Embryonic Period Flashcards
Embronic Period
- critical period of rapid growth
- primordia of all the organs and organ systems appear from the 3 germ layers: organogenesis
- sensitive to substances that induce congenital malformations: teratogens
Duration of period
3rd-8th week
Where does the fusion of the neural fold begin?
Cervical region (5th somite) and proceeds cranially and caudally.
Grastrulation
occurs during the 3rd week and includes neurulation
Neurulation
neural plate and beginning of neural tube formation
Where does folding occur?
cranial and caudal ends (head and tail fold) and sides (lateral folds)
What embryonic layers form the oropharyngeal and cloacal membrane?
ectoderm and endoderm
What region is the organizer of the body axes?
Node in the dorsal region
Nodal function
initiates and maintains primitive streak.. a TGFB famili
ACE
Anterior visceral endoderm: establishes cranial end before gastrulation
Important TFs for head formation
secreted by ACE: OTX2, Lim1, HESX1 and cerberus… inhivit nodal activity in cranial end of embryo
BMP4
Once streak is formed, BMP4 and FGF ventralize the mesoderm to contribute to kidneys, blood, and body wall of mesoderm
Goosecoid: what it activates and effects
activates chordin, nogging, and follistatin to inhibit BMP expression on the dorsal mesoderm in the cranial region… contributes to regulation of head formation
Brachyury: regulation and location of expression
gene that regulates dorsal mesoderm in middle and caudal regions. Expressed in the node, notochordal precursol cells and notochord
Where to the TFs of brachyury bind?
bind to a T box in the DNA
What disease is caused by the absence of Brachyury?
sirenomelia or caudal dusgenesis
What genes regulate the cranio-caudal axis?
Homeobox genes
Grastrulation associated defects?
conjoined twins by over-expression of goosecoid or sirenomelia by absence of Brachyury
What disease is cause d be the over-expression of Goosecoid?
conjoined twins
What genes regulate the formation of the left side?
Brachyury in the notochord is essential for expression of Nodal, Lefty-1, and Lefty-2
What genes regulate the formation of the right side?
SHH (sonic hedgehog) by repressing expression of left side genes and snail (TF essential to establish the right side)
Surface ectoderm derivatives?
-Epidermis and its derivatives: nails, hair, lens, epithilium of sweat glands, sebaceous glands, and mammary glans. -Sensory placodes (auditory and nasal placodes) - Terminal portion of the anal canal, oral cavity and its derivatives: parotid glands, adenohypophysis, and enamel of teeth. -Neural Tube -Neural Crest
What are derivatives of the neural tube?
-nervous tissue of the brain (including macroglia) -Spinal cord -Pineal Gland -Retina and optic nerve -posterior part of pituitary gland
What are derivatives of the neural crest?
-PNS (including ganglia and schwann cells) - Melanocytes -Dental papilla -Meninges - Mesenchyme and visceral skeleton of head and neck - Chromaffin cells of the adrenal medulla - Parafollicular cells of thyroid gland
The mesodermal germ layer gives rives rise to what three layers?
Paraxial Mesoderm, Intermediate mesorderm, amd lateral plate mesoderm
Paraxial mesoderm gives rise to… when and where
somites by the end of the 3rd week.. first appear in the cephalic (occipital) region, then cephalocaudally -3 pairs of somites/day until 42-44 appear in the 5th week.
What do somites give rise to?
the axial skeleton: 1st occipital and last five to seven cocygeal somites later disappear
Sclerotome
segmented somites that give rise to tendon cartiladge of bone component and vertebral column
Myotome
segmented somite; limb precursors and muscles of the back
Dermatome
segmented somites; dermis and subcutaneous tissue of the skin
Intermediate mesoderm give rise to… when
Urinary system and gonads…day 21
Lateral plate mesoderm can be divided into
Parietal mesoderm layer and visceral mesoderm layer
Parietal mesoderm + ectoderm:
somatopleure
Visceral mesoderm + endoderm:
splanchopeure
Parietal mesoderm gives rise to…
a serious of membranes lining the: - thoracic cavity (parietal pleura) -covering of the heart (pericardium) - peritoneal cavity (peritoneum)
Visceral layer gives rise to…
a serious of membranes lining the: -organs of the abdominal cavity
What are other derivatives of the lateral plate mesoderm?
-primordial heart -blood and lymphatic cells -spleen -adrenal cortex -connective tissue and muscle of viscera
Vasculogenesis
vessels arrive from blood islands (mesoderm of yolk sac and lateral plate mesoderm)
Angiogenesis
new vessels sprout from existing one
What gives rise to the cardiogenic area?
Heart primorium
What molecule regulates blood vessel formation? function in each pathway
VEGF: blood vessel formation PDGF and TGFB: maturation and modeling of blood vessels
VEGF and vasculogenesis
-FGF stimulates VEGF secretion -Hemagioblasts are formed: blood cell and blood vessels precursors -tube formation with angioblasts (blood vessel precursors) endothelial cells) and hematopoietic stem cells (blood cells precursors
VEGF and angiogenesis
VEGF stimulates proliferation of endothelial cells at point where new vessels will sprout
what can arise from abnormal vessel growth?
capillary hemangiomas: - most common tumor of infancy -associated with craniofacial structures -might be associated with high levels of IGF-1 -most disappear or treated with laser and steroid
What organs do hematopoietic stem cells colonize? where do they arise and when do they colonize?
they arise from mesoderm surroiunding the aorta colonize the: -liver 9wks -spleen and thymus: 12wks - bone marrow 28wks
Primordial cardiovascuular system at the end of the 3rd wk
the heart tubes have fused to form a tubular heart that is joind to veseels in the embryo, yolk sac,connecting stalk, and chorion -Precardial coelom -Endocardial heart tube
Endodermal derivatives
GI tract epithilium, liver, pancreas, urinary bladder, and urachus, allantois, cloaca, hindgut, gallbladder, pharyngeal pouches, and lung bud
What presents in a 7-somite embryo?
embryonic disk bulges into the amniotic cavity, heand and tail folds, and precardial cavity exists
When and where does the bucopharyngeal membrane rupture?
4th wk: leaves open connection between the amniotic cavity and the primitive gut… in foregut
When and where does the cloacal membrane rupture?
7th wk: opening for the anus… in the hindgut
How do the midgut and yolk sac communicate temporarily? Which one is obliterated after and when?
vitelline duct, the vitelline duct is obliterated… by 2mo. the yolk sac is redundat and it shrivels away
When do the invagination of the primitive streak stop?
4th wk, then it shrivels and disappears
What structures are present in the 4th week?
Neural tube, otic pit (primordium of ear), lens placode (primordium of lens), uppder limb bud, heart prominence, forebrain prominence, and caudal eminence
What structures are present in the 5th week?
Cervical sinus, and mesonephric ridge (future site of mesonephric kidneys)… minor body changes, growth of head (towards the hear prominence), cervical sinus is visible
What structures are present in the 6th week?
Digital rays of hand plate and auricular hillocks forming auricle of external ear
What structures are present in the 7th week?
notches between digital rays -reduction of communication between the yolk sac and primordial gut -umbilical herniation where intestines enter the extraembryonic coelom
What structures are present in the 8th week?
-tail-like caudal eminecence is present at the beginning but then disappears -scalp vascular plecus (band around head) -digist completely separated -purseposeful limb movement: ossification occurs in the femur -distinct human characteristics but still disproportion between head and trunk sexless appearance
How can the embryonic age be estimated?
-Greatest length (GL): 3rd and 4th wks, embryos are straight -Crown-Rump-Length (CRL): older embryos, curved embryos -Crown-Heel-Length (CHL): 8th week embryos
Carnegie Stage
criteria for estimating development stages in human embryos
What is used to determine stage of pregnancy?
chorionic cavity (gestational sac)
CRL 25mm
7-8 wks has chrion, amnion and yolk sack
CRL 4.8mm
4.5 wk embryo: chorion cavity and yolk sack
9wk fetus
amniotic fluid, placenta, and uterin wall can be seen in ultrasound
Neurulation steps and when
Neural fold appears, neural crests go up beacuse of it, neural fold aproach each other and fuse forming the neural tube (22 days)
Where does the neural fold fusion begin?
in the cervical region (5th somite) and proceeds cranially and caudally
Why does folding of the embryo occur and where?
it occurs from rapid growth at the site of the future brain and spinal cord
Folding occurs at:
- cranial and caudal ends
- sides (lateral folds)
- constriction at the embryo-yolk sac junction
How ar cranial and caudal regions produced?
folding of the ends of the embryo ventrally produces head and tail folds
