Lecture 39-Female Reproductive System_2023.pdf

FEMALE REPRODUCTIVE SYSTEM • Master of Arts in Biomedical Sciences • Dr. Roballo LEARNING OBJECTIVES 1. Describe the internal anatomy of the female reproductive tract. 2. Describe the Tanner stages of puberty and associated terminology (ex: thelarche) 3. Describe how the changes in ovarian ste...

FEMALE REPRODUCTIVE SYSTEM • Master of Arts in Biomedical Sciences • Dr. Roballo LEARNING OBJECTIVES 1. Describe the internal anatomy of the female reproductive tract. 2. Describe the Tanner stages of puberty and associated terminology (ex: thelarche) 3. Describe how the changes in ovarian steroids produce the proliferative and secretory phases of the uterine endometrium and menstruation and the changes in basal body temperature during the menstrual cycle. 4. List the different stages of ovarian follicle maturation. ANATOMY OF THE FEMALE SEXUAL ORGANS • Human female reproductive tract, including the ovaries, fallopian tubes (also called uterine tubes ), uterus, and vagina. • Reproduction begins with the development of ova in the ovaries. • In the middle of each monthly sexual cycle, a single ovum is expelled from an ovarian follicle into the abdominal cavity near the open fimbriated ends of the two fallopian tubes. REPRODUCTIVE FUNCTION IN THE HUMAN FEMALE IS INHERENTLY CYCLIC • Reproductive function in human females is controlled by hormones that emanate from the hypothalamic-pituitary-gonadal axis. • The release of a mature ovum from an ovary, known as ovulation, is the dominant event of the menstrual cycle. • Ovulation is spontaneous and regulated by cyclic functional interactions among signals coming from the hypothalamus, the anterior pituitary, and the ovaries. • Although many aspects of female reproduction are cyclic, maturation and atresia of the functional units of the ovaries-the ovarian follicles-are continuous processes that occur throughout reproductive life. • The ovaries are not the only female organs that undergo rhythmic changes. Alterations in cervical and uterine function are controlled by changes in the circulating concentrations of ovarian hormones, that is, the estrogens and progestins. • For example, the uterine endometrium thickens under the influence of ovarian hormones and deteriorates and sloughs at the end of the cycle when ovarian estrogen and progestin secretion diminishes. Menstruation reflects this periodic shedding of the endometrium. THE FEMALE ACCESSORY SEX ORGANS INCLUDE THE FALLOPIAN TUBES, THE UTERUS, THE VAGINA, AND THE EXTERNAL GENITALIA • The fallopian tube provides a pathway for the transport of ova from the ovary to the uterus. • The distal end of the fallopian tube expands as the infundibulum, which ends in multiple fimbriae. • The infundibulum is lined with epithelial cells that have cilia that beat toward the uterus. The activity of these cilia and the contractions of the wall of the fallopian tube, particularly around the time of ovulation, facilitate transport of the ovum. • The uterus is a complex, pear-shaped, muscular organ that is suspended by a series of supporting ligaments. It is composed of a fundus, a corpus, and a narrow caudal portion that is called the cervix. • The uterus is continuous with the vagina via the cervical canal. The cervical glands lining the cervical canal produce a sugar-rich secretion, the viscosity of which is conditioned by estrogen and progesterone. • The human vagina is about 10 cm in length and is a single, expandable tube. The vagina is lined by stratified epithelium and is surrounded by a thin muscular layer. • The ovaries lie on the sides of the pelvic cavity • A layer of mesothelial cells covers the surface of the ovary. • The cortex of the ovary in a mature female contains developing follicles and corpora lutea in various stages of development • These elements are interspersed throughout the stroma, which includes connective tissue, interstitial cells, and blood vessels. The medulla comprises large blood vessels and other stromal elements. PUBERTY MARKS THE TRANSITION TO CYCLIC , ADULT REPRODUCTIVE FUNCTION • Puberty is the transition from a noncyclic, relatively quiescent reproductive endocrine system to a state of cyclic reproductive function that allows procreation. • Puberty involves the beginning of menstrual cycles (menarche), breast development (thelarche), and an increase in adrenal androgen secretion (adrenarche). STAGES IN FEMALE PUBERTY STAGE BREAST DEVELOPMENT PUBIC HAIR 1 Preadolescent. Only papillae are elevated Preadolescent. No pubic hair is present, only vellus hair, as on the abdomen 2 Breasts and papillae are both elevated, and the diameter of the areolae increases Pubic hair is sparse, mainly along the labia majora 3 The breasts and areolae further enlarge Pubic hair is darker, coarser, and curlier and spreads over the pubis 4 The areolae and papillae project out beyond the level of the expanding breast tissue The pubic hair is of adult type, but covers an area smaller than in most adults 5 With further enlargement of the breast, the areolae are now on the same level as the rest of the breast. Only the papillae project. Adult pattern Adult pattern • B: Plot of how estrogen levels negatively feed back on gonadotropin secretion by the gonadotroph cells of the anterior pituitary. • In childhood, even very low estrogen levels are sufficient to fully suppress gonadotropin output. • In adolescence, higher levels of estrogens are required. • In the adult woman, estrogens must be at very high levels to suppress gonadotropin release. HYPOTHALAMIC-PITUITARY-GONADAL AXIS AND CONTROL OF THE FEMALE MENSTRUAL RHYTHM • The menstrual cycle reflects a complex interplay between the brain, the pituitary gland, and the ovary. • Although menstrual cycles are generally regular during the reproductive years, the length of the menstrual cycle may be highly variable because of disturbances in neuroendocrine function. • The mean menstrual cycle is 28 days long, but considerable variation occurs during both the early reproductive years and the premenopausal period. • Irregular menses during adolescence and the premenopausal period occur primarily because of the increased frequency of anovulatory cycles. • The hypothalamic-pituitary-ovarian axis drives the menstrual cycle • Gonadotropin-releasing hormone binds to receptors on the surface of gonadotrophs of the anterior pituitary. The result is the synthesis and release of both follicle-stimulating hormone and luteinizing hormone from the gonadotrophs. • The menstrual cycle is a cycle of the hypothalamicpituitary-ovarian axis, as well as a cycle of the targets of the ovarian hormones: the endometrium of the uterus. CYCLIC CHANGES IN O VA R I A N S T E RO I D S E C R E T I O N P RO D U C E CHANGES IN THE E N D O M E T R I U M T H AT ARE RESPONSIBLE FOR THE MENSTRUAL RHYTHM • Therefore, the menstrual cycle includes both an ovarian cycle-which includes the follicular phase, ovulation; • And the luteal phase-and the endometrial cyclewhich includes the menstrual, the proliferative, and the secretory phases. HORMONAL CH A N GE S D UR IN G THE M E N ST RUA L CY CLE CYCLIC CHANGES IN OVARIAN STEROID SECRETION PRODUCE CHANGES IN THE ENDOMETRIUM THAT ARE RESPONSIBLE FOR THE MENSTRUAL RHYTHM • The "menstrual cycle" actually involves cyclic changes in two organs: the ovary and the uterus • The ovarian cycle includes the follicular phase and the luteal phase, separated by ovulation. • The endometrial cycle includes the menstrual, the proliferative, and the secretory phases. • The first phase of the ovarian cycle is the follicular phase, which begins with the initiation of menstruation and averages about 14 days in length. FSH levels start to rise in the late luteal phase of the preceding cycle. Shortly thereafter, early in the follicular phase, LH levels rise as well. After the initiation of follicle development, the granulosa cells of the follicles increase production of the estrogen estradiol. • Under the influence of the rise in estradiol secretion by the ovary, the endometrium of the uterus undergoes rapid and continuous growth and maturation. This period is the proliferative phase of the endometrial cycle. • Just before ovulation, the rise in estradiol secretion becomes more rapid and, by a positive feedback effect on the anterior pituitary, triggers a surge in LH, which causes ovulation. Also occurring just before ovulation is a smaller FSH surge that is triggered by a rise in progesterone INITIATION OF OVULATION • Within a few hours, two events occur, both of which are necessary for ovulation: • 1. The theca externa (i.e., the capsule of the follicle) begins to release proteolytic enzymes from lysosomes. These enzymes cause dissolution of the follicular capsular wall and consequent weakening of the wall, resulting in further swelling of the entire follicle and degeneration of the stigma. • 2. Simultaneously there is rapid growth of new blood vessels into the follicle wall. At the same time, prostaglandins (local hormones that cause vasodilation) are secreted into the follicular tissues. OVARIAN FOLLICLE GROWTH—THE FOLLICULAR PHASE OF THE OVARIAN CYCLE • Female child is born, each ovum is surrounded by a single layer of granulosa cells; • The ovum, with this granulosa cell sheath, is called a primordial follicle, as shown in the figure. • Throughout childhood, the granulosa cells are believed to provide nourishment for the ovum and to secrete an oocyte maturation inhibiting factor that keeps the ovum suspended in its primordial state in the prophase stage of meiotic division. • Puberty, when FSH and LH from the anterior pituitary gland begin to be secreted in significant quantities, the ovaries (together with some of the follicles within them) begin to grow. • The first stage of follicular growth is moderate enlargement of the ovum, which increases in diameter 2fold to 3-fold. That stage is followed by growth of additional layers of granulosa cells in some of the follicles. These follicles are known as primary follicles. THE ENDOMETRIAL CY CLE • The ovarian cycle includes the follicular phase-in which the follicle develops-and the luteal phase-in which the remaining follicular cells develop into the corpus luteum. The endometrial cycle has three parts: the menstrual, the proliferative, and the secretory phases Monthly Endometrial Cycle and Menstruation Associated with the monthly cyclical production of estrogens and progesterone by the ovaries is an endometrial cycle in the lining of the uterus that operates through the following stages: (1) proliferation of the uterine endometrium; (2) development of secretory changes in the endometrium; and (3) desquamation of the endometrium, which is known as menstruation H Y P OT H A LA M I CP IT UITA RYOVA R IA N A XIS • Estrogens in the female are derived from the ovary and the adrenal gland and from peripheral conversion in adipose tissue. • In a nonpregnant female, estradiol, the primary circulating estrogen, is secreted principally by the ovary. • The precursor for the biosynthesis of the ovarian steroids is cholesterol. S TA RT I N G F RO M C H O L E S T E RO L , T H E O VA RY S Y N T H E S I Z E S ESTRADIOL, THE M A J O R E S T RO G E N , A N D P RO G E S T E RO N E , THE MAJOR P RO G E S T I N • Cholesterol is a 27-carbon sterol that is both ingested in the diet and synthesized in the liver from acetate • Biosynthesis of the ovarian steroids INTERACTION OF FOLLICULAR THECA AND GRANULOSA CELLS • Interaction of follicular theca and granulosa cells for production of estrogens. The theca cells, under the control of luteinizing hormone (LH), produce androgens that diffuse into the granulosa cells. In mature follicles, follicle-stimulating hormone (FSH) acts on granulosa cells to stimulate aromatase activity, which converts the androgens to estrogens. AC, Adenylate cyclase; ATP, adenosine triphosphate; cAMP, cyclic adenosine monophosphate; LDL, low-density lipoproteins. Two-cell, two-gonadotropin model B E C AU S E O F T H E I R U N I Q U E P H YS I O L O G I C A L P RO P E RT I E S , NEITHER THE THECA/THECALUTEIN CELLS NOR THE GRANULOSA/GRANULOSA-LUTEIN CELLS CAN MAKE E S T RO G E N S B Y T H E M S E LV E S THANK YOU