Flashcards in Lab 4: Reproductive System Deck (73):
In humans, spermatogenesis takes ...
Spermatogonia are types of ...
Describe the two fates of the spermatogonia after mitosis.
1) Some remain near the basement membrane in an undifferentiated state to serve as a reservoir of cells for future cell division.
2) Rest lose contact with basement membrane, squeeze through tight junctions of the blood-testis barrier, undergo developmental changes, and differentiate into primary spermatocytes.
Does replication of DNA occur to primary spermatocytes or secondary spermatocytes?
What unique process occurs during spermatogenesis?
As spermatogenic cells proliferate, they fail to complete cytoplasmic separation (cytokinesis). The cells remain in contact via cytoplasmic bridges through their entire development.
What is the purpose of the unique process of spermatogenesis?
This pattern of development most likely accounts for the synchronised production of sperm in any given area of the seminiferous tubule. The larger x chromosome may carry genes needed for spermatogenesis that are lacking on the smaller Y chromosome.
What occurs during spermiation?
Sperm are released from their connections to sustentacular cells.
What two systems are the mammary glands a part of?
Integumentary and female reproductive system
What hormones do ovaries secrete?
Progesterone, estrogens, inhibin and relaxin
What holds ovaries in position?
A series of ligaments.
What is the broad ligament?
A fold of the parietal peritoneum.
How does he broad ligament attach to the ovaries?
By a double-layered fold of peritoneum called the mesovarium.
What does the ovarian ligament anchor?
Anchors the ovaries to the uterus
What anchors the ovaries to the pelvic wall?
What is the purpose of the hilum of an ovary?
Point of entrance and exit for blood vessels and nerves along which the mesovarium is attached.
List the layers of the ovary
Describe the germinal epithelium.
Layer of simple epithelium that covers the surface of the ovary.
Describe the tunica albuginea.
A whitish capsule of dense irregular connective tissue located immediately deep to the germinal epithelium.
Describe the ovarian cortex.
A region just deep to the tunica albuginea. It consists of ovarian follicles surrounded by dense irregular connective tissue that contains collagen fibres and fibroblast-like cells called stromal cells.
Describe the ovarian medulla.
Deep to the ovarian cortex. The border between the cortex and medulla is indistinct, but the medulla consists of more loosely arranged connective tissue and contains blood vessels, lymphatic vessels, and nerves.
Where are ovarian follicles found? What do they consist of?
In the cortex. They consist of oocytes in various stages of development, plus the cells surrounding them.
When the surrounding cells of an oocyte form a single layer, they are called ...
Later in development, when they form several layers, they are referred to as ...
What do the surroundings cells of an oocyte do?
Nourish the developing oocyte and begin to secrete oestrogen as the follicle grows larger.
What is a mature follicle?
A large, fluid-filled follicle that is ready to rupture and expel its secondary oocyte.
What does the corpus luteum contain? What does it produce? What does it then form?
The remnants of a mature follicle after ovulation.
Produces progesterone, estrogens, relaxin and inhibin until it degenerates into fibrous scar tissue called the corpus albicans.
What happens to the primordial (primitive) germ cells during early fetal development?
Migrate from yolk sac to the ovaries.
What happens to germ cells after they have migrated to the ovaries?
Differentiate into oogonia
What are oogonia?
Diploid stem cells that divide mitotically to produce millions of germ cells.
Before birth. most germ cells degenerate in a process known as ...
However, what happens to a few?
A few develop into larger cells called primary oocytes that enter prophase of meiosis I during fetal development, but do not complete this phase until after puberty.
Describe the oocytes during the arrested stage of development.
Each primary oocyte is surrounded by a single layer of flat follicular cells and the entire structure is called a primordial follicle.
What does the ovarian cortex surrounding the primordial follicle consist of?
Collagen fibres and fibroblast-like stromal cells.
Describe the two layers of the theca that develop in a secondary follicle.
Theca interna: A highly vascularised internal layer of cuboidal secretory cells that secrete estrogens.
Theca externa: An outer layer of stromal cells and collagen fibres.
When is the first polar body formed?
While in the Graafian follicle, just before ovulation, the diploid primary oocyte completes meiosis I, producing two haploid cells of unequal size. The smaller is called the first polar body.
What is the first polar body made up of?
A packet of discarded nuclear material.
When does meiosis II stop in a secondary follicle?
What is expelled at ovulation?
Secondary oocyte, first polar body, corona radiata
When does meiosis II resume?
If a sperm penetrates the secondary oocyte.
Describe the formation of the second polar body.
The secondary oocyte splits into two haploid cells of unequal size. Larger is the ovum or mature egg and smaller is the second polar body.
In total, what is formed due to oogenesis?
3 polar bodies and one ovum
Distinguish between the ovarian and uterine cycles.
O: A series of events in the ovaries that occur during and after the maturation of an oocyte.
U: A concurrent series of changes in the endometrium of the uterus to prepare it for the arrival of a fertilised ovum that will develop there until birth.
What happens to ovarian hormones if fertilisation does not occur?
Hormones wane, which causes the stratum functionalis of the endometrium to slough off.
What does the term female reproductive cycle encompass?
The ovarian and uterine cycles, the hormonal changes that regulate them and the related cyclical changes in the breasts and cervix.
What does FSH and LH stimulate in the follicle?
FSH: Initiates follicular growth
LH: Stimulates further development of the ovarian follicles. Triggers ovulation and formation of corpus luteum. Causes corpus luteum to produce and secrete oestrogens, progesterone, relaxin, and inhibin.
Both stimulate follicles to secrete oestrogens: LH stimulates theca cells to produce androgens. Under influence of FSH, androgens are taken up by the granulosa cells of the follicle and then converted into oestrogens.
What are the functions of the oestrogens secreted by ovarian follicles?
1) Promote development and maintenance of female reproductive structures, secondary sex characteristics and the breasts.
2) Increase protein anabolism, including the building of strong bones.
3) Lower blood cholesterol.
4) Moderate levels inhibit both the release of GnRH by the hypothalamus and secretion of LH and FSH by the anterior pituitary.
In what regard are oestrogens synergistic with human growth hormone?
They increase protein anabolism.
What is the function of progesterone? What is it mainly secreted by?
Cells of the corpus luteum.
Cooperates with oestrogens to prepare and maintain the endometrium for implantation of a fertilised ovum and to prepare mammary glands for milk secretion. High levels also inhibit secretion of GnRH and LH.
What are the functions of relaxin?
Relaxes the uterus by inhibiting contractions of the myometrium. Implantation of a fertilised 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, it also increase the flexibility of the pubic symphysis and may help dilate the uterine cervix, both of which ease delivery of the baby.
What is inhibin secreted by? What are its functions?
The granulosa cells of growing follicles and the corpus luteum after ovulation. It inhibits secretion of FSH and to a lesser extent, LH.
What are the four stages of the female reproductive cycle?
What are the events in the ovaries during the menstrual phase?
Under the influence of FSH, several primordial follicles develop into primary follicles and then into secondary follicles. Takes a long time, so a follicle that begins to develop at the beginning of a particular menstrual cycle may not reach maturity and ovulate until several menstrual cycles.
What does the menstrual flow consist of?
Why does this discharge occur?
Menstrual flow consists of blood, tissue fluid, mucus, and epithelial cells shed from the endometrium.
Occurs because the declining levels of progesterone and oestrogens stimulate release of prostaglandins that cause the uterine spiral arterioles to constrict. The cells they supply become oxygen-deprived and start to die. Eventually, the entire stratum functionalis sloughs off.
What is the preovulatory phase?
The time between the end of menstruation and ovulation. Most variable
Describe the events in the ovaries during the preovulatory phase.
Some of the secondary follicles in the ovaries begin to secrete oestrogens and inhibin. Dominant follicle selected. Oestrogens and inhibin secreted by it decrease the secretion of FSH, which causes other follicles to stop growing and undergo atresia.
What phases make up the follicular phase?
Menstrual and preovulatory
What happens in the uterus during preovulatory phase?
Oestrogens liberated into blood by growing ovarian follicles stimulate the repair of the endometrium. Cells of the stratum basale undergo mitosis and produce a new stratum functionalis. As the endometrium thickens, the short, straight endometrial glands develop and the arterioles coil and lengthen as they penetrate the stratum functionalis.
During ovulation, the secondary oocyte remains surrounded by its ... and ...
What is a consequence of the high levels of oestrogen during the last part of the preovulatory phase?
Positive feedback effect on the cells that secrete LH and GnRH
Describe the three steps for stimulation of ovulation.
1) A high concentration of oestrogens stimulates more frequent release of GnRH from the hypothalamus. Also stimulates gonadotrophs to secrete LH.
2) GnRH promotes release of FSH and additional LH.
3) LH causes rupture of the mature follicle and expulsion of a secondary oocyte.
What is meant by mittelschmerz?
From time to time, an oocyte is lost into the pelvic cavity, where it later disintegrates. The small amount of blood that sometimes leaks into the pelvic cavity from the ruptured follicle can cause pain.
What is the most constant part of the female reproductive cycle?
What occurs after ovulation?
The mature follicle collapses and the basement membrane between the granulosa cells and theca interna breaks down. Theca interna cells mix with granulosa cells as they all become transformed into corpus luteum cells under the influence of LH. Stimulated by LH, the corpus luteum secretes progesterone, oestrogens, inhibin and relaxin. Luteal cells also absorb the blood clot.
When does a corpus haemorrhagicum form?
When a blood clot forms from minor bleeding of the ruptured follicle.
How long does the corpus luteum survive for if the oocyte is not fertilised? What occurs after?
Its secretory activity declines, and it degenerates into a corpus albicans. As the levels of progesterone, oestrogens and inhibin decrease, release of GnRH, FSH, and LH rise due to loss of negative feedback suppression by the ovarian hormones. Follicular growth resumes and new ovarian cycle begins.
What happens to the corpus luteum if the oocyte is fertilised?
Persists past its normal 2-week life span. It is rescued from degeneration by human chorionic gonadotrophin.
What is hCG produced by?
The chorion of the embryo about 8 days after fertilisation.
What are the events in the uterus during the postovulatory phase?
Progesterone and osterogens prodiced by the corpus luteum promote growth and coiling of the endometrial glands, vascularisation of the superficial endometrium and thickening of the endometrium.
Why is the postovulatory also called the secretory phase of the uterine cycle?
Because of the secretory activity of the endometrial glands, which begin to secrete glycogen.
What can disrupt the female reproductive cycle?
Weight loss, low body weight, disordered eating, vigorous physical activity
What is amenorrhea?
Absence of menstruation.
What causes amenorrhea in female athletes?
Reduced secretion of GnRH, which decreases the release of LH and FSH. Ovarian follicles thus fail to develop, ovulation does not occur, synthesis of oestrogens and progesterone wanes, and monthly menstrual bleeding ceases.
Why does a low amount of body fat contribute to female athlete triad?
Low levels of the hormone leptin, secreted by adipose cells.
What are the three aspects of female athlete triad?
Disordered eating, amenorrhea, osteoporosis