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ODULE 11.2: THE UROGENITAL SYSTEM - M SEXUAL REPRODUCTION: AN EVOLUTIONARY ANIMAL REPRODUCTION & DEVELOPMENT ENIGMA Reproduction in the An...
ODULE 11.2: THE UROGENITAL SYSTEM - M SEXUAL REPRODUCTION: AN EVOLUTIONARY ANIMAL REPRODUCTION & DEVELOPMENT ENIGMA Reproduction in the Animal Kingdom exual Females: Have half as many daughters as S asexual females. It is also the “twofold cost” of exual Reproduction: The creation of an offspring S sexual reproduction (a male is needed, but in by fusion of a male gamete (sperm) and female asexual reproduction only females are required). gamete (egg) to form a zygote. Despite this, almost all eukaryotic species reproduce sexually. sexual Reproduction: The creationofanoffspring A without the fusion of egg and sperm. MECHANISMS OF ASEXUAL REPRODUCTION udding: A simple form of asexual reproduction B found only among invertebrates. yproducingoffspringofvariedphenotypes,sexual B reproduction may enhance reproductive success of parents when environmental factors change relatively rapidly. sexual reproduction is expected to be most A advantageous instable, favorable environments. F ission: It is found in many invertebrates. It is the Reproductive Cycles separation ofaparentintotwoormoreindividuals of about the same size. It is controlled by hormones and environmental cues. Most animals exhibit reproductive cycles related to changing seasons(climatechangecan decrease reproductive success). S ome organisms can reproduce sexually or asexually, depending on the conditions (Ex: Jellyfish). F ragmentation: It is the breaking of the body into pieces, some or all of whichdevelopintoadults.It must be accompanied by regeneration, the regrowth of lost body parts. arthenogenesis: It is the development of a new P individual from an unfertilized egg. It is mainly observed in invertebrates, but is observed rarelyin some vertebrates. 21 VARIATION IN PATTERNS OF SEXUAL REPRODUCTION ll fertilization requires critical timing, often A F or many animals, finding a partner for sexual mediated by environmental cues, pheromones, reproduction may be challenging. and/or courtship behavior. ermaphroditism: Each individual has male and H GAMETE PRODUCTION & DELIVERY female reproductive systems. Two hermaphrodites can mate. Some can self-fertilize. onads:Theseareorgansthatreproducegametes. G Ex: Clown fish, slugs, A. uniparens females Some simple systems do not have gonads, but gametesfromundifferentiatedtissue(cellsliningthe coelom). ost insects have separate sexes with complex M reproductive systems. anyfemaleinsectshaveaspermatheca,inwhich M sperm is stored during copulation. exReversals:Somespeciesexhibitmaletofemale S reversal (like certain oysters), while others exhibit T he gametes it produces is the sperm while the female to male reversal (like coral reef fish). gonad is the testes in this example. F ERTILIZATION It is the union of egg and sperm and plays an important part in sexual reproduction. xternal Fertilization: Eggs shed by the female are E fertilized by sperm in an external environment. moisthabitatisrequiredtoallowspermtoswimto A the egg and to prevent the gametes from drying out. T hegonadthistimeistheovarywhilethegametes pawning: Individuals cluster in the same area S it produces is the egg. to release their gametes into the water at the same time. loaca: It is a common opening between the C external environment and the digestive, excretory, InternalFertilization:Spermaredepositedinornear and reproductive systems. the female reproductive tract, and fertilization occurs within the tract. It requires behavioral It is common in non-mammalian vertebrates. interactions between and compatible copulatory Mammals usually have a separate opening to the organs. digestive tract. 22 HUMAN MALE REPRODUCTIVE ANATOMY T he external reproductive organs include the ucts: From the seminiferous tubules, sperm pass D scrotum and penis. into the coiled ductof theepididymis. The internal organs include: uring ejaculation, sperm are propelled through D Gonads: produce sperm and hormones thevasdeferensandtheejaculatoryduct,thenexit Accessoryglands:secreteproductsneeded the penisthrough theurethra. for sperm movement Ducts: carry sperm and glandular secretions Accessory Glands: emen: Composed of sperm + secretions from S three sets of accessory glands. eminal Vesicles: Contribute about 60% of the S total volume of semen (1). rostate Gland: Secretes its products directly P into the urethra (2). ale Gonads / Testes: It consists of highly coiled M ulbourethral Glands: Secrete a clear mucus B tubes. The sperm form inseminiferous tubules. that neutralizes acidic urine remaining in the urethra (3). T he Leydig cells surrounding the tubules produce hormones. The testes are held outside the enis: It is composed of three cylinders of spongy P abdominal cavity in the scrotum where erectile tissue. temperature is lower. lans: Also calledtheheadofthepenis,hasa G thinner skin covering than the shaft repuce: It is a fold of skin that surrounds the P glans. HUMAN FEMALE REPRODUCTIVE ANATOMY External Reproductive Structures agina: It isamuscularbutelasticchamberthatis V the repository for sperm during copulation and serves as the birth canal. 23 It opens to the outsideatthevulva,whichconsists of the following: (1) labiamajora,(2)labiaminora, (3) hymen, and (4) clitoris. litoris:Ithasaheadcalledaglanscoveredbythe C prepuce, a small hood of the skin. Internal Reproductive Structures ogenesis: The development of a mature egg; a O prolonged process. Immature eggs form in the femaleembryobutdonotcompletedevelopment until years later. F emaleGonads/Ovaries:Thisliesintheabdominal cavity. achovarycontainsmanyfollicles,whichconsistof E oocytessurrounded by support cells. viduct / Fallopian Tube: It is where the egg cell O travels from the ovary to the uterus. ndometrium / Uterus Lining: It has many blood E vessels. ervix: This is where the uterus narrows. It then C opens into the vagina. S econdary oocyte will start after the female undergoes puberty. AMETOGENESIS G It is the production of gametes. S permatogenesis differs from Oogenesis in Three Ways permatogenesis: It is the formation of sperm; S continuous and prolific. Hundreds of millions of 1: All four products of meiosisdevelopintosperm # sperm are produced per day; each sperm takes while onlyone of the fourbecomes anegg. about 7 weeksto develop. 2: # Spermatogenesis occurs throughout adolescence and adulthood. 3: Sperm are produced continuously without # prolonged interruptions in oogenesis. 24 HUMAN REPRODUCTION & HORMONES F ollicularPhase:Itischaracterizedbyfolliclegrowth Human reproduction is coordinated by hormones. and an increase in estradiol. It ends at ovulation and thesecondary oocyte is released. onadotropin-releasing hormone (GnRH): It is G secretedbythehypothalamus.Itdirectstherelease L utealPhase:Itiswherefolliculartissueisleftbehind of FSH (follicle-stimulating hormone) and LH totransform into a corpus luteum. (luteinizing hormone) from the anterior pituitary. orpus Luteum: It secretes progesterone and C F SH and LH: They regulate the processes in the estradiol,whichexertnegativefeedbackonthe gonads and theproduction of sex hormones. hypothalamus and pituitary. Testosterone:It is themain androgen. strogen: It consists mainly of estradiol and E progesterone. S ex hormones serve many functions in addition to gamete production,includingsexualbehaviorand L H surge triggers ovulation. The corpus luteum is the development of primary and secondary sex thenformedandsendssignalstothehypothalamus characteristics. and pituitary to decreasethesecretionofFSHand LH which prevents another egg to be released. ormonal Control of the Female Reproductive H Cycles THE UTERINE (MENSTRUAL) CYCLE T he secretion of hormones and the reproductive roliferative Phase: It is the thickening of the P events they regulate arecyclic. endometrium and it coincides with the follicular phase. rior to ovulation, the endometrium thickens with P blood vessels in preparation for embryo ecretory Phase: It is the secretionofnutrientsand S implantation. coincides with the luteal phase. If an embryo does not implant the endometrium, enstrual Flow Phase: The shedding o M f the the endometrium is shed in a process called endometrium coincides with the growth of new menstruation. ovarian follicles. ormones closely link the two cycles of female H reproduction. UterineCycle(MenstrualCycle):Changesin the uterus Ovarian Cycle: Changes in the ovaries. T HE OVARIAN CYCLE ItisthesequentialreleaseofGnRHthenFSHandLH which stimulates follicle growth. rogesterone and estradiol promote thickening of P endometrium. 25
