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Chapter 46

Chapter 46. Animal Reproduction. Mechanisms of Asexual Reproduction. Fission - separation of a parent into two or more individuals of about the same size Budding - new individuals arise from outgrowths of existing ones

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Chapter 46

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  1. Chapter 46 Animal Reproduction

  2. Mechanisms of Asexual Reproduction • Fission- separation of a parent into two or more individuals of about the same size • Budding- new individuals arise from outgrowths of existing ones • Fragmentation- is breaking of the body into pieces, which develop into adults • Parthenogenesis is the development of a new individual from an unfertilized egg

  3. Sexual Reproduction: Advantages • An increase in variation in offspring • An increase in the rate of adaptation • A shuffling of genes and the elimination of harmful genes from a population

  4. Ensuring the Survival of Offspring • External fertilization produce more gametes than species with internal fertilization • Internal fertilization provide greater protection of the embryos and more parental care

  5. Female Reproductive Anatomy Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) Cervix Urethra Shaft Vagina Clitoris Glans Prepuce Labia minora Labia majora Vaginal opening Animation: Female Reproductive Anatomy

  6. Oviduct Ovaries Follicles Corpus luteum Uterine wall Uterus Endometrium Cervix Vagina

  7. Female Reproductive Anatomy • Each ovary contains many follicles,which consist of a partially developed egg (oocyte) • Oogenesis- Once a month, an oocyte develops into an ovum (egg) Ovulation expels an egg cell from the follicle • The remaining follicular tissue grows within the ovary, forming a mass (corpus luteum) • The corpus luteum secretes hormones that help to maintain pregnancy • If the egg is not fertilized, the corpus luteum degenerates

  8. Female Reproductive Anatomy • Oviduct (fallopian tube)- path that an egg cell travels from the ovary to the uterus • Uterus (womb)- where a fertilized egg will implant and develop into a fetus • Endometrium- the uterus lining • Cervix- narrow opening between uterus and vagina • Vagina- repository for sperm during copulation and serves as the birth canal

  9. Male Reproductive Anatomy (Urinarybladder) (Urinaryduct) Seminal vesicle (Rectum) (Pubic bone) Vas deferens Erectiletissue Ejaculatory duct Prostate gland Urethra Penis Bulbourethral gland Glans Vas deferens EpididymisTestisScrotum Prepuce Animation: Male Reproductive Anatomy Animation: Male Hormones

  10. Seminalvesicle(behind bladder) (Urinarybladder) Prostate gland Bulbourethralgland Urethra Erectile tissueof penis Scrotum Vas deferens Epididymis Testis

  11. Male Reproductive Anatomy • Scrotum- hold testes outside of the abdominal cavity where the temperature is lower • Testes- highly coiled tubes surrounded by connective tissue • Seminiferoustubules- site of sperm formation • Epididymis- coiled tubules connecting to seminiferous tubules • Vas deferens- pathway for sperm to travel from the epidiymis • Prostate gland- secretes anticoagulant enzymes and sperm nutrient • Bulbourethral glands- secrete a mucus that neutralizes urine remaining in the urethra

  12. Gametogenesis • Spermatogenesis- production of mature sperm. • Sperm are small, motile, and produced throughout the life of a male. Four sperm are produced in meiosis • Oogenesis- development of mature oocytes (eggs) and can take many years • Eggs contain stored nutrients, very large. One egg forms in meiosis

  13. Epididymis Seminiferous tubule Sertoli cellnucleus Spermatogonium Primary spermatocyte Testis Cross sectionof seminiferoustubule Secondary spermatocyte Spermatids(two stages) Sperm Lumen ofseminiferous tubule

  14. Primordial germ cell in embryo Mitotic divisions Spermatogonialstem cell 2n Mitotic divisions Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I n n Secondary spermatocyte Meiosis II Earlyspermatid n n n n Differentiation (Sertolicells provide nutrients) Sperm n n n n

  15. Ovary Rupturedfollicle Primaryoocytewithinfollicle Ovulatedsecondary oocyte Growingfollicle Corpus luteum Mature follicle Degeneratingcorpus luteum

  16. In embryo Primordial germ cell Mitotic divisions 2n Oogonium Mitotic divisions Primary oocyte(present at birth), arrestedin prophase of meiosis I 2n Completion of meiosis Iand onset of meiosis II Firstpolarbody n n Secondary oocyte,arrested at metaphase of meiosis II Ovulation, sperm entry Completion of meiosis II Secondpolarbody n Fertilized egg n

  17. Sex Hormones • Androgens (ex: testosterone), Estrogens (ex: estradiol), Progestins (ex: progesterone) • GnRH (gonadtropin-releasing hormone) secreted by the hypothalamus • FSH (follicle-stimulating hormone) and LH(luteinizing hormone)- secreted by the anterior pituitary

  18. The Reproductive Cycles of Females • Prior to ovulation, the endometrium thickens with blood vessels in preparation for embryo implantation • If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation Animation: Ovulation

  19. (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus – Stimulated by high levelsof estradiol + GnRH Inhibited by low levels of estradiol Anterior pituitary – LH FSH Pituitary gonadotropinsin blood (b) LH FSH FSH and LH stimulatefollicle to grow LH surge triggersovulation Ovarian cycle (c) Corpusluteum Degeneratingcorpus luteum Growing follicle Maturingfollicle Luteal phase Ovulation Follicular phase Days | | | | | | | | 20 25 14 15 28 5 10 0

  20. (d) Ovarian hormones in blood Peak causesLH surge Progesterone Estradiol Ovulation Estradiol level very low Progesterone and estra-diol promote thickeningof endometrium (e) Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days | | | | | | | | 0 14 15 20 25 28 5 10

  21. Menstrual Versus Estrous Cycles Menopause- the cessation of ovulation and menstruation • Menstrual cycles (humans and some other primates) • The endometrium is shed from the uterus during menstruation • Sexual receptivity is not limited to a timeframe • Estrous cycles (characteristic of most mammals) • The endometrium is reabsorbed by the uterus • Sexual receptivity is limited to a “heat” period • The length and frequency of estrus cycles varies from species to species

  22. Conception, Embryonic Development, and Birth • Human chorionic gonadotropin (hCG)- prevents menstruation

  23. Cleavage 3 Cleavage continues 4 Ovary Fertilization 2 The blastocystimplants 5 Uterus Ovulation 1 Endometrium (a) From ovulation to implantation Endo-metrium Inner cell mass Cavity Trophoblast Blastocyst (b) Implantation of blastocyst

  24. First Trimester First Trimester • The first trimester is the main period of organogenesis, development of the body organs • All the major structures are present by 8 weeks, and the embryo is called a fetus Second Trimester • The fetus grows and is very active Third Trimester • The fetus grows and fills the space within the embryonic membranes

  25. Maternalarteries Maternalveins Placenta Maternalportionof placenta Umbilical cord Chorionic villus,containing fetalcapillaries Fetalportion ofplacenta(chorion) Maternal bloodpools Uterus Umbilicalarteries Fetal arteriole Fetal venule Umbilicalvein Umbilical cord

  26. (a) 5 weeks

  27. (b) 14 weeks

  28. (c) 20 weeks

  29. Oxytocin Estradiol + fromovaries from fetusand mother’sposterior pituitary Induces oxytocinreceptors on uterus Positive feedback Stimulates uterusto contract Stimulates placenta to make + Prostaglandins Stimulate morecontractionsof uterus

  30. Placenta Umbilical cord Uterus Cervix Dilation of the cervix 1

  31. Expulsion: delivery of the infant 2

  32. Uterus Placenta (detaching) Umbilical cord Delivery of the placenta 3

  33. Contraception and Abortion • Preventing release of eggs and sperm (birth control pills) • Keeping sperm and egg apart (condom, diaphragm) • Rhythm method (natural family planning)- is to refrain from intercourse when conception is most likely

  34. Sterilization is permanent and prevents the release of gametes • Tubal ligation ties off the oviducts • Vasectomy ties off the vas deferens • Abortion is the termination of a pregnancy • Spontaneous abortion (miscarriage) occurs in up to one-third of all pregnancies • RU486 results in an abortion within the first 7 weeks of a pregnancy

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