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CHAPTER 46

CHAPTER 46. ANIMAL REPRODUCTION. OVERVIEW. TWO MODES OF REPRODUCTION ARE FOUND IN ANIMALS; ASEXUAL AND SEXUAL ASEXUAL REPRO . = PRODUCTION OF OFFSPRING WHOSE GENES COME FROM ONE PARENT WITHOUT THE FUSION OF EGG AND SPERM

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CHAPTER 46

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  1. CHAPTER 46 ANIMAL REPRODUCTION

  2. OVERVIEW • TWO MODES OF REPRODUCTION ARE FOUND IN ANIMALS; ASEXUAL AND SEXUAL • ASEXUAL REPRO. = PRODUCTION OF OFFSPRING WHOSE GENES COME FROM ONE PARENT WITHOUT THE FUSION OF EGG AND SPERM • SEXUAL REPRO = PRODUCTION OF OFFSPRING BY THE FUSION OF GAMETES TO FORM A DIPLOID ZYGOTE • THE GAMETES ARE FOMED BY MEIOSIS • THE OVUM IS USUALLY LARGE, NONMOTILE, WHILTE THE SPERM IS USUALLY SMALL AND MOTILE • INCREASED GENETIC VARIABLITY DUE TO A COMBO OF GENES INHERITED FROM BOTH PARENTS

  3. ASEXUAL REPRODUCTION • FISSION = THE SEPARATION OF A PARENT INTO 2 OR MORE INDIVIDUALS OF APPROXIMATELY EQUAL SIZE • BUDDING = OCCURS WHEN A NEW INDIVIDUAL SPLITS OFF FROM EXISTING ONE • FRAGMENTATION = BREAKING OF THE BODY INTO SEVERAL PIECES, EACH OF WHICH DEVELOPS INTO A COMPLETE ADULT

  4. REPRO. CYCLES & PATTERNS • MOST ANIMALS HAVE REPRODUCTIVE CYCLES, OFTEN RELATED TO CHANGING SEASONS • ANIMALS EMPLOY VARIOUS PATTERNS OF REPRODUCTION AND MAY USE EITHER SEXUAL OR ASEXUAL REPRO. EXCLUSIVELY OR ALTERNATE BTW. THE TWO • PARTHENOGENESIS = DEVELOPMENT OF AN EGG WITHOUT FERTILIZATION • PLAYS A ROLE IN THE SOCIAL ORGANIZATION OF SOME INSECTS • HERMAPHRODITISM - A SOLUTION FOUND IN MANY ANIMALS THAT MAY HAVE DIFFICULT FINDING A MEMBER OF THE OPPOSITE SEX • EACH INDIVIDUAL HAS BOTH FUNCTIONAL MALE AND FEMALE REPRO. PARTS

  5. SEQUENTIAL HERMAPHRODITISM • AN INDIVIDUAL REVERSES ITS SEX DURING ITS LIFETIME • SOME SPECIES ARE PROTOGYNOUS (FEMALE FIRST); OTHERS ARE PROTANDROUS (MALE FIRST) • REVERSAL IS OFTEN ASSOCIATED WITH AGE AND SIZE • EXAMPLES: PROTOGYNOUS = WRASSE PROTANDROUS = OYSTERS

  6. INTERNAL FERTILIZATION • OCCURS WHEN SPERM ARE DEPOSITED IN OR NEAR THE FEMALE REPRO. TRACT AND FERTILIZATION OCCURS WITHIN THE FEMALE’S BODY • USUALLY REQUIRES MORE SOPHISTICATED REPRO. SYSTEMS AND COOPERATIVE MATING BEHAVIORS • COPULATORY ORGANS FOR SPERM DELIVERY AND RECEPTACLES FOR SPERM STORAGE AND TRANSPORT MUST BE PRESENT • MATING BEHAVIORS MUST INCLUDE SPECIFIC REPRO. SIGNALS FOR COPULATION TO OCCUR

  7. EXTERNAL FERTILIZATION • EGGS ARE SHED AND FERTILIZED BY A MALE’S SPERM IN THE ENVIRONMENT • OCCURS ALMOST ALWAYS IN MOIST HABITATS TO PREVENT DESSICATION AND TEMP. STRESS • SOME AQUATIC INVERTS HAVE NO CONTACT BTW. PARENTS • VERY LARGE NUMBERS OF ZYGOTES, VERY FEW SURVIVE TO COMPLETE DEVELOPMENT • ENVIRONMENTAL CUES AND PHEROMONES TRIGGER RELEASE OF MATURE GAMETES IN CLOSE PROXIMITY • IN VERTS, COURTSHIP BEHAVIOR INCREASES THE PROBABILITY OF SUCCESSFUL FERTILIZATION AND PERMITS MATE SELECTION • FISH AND AMPHIB EGGS ARE COVERED WITH A GELATINOUS COAT, PERMITS FREE EXCHANGE OF GASES AND WATER

  8. PHEROMONES • CHEMICAL SIGANLS BTW. ORGANISMS OF THE SAME SPECIES, AMY BE OPERATIVE IN ORGANISMS THAT USE EITHER INTERNAL OR EXTERNAL FERT. • ARE EASILY DISPERSED IN THE ENVIRONMENT AND ARE ACTIVE IN MINUTE AMTS. • SEX ATTRACTANTS IN INSECTS MAY BE EFFECTIVE AT DISTANCES OF UP TO ONE MILE

  9. INTERNAL FERTILIZATION • SPECIES WITH INTERNAL FERT. USUALLY PRODUCE FEWER ZYGOTES and PROVIDE MORE PARENTAL PROTECTION THAN SPECIES WITH EXT. FERTILIZATION • EGGS RESISTANT TO HARSH ENVIRONMENTS ARE PRODUCED BY MANY REPTILES, BIRDS AND MONOTREMES • MAMMALS POSSESS REPRODUCTIVE TRACTS THAT PROTECT EMBRYONIC DEVELOPMENT

  10. COMPLEX REPRO. SYSTEMS • THE ONLY PREREQUISITE FOR SEXUAL REPRODUCTION IS THAT THE ANIMAL POSSESSES THE CAPABILITY TO PRODUCE AND DELIVER GAMETES TO THE GAMETES OF THE OPPOSITE SEX’ • THE SIMPLEST SYSTEMS DO NOT CONTAIN DISTINCT GONADS • THE COMPLEXITY OF THE REPRODUCTIVE SYSTEM IS NOT NECESSARILY RELATED TO THE PHYLOGENETIC POSITION OF THE ANIMAL (EX: FLATWORM)

  11. FLATWORM: ONE OF THE MOST COMPLEX REPRO. SYSTEMS

  12. MOST INSECTS HAVE SEPARATE SEXES AND COMPLEX REPRODUCTIVE STRUCTURES

  13. VERTEBRATES • THE REPRO SYSTEMS OF VERTS ARE ALL SIMILAR, BUT DO HAVE SOME IMPORTANT DIFFERENCES • MOST MAMMALS HAVE SEPARATE OPENINGS FOR DIGESTIVE, EXCRETORY, AND REPRO. TRACTS, WHILE MANY NONMAMMALIAN VERTS HAVE ONLY A COMMON OPENING, THE CLOACA • SOME MAMMALS, BIRDS AND SNAKES HAVE A UTERUS WITH ONLY ONE BRANCH, WHILE MOST OTHER VERTS HAVE A UTERUS THAT IS PARTLY OR COMPLETELY DIVIDED INTO CHAMBERS • NONMAMMALIAN VERTS DO NOT HAVE WELL DEVELOPED PENISES AND USE OTHER MECHANISMS TO TRANSFER SPERM

  14. HUMAN MALE • THE EXTERNAL GENITALIA INCLUDES THE SCROTUM AND PENIS • THE INTERNAL REPROORGANS CONSIST OF THE GONADS (TESTES), ACCESSORY GLANDS, AND ASSOCIATED DUCTS • TESTES DEVELOP IN THE ABDOMEN AND DESCEND INTO THE SCROTUM JUST BEFORE BIRTH. THIS IS IMPORTANT SINCE SPERM CANNOT DEVELOP AT NORMAL BODY TEMP.

  15. THE TESTES ARE MADE OF HIGHLY COILED TUBES SURROUNDED BY LAYERS OF CONNECTIVE TISSUE • THE SEMINIFEROUS TUBULES ARE WHERE SPERM FORM • INTERSTITIAL CELLS, OR LEYDIG CELLS, ARE SCATTERED BTW. THE TUBULES AND PRODUCE TESTOSTERONE AND OTHER ANDROGENS • SPERM PASS FROM THE SEMI. TUBULES INTO THE TUBULES OF THE EPIDIDYMIS • THESE COILED TUBULES ARE WHERE SPREM ARE STORED AND MATURE

  16. MALE REPRODUCTIVE ANATOMY

  17. AT EJACULATION, SPERM ARE FORCED THRU THE VAS DEFERENS, WHICH IS A MUSCULAR DUCT RUNNING FROM EPIDIDYMIS TO THE EJACULATORY DUCT • THE EJACULATORY DUCT FORMS BY THE JOINING OF THE 2 VAS DEFERENS DUCTS WITH THE DUCT FROM THE SEMINAL VESICLES • THE EJACULATORY DUCT OPENS INTO THE URETHRA, THE TUBE THAT RUNS THRU THE PENIS AND DRAINS BOTH THE EXCRETORY AND REPRODUCTIVE SYSTEMS

  18. THERE ARE 3 SETS OF ACCESSORY GLANDS ASSOCIATED WITH THE MALE SYSTEM. THESE GLANDS ADD THEIR SECRETIONS TO THE SEMEN. • 1) SEMINAL VESICLES: IS LOCATED BELOW AND BEHIND THE BLADDER AND EMPTIES INTO THE EJACULATORY DUCT • SECRETE A FLUID CONTAINING MUCUS, A.A.’S, FRUCTOSE, AND PROSTAGLANDINS (FOR PROMOTING UTERINE CONTRACTIONS) • 2) PROSTATE GLAND: LARGE GLAND THAT SURROUNDS THE UPPER PORTION OF, AND EMPTIES DIRECTLY INTO, THE URETHRA • IT SECRETES A THIN, MILKY ALKALINE FLUID THAT CONTAINS SEVERAL ENZYMES

  19. 3) BULBOURETHRAL GLANDS: A PAIR OF SMALL GLANDS BELOW THE PROSTATE THAT EMPTY INTO THE URETHRA AT THE BASE OF THE PENIS • SECRETE A CLEAR MUCUS BEFORE SPERM EJACULATION • THE FLUID NEUTRALIZES ANY ACIDIC URINE REMAINING IN THE URETHRA ***PROSTAGLANDINS IN THE SEMEN- THINS THE MUCUS AT THE OPENING OF THE UTERUS AND STIMULATES CONTRACTIONS OF THE UTERINE MUSCLE TO HELP THE SEMEN MOVE UP THE UTERUS

  20. HUMAN FEMALE • MORE COMPLICATED THAN THAT OF THE MALE; IT POSSESSES STRUCTURES NOT ONLY FOR THE PRODUCTION OF FEMALE GAMETES, BUT ALSO TO HOUSE THE EMBRYO AND FETUS • THE INTERNAL REPRODUCTIVE ORGANS ARE THE OVARIES AND ASSOCIATED DUCTS AND CHAMBERS, WHICH ARE INVOLVED WITH GAMETES, BUT ALSO TO HOUSE THE EMBRYO AND FETUS • THE EXTERNAL GENITALIA INCLUDE THE CLITORIS AND THE TWO SETS OF LABIA THAT SURROUND THE CLITORIS AND VAGINAL OPENING

  21. FEMALE REPRODUCTIVE ANATOMY

  22. OVARIES • THE OVARIES ARE LOCATED IN THE ABDOMINAL CAVITY AND ENCLOSED IN A TOUGH PROTECTIVE CAPSULE • A MESENTARY FLANKS AND ATTACHES EACH OVARY TO THE UTERUS • EACH OVARY CONTAINS MANY FOLLICLES (ONE EGG CELL SURROUNDED BY FOLLICLE CELLS, WHICH NOURISH AND PROTECT THE DEVELOPING EGG) • ALL ARE FORMED AT BIRTH • FOLLICLE CELLS ALSO PRODUCE ESTROGENS • STARTING AT PUBERTY, AND CONTINUING TO MENOPAUSE, ONE FOLLICLE MATURES AND RELEASES ITS EGG CELL DURING EACH MENSTRUAL CYCLE

  23. OVULATION • DURING OVULATION, THE EGG IS EXPELLED FROM THE FOLLICLE. THE REMAINING FOLLICULAR TISSUE FORMS THE CORPUS LUTEUM, WHICH SECRETES PROGESTOERONE (MAINTAINS THE UTERINE LINING) AND ADDITIONAL ESTROGEN • IF THE EGG IS NOT FERTILIZED, THE CORPUS LUTEUM DEGENERATES • THE EGG CELL IS EXPELLED INTO THE ABDOMINAL CAVITY NEAR THE OPENING OF THE OVIDUCT • CILIA LINING THE OVIDUCT DRAW IN THE EGG CELL AND CONVEY IT TO THE UTERUS • THE UTERUS (OR WOMB) IS A THICK MUSCULAR ORGAN THAT CAN EXPAND TO ACCOMMODATE A 4 KG FETUS • THE INNER UTERINE LINING, THE ENDOMETRIUM, IS RICHLY SUPPLIED WITH BLOOD VESSELS

  24. REMAINING FEMALE REPRODUCTIVE STRUCTURES • CERVIX = THE NECK OF THE UTERUS WHICH OPENS INTO THE VAGINA • VAGINA = THIN-WALLED CHAMBER THAT IS THE REPOSITORY FOR SEMEN DURING COPULATION; ALSO FORMS THE BIRTH CANAL • HYMEN= A VASCULARIZED MEMBRANE, USUALLY COVERS THE VAGINAL OPENING FROM BIRTH UNTIL RUPTURED • VESTIBULE = CHAMBERLIKE AREA FORMED BY THE 2 PAIRS OF SKIN FOLDS COVERING THE VAGINAL ORIFICE AND URETHRAL OPENING • LABIA MINORA = THE SLENDER SKIN FOLDS BORDERING THE VESTIBULE\ • LABIA MAJORA = A PAIR OF THICK, FATTY RIDGES ENCLOSING AND PROTECTYING THE LABIA MINORA AND VESTIBULE

  25. CLITORIS = BULB OF ERECTILE TISSUE AT FRONT OF VERTIBULE-COVERED BY A PREPUCE (HOOD OF SKIN) • BARTHOLIN’S GLANDS = SMALL GLANDS LOCATED NEAR THE VAGINAL OPENING THAT SECRETE MUCUS INTO THE VERTIBULE DURING SEXUAL AROUSAL, WH ICH FACILITATES INTERCOURSE BY LUBRICATING THE VAGINA

  26. MAMMARY GLANDS • IMPORTANT TO MAMMALIAN REPRODUCTION, ALTHOUGH NOT ACTUALLY A PART OF THE REPRODUCTIVE SYSTEM • THEY CONSIST OF SMALL SACS OF EPITHELIAL TISSUE THAT SECRETE MILK • THE MILK DRAINS INTO A SERIES OF DUCTS THAT OPEN AT THE NIPPLE • IN A NONLACTATING FEMALE MAMMAL, THE MAMMARY GLANDS ARE COMPOSED PRIMARILY OF ADIPOSE TISSUE

  27. HUMAN SEXUAL RESPONSE • PHYSIOLOGICAL REACTIONS THAT PREDOMINATE IN BOTH SEXES CAN BE DIVIDED INTO TWO TYPES: • 1) VASOCONGESTION = THE FILLING OF A TISSUE (PENIS, CLITORIS) WITH BLOOD DUE TO AN INCREASED BLOOD FLOW THRU THE ARTERIES OF THAT TISSUE • 2) MYOTONIA = INCREASED MUSCLE TENSION, AND BOTH SKELETAL AND SMOOTH MUSCLES MAY SHOW SUSTANIED OR RHYTHMIC CONTRACTIONS

  28. 4 PHASES OF THE SEXUAL RESPONSE CYCLE • 1) EXCITEMENT PHASE = THE VAGINA AND PENIS ARE PREPARED FOR COITUS • VASOCONSTRICTION AND MYOTONIA • 2) PLATEAU PHASE =CONTINUES RESPONSES OF EXCITEMENT PHASE • VAGINA FORMS A DEPRESSION TO RECEIVE SPERM; THE OUTER 1/3 BECOMES VASOCONGESTED, THE INNER 2/3 SLIGHTLY EXPAND, AND THE UTERUS ELEVATES • IN BOTH SEXES, THE HEART RATE RISES AND BREATHING RATES INCREASE IN RESPONSE TO STIMULATION OF THE AUTONOMIC N.S.

  29. ORGASM IS THE THIRD AND SHORTEST PHASE; IT IS CHARACTERIZED BY RHYTHMIC, INVOLUNTARY CONTRACTIONS IN THE REPRODUCTIVE SYSTEMS OF BOTH SEXES • 2 STAGES OCCUR IN MALES: • 1) EMISSION IS THE FORCING OF SEMENT INTO THE URETHRA DUE TO CONTRACTION OF GLANDS • 2) EXPULSION (EJACULATION) EXPELS THE SEMEN DUE TO URETHRAL CONTRACTIONS • IN FEMALES, THE UTERUS AND OUTER VAGINA CONTRACT BUT THE INNER 2/3 OF THE VAGINA DO NOT • 4) RESOLUTION = REVERSES THE RESPONSES OF EARLIER PHASES AND COMPLETES THE CYCLE • VASOCONGESTED ORGANS RETURN TO NORMAL SIZE AND COLOR; MUSCLES RELAX

  30. SPERMATOGENESIS • THE PRODUCTION OF MATURE SPERM CELLS IN ADULT MALES • A CONTINUOUS PROCESS IN ADULT MALES, WHICH CAN RESULT IN 100 TO 650 MILLION SPERM CELLS PER EJACULATION ON A DAILY BASIS • OCCURS IN SEMINFEROUS TUBULES OF THE TESTES • THE THICK HEAD OF A SPERM CELL CONTAINS THE HAPLOID NUCLEUS TIPPED WITH THE ACROSOME, WHICH CONTAINS ENZYMES TO AID IN EGG PENETRATION • BEHIND THE HEAD, THE SPERM CELL CONTAINS MANY MITOCHONDRIA THAT PROVIDE ATP FOR FLAGELLA MOVEMENT

  31. SPERMATOGENESIS

  32. STRUCTURE OF SPERM

  33. OOGENESIS • THE DEVELOPMENT OF OVA • BEGINS IN THE EMBRYO WHEN PRIMORDIAL GERM CELLS UNDERGO MITOTIC DIVISIONS TO PRODUCE DIPLOID OOGONIA • EACH OOGONIUM WILL DEVELOP INTO A PRIMARY OOCYTE BY THE TYPE OF BIRTH OF THE FEMALE • BETWEEN BIRTH AND PUBERTY, PRIMARY OOCYTES ENLARGE AND THEIR SURROUNDING FOLLICLES GROW • THEY REPLICATE THEIR DNA AND ENTER PROPHASE I AND REMAIN THERE UNTIL ACTIVATED BY HORMONES • AFTER PUBERTY, DURING EACH OVARIAN CYCLE, FSH STIMULATES A FOLLCILE TO ENLARGE AND THE PRIMARY OOCYTE WITHIN COMPLETES MEIOSIS I • LH TRIGGERS OVULATION AND THE SECONDARY OOCYTE IS RELEASED FROM FOLLICLE

  34. OOGENESIS

  35. DIFFERENCES BTW. SPERMATOGENESIS & OOGENESIS • 1) IN SPERMATOGENESIS, ALL 4 PRODUCTS OF MEIOSIS I AND II BECOME MATURE SPERMATOZOA. IN OOGENESIS, THE UNEQUAL CYTOKINESIS, WHICH OCCURS DURING MEIOSIS I AND II, RESULTS IN MOST OF THE CYTOPLASM BEING IN ONE DAUGHTER CELL, WHICH WILL FORM THE SINGLE OVUM- THE OTHER CELLS (POLAR BODIES) WILL DEGENERATE

  36. 2) SPERMATOGENESIS IS A CONTINUOUS PROCESS THROUGHOUT THE REPRODUCTIVE LIFE OF THE MALE. ALL POTENTIAL OVA THAT CAN BE PRODUCE VIA OOGENESIS WILL BE PRESENT AS PRIMARY OOCYTES IN THE OVARIES AT THE TIME OF THE FEMALE’S BIRTH • 3) SPERMATOGENESIS OCCURS AS AN UNINTERRUPTED SEQUENCE. IN OOGENESIS, LONG “RESTING” PERIODS OCCUR BETWEEN THE FORMATION OF THE INITIAL STEPS AND FINAL PRODUCTION OF THE OVUM

  37. MALE HORMONES • ANDROGENS ARE DIRECTLY RESPONSIBLE FOR FORMATION OF PRIMARY SEX CHARACTERISITICS (REPRODUCTIVE ORGANS) AND SECONDARY SEX CHARACTERISTICS (DEEPENING OF VOICE, HAIR GROWTH…) • ANDROGENS ARE STEROID HORMONES PRODUCED PRIMARILY BY THE LEYDIG CELLS OF THE TESTES • TESTOTERONE IS THE MOST IMPORTANT ANDROGEN PRODUCED • ANDROGENS ARE ALSO POTENT DETERMINANTS OF SEXUAL AND AGGRESSIVE BEHAVIORS • GnRH FROM THE HYPOTHALAMUS STIMULATES THE ANT. PITUITARY TO RELEASE LH (STIMULATES ANDROGEN PRODUCTION) AND FSH (ACTS ON SEMINIFEROUS TUBULES TO INCREASE SPERM PRODUCTION)

  38. MALE REPRODUCTIVE HORMONAL CONTROL

  39. VIDEO: MALE REPRODUCTIVE SYSTEM

  40. VIDEO: FEMALE REPRODUCTIVE SYSTEM I

  41. VIDEO: FEMALE REPRODUCTION II

  42. FEMALE HORMONES • HORMONAL CONTROL IN FEMALES IS MORE COMPLICATED AND REFLECTS THE CYCLIC NATURE OF FEMALE REPRODUCTION. FEMALE MAMMALS DISPLAY 2 DIFFERENT TYPES OF CYCLES: ESTROUS AND MENSTRUAL

  43. ESTROUS CYCLES • OCCURS IN NON-PRIMATE MAMMALS • OVULATION OCCURS AFTER THE ENDOMETRIUM THICKENS AND VASCULARIZES • IF PREGNANCY DOES NOT OCCUR, THE ENDOMETRIUM IS REABSORBED BY THE UTERUS • PRONOUNCED BEHAVIORAL CHANGES OCCUR • ESTRUS IS THE PERIOD OF SEXUAL ACTIVITY SURROUNDING OVULATION AND IS THE ONLY TIME MOST NON-PRIMATE MAMMALS WILL COPULATE. IT VARIES AMONG SPECIES

  44. MENSTRUAL CYCLE • OCCURS IN HUMANS AND MANY OTHER PRIMATES • OVULATION OCCURS AFTER THE ENDOMETERIUM THICKENS AND VASCULARIZES • IF PREGNANCY DOES NOT OCCUR, THE ENDOMETRIUM IS SHED FROM THE UTERUS THRU THE CERVIX AND VAGINA DURING MENSTRUATION • THE TERM MENSTRUAL CYCLE REFERS TO THE CHANGES THAT OCCUR IN THE UTERUS DURING THE REPRODUCTIVE CYCLE • IN HUMAN FEMALES, THE CYCLE VARIES FROM ONE WOMAN TO ANOTHER • USUALLY RANGES FROM 20-40 DAYS • SOME WOMEN HAVE VERY REGULAR CYCLES; OTHERS DO NOT

  45. 3 PHASES OF MENSTRUATION • 1) MENSTRUAL FLOW PHASE : MOST OF ENDOMETRIUM IS BEING LOST FROM THE UTERUS • PERSISTS ONLY A FEW DAYS • THE FIRST DAY OF THIS PHASE IS USUALLY DESIGNATED DAY 1 OF THE CYCLE • 2) PROLIFERATIVE PHASE: LASTS ONE TO TWO WEEKS AND INVOLVES THE REGENERATION AND THICKENING OF THE ENDOMETRIUM • 3) SECRETORY PHASE: LASTS ABOUT 2 WEEKS AND IS A TIME WHEN THE ENDOMETRIUM CONTINUES TO DEVELOP • ENDOMETRIUM BECOMES MORE VASCULARIZED, AND DEVEOPS GLANDS WHICH SECRETE A GLYCOGEN-RICH FLUID • IF AN EMBRYO DOES NOT IMPLANT IN THE LINING, A NEW MENSTRUAL FLOW PHASE BEGINS

  46. THE MENSTRUAL CYCLE

  47. OVARIAN CYCLE • PARALLELS THE MENSTRUAL CYCLE • 1) FOLLICULAR PHASE: TIME DURING WHICH SEVERAL FOLLICLES IN THE OVARIES BEGIN TO GROW • THE EGG CELLS WITHIN THE FOLLICLES ENLARGE AND THE FOLLICLE CELL COAT BECOMES MULTILAYERED • ONLY ONE OF THE GROWING FOLLICLES WILL CONTINUE TO MATURE WHILE THE OTHERS DEGENERATE • A FLUID-FILLED CAVITY DEVELOPS IN THE MATURING FOLLICLE AND GROWS LARGE ENOUGH TO FROM A BULGE ON THE SURFACE OF THE OVARY • ENDS WITH OVULATION, MARKED BY ERUPTION OF THE FOLLICLE AND EXPULSION OF THE EGG FROM THE OVARY • 2) LUTEAL PHASE • BEGINS AFTER OVULATION • FOLLICULAR TISSUE REMAINING IN THE OVARY FORMS A CORPUS LUTEUM • THE CORPUS LUTEUM IS ENDOCRINE TISSUE THAT SECRETES FEMALE HORMONES

  48. HORMONAL CONTROL OF MENSTRUATION • 5 HORMONES WORK TOGETHER TO COORDINATE THE MENSTRUAL CYCLE. THIS COORDINATION SYNCHRONIZES FOLLICLE GROWTH AND OVULAITON WITH PREPARATION OF THE UTERINE LINING FOR EMBRYO IMPLANTATION.

  49. THE MENSTRUAL CYCLE

  50. DURING THE FOLLICULAR PHASE OF THE OVARAIN CYCLE, GnRH SECRETED BY THE HYPOTHALAMUS STIMULATES THE ANT. PITUITARY TO SECRETE SMALL QUANTITIES OF FSH AND LH. • FSH STIMULATES THE IMMATURE FOLLICLES IN THE OVARY TO GROW AND THESE FOLLICLE CELLS SECRETE SMALL AMOUNTS OF ESTROGEN • AS THE FOLLICLE CONTINUES TO GROW, THE AMT. OF ESTROGEN SECRETED INCREASES. THE MATURE FOLLICLE SECRETES A LARGE AMT. OF ESTROGEN

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