BIOL 1260: fetal development Flashcards
cleavage
is the rapid cell division of a fertilized egg into a large number of cells; the embryo size remains the same but the cells get smaller
normal mitosis phases
is typically a growth phase, a S phase, a growth phase, and then a mitosis stage
cleavage phases of mitosis
instead of growth stages, there is only S and M phases; this results in daughter cells that don’t grow but remain half the size of their parent
gastrulation
is cell movements that result in the establishment of embryonic germ layers
3 germ layers
mesoderm, ecoterm, and endoderm
endoderm
inner layer of embryos that develops into the gut, liver, and lungs
mesoderm
is the middle embryonic layer and develops into the skeleton, muscle, kidney, heart, and blood
ectoderm
outside embryonic layer that develops into the skin and nervous system
coelom
the hollow cavity established by embryonic germ layers and is only found in mammals
insects vs vertebraes CNS
for insects, the CNS is on the ventral side not like dorsal side like in vertebrates
what occurs at the same time as cleavage?
the embryo is moving closer to the uterus
when does the embryo reach the uterus?
day 3-5; it implants in the uterus around day 7
what stage is the embryo at when it reaches the uterus?
the 128 cell blastocyst
mammalian cleavage
is rotational, meaning each cleavage is perpendicular to the previous cleavage, resulting is a less symmetrical cleavage appearance
totipotent meaning
these cells can give rise to all cells of the embryo, including embryonic stem cells and extraembryonic structures
how many cells of the embryo are in the totipotent phase?
8
compaction
occurs at the 8 cell stage when the cells become so tightly adhered to each other that you can no longer see the boundaries between them
significance of compaction
at this phase, the inside and the outside are being established; the inside will become the embryo and the outside if the extra embryonic tissue
morula
is the 16-32 cell stage
morula structure
has a small group of internal cell mass and the larger group that is the trophoblast
inner cell mass
will give rise to the embryo as these cells are pluripotent
what does the inner cell mass give rise to?
the yolk sac, the allantois, and amnion
pluripotent meaning
this is found in the ICM and means these cells can give rise to every cell type except trophoblast
trophoblast
larger group of outer cells that give rise to the chorion
chorion
extra embryonic tissue that becomes a portion of the placenta
blastocyst
is the 64+ cell stage
cavitation meaning and structure of cells
trophoblast cells secrete Na+ and other ions into the spaces between the cells via osmosis; this is done via Na+/K+ ATPase on the apical surface and Na+/H+ antiporter on the basal side
blastocyst structure
the cells on the outside form a hollow sphere, the cells at the top is inner cell masses, and at the bottom is the blastocyst cavity; also surrounded by a zona pellucida
blastocyst hatching
this occurs at the 64 cell stage once the embryo is in the uterus and squeezes out of the glycoprotein layer through secreting enzymes by the trophoblast
zona pellucida function for embryos
this prevents the embryo from implanting in the oviduct, thus preventing ectopic pregnancy
implantation
is when the hatched blastocyst secretes enzymes to digest endometrium ECM that allows it to bury itself into the uterine wall
mammal embryo nutrition
yolk sac is limited and most nutrition is from the placenta
what does the trophoblast develop into?
the cytotrophoblast and then the syncytiotrophoblast
what collectively become the chorion?
the cytotrophoblast and then the syncytiotrophoblast
what does the hypoblast become?
the yolk sac
what does the epiblast become?
the embryonic epiblast which then becomes the 3 germ layer
timing for egg fertilization
most likely to occur if intercouse occurs 2 days before ovulation to one day after
pH of sperm leaving the testis
7.4
pH of sperm in the epididymis
6.5
pH of sperm in the semen
6.9
pH of the oviduct
7.4
pH and sperm structure
the changing pH of the location of the sperm allows them to become functional and swim; specifically, in the oviduct they gain functional to swim
capication
refers to the structural changes of the sperm due to pH levels, allowing them to gain their ability to swim and to allow their plasma membrane to fuse with the oocyte
changes to the head of the sperm during capacitation
the secretions from the female tract remove glycoproteins and cholesterol from the head, allowing them to be more attractive to oocytes
anatomy of the ovum
the ovum is surrounded by the polar body, the zona pellucida, and some granulosa cells (corona radiata)
when is fertilization considered to occur?
when the head of the sperm meets the plasma membrane of the ovum
what happens to the ovum when fertilization occurs?
the oocyte completes meiosis II
syngamy
is the process of 2 haploid nucleus forming a zygote
day 1 post fertilization
2 cells are present due to 1 cleavage
day 2 post fertilization
4 cells due to 2 cleavages
day 4 post fertilization
compaction has occurred and the morula is now present (16-32 cells)
day 5 post fertilization
the blastocyst is present and hatching begins
uterine milk
this nourishes the morula and is a glycogen rich secretion from the endometrial glands; it also establishes the blastocyst cavity
day 7 post fertilization
the blastocyst undergoes implantation
where does implantation occur in the uterus?
the posterior fundus or the body of the uterus
blastocyst implantation position
it orientents itself so the inner cell mass faces the uterine wall
what occurs to the endometrium after implantation?
the endometrial glands enlarge and this become more vascularized
decidua
the endometrium after implantation has occured
different regions of the decidua
the decidua basalis, the decidua capsularis, and the decidua peristalsis
decidua basalis
is the portion of the endometrium between the embryo and the stratum basalis
decidua capsularis
the portion of the endometrium between the embryo and the uterine cavity and is a single cell layer thick
decidua peristalsis
is the remaining part of the endometrium that are not either of the other 2
2 phases that occur in late human embryonic development
gastrulation and neurulation
what occurs after implantation?
the trophoblast divides into 2 layers: the cytotrophoblast (holds the shape of the embryo) and the syncytiotrophoblast (this penetrates deep into the uterus); the hypoblast is also forming
what forms the hypoblast
the inner cell mass
yolk sac functions (6)
supplies nutrients to the embryo for the first couple of weeks; is the source of blood cells; is the site for PCGs; forms part of the gut; acts as a shock absorber; and prevents desiccation
when is the yolk sac useful?
2-6 weeks
lacunae
are regions surrounding the embryo that pool with maternal blood to supply the embryo
neurulation
begins with the formation of the notochord from the mesoderm, with then becomes the neural tube and this develops into the CNS
when does neurulation occur?
about 22 days post fertilization
chorionic villi
are pockets of fetal blood that absorb blood from the lacunae through the syncytiotrophoblast and the cytotrophoblast to provide nutrition and remove waste products
what carries nutrient rich blood to the fetus?
the umbilical vein
what carries fetal waste back to the blood?
the umbilical artery
2 components of the placenta
the decidua basalis (maternal component) and the chorionic villi (fetal component)
how does fetal and maternal blood not mix?
via the two layers separating the placenta structure that are the syncytiotrophoblast and the cytotrophoblast
when does organogenesis occur?
begins at week 4 and completes around week 8
weeks 5 to 8
the brain is rapidly developing, along with the head, the four heart chambers are established, limbs with digits appear, and external genitals begin to differentiate
embryo vs fetus
fetus is 9th week post fertilization until birth and embryo is pre 9th week
allometry meaning
the growth of structure, however, the growth is not relative to each other as the head develops much faster
fetal circulation 3 important structures
ductus venosus, forearm ovale, and ductus arteriosus
ductus venosus
allows the umbilical vein to bypass the hepatic portal circulation
forearm ovale
is a gap connecting the right and left atrium, allowing for the pulmonary circulation to be bypassed
ductus arteriosus
connects the pulmonary trunk to the descending aorta, allowing for the pulmonary circulation to be bypassed
why can the pulmonary circuit be bypassed?
because O2 is being supplied by the placenta
when can pregnancy hormonal changes be detected?
8 days post fertilization and peaks around 9 weeks
first pregnancy hormone that can be detected?
human chorionic gonadotropin
function of human chorionic gonadotropin
rescues the corpus luteum from degenerating until the placenta can form which is during the third or fourth month of pregnancy
significance of the corpus luteum for pregnancy
it supplies hormones to the endometrium, prepares the mammary glands, and creates other changes in the maternal body for pregnancy
relaxin functions
increases flexibility of the pubic symphysis and dilates the cervix during labour
what hormones does the placenta produce?
human chorionic somatomammotropin (the larger the placenta, the more produced) and corticotropin releasing hormone
function of human chorionic somatomammotropin
prepares the mammary glands for lactation, enhances growth by protein synthesis, and decreases glucose use and increase fatty acid use for ATP production
primary ATP source for the fetus
fatty acids
corticotropin releasing hormone
this establishes the timing of labour and helps to increase cortisol secretions
significance of cortical secretions
helps to prepare the baby’s lungs to prepare for breathing on its own, as well as triggering surfactant to develop
levels of hormones throughout pregnancy
estrogen and progesterone gradulary increase and there is a large spike of hCG at the beginning
4 hormones produced by the placenta
hCg, relaxin, hCs, and corticotropin releasing hormone
