final Flashcards
cortical reaction
prevents penetration by additional spermatozoa
in addition to altering zona pellucida, also reduces ability of oocyte plasma membrane to fuse with additional spermatozoa
cortical granules
during 1st and 2nd meiotic divisions of oogenesis, cortical granules move to the periphery of oocyte cytoplasm
contents are mucopolysaccharides, proteases, plasminogen activator, acid phosphase, peroxidase
exocytosis
after membrane fusion b/t oocyte and spermatozoon, cortical granules undergo exocytosis; contents released into perivitelline space
results in zona block
zona block
process where zona pellucida undergo biochemical changes so more sperm cannot penetrate.
prevents polyspermy
vitelline block
another mechanism to prevent polyspermy
syngamy
fusion of male and female pronuclei
final step of fertilization
supefecundation
spermatozoa from all males are eligible to fertilize oocytes (dogs: long sperm viability so oocytes can be fertilized by several males)
fusion protien
actual fusion of oocyte plasma membrane with equatorial segment is brought about by fusion protein
prior to acrosome reaction fusion protein is inactive
after vesiculation and release of acrosomal contents fusion protien is activated enabling sperm membrane to fuse/bind with oocyte membrane
Release of acrosomal enzymes
allows spermatozoon to digest its way through the zona pellucida
capacitation
changes sperm go through in female tract to become completely fertile
site varies b/t species. takes several hours
sialomucin
low viscosity
produced by cells in basal areas of cervical crypts
sperm swim into it “privalaged pathway”
sulfomucin
viscous
produced by apical portions of the cervical epithelium covering tips of cervical folds
sperm wash out if encounter sulfomucin
2 types of cervical mucus
sulfomucin
sialomucin
sustained transport phase
transported in “trickle-like” effect from cervical resivoirs and UTJ
move to isthmus and attach to oviduct epithelium “docking”
docking elicits signal cascade that promote viability
die 6-10 hrs after insemination if no docking
rapid transport phase
used to think good b/c delivered to oocyte quickly
sperm arriving in minutes not reliable
phases of spermatozoa transport
rapid transport
sustained transport
spermatozoa are lost from the female tract by:
phagocytosis by neutrophils
retrograde transport
embryo
an organism in the early stages of development and can’t be distinguished as a member of a specific species
zygote (ootid)
stage of embryo development when the male and female pronuclei can be observed, a newly fertilized embryo
fetus
apotential offspring that is still within the uterus but is generally recognizable as a member of a given species
conceptus
the product of conception
includes:
embryo during early embroynic stage
the embryo and extaembryonic membranes during the preimplantation stage
the fetus and placenta during the post-attatchment phase
blastomere
individual cell of an early, multicellular embryo
in early stages of embryogenesis each blastomere has potential to develop into separate offspring
undergo divisions until there are 16 daughter cells
cleavage divisions
zygote undergoes series of miotic divisions
first cleavage generates 2-cell embryo; cells are blastomeres
only occur b/t 1 cell and blastocyst stages
all take place in the zona pellucida
totipotent
blastomeres from the 2, 4, 8, 16 embryos are totipotent
ability of a single cell (blastomere) to give rise to a complete fully formed individual
morula
when a solid ball of cells is formed and individual blastomeres can no longer be counted accurately (called morula)
outer cells begin to be compacted more than the cells in the center. cells begin to separate into 2 populations (inner & outer cells)
types of cells that form in the morula phase
inner
outer
gap junctions
cells in inner part or morula develop gap junctions
allow for intercellular communications
tight junctions
outer cells form tight junctions
believed to alter permeability of outer cells
once formed fluid begins to accumulate inside the embryo
believed to be because of sodium pump in outer cells of morula
blastocoele
water diffuses through zona pellucida into embryo and to form fluid filled cavity (blastocoele)
hatching of blastocyst is governed by 3 forces
growth and fluid accumulation within blastocyst
production of enzymes by the trophoblastic cells
contraction of the blastocyst
blastocyst
when distinct cavity is recognizable embryo is called a blastocyst
inner cell mass
will become the body of the embryo
trophoblast
will become the chorion (placenta)
2 groups of mammalian embryos
Domestic animals:
preattatchment period is long (several weeks)
extensive extraembryonic membranes form by a folding process that generates the amnion, chorion, and allantochorion
Primates:
blastocyst implants soon after it enters the uterus
extraembryonic membrans form after implantation/attachment
extraembryonic membranes of preattachment embryo consist of:
yolk sac
chorion
amnion
allantois
extraembryonic membranes
set of membranes that cause dramatic growth of the conceptus
pig, sheep and cow have long filamentous/ threadlike blastocysts prior to attatchment
mare: blastocysts remain sphere
primative endoderm
mesoderm
give rise to chorion and amnion
yolk sac develops from the primative endoderm
additional cell layer that grows beneath but in contact with the inner cell mass, continue to grow downward and eventually line the trophoblast
allantois
fluid filled sac that collects liquid waste from the embryo
as embryo grows it will expand and eventually make contact with the chorion. eventually fuses together
allantochorion
as embryo grows allantois will expand and eventually make contact with the chorion. eventually fuses together
maternal recognition of pregnancy
must happen before luteolysis
interferons
in ewe and cow
proteins that signal for prevention of luteolysis
cytokines (immune cell hormones) secreted by many types of cells (leukocytes, fibroblasts, lymphocytes, and trophoblastic cells) best known for their ability to inhibit virus replication
oIFN-T. & bIFN-T
oIFN-t binds to endometrium and inhibits oxytocin receptor synthesis
maternal recognition sow
conceptus produces estradiol (the signal for maternal recognition) (prevents luteolysis)
PGF2a is produced in significant quantities, rerouted to uterine lumen
MUST be 2 conceptuses present in each uterine horn for pregnancy to be maintained.
maternal recognition mare
presence of conceptus prevents luteolysis
conceptus must move from one uterine horn to the other (12-14 times/day during days 12, 13, & 14) (conceptus does not elongate like other species) probably has to happen to distribute pregnancy recognition factors to endometrial cells (don’t know what factors are)
maternal recognition human
at time of implantation 7-9 days after ovulation conceptus begins to secrete hCG
acts on CL to inhibit intraovarian luteolysis
chorionic villus
functional unit of the fetal placenta
exchange apparatus, provides increased surface area so that exchange is maximized
placenta classifications
diffuse
zonary
discoid
cotyledonary
diffuse placenta
pig & mare
pig: uniform distribution; initial attachment around day 12
mare: specialized microzones of chorionic villi (microcotyledons) distributed over entire surface. Also contain endometrial cups (trophoblastic and endometrial origin) 5-10 cups over surface of placenta. Cups produce eCG & develop b/t days 35 and 60. after day 60 they are no longer used
zonary placenta
dogs and cats
girdle like; single band around middle; broad zone
2nd region: consists of highly pigmented ring at either end of the central zone. consists of small hematomas (blood clots). pigmented zone also refered to as paraplacenta; thought to be important in iron transport
3rd region: transparent zone on distal ends of chorion, has poor vascularity
discoid placenta
human, rodent, rabbit, primates
1-2 disc-shaped areas
cotyledonary
cow, ewe, deer (ruminants)
cotyledons (many circles of villi)
sheep: 90-100 cotyledons
cow: 70-120 cotyledons
placentome: (point of interface) consists of a fetal cotyledon and maternal cotyledon originating from caruncular regions of uterus. In cow CONVEX, in ewe CONVAVE
Epitheliochorial placenta
prefix maternal sufix fetal
6 layers 7 layers?
sow and mare
also ruminants but endometrial epithelium erodes and regrows causing exposure to maternal capillaries (syndesmochorial)
binucleate giant cells found in ruminant placenta
binucleate giant cells
large and have 2 nuclei
appear around day 14 in sheep and day 18-20 in cow
originate from trophoblast and thought to be formed continuously
20% of fetal placenta
migrate from chorionic epithelium and invade endometrial epithelium
transfer complex molecules from fetal to maternal placenta
secrete pregnanacy specific protein B (PSPB) also called pregnancy associated glycoproteins(PAG)
endotheliochorial placenta
5 layers
dog and cat
complete erosion of endometrial epithelium
maternal capillaries directly exposed to epithelial cells of chorion
hemochorial placenta
3 layers
primates and rodents
chorionic epithelium in direct opposition of maternal pools of blood
nutrients and gases exchanged directly from maternal blood and only has to go through 3 layers of tissue
hemoendothelial
1 layer
rabbit, rat, guinea pig
barriers to waste, nutrients, and gaseous transfer almost nonexistant
chorionic capillaries immersed in pools of blood and material directly transferred from maternal blood pools through a single layer of chorionic capillary endothelium
placental exchanges
simple diffusion: (gases and water pas from high to low concentrations)
facilitated diffusion: (glucose and other metabolically important materials such as amino acids are transported by facilitated diffusion using specific carrier molecules)
active transport:
What can & cannot pass through placenta
can:
fetal formed fatty acids
water soluble vitamins B & K (easier than fat soluble)
minerals
toxic & potentially pathonenic compounds (ethyl alcohol, lead, phosphorus, mercury)
drugs & pharmaceuticals (antibodies)
microorganisms
viruses
imunoglobulins
smaller molecular weight hormones (steroids, thyroid hormone, catecholamines (epi & norepi)
Cannot:
maternal proteins
nutritionally based lipids
large peptide hormones (thryroid stimulating hormone, adrenal cortical stimulating hormone, growth hormone, insulin, glucagon)
teratogenic (abnormal development/ birth defects):
LSD, amphetamines, lithium, diethylstilbestrol, thalidomide
Placenta secretes hormones that can:
(placenta is also transitory endocrine organ)
stimulate ovarian function
maintain pregnancy
influence fetal growth
stimulate mammary function
assist in parturition
first major gonadotropin of placental origin
eCG
produced by endometrial cups in mare
second major gonadotropin of placental origin
hCG
not specific to humans (found in other primates)
can be detected in urine of pregnant female by day 8-10 of gestation (used in human pregnancy tests)
CL during pregnancy
not needed in some species for whole duration of pregnancy b/c placenta takes over secretion of progesterone (ewe, mare, human)
sow, rabbit: if CL removed pregnancy will terminate
cow: if removed up to 8 months pregnancy will terminate
Placenta produces:
progesterone
estradiol
also produces placental lactogen (polypeptide hormone) also called somatomammotropin.
found in rats, mice, sheep, cows, humans
similar to GH
stimulate mammary gland
who triggers partuition
fetus
3 stages of partuition
initiation of myometrial contractions (removal of progesterone block)
expulsion of fetus
expulsion of fetal membranes
distocia
difficult birth
relaxin
glycoprotein produced by either CL or placenta (depends on species)
synthesis of relaxin stimulated by PGF2a
causes softening of connective tissue in cervix and promotes elasticity of pelvic ligaments
