# Tortora's Principles of Anatomy and Physiology by Gerard J. Tortora, Bryan H. Derrickson >[!Abstract] Description > The phenomenally successful Principles of Anatomy and Physiology continues to set the discipline standard with the 15th edition. Designed for the 2-semester anatomy and physiology course, Principles of Anatomy and Physiology combines exceptional content and outstanding visuals for a rich and comprehensive classroom experience. Enhanced for a digital delivery, the 15th edition, gives students the ability to learn and explore anatomy and physiology both inside and outside of the classroom. %% ## The Female Reproductive Cycle ### [[GnRH is secreted by the hypothalamus]] ### [[GnRH controls the ovarian and uterine cycles]] > Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus controls the ovarian and uterine cycles (Figure 28.23). ^hiamj ### [[GnRH stimulates the release of FSH and LH]] ### [[FSH is released from the anterior pituitary gland]] ### [[LH is released from the anterior pituitary]] > GnRH stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. ^j9762 ### [[FSH initiates follicular growth]] ### [[LH stimulates further development of the ovarian follicles]] > FSH initiates follicular growth, while LH stimulates further development of the ovarian follicles. ^jnq7y ### [[follicles secrete oestrogen]] > In addition, both FSH and LH stimulate the ovarian follicles to secrete estrogens. ^o11rs ### [[LH triggers ovulation]] ### [[LH promotes formation of the corpus luteum]] > At midcycle, LH triggers ovulation and then promotes formation of the corpus luteum, the reason for the name luteinizing hormone. ^zrclu ### [[the corpus luteum produces progesterone & oestrogen, relaxin & inhibin during the luteal phase]] > Stimulated by LH, the corpus luteum produces and secretes estrogens, progesterone, relaxin, and inhibin. ^ydir5 ### [[there are 3 main oestrogens]] > At least six different estrogens have been isolated from the plasma of human females, but only three are present in significant quantities: beta (β)-estradiol (es-tra-D-I-ol), estrone, and estriol (ES-trē-ol). ^9fmfx ### [[in nonpregnant women, oestradiol is the main oestrogen]] ### [[oestradiol is produced from cholesterol in the ovaries]] > In a nonpregnant woman, the most abundant estrogen is β-estradiol, which is synthesized from cholesterol in the ovaries. ^ifky3 ### [[functions of oestrogen]] > Estrogens secreted by ovarian follicles have several important functions (Figure 28.23): > They: ### [[oestrogen promotes development and maintenance of female reproductive structures]] ### [[oestrogen promotes development and maintenance of secondary sex characteristics]] > 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. ^n5ht1 ### [[oestrogen increases protein anabolism]] > Increase protein anabolism, including the building of strong bones. In this regard, estrogens are synergistic with human growth hormone (hGH). ^jxa8c ### [[oestrogen lowers blood cholesterol]] > 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. ^-hlfz ### [[oestrogen prepares the uterus for pregnancy by stimulating the repair and thickening of the endometrium]] > 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. ^qs13v ### [[moderate levels of oestrogen inhibit the release of GnRH, FSH, and LH]] > Moderate levels in the blood inhibit both the release of GnRH by the hypothalamus and secretion of LH and FSH by the anterior pituitary. ^15955 ### ??? > 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 inhibit the secretion of GnRH and LH]] > High levels of progesterone also inhibit secretion of GnRH and LH. ^2eugn ### [[ relaxin produced by the corpus luteum relaxes the uterus]] > The small quantity of 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. ^6lb4c ### [[the placenta produces relaxin to relax the uterine smooth muscle]] > During pregnancy, the placenta produces much more relaxin, and it continues to relax uterine smooth muscle ^h0pad ### [[relaxin increases the flexibility of the pubic symphysis]] ### [[relaxin may help to dilate the cervix]] > 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. ^wlnyk ### [[the ovarian cycle encompasses events in the ovaries]] > The ovarian cycle is a series of events in the ovaries that occur during and after the maturation of an oocyte. ^kus4e ### [[the uterine cycle is a series of changes in the endometrium of the uterus]] > The uterine (menstrual) cycle is a concurrent series of changes in the endometrium of the uterus to prepare it for the arrival of a fertilized ovum that will develop there until birth ^pbsmd ### [[if fertilisation does not occur, hormones wane leading to menstruation]] > If fertilization does not occur, ovarian hormones wane, which causes the stratum functionalis of the endometrium to slough off. ^ps1x4 ### [[the menstrual cycle is more accurately termed the female reproductive cycle]] > The general term female reproductive cycle encompasses the ovarian and uterine cycles, the hormonal changes that regulate them, and the related cyclical changes in the breasts and cervix. ^5yyvp ### [[IMAGE Secretion and physiological effects of ostrogens, progesterone, relaxin, and inhibin in the female reproductive cycle]] - Dashed red lines indicate negative feedback inhibition - The uterine and ovarian cycles are controlled by gonadotropin-releasing hormone (GnRH) and ovar- ian hormones (estrogens and progesterone). ![[Screenshot 2023-03-21 at 14.43.06.png]] ### [[inhibin is secreted by growing follicles and the corpus luteum]] ### [[inhibin inhibits secretion of FSH and to a lesser extent LH]] > Inhibin is 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. ^8lug7 ## Phases of the Female Reproductive Cycle ## Menstrual Phase ### [[the average duration of menstrual flow is between four to six days]] > The menstrual phase (MEN-stroo-al), also called menstruation (men′-stroo-A--shun) or menses (MEN-sēz = month), lasts for roughly the first 5 days of the cycle. (By convention, the first day of menstruation is day 1 of a new cycle.) ^lts16 ## Events in the ovaries ### [[FSH promotes the development of several primordial follicles into primary follicles and then into secondary follicles]] > Under the influence of FSH, several primordial follicles develop into primary follicles and then into secondary follicles. ^2n486 ### [[the development of follicles take several months]] > This developmental process may take several months to occur. Therefore, a follicle that begins to develop at the beginning of a particular menstrual cycle may not reach maturity and ovulate until several menstrual cycles later. ^r3-2x #### [Page 1088](highlights://Principles%20of%20Anatomy%20and%20Physiology%20234#page=1104) ## Events in the uterus ### [[menstrual flow is not just blood]] > Menstrual flow from the uterus consists of 50–150 mL of blood, tissue fluid, mucus, and epithelial cells shed from the endometrium ^9ypol ### [[menstruation occurs when prostoglandins cause constriction of the arterioles in the uterus resulting in endometrial ischemia]] > This discharge occurs because the declining levels of progesterone and estrogens stimulate release of prostaglandins that cause the uterine spiral arterioles to constrict. As a result, the cells they supply become oxygen-deprived and start to die. Eventually, the entire stratum functionalis sloughs off. At this time the endometrium is very thin, about 2–5 mm, because only the stratum basalis remains. The menstrual flow passes from the uterine cavity through the cervix and vagina to the exterior. ^058cq ## Preovulatory Phase ## Events in the Ovaries ### [[secondary follicles begin to secrete oestrogen and inhibin]] > Some of the secondary follicles in the ovaries begin to secrete estrogens and inhibin. ^efeam ### [[the one dominant secondary follicle becomes the mature follicle]] > By about day 6, a single secondary follicle in one of the two ovaries has outgrown all of the others to become the dominant follicle ### [[oestrogen signals the brain to slow down FSH production causing all other follicles to stop growing and disintegrate]] > Estrogens and inhibin secreted by the dominant follicle decrease the secretion of FSH, which causes other, less well-developed follicles to stop growing and degenerate. ^ifd49 ### [[nonidentical twins or triplets result when two or three secondary follicles become co-dominant and later are ovulated and fertilised at about the same time]] > Fraternal (nonidentical) twins or triplets result when two or three secondary follicles become codominant and later are ovulated and fertilized at about the same time. ^5r--x ### [[the one dominant secondary follicle becomes the mature follicle]] > Normally, the one dominant secondary follicle becomes the mature (graafian) follicle, which continues to enlarge until it is more than 20 mm in diameter and ready for ovulation (see Figure 28.13). This follicle forms a blisterlike bulge due to the swelling antrum on the surface of the ovary. ^yvzoy ### [[the mature follicle continues to increase the production of oestrogen]] > During the final maturation process, the mature follicle continues to increase its production of estrogens (Figure 28.24). ^rna4n ### [[with reference to the ovarian cycle the follicular phase includes menstruation & preovulatory phase]] ### [[the term "follicular phase" is used to describe the process of the ovarian follicles maturing and developing oocytes]] > With reference to the ovarian cycle, the menstrual and preovulatory phases together are termed the follicular phase (fo-LIK-ū-lar) because ovarian follicles are growing and developing. ^hjl0- ## EVENTS IN THE UTERUS ### [[oestrogen prepares the uterus for pregnancy by stimulating the repair and thickening of the endometrium]] > Estrogens liberated into the blood by growing ovarian follicles stimulate the repair of the endometrium; cells of the stratum basale undergo mitosis and produce a new stratum functionalis. ^4gnjn > As the endometrium thickens, the short, straight endometrial glands develop, and the arterioles coil and lengthen as they penetrate the stratum functionalis. ### [[during the follicular phase the thickness of the endometrium doubles to about approximately 4–10 mm]] > The thickness of the endometrium approximately doubles, to about 4–10 mm. ^6wudd ### [[with regards to the uterine cycle the preovulatory phase is also termed the proliferative phase]] > With reference to the uterine cycle, the preovulatory phase is also termed the proliferative phase (prō-LIF-er-a-tiv) because the endometrium is proliferating. ^ntzbk ## Ovulation ### [[ovulation is the rupture of the mature follicle and the release of an egg]] > 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. ^3z5qb ### [[high levels of oestrogen result in positive feedback]] > The high levels of estrogens during the last part of the preovulatory phase exert a positive feedback effect on the cells that secrete LH and gonadotropin-releasing hormone (GnRH) and cause ovulation ^0ifg1 ### [[high levels of oestrogen stimulates more frequent release of GnRH from the hypothalamus]] > A high concentration of estrogens stimulates more frequent release of GnRH from the hypothalamus. ^4llbg ### [[high levels of oestrogen stimulates gonadotrophs in the anterior pituitary to secrete LH]] > It also directly stimulates gonadotrophs in the anterior pituitary to secrete LH. ^72f5w ### [[GnRH promotes the release of FSH and additional LH by the anterior pituitary]] > GnRH promotes the release of FSH and additional LH by the anterior pituitary. ^t11wv ### [[LH causes rupture of the mature follicle and release of an egg]] ### [[ovulation occurs around 9-12 hours after the peak of the LH surge]] > LH causes rupture of the mature (graafian) follicle and expulsion of a secondary oocyte about 9 hours after the peak of the LH surge. ^fsp1y ### [[pain around ovulation can be caused by a small amount of blood leaking into the pelvic cavity from the ruptured follicle]] > The small amount of blood that sometimes leaks into the pelvic cavity from the ruptured follicle can cause pain, known as mittelschmerz (MIT-el-shmārts = pain in the middle), at the time of ovulation. ^nlg5c ## Postovulatory Phase ## Events in one ovary ### [[the remains of the dominant follicle become the corpus luteum during the luteal phase]] > After ovulation, the mature follicle collapses, and the basement membrane bet ween the granulosa cells and theca interna breaks down. Once a blood clot forms from minor bleeding of the ruptured follicle, the follicle becomes the corpus hemorrhagi- cum (hem′-o-RAJ-i-kum; hemo- = blood; rrhagic- = bursting forth) (see Figure 28.13). Theca interna cells mix with the granulosa cells as they all become transformed into corpus luteum cells under the influence of LH. ^uzwq6 ### [[the corpus luteum absorbs the blood clot]] > The luteal cells also absorb the blood clot. With reference to the ovarian cycle, this phase is also called the luteal phase (LOO-tē-al). ^bmvkh ### [[if we do not conceive the corpus luteum function will stop within 14 days after ovulation (and will become the corpus albicans)]] > Later events in an ovary that has ovulated an oocyte depend on whether the oocyte is fertilized. If the oocyte is not fertilized, the corpus luteum has a life span of only 2 weeks. Then, its secretory activity declines, and it degenerates into a corpus albicans (see Figure 28.13). ^3pe7r ### [[if we conceive the corpus luteum will persists past its normal 2-week life span]] > If the secondary oocyte is fertilized and begins to divide, the corpus luteum persists past its normal 2-week life span. It is “rescued” from degeneration by human chorionic gonadotropin (hCG) (kō-rē- ON-ik). This hormone is produced by the chorion of the embryo beginning about 8 days after fertilization. Like LH, hCG stimulates the secretory activity of the corpus luteum. The presence of hCG in mater- nal blood or urine is an indicator of pregnancy and is the hormone detected by home pregnancy tests. ^mmztr ## Events in the uterus ### [[progesterone and oestrogen further prepares the endometrium for possible pregnancy]] > Progesterone and estrogens produced by the corpus luteum promote growth and coiling of the endometrial glands, vascularization of the superficial endometrium, and thickening of the endometrium to 12–18 mm (0.48–0.72 in.). Because of the secretory activity of the endometrial glands, which begin to secrete glycogen, this period is called the secretory phase of the uterine cycle. These preparatory changes peak about 1 week after ovulation, at the time a fertilized ovum might arrive in the uterus. ^-gqje ### [[if fertilisation does not occur, hormones wane leading to menstruation]] > If fertilization does not occur, the levels of progesterone and estrogens decline due to degeneration of the corpus luteum. Withdrawal of progesterone and estrogens causes menstruation. ^05t08 #### [Page 1091](highlights://Principles%20of%20Anatomy%20and%20Physiology%20234#page=1107) ## [[IMAGE Summary of hormonal interactions in the ovarian and uterine cycles]] > Hormones from the anterior pituitary regulate ovarian function, and hormones from the ovaries regulate the changes in the endometrial lining of the uterus. ![[Screenshot 2023-03-21 at 14.45.30.png]] ## The female reproductive cycle > The length of the female reproductive cycle typically is 24 to 36 days; the preovulatory phase is more variable in length than the other phases. (a) Events in the ovarian and uterine cycles and the release of anterior pituitary hormones are correlated with the sequence of the cycle’s four phases. In the cycle shown, fertilization and implantation have not occurred. (b) Relative concentrations of anterior pituitary hormones (FSH and LH) and ovarian hormones (estrogens and progesterone) during the phases of a normal female reproductive cycle. > Estrogens are the primary ovarian hormones before ovulation; after ovulation, both progesterone and estrogens are secreted by the corpus luteum. ![[Tortora menstrual cycle graph.png]] ## High levels of estrogens exert a positive feedback effect (red arrows) on the hypothalamus and anterior pituitary, thereby increasing secretion of GnRH and LH. > At midcycle, a surge of LH triggers ovulation. ![[Screenshot 2023-03-21 at 14.44.41.png]]