Reproductive System

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Reproductive System

• Chapter 46

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Modes of Animal Reproduction

• asexual
• creation of a new individual whose genes all come
  from one parent without fusion of egg sperm
• sexual
• creating of offspring by fusion of haploid
  gametes (egg sperm) to form a diploid zygote

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Mechanisms of Asexual Repro.

• fission
• separation of a parent into 2 or more individuals
  of approx. equal size
• budding
• new individual arises from outgrowths
  of existing individuals
• fragmentation
• breaking of the body into several pieces, some of
  which can develop into new adults by regeneration

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Advantages of Asexual Repro.

• do not need to find a mate
• create numerous offspring in a short period of
  time
• asexual reproduction is most advantageous in
  stable, favorable environments

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Gametogenesis

• females oogenesis
• starts before birth resumes monthly after
  puberty
• involves unequal cytokinesis
• creates one large cell that becomes the egg
  (ovum) three smaller cells called polar bodies
  that degenerate
• males spermatogenesis
• continuous process starting at puberty
• produces mature sperm from all four cells that
  result from meiosis

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Fertilization(union of egg sperm)

• external fertilization
• females release eggs into a wet environment where
  they are fertilized by the male
• wet environment required so gametes do not dry
  out sperm can swim to egg
• internal fertilization
• sperm are deposited in or near the female
  reproductive tract fertilization occurs within
  the tract
• adaptation to terrestrial life

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Reproductive Cycle of Animals

• humans primates menstrual cycle
• endometrial lining of uterus is shed causing
  menstruation
• other mammals estrous cycle
• endometrium is reabsorbed (no extensive bleeding)

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Female Reproductive Anatomy
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Ovaries

• contain follicles each consisting of 1 egg
• starting at puberty continuing until menopause,
  one follicle matures and releases its egg each
  month
• follicle cells produce estrogens (primary female
  sex hormones)
• egg is expelled from follicle during ovulation
• remaining follicle tissue forms a solid mass
  called the corpus luteum that secretes additional
  estrogens progesterone (helps maintain uterine
  lining during pregnancy)
• corpus luteum disintegrates if egg is not
  fertilized

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Oviducts

• aka fallopian tubes
• lined by cilia that move egg to uterus
• site of fertilization

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Uterus

• aka womb
• thick, muscular organ that can expand during
  pregnancy to accommodate the growing fetus
• inner lining endometrium
• richly supplied with blood vessels
• neck of uterus cervix
• opens into vagina

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Vagina

• repository for sperm
• serves as birth canal
• opens to outside at the vulva

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Female Reproductive Cycle

• begins with the release of GnRH from the
  hypothalamus
• GnRH stimulates the pituitary gland to secrete
  small amounts of FSH LH
• FSH LH stimulate follicle growth
• growing follicle cells produce estrogen
• the increasing level of estrogen
• signals the uterine lining (endometrium) to
  thicken
• initially inhibits the release of FSH LH by the
  pituitary

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• as estrogen levels continue to rise, FSH LH are
  released again and their levels rise sharply
• LH induces the final maturation of the follicle
• approx. 1 day after LH surge, the follicle
  releases its egg (ovulation)
• LH stimulates the transformation of the remaining
  follicular tissue to the corpus luteum
• corpus luteum secretes progesterone (P)
  estrogen (E)
• the rise in P E levels
• inhibit release of FSH LH by pituitary
• stimulate development maintenance of
  endometrium

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• if egg is not fertilized, the corpus luteum
  disintegrates which causes the levels of P E to
  decreases sharply
• the decrease in P E levels
• causes disintegration of endometrial lining
  leading to menstruation
• liberates the hypothalamus pituitary gland so
  they can secrete enough FSH to initiate the next
  cycle

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male Reproductive Anatomy
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Testes

• consist of highly coiled tubes called
  seminiferous tubules where sperm form
• other cells (Leydig cells) produce testosterone
  other androgens
• held outside of the abdominal cavity in the
  scrotum which is about 2?C cooler (otherwise
  sperm cannot develop)

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Ducts

• sperm move from seminiferous tubules into the
  coiled tubules of the epididymis
• takes approx. 20 days
• during this time, sperm become motile gain the
  ability to fertilize
• during ejaculation, sperm are propelled from the
  epididymis through the muscular vas deferens
• the vas deferens joins a duct from the seminal
  vesicle forming a short ejaculatory duct
• the ejaculatory duct opens into the urethra

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Glands

• seminal vesicles
• secrete a thick fluid that contributes 60 of
  the total volume of semen contains fructose
  (which provides energy for sperm)
• prostate
• secretes a thin fluid into the urethra that
  contains anticoagulant enzymes citrate (a sperm
  nutrient)
• bulbourethral glands
• secrete a clear mucus that neutralizes any acidic
  urine remaining in the urethra

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Penis

• delivers sperm to vagina during intercourse
• once sperm are in the female reproductive tract
• prostaglandins in semen cause the mucus at the
  opening of the uterus (cervix) to thin the
  uterine muscles to contract (helps move semen
  into the uterus)
• alkalinity of semen neutralizes the acidic
  environment of the vagina (protects sperm)
• semen coagulates initially to make it easier for
  uterine contractions to move it along but, once
  in uterus, anticoagulants liquefy the semen so
  sperm can swim