larger cell, the secondary oocyte, eventually leaves the ovary during ovulation. The smaller cell, called the first polar body, may or may not complete meiosis and produce second polar bodies; in either case, it eventually disintegrates. Therefore, even though oogenesis produces up to four cells, only one survives.

How does the diploid secondary oocyte become an ovum—the haploid female gamete? Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers. Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a (haploid) sperm, becomes the first diploid cell of the new offspring (a zygote). Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote.

The larger amount of cytoplasm contained in the female gamete is used to supply the developing zygote with nutrients during the period between fertilization and implantation into the uterus. Interestingly, sperm contribute only DNA at fertilization —not cytoplasm. Therefore, the cytoplasm and all of the cytoplasmic organelles in the developing embryo are of egg-derived origin. This includes mitochondria, which contain their own DNA. Scientific research in the 1980s determined that mitochondrial DNA was maternally inherited, meaning that you can trace your mitochondrial DNA directly to your biological mother, her mother, and so on back through your female ancestors.
Again, ovarian follicles are oocytes and their supporting cells. They grow and develop in a process called folliculogenesis, which typically leads to ovulation of one follicle approximately every 28 days, along with death to multiple other follicles. The death of ovarian follicles is called atresia, and can occur at any point during follicular development. Recall that, a female infant at birth will have one to two million oocytes within the ovarian follicles, and that this number declines throughout life until menopause, when no follicles remain. As you’ll see next, follicles progress from primordial, to primary, to secondary and tertiary stages prior to ovulation—with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation.

Folliculogenesis begins with follicles in a resting state. These small primordial follicles are present in newborn females and are the prevailing follicle type in the adult ovary (Figure 2). Primordial follicles have only a single flat layer of support cells, called granulosa cells, that surround the oocyte, and they can stay in this resting state for years—some until right before menopause.

After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary follicles. Primary follicles start with a single layer of granulosa cells, but the granulosa cells then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate. As the granulosa cells divide, the follicles—now called secondary follicles (see Figure 2)—increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells—cells that work with the granulosa cells to produce estrogens.

Within the growing secondary follicle, the primary oocyte now secretes a thin acellular membrane called the zona pellucida that will play a critical role in fertilization. A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum. Follicles in which the antrum has become large and fully formed are considered tertiary follicles (or antral follicles). Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary. Keep in mind that most follicles don’t make it to this point. In fact, roughly 99 percent of the follicles in the ovary will undergo atresia, which can occur at any stage of folliculogenesis.
The process of development that we have just described, from primordial follicle to early tertiary follicle, takes approximately two months in humans. The final stages of development of a small cohort of tertiary follicles, ending with ovulation of a secondary oocyte, occur over a course of approximately 28 days. These changes are regulated by many of the same hormones that regulate the male reproductive system, including GnRH, LH, and FSH.

As in males, the hypothalamus produces GnRH, a hormone that signals the anterior pituitary gland to produce the gonadotropins FSH and LH (Figure 3). These gonadotropins leave the pituitary and travel through the bloodstream to the ovaries, where they bind to receptors on the granulosa and theca cells of the follicles. FSH stimulates the follicles to grow (hence its name of follicle-stimulating hormone), and the five or six tertiary follicles expand in diameter. The release of LH also stimulates the granulosa and theca cells of the follicles to produce the sex steroid hormone estradiol, a type of estrogen. This phase of the ovarian cycle, when the tertiary follicles are growing and secreting estrogen, is known as the follicular phase.

The more granulosa and theca cells a follicle has (that is, the larger and more developed it is), the more estrogen it will produce in response to LH stimulation. As a result of these large follicles producing large amounts of estrogen, systemic plasma estrogen concentrations increase. Following a classic negative feedback loop, the high concentrations of estrogen will stimulate the hypothalamus and pituitary to reduce the production of GnRH, LH, and FSH. Because the large tertiary follicles require FSH to grow and survive at this point, this decline in FSH caused by negative feedback leads most of them to die (atresia). Typically only one follicle, now called the dominant follicle, will survive this reduction in FSH, and this follicle will be the one that releases an oocyte. Scientists have studied many factors that lead to a particular follicle becoming dominant: size, the number of granulosa cells, and the number of FSH receptors on those granulosa cells all contribute to a follicle becoming the one surviving dominant follicle.

When only the one dominant follicle remains in the ovary, it again begins to secrete estrogen. It produces more estrogen than all of the developing follicles did together before the negative feedback occurred. It produces so much estrogen that the normal negative feedback doesn’t occur. Instead, these extremely high concentrations of systemic plasma estrogen trigger a regulatory switch in the anterior pituitary that responds by secreting large amounts of LH and FSH into the bloodstream (see Figure 3). The positive feedback loop by which more estrogen triggers release of more LH and FSH only occurs at this point in the cycle.

It is this large burst of LH (called the LH surge) that leads to ovulation of the dominant follicle. The LH surge induces many changes in the dominant follicle, including stimulating the resumption of meiosis of the primary oocyte to a secondary oocyte. As noted earlier, the polar body that results from unequal cell division simply degrades. The LH surge also triggers proteases (enzymes that cleave proteins) to break down structural proteins in the ovary wall on the surface of the bulging dominant follicle. This degradation of the wall, combined with pressure from the large, fluid-filled antrum, results in the expulsion of the oocyte surrounded by granulosa cells into the peritoneal cavity. This release is ovulation.

In the next section, you will follow the ovulated oocyte as it travels toward the uterus, but there is one more important event that occurs in the ovarian cycle. The surge of LH also stimulates a change in the granulosa and theca cells that remain in the follicle after the oocyte has been ovulated. This change is called luteinization (recall that the full name of LH is luteinizing hormone), and it transforms the collapsed follicle into a new endocrine structure called the corpus luteum, a term meaning “yellowish body” (see Figure 2). Instead of estrogen, the luteinized granulosa and theca cells of the corpus luteum begin to produce large amounts of the sex steroid hormone progesterone, a hormone that is critical for the establishment and maintenance of pregnancy. Progesterone triggers negative feedback at the hypothalamus and pituitary, which keeps GnRH, LH, and FSH secretions low, so no new dominant follicles develop at this time.

The post-ovulatory phase of progesterone secretion is known as the luteal phase of the ovarian cycle. If pregnancy does not occur within 10 to 12 days, the corpus luteum will stop secreting progesterone and degrade into the corpus albicans, a nonfunctional “whitish body” that will disintegrate in the ovary over a period of several months. During this time of reduced progesterone secretion, FSH and LH are once again stimulated, and the follicular phase begins again with a new cohort of early tertiary follicles beginning to grow and secrete estrogen.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

The unequal cell division of oogenesis produces one to three polar bodies that later degrade, as well as a single haploid ovum, which is produced only if there is penetration of the secondary oocyte by a sperm cell.

(a) The maturation of a follicle is shown in a clockwise direction proceeding from the primordial follicles. FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells. Once the follicle is mature, it ruptures and releases the oocyte. Cells remaining in the follicle then develop into the corpus luteum. (b) In this electron micrograph of a secondary follicle, the oocyte, theca cells (thecae folliculi), and developing antrum are clearly visible. EM × 1100. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

The hypothalamus and pituitary gland regulate the ovarian cycle and ovulation. GnRH activates the anterior pituitary to produce LH and FSH, which stimulate the production of estrogen and progesterone by the ovaries.

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. The ovaries produce oocytes, the female gametes, in a process called oogenesis.
  2. As with spermatogenesis, meiosis produces the haploid gamete (in this case, an ovum).
  3. However, it is completed only in an oocyte that has been penetrated by a sperm.
  4. In the ovary, an oocyte surrounded by supporting cells is called a follicle.
  5. In folliculogenesis, primordial follicles develop into primary, secondary, and tertiary follicles.
  6. Early tertiary follicles with their fluid-filled antrum will be stimulated by an increase in follicle stimulating hormone (or FSH) to grow in the 28-day ovarian cycle.
  7. Supporting granulosa and theca cells in the growing follicles produce estrogens, until the level of estrogen in the bloodstream is high enough that it triggers negative feedback at the hypothalamus and pituitary.
  8. This results in a reduction of FSH and luteinizing hormone (or LH), and most tertiary follicles in the ovary undergo atresia (which means that they die).
  9. One follicle, usually the one with the most FSH receptors, survives this period and is now called the dominant follicle.
  10. The dominant follicle produces more estrogen, triggering positive feedback and the LH surge that will induce ovulation.
  11. Following ovulation, the granulosa cells of the empty follicle luteinize and transform into the progesterone-producing corpus luteum.
  12. The ovulated oocyte with its surrounding granulosa cells is picked up by the infundibulum of the uterine tube, and beating cilia help to transport it through the tube toward the uterus.
  13. Fertilization occurs within the uterine tube, and the final stage of meiosis is completed.
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