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Human Biology (BIOL 104)

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

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Title: Human Biology (BIOL 104)


1
Human Biology (BIOL 104)
  • Talk Ten
  • Human Development
  • Chapter 17

2
How do we develop?
  • On ovulation day, egg and sperm fuse to form
    zygote.
  • 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.
  • Baby grows grows grows into child, child
    undergoes puberty and becomes adult.
  • Adult lives, works, reproduces (perhaps), gets
    gray hair and croaks.

3
REMEMBER!!!!!!!!!
  • 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.

4
Remember - Fertilization
  • Egg must develop and be released on ovulation
    day.
  • 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.

5
Remember - Fertilization
  • Sperm must undergo capacitation--process of
    activation by substances in female vaginal tract
    fluids.
  • Sperm motor from vagina up through cervix,
    uterus, to the oviduct.
  • Many sperm attempt fertilization, only one
    succeeds (except for twins).

6
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

7
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

8
Gastrulation
  • 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
    system.
  • Mesoderm--(red)--will form muscles, kidneys,
    connective tissue, and reproductive organs.
  • Endoderm--(yellow)--will form digestive tract,
    lungs, liver and bladder.

9
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10
Figure 12.8b
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13
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

14
The Placenta
  • Nutrient and Gas Exchange between fetus and
    mother.
  • Fetal side--from chorion.
  • Maternal side--from uterine tissue
  • Blood of fetus and mother do not mix.
  • Fetal chorionic villi project into maternal
    blood.
  • Exchange occurs across membranes.
  • Umbilical cord stretches between placenta and
    fetus.

15
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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19
Overview of Human Development
20
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
    nipple.

21
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.

22
Birth--Stages
  • Stage I
  • water breaks
  • cervix dilates

23
Birth--Stages
  • Stage II
  • Contractions increase to every 1-2 min, baby
    emerges.
  • Episiotomy (cut vaginal orifice) can prevent
    ripping. Baby emerges, umbilical cord cut.

24
Birth--Stages
  • Stage III
  • Placenta is delivered about 15min after birth.
  • Remember our altruistic trophoblast cells!

25
Twins/Multiple Births
  • Two types
  • Monozygotic
  • From one egg
  • Identical
  • Dizygotic
  • From two eggs
  • Fraternal
  • Not identical

26
Identical twins
  • One zygote
  • Splits in 2
  • No one knows why!
  • Completely random does NOT run in families
  • Same exact DNA
  • Natures clones

27
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

28
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
    shared.

29
Birth Defects
  • 1 in 16 newborns (6.25 out of 100) born with
    birth defect. Many minor, but some serious or
    fatal.
  • 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,
    thalidomide,.
  • pathogens--rubella, HIV, STDs, listeria..

30
Genetic screening
  • Amniocentesis--remove fluid from amniotic cavity.
  • Analyze cells for genetic abnormalities.
    Performed 15th -17th week of pregnancy

31
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

32
Genetic screening
  • Screening eggs--obtain eggs and test a polar body
    (eggs clone).
  • If polar body is normal, fertilize and implant
    the egg.

33
Sexual life cycles
  • Haploid Gametes join to form a zygote
  • Somatic cells divide by Mitosis to produce adult
    organism
  • Meiosis produces gametes in sex cells

34
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
    individuals.

35
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

36
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

37
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
    development
  • 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

38
Sex Determination
39
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.
40
Sex Determination
  • Two copies of DAX (double X) inactivate SRY, thus
    this individual would be genetically male, but
    look female.

41
Sex Determination
42
Figure 2.16 (3)
Sex Determination
43
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

44
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45
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.

46
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

47
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

48
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

49
Complete Androgen Insensitivity Syndrome
  • It is a genetic disorder that causes XY fetuses
    to become impassive to androgens or male
    hormones.
  • 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
    area.
  • Complete androgen insensitivity syndrome is
    frequently confirmed at puberty when an
    individual is supposed to start menstruating but
    does not.

50
Partial Androgen Insensitivity Syndrome
  • Characteristically leads in confusing sexual
    organ.
  • 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.

51
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

52
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
    intersex
  • These people are altered surgically to make them
    conform to one sex or the other
  • Should there be five genders instead of two?

53
The end!
  • Any questions?
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