Reproduction Brea Alotaya Bianca Arguilla Natasha Guenther
Reproduction in the Animal Kingdom • Sexual Reproduction • Creation of offspring by a fusion of haploid gametes to form a zygote • Asexual Reproduction • Creation of new individuals whose genes come from the one parent • Mechanisms: • Fission: separation of parent into 2 or more individuals • Budding: new individuals arise from outgrowths of existing ones. Offspring either detach from parent or form extensive colonies like that of stony corals which are really thousands of cnidarians. • Fragmentation and Regeneration: the breaking of the body into several pieces where some or all will develop into mature adults and is accompanied by regeneration (for animals), or the regrowth of lost body parts • Several Advantages: • Enables isolated animals to produce offspring • Idea for colonizing a habitat • Perpetuates successful genotypes successfully
Reproductive Cycles and Patterns • Reproductive cycles controlled by a combo of hormonal and environmental cues • Animals produce asexually, sexually & even alternate betwixt the 2 • In aphids and Daphnia females produce 2 types of eggs: one fertilized egg and one unfertilized egg that develops via parthenogenesis • Male honeybees produced parthenogentically • Whiptail lizards have no males. They imitate courtship and mating behavior. During breeding, one female mimics a male. Sexual stimuli is necessary for successful breeding • Hermaphroditism • Found in sessile animals or parasites • Sequential Hermaphroditisim: an individual reverses its sex during lifetime
Fertilization Mechanisms External Fertilization Internal Fertilization Sperm deposited in or near female reproductive tract An adaption that allows sperm to reach an egg in a dry environment; requires cooperative behavior and structural adaptations • Eggs are released into a wet environment where they are then fertilized by male • Moist habitat required to prevent gametes from drying out • Environmental cues like temp. or day length can cause population to release gametes, or chemical signals trigger release, or courtship behavior
Gamete Production • Animals have systems that produce gametes and make then available to ones of the opposite sex • Systems are varied, but the least complex of reproductive systems do not have gonads, organs that produce gametes in most animals • Complex reproductive systems contain accessory tubes and glands that aid developing embryos • Most insects have complex reproductive systems. Many species have females whose reproductive systems include a spermatheca, a sac that stores sperm for a year or more
Female Reproductive Organs • Ovaries: female gonads. Each ovary is enclosed in a protective capsule and contains about 400,000 follicles (an egg surrounded by layers of follicles cells that nourish and protect the developing egg) • Follicle cells produce estrogens • Egg cell expelled from follicle via ovulation. Follicle tissue that is remaining forms a solid mass called the corpus luteum “yellow body.” The corpus luteum secretes estrogen and progesterone (maintains uterine lining during pregnancy) • Oviducts and Uterus • The Oviduct, or fallopian tube is a funnel-shaped opening comprised of simple squamous epithelial tissue. Cilia lining the epithelium help collect the egg cell and convey it down to the uterus. • The uterus is a muscular organ. The inner lining of the uterus, or the endometrium is filled with blood vessels and the neck of the uterus is called the cervix. • Vagina and Vulva • Vagina: thin-walled chamber where sperm is ejaculated during copulation, opens to the vulva • Hymen: tissue that covers vaginal opening • Vestibule: recess where the vaginal opening and urethral openings are. Bordered by the labia minora, slender skin folds, and the labia majora, thick, fatty ridges that protects the labia minora and vestibule. • Clitoris: short shaft supporting a rounded glans, or head and supplied with nerve endings • During arousal, the clitoris, vagina, and labia minora are filled with blood and enlarge and Bartholin’s glands secrete mucus into the vestibule
Male Reproductive Organs • External organs include the scrotum and penis and the internal ones consist of the gonads and accessory glands • Testes: male gonads that are comprised of tubes called the seminiferous tubules where sperm forms • Leydig cells located w/i the tubules produce testosterone and other androgens • Sperm cannot be produced at body temperature of most mammals, so the testes of humans and others are located in the scrotum, a fold of the body wall whose temperature is about 2°C below the abdominal cavity • Ducts • From the seminiferous tubules, the sperm pass into the epidymis, more coiled tubules. During this 20 day long passage, the sperm become motile and are able to fertilize an egg. • During ejaculation, the sperm are propelled from the epidymis to the vas deferens. These ducts joins a duct from the seminal vesicle to form an ejaculatory duct. This duct opens into the urethra, where males pee and ejaculate from.
Men Continued… • 3 Sets of Accessory Glands: • Seminal Vesicles: 60% of semen. Fluid is thick, yellowish, and alkaline • Prostate Gland: largest of the semen-secreting gland and is secreted directly into urethra. Fluid is thin and milky and contains anticoagulant enzymes. • Bulbourethral glands: small and before ejaculation, they secrete a clear mucus that neutralizes any urine still in the urethra • Alkalinity of semen helps neutralize acidic environment of vagina. Sperm coagulates when first ejaculated, but the anticoagulant enzymes from the prostate gland liquefy the semen, and the sperm can begin swimming • The Penis • Made up of 3 cylinders of spongy erectile tissue which fills with blood during sexual arousal. The pressure from the filled tissue seals off veins that drain the penis. Some mammals have a baculum, a bone that helps stiffen penises. • Main shaft of the penis is covered by thick skin whereas the head, or glans penis is covered with thinner skin and is more sensitive to stimulation. • The prepuce: foreskin • Guys- this serves as a warning: impotence can be a result of alcohol and drugs. So don’t do drink or smoke, or any of that nonsense • Viagra works by using NO which enhances relaxation of smooth muscles in the blood vessels of the penis and thus achieve an erection
Just an FYI- both men and women have mammary glands. Sacs of epithelial tissues secrete milk. Low estrogen levels in males prevents the secretory apparatus .
Sexual Arousal • 2 types of physioligical reactions • Vasocongestion: filling of a tissue with blood via increase of blood flow • Myotonia: tension of skeletal and smooth muscles • Sexual Response has 4 phases: • Excitement: vasocongestion occurs in the penis and clit; testes, labia, and breasts enlarge and myotonia results in erected nipples and tension of the arms and legs • Prep for coitus, or sex • Plateu: responses of first stage continue. In females, outer 1/3 of vajj becomes vasocongested and rest expands. This change froms a depression that receives sperm. Breathing and heart rate increases b/c of stimulation of autonomic nervous system • Orgasm: rhythmic, involuntary contractions (shortest of phases) • Males: 2 stages- emission, or contraction of glands and ducts that force semen into urethra and expulsion, or ejaculation • Females: uterus and outer vajj contract • Resolution: reverses responses to earlier stages
The Embryo! • Pregnancy, or gestation: carrying an embryo(s) in the uterus. • Humans: avg. of 38 weeks • Dogs: 60 days • Elephants: 600 days or more • Conception • Fertilization of an egg, occurs in oviduct • Resulting zygote divides via cleavage and continues till the embryo becomes a ball of cells. • 1 week after fertilization, cleavage has produced an embryonic stage, or the blastocyst, which is a sphere of cells with a cavity • The embryo secretes a hormone that signals its presence. One hormone, the human chorionic gonadotropin (HCG), acts like LH to maintain secretion of progesterone and estrogen by the corpus luteum through first few months of pregnancy. • If there is a lack of HCG, decline in LH results in menstruation and loss of the embryo (pregnancy tests)
Embronic Development First Trimester Most radical change for the embryo Endometrium begins to grow over the blastocyst, and from the endometrium the embryo receives its nutrients for the first 2- 4 weeks. The trophoblast, or outer layer of the blastocyst grows and mingles with the endometrium to eventually form the placenta, the disk-shaped organ that contains embryonic and maternal blood vessels Main period of organogenesis, development of body organs. By end of 8th week all major structures are present and is called a fetus. Mother sees high levels of progesterone. Mucus in cervix forms a plug and uterus and breasts enlarge
Continued Embryonic Development Second Trimester • Fetus grows about 30 cm, very active • Hormone levels stabilize as HCG declines • Corpus Luteum deteriorates and placenta takes over progesterone production Third Trimester Growth of fetus to about 50 cm and 3-4 kg Mother’s abdominal organs become displaced leading to frequent urination and back pains Local regulators and hormones induce labor.
Labor 3 Stages Complex interplay of local regulators and hormones induces and regulates labor, process of childbirth. What triggers labor? Estrogen induces the formation of oxytocin, which is produced by the fetus and mother’s posterior pituitary receptors on uterus. Oxytocin stimulates the contractions and the secretion of prostaglandins Parturition, or birth occurs due to the series of strong, rhythmic uterine contractions. Lactation: postnatal care. After birth, decreasing levels of progesterone allow prolactin secretion. Mammary glands’ release of milk also controlled by oxytocin
Mother’s Immune Tolerance • Pregnancy is an immunological phenomenon • ½ of embryo’s genes come from the father, so ½ of chemical markers present is foreign to the mother. Why, then, does the mother’s body not reject the embryo? • Trophoblast is the key!! The trophoblast brings about the implantation into the endometrium and later to develop into the placenta • During early pregnancy, the trophoblast prevents the mother’s immune system from rejecting the blastocyst by rejecting signal molecules with immunosuppressive effects, including HCG, prostaglandin, interleukins, and an interferon. Combo of these interferes with immune rejection via acting on mommy’s T lymphocytes. • OR the trophoblast and the placenta secrete an enzyme that breaks down tryptophan, an amino acid necessary for T cell survival and function • OR there is an absence of histocompatibility antigens on placental cells and the secretion of hormone that induces a “death activator” membrane protein (FasL) on placental cells.
Contraception • Contraception: deliberate prevention of pregnancy • Temporary abstinence, or the rhythm method of birth control or natural family planning • Involves timing ovulation period • Barrier Methods • Condoms, most commonly used my males • Diaphragm, most commonly used by females, it is a dome shaped rubber cap fitted into vajj • Cervical cap, held in place via suction • “female condom” • Birth controls pills, pregnancy rates of 1%. Combo of synthetic estrogen and progestin. Acts by negative feedback to stop the release of GnRH and thus of FSH and LH • Tubul ligation: women cauterize sections of the oviducts • Vasectomy: cutting of the vas deferens • Abortion: not a contraceptive, just a means to rid the body of the fetus
Modern Reproductive Technology • ART- assisted reproductive technology • Surgically removing eggs from ovaries and fertilizing the eggs • In vitro fertilization: most common ART procedure. Oocytes mixed with sperm in culture dished. • ZIFT: zygote intrafallopian transfer. Eggs fertilized in vitro and zygotes transferred imm. to oviducts • GIFT: gamete intrafallopian transfer. Eggs not fertilized in vitro. Eggs and sperm placed in the oviducts