Chapter 46: Animal Reproduction

Overview Asexual (one parent) Sexual (fusion of haploid gametes) fission (parent separation) budding (corals) gemmules (porifera) fragmentation & regeneration (inverts) Sexual (fusion of haploid gametes) gametes (sex cells) zygote (fertilized egg) ovum (unfertilized egg) spermatozoon (male gamete) Hermaphrodatism (rare mates) Video: Hydra Budding

Reproductive cycles Parthenogenesis unfertilized egg development; (honeybees) Hermaphroditism both male & female reproductive systems; sessile & burrowing organisms (earthworms) Sequential hermaphroditism reversal of gender during lifetime protogynous (female 1st) protandrous (male 1st)

Mechanisms of sexual reproduction Fertilization (union of sperm and egg) external Internal Spermatheca: stores sperm from copulation in some insects Pheromones chemical signals that influence the behavior of others (mate attractants)

Mammalian reproduction, I The Human Male Testes: male gonads Seminiferous tubules: sperm formation Leydig cells: hormone production Scrotum: outside body temp. Epididymis: sperm development Vas deferens: sperm propulsion Seminal vesicles: semen Prostate gland: anticoagulant; nutrients Bulbourethral glands: acid neutralizer Penis/urethra: semen delivery

Mammalian reproduction, II Oviduct Ovary The Human Female Ovaries: female gonads Follicle: egg capsule Corpus luteum: hormone secretion Oviduct: fertilization Uterus/endometrium: womb/lining Cervix/vagina: sperm receptacle Uterus (Urinary bladder) (Rectum) (Pubic bone) Cervix Urethra Vagina Shaft Glans Clitoris Prepuce Labia minora Labia majora Vaginal opening Oviduct Ovaries Follicles Corpus luteum Uterus Uterine wall Endometrium Cervix Vagina

Animation: Male Hormones Spermatogenesis Animation: Male Hormones Puberty until death! Seminiferous tubules: location Primordial germ cell (2N): differentiate into…. Spermatogonium (2N): sperm precursor Repeated mitosis into…. Primary spermatocyte (2N) 1st meiotic division Secondary spermatocyte (1N) 2nd meiotic division Spermatids (1N): Sertoli cells…. Sperm cells (1N)

– – – Hypothalamus GnRH Anterior pituitary FSH LH Sertoli cells Fig. 46-13 – Hypothalamus GnRH – – Anterior pituitary FSH LH Negative feedback Negative feedback Sertoli cells Leydig cells Figure 46.13 Hormonal control of the testes Inhibin Spermatogenesis Testosterone Testis

Animation: Post Ovulation Oogenesis Animation: Ovulation Animation: Post Ovulation As embryo until menopause... Ovaries Primordial germ cells (2N) Oogonium (2N) Primary oocyte (2N) Between birth & puberty; prophase I of meiosis Puberty; FSH; completes meiosis I Secondary oocyte (1N); polar body Meiosis II; stimulated by fertilization Ovum (1N); 2nd polar body

Animation: Post Ovulation The female pattern Estrous cycle (many mammals) Menstrual cycle (humans and many otherprimates): Ovarian/Menstrual cycles: follicular phase: follicle growth ovulation: oocyte release luteal phase: hormone release Animation: Post Ovulation

The blastocyst implants Fig. 46-15 3 Cleavage Cleavage continues 4 Ovary 2 Fertilization Uterus The blastocyst implants 5 1 Ovulation Endometrium (a) From ovulation to implantation Figure 46.15 Formation of the zygote and early post-fertilization events Endo- metrium Inner cell mass Cavity Trophoblast Blastocyst (b) Implantation of blastocyst

Embryonic & fetal development Orgasm: rhythmic contractions of reproductive structures Gestation: pregnancy 1st trimester: organogenesis fetus (week 8; all adult features) HCG hormone (menstruation override; pregnancy test detection) Parturition: birth Labor: uterine contractions Lactation: prolactin & oxytocin

Fig. 46-16 Maternal arteries Maternal veins Placenta Maternal portion of placenta Umbilical cord Chorionic villus, containing fetal capillaries Fetal portion of placenta (chorion) Maternal blood pools Figure 46.16 Placental circulation Uterus Umbilical arteries Fetal arteriole Fetal venule Umbilical cord Umbilical vein

from fetus and mother’s posterior pituitary Fig. 46-18 Estradiol Oxytocin + from ovaries from fetus and mother’s posterior pituitary Induces oxytocin receptors on uterus Positive feedback Stimulates uterus to contract Stimulates placenta to make + Figure 46.18 A model for the induction of labor Prostaglandins Stimulate more contractions of uterus

Contraception and Abortion Contraception: deliberate prevention of pregnancy Contraceptive methods fall into three categories: Preventing release of eggs and sperm Keeping sperm and egg apart Preventing implantation of an embryo Rhythm method (natural family planning): 10-20% = baby Coitus interruptus = unreliable Barrier methods: less than 10% = baby A condom fits over the penis A diaphragm is inserted into the vagina before intercourse Intrauterine devices: less than 1% = baby Female birth control pills: less than 1% = baby

Figure 46.20 Mechanisms of several contraceptive methods Male Female Method Event Event Method Production of sperm Production of primary oocytes Vasectomy Combination birth control pill (or injection, patch, or vaginal ring) Sperm transport down male duct system Oocyte development and ovulation Abstinence Abstinence Condom Female condom Coitus interruptus (very high failure rate) Sperm deposited in vagina Capture of the oocyte by the oviduct Tubal ligation Spermicides; diaphragm; cervical cap; progestin alone (as minipill, implant, or injection) Sperm movement through female reproductive tract Transport of oocyte in oviduct Figure 46.20 Mechanisms of several contraceptive methods Meeting of sperm and oocyte in oviduct Morning-after pill; intrauterine device (IUD) Union of sperm and egg Implantation of blastocyst in endometrium

Detecting Disorders During Pregnancy Amniocentesis and chorionic villus sampling are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis Noninvasive = usually ultrasound imaging Genetic testing of fetus poses ethical questions, can present parents with difficult decisions

Treating Infertility Modern technology can provide infertile couples with assisted reproductive technologies In vitro fertilization (IVF): mixes eggs with sperm in culture dishes, returns embryo to uterus at 8 cell stage Also medications to encourage ovulation like clomed