Physiology of Female Reproduction

Physiology of Female Reproduction Female system functions to produce oocytes on a regular monthly cycle for the purpose of fertilization—this process is regulated by hormones while neural mechanisms govern the sexual response Hormones have the greatest influence for they control reproductive organ development, ovulation and menstruation and maintain pregnancy. They arise from the hypothalamus, the anterior pituitary gland and the ovaries

Hormonal Mechanisms a. Development of Reproductive cycles and Puberty During childhood the ovaries grow at a slow rate and secrete small amounts of estrogen Near puberty the hypothalamus begins to release gonadotropin-releasing hormone (GnRH) which diffuses to the anterior pituitary gland and triggers to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH) which targets the ovaries FSH acts upon the primary follicles of the ovary causing them to begin their process of maturation

Development of Reproductive Cycles and Puberty Hormonal Mechanisms Follicle cells produce increasing levels of estrogen and progesterone LH promotes secretion of hormones further Increased estrogen and progesterone levels present in the bloodstream for the first time bring about the first episode of menstrual bleeding—menarche

Hormonal Control of Female Reproductive Functions estrogens inhibit LH and FSH during most of the reproductive cycle 22-43

Development of Reproductive Cycles and Puberty Puberty brings about many body changes—secondary sexual characteristics enlargement of vagina, uterus tubes and external genitalia promotes the accumulation of fat in the breast, thighs and buttocks stimulates the development of the duct system within the mammary glands absorption of calcium and phosphorus into certain bones—leads to a wider pelvis and narrow shoulders

Development of Reproductive Cycles and Puberty Ovaries are the major source of the second female sex hormone—progesterone Brings about changes in the uterus during the menstrual cycle During pregnancy progesterone is produced by the placenta and assists in maintaining the uterus and preparing the breast for lactation

Hormonal Mechanisms b. Menstrual Cycle Also called the uterine cycle Occurs in women until about the age of 50 Affects the endometrium of the uterus on a monthly basis and is in response to changes in levels of ovarian hormones in the blood Ends in menses or menstrual bleeding—a mild hemorrhage caused by the sloughing off of part of the endometrium and its exit from the uterus Typical cycle is about 28 days First day of menses marks day 1 of the menstrual cycle

Menstrual Cycle 3 or 4 days of menses, rising levels of estrogenregeneration of the endometrium—this continues for 14 days Stage is called the proliferative phase—growth of the endometrium Estrogen levels rise during this period because of the presence of FSH and LH stimulate the development of follicles in the ovary Follicles release estrogen as they reach maturity Estrogen acts on the cells of the uterus causing them to rapidly divide—endometrium thickens

Menstrual Cycle As estrogen increases, GnRH secretion by the hypothalamus is also increased by positive feedback GnRH stimulates more FSH and LH from the pituitary glandestrogen continues to increase At day 14, FSH and LH increase dramatically in response to GnRH Increase of LH stimulates ovulation—around day 14 or 10 days after menses

Menstrual Cycle Following ovulation, the follicle cells are converted to a corpus luteum within the ovary—secretes progesterone and small amounts of estrogen Progesterone increases and estrogen decreases—this inhibits continued LH and FSH secretion so their levels decline Progesterone promotes development of the endometrium by stimulating cell growth and secretes nourishing fluid—period of time between ovulation and the next menses is called secretory phase 7 or 8 days after ovulation, the endometrium has become prepared to receive the embryo

Menstrual Cycle If the oocyte released in ovulation is not fertilized, the corpus luteum begins to degenerate at about day 24 of the cycle progesterone and estrogen levels fall rapidly causing arterioles in the endometrium to constrict This reduces the supply of blood to the thickened uterine lining Causes damage to capillary wall blood leaks form the damage and pools beneath the outer layer of the endometrium Endometrium separates from the uterine wall—creates a flow of blood and degenerating tissue that flows out of the uterus

Menstrual Cycle Usually by day 28 menses begins and a new menstrual cycle starts all over.

Female Reproductive Cycle 22-46

Hormonal Mechanisms Menopause By 45 or 50 menstrual cycles become less regular and ovulation may not occur each time—female climacteric Five to seven years later the menstrual cycle stops completely—menopause Caused by changes within the ovary—follicles are less sensitive to the influences of FSH and LH fewer follicles are stimulated to mature and secrete estrogen & fewer corpora leutea are produced to secrete progesterone decrease in size of the uterus, reduction in lubricating fluid secretion and thinning of all epithelial tissues Changes are often accompanied by “hot flashes”—caused by dilation of blood vessels in the skin

Physiology of Female Reproduction Neural mechanisms govern the physiological responses to sexual stimulation

Neural Mechanisms Neural Mechanisms a. The vulva contains structures that receive a supply of sensory nerves Nerves respond to touch and send sensory impulses to the spinal cord Parasympathetic fibers form the cord t the vulva where erectile tissue dilates The vagina responds as its walls swell with blood to prepare for the entry of the penis Parasympathetic impulses stimulate secretion of mucus by the vestibular gland for lubrication

Neural Mechanisms b. The combined effect of stimulating the sensitive tissues of the vulva and vagina leads to orgasm Intense pleasure followed by complete relaxation Surge of psychological and physical warmth Does not require sexual intercourse Ease of orgasm varies among individuals Orgasm begins with the peristaltic contractions of muscles associated with the perineum, the walls of the vagina and the walls of the uterus and uterine tubespromote further stimulation and assist the movement of sperm through the female tract

Erection, Lubrication, and Orgasm 22-42