Animal Reproduction

1. Animal Reproduction Ch. 46

2. Asexual Reproduction • Formation of offspring from one parent only • No fusion of egg and sperm; no mixing of genetic material • Advantages of Asexual Repro • Can reproduce without finding a mate • Lots of offspring in short period of time • In stable environments, allows for the perpetuation of successful genotypes

3. Asexual Reproduction • Fission: parent separates into two or more approximately equal sized individuals • Budding: new individuals split off from existing ones • Fragmentation: the breaking of the body into several pieces, some or all of which develop into complete adults

4. Sexual Reproduction • Formation of offspring by the fusion of haploid gametes • Ovum: female gamete; usually large and nonmotile • Spermatozoan: male gamete; usually small and motile • Increases genetic variation among offspring

5. Sexual Reproduction • Animals can reproduce sexually or asexually depending on environmental conditions • Ex: Daphnia reproduce sexually when conditions are not favorable; do parthenogenesis when favorable • Parthenogenesis: process by which an unfertilized egg develops into (often) haploid adult

6. Sexual Reproduction • Hermaphroditism: one individual is functional as both a male and a female • Some self-fertilize • Most mate with another member of the same species • Each individual receives and donates sperm • Results in twice as many offspring as would occur if only one set of eggs were fertilized

7. Sexual Reproduction • Sequential hermaphroditism: an individual reverses its sex during its lifetime based upon environmental conditions, size, age, etc. • Protogynous: female first sequential hermaphroditism • Protandrous: male first sequential hermaphroditism

8. Male Reproductive Structures • Reproductive Anatomy of the Human Male • Scrotum and the penis are the external components of the reproductive system • Internal reproductive organs consist of gonads, accessory sex glands, and ducts

9. Male Reproductive Structures • Scrotum: sack that holds the testes; keeps testes cooler for proper sperm formation • Testes: primary reproductive organ; male gonads • Seminiferous tubules: tubes within the testes that produce sperm • Leydig cells, between seminiferous tubules, produce androgens Testis Scrotum

10. Male Reproductive Structures • Sperm: male sex cell; head, midpiece, and tail

11. Male Reproductive Structures • Sperm • Head: holds nucleus; capped with the acrosome – has digestive enzymes that punch hole in egg membrane and allow for insertion of nucleus • Midpiece: contains mitochondria • Tail: flagellum

12. Male Reproductive Structures • FSH and LH – hormones that stimulate testes to make testosterone • Testosterone – hormone that stimulates development of sperm

13. Vas deferens Epididymis Male Reproductive Structures • Epididymis – sperm are stored here and mature • Takes ~ 20 days for sperm to pass thru • Sperm become motile and gain the ability to fertilize • Vas deferens – sperm are forced here after storage • Vas deferens passes thru 3 glands which provide fluid and nourishment for sperm

14. Urethra Male Reproductive Structures • Semen – sperm and seminal fluid; contains 50-500 million sperm • Urethra – vas deferens merges with this tube that leads to outside of body • Penis – structure adapted for internal fertilization of egg; release sperm in vaginal canal

17. Male Reproductive Structures Seminal vesicle • 3 sets of glands contribute fluids: • Seminal vesicles – secrete fluid containing fructose and prostaglandins into vas deferens • Prostate gland – surrounds urethra at point where vasa deferentia enter; secretes milky, alkaline fluid into urethra • Bulbourethral glands – secrete an alkaline mucus into urethra Prostate gland Bulbourethral gland

18. Female Reproductive Structures Ovary Fallopian tube • Ovaries – primary reproductive organ that produces eggs or ovum • Fallopian tubes (oviducts) – tubes through which egg/sperm travel (ova fertilized here!!) • Uterus – muscular cavity where a fertilized ovum implants and develops • Cervix – opening of the uterus • Vagina – birth canal; leads to outside of body Uterus Vagina Cervix

21. Female Reproductive Structures • Pituitary, at puberty, releases FSH and LH to stimulate ovaries to produce estrogen and stim development of 2O sex characteristics • Each ovary contains about 400,000 primary follicles surrounding an ovum • Follicles are groups of cells that prepare ovum for release • Women are born with ALL of their ova • Approx. 500 of 400,000 will be released

22. Cyclic Changes in Ovary & Uterus • Regulated by hormones: • GnRH – produced by hypothalamus; regulates release of FSH & LH from anterior pituitary • FSH – produced by anterior pituitary; stimulates development of follicles • LH – produced by anterior pituitary; triggers ovulation and formation of corpus luteum

23. Cyclic Changes in Ovary & Uterus • Estrogen – produced by follicle cells and corpus luteum; causes endometrium (uterine lining) to thicken • Progesterone – produced by corpus luteum of ovary; increases thickness of endometrium • Ovarian and menstrual cycles occur about every 28 days (puberty through menopause)

24. Cyclic Changes in Ovary & Uterus • Follicle phase (~10 days): development of follicle  increase in estrogen • Ovulation (~3 days): release of mature ovum  increase of FSH and LH • Luteal phase (~10 days): “corpus luteum” releases progesterone; prepares uterine lining for implantation • Menstruation (~5 days): hormone levels decrease; unfertilized egg and uterine lining is shed

25. Cyclic Changes in Ovary & Uterus • Estrogen