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Chapter 20
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STEPS TO
FERTILIZATION
-several hundred sperm
produce enough
enzymes for one to
penetrate the oocyte
-enzymes then harden
the zona pellucida to
prevent more sperm
from entry
-Sex cells with 23
chromosomes
-Zygote with 46
chromosomes
GROWTH AND DEVELOPMENT INTRODUCTION
GROWTH - increase in size
DEVELOPMENT - change from one life phase to the next,
includes growth
PRENATAL - fertilization to birth
POSTNATAL - birth to death
FERTILIZATION - union of an egg and a sperm cell
PREGNANCY - implantation into the uterus; consists of three
trimesters - 38 weeks total
TRANSPORT OF SEX CELLS - cilia in the uterine tubes move
the egg along; sperm cells have tails to move promoted by
prostaglandins; muscular contractions of the uterus and uterine
tubes help move the sperm
- estrogen is needed to make the cervical mucus thin to promote
sperm survival
HUMAN PRENATAL DEVELOPMENT - three days to move through the
uterine tube. Morula - 16 cell “ball” which turns into a blastocyst after
three days and attaches to the endometrium after the 1st week of
development.
BLASTOCYST IMPLANTATION
and trophoblast development
The trophoblast will form the
placenta that secretes hCG
Start of the embryonic stage 8 weeks (embryo)
After 8 weeks = fetus rudimentary organs
Placenta - vascular structure
that attaches the embryo to
the uterine wall
-exchanges nutrients, gases,
and wastes
- secretes hormones
FEMALE INFERTILITY
Termed after one year of inability to conceive
Causes:
Insufficient gonadotropic hormones (LH/FSH) that prevent
ovulation
hCG (human chorionic gonadotropin) and hMG (human menopausal
gonadotropin) are used to stimulate ovulation - risk of
overstimulation => multiple secondary oocytes released =>
possibility of multiple pregnancies
Endometriosis - small pieces of uterine lining implanted in the
abdominal cavity. The tissue sheds like uterine tissue so blood
builds up in the abdominal cavity and causes pain and fibrotic tissue
growth around structures like the ovaries
STD/Is - infections can scar uterine tubes and plug cervix preventing
sperm and oocyte movement
TESTS TO ASSESS FEMALE INFERTILITY &
TREATMENTS
HORMONE FLUX
DURING PREGNANCY
Spontaneous abortion - occurs if
corpus luteum degenerates about
two weeks after ovulation; when
it degenerates estrogens and
progesterones decline rapidly
Human chorionic gonadotropin
(hCG) prevents abortion;
trophoblasts secrete hCG
LH maintains the corpus luteum
and secretes estrogens and
progesterone to maintain the
uterine wall
hCG inhibits LH and FSH
release which stops the
menstrual cycle
The placenta secretes hormones
after the 1st trimester
PLACENTAL SECRETIONS
Placental lactogen- prepares the mammary glands for secretion of
milk
Relaxin - inhibits smooth muscles in the myometrium until birth
occurs; relaxes the symphysis pubis and sacroiliac joints
Placental estrogens - enlarge the vagina and external reproductive
organs in preparation for birth
The parathyroid stimulates high calcium concentrations in the
blood and adrenal secretion of aldosterone contributes to fluid
retention
HORMONAL CHANGES DURING PREGNANCY
EMBRYONIC STAGES - ectoderm and endoderm form first with the
mesoderm forming in between them
By the end of week 4 head and jaws form; the
heart beats and limb
buds develop
By weeks 5-7 - the head
grows rapidly, the face
eyes, nose and mouth
become more
recognizable; the limbs
elongate; fingers and
toes develop and
webbing dissolves
By the end of week 7 all internal organs are
present
Figure 20.09
PLACENTAL
MEMBRANE
The layers of cells of
the trophoblast secretes
proteolytic enzymes
that break down
endometrial tissue
providing nutrients for
the embryo and create
vessels and the
placenta
Oxygen and nutrients
diffuse from mom’s
blood to fetus and
carbon dioxide and
wastes diffuse from the
embryo to mom
Embryonic portion
of the placenta =
chorion and villi
Maternal portion =
uterine wall
(decidua basalis)
AMNION AND
AMNIOTIC FLUID
Amnion - surrounds the
embryo by week 2
Amniotic fluid - fills
space between the amnion
and embryonic disc;
provides cushion
Umbilical cord - embryo
attaches to the chorion
and placenta
Three vessels of the
umbilical cord - two
arteries and one vein
Fetus suspended by the
umbilical cord
Figure 20.13
YOLK SAC AND ALLANTOIS
The yolk sac gives rise to the cells that become sex cells
The allantois turns into the umbilical arteries and vein
Teratogens - can cause birth defects during pregnancy
FETAL STAGE
Begins at the end of the
8th week and goes until
birth
3rd month - body
lengthening; ossification
centers develop
12th week - sex can be
determined
4th month - lower limbs
lengthen; reacts to loud
noises
5th month - skeletal
muscles contract and baby
moves; hair grows on head
MONTHS 6-9 DEVELOPMENT CHANGES
6th month - weight gain; eyebrows and eyelashes develop
7th month - fat is deposited in subcutaneous tissue; eyelids reopen;
40 centimeters in length at this point
8th month - organs specialize and grow; testes descend into the
scrotum
9th month - 50 cm in length; sebum and dead epidermal cells coat
skin; hair on the scalp; fingers and toes with nails; skull bones mostly
ossified; fetus turns toward a downward position
FETAL BLOOD
CIRCULATION
Fetal blood has a higher affinity for
oxygen
Umbilical vein brings baby oxygenated
blood
Half of the blood goes into the liver and
the rest to the ductus venosus
The ductus venosus joins the IVC where
oxygenated blood from the placenta
mixes with deoxygenated blood from the
fetus
Fetal lungs are nonfunctional - blood
from the IVC enters the right atrium and
is shunted to the left atrium via the
foramen ovale
Blood bypasses the lungs via ductus
arteriosus - connects pulmonary trunk to
the descending aortic arch
Blood from the SVC by passes the lungs
using the ductus arteriosus but is
prevented from entering cardiovascular or
brain blood circulation
Deoxygenated blood enters umbilical
arteries from the internal iliac arteries to
go to the placenta for re-oxygenation
THE BIRTH PROCESS
MILK PRODUCTION
AND SECRETION
Estrogens stimulate ductile
extension and branching and deposit
fat around them
Progesterone causes alveolar gland
creation and ends of ducts
Breast size doubles during
pregnancy
Placental expulsion causes prolactin
release and milk is secreted
Colostrum is what is secreted in the
first few days and has more protein
Ejection of milk requires contraction
of myoepithelial cells around the
alveolar glands
Suckling or stimulation of receptors
on the nipple or areola cause the
reflex reaction
Oxytocin causes myoepithelial cells
to contract
If milk is not removed regularly
prolactin is inhibited within one
week and milk production ends
NEONATE CHANGES
Neonatal period - starts at
birth and goes to 4 weeks
Excrete dilute urine - easy
to be dehydrated
Umbilical vessels constrict
Ductus venosus constricts
and becomes a ligament of
the liver
Foramen ovale closes with
heart pressure changes full closure may take a year
Ductus arteriosus constricts
and becomes ligamentum
arteriosum in 15 minutes
GENETICS
Genetics - how genes are passed from one generation to the next
Autosomes - pairs 1-22
Sex Chromosomes - X and Y chromosomes
XX = FEMALE; XY = MALE
Alleles - slightly different forms of a gene
Homozygous - two identical alleles of a gene
Heterozygous - two different alleles of a gene
Genotype - combination of alleles, for one or many genes
Phenotype - appearance, health condition (ex: green eyes)
MODES OF INHERITANCE
The way we inherit genes from
mom and dad
Autosomal dominant - masks
expression of a recessive allele - it
causes a trait or disease; usually an
X chromosome linked trait; start in
adulthood
Autosomal recessive - two
recessive alleles from each parent
elicit a trait; early onset; X linked
in females
X-linked recessive - males with
these; hemophilia and
colorblindness
MULTIFACTORIAL TRAITS
Influenced by environmental factors such as nutrition, exposure to
toxins and pathogens
Several genes contribute to phenotypes
Height, skin color and intelligence are polygenic traits that vary
As nutrition improved individuals became taller over the years
Heart disease, diabetes, hypertension and cancers are multifactorial
and are polygenic traits
Box Figure 20.c
Box Figure 20.d