SEXUAL REPRODUCTION

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SEXUAL REPRODUCTION

• From the time we are teenagers through mid-life
  or longer, we are capable of sexually
  reproducing. Sex plays a major role in much of
  our culture -- we see it in our fashion,
  literature, music, television and movies.
• From a biological standpoint, the goal of sex is
  to merge two sets of genetic information, one
  from the father and one from the mother, to make
  a baby that is genetically different from either
  parent.
• A fertilized egg is shown below

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DEVELOPMENT OF SEX ORGANS

• When we first develop, we have two sets of
  organs one that can develop into the female sex
  organs (Mullerian duct) and one that can develop
  into the male sex organs (Wolffian ducts). Which
  sex organs develop depends on the presence of the
  male hormone testosterone (in humans, the default
  sex is female)
• If the embryo is a male (XY chromosomes), then
  testosterone will stimulate the Wolffian duct to
  develop male sex organs, and the Mullerian duct
  will degrade.

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• If the embryo is female (XX), then no
  testosterone is made. The Wolffian duct will
  degrade, and the Mullerian duct will develop into
  female sex organs. The female clitoris is the
  remnants of the Wolffian duct.
• If the embryo is a male (XY), but there is a
  defect such that no testosterone is made, then
  the Wolffian duct will degrade, and the Mullerian
  duct will develop into non-functional female sex
  organs.
• Sex-organ development is determined by the third
  month of development.

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Plumbing

• The primary goal of sex is to merge the sperm and
  egg (fertilization) to make a baby.
• In many organisms, sex occurs outside of the
  body.
• For example, in most fish or amphibians, females
  lay eggs somewhere (usually on the sea/river
  bed), the male comes along and sprays the eggs
  with sperm and fertilization takes place.

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• In reptiles and mammals (including humans),
  fertilization takes place inside the body of the
  female (internal fertilization).
• This technique increases the chances of
  successful sexual reproduction.
• Because we use internal fertilization, our sexual
  organs are specialized for this purpose. Let's
  take a closer look at the sexual organs in males
  and females.

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ANATOMY OF MALE REPRODUCTIVE SYSTEM
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PHYSIOLOGY (FUNCTION) OF THE MALE REPRODUCTIVE
SYSTEM

• TESTES/TESTIS(SING.) PRODUCE SPERM AND
  TESTOSTERONE (MALE SEX HORMONE)

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• TESTOSTERONE STARTS BEING PRODUCED AT PUBERTY.
  SOME OF THE EFFECTS ON THE INDIVIDUAL ARE
• HAIR GROWTH ON BODY
• VOICE DEEPENS
• BODY GROWS BROADENS/LENGTHENS
• REPRODUCTIVE SYSTEM BEGINS TO WORK
• STIMULATES INTEREST IN OPPOSITE SEX

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• SCROTUM HOLDS TESTES AND REGULATES TEMPERATURE
  OF TESTES
• PENIS PLACES SEMEN IN VAGINA
• SEMEN FLUID CONTAINING SPERM AND SECRETIONS
  FROM
• THE SEMINAL VESICLES
• PROSTATE GLAND
• COWPERS GLAND (MOSTLY LUBRICATION)

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• VAS DEFERENS (SPERM DUCT) - CARRIES SPERM FROM
  THE EPIDIDYMIS TO THE URETHRA
• EPIDIDYMIS STORES SPERM FROM TESTES
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  n3.htm

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ANATOMY OF FEMALE REPRODUCTIVE SYSTEM
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PHYSIOLOGY ( FUNCTION) OF FEMALE REPRODUCTIVE
SYSTEM

• OVARY PRODUCES OVA (EGGS) AND ESTROGEN AND
  PROGESTERONE
• ESTROGEN PROGESTERONE FEMALE SEX HORMONES
  START BEING PRODUCED AT MENARCHE. SOME OF THE
  EFFECTS ON THE INDIVIDUAL ARE
• HAIR GROWTH ON BODY
• BODY SHAPE CHANGES
• VOICES CHANGES
• REPRODUCTIVE SYSTEM MENSTRUAL CYCLE BEGINS
• STIMULATES INTEREST IN OPPOSITE SEX

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• FALLOPIAN TUBES CARRY THE OVA TO THE UTERUS.
  EGGS MUST BE FERTILIZED IN TUBES TO DEVELOP
• UTERUS PLACE FOR FERTILIZED OVA TO DEVELOP INTO
  AN EMBRYO, FETUS, AND BECOME A BABY
• CERVIX CIRCULAR MUSCLE OPENING TO THE UTERUS
  THROUGH WHICH SPERM MUST ENTER DILATES SO THAT
  BABY CAN PASS THROUGH DURING BIRTH
• VAGINA STRUCTURE THAT RECEIVES THE PENIS DURING
  SEXUAL INTERCOURSE. ALSO CALLED THE BIRTH CANAL
  SINCE THE BABY PASSES THROUGH THE VAGINA DURING
  BIRTH
• URETHRA CARRIES URINE OUT OF THE BODY
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  n4.htm

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MENSTRUAL CYCLE

• Cycles Timing is Everything
• Remember that, biologically, the main goal of
  sexual reproduction is to have the sperm combine
  with the egg to make a baby.
• With respect to the man, age is not critical. Men
  are capable of producing sperm that can fertilize
  an egg at any time from the onset of puberty
  until they die (there have been many cases in
  which men in their 70s and 80s have conceived
  children with younger women).
• In contrast, women typically can release
  fertilizable eggs from the time of puberty until
  their late 40s or early 50s. After that time,
  their ovaries stop releasing eggs and they
  undergo various biochemical and physiological
  changes, the sum of which is called menopause.
• Although women are capable of conceiving a child
  from puberty to menopause, the timing of sexual
  intercourse is critical to the success of sexual
  reproduction. Women have an ovulatory cycle, or
  menstrual cycle, made up of complex physiological
  and biochemical changes that are linked to the
  timing of reproduction.
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  n8.htm

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Fertilization

• The long journey to fertilization must be
  completed within 12 to 48 hours, before the sperm
  die. They must first cross the barrier of the
  cervix, which will be thin and watery if the
  woman has just ovulated (for our purposes, we
  will assume that sexual intercourse has occurred
  within a couple of hours after ovulation).
• Once the sperm have traversed the cervical mucus,
  they travel up the moist lining of the uterus
  into the Fallopian tubes (only one of the
  Fallopian tubes contains an egg, so many sperm
  travel in the wrong direction). Fewer than 1,000
  sperm out of the millions in the semen actually
  reach the Fallopian tubes.

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• Many sperm surround the egg in the Fallopian
  tube. The head of each sperm (acrosome) releases
  enzymes that begin to break down the outer,
  jelly-like layer of the egg's membrane, trying to
  penetrate the egg.
• Once a single sperm has penetrated, the cell
  membrane of the egg changes its electrical
  characteristics (depolarizes). This electrical
  signal causes small sacs just beneath the
  membrane (cortical granules) to dump their
  contents into the space surrounding the egg.
• The contents swell, pushing the other sperm far
  away from the egg (cortical reaction). The other
  sperm die within 48 hours. The cortical reaction
  ensures that only one sperm fertilizes the egg.

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• The fertilized egg is now called a zygote. The
  depolarization caused by sperm penetration
  results in one last round of division in the
  egg's nucleus, forming a pronucleus containing
  only one set of genetic information.
• The pronucleus from the egg merges with the
  nucleus from the sperm. Once the two pronuclei
  merge, cell division begins immediately.
• The dividing zygote gets pushed along the
  Fallopian tube. By approximately four days after
  fertilization, the zygote has about 100 cells and
  is called a blastocyst.
• When the blastocyst reaches the uterine lining,
  it floats for about two days, finally implanting
  in the uterine wall by the sixth day after
  fertilization. Once implanted, the blastocyst
  secretes hCG, which rescues the corpus luteum and
  signals that a successful pregnancy has begun.

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• Fertilized egg, showing two pronuclei beginning
  to divide (left) and reaching an eight-celled
  stage within 72 hours (right) (Photo courtesy
  Georgia Reproductive Specialists)
• http//science.howstuffworks.com/human-reproductio
  n10.htm