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Human Biology (BIOL 104)


Human Biology (BIOL 104) Talk Ten: Human Development Chapter 17 – PowerPoint PPT presentation

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Title: Human Biology (BIOL 104)

Human Biology (BIOL 104)
  • Talk Ten
  • Human Development
  • Chapter 17

How do we develop?
  • On ovulation day, egg and sperm fuse to form
  • Zygote divides, implants onto uterus and grows
    into Embryo and hangs out for about 9 months.
  • Embryo decides it is time to breathe air, fetal
    adrenal glands trigger contractions and out comes
  • Baby grows grows grows into child, child
    undergoes puberty and becomes adult.
  • Adult lives, works, reproduces (perhaps), gets
    gray hair and croaks.

  • If viable sperm contact an egg at the time of
    ovulation fertilization will occur.
  • This typically occurs on day 14. Remember Day
    1 is first day of menstruation.
  • The fertilized egg will implant on day 6.
  • The new embryo will begin to produce HCG--Human
    Chorionic Gonadotripin.
  • HCG maintains the corpus luteum and allows the
    production of progesterone and estrogen until the
    placenta takes over this task.

Remember - Fertilization
  • Egg must develop and be released on ovulation
  • Egg must be correctly positioned in the oviduct
    and attract sperm.
  • Vaginal tract must activate sperm.
  • Hormonal levels must be exact.
  • Ensure only one sperm joins with egg.

Remember - Fertilization
  • Sperm must undergo capacitation--process of
    activation by substances in female vaginal tract
  • Sperm motor from vagina up through cervix,
    uterus, to the oviduct.
  • Many sperm attempt fertilization, only one
    succeeds (except for twins).

Development before Implantation
  • Fertilization
  • Cleavage successive rounds of cell division. A
    one cell zygote--2 cell--4 cell--8 cell--.
  • Cleavage occurs in the oviduct.
  • Morula 16 cell stage--enters the uterus
  • .
  • Key cell differentiation step
  • Trophoblast
  • Inner Cell Mass

Development before Implantation
  • Blastocyst
  • Hollow ball of cells.
  • Each cell is called a blastomere.
  • Inner cell mass--become the embryo.
  • Trophoblast--Incredible Altruistic Cells!
  • Escape from the Zona Pellucida
  • Digest through Endometrium
  • Initiate HCG secretion
  • Form the Placenta

  • Truly the most important day of your life!
  • Process of forming 3 germ layers--this process
    requires cell movement.
  • Each germ layer forms specific tissues and organs
  • Ectoderm--(blue)--will form skin and nervous
  • Mesoderm--(red)--will form muscles, kidneys,
    connective tissue, and reproductive organs.
  • Endoderm--(yellow)--will form digestive tract,
    lungs, liver and bladder.

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Figure 12.8b
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Extraembryonic Membranes
  • Establishing extraembryonic membranes is
    critical. These membranes protect the embryo and
    link embryo to mother
  • Amnion--provides fluid environment for fetus.
  • Chorion--becomes the placenta--site of gas and
    nutrient exchange with mother.
  • Allantois--becomes unbilical blood vessels

The Placenta
  • Nutrient and Gas Exchange between fetus and
  • Fetal side--from chorion.
  • Maternal side--from uterine tissue
  • Blood of fetus and mother do not mix.
  • Fetal chorionic villi project into maternal
  • Exchange occurs across membranes.
  • Umbilical cord stretches between placenta and

Pregnancy The Prenatal Period
  • Last 3 months fetal brain cells rapidly divide
  • GI and respiratory systems last to develop
  • Fetal period
  • Week 8 through birth
  • Rapid growth
  • 5th month skeletal muscles active
  • 6th month gains weight

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Overview of Human Development
Mammary glands
  • Are present in both males and females.
  • Are not a component of the reproductive system.
  • Contain epithelial tissue that secrete milk.
  • Milk drains into a series of ducts opening at the

Birth--Hormonal Control
  • Fetus--HypothalamusCortisol Releasing Hormone
  • Fetus--Anterior pituitary --ACTH
  • Fetus--Adrenal Gland produces Cortisol and DHEAS.
  • Cortisol from fetus converted to prostaglandins
    in placenta--these begin contractions.
  • DHEAS from fetus converted to estriol in
    placenta--these promote oxytocin in mother.
  • Oxytocin (from Posterior pituitary) in mother
    begins labor.
  • Cervical stretching--positive feedback.

  • Stage I
  • water breaks
  • cervix dilates

  • Stage II
  • Contractions increase to every 1-2 min, baby
  • Episiotomy (cut vaginal orifice) can prevent
    ripping. Baby emerges, umbilical cord cut.

  • Stage III
  • Placenta is delivered about 15min after birth.
  • Remember our altruistic trophoblast cells!

Twins/Multiple Births
  • Two types
  • Monozygotic
  • From one egg
  • Identical
  • Dizygotic
  • From two eggs
  • Fraternal
  • Not identical

Identical twins
  • One zygote
  • Splits in 2
  • No one knows why!
  • Completely random does NOT run in families
  • Same exact DNA
  • Natures clones

Fraternal Twins
  • 2 separate eggs get fertilized with 2 different
    sperm cells
  • More than one egg got released during ovulation
  • Siblings
  • Can be sisters
  • Brothers
  • Brother and sister
  • Tends to run in families

Conjoined Twins
  • Used to be called Siamese twins
  • First well known case was in Siam
  • Identical twins that never completely separated
    during development
  • Sometimes can be separated, depending on what is

Birth Defects
  • 1 in 16 newborns (6.25 out of 100) born with
    birth defect. Many minor, but some serious or
  • 20 of defects (3.125 out of 1000) are genetic.
  • Causes
  • neural tube closure problems--folic acid.
  • drugs--aspirin, caffeine, alcohol, vitamin A
    creams, cigarette smoke, cocaine, heroine,
  • pathogens--rubella, HIV, STDs, listeria..

Genetic screening
  • Amniocentesis--remove fluid from amniotic cavity.
  • Analyze cells for genetic abnormalities.
    Performed 15th -17th week of pregnancy

Genetic screening
  • Chorionic villi sampling--remove villi by
    suction, test for genetic abnormalities.
  • Performed 5th to 12th week of pregnancy, chance
    of risk for fetus

Genetic screening
  • Screening eggs--obtain eggs and test a polar body
    (eggs clone).
  • If polar body is normal, fertilize and implant
    the egg.

Sexual life cycles
  • Haploid Gametes join to form a zygote
  • Somatic cells divide by Mitosis to produce adult
  • Meiosis produces gametes in sex cells

Genes on sex chromosomes determine Sex and
sex-linked traits
  • Micrograph of the chromosomes of an organism
    paired and numbered.
  • Used to check for chromosomal abnormalities in

Sex Determination
  • All embryos start on a neutral or "indifferent"
    path. The 4 week old embryo is indifferent
  • By 7 weeks, the SRY (sex-related) gene encoded by
    the short arm of the Y chromosome begins to roar!
  • Testis determining factor (TDF) converts
    progesterone to testosterone

Sex Determination
  • Testis-determining factor (TDF) is a general term
    for the gene (or product thereof) that results
    in maleness in humans and some other species.
  • Its expression directly or indirectly causes the
    development of primary sex cords, which will
    later develop to seminiferous tubules.
  • These cords form in the central part of the
    yet-undifferentiated gonad, turning it into
    a testis.
  • The testis then starts secreting testosterone and
    the Mullerian Inhibiting Substance

Sex Determination
  • Indifferent embryos have two sets of ducts
  • Müllerian ducts--will be come the future
    oviducts--thus female.
  • Wolfian ducts--will become the future vas
    deferens--thus male
  • dependent on testosterone for its continued
  • The testes also produce an anti-Müllerian hormone
    that promotes regression of the Müllerian ducts
  • without SRY, the indifferent embryo will
    naturally develop into a female

Sex Determination
Sex Determination
DAX1 (dosage-sensitive sex reversal, adrenal
hypoplasia critical region, on chromosome X, gene
1) is a nuclear receptor protein Encodes a
protein that lacks the normal DNA-binding
domain contained in other nuclear receptors. The
encoded protein acts as a dominant-negative
regulator of transcription of other nuclear
receptors, including steroidogenic factor
1. This protein also functions as an anti-testis
gene by acting antagonistically to SRY.
Sex Determination
  • Two copies of DAX (double X) inactivate SRY, thus
    this individual would be genetically male, but
    look female.

Sex Determination
Figure 2.16 (3)
Sex Determination
Sex Chromosomal Disorders
  • Turner Syndrome XO only one sex chromosome
  • Short, thick neck and stature
  • Do not undergo puberty, or menstruate,
  • no breast development
  • Kleinfelter Syndrome XXY
  • Testis and prostate underdeveloped
  • No facial hair
  • Brest development
  • Long arms and legs big hands and feet
  • Can be mentally handicapped

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Androgen Insensitivity Syndrome
  • Androgen, also called androgenic
    hormones or testoids, is the generic term for any
    natural or synthetic compound, usually a steroid
    hormone, that stimulates or controls the
    development and maintenance of male
    characteristics in vertebrates by binding
    to androgen receptors.
  • This includes the activity of the
    accessory male sex organs and development of
    male secondary sex characteristics.
  • Androgens are also the original anabolic
    steroids and the precursor of all estrogens,
    the female sex hormones.
  • The primary and most well-known androgen
    is testosterone.

Androgen Insensitivity Syndrome
  • The effects that androgens have on the human body
    --- virilization, masculinization, anabolism,
    etc. --- are not brought about by androgens
    themselves, but rather are the result of
    androgens bound to androgen receptors
  • the androgen receptor mediates the effects of
    androgens in the human body.
  • Likewise, under normal circumstances, the
    androgen receptor itself is inactive in the cell
    until androgen binding occurs
  • Figure by Jonathan Marcus, based on an original
    drawing by Dr. Marianne D Sadar (Meehan KL, Sadar
    MD. Front Biosci. 2003 May

Androgen Insensitivity Syndrome
  • Normal function of the androgen receptor.
  • Testosterone (T) enters the cell and, if
    5-alpha-reductase is present, is converted into
    dihydrotestone (DHT).
  • Upon steroid binding, the androgen receptor (AR)
    undergoes a conformational change and releases
    heat shock proteins (hsps).
  • Figure by Jonathan Marcus, based on an original
    drawing by Dr. Marianne D Sadar (Meehan KL, Sadar
    MD. Front Biosci. 2003 May

Androgen Insensitivity Syndrome
  • Normal function of the androgen receptor.
  • Phosphorylation (P) occurs before and / or after
    steroid binding.
  • The AR translocates to the nucleus where
    dimerization, DNA binding,and the recruitment of
    coactivators occur.
  • Target genes are transcribed (mRNA) and
    translated into proteins
  • Figure by Jonathan Marcus, based on an original
    drawing by Dr. Marianne D Sadar (Meehan KL, Sadar
    MD. Front Biosci. 2003 May

Complete Androgen Insensitivity Syndrome
  • It is a genetic disorder that causes XY fetuses
    to become impassive to androgens or male
  • They are born appearing externally female even if
    they are genetically male.
  • Inside there is an undersized vagina with no
    uterus, fallopian tubes, or ovaries.
  • There are testicles in the abdomen or the groin
  • Complete androgen insensitivity syndrome is
    frequently confirmed at puberty when an
    individual is supposed to start menstruating but
    does not.

Partial Androgen Insensitivity Syndrome
  • Characteristically leads in confusing sexual
  • The clitoris is enlarged or, otherwise, the penis
    is undersized and exhibits hypospadias.
  • the opening of the urethra is situated on the
    underside of the penis instead of at its tip
  • Partial androgen insensitivity may possibly be
    fairly frequent, and has been recommended as the
    reason for sterility in a lot of men whose sexual
    organs are of characteristically male form.
  • People with confusing sexual organs have normally
    been subjected to surgery during infancy.
  • Surgery on the sexual parts is necessary only
    when it is essential for the health of the child.

Issues of sex determination
  • So, clearly being Male or Female isnt as cut and
    dry as people have been led to believe!
  • 17 out of 1,000 people are really neither
  • XY, but Female anatomy
  • XX, but Male anatomy
  • Both Female and Male anatomy
  • Other genes, such as testosterone receptor on
    chromosomes other than X and Y chromosomes have a
    role in sexual development

Issues of sex determination
  • So, some people fall between Male and Female
  • Due to chromosomal variation
  • Variations in SYR gene
  • Testosterone receptor gene
  • All of the different variations are known as
  • These people are altered surgically to make them
    conform to one sex or the other
  • Should there be five genders instead of two?

The end!
  • Any questions?