Reproductive System Evolutionary success is determined by reproductive success Reproductive Strategies in animals: 1.Asexual – one parent, offspring genetically identical to parent –budding – a miniature version of the adult grows directly on adult (sponges, cnidarians) –fission followed by regeneration (fragmentation) – animal disintegrates into two or more pieces and each piece regenerates entire body (some annelids, flatworms, a few brittle stars) –parthenogenesis – females only, haploid egg cells develop into adults without being fertilized (bees, some fish, amphibians, insects, reptiles) – some species of fish and lizards have completely done away with males

Parthenogenic Lizards

2.Sexual reproduction – requires union of egg and sperm (fertilization) male produces sperm, female produces eggs –Hermaphrodites – have both male and female gonads –may self-fertilize (internal parasites) but usually exchange sperm between individuals

External Fertilization gametes unite outside of the parents’ bodies more common in aquatic animals (aquatic inverts, most fish, many amphibians vast numbers of eggs and sperm are released at one time – spawning synchronized release of gametes achieved by signals (pheromones), behaviors (courtship), and environmental cues (seasonal changes, daylength)

External Fertilization

Internal Fertilization sperm are taken into female’s body and fertilization occurs internally copulation – behavior by which the male deposits sperm directly into the reproductive tract of female spermatophores – some males package their sperm in a container and drops it on the ground – female finds it and fertilizes herself by inserting it into her reproductive cavity deposit of sperm must coincide with ovulation (release of egg) – resulting in the need for mating behaviors, breeding seasons, or storage of sperm until eggs are ready (snails, insects) fertilized eggs are either enclosed in protective shell and released or held in female’s body for embryo. development

Amniotic Egg land vertebrate eggs (birds, reptiles) consist of: amnion – encloses a fluid-filled chamber housing embryo allantois – retains metabolic wastes of embryo, has blood vessels near shell for gas exchange yolk sac – encloses embryo’s food supply chorion – outer membrane surround embryo and other membranes

Human Reproductive System mammals use internal fertilization and embryo is retained in female for development

Male Reproductive System main organ: testes located at the base of the abdominal cavity develop from same embryonic tissue as female ovaries descend at time of birth into scrotum through inguinal canal – canal closes off with connective tissue inguinal hernia – point of weakness, excessive strain may cause a rupture (most common hernia in human males)

Testes have 2 functional components: seminiferous tubules – produces sperm, only functional at slightly lower body temp. scrotal sac approx. 1.5 degrees C cooler than abdom. epididymis – coiled tube where sperm travel from seminiferous tubules – lie on top of testes – sperm stored here and acquire ability to swim interstitial cells – secrete male sex hormone testosterone

Vas deferens – 2 long ducts that carry sperm from epididymis to urethra (common duct for passage of sperm and urine) urethra passes through penis and empties to outside as sperm passes through the vas deferens, sperm is mixed with seminal fluids to form semen – seminal fluids are secreted by seminal vesicles, prostate gland, and Cowper’s gland (bulbourethral gland) seminal fluid functions as: vehicle for transport of sperm, lubricates passages where sperm pass, acts as a buffer fluid to protect sperm from acids in female reprod tract, contains fructose for source of energy

Hormonal control of male reproduction during embryological development – small amts of testosterone cause differentiation of male structures testosterone levels remain low until onset of puberty (no sperm production) hypothalamus produces gonadotropic releasing hormone (GnRH) to anterior pituitary ant. pituitary release luteinizing hormone (LH) and follicle stimulating hormone (FSH) LH stimulates interstitial cells of testes to produce testosterone FSH and testosterone stimulates spermatogenesis secondary sex characteristics result from testosterone (beard, pubic hair, deepening of voice, development of larger and stronger muscle)

Female Reproductive System Ovaries – located in abdom cavity – held in place by ligaments – produce gametes and sex hormones at time of birth, ovaries already contain hundreds of thousands of oocytes (primordial egg cells) each oocyte is enclosed in a follicle – each month when egg ripens, follicle grows and fills with fluid and bulges on surface of ovary – ovulation occurs and egg is released into body cavity

Ovulation Follicles in ovary

egg is taken up by oviducts (Fallopian tubes) fertilization must occur in upper third of oviduct for baby to result egg finishes maturation (completes meiosis II) with penetration of sperm, nuclei fuse

Oviducts empty directly into uterus about the size of a fist lies in lower portion of abdomen behind bladder muscular sac with thick walls of smooth muscle, lined with mucous, contains many blood vessels location where fertilized egg implants and develops lower end of uterus connects to vagina (birth canal) muscular tube leading to outside cervix – opening from vagina to uterus

Hormonal control of female reproductive system hypothalamus begins releasing GnRH at puberty stimulating ant. pituitary to release FSH and LH FSH and LH stimulate the ovaries to produce estrogen and progesterone – starts menstrual cycle estrogen stimulates development of secondary sex characteristics (pubic hair, broadening of pelvis, devel. of breasts, distribution of fat, changes in voice)

Estrous Cycle in Mammals rhythmic variation in the condition of the reproductive tract and sexual readiness females of most species of mammal will only accept the male in copulation during brief periods near time of ovulation – female is in estrus (“in heat”) – if fertilization does not occur, uterine lining is reabsorbed humans and higher primates do not have distinct heat period – female is somewhat receptive throughout cycle, if fertilization does not occur, uterine lining is sloughed off during a period of bleeding – menstruation

Human Menstrual Cycle averages every 28 days 1 st day of menstruation is day one of cycle days 1 – 7 – lining is sloughed off (lining is thin) Follicular Phase (lasts 9 to 10 days after menstrual flow) – ant. pituitary releases FSH stimulating the maturation of several follicles (only 1 will complete maturation) – also stimulates ovaries to secrete estrogen –estrogen stimulates thickening of uterine lining –estrogen stimulates hypothalamus to release GnRH to stimulate ant. pituitary to release an abrupt surge of LH – LH surge is followed by ovulation (around the middle of the cycle)

Luteal phase (lasts approx. 13 – 15 days) – after ovulation, LH stimulates ruptured follicle to form the corpus luteum – continues to release estrogen and also progesterone –progesterone support uterine lining (also inhibits production of FSH and LH) –if no fert. occurs – corpus luteum atrophies, progesterone levels drop and lining is shed

Hormonal control of pregnancy once fertilized, egg immediately becomes impermeable to other sperm cells – membrane changes consistency – forms zygote cell division occurs as zygote travels down oviduct to uterus – embryo forms – implants in wall of uterus 8 – 10 days after fert. after implantation – fert. egg forms: embryo, umbilical cord (blood vessels connect baby and mother), and placenta (formed from embryonic and uterine tissues – blood systems of baby and mother come in close contact but never actually mix – exchange occurs between circ. systems) fertilized egg produces human chorionic gonadotropin (HCG) which keep corpus luteum in place – continues to produce progesterone to sustain pregnancy – eventually placenta takes over production of estrogen and progesterone to maintain uterine lining

Hormonal control of Parturition (birth) progesterone inhibits contractions of the uterus progesterone levels begin to drop near the end of the pregnancy muscle fibers in uterine wall develop additional receptors for oxytocin (causes contractions) which is released by the pituitary gland uterus becomes more sensitive to oxytocin and contractions get stronger uterine muscle fibers produce prostaglandins in response to oxytocin which further stimulate contractions