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259 Cards in this Set

  • Front
  • Back
embryogenesis (organogenesis)
process of progressing from a single cell through the period of establishing organ pirmordia (first 8 weeks of development)
fetal period
from end of embryogenesis to birth, time when differentiation continues while the fetus grows and gains weight
study of the embryological origins and causes for birth defects, interest INC b/c of thaliodomide (caused birth defects in children (phocomelia) but administered as an antinauseant)
grafting experiments and signaling
showed examples of signaling between tissues
-ex: grafting the primitive node from its normal position to another showing that this structure could induce a second body axis
-ex: a piece of tissue from the zone of polarizing activity was grafted to the anterior border of a second limb, then digits on the host limb would be duplicated as the mirror image of each other
zone of polarizing activity (ZPA)
posterior signaling region
sonic hedgehog
signaling molecule in the fetus
regulation of gene expression
1. different genes may be transcribed
2. nuclear DNA transcribed from a gene may be selectively processed to regulate which RNAs reach the cytoplasm to become messenger RNAs
3. mRNAs may be selectively translated
4. proteins made from the mRNAs may be differentially modified
PAX 6 transcription factor
participates in pancreas, eye, and neural tube development, contains three separate enhancers, each of which regulates the gene’s expression in the appropriate tissue
splicing isoforms
proteins derived from the same gene, also called splice variants
when one group of cells or tissues cause another set of cells or tissues to change their fate, (inducer-produces signal and responder-receives signal)
capacity to respond to an induction signal, requires activation of the responding tissue by a competence factor
epithelial-mesenchymal interactions
inductive interaction that occurs between epithelial and mesenchymal cells
-ex: gut endoderm and surrounding mesenchyme to produce gut derived organs (liver and pancreas)
-ex: limb mesenchyme with overlying ectoderm to produce limb outgrowth and differentiation
paracrine interactions
proteins synthesized by one cell diffuse over short distances to interact with other cells
paracrine factors (or growth and differentiation factors (GDFs)
diffusable proteins responsible for paracrine siganlling, lots but grouped into four families (fibroblast growth factors, WNT, hedgehog, and transforming growth factor beta)
juxtacrine interactions
do not involve diffusible proteins when interacting with cells, works in three ways:
1. a protein on one cell surface interacts with a recptor on an adjacent cell in a process analogous to paracrine signaling (ex: Notch pathway)
2. ligands in the extracellular matrix secreted by one cell interact with their receptors on neighboring cells
3. there is direct transmission of signals from one cell to another by gap junctions
FGFs (fibroblast growth factors)
activate a collection of tyrosine rectport kinases called fibroblast growth factor receptors (FGFRs), these activate various signaling pathways, particularly important for angiogenesis, axon growth and mesoderm differentitation
hedgehog proteins
three (desert, Indian and sonic), receptor is Patched (binds to smoothened protein)
sonic hedgehog
involved in a number of developmental events including limb patterning, neural tube induction and patterning, somite differentiation, gut regionalization, and others
smoothened protein
transduces the hedgehog signal, inhibited by patched until the hedgehog protein binds to this receptor
WNT proteins
at least 15 different proteins, receptors are members of the frizzled family, involved in regulating limb patterning, midbrain development and some aspects of somite and urogenital differentiation among other actions
TGF-beta superfamily (transforming growth factor)
includes the transforming growth factor betas, bone morphogenetic proteins, the activin family, the Mullerian inhibiting factor and others, important for extracellular matrix formation and epithelial branching that occurs in lung, kidney and salivary gland development, bone formation, regulating cell division, cell death and cell migration
primordial germ cells (PGCs)
gametes derive from here, formed in the epiblast during the second week and that move to the wall of the yolk sac, migrate to gonads in fourth week
maturation/differentiation of PGCs, undergo a number of mitotic divisions, some continue dividing by mitosis but some arrest their cell division in prophase of meiosis 1 to form primary oocytes, by 7th month most have degenerated except for those near the surface, by birth none are left, are all primary ooctye
primary oocyte
individually surrounded by a layer of flat epithelial cells (follicular cells), forming a primordial follicle, oogonia arrested in meiosis 1, do not finish their first meiotic division before puberty is reached, thought to be around 600k-800k at birth, only about 500 ovulated
diplotene stage
resting stage during prophase that is characterized by a lacy network of chromatin
oocyte maturation inhibition (OMI)
produce the arrested diplotene stage by secreting a small peptide by follicular cells
stages of follicular growth
1. primary or preantral
2. secondary or antral
3. preovulatory (Graafian follicle)
primary follicle
primary oocyte is surrounded by granulosa cells (stratified epithelium that changed from flat follicular cells to cuboidal in shape)
theca folliculi
stromal cells that surround the granulose cells, organize into an inner theca interna and an outer thece externa
zona pellucida
a layer of glycoproteins on the surface of the oocyte secreted by the granulosa cells
spaces begin to appear between granulose cells, initially crescent shaped, then enlarges
secondary (vesicular) follicle
follicle with an antrum
Graafian follicle
a mature secondary follicle that has the potential for ovulation, large atrum
cumulus oophorus
mound of granulose cells that surround the oocyte after turning into a mature secondary follicle
atretic follicles
those follicles that begin to grow and develop but degenerate, only one follicle reaches full maturity
luteinizing hormone (LH) in oocyte formation
surges after maturation of secondary follicle, induces the preovulatory growth phase
preovulatory growth phase
secondary follicle (with a primary oocyte) enters completes meiosis I and forms a secondary oocyte and 1 polar body, cell then enters meiosis II but rests at metaphase II until 3 hours before ovulation, meiosis II is completed only if the secondary oocyte is fertilized, otherwise the cell degenerates 24 hours
perivitelline space
space where the 1st polar body is separated from the secondary oocyte and zona pellucida,
begins at puberty, transform spermatogonia into spermatozoa, regulated by LH (binds to Leydig cells and stinulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis)
sustentacular cells (Sertoli cells)
supporting cells that are derived from the surface epithelium of the gland, protect the germ cells, participate in their nutrition and assist in the release of mature spermatozoa
seminiferous tubules
sex cords mature into this when they acquire lumen, at the same time PGC give rise to spermatogonial stem cells
type A spermatogonia
initiation of spermatogenesis, arise from the spermatogonial stem cell population, undergo a limited number of mitotic division to form a clone of cells, have contact throughout their entire differentiation bec. cytokinesis is incomplete, only after mature spermatids are made do they lose cytoplasmic connections with each other to leave residual bodies
type B spermatogonia
arise from type A and give rise to primary spermatocytes through mitosis
primary spermatocytes
enter a prolonged prophase (22 days) then create secondary spermatocytes through meiosis 1
secondary spermatocytes
give rise to spermatids through meiosis 2
Follicle stimulating hormone (FSH)
stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins
LH role in spermatogenesis
regulates spermatogenesis, binds to receptors on Leydig cells and stimulates testosterone formation, testosterone binds to sertoli cells to promote spermatogenesis
series of changes resulting in the transformation of spermatids into spermatozoa, includes:
1. formation of the acrosom
2. condensation of the nucleus
3. formation of neck, middle piece and tail
4. shedding of most of the cytoplasm
time for spermatogonia to become spermatozoon
74 days, when fully formed enter seminiferous tubules, pushed towards the epididymis where they reach full motility
gonadotropoin-releasing hormones
produced by the hypothalamus, acts on cells of the anterior pituitary, which in turn secretes gonadotropins
follicle stimulating hormone (FSH)
a gonadotropin, stimulate and control cyclic changes in the ovary, stinulate 15 to 20 primary stage follicles to grow (of which only one matures), also stimulates maturation of follicular cells surrounding the oocyte, stimulate primary follicle to secondary follicle
luteinizing hormone (LH)
a gonadotropin, stimulates and controls cyclic changes in the ovary, elevates concentrations of maturation-promoting factor (which allows entrance into meiosis II), stimulates production of progesterone by follicular stromal cells and causes follicular rupture and ovulation
corpus atreticum
made when a follicle becomes atretic, oocyte and surrounding follicular cells degenerate and replaced by connective tissue
Growth differentiation factor 9 (GDF9)
member of the TGF-beta family, mediates proliferation of follicular cells
1. cause the uterine endometrium to enter proliferative phase
2. cause thinning of the cervical mucus to allow passage of sperm
3. stimulate the pituitary gland to secrete LH
LH surge
1. elevates conc. of maturation promoting factor (which causes oocytes to complete meiosis I and initiate meiosis II
2. stimulates production of progesterone by follicular stromal cells (luteinization)
3. causes follicular rupture and ovulation
4. INC collagenase activity resulting in digestion of collagen fibers surrounding the follicle
5. INC prostaglandin levels which causes local muscular contractions in the ovarian wall
an avascular spot that appears at the apex of the ovary
corona radiata
made from cumulus oophorus cells surrounding the zona pellucida after ovulation
corpus luteum
formed from lutean cells (which arise from theca interna cells and remaining granulose cells after ovulation), secrete progesterone, causes the uterine mucosa to enter progestational or secretory stage in preparation for implantation of the embryo
fimbriae of the uterine tube
sweep over the surface of the ovary, carries oocyte to the uterine tube
cilia in the uterine tube
propel the oocyte in the uterine tube to the uterine lumen in 3 to 4 days
corpus albicans
occurs if fertilization does not occur, fibrotic scar tissue from degenerated lutean cells of the corpus lutean, associated with a dec in progesterone production leading to menstrual bleeding
human chorionic gonadoctrophin (hCG)
prevents degeneration of corpus luteum if the oocyte is fertilized, secreted by the syncytiotrophoblast of the developing embryo
corpus luteum graviditatis
formed from corpus luteum after fertilization
ampullary region of the uterine tube
fertilization occurs here, widest part of the tube and is close to the ovary
corona radiate
composed of cumulus cells, first site of sperm penetration
capacitation of spermatozoon
a period of conditioning in the female reproductive tract, last 7 hours, entails epithelial interactions between the sperm and mucosal surface of the tube, a glycoprotein coat and seminal plasma proteins are removed from the acrosome, allows for passage through the corona cells
acrosome reaction of spermatocyte
occurs after binding to the zona pellucida, induced by zona proteins, release of enzymes needed to penetrate the zona pellucida
phases of fertilization
1. penetration of the corona radiate
2. penetration of the zona pellucida
3. fusion of the oocyte and sperm cell membranes
reaction of zona after sperm touches zona
contact results in release of lysosomal enzymes from cortical granules, causes a prevention in more sperm penetration and inactivates species specific receptor on the zona pelucida sites for spermatozoon
egg response after spermatozoon enters the oocyte
1. cortical and zona reactions
2. resumption of the second meiotic division
3. metabolic activation of the egg (also replication and mitosis of male and female pronuclei forming two cell stage of zygote)
timeline of two cell stage to morula
two cell stage-30 hours after fertilization
four cell stage-40 hours after fertilization
12 to 16 cell stage-3 days
morula-4 days
small cells formed by a series of mitotic divisions after the 2-cell stage
significance of the 8-cell stage
maximize contact with each other forming a compact ball of cells held together by tight junctions (compaction)
segregation of inner (rise to embryo proper) and outer cell mass (trophoblast) at 8 cell stage
16 cell stage, enters the uterine cavity and fluid begins to penetrate through the zona pellucida forming a cavity (blastocele)
embryo with a blastocele
cells of the inner cell mass of the blastomere turn into this
cells of the outer cell mass of the blastomere turn into this, flattened and form the epithelial wall of the blastocyst
implantation of the blastocyst
can occur once the zona pellucida degenerates, occurs on the 6th day when trophoblast cells penetrate the epithelial cells of the uterine mucosa, mediated by L-selectin on the trophoblast and carbohydrate receptors on the mucosa, furthered by integrins on the trophoblast and fibronectin (migration) and laminin (attachment) on the uterine epithelia
layers of the wall of the uterus
1. endometrium (mucosa lining the inside wall)
2. myometrium (thick layer of smooth muscle)
3. perimetrium (peritoneal covering lining the outside wall)
stages of the endometrium during menstrual cycle
1. follicular or proliferative phase
2. secretory or progestational phase
3. menstrual phase
proliferative phase of the menstrual cycle
begins at the end of the menstrual phase, under the influence of estrogen, parallels growth of the ovarian follicle, associated with the regeneration of glands and arteries following the menstrual phase
secretory phase of the menstrual cycle
begins approximately 2 to 3 days after ovulation, responds to progesterone produced by the corpus luteum, occurs at time of implantation
menstrual phase of the menstrual cycle
occurs if fertilization does not occur, shedding of the endometrium, if fertilization does occur then the endometrium assists in implantation and contributes to the placenta, bleed out the spongy and compact layer, keep basal layer
three layers of the endometrium following implantation
superficial compact layer, intermediate spongy layer and thin basal layer
trophoblast at 8th day
differentiates into two layers, the cytotrophoblast (inner layer of mononucleated cells) and the syncytiotrophoblast (outer multinucleated zone without distinct cell boundaries)
have the ability to undergo mitosis (whereas the syncytiotrophoblast does not), cells divide and migrate into the syncytiotrophoblast
embryoblast at 8th day
differentiates into two layers, hypoblast layer (layer of small cuboidal cells adjacent to the blastocyst cavity) and the epiblast layer (layer of high columnar cells adjacent to the amniotic cavity
bilaminar disk
formed by the epiblast and hypoblast
amniotic cavity
small cavity within the epiblast
epiblast cells adjacent to the cytotrophoblast, secrete amniotic fluid into the amniotic cavity
fibrin coagulum
close the penetration defct in the surface epithelium of the blastocyst
lacunar stage of the 9th day
vacuoles in the syncytium fuse and form large lacunae during this stage
exocoelomic (Heuser) membrane
hypoblast cells that are flattened form this thin membrane, lines the inner surface of the cytotrophoblast, along with the hypoblast forms the lining of the primitive yolk sac
blastocyst at 11th-12th day
completely embedded in the endometrial stroma, produces a protrusion into the lumen of the uterus, trophoblast has lacunar spaces in the syncytiotrophoblast forming a communication network
maternal capillaries, become continuous with the syncytiotrophoblast lacunae and maternal blood enters the lacunar system
uteroplacental circulation
established by the continual erosion of maternal sinusoids
extraembryonic mesoderm
loose connective tissue found between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity, eventually covers the amniotic cavity as well
extraembryonic coelom (chorionic cavity)
large cavities found within the extraembryonic mesoderm, surrounds the primitive yolk sac and amniotic cavity and enlarges separating the trophoblast from the embryoblast except at the connecting stalk
extraembryonic somatopleuric mesoderm
the extraembryonic mesoderm lining the cytotrophoblast and amnion
extraembryonic splanchnopleuric mesoderm
the lining covering the yolk sac
decidua reaction
endometrium at 11th-12th day, becomes polyhedral and loaded with glycogen and lipids, intercellular spaces are filled with extravasate, occur throughout the endometrium
primary villi in the trophoblast at the 13th day
cytrotrophoblast cells that proliferate and penetrate into the syncytiotrophoblast
secondary (or definitive) yolk sac
much smaller than the original primitive yolk sac, cavity formed within the exocoelomic cavity by hypoblast cells
chorionic plate
the extraembryonic mesoderm lining the inside of the cytotrophoblast
umbilical cord
develops from the connecting stalk when infiltrated with blood vessels
exocoelomic cysts
occur when the primitive yolk sac pinch off and form these cavities
week of twos
2nd week of development, trophoblast to two layers, embyroblast to two layers, extraembryonic mesoderm splits into two layers, two cavities
the process that establishes the three germ layers
primitive streak
beginning of gastrulation, forms at the surface of the epiblast
primitive node
found on the cephalic end of the streak, consists of a slightly elevated area surrounding the small primitive pit
invagination of epiblast cells
epiblast cells slip through the primitive streak
fibroblast growth factor 8 (FGF8)
control invagination of epiblast cells, secreted by streak cells, controls movement by down regulating E cadherin (which would normally bind epiblast together), regulates brahyury expression
brachyury (T)
1. responsible for cell specification of epiblast cells into mesoderm, specifically in dorsal mesoderm formation middle and caudal regions, absence leads to shortening of the embryonic axis
2. essential in the expression of Nodal, Lefty-1 and Lefty-2
created from epiblast cells that displace/attach to the hypoblast, may also come from extraembryonic mesoderm as well (debated)
mesoderm (intraembryonic)
created from epiblast cells that lie between the endoderm cells and epiblast
created from the remaining epiblast cells that do not migrate through the primitive streak
prechordal plate
forms between the tip of the notochord and the buccopharyngeal membrane, derived from some of the first cells that migrate through the node in a cephalic direction, important for induction of the forebrain
buccopharyngeal membrane
at the cranial/cephalic end, consists of a small region of tightly adherent ectoderm and endoderm with no mesoderm, represent the future opening of the oral cavity
prenotochordal cells
cells that invaginate in the primitive pit and move toward the cephalic/cranial end of the embryo until they reach the prechordal plate
notochordal plate
midline of the embryo consisting of two cell layers (prenotochordal cells and hypoblast), eventually forms the notochord when it detaches from the endoderm
definitive notochord
formed from notochordal cells that proliferate and detach from the endoderm, a solid cord of cells, serves as the basis for the axial skeleton, cranial end forms first
neuroenteric canal
temporarily connects the amniotic and yolk sac cavities, found where primitive pit forms an indentation in the epiblast
cloacal membrane
found at the caudal/tail end of the embryo, similar in structure to the buccopharyngeal membrane, consists of ectoderm and endoderm cells w/ no intervening mesoderm
allantoenteric diverticulum (allantois)
appears around the 16th day of development, a small diverticulum from the posterior wall of the yolk sac, appears when the cloacal membrane appears, in humans is rudimentary but may be involved in abnormalities of bladder development, forms part of the umbilical cord
establishment of body axis
occurs before and during gastrulation
anterior visceral endoderm (AVE)
found at the anterior (cranial end), expresses genes essential for head formation and anteroposterior axis
transcription factors OTX2, LIM2 and HESX1 and secreted Cerberus
genes essential for head formation, establish cranial end before gastrulation
member of the transforming growth factor-beta family, responsible for initiating and maintaining the primitive streak
bone morphogenic protein 4 (BMP4)
secreted throughout the embryonic disc, with the help of FGF, mesoderm is ventralized to form kidneys, blood and body wall mesoderm
chordin (activated by goosecoid), noggin and follistatin
antagonize BMP4 and prevent all mesoderm from being ventralized, the cranial mesoderm is dorsalized into notochord, somites and somitomeres
maintains the node and later induces regional specificity in the forebrain and midbrain areas, without this, embryos fail to gastrulate properly
fibroblast growth factor 8
secreted by cells in the node when the primitive streak appears, induces expression of Nodal on the left side only, with Lefty-2, upregulates PITX2
a homeobox containing transcription factor responsible for establishing left sidedness
expressed on the left side of the floor plate of the neural tube, may act as a barrier to prevent left-sided signals from crossing over
Sonic hedgehog (SHH)
may also act like lefty-1 and prevent left-sided genes from crossing over
Snail transcription factor
restricted to the right lateral plate mesoderm and regulates effector genes responsible for establishing the right side
importance of cilia on cells in the node
affects left-right development, important in creating a beating motion that creates a gradient of Nodal on the left, abnormalities may lead to laterality defects
fate map of epiblast
1. cranialmost-notochord
2. more posteriorly through the node and cranialmost of the streak-paraxial mesoderm
3. next portion of the streak-intermediate mesoderm
4. more caudal part-lateral plate mesoderm
5. most caudal part-extraembryonic mesoderm
primitive streak at 4th week
regresses, rapidly shrinks and disappears
differentiation of germ layers
at the cephalic end starts during the middle of the third week, at the caudal end starts at the end of the fourth week, leads to cephalocaudal development
secondary villus
occurs when mesoderm penetrates a primary villus
villus capillary system
formed from mesodermal cells in secondary villi that differentiate into blood cells and small blood vessels, forms tertiary villus (definitive placental villus)
tertiary villus
make contact with capillaries developing in mesoderm, establish contact with the intraembryonic circulatory system connecting the placenta and the embryo
start of the heart beat
fourth week
outer cytotrophoblast cells
cytotrophoblast cells that have penetrated the synctium, surrounds the trophoblast entirely
stem (anchoring) villi
extend from the choriaonic plate to the decidua basalis (where the placenta forms)
free (terminal) villi
branch from the sides of stem villi
umbilical cord
connection between placent and embryo
embryonic period (organogenesis)
from 3rd to 8th week, time when the germ layers give rise to a number of specific tissues and organs
neural plate
induced by the notochord and prechordal mesoderm, make up the neuroectoderm
caused by induction of the neuroectoderm
FGF and BMP4 role in neurulation
causes induction of the neural plate, FGF promotes neural pathway, BMP4 causes the ectoderm to become the epidermis and mesoderm to form intermediate and lateral plate mesoderm
neutralization of ectoderm
caused by noggin, chordin and follistatin by inhibiting BMP4 after forming epidermis, cause mesoderm to become notochord and paraxial mesoderm
WNT3a and FGF role in neurulation
responsible for caudal neural plate structures (hindbrain and spinal cord)
retinoic acid
plays a role in organizing the cranial-to-caudal axis, regulates homeobox genes
neural folds
found at the end of the third week, elevations of the neural plate
neural groove
the depressed midregion of the neural plate
neural tube
formed from the folding and fusion of the neural folds, starts at the cervical region (5th somite) and continues caudally and cephalically
cranial and caudal neuropores
communication point for caudal and cephalic end with the amniotic cavity, cranial closure occurs at about day 25 (18-20 somite) while the posterior neuropore closes at day 27 (25 somite), marks the completion of neurulation
spinal cord
formed at the end of neurulation, a closed tubular structure with a narrow caudal portion
brain vesicles
dilations found at the broader cephalic portion
neural crest
cells found at the lateral border of the neuroectoderm (neural folds), enter the mesoderm just before the neuropores close
pathways available for neural crest cells from the trunk
1. a dorsal pathway through the dermis, enter the ectoderm to form melanocytes
2. a ventral pathway through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells and cells of the adrenal medulla
pathways available for neural crest cells from the cranial neural folds
1. contribute to the craniofacial skeleton (as well as neurons for cranial ganglia)
2. glial cells
3. melanocytes…table on pg 72, table 6.1
BMP and FGFs in neural crest cells
initiates induction of neural crest cells
otic placodes
ectodermal thickening found when the neural tube closes, during further development, these invaginate and form the otic vesicles important for hearing and maintenance of equilibrium
lens placodes
ectodermal thickening found when the neural tube closes, invaginate and during the fifth week form the lenses of the eyes
paraxial mesoderm
thickened plate of tissue found at the midline
lateral plate
mesoderm layer that remains thin and is more lateral compared to the paraxial mesoderm, divided into two layers
1. a layer continuous with mesoderm covering the amnion called the somatic or parietal mesoderm layer
2. a layer continuous with mesoderm covering the yolk sac called the splanchnic or visceral mesoderm layer
intraembryonic cavity
cavity lined by the parietal and visceral mesoderm layer, this cavity is continuous with the extraembryonic cavity
intermediate mesoderm
connects paraxial and lateral plate mesoderm
segments of paraxial mesoderm beginning at the third week, first appear in the cephalic region then continues on in a cephalocaudal direction
formation of somitomeres and segmentations of the neural plate in the cephalic region, contribute to the mesenchyme in the head
organization of somitomeres in the occipital region caudally, first appears at day 20, new ones appear in a craniocaudal direction (at about 3 pairs/day), at the end of the 5th week have about 42 to 44 pairs, precursors to the ribs, can count somites to determine age of embryo
segmentation clock
established by cyclic genes, determines the formation of segmented somites
Notch and WNT as cyclic genes in somite production
are expressed in an oscillating pattern in presomitic mesoderm, periodically activate segment-patterning genes that regulate somite formation
retinoic acid and FGF8 on somite production
RA upregulates patterning genes, FGF8 represses RA activity and inhibits maturation of presomitic mesoderm into somites
cells of the ventral and medial walls of the somite that surround the notochord and form mesenchyme (forms tendon and bone component)
dorsolateral portion of the somite
migrate as precursors of the limb and body wall musculature
dorsomedial portion of the somite
proliferate and migrate down the ventral side of the remaining dorsal epithelium to form the myotome (muscles of the back)
remaining dorsal portion of the somite
form the dermatome (dermis and subQ tissue of the skin)
consists of the dermatom, myotome and sclerotome
noggin and sonic hedgehog and somite differentiation
produced by the notochord and neural tube, induce the ventromedial portion of the somite to become sclerotome
PAX1 and sclerotome
expressed by sclerotome cells, a transcription factor, initiates the cascade of cartilage and bone forming genes for vertebral formation
PAX3 and dermomyotome
initiates dermomyotome region of the somite
intermediate mesoderm
differentiates into urogenital structures
segmental cell clusters in the cervical and upper thoracic region, from intermediate mesoderm
nephrogenic cord
an unsegmented mass of tissue more caudal, from intermediate mesoderm
parietal mesoderm
line the intraembyonic cavity, form the lateral and ventral body wall
visceral mesoderm
surrounds organs, forms the wall of the gut
mesothelial and serous membranes
formed by the parietal mesoderm surrounding the intraembryonic cavity, will line the periotoneal, pleural, and pericardial cavity and secrete serous fluid
vessels arise from blood islands, first blood islands arise from mesoderm surrounding the wall of the yolk sac at 3 weeks
entails sprouting from existing vessels
precursors of blood cell and vessel formation, form hematopoeiteic stem cells if found in center of blood islands, forms angioblasts if found peripherally, induced by vascular endothelial growth factor (VEGF) which is secreted by surrounding mesoderm cells
precursors of blood vessels, induced to form endothelial cells by VEGF
PROX1 and vessel differentiation
the master gene for lymphatic vessel differentiation, vessel outgrowth is patterned
aorta-gonad-mesonephros region (AGM)
mesoderm surrounding the aorta that give rise to the definitive heamtopoietic stem cells
cephalocaudal folding
embryonic disc begins to fold cephalocaudally, more endoderm enters the body proper
formed by the endoderm at the anterior part
formed by the endoderm at the tail region
found between the foregut and hindgut, communicates with the yolk sac by way of the vitelline duct
buccopharyngeal membrane and foregut
foregut is temporarily covered by the buccopharyngeal membrane, by the 4th week, the membrane ruptures, establishing an open connection between the amniotic cavity and the primitive gut
cloacal membrane and hindgut
hindgut is termporarily covered by the cloacal membrane, membrane breaks down at week 7 and creates the anus
partial incorporation of the allantois into the body of the embryo
yolk sac
is vestigial in humans, probably has a nutritive role only in early stages of development
endodermal germ layer
gives rise to the epithelial lining of the primitive gut and the intraembryonic portions of the allantois and vitelline duct, eventually forms the epithelial lining of the respiratory tract, the parenchyma of the thyroid, parathyraoids, liver and pancreas, the reticular stroma of the tonsils and thymus, the epithelial lignin gof the urinary bladder and urethra, and the epithelial lining of the tympanic cavity and auditory tube
homeobox genes
have a homeobox (a DNA binding motif), code fro transcription factors that activate cascades of genes regulating phenomena such as segmentation and axis formation
homeotic clusters
group of hoemobox genes
in drosophila, important in specifying the craniocaudal axis, contain the Antennapedia and Bithorax classes (which are organized on a single chromosome as a functional unit), genes specifying more cranial structures lie at the 3’ end of DNA and are expressed first with genes controlling posterior development expressed sequentially and lying INC toward the 5’ end
conserved forms of Hom-C in humans, lie on separate chromosomes
paralogous groups
genes with the same number but belong to different clusters, play a role in cranial-to-caudal patterning of the derivatives of all three germ layers
crown-rumb length (CRL)
used to indicate the age of the embryo during the second month of development (it is difficult to count somites), measurement from the vertex of the skull to the midpoint between the apices of the buttocks
appearance of the embryo during the second month
INC head size, formation of limbs, face, ears, nose and eyes
crown-heel length (CHL)
measurement from the vertex of the skull to the heel (standing height), used to determine age of the fetus
length of pregnancy
38 weeks after fertilization, or 280 days after the LNMP
head size at different months
half of the CRL at 3rd month, 1/3 of CHL at 5th month, ¼ of CHL at birth
physical characteristics at the third month
face beomces more human like, eyes, move to the ventral aspect of the face, ears come to lie close to their final position, limbs reach their relative length in comparison with the rest of the body, presence of primary ossification centers, external genitalia develop (can tell sex of the baby), muscular activity
physical characteristics at the 4th and 5th month
rapid lengthening of the fetus, less than 500 g at end of 5th month, covered with lanugo hair (fine hair), eyebrows and head hair are also visible, movements of the fetus can be felt by the mother
physical characteristics during the second half of intrauterine life
weight INC considerably (esp during the last 2.5 months), skin is reddish and wrinkly during the 6th month, at 7 months 1100g,
vernix caseosa
a white, fatty substance that covers the skin, composed of secretory products from sebaceous glands
ninth month and size of head
largest circumference of the body
characteristics at birth
3000-4000 g, CRL of 36 cm, and CHL of 50 cm
biparietal diameter (BPD)
measurements commonly used in the 16th to 30th weeks
spiral arteries
maternal blood is delivered to the placenta through these, found in the uterus
endovascular invasion
occurs by cytotrophoblast cells, causes erosion of the spiral vessels to release blood into the intervillous spaces, cytotrophoblast cells undergo an epithelial to endothelial transition, transform spiral arteries into large-diameter, low-resistance vessels that can provide INC quantities of maternal blood to intervillous spaces
syncytial knots
pieces of syncytium that break off and enter the maternal circulation and usually degenerate without causing any symptoms
chorion frondosum
bushy chorion, villi found on the embryonic pole that grow and expand
chorion laeve
smooth, degenerated villi on the abembryonic pole
the functional layer of the endometrium, shed during parturition
decidua basalis
the decidua over the chorion frondosum, consists of a compact layer of large cells (decidual cells), has abundant amounts of lipids and glycogen
decidual layer
the layer of the decidua basalis that has lots of lipids and glycogen, tightly connected to the chorion
deciduas capsularis
decidua over the abembryonic pole
decidua parietalis
the uterine wall, fuses with the chorion leave obliterating the uterine lumen
compsed of the chorion frondosum and the decidua basalis
amnio-chorionic membrane
fusion of the chorion with the amnion, obliterates the chorionic cavity, this membrane ruptures when the water breaks, third month
placenta at four months
composed of two parts
1. a fetal portion, formed by the chorion frondosum, bordered by the chorionic plate
2. a maternal portion, formed by the decidua basalis, bordered by the decidual plate
junctional zone
trophoblast and decidual cells intermingle here
villous tree
fetal, grows into the intervillous blood lakes (maternal)
decidual septa
formed from the decidua esp. during the 4th and 5th months, project into intervillous spaces but do not reach the chorionic plate, core of maternal tissue but covered on the surface by syncytium
compartments of the placenta that result from the formation of septum, receive blood from 80 to 100 spiral areries
full-term placenta
15 to 25 cm, 500 to 600 g, torn from the uterine wall and birth and expelled about 30 mins after childbirth
endometrial veins
drains blood from the intervillous lakes back into the maternal circulation
placental membrane (placental barrier)
separates maternal and fetal blood, initially composed of 4 layers
1. the endothelial lining of fetal vessels
2. the connective tissue in the villus core
3. the cytotrophoblastic layer
4. the syncytium
from the fourth month on, the placental membrane thins, INC rate of exchange
functions of the placenta
1. exchange of metabolic and gaseous products between maternal and fetal bloodstreams
2. production of hormones
immunological competence
begins to develop late in the first trimester, fetus makes all of the components of complement, immunoglobins consist almost entirely of maternal immunoglobin G (IgG)
transported from mother to fetus at 14 weeks, fetus gains passive immunity against various infectious diseases, newborns do make some, but adult levels are not attained until 3
hormones of the placenta
1. progesterone-enough at 4th month to maintain pregnancy without corpus luteum
2. estrogenic hormones-predominantly estriol, max level reached at end of pregnancy, stimulate uterine growth and development of the mammary glands
3. somatomammotrophic-a growth hormone like substance, gives the fetus priority on maternal blood flucose and makes the mother somewhat dabetogenic, also promotes breast development for milk production
primitive umbilical ring
oval line of reflection between the amnion and embryonic ectoderm, structures that pass through the ring at the fifth week of development include:
1. the connecting stalk, containing the allantois and the umbilical vessels
2. the yolk stalk (vitelline duct)
3. canal connecting the intraembryonic and extraembryonic cavities
primitive umbilical cord
rapid growth of the amniotic cavity causes an envelopment of the connecting and yolk sac stalks giving rise to this, does contain some intestinal loops and the remnant of the allantois, eventually when the allantois and vitelline duct and vessels are obliterated all that is left in the cord are umbilical vessels and Wharton’s jelly (protective layer for blood vessels)
amniotic fluid
derived in part by amniotic cells but primarily from maternal blood, fluid amount increases with age, acts as a protective cushion, absorbs jolts, prevents adherence of the embryo to the amnion and allows for fetal movements, replaced every 3 hours
dizygotic twins (fraternal)
dizygotic twins, result from simultaneous shedding of two oocytes and fertilization by different spermatozoa, no resemblance except for that associated with bros and sis., implant individually, usually develops its own placenta, amnion, and chorionic sac, sometimes placentas and even chorionic sacs may fuse
monozygotic twins (identical)
develops from a single fertilized ovum, result from splitting of the zygote at various stages of development, can occur:
1. as early as the two cell stage, blastocysts implant separately and each embryo has its own placenta and chorionic sac
2. usually occurs at the early blastocyst stage, inner cell mass splits into two separate groups of cells, have a common placenta and a common chorionic cavity, but separate amniotic cavities
3. separate at the bilaminar germ disc stage, just before the appearance of the primitive streak, two partners with a single placenta and a common chorionic and amniotic sac
partuition (birth)
uterine myometrium does not respond to partuition during the first 34-38 weeks, during the last 2 to 4 weeks, tissue changes in preparation for the onset of labor, leads to thickening of the myometrium and a softening and thinning of the lower region and cervix
1. effacement (thinning and shortening) and dilation of the cervix
2. delivery of the fetus
3. delivery of the placenta and fetal membranes
stage 1 of labor
produced by uterine contraction shtat force the amniotic sac against the cervical canal like a wedge
stage 2 of labor
assisted by uterine contractions, also a force that is provided by INC intra-abdominal pressure from contraction of abdominal muscles
stage 3 of labor
requires uterine contractions and is aided by increasing intra-abdominal pressure