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Information about reprolecture

Published on January 15, 2008

Author: Modest


Reproduction:  Reproduction Larry Katz Animal Sciences 732-932-7426 Slide2:  Power Point Presentation for Katz lectures available at Review Session for First Exam: Sunday, Feb 19 2 pm Hickman 138 Lecture Topics:  Lecture Topics Asexual reproduction Sexual reproduction Human male reproduction The production of sperm The male reproductive apparatus Regulation of male reproduction Human female reproduction Production of ova The female reproductive apparatus The breasts The menstrual cycle The sexual response Fertilization Regulation of early development and birth Birth control Sexually transmitted disease Asexual Reproduction:  Asexual Reproduction Many animals can reproduce asexually – by one parent giving rise to offspring that are genetically identical to the parent Involves splitting, budding or fragmentation of the parent Is advantageous when population density is low and mates are not readily available. Some animals reproduce both sexually and asexually Parthenogenesis is the development of an unfertilized egg into an adult Is common among some mollusks, crustaceans, insects, and some reptiles Usually parthenogenesis alternates with sexual reproduction Can be a mechanism to rapidly produce offspring when conditions are favorable Asexual reproduction is fastest way to achieve reproduction Sexual Reproduction:  Sexual Reproduction Sexual reproduction is the most common type of animal reproduction Involves the fusion of two types of haploid gametes – sperm and egg Male contributes a sperm; female the ovum; each provides unique genetic information Fusion of the gametes produces a zygote, which develops into a new complete organism Involves complex structure, function and behavioral adaptations Types of Sexual Reproduction:  Types of Sexual Reproduction Sperm are typically small and motile; eggs are large and nonmotile External fertilization involves fusion of egg and sperm outside the body Many aquatic organisms fertilize gametes externally Release gametes simultaneously into water; requires prodigious production of gametes; meet by chance Internal fertilization involves delivery of sperm to the female body More reliable; female body provides watery medium for sperm movement and houses the developing embryo Most terrestrial animals, sharks and aquatic reptiles, birds and mammals Usually involves two different individuals Hermaphroditism is a form of sexual reproduction in which a single organism produces both eggs and sperm Some hermaphrodites are simultaneously male and female; others are first functionally one sex, then the other Asexual vs. Sexual Reproduction:  Asexual vs. Sexual Reproduction If asexual reproduction is so efficient, why do most animals reproduce sexually, which is so much more complex and expensive energetically? Sexual reproduction maintains diversity in a species; by mixing genetic components and recombining them, the offspring is much more complex and able to adapt to a changing environment and may be able to better survive than either parent But what are the main issues? Possible answers: Adaptive mutations can pass through a population via sexual reproduction Perhaps sexual selection removes harmful mutations. Asexual organisms inherit all characteristics of parent Sexual organisms mix genes so can lose or at least dilute the impact of non-adaptive mutations The Male Reproductive System :  The Male Reproductive System The male urinary and reproductive system are combined together as a system of tubes The testes reside in the scrotum The products of the testes (the sperm) move through the epididymis to the vas deferens around the sides and front of the scrotum The vas deferens passes over the pubic bone and bladder to the seminal vesicle, which is located under the bladder The vas then passes through the prostate where it is renamed the ejaculatory duct and where it joins with the urinary duct – the urethra The urethra receives input from the bulbourethral gland before it enters the base of the penis and the corpora cavernosa, through the caudal region of the penis and through the glans penis The Human Male Reproductive System:  The Human Male Reproductive System The Testis:  The Testis The paired testes produce gametes and hormones The testes hang below the body housed in the scrotum, maintains testes at lowered temperature If the testes do not drop during development the individual will become sterile The testes pass through the inguinal canal, carrying blood and nerves in the spermatic cord Sperm are produced by spermatogenesis in the seminiferous tubules Sperm are collected into the epididymis that lead to the vas deferens Spermatogenesis:  Spermatogenesis Spermatogenesis occurs within the testes, in the seminiferous tubules Spermatogonia divide by mitosis to form more spermatogonia Some spermatogonia become primary spermatocytes which undergo spermatogenesis (sperm production by meiosis) Primary spermatocytes produce secondary spermatocytes, which produce spermatids Four haploid spermatids are produced by one diploid primary spermatocyte Meiosis:  Meiosis Second Meiotic Division:  Second Meiotic Division Development of Mature Sperm:  Development of Mature Sperm Spermatids differentiate into a mature sperm by developing a flagellum, an enzyme cap (the acrosome) which is derived from the Golgi complex – and is a modified lysosome – and by shedding cytoplasm The Sertoli cells, which supply nutrients to the sperm, phagocytize much of the cytoplasm of the spermatid Sertoli cells are held together with tight junctions that separate spermatogenesis from the blood supply The midpiece is located at the base of the flagellum, and is supplied with mitochondria Sperm develop at a temperature lower than the core body temperature in the scrotum The inguinal canals connect the scrotum to the pelvic cavity and contain the vessels, nerves, muscles, and ducts Pampiniform Plexus:  Pampiniform Plexus Fig 3-9 page 58 Spermatogenesis:  Spermatogenesis Ducts and Tubules Store and Transport Sperm:  Ducts and Tubules Store and Transport Sperm Sperm leave the seminiferous tubules and move into tubules of the epididymis Sperm mature in the epididymis and may be stored there Sperm are ejaculated from the epididymis into the vas deferens, which passes into the pelvic cavity The vas deferens leads to the ejaculatory duct, which passes through the prostate gland and empties into the urethra The urethra may carry urine or semen, and passes out through the penis The Accessory Glands And the Sexual Response:  The Accessory Glands And the Sexual Response The accessory glands produce the fluid portion of semen A single ejaculate of about 3.5 mL of semen contains about 400 million sperm cells The paired seminal vesicles secrete a fluid rich in fructose and prostaglandins The single prostate gland, located under the bladder, secretes an alkaline fluid rich in prostaglandins Helps to neutralize the acidic environment of the vagina Alkaline environment is crucial to the generation of active motility in sperm – called capacitation The paired bulbourethral glands produce a mucous secretion which lubricates the penis, facilitating penetration Semen is the sperm suspended in the fluid productions of the seminar vesicles The Human Male Accessory Glands:  The Human Male Accessory Glands Penis :  Penis Fig 3-21 Male Infertility:  Male Infertility Over the past 30 years, the sperm content of semen has dropped dramatically In the 1970s sperm content of an average ejaculate was ~100 million / mL; now it is ~60 million / mL It is thought that low sperm count is attributable to drug usage, alcohol abuse, cigarette smoking and possibly industrial and environmental toxins The Penis:  The Penis The penis is an erectile copulatory organ that transfers sperm to the female The glans is the enlarged tip of the penis The prepuce, or foreskin, is removed from the glans in a circumcision The cavernous bodies are three columns of erectile tissue During arousal, the arteries in the cavernous bodies dilate, which causes swelling which prevents venous drainage of the penis Bones are found in the penises of some mammals such as bats, rodents, and some primates Hormonal Regulation of Male Reproduction:  Hormonal Regulation of Male Reproduction The hypothalamus, pituitary, and testes interact to regulate male reproduction At about age 10, the hypothalamus secretes gonadotropin-releasing hormone (GnRH) GnRH stimulates the anterior pituitary to secrete the gonadotrophic hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH) FSH stimulates Sertoli cells to secrete androgen-binding hormone (ABP) ABP results in development of the seminiferous tubules and stimulates spermatogenesis LH, also called interstitial cell stimulating hormone, stimulates the interstitial cells to secrete testosterone Inhibin, secreted by the Sertoli cells, inhibits FSH production Testosterone stimulates spermatogenesis, growth, and development of the male primary and secondary sexual characteristics Feedback Loops :  Feedback Loops Interstitial cell production of testosterone, stimulates Sertoli cell production of ABP to further stimulate spermatogenesis Sertoli cells’ production of ABP binds testosterone in the testes Sertoli cell secretion of inhibin inhibits production of FSH by the anterior pituitary Testosterone production inhibits GnRH production which in turn inhibits LH production Testosterone:  Testosterone Is responsible for the growth of the reproductive organs and male primary sex characteristics (the male organs) Also stimulates the secondary sex characteristics at puberty, including change of voice, muscle development, growth of facial and body hair In the brain, testosterone is converted to estradiol In castration before puberty, the male remains childlike sex organs and develops no male secondary sex characteristics Castration after puberty causes increased secretion of male hormones by the adrenal glands maintains masculine characteristics The Human Female Reproductive System:  The Human Female Reproductive System The female produces gametes and incubates the embryo The female reproductive system is adapted to produce eggs, receive the penis and sperm and protect and nourish the embryo during and after pregnancy The processes of the female reproductive system are regulated by hormones secreted by the ovaries, the hypothalamus and the anterior lobe of the pituitary gland The Female Reproductive System:  The Female Reproductive System The Female Reproductive Organs :  The Female Reproductive Organs The ovaries produce ova via oogenesis, which includes meiosis, described later Ova are picked up by the oviduct (i.e. uterine tube) This connects with the muscular uterus The uterus ends in the cervix, which is the opening to the vagina The vagina opens to the vulva, the external female organs Unlike the male system, the female urinary tract and reproductive tract do not merge Oogenesis: Meiosis I:  Oogenesis: Meiosis I The ovaries produce gametes and sex hormones Oogenesis occurs in the ovaries Oogenesis begins with the development of oogonia, which become primary oocytes during prenatal development Each primary oocyte and the cells surrounding it form a follicle Each month, a primary oocyte completes the first meiotic development forming a first polar body and the secondary oocyte Oogenesis: Meiosis I:  Oogenesis: Meiosis I Meiosis II of Oogenesis:  Meiosis II of Oogenesis The first polar body may undergo a further division or not; in either event, the polar bodies ultimately disintegrate The secondary oocyte remains in meiosis II until fertilization Oogenesis results in one haploid ovum Oogenesis: Meiosis II:  Oogenesis: Meiosis II Production of the 2O Oocyte:  Production of the 2O Oocyte The cells of the follicle secrete fluid, as well as estrogens Typically, one follicle matures fully each month The secondary oocyte is ejected from the follicle during ovulation The remaining follicular cells form the corpus luteum The corpus luteum is a temporal endocrine organ that secretes progesterone and estrogens The Oviduct:  The Oviduct The oviduct receives the secondary oocyte,which moves by peristalsis and ciliary beating down the oviduct toward the uterus A successful fertilization occurs in the oviduct The Uterus:  The Uterus The uterus incubates the embryo The lining of the uterus, the endometrium, thickens each month in preparation for pregnancy, and if that does not occur, is shed in menstruation A fertilized egg implants in the endometrium Endometriosis is a disorder in which the endometrial tissue migrates and grows in other areas, such as the oviducts or on the ovaries The cervix is the neck of the uterus and is a common site of cancer Detection of cervical cancer is by the Pap spear The vagina receives sperm The vagina is a muscular tube that receives the penis, and is part of the birth canal Internal Organs of the Female:  Internal Organs of the Female The Vulva:  The Vulva The vulva are external genital structures The vulva includes the labia minora (inner folds) and the labia majora (outer folds with hair) The labia minora form the prepuce of the clitoris The clitoris is homologous to the penis The clitoris is a center of sexual sensation in the female The mons pubis is a fatty pad covering the pubic symphysis, covered with hair after puberty The hymen is a thin ring of tissue surrounding the vaginal opening The Vulva:  The Vulva The Breasts:  The Breasts The breasts function in lactation Each breast is composed of lobes of glandular tissue surrounded by adipose tissue The alveoli are the clusters of glandular cells Ducts from the alveoli lead to the nipple Lactation is the production of milk, stimulated by estrogens and progesterone Colostrum is produced immediately after childbirth Prolactin stimulates the production of true milk Oxytocin stimulates the expulsion of milk The Breast:  The Breast Regulation Of Female Reproduction:  Regulation Of Female Reproduction The hypothalamus, pituitary, and ovaries interact to regulate female reproduction Estrogens are responsible for the secondary sexual characteristics of the female Broadening of the pelvis, development of breasts, and the development of subcutaneous fat The menstrual cycle typically begins at around age 12 and continues until approximately 50 years of age – at menopause Is regulated by hormones of the hypothalamus, anterior pituitary, and ovaries Hormone Levels Vary During the Cycle:  Hormone Levels Vary During the Cycle Hormones, Follicle, and Endometrial Development:  Hormones, Follicle, and Endometrial Development During the menstrual phase, in which the endometrium is shed, GnRH is released, which stimulates the anterior pituitary to release FSH and LH FSH stimulates the development of a few follicles in the ovary During the preovulatory phase, the developing follicles secrete estrogens Estradiol stimulates the development of the endometrium and the follicular cells Hormones and the Menstrual Cycle:  Hormones and the Menstrual Cycle LH stimulates theca cells to grow & produce androgens One dominant follicle continues to grow Granulosa cells of that follicle respond to LH & FSH & secrete estrogen Estradiol peaks in the late preovulatory stage & causes a surge in LH because it stimulates the anterior pituitary Granulosa cells secrete inhibin and finally have effect on FSH blood concentrations so FSH drop off just prior to ovulation Late Postovulatory:  Late Postovulatory The LH-surge causes ovulation & supports development of the follicle residual, the corpus luteum The postovulatory phase occurs after ovulation The corpus luteum is itself a gland and secretes progesterone and estrogen as well as inhibin The Menstrual Cycle:  The Menstrual Cycle The corpus luteum begins to degrade after ~8 days. Progesterone support falls off, and the endometrium arteries constrict Menstruation begins; anterior pituitary inhibition drops and it begins to secrete LH and FSH again This cycle repeats every ~ 28 days Hormonal Control of Early Pregnancy:  Hormonal Control of Early Pregnancy To the right is the full sequence of hormonal and physical changes in the case of no pregnancy. If fertilization does occur, implantation occurs in the uterus on about the 7th day after fertilization Membranes produce CG (human chorionic gonadotropin) which signal pregnancy Premenstrual Syndrome:  Premenstrual Syndrome Experienced by some women, hours to days before menstruation, ends quickly after menstruation begins Includes fatigue, anxiety, depression, irritability, headache, edema and skin problems Serotonin blockers can, in some cases ease the symptoms Sexual Activity:  Sexual Activity The sexual response involves physiological changes In both males and females, vasocongestion results in engorgement of the penis and clitoris with blood Sexual response includes sexual desire, excitement, orgasm, and resolution Orgasm may result from coitus In males, orgasm is accompanied by ejaculation Resolution is a homeostatic mechanism following orgasm Fertilization:  Fertilization The ovum remains fertile for only ~ 24 hrs postovulation; sperm remain alive in the woman’s reproductive tract for several days. Thus, fertilization is most likely on the day of ovulation or a day or so preceding Fertilization is the fusion of sperm and egg Sperm must pass through a plug of mucus in the cervix, which becomes thin at the time of high estrogen Mucus becomes sticky after ovulation; this blocks sperm Sperm are ‘capacitated’ after having been in contact with the female secretions for some time. Fertilization and implantation is referred to as conception Successful penetration of the egg by a sperm is dependent on many sperm surrounding the egg Fertilization is accompanied by an action potential in the egg which stops further sperm entry (fast block to polyspermy) Further changes occur on the outside of the egg to block further sperm after fertilization (slow block to polyspermy) The ovum completes the second meiotic division after sperm entry Conception :  Conception Once inside, the sperm loses its tail and the nucleus expands to form the male pronucleus The female and male pronuclei fuse and then the first division occurs Implantation:  Implantation If fertilization occurs, development begins as the embryo is moved to the uterus After about 3 days the embryo implants in the endometrium Membranes that develop around the embryo secrete hCG, human chorionic gonadotropin hCG stimulates the corpus luteum to continue to secrete progesterone The uterine lining continues to thicken and strengthen and the embryo is able to implant After ~ 3 months, the corpus luteum degrades and the placenta takes over nourishment of the embryo Uterine tissues begin to form the placenta The placenta itself secretes estrogen and progesterone Implantation:  Implantation Hormones and Birth:  Hormones and Birth Pregnancy is about 38 weeks long Parturition, the process of giving birth, is initiated by prostaglandins in humans Toward the end of pregnancy estrogen again increases, and stimulates the formation of gap junctions in the uterine muscle Oxytocin receptors form in the uterus; when released the uterine wall contracts strongly Oxytocin also stimulates prostaglandin production which can also powerfully stimulate uterine muscle contraction The placenta releases a corticotropin-like hormone that causes more estrogen release Labor:  Labor Labor may be divided into three stages Dilation of the cervix and the rupture of the amnion Delivery of the fetus Expulsion of the placenta and fetal membranes Cervical Dilation:  Cervical Dilation At the end of pregnancy, the uterine muscle is stimulated to contract Involuntary contractions lead toward labor, when contractions are ~ 10-15 minutes apart The fetus moves toward the cervix, head down The cervix dilates (opens) to a maximum diameter of 10 cm and thins (effaces) The amnion (the fetal sac) ruptures and fluid flows from the vagina (‘breaking water’) The fetus is delivered by powerful contractions of the uterine muscle The umbilicus is squeezed an largely emptied of blood into the newly-born baby, is cut/tied off by the physician The obstetrician may then inject the mother with oxytocin to cause powerful contractions of the uterus to expel the placenta, or merely pull the placental membranes out Artificial Mechanisms of Fertility:  Artificial Mechanisms of Fertility A catheter is used to inject sperm directly into the cervix Transfer into the uterus is called intrauterine insemination (IUI) – success rate is ~10% In IVF – in vitro fertilization Woman takes fertility drugs Ova are harvested and fertilized outside of the body Embryos are selected, screened for abnormalities, Now fairly common, success rate is ~20% Gamete intrafallopian transfer (GIFT) a laparoscope is used to guide ova and sperm into the oviduct Zygote intrafallopian transfer (ZIFT) the zygotes are placed in the oviduct Host mothering is used in cases where the genetic mother is fragile and can lead to higher fertility for that mother without the stress of carrying to term. Common for domesticated animals, and endangered wild animals in zoological parks. A newborn bongo with its surrogate eland mother:  A newborn bongo with its surrogate eland mother Birth Control:  Birth Control Contraception is any method which separates sexual intercourse from reproduction A heterosexually active woman who uses no form birth control has a 90% chance of becoming pregnant in a year In the United States, more than half of the women who became pregnant each year did not plan to do so Birth control is very helpful in allowing couples to control their fertility and plan their families Most Hormone Contraceptives Prevent Ovulation:  Most Hormone Contraceptives Prevent Ovulation Oral contraceptives, progestin implants, and injectable progestin are hormone contraceptives Oral contraceptives are the most common type, and are very effective if taken properly Oral contraceptives are contraindicated if the woman is over the age of 35, has hypertension or smokes “Morning-after” pills prevent implantation Depo-Provera prevents ovulation by suppressing anterior pituitary function Depo-Provera is injected every 3 months Norplant involves implantation of progestin capsules which also prevent ovulation Norplants are effective for about 5 years Other Contraceptives:  Other Contraceptives Use of the intrauterine device (IUD) has declined IUDs act by interfering with implantation; they also may destroy the fertilized ovum Other common contraceptive methods include the diaphragm and condom The diaphragm prevents passage of the sperm into the cervix, and is typically used with spermicidal jelly or cream Condoms prevent semen from entering the female reproductive tract and provide some protection from transmission of sexually transmitted diseases Emergency contraception is available Post-coital pills are available to prevent pregnancy - ~75% effective Mifepriston, or RU-486 (‘morning-after pill’), binds competitively with progesterone receptors in the uterus, blocks normal action and uterine contractions occur Sterilization :  Sterilization Sterilization renders an individual incapable of producing offspring Sterilization is the most common contraceptive method for couples in which the woman is over the age of 30 Male sterilization is performed by vasectomy The vas deferens are cut on the posterior side of the scrotum in this popular procedure 70% of vasectomies can be successfully reversed Female sterilization is by tubal ligation The uterine tubes are cut laproscopically Abortion :  Abortion There are three types of abortion Spontaneous abortions (miscarriages) occur without intentional intervention Therapeutic abortions are performed to maintain the health of the mother Abortion as a means of birth control is the most controversial method Most abortions during the first trimester are performed by a suction method Many are performed chemically, with a drug called methotrexate, which is much like RU-486 Most later abortions are performed by a dilation and evacuation (D & E) Prostaglandins are being used now to aid 2nd trimester abortions STDs Are a Major Health Problem:  STDs Are a Major Health Problem Sexually transmitted diseases (STDs) – also venereal diseases, are spread by sexual contact More than 250 million people are infected each year with gonorrhea; more than 50 million with syphilis, worldwide In the US, >65 million people have an incurable STD; >15 million more per year Most common is chlamydia Most common cause of pelvic inflammatory disease

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