Transcript Human Development

Human Biology (BIOL 104)
Talk Ten:
Human Development
Chapter 17
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.
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.
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.
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).
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
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.
Figure 12.8b
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 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.
Pregnancy:
• Fetal period
– Week 8 through
birth
– Rapid growth
– 5th month – skeletal
muscles active
– 6th month – gains
weight
The Prenatal Period
– Last 3 months – fetal
brain cells rapidly
divide
– GI and respiratory
systems last to develop
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
nipple.
Birth--Hormonal Control
• Fetus--Hypothalamus—Cortisol 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.
Birth--Stages
• Stage I:
• water breaks
• cervix dilates
• Stage II:
Birth--Stages
• Contractions
increase to every 12 min, baby emerges.
• Episiotomy (cut
vaginal orifice) can
prevent ripping.
Baby emerges,
umbilical cord cut.
Birth--Stages
• 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
• Nature’s 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 shared.
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..
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 organism
• 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
individuals.
Sex Determination
• All embryos start on a neutral or
"indifferent" path. The 4 week
old embryo is indifferent
• By 7 weeks, the SRY (sexrelated) 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 development
• The testes also produce an antiMüllerian 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 dominantnegative 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
Sex
Determination
Figure 2.16 (3)
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
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 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.
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.
Issues of sex determination
• So, clearly being Male or Female isn’t 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 intersex
– 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?