The Reproductive System Chapter 53 The Reproductive System You are not responsible for the more detailed descriptions of reproduction in fishes, amphibians, reptiles and birds on pages 1070 – 1072. You are only responsible for the hormones we discuss in class We will draw upon a few topics from Chapter 54 about fetal development The Reproductive System

Sexual vs. asexual reproduction Asexual reproduction: produces genetically identical cells fission (prokaryotes) budding Asexual reproduction Genetically identical cells are produced from a single parent cell through mitosis Single-celled organisms utilize fission Cnidarians reproduce by budding (offspring develop as a growth on the body of the parent) The Reproductive System

The Reproductive System Why sex? Protozoa Fish Amphibians Bacterial conugation Fungi Vertebrate sexual reproduction evolved in in the ocean before vertebrates colonized land Marine bony fish use external fertilization -Eggs and sperm are released into the water where union of free gametes occurs Most other vertebrates use internal fertilization -Sperm are introduced into the female reproductive tract Fishes -In most species of bony fish, fertilization is external -Thousands of eggs are fertilized, but only a few individuals grow to maturity -In most species of cartilaginous fish, fertilization is internal -Development of young is viviparous Amphibians-In most species fertilization is external -Eggs of most species develop in water -With some interesting exceptions -Development is divided into embryonic, larval and adult stages How does sex contribute to natural selection? The Reproductive System

The Reproductive System How is sex determined? Environmentally controlled Temperature Community structure Genetically controlled -- e.g., Sex-determining Region of the Y chromosome) -- Female condition is default in mammals Humans Embryonic gonads indifferent for first 40 days SRY gene on Y converts gonads to testes Testosterone promotes male development The Reproductive System

Interesting “twists” to sexual determination Hermaphroditism One individual has both types of reproductive organs Plants, earthworms May be sequential Protogyny – female-to-male change Protandry – male-to-female change (e.g. Nemo!) Parthenogenesis Females produce offspring from unfertilized eggs Nemo = protandrous hermaphrodite The Reproductive System

Oviparity in male midwife toad Copyright © 2000 Michael Frede Reproductive strategies have evolved toward internal fertilization and development Why is internal fertilization better than external? Why is internal development Oviparity in male midwife toad Copyright © 2000 Michael Frede Human viviparity The Reproductive System

Reproduction in mammals Internal fertilization All female mammals produce milk Mammals are of three types: Monotremes lay eggs. Marsupials give birth to incompletely developed fetuses, which mature in mother’s pouch. Placentals retain young in uterus for long periods of development. The Reproductive System

Reproduction in Humans Humans are Placental, genetically determined sex Complex reproductive biology; Hormonal regulation influences Development & 2O sexual characteristics Mating behavior Gender identification We share hormones -- differ in quantity and effects Female reproductive biology particularly complicated -- Mating receptiveness uncoupled from Estrus -- unlike other mammals The Reproductive System

The Reproductive System What are the characteristics of the Male Reproductive System? Anatomy Erection What are 1O and 2O sexual characteristics? 2O characteristics Testosterone Androstenedione abuse Contraception condom vasectomy The Reproductive System

The Reproductive System Hormonal regulation is “Endocrine” -- Hormones move between organs Pituitary hormones FSH – stimulates spermatogenesis LH – stimulates testosterone synthesis Testosterone Androstenedione abuse The Reproductive System

The Reproductive System Spermatogenesis In the wall of the seminiferous tubule, a spermatogonium divides by mitosis to produce two diploid cells One later undergoes meiosis, the other remains as a spermatogonium The diploid cell that begins meiosis is called a primary spermatocyte It undergoes meiosis I, producing two haploid secondary spermatocytes Each secondary spermatocyte undergoes meiosis II to produce two haploid spermatids The seminiferous tubules also contain supporting cells called Sertoli cells Nurse developing germ cells Help convert spermatids into spermatozoa (sperm) by engulfing their extra cytoplasm Several developmental stages Primary vs. secondary spermatocytes Spermatid Spermatozoa The Reproductive System

The Reproductive System What are the characteristics of the Female Reproductive System? Anatomy Pathway of egg travel Pregnancy Contraception: diaphragm tubal ligation spermicides IUD The Reproductive System

The Reproductive System Hormonal control the female reproductive system What is the ovarian cycle? Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Follicle & corpus luteum What is the uterine cycle? Estrogen & Progesterone Endometrium & Menstruation Other forms of contraception Rhythm method Chemical contraceptives oral: (The “Pill’) Implant (“Norplant”) Injectable The Reproductive System

The Reproductive System What happens after fertilization? Completion of meiosis Implantation in endometrium Ectopic pregnancy The Reproductive System

The Reproductive System Hormonal changes upon pregnancy Roles of embryo and corpus luteum Progesterone Estrogen Human Chorionic Gonadotropin (HCG) What happens if the female reproductive cycle becomes disrupted? Amenorrhia Menopause The Reproductive System

The Reproductive System Assisted pregnancy Artificial insemination Gamete Intrafallopian transfer In-vitro fertilization Gamete donation Surrogate mothering Pictures used with the permission of Dr. Clemens M. Grosskinsky, ORM, Columbus The Reproductive System

The Reproductive System What are the functions of the amnion and placenta? Amniotic sac & fluid Maternal and fetal circulatory systems -- no connection Exchange of nutrients gasses wastes Chorionic villi The Reproductive System

The Reproductive System What are the stages of fetal development? Trimesters Embryonic stage Fetal stage Sensitive periods Fetal alcohol syndrome 4 weeks 3 months 6 months The Reproductive System

The Reproductive System How can Congenital Defects be tested for? Amniocentesis Chorionic villi sampling Perform karyotype The Reproductive System

The Reproductive System Labor and Birth Fetal position -- why is ‘breach’ position bad Uterine contractions Dilation of cervix Extraction of the placenta The Reproductive System