Physiology Lecture 25 PDF

Physiology Lecture 25 Puberty and reproductive years establishing its functional and structural maturation, as a function of hypothalamic-pituitary- gonadal axis Sex hormone synthesis and control mechanisms...

Physiology Lecture 25 Puberty and reproductive years establishing its functional and structural maturation, as a function of hypothalamic-pituitary- gonadal axis Sex hormone synthesis and control mechanisms Menstrual cycle Gonadal sex Testes: Germ cells: Produce sperm. Leydig cells: Release testosterone. Sertoli cells: Support germ cell development and release inhibin. Ovaries: Germ cells: Produce ova (eggs). Granulosa cells: Support egg development and release estrogen. Theca cells: Produce androgens, which are precursors for estrogen. Functions of hormone- releasing cells in testes Supporting maturation of sperm, and synthesis and secretion of testosterone & (antimullerian hormone). Functions of hormone- releasing cells in testes ovaries Development and maturation of ova, and synthesis and secretion of estrogen and progesterone male genital The epididymis is where sperm undergo maturation and gain motility. The vas deferens acts as a conduit, propelling sperm during ejaculation. Physiology Lecture 25 1  The seminal vesicles produce alkaline seminal fluid rich in fructose to nourish sperm. The ejaculatory ducts merge sperm and seminal fluid. The prostate gland contributes enzymes (e.g., PSA) and other compounds that liquefy semen and enhance fertility potential. female genital Fallopian tubes: Transport ova from the ovaries to the uterus; also the site of fertilization. Uterus: A muscular organ where the fertilized egg implants and develops into a fetus. Upper one-third of the vagina: Part of the birth canal and involved in sexual reproduction. male and female External genitalia Male external genitalia: 1. Penis: The organ involved in sexual intercourse and urination. 2. Scrotum: The sac that houses and protects the testes, regulating their temperature for sperm production. Female external genitalia: 1. Clitoris: The sensitive organ responsible for sexual pleasure. 2. Labia majora: The outer folds of skin that protect the vaginal opening. 3. Labia minora: The inner folds of skin, surrounding the vestibule and clitoris. 4. Lower two-thirds of the vagina: The external part of the vaginal canal involved in sexual intercourse and childbirth Y chromosome The Y chromosome is the determinant for MALE gonadal and phenotypic sex, because testis-determining gene is located on Y chromosome. The differentiation of male phenotype is determined by the presence of Physiology Lecture 25 2  The presence of testes drives male phenotype differentiation. Sertoli cells produce anti-Müllerian hormone (AMH), which inhibits the development of female reproductive structures. Leydig cells produce testosterone, promoting the development of male internal and external genitalia. The differentiation of female phenotype is independent on the presence of ovaries, but is dependent on the absence of testes/two hormones from sertoli and leydig sex duct system one duct develops other one regresses depends on gonads In males, the Wolffian ducts develop into male reproductive structures (e.g., epididymis, vas deferens) in the presence of testosterone, while the Müllerian ducts regress. In females, the Müllerian ducts develop into female reproductive structures (e.g., fallopian tubes, uterus), while the Wolffian ducts regress in the absence of testosterone. production of sex hormones Progesterone is first converted to testosterone by the enzyme CYP17 (17α-hydroxylase/17,20 lyase) testosterone is then converted to estrogen by the enzyme aromatase. 5α-reductase Testosterone converted into a potent DHT male vs female estrogen In males, testicular aromatase- induced estrogen primarily functions in spermatogenesis, while estrogen produced by aromatase in other tissues contributes mainly to circulating estrogen levels. Physiology Lecture 25 3  In females, circulating estrogen is primarily released from the ovaries. aromatase Aromatase is an enzyme found in tissues such as the gonads, skin, adipose tissue, blood vessels, and muscles. It is responsible for converting testosterone into 17β-estradiol (E2), a potent form of estrogen. androgenic effects develop male sec characteristic circulating estrogen in males and females in male made in peripheral tissuew in female made in ovaries Effects of estrogen on both sex on skeleton promoting survival of osteoblasts and inhibiting osteoclasts. Deficiency of estrogen causes osteoporosis Leydig cell stimulated by LH cam make progesterone's and testosterone Sertoli function uses FSH can make estrogen because of aromatase activated by FSH testosterone that is responsible for a) degerming male phenotype (in the embryogenesis) b) spermatogenesis c) all androgenic responses. sertoli cell functions Providing antimüllerian hormone for male phenotype development (in the embryogenesis). Physiology Lecture 25 4  Providing structural and nutritional support for germ cell development. Conversion of testosterone to estrogen via aromatase for the spermatogenesis. Producing inhibin to control the pituitary release of FSH What triggers the start of puberty? Puberty starts with the predominant release of GnRH (gonadotropin-releasing hormone) in a pulsatile manner, particularly during a child's sleeping hours. What is the pulsatile release pattern of GnRH? GnRH is released for 5–25 minutes every 60–90 minutes per pulse. Why is the pulsatile release of GnRH significant? The pulsatile release provides a time frame for receptor replenishment, ensuring effective hormone signaling. what does GnRH do stimulates the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone). Which hormone's secretion best matches the pulsatile pattern of GnRH? LH (luteinizing hormone) gonadotropin levels in elders higher than adults positive feedback of sex hormones only in females negative feedback in males When testosterone reaches the desired level, it suppresses GnRH secretion from the hypothalamus and LH release from the anterior pituitary. Physiology Lecture 25 5  Inhibin, produced by Sertoli cells, specifically reduces FSH secretion from the anterior pituitary. both theca cell and granulosa cells contain LH receptors so they can both produce progesterone and androgen when progesterone is made in the ovaries, they can be released into blood circvulation all androgen from theca cell Androgens produced by theca cells under LH stimulation diffuse into granulosa cells, where FSH stimulates aromatase to convert the androgens into estrogens. The estrogen is then released into the bloodstream. negative feedback in females estrogen and progesterone both have negative feedback on hypothalamus and anterior pituitary female positve feedback At very high estrogen levels, estrogen exerts positive feedback on the hypothalamus and anterior pituitary, leading to a surge of LH and FSH. Granulosa cells also release activin, which enhances FSH production. This surge triggers ovulation. ovarian cycle Follicular phase (Day 1–14): Dominated by FSH and estrogen. FSH stimulates follicle growth, while rising estrogen levels prepare the endometrium and exert feedback to regulate FSH and LH. Ovulation phase (Day 14): Triggered by a surge in LH, which causes the dominant follicle to release the oocyte. Luteal phase (Day 14–28): Dominated by progesterone, produced by the corpus luteum to maintain the endometrium. Estrogen is also present at moderate levels. Physiology Lecture 25 6  LH surge necessary for ovulation estrogen feedback in menstral cycle negative until few days befor ovilation, then it is positve after ovulation what happens to theca and granulosa cells After ovulation, under the influence of high LH levels, theca and granulosa cells undergo luteinization, transforming into luteal cells. These luteal cells form the corpus luteum and secrete large amounts of progesterone and smaller amounts of estrogen to support potential implantation and early pregnancy. why luteal phase has higher progesterone than estrogen This is due to the lack of CYP17, which is necessary for estrogen production, and the presence of inhibin, which reduces FSH secretion, limiting the further stimulation of estrogen production. if no fertilization progesterone and estrogen decrease, so negative feedback is removed which increases LH and FSH and stimulate new follicle development endometrium breaks down for menstration uterus cycles proliferative phase The proliferative phase of the uterine cycle aligns with the follicular phase. Rising levels of estrogen stimulate the thickening of the endometrial lining. Cervical mucus becomes abundant, thin, watery, and alkaline, creating a favorable environment for sperm penetration. This condition typically lasts until approximately 48 hours after ovulation. uterus secretory phase During the secretory phase, progesterone predominates. It causes the endometrial lining to become more glandular and prepared for potential implantation. Physiology Lecture 25 7  Cervical mucus becomes viscous and acidic, which serves to prevent additional sperm from entering, as well as creating a less favorable environment for fertilization. ovaries menstrual phase During the menstrual phase, the decline in progesterone and estrogen levels triggers the shedding of the endometrial lining. Prostaglandins (PGs) are released, causing vasoconstriction in the uterus to initiate shedding, while also causing vasodilation in systemic circulation, which can contribute to symptoms like low blood pressure and fatigue. progesterone and temperature higher because change thermal regulator Physiology Lecture 25 8