From Cell to
Human
….
• http://www.youtube.com/watch?v=Q6uc
KWIIFmg&feature=related
Cell
Cells
• Cells are the smallest living unit
of life
• Cells have a nucleus, cytoplasm,
and plasma membrane
• Cells make proteins
• Cells have DNA in their nucleus
• Cells divide to make new cells
Genes and Proteins
• Proteins do the work of the cell:
growth, maintenance, response
to the environment,
reproduction, etc.
• Proteins are chains of amino
acids.
Genes and Proteins
• The sequence of amino acids in
each protein is coded in the
DNA as a specific sequence of
A, C, G and T bases: a gene.
• Each gene codes for a different
protein.
Genes and Proteins
• All cells within an organism have
the same genes.
• What makes cells different
from each other is that
different genes are turned on
and turned off in different
cells.
Cell Division
• The DNA must be copied and
then divided exactly so that
each cell gets an identical copy.
Cell Division
• Two types of cell division
–Mitosis
• For growth and repair
–Meiosis
• For formation of
gametes sperm and egg
Cell Division
All complex
organisms
originated from
a single
fertilized egg.
Cell Division
Every cell in
your body
started here,
through cell
division the
numbers are
increased
Cell Division
Cell then
specialise and
change into
their various
roles
Mitosis
Mitosis
• Mitosis is the process by which
new body cell are produced for:
–Growth
–Replacing damaged or old cells.
This is a complex process
requiring different stages
Parent cell
Chromosomes
are copied &
double in number
Chromosomes
now split
2 daughter cells
identical to
original
Mitosis
• All daughter cells contain the
same genetic information from
the original parent cell from
which it was copied.
• Every different type cell in
your body contains the same
genes, but only some act to
make the cells specialize – e.g.
into nerve or muscle tissue.
Mitosis – bone cell slides
2
1
Parent cell
3
Chromosomes copied
4
Copies separating
5
2 daughter cells
Rat – epithelial cells
Animated Mitosis Cycle
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase &
Cytokinesis
http://www.cellsalive.com/mitosis.htm
Interphase
occurs before mitosis begins
• Chromosomes are copied
(# doubles)
• Centrioles replicate
Nucleus
CELL MEMBRANE
Cytoplasm
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Early Prophase
• Chromosomes appear as threadlike
coils (chromatin) during interphase
• At the start of prophase, (early
prophase), chromatin condenses
and coils into chromosomes.
Nucleus
CELL
MEMBRANE
Cytoplasm
Prophase
1st and Longest step in Mitosis
• Mitosis begins (cell begins to divide)
• Centrioles (or poles) begin to move to
opposite ends of the cell.
• Asters are seen
Sister chromatids
Centrioles
Spindle fibers
Prophase
• Chromosomes are condensed into sister
Chromotids held together by a button-like
body called a centromere
• Nucleoli dissappear
• Spindle fibers form between the poles.
Sister chromatids
Centrioles
Spindle fibers
Prophase
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
2nd step in Mitosis
• Chromatids (or pairs of chromosomes)
attach to the spindle fibers.
• Chromosomes cluster at the middle of the
cells, with their centromeres aligned at the
exact center, called the metaphase plate
Centrioles
Spindle fibers
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
3rd and shortest step in Mitosis
• Chromatids (or pairs of chromosomes)
separate and begin to move to opposite ends
of the cell.
• Cells elongate. Chromosomes look V-shaped
Centrioles
Spindle fibers
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase
4th step in Mitosis
• Two new nuclei form, nuclear envelope
forms from rough ER
• Chromosomes uncoil and appear as
chromatin (threads rather than rods).
• Spindle dissappears. Mitosis ends.
Nuclei
Chromatin
Nuclei
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesis
• Cytokinesis begins during late
anaphase and continues through and
beyond telephase
• A contractile ring of microfilaments
forms at the cleavage furrow and
squeezes cells apart
Cytokinesis
• Cell membrane moves inward to
create two daughter cells – each
with its own nucleus with identical
chromosomes.
Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Cell Cycle
35
Mitosis
• Cells divide by mitosis to make
identical daughter cells
Cell Division
• Mitosis – Division of the nucleus
• Cytokinesis – Division of the
cytoplasm
Mitosis Animation
http://www.youtube.com/watch?v=NR0mdDJM
HIQ&feature=fvwrel
Summary of Mitosis
• Prophase:
• Chromosomes condense
• Nuclear envelope
disappears
• Centrioles move to
opposite sides of the
cell
• Spindle forms and
attaches to
centromeres on the
chromosomes
Summary of Mitosis
• Metaphase
• Chromosomes lined up
on equator of spindle
• Centrioles at opposite
ends of cell
Summary of Mitosis
• Anaphase
• Centromeres divide:
each 2-chromatid
chromosome becomes
two 1-chromatid
chromosomes
• Chromosomes pulled to
opposite poles by the
spindle
Summary of Mitosis
• Telophase
• Chromosomes decondense into
chromatin
• Nuclear envelope
reappears
• Cytokinesis: the
cytoplasm is divided
into 2 cells
Quiz
Next Time
Shiloh Pepin
From Cell to
Human
….
Part 2
Meiosis Video
• http://www.youtube.com/watch?v=mKW
xeMMFTEU
Meiosis
• There is a special type of cell
division to make a sperm or egg
• To make gametes, cells must
undergo meiosis
Why do we need meiosis?
• Meiosis is necessary to halve the
number of chromosomes going
into the sex cells
• Why halve the chromosomes in
gametes?
Why do we need meiosis?
At fertilization the male and
female sex cells will provide ½ of
the chromosomes each – so the
offspring has genes from both
parents
Meiosis
• The form of cell division by
which gametes, with half the
number of chromosomes, are
produced.
• Diploid (2n)  haploid (n)
• Meiosis is sexual reproduction.
• Two divisions (meiosis I and
meiosis II).
Meiosis
• Sex cells divide to produce
gametes (sperm or egg).
• Gametes have half the number
of chromosomes.
Meiosis
• Meiosis only in gonads (testes
or ovaries).
Male: spermatogenesis
Female: oogenesis
Meiosis
• Meiosis is similar to mitosis
with some chromosomal
differences.
Meiosis
Parent cell –
chromosome
pair
Chromosomes
copied
1st division pairs split
2nd division –
produces 4 gametes
Meiosis
Gamete cells
have ½ the
original
number of
chromosomes
Spermatogenesis
human
sex cell
n=23
sperm
n=23
n=23
2n=46
haploid (n)
n=23
n=23
diploid (2n)
n=23
meiosis I
meiosis II
Meiosis – mouse testes
Parent cell
1st division
2nd division
4 gametes
Interphase I
• Similar to mitosis interphase.
• Chromosomes replicate (S
phase)
• Each duplicated chromosome
consist of two identical sister
chromatids attached at their
centromeres.
• Centriole pairs also replicate.
Interphase I
• Nucleus and nucleolus visible.
chromatin
nuclear
membrane
cell membrane
nucleolus
Meiosis I (four phases)
• Cell division that reduces the
chromosome number by onehalf. - Four phases:
a. prophase I
b.metaphase I
c. anaphase I
d. telophase I
Prophase I
• Longest and most complex
phase (90%).
• Chromosomes condense.
• Synapsis occurs: homologous
chromosomes come together to
form a tetrad.
• Tetrad is two chromosomes or
four chromatids (sister and
nonsister chromatids).
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
Homologous Chromosomes
• Pair of chromosomes (maternal
and paternal) that are similar
in shape and size.
• Homologous pairs carry genes
controlling the same inherited
traits.
• Each locus (position of a gene)
is in the same position on
homologues.
Homologous Chromosomes
• Humans have 23 pairs of
homologous chromosomes.
a. 22 pairs of autosomes
b.1 pair of sex chromosomes
Homologous Chromosomes
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal
Crossing Over
• Crossing over (variation) may
occur between nonsister
chromatids at the chiasmata.
• Crossing over: segments of
nonsister chromatids break and
reattach to the other
chromatid.
• Chiasmata (chiasma) are the
sites of crossing over.
Crossing Over - variation
nonsister chromatids
Tetrad
chiasmata: site
of crossing over
variation
Sex Chromosomes
XX chromosome - female
XY chromosome - male
Prophase I
spindle fiber
aster
fibers
centrioles
Metaphase I
• Shortest phase
• Tetrads align on the metaphase
plate.
Metaphase I
• INDEPENDENT ASSORTMENT
OCCURS:
1. Orientation of homologous
pair to poles is random.
2. Variation
3. Formula: 2n
Example: 2n = 4, then n = 2
thus 22 = 4 combinations
Metaphase I
OR
metaphase plate
metaphase plate
Question:
• In terms of Independent
Assortment -how many
different combinations of
sperm could a human male
produce?
Answer
• Formula: 2n
• Human chromosomes:2n = 46
n = 23
• 223 = ~8 million combinations
Anaphase I
• Homologous chromosomes
separate and move towards the
poles.
• Sister chromatids remain
attached at their centromeres.
Anaphase I
Telophase I
• Each pole now has haploid set
of chromosomes.
• Cytokinesis occurs and two
haploid daughter cells are
formed.
Telophase I
Meiosis II
• No interphase II
(or very short - no more DNA
replication)
• Remember: Meiosis II is
similar to mitosis
Prophase II
• same as prophase in mitosis
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
Telophase II
•
•
•
•
Same as telophase in mitosis.
Nuclei form.
Cytokinesis occurs.
Remember: four haploid
daughter cells produced.
gametes = sperm or egg
Telophase II
Meiosis
sex cell
n=2
sperm
n=2
n=2
2n=4
haploid (n)
n=2
n=2
diploid (2n)
n=2
meiosis I
meiosis II
Variation
• Important to population as the
raw material for natural
selection.
• Question:
What are the three sexual
sources of genetic variation?
Answer:
1. crossing over (prophase I)
2. independent assortment
(metaphase I)
3. random fertilization
Remember: variation is good!
Question:
• A cell containing 20
chromosomes (diploid) at the
beginning of meiosis would, at
its completion, produce cells
containing how many
chromosomes?
Answer:
• 10 chromosomes (haploid)
Karyotype
• A method of organizing the chromosomes of a
cell in relation to number, size, and type.
Actual Human Karyotype Picture
Male or
female?
Male!
Fertilization
• The fusion of a sperm and egg to
form a zygote.
• A zygote is a fertilized egg
n=23
egg
sperm
n=23
2n=46
zygote
Question:
• A cell containing 40 chromatids
at the beginning of meiosis
would, at its completion, produce
cells containing how many
chromosomes?
Answer:
• 10 chromosomes
Sometimes there are
mistakes!
Meiosis – division error
Chromosome pair
Meiosis error - fertilization
Should the
gamete with the
chromosome pair
be fertilized
then the
offspring will
not be ‘normal’.
Meiosis error - fertilization
In humans this
often occurs
with the 21st
pair – producing
a child with
Downs Syndrome
21 trisomy – Downs Syndrome
Can you see
the extra 21st
chromosome?
Is this
person male
or female?
Quiz
Next Time
From Cell to
Human
….
Information
about
Chromosomal
Disorders
Mistakes in Meiosis
• About 1 in 150
babies is born
with a
chromosomal
abnormality
Mistakes in Meiosis
• When a gamete (egg or sperm cell)
with the wrong number of
chromosomes joins with a normal
gamete (egg or sperm cell), the
resulting embryo has a chromosomal
abnormality.
Mistakes in Meiosis
• Chromosomal abnormalities usually
result from an error that occurred
when an egg or sperm cell was
developing
• An egg or sperm cell may divide
incorrectly, resulting in an egg or
sperm cell with too many or too few
chromosomes.
Mistakes in Meiosis
• In most cases, an embryo with the
wrong number of chromosomes does
not survive. The pregnant woman has
a miscarriage. This often happens
very early in pregnancy, before a
woman may realize she's pregnant. Up
to 75 percent of first trimester
miscarriages are caused by
chromosomal abnormalities in the
embryo
Mistakes in Meiosis
• A baby can be born with too many
or too few chromosomes
• These errors in the number or
structure of chromosomes can
cause a wide variety of birth
defects ranging from mild to
severe.
Mistakes in Meiosis
• A common type of chromosomal
abnormality is called a trisomy. This
means that an individual has three
copies, instead of two, of a specific
chromosome.
Trisomy 21 – Down Syndrome
• Individuals with Down syndrome have
three copies of chromosome 21.
• Children with Down syndrome have
varying degrees of mental
retardation, characteristic facial
features and, often, heart defects
and other problems.
• The risk of Down syndrome and
other trisomies increases with
maternal age.
Trisomy 21 – Down Syndrome
• Down syndrome is one of the most
common chromosomal abnormalities,
• The risk of having a live-born baby
with Down syndrome is about:
• 1 in 1,250 for a woman at age 25
• 1 in 1,000 at age 30
• 1 in 400 at age 35
• 1 in 100 at age 40
Trisomy 13 & Trisomy 18
• Extra copy of chromosome 13 or 18.
• More severe than Down syndrome,
less common.
• About 1 in 10,000 babies is born
with trisomy 13 (Patau syndrome),
• About 1 in 6,000 with trisomy 18
(Edwards syndrome)
• Severe mental retardation & many
physical birth defects. Most die
before their first birthday.
X and Y chromosomal
abnormalities
• About 1 in 500 babies has missing
or extra sex chromosomes
• Sex chromosome abnormalities may
cause infertility, growth
abnormalities, and in some cases,
behavioral and learning problems.
However, most affected individuals
live fairly normal lives.
Turner Syndrome
Affects about 1 in 2,500 girls
Missing all or part of one X chromosome.
Usually infertile
Does not undergo normal pubertal changes
unless treated with sex hormones.
• Affected girls are short, though
treatment with growth hormones can help
increase height.
• Other health problems may include heart
or kidney defects.
• Normal intelligence
•
•
•
•
Triple X
• About 1 in 1,000 females have an
extra X chromosome
• Affected girls tend to be tall.
• No physical birth defects, undergo
normal puberty, fertile, normal
intelligence
Klinefelter Syndrome XXY
• Affects about 1 in 500 to 1,000
boys
• Normal intelligence
• As adults, they produce lower-thannormal amounts of the male
hormone testosterone (and often
are treated with this hormone)
• Infertile
XYY Syndrome
• Affects 1 in 1,000 males
• Affected males are sometimes
taller than average
• Normal sexual development
• Fertile
• Normal intelligence
From Cell to
Human
….
Part 3
From Egg to Embryo
• Pregnancy – events that occur
from fertilization until the
infant is born
• Conceptus – the developing
offspring
• Gestation period – from the last
menstrual period until birth
(280 days)
From Egg to Embryo
• Preembryo – conceptus from
fertilization until it is two
weeks old
• Embryo – conceptus during the
third through the eighth week
• Fetus – conceptus from the
ninth week through birth
• At birth it is called an Infant
Relative Size of Human Conceptus
Figure 28.1
Accomplishing Fertilization
• The oocyte is viable for 12 to
24 hours
• Sperm is viable 24 to 72 hours
• For fertilization to occur, coitus
must occur no more than:
–Three days before ovulation
–24 hours after ovulation
Accomplishing Fertilization
• Fertilization – when a sperm
fuses with an egg to form a
zygote
Sperm Transport and Capacitation
• Fates of ejaculated sperm
–Milllions leak out of the vagina
immediately after deposition
–Millions are destroyed by the
acidic vaginal environment
–Millions fail to make it through
the cervix
Sperm Transport and Capacitation
• Those sperm that do reach the
cervix
–Dispersed in the uterus cavity by
uterine contractions
– thousands are destroyed by
phagocytic leukocytes
–Only a few thousand (sometimes
less than 200) reach the uterine
tubes
Sperm Transport and Capacitation
• Sperm must undergo capacitation
before they can penetrate the
oocyte
• Gradually over 6 to 8 hours
membrane proteins are removed
and cholesterol is depleted
• Enables membranes to become
fragile so the hydrolytic enzymes in
their acrosomes can be released
Acrosomal Reaction and Sperm
Penetration
• An ovulated oocyte is encapsulated
by:
–The corona radiata and zona
pellucida
–Thick layer of extracellular
matrix
Acrosomal Reaction and Sperm
Penetration
• Sperm binds to the zona pellucida
and undergoes the acrosomal
reaction
–Enzymes are released near the
oocyte
–Hundreds of acrosomes release
their enzymes to digest the zona
pellucida
–The first sperm there will not be
able to penetrate
Acrosomal Reaction and Sperm
Penetration
• Once a sperm makes contact with
the oocyte’s membrane its nucleus
is pulled into the oocyte cytoplasm
Acrosomal Reaction & Sperm Penetration
Figure 28.2a
Blocks to Polyspermy
• Only one sperm is allowed to
penetrate the oocyte
• Two mechanisms ensure monospermy
–Fast block to polyspermy
–Slow block to polyspermy
• If polyspermy does occur, embryos
are nonviable and die
Blocks to Polyspermy
–Fast block to polyspermy –
membrane depolarization prevents
sperm from fusing with the oocyte
membrane
–Slow block to polyspermy – zonal
inhibiting proteins (ZIPs):
• Destroy sperm receptors
• Cause sperm already bound to
receptors to detach
Completion of Meiosis II and
Fertilization
• Upon entry of sperm, the secondary
oocyte:
–Completes meiosis II
–Casts out the second polar body
Completion of Meiosis II and
Fertilization
• The ovum nucleus swells, and the
two nuclei approach each other
• When fully swollen, the two nuclei
are called pronuclei
• Fertilization – when the pronuclei
come together
Events
Immediately
Following
Sperm
Penetration
Figure 28.3
Preembryonic Development
• The first cleavage produces two
daughter cells called blastomeres
• Morula – the 16 or more cell stage
(72 hours old)
• By the fourth or fifth day the
preembryo consists of 100 or so
cells (blastocyst)
Preembryonic Development
• Blastocyst – a fluid-filled hollow
sphere composed of:
–A single layer of trophoblasts
(large flat cells)
–An inner cell mass (smaller round
cells)
Preembryonic Development
• Trophoblasts take part in placenta
formation
• The inner cell mass becomes the
embryonic disc
Cleavage: From Zygote to Blastocyst
Degenerating
zona pellucida
Inner cell mass
Blastocyst cavity
Blastocyst
cavity
(a) Zygote
(fertilized egg)
Fertilization
(sperm meets
egg)
(b) 4-cell stage
2 days
(a)
(c) Morula
3 days
(d) Early blastocyst
4 days
Trophoblast
(e) Implanting
blastocyst
6 days
(b)
(c)
Ovary
Uterine tube
(d)
Oocyte
(egg)
Ovulation
(e)
Uterus
Endometrium
Cavity of
uterus
Figure 28.4
Implantation
• Begins six to seven days after
ovulation when the trophoblasts
adhere to a properly prepared
endometrium
Implantation
• The trophoblasts then proliferate
and form two distinct layers
–Cytotrophoblast – cells of the
inner layer that retain their cell
boundaries
–Syncytiotrophoblast – cells in the
outer layer that lose their plasma
membranes and invade the
endometrium
Implantation
• The implanted blastocyst is covered
over by endometrial cells
• Implantation is completed by the
fourteenth day after ovulation
Implantation of the Blastocyst
Figure 28.5a
Implantation of the Blastocyst
Figure 28.5b
Placentation
• Formation of the placenta from:
–Embryonic trophoblastic
tissues
–Maternal endometrial tissues
Placentation
Figure 28.7ac
Placentation
Figure 28.7d
Placentation
Figure 28.7f
Germ Layers
• The blastocyst develops into a
gastrula with three primary germ
layers: ectoderm, endoderm, and
mesoderm
• Before becoming three-layered, the
inner cell mass subdivides into the
upper epiblast and lower hypoblast
• These layers form two of the four
embryonic membranes
Embryonic Membranes
• Amnion – epiblast cells form a
transparent membrane filled with
amniotic fluid
–Provides a buoyant environment
that protects the embryo
–Helps maintain a constant
homeostatic temperature
–Amniotic fluid comes from
maternal blood, and later, fetal
urine
Embryonic Membranes
• Yolk sac – hypoblast cells that form
a sac on the ventral surface of the
embryo
–Forms part of the digestive tube
–Produces earliest blood cells and
vessels
–Is the source of primordial germ
cells
Embryonic Membranes
• Allantois – a small outpocketing at
the caudal end of the yolk sac
–Structural base for the umbilical
cord
–Becomes part of the urinary
bladder
• Chorion – helps form the placenta
–Encloses the embryonic body and
all other membranes
Gastrulation
• During the 3rd week, the twolayered embryonic disc becomes a
three-layered embryo
• The primary germ layers are
ectoderm, mesoderm, and endoderm
• Primitive streak – raised dorsal
groove that establishes the
longitudinal axis of the embryo
Primary Germ Layers
• Serve as primitive tissues from
which all body organs will derive
Quiz
Next time
Study Guide
From Cell to
Human
….
Part 4
Remember
• During the 3rd week, the twolayered embryonic disc becomes a
three-layered embryo
• The primary germ layers are
ectoderm, mesoderm, and endoderm
• Primitive streak – raised dorsal
groove that establishes the
longitudinal axis of the embryo
Primary Germ Layers
• Serve as primitive tissues from
which all body organs will derive
Primary Germ Layers
• Ectoderm – forms structures of the
nervous system and skin epidermis
• Endoderm – forms epithelial linings
of the digestive, respiratory, and
urogenital systems
• Mesoderm – forms all other tissues
• Endoderm and ectoderm are
securely joined and are considered
epithelia
Primary Germ Layers
Figure 28.8a-
Primary Germ Layers
Figure 28.8eh
Organogenesis
• Gastrulation sets the stage for
organogenesis, the formation of
body organs
• By the 8th week all organ systems
are recognizable
Specialization of Ectoderm
• Neurulation – the first event of
organogenesis gives rise to the
brain and spinal cord
• Ectoderm over the notochord
thickens, forming the neural plate
• The neural plate folds inward as a
neural groove with prominent neural
folds
Specialization of Ectoderm
• By the 22nd day, neural folds fuse
into a neural tube, which pinches
off into the body
• The anterior end becomes the
brain; the rest becomes the spinal
cord
• By the end of the second month
brain waves can be recorded
Specialization of Ectoderm:
Neuralization
Figure 28.9a,
b
Specialization of Ectoderm:
Neuralization
Figure 28.9c,d
Specialization of Endoderm
• Embryonic folding begins with
lateral folds
• Next, head and tail folds appear
• An endoderm tube forms the
epithelial lining of the GI tract
Specialization of Endoderm
• Organs of the GI tract become
apparent, and oral and anal openings
perforate
• Endoderm forms epithelium linings
of the hollow organs of the
digestive and respiratory tracts
Folding of the Embryonic Body
Figure 28.10ad
Endodermal Differentiation
Figure 28.11
Specialization of the Mesoderm
• First evidence is the appearance of
the notochord
• Three mesoderm aggregates appear
lateral to the notochord
–Somites, intermediate mesoderm,
and double sheets of lateral
mesoderm
Specialization of the Mesoderm
• The 40 pairs of somites have three
functional parts:
– Sclerotome – produce the vertebrae
and ribs
– Dermatome – help form the dermis of
the skin on the dorsal part of the
body
– Myotome – form the skeletal muscles
of the neck, trunk, and limbs
Specialization of the Mesoderm
• Intermediate mesoderm forms the
gonads and the kidneys
• Lateral mesoderm consists of
somatic and splanchnic mesoderm
Specialization of the Mesoderm
• Somatic mesoderm forms the:
– Dermis of the skin in the ventral region
– Parietal serosa of the ventral body
cavity
– Bones, ligaments, and dermis of the
limbs
• Splanchnic mesoderm forms:
– The heart and blood vessels
– Most connective tissues of the body
Specialization of the Mesoderm
Figure 28.12
Development of Fetal Circulation
• By the end of the 3rd week:
–The embryo has a system of
paired vessels
–The vessels forming the heart
have fused
Development of Fetal Circulation
• Unique vascular modifications seen in
prenatal development include umbilical
arteries and veins, and three vascular
shunts (occluded at birth)
– Ductus venosus – venous shunt that
bypasses the liver
– Foramen ovale – opening in the
interatrial septa to bypass pulmonary
circulation
– Ductus arteriosus – transfers blood
from the right ventricle to the aorta
• The umbilical vein delivers nutrient
and oxygen rich blood to the
embryo
• Umbilical arteries return oxygen
poor and waste laden blood to the
placenta
Circulation
in Fetus
and
Newborn
Figure 28.13
From Cell to
Human
….
Part 5 (on part
4 note sheet)
8 weeks
• End of embryonic period – now a
fetus
• Head as large as body – brain waves
• Liver large and begins to form
blood cells
• Limbs present, digits were webbed,
starting now to be free
• Ossification of bones begin
8 weeks
• Cardiovascular system fully
functional (Heart has been pumping
since week 4)
• All body systems present
• Weight 2 grams
9-12 weeks
Body lengthening
Brain continues to enlarge
Retina of eye present
Facial features present
Blood cell formation begins in bone
marrow
• Sex able to be detected from genitals
•
•
•
•
•
13-16 weeks
• Blinking of eyes and sucking motions
of lips occur
• Kidneys are formed
• Most bones distinct, joints are
apparent
17-20 weeks
• Vernix caseosa (from oil glands)
covers body
• Lanugo (fine silky hair) covers skin
• Fetal position assumed
• Mother feels muscular activity of
fetus
21-30 weeks
• Weight increases
• May survive if born at 27-28 weeks,
but temperature regulation and
lungs not all way formed
• Eyes are open
• Skin is wrinkled and red
• Fingernails and toenails present
30-40 weeks
• Skin whitish pink
• Hypodermis formed
• Weight 6-10 pounds
Birth!
Is it a boy or girl?
• Remember…
• Females have two X chromosomes;
males have one X and one Y
• Hence, all eggs have an X
chromosome; half the sperm have
an X, and the other half a Y
• A single gene on the Y chromosome,
the SRY gene, initiates testes
development and determines
maleness
Developmental Aspects
• 5th week – gonadal ridges form and
paramesonephric (Müllerian) ducts
form in females, mesonephric
(Wolffian) ducts develop in males
• Shortly later, primordial germ cells
develop and seed the developing
gonads destined to become
spermatogonia or oogonia
Developmental Aspects
• Male structures begin development
in the 7th week; female in the 8th
week
• External genitalia, like gonads, arise
from the same structures in both
sexes
Development of Internal
Reproductive Organs
Figure 27.24
Male
Female
Development of Internal
Reproductive Organs
Figure 27.24
Development of Internal
Reproductive Organs
Figure 27.24
Male
Female
Development of External Genitalia
male
• In the presence of
testosterone
• Genital tubercle
enlarges forming
the penis
• Urethral groove
elongates and
closes completely
female
• In the absence of
testosterone
• Genital tubercle
gives rise to the
clitoris
• The urethral
groove remains
open
Development of External Genitalia
male
• Urethral folds give
rise to the penile
urethra
• Labioscrotal
swellings develop
into the scrotum
female
• The urethral
folds become
labia minora
• The labioscrotal
swellings become
labia majora
Development Aspects: Descent of
the Gonads
• About 2 months before birth and
stimulated by testosterone, the
testes leave the pelvic cavity and
enter the scrotum
• Ovaries also descend, but are
stopped by the broad ligament at
the pelvic brim
Homeostatic imbalance
• Many substance cross placental
barriers and enter fetal blood –
dangerous!
• Alcohol, nicotine, many drugs,
infections (like measles) all cross
barriers
Homeostatic imbalance
• When mother drinks, her fetus
becomes inebriated
–may result in fetal alcohol
syndrome typified by a small
head, mental retardation, and
abnormal growth
Homeostatic imbalance
• Nicotine hinders oxygen delivery to
the fetus
–Impairing normal growth and
development
Homeostatic imbalance
• The sedative thalidomide
sometimes results in deformed
infants with short flipperlike legs
or arms
Quiz
Next time
Test
On Thursday
Complete Study Guide for next time
• Rest of these slides not in this unit.
Effects of Pregnancy: Anatomical
Changes
• Chadwick’s sign – the vagina develops a
purplish hue
• Breasts enlarge and their areolae
darken
• The uterus expands, occupying most of
the abdominal cavity
• Lordosis is common due to the change of
the body’s center of gravity
• Relaxin causes pelvic ligaments and the
pubic symphysis to relax
• Typical weight gain is about 29 pounds
Relative Uterus Size During
Pregnancy
Figure 28.15
Effects of Pregnancy: Metabolic
Changes
• The placenta secretes human placental
lactogen (hPL), also called human chorionic
somatomammotropin (hCS), which
stimulates the maturation of the breasts
• hPL promotes growth of the fetus and
exerts a maternal glucose-sparing effect
• Human chorionic thyrotropin (hCT)
increases maternal metabolism
• Parathyroid hormone levels are high,
ensuring a positive calcium balance
Effects of Pregnancy:
Physiological Changes
• GI tract – morning sickness occurs due to
elevated levels of estrogen and
progesterone
• Urinary system – urine production
increases to handle the additional fetal
wastes
• Respiratory system – edematous and nasal
congestion may occur
– Dyspnea (difficult breathing) may develop late
in pregnancy
Effects of Pregnancy:
Physiological Changes
• Cardiovascular system – blood volume
increases
25-40%
– Venous pressure from lower limbs is
impaired, resulting in varicose veins
Parturition: Initiation of Labor
• Estrogen reaches a peak during the last weeks of
pregnancy causing myometrial weakness and
irritability
• Weak Braxton Hicks contractions may take place
• As birth nears, oxytocin and prostaglandins cause
uterine contractions
• Emotional and physical stress:
– Activates the hypothalamus
– Sets up a positive feedback mechanism, releasing
more oxytocin
Parturition: Initiation of Labor
Figure 28.16
Stages of Labor: Dilation Stage
• From the onset of labor until the cervix
is fully dilated (10 cm)
• Initial contractions are 15–30 minutes
apart and 10–30 seconds in duration
• The cervix effaces and dilates
• The amnion ruptures, releasing amniotic
fluid (breaking of the water)
• Engagement occurs as the infant’s head
enters the true pelvis
Stages of Labor: Dilation Stage
Figure 28.17a,
b
Labor:
Expulsion
Stage
• Stages
From fullof
dilation
to delivery
of the
infant
• Strong contractions occur every 2–3
minutes and last about 1 minute
• The urge to push increases in labor
without local anesthesia
• Crowning occurs when the largest
dimension of the head is distending the
vulva
Stages of Labor: Expulsion Stage
Figure 28.17c
Stages of Labor: Expulsion Stage
• The delivery of the placenta is
accomplished within 30 minutes of birth
• Afterbirth – the placenta and its
attached fetal membranes
• All placenta fragments must be removed
to prevent postpartum bleeding
Stages of Labor: Expulsion Stage
Figure 28.17d
Extrauterine Life
• At 1-5 minutes after birth, the infant’s
physical status is assessed based on five
signs: heart rate, respiration, color,
muscle tone, and reflexes
• Each observation is given a score of 0 to 2
• Apgar score – the total score of the above
assessments
– 8-10 indicates a healthy baby
– Lower scores reveal problems
First Breath
• Once carbon dioxide is no longer removed
by the placenta, central acidosis occurs
• This excites the respiratory centers to
trigger the first inspiration
• This requires tremendous effort – airways
are tiny and the lungs are collapsed
• Once the lungs inflate, surfactant in
alveolar fluid helps reduce surface tension
of Fetal
Blood
Vessels
• Occlusion
Umbilical arteries
and vein
constrict
and
become fibrosed
• Fates of fetal vessels
– Proximal umbilical arteries become superior
vesical arteries and distal parts become the
medial umbilical ligaments
– The umbilical vein becomes the ligamentum
teres
– The ductus venosus becomes the ligamentum
venosum
– The foramen ovale becomes the fossa ovalis
– The ductus arteriosus becomes the
ligamentum arteriosum
Transitional Period
• Unstable period lasting 6-8 hours after
birth
• The first 30 minutes the baby is alert
and active
– Heart rate increases (120-160 beats/min.)
– Respiration is rapid and irregular
– Temperature falls
Transitional Period
• Activity then diminishes and the infant
sleeps about three hours
• A second active stage follows in which
the baby regurgitates mucus and debris
• After this, the infant sleeps, with
waking periods occurring every 3-4
hours
Lactation
• The production of milk by the mammary
glands
• Estrogens, progesterone, and lactogen
stimulate the hypothalamus to release
prolactin-releasing hormone (PRH)
• The anterior pituitary responds by
releasing prolactin
Lactation
• Colostrum
– Solution rich in vitamin A, protein, minerals,
and IgA antibodies
– Is released the first 2–3 days
– Is followed by true milk production
Lactation and Milk Let-down
• After birth,
Reflex
milk
production is
stimulated by
the sucking
infant
Figure 28.18
Breast Milk
• Advantages of breast milk for the infant
– Fats and iron are better absorbed
– Its amino acids are metabolized more efficiently
than those of cow’s milk
– Beneficial chemicals are present – IgA, other
immunoglobulins, complement, lysozyme,
interferon, and lactoperoxidase
– Interleukins and prostaglandins are present,
which prevent overzealous inflammatory
responses
– Its natural laxatives help cleanse the bowels of
meconium
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