Chapter 46 Animal Reproduction

1. Chapter 46Animal Reproduction By: Audrey Del Re and Becca Krauss

2. Two Types of Reproduction • Asexual - involves two-step process: fragmentation & regeneration • Sexual - Majority of eukaryotic species reproduce sexually - fusion of haploid gametes forms diploid cell, zygote

3. Asexual Reproduction • Types: • Budding: separation of parent organism into two individuals of equal size • Fission: new individuals arise from outgrowths of existing ones • Parthenogenesis: an egg develops without being fertilized • Advantages: • In stable, favorable environments because it keeps passing on successful genotypes • Two step process: • Fragmentation: the breaking of the body into several pieces • Regeneration: the regrowth of the lost body part

4. Sexual Reproduction • Advantages: • Production of various phenotypes, may enhance reproductive success in changing environment. • Shuffling of genes during sexual reproduction might get rid of unwanted genes quickly. • Reproductive cycle: • Controlled by hormones regulated by the environment • Females go through ovulation • Occurs at the midpoint of each cycle • Some organisms switch between sexual and asexual due to the environment • Reproductive Patterns: • Hermaphroditism • Sex reversal

5. Fertilization • The union of sperm and egg • External Fertilization: eggs released into environment, where the male fertilizes them • Needs moist habitat • Spawning: process where entire species releases their gametes into the water at about the same time. • Chemical or environmental triggers to release gametes • Non-synchronous fertilization in a population • One female’s eggs to one male • Courtship behavior • Leads to mate selection and higher probability of success. • Produces a lot of gamete, few survive.

6. Fertilization • Internal Fertilization: sperm are released in or near the female reproductive tract, where fertilization then occurs • Pheromones: chemicals released by organisms that act as a mate attractant • During mating, sperm are ejaculated into the female reproductive system • Produce fewer zygotes • Gonads: the organs that produce gametes in most animals

7. Female Reproductive Organs • External Structure: • Clitoris and vaginal opening surrounded by two sets of labia • Internal Organs Function: • Produces eggs and reproductive hormones • Houses the embryo and fetus • Internal Organs Structure: (gonads) • Pair of ovaries on each side of the uterus • Outer layer has follicles made up of oocytes (partially developed eggs) • Oogenesis: formation and development of ovum • Before ovulation follicles produce estradiol (primary female sex hormone) • If no fertilization occurs the corpus luteum degenerates and is released • Menstrual cycle then starts over

8. Female Reproductive Organs Continued • Oviduct: (fallopian tubes) connects the uterus and the ovaries • Contractions of the oviduct and cilia help the egg travel down to the uterus • Uterus: (womb) thick muscular organ that expands during pregnancy • Endometrium: inner lining; richly supplied with blood vessels • Cervix:neck of the uterus; opens into the vagina. • Vagina: muscular, but elastic chamber; the sire for insertion of the penis and deposition of sperm; birth canal • Vulva: collective term for the external female genitals • Labia majora: encloses and protects the rest of the vulva • Mammary glands: produces milk in the breasts • Usually only in females

9. Male Reproductive Organs • External Structure: • Scrotum and penis • Internal Organs Function: • Produces sperm and reproductive hormones • Ducts that carry sperm and secretions • Testes: male gonads • Seminiferous tubules: where sperm forms • Leydig cells: produces testosterone • Scrotum: maintains testis temperature • Testicle: testes within a scrotum • Ejaculation: the sperm is released from the epididymis through the vas deferens • Urethra: outlet for excretions • Accessory glands: produce secretions that combine with sperm to make semen • Seminal vesicles, prostate gland, bulbourethral glands • Penis: contains urethra and three cylinders of erectile tissues

10. Human Sexual Response • Physical reactions predominant in both sexes: • Vascongestion: the filling of a tissue with blood • Myotonia: increased muscle tension • Four phases of sexual response cycle: • Excitement: prepares the vagina and penis for coitus • Plateau: excitement symptoms continue; breathing and heart rate increase • Orgasm • Male has two stages: Emission and Expulsion • Female: the uterus and outer vagina contract • Females can have multiple; males need to recover after each • Resolution: reverses the responses of the earlier stages

11. Gametogenesis • The production of gametes • Spermatogenesis: formation and development of sperm • Continuous; in the testes • Oogenesis: development of mature eggs • Development does not complete for years • Differences: • Sperm: all four products of meiosis develop into mature gametes Eggs: meiosis is unequal • Sperm: mitotic division throughout most of life Eggs: mitotic divisions are complete before birth • Sperm: produces mature sperm in continuous sequence Eggs: have long interruptions

12. Hormones Regulate Reproduction • Hypothalamus secretes gonadotropin-releasing hormone (GnRH) • Triggers anterior pituitary to secrete Follicle Stimulating Hormones (FSH) and Luteinizing Hormone (LH) • Regulates gametogenesis (regulates sex hormone production) • Principal Sex Hormones • Male: androgens (testosterone) • Female: estrogens (estradiol, progesterone) • Induce formation of secondary sex characteristics

13. Hormonal Control • Male: testosterone regulates blood levels of GnRH, FSH, and LH through inhibitory effects on hypothalamus and anterior pituitary • Inhibin: reduces FSH secretion by pituitary gland • Together, these negative feedback circuits maintain androgen production at ideal levels • Female: two cycles • Menstrual/Uterine Cycle: changes in uterus; shedding of endometrium from uterus (if no pregnancy) • Estrdiol is involved • Ovarian cycle: cyclic events that occur in the ovaries

15. Conception, Embryonic Development, and Birth • Conception aka fertilization: sperm fuses with egg • Cleavage: 24 hours after conception, process of dividing zygote • After 2-3 days, embryo arrives at uterus as 16-celled ball • Blastocyst: 1 week after fertilization, embryonic stage • Embryo implants into endometrium • Human chorionic gonadotropin (hCG): secreted by implanted embryo, maintains secretions of progesterone and estrogens • Pregnancy/Gestation: condition of carrying 1+ embryos • 266 days/38 wks

16. Pregnancy Trimesters • three months each • First Trimester: • 2-4 weeks embryo obtains nutrients directly from the endometrium • Placenta: formed by outer layer of blastocyst (trophoblast) and the endometrium • Organogenesis: the development of the body organs • 4th week heart begins beating • 8th week FETUSand heartbeat detectable • Second Trimester: • 30cm in length and is very active • Third Trimester: • 50cm in length; 3-4kg • LABOR: process by which childbirth occurs; induced by estradiol • Dilation • Delivery of baby • Delivery of placenta

17. Contraceptives, Abortion, and Repro. Tech. • Deliberate prevention of pregnancy • Temporary Abstinence/Rhythm Method/Natural Family Planning • Withdrawal • Barrier Methods: Condom, Birth Control, Diaphragm • Sterilization: tubal ligation, vasectomy • Abortion: forced miscarriage • Detecting Disorders: ultrasound imaging, amniocentesis, chorionic villus sampling, blood sample from mother • Treating Infertility: assisted reproductive technologies, in vitro fertilization, intracytoplasmic sperm injection

18. THE END!!!!!!!