lecture 23 - development and inheritance Flashcards
gestation
pregnancy - 38 weeks from fertilization to birth
prenatal development (what is it, and its stages) (2)
time from fertilization to birth
embryonic period
- fert to 8 weeks (embryo)
- all principal adult organs present
fetal development
- week 9 to birth
- placenta now functional
can also be divided into 3 trimesters (1,2,3)
neonatal period
first 28 days after birht
embryonic period - week 1 events (4)
fertilization
cleavage of zygote
blastocyst formation
implantation
fertilization
haploid sperm + secondary oocyte = zygote (2n)
when does fert oocur
within 12-24 hours post ov
how long are oocytes and sperm viable for
oocyte - 24 hours
sperm - 48 hours
how are sperm attracted to the oocyte
via capacitation
capacitation
series of changes that allow sperm to fertilize the oocyte
flagella beat more rapidly
removal of cholesterol and proteins from plasma membrane near acrosome that prepare sperm for fusion
corona radiata
layer of granulosa cells around oocyte
zona pellucida
glycoprotein layer between plasma membrane and corona radiata of oocyte
ZP3
glycoprotien in zona pellucida that acts as a sperm receptor
what happens when a sperm binds to ZP3
sperm cells release acrosomal enzymes and digest a path thru zona pellucida
fusion of sperm and oocyte cause 2 blocks.
waht do these things do?
fast block
- depolarization of oocytes membrane so it cant fuse with another sperm
slow block
- hardening of zona pellucida that inactivates ZP3
blocking prevents polyspermy
polyspermy
fertilization by more that 1 sperm
syngamy
fusion of male and female pronuclei
zygote
fertilized ovum
fraternal twins (dizygotic) are formed by:
independent release of 2 oocytes fertilized by 2 separate sperm
genetically as different as 2 siblings
identical twins (monozygotic) are formed by:
a zygote that splits into two embryos within 8 days post fertilization
conjoined twins are formed by:
zygote that separates MORE than 8 days after fertilization
cleavage of zygote
rapid mitotic cell division of zygote
blastomeres
Progessively smaller cells produced by cleavage
morula
formation of solid sphere of cells that is still surrounded by the zona pellucida
what day is the morula formed
4
blastocyst formation
day 5
morula enters uterine cavity
- fluid from endometrial glands enters morula and reorganized blastomeres to form the blastocyst
- fluid nourishes the morula and the zona pellucida is shed
the morula is now called a blastocyst
endometrial glands secrete
uterine milk (fluid that forms blastocyst from morula)
blastocyst gives rise to two different cell populations (2) what are they and what do tehy develop into?
embryoblast (inner)
- develops into embryo
trophoblast (outer)
- develops into outer chorionic sac
implantation happens by day:
6
implantation
attachment of blastocyst to endometrium
embryoblast is oriented to face the endometrium
once attached (implantation) what happens to the endometrium and blastocyst?
endo
- becomes more vascularized
blastocyst
- secretes enzymes, burrows into endometrium
what do trophoblast cells secrete, and what does it do/
hCG, human chorionic gonadotropin
maintains corpus luteum, allowing for sustained secretion of estrogen and progesterone, preventing menstruation
decidua (what is it, + 3 layers)
functional layer of endometrium formed after implantation
basal - nourishes embryo, surrounds it in endometrium
capsular - part of endometrium that covers embryo from lumen of uterus (part of basal and parietal)
parietal - remaining part of modified endometrium in noninvolved areas
ectopic pregnancy
development of an embryo outside the uterine cavity, usually in tubes
can be due to:
- scarring
- smoking (destruction of cilia)
- peristalsis defect
- abnormal tubal anatomy
can also occur in ovaries, abdominal cavity, or cervix
is not removed place will rupture leading to hemorrhage and maybe death
embryonic period - week 2 events (6)
development of trophoblast
development of bilaminar embryonic disc
development of amnion
development of umbilical vesicle
development of sinusoids
development of chorion
development of trophoblast occurs in week:
2
development of trophoblast can only occur in trophoblast cells that are:
in contact iwth the endometrium
development of trophoblast (2)
trophoblasts contacting endometrium rapidly divide into two layers
syncytiotrophoblast - outermost layer
- secretes enzymes that allow blastocytes to burrow during implantation
cytotrophoblast - inner layer between syncytiotrophoblasts and embryoblast
both of these layers will become part of the chorion as they grow
what will teh two layers of trophoblasts become part of, and what are they
syncytiotrophoblast (inner), and cytotrophoblasts (outer) become part of the chorion
when does the embryoblast differentiate into two layers?
around day 8
bilaminar embryonic disc is formed from
differentiation of the embryoblast in week 2
parts of the bilaminar embryonic disc (2) and what they will form in the body
hypoblast (outer) - layer of cuboidal cells
- this will form lining of GI/respiratory tracts (primitive endoderm)
epiblast (inner) - layer of columnar cells
- this will form the epidermis and nervous system (primitive ectoderm)
amniotic cavity appears within the:
appears within the epiblast
bordered by amnion and epiblast
amnion
single layer of squamous cells that develop from the epiblast
creates amniotic cavity which surrounds the entire embryo
functions of amniotic fluid (three)
absorbs shock
regulates temp
prevents adhesion of fetal skin with surrounding strucutres
amniotic fluid is made of (2) and contains (1) that can be used for (1)
maternal blood and fetal urine
embryonic cells
can be used for amniocentesis (examination of fetal cells)
development of umbilical vesicle occurs in week:
2
development of umbilical vesicle
forms as hypoblast cells differentiate
bilaminar embryonic disc is now between amnio and yolk sac
by day 12, yolk sac cells form;
extraembryonic endoblast
(outer ‘shell” or wall of yolk sac)
what forms the wall of the umbilical vesicle
extraembryonic endoblast and hypoblast
functiosn of the umbilical vesicle (6)
supply nutrients to embryo
- contains primordial germ cells that migrate to gonads
- source of blood cells in week 3-6
- forms part of gut in 4th week
- shock absorber
- prevents drying out of embryo
development of sinusoids
syncytiotrophoblasts continue to expand
- trophoblastic lacunae form
- trophoblastic lacunae fuse to form vascular circles
- surrounding endometrial capillaries dilate to form maternal sinusoids
trophoblastic lacunae
lacunae that fuse ot form vascular circles
maternal sinusoids
dilated endometrial capillaries
vascular circles
where maternal blood and secretions will enter
extraembryonic mesoderm develops from
umbilical vesicle and forms CT layer surrounding umbilical and amnion
what forms the chorion
extraembryonic mesoderm and trophoblast
this is also the embryonic contribution to the placenta
extraembryonic coelon
whatdoes it form?
large cavities in the mesoderm that have fused
forms chorionic cavity
chorion functions
(secrete? supress?
surrounds embryo/fetus
- secretes hCG
- sepresses maternal immune response against fetus
(secretes proteins that block antibody production in mother)
connecting stalk
connects bilaminar disc to trophoblast
band of extraembryonic mesoderm that will become the umbilical cord
when does the connecting stalk form
in week 2
embryonic period - week 3 events (6)
gastrulation
neurulation
development of somites
development of intraembryonic coelem
development of cadiovascular system
development of chorionic villi and placenta
3 germ layers form in week
3
what week to the 3 germ layers lay teh groundwork for organ developmetn
4
gastrulation
process where the bilaminar dic undergoes reorganization to form a trilaminar disc, making the 3 germ layers
groove forme in gastrulation is called:
what does it do
the primitive streak
defines the head vs tail and left vs right on the embryo
endoderm and ectoderm are _____, while mesoderm is ______
endo/ecto are tightly packed epi cells
meso = loosely organized CT
what will the endoderm become
epi lining of GI/respiratory tract, urinary tract, reproductive tract
what will mesoderm become
muscel, bone, CT, cardiovascular system, peritoneum
what will ectoderm become
skin epidermis, nervous system
notochordal process
hollow tube formed by mesoderm cells from the primative node migrating
a few days later, the tube forms a solid cylinder called the notochord
induction during gastrulation
notochord secretes substances that cause nearby unspecialized mesoderm cells to become verebral bodies
notochord will form intervertebral discs
during gastrolation, ectodermal cells will become the:
neural plate
oropharyngeal membrane
forms the oral cavity in week 4
small depression where the endoderm and ectoderm meet at the head end
cloacal membrane
openings for anus, urinary, and reproductinve tracts formed in week 7
small depression where endo/ectoderm meet at the tail end
allantois + function
vascularized outpouching from umbilical vesicle
helps in early formation of blood vessels and urinary bladder development
imperforate anus
anal defect in 1-4-5k kids
persistence of cloacal membrane
neurulation
process by which neural plates, neural folds and neural tubes form
the neural plate develops the:
neural fold as the lateral edges become elevated
neural groove
depressed mid region of neural plate forms the neural groove
neural fold fuse to form:
neural tube
neural tube
progess from mid region to head and tail regions
neural crest is formed by
ectodermal cells from neural tube
neural tube develops into:
brain and spinal cord
neural crest cells form:
where are they?
all sensory neurons
found on either side of the neural tube (green things)
primary brain vesicles
3 enlarged areas at the head end of the neural tube
neural tube defects (2)
spina bifida
- failure of spine and spinal cord to form properly
- meninges and spinal cord can protrude from vertebral column
anencephaly
- failure of cranial bones to surround brain tissue leading to degeneration
somites
chain of cube shaped blockes formed by the mesoderm near teh notochord
formed by mesoderm breakup
red blobs on either side of neural tube
parts of the somite and what they become
myotomes
- skeletal muscle of neck trunk and limbs
dermatomes
- dermis and CT
sclerotomes
- vertebrae and ribs
how many pairs of somites fo human have
42-44
this number can indicate the age of an emrbyo
intraembryonic coelom
spaces formed by mesoderm cells from the primative streak rearranging merging into a larger cavity
small groove on either side under somites
what does the intraembryonic coelom (cavity) split into (2)
splanchnopleuric mesenchyme
somatopleuric mesenchyme
splanchnopleuric mesenchyme, formed from the splitting on the intraembryonic coelom, forms waht
heart
somatopleuric mesenchyme, formed from the splitting on the intraembryonic coelom, forms waht
bones, ligaments, blood vessels etc
angiogenesis
formation of new blood vessels
angiogenesis occurs in week
3
why does angiogenesis happen
because the umbilical vesicle cant provide enough nutrients, so blood vessels are needed
steps of angiogenesis (
mesoderm cells in teh umbilical vesicle become hamngioblasts, then angioblasts
these cells form blood islands that fuse
spaces in the blood islands will form teh lumen of blood vessels
blood cells and plasma then develop is structures outside the embryo
development of the cardiovascular system
angiogenesis
- mesoderm cells in umbilical vesicle form blood islands
- islands fuse
- spaces between become lumen of future vessels
when will blood start to form in the liver
week 5
when will blood start to form in the red marrow, spleen, and thymus
week 12
what structure does the heart develop from and in what week
splanchnopleuric mesenchyme, in week 3
what forms the primative heart tube
a pair of primordial tubes made from mesoderm cells
primative heart tube function
joins blood vessels in other parts of the embryo, connective stalk, chorion, and umbilical vesicle
forms primitive cardiovascular system
somites differentiate into (3), and each of these forms what
myotomes
- skeletal muscle of limbs/trunk
dermatomes
- dermis and CT
sclerotomes
- vertebrae, ribs
