2. More than one sperm penetrating oocyte ( or polyspermy) causes death because of abnormal chromosome number
3. mechanisms
no more sperm can penetrate easily
b. Cortical response
materials in the
cell cytoplasm force attaching sperms off oocyte
2. New cell, the zygote,
has 46 chromsomes ,
23 from mom and 23 from dad
Describe the funcitn of each gender's sex cell. Identify the number of chromosomes
in each..
II. Embryonic processes
and events
A. processes begin
and then continue throughout development
1. Cleavage
process like mitosis but without a chance for cell growth, producing more but increasingly smaller cells that cling together
2. Migration
process in which cells move from one spot to another changing within the embryo, adding new embryonic structures3. Differentiation
process in which some cells change to form new cell types, allowing new cell types to form.
B. Embryonic events happen only once
1.Fertilization-fusion of secondary oocyte and sperm
2. Implantation-embedding of blastocyst stage in endometrium
Distinguish
processes from events.
III. Embryonic Developmental stages
A. Zygote stage (day 1, result of fertilization event)
Single cell has chromsomes from dad but chromosomes and all other cellular structures
from mom (i.e., mitochondria, etc.)
B. Morula stage (days 3-4,
result of cleavage)
Solid ball of cells, of greater than 12 cells, where cells (blastomeres) are
all biochemically the same and have the capability to become any tissue
in adult body (same as embryonic stem cells)
C. Early Blastocyst stage (days 5-8, result of further cleavage, as well as
migration and differentiation)
Hollow ball of cells, consists of two different types of cells.
....become embryonic part of placenta (chorion) that produces human chorionic gonadotropin ( which tells Mom's corpus luteum to produce progesterone to maintain endometrium).
....produce enzymes to promote implantation
b. Inner cell mass cells
eventually become the embryo. This mass becomes two layered disk (bilaminar
disk).
three layered, flat (trilaminar disk) embryo implanted in endometrium
eventually forms skin and nervous system
b. Endoderm
eventually forms
epithelial linings (mucosal layers) of digestive, urogenital and respiratory
systems
c. Mesoderm
eventually forms
bone, muscle, blood and vessels, organs of reproductive and urinary systems
sac that contains fluid surrounding embryo penetrated by umbilicus from embryo to placenta
amniocentesis is used to determine biochemical and genetic disorders.
b. Chorion
derived from trophoblasts
to form part of placenta (to provide nourishment to embyro)
encloses all membranes
and embryo
E. Neurula stage (end of
third week)
ectoderm
of embryonic plate infolds to form central nervous system, hence name.
trilaminar disk begins to fold into
cylinder.
F. One month stage
trilaminar disk has folded
into cylindrical, tadpole-like embryo.
Heart and gut begin and
continue to form.
Limb buds appear.
G. Two month stage (5-8 weeks)
Limb buds recognizable
as appendages with digits at week 8
Sexual genitalia begin to form at week 8.
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Fetal stages
A. Third Month stage (9-12 weeks)
Sex can be determined. Head with eyes and ears obvious. Urine excreted into
amnion. Bones begin to be ossified.
Placenta is now forming adequate estrogen and progesteron to maintain endometrium.
HCG levels drop.
B. 4th through 8th months (12-36 weeks)
continued formation of organs and structures.
movements become detectable
surfactant forms at end of this period.
C. Full term (38 weeks)
Baby is head down and read for birth.
Distinguish
developmenta stages. Identify key structures formed during each stage.
1. Estrogen
Increasing levels of estrogen promote readiness of breasts, maintains endometrium and causes mother's body to store fat and water in preparation for childbirth.
2. Progesterone
Increasing levels of progesterone inhibit myometial contractions.
3. HCG
During first three months, hCG is produced by chorion (part of placenta) of
embryo. Targets Corpus luteum which then maintains progesterone production to
maintain endometrium.
4. Relaxin
Produced by ovaries and then the placenta-reduces myometrial contraction during
pregnancy. Also relaxes ovarian ligaments and pubic symphyses prior to labor
to ease birthing.
5. Prolactin
Produced by Anterior pituitary in response to baby suckling. Targets mammary
glands to promote milk production. More suckling then more milk produced---positive
feedback loop.
6. Oxytocin
Produced by Hypothalamus neurosecretory cells (released from Posterior pituitary
axonal end of those neurons) in response to stretching of uterine cervix (baby
moving).. Targets myometrium to increase contractions during birth. More moving
then more birth contractions---positive feedback loop.
Produced by Hypothalamus neurosecretory cells (released from Posterior pituitary axonal end of those neurons) in response to suckling. Also targets myoepithelial cells surrounding mammary glands and ducts to eject milk. More suckling then more milk ejected---positive feedback loop.
Describe
role of hormones of pregnancy, birth, milk ejection and milk production.
VI. Genetics
A. Basic information
1. Inherited information on which proteins to make and how to make them (protein
synthesis) is found in sequences of nucleotides called genes. Many genes make
up a single DNA molecule. DNA is not condensed most of the time (interphase)
so is available to code for proteins. During division processess (mitosis and
meiosis) DNA is condensed into chromosomes to aid in movment to newly produced
cells.
2. Each gene codes for a proteinthat determines a specific body trait. For example,
there are genes for membrane proteins, genes for metabolic enzymes, etc. The
expression of these genens affect a cell's appearance and activity (a trait)
a. autosomal traits (on all DNA molecules) are those that affect general body
b. sex traits (only on the so-called sex chromosomes, i.e., X and Y) affect
expression of gender.
3. There are 23 pairs of DNA molecules ( or chromosomes) in normal body cells-one
set from mom and one set from dad. As such , there are two complete sets of
genes that produce the same protein type and therefore determine the same traits
efficiency of metabolic enzymes, type of chloride membrane transporter protein).
These pairs of chromosomes are called homologous pairs because gene for same
protein is found at same location on both chromosomes of the pair.
4. Because there are homologous chromosomes each cell has two versions of a
gene. Each version is called an allelle.
a. Both alleles can produce exactly the same protein (known as homozygous condition)
b. Alleles can produce slightly
different proteins (known as heterozygous condition)