Embryology Flashcards
what process characterizes the transition from morula to blasocyst
water movement into the marula (ie cavitation) transforms the embryo into a blastocyte
steps in fertilization
what blocks polyspermy
cortical granules released from the egg
blastomere vs blastocysts
blastomere is just another word for the cells of the developing embryo –> it takes a different name because the cells are totipotent (each one can form a complete embryo by itself)
Blastocyst –> what used to be the morula is now fluid filled and considered to be distinguished by having 2 zones: trophoblast (future placenta) and embyroblast
T/F: all germ layers derive from the epiblast
TRUE
when is the developing embryo most sensitive to teratogens
weeks 3-8
what is this birth defect
sacrococcygeal teratoma
it is comon and consists of all tisue types because it developed from pluripotent stem cells
what is this birth defect
Sirenomelia (mn: siren songs of mermaids)
aka caudal dysgenesis
caused by insuffficient mesoderm
what is situs inversus?
a birth defects caused by dysfunction of the cilia around primitive node and there is a complete transposition of L/R axis…
serotonin (5HT) significant in determining the assymetry of organs following tthis and can cause comlete switch of viscera (including heart) in the thorax and abdomen.
what is the likely diagnosis?
fetal alcohol syndrome
B - anencephaly
answer: B –> trophoblast
what is the role of AER (apical epidermal ridges) in development of limbs?
forms a thickening at the distal end of lumb buds. Produces fibroblast growth factor (FGF) which interacts with underlying mesoderm to promote limb outgrowth.
what are the possible complications of osteopetrosis
anemia, hepatosplenomegaly, immunodificencies, cranial neuropathies
what are the known teratogens to cause limb and digit malformations
- drugs
- valproate
- phentoin
- warfarin
- toxins: cocaine, alcohol
- maternal conditions
- gestational diabetes
- varicella zoster
What muscle group derives from the epimere?
intrinsic muscles of the back
(all others derive from the hypomere)
what is the condition?
chondroplasia (or pseudochondroplasia) activating mutation in FGFR3 (fibroblast growth factor) that impaired proliferation of cartilage in the growth plate leading to shorter long bones
What is the first step in endochondral ossification?
artery invades the middle of cartilage
What condition arises due to excessive growth hormone release after the growth plates have closed?
acromegaly
T/F: only myotomes derive from mesoderm
FALSe
All bones of the upper limb form from lateral plate
mesoderm that condenses along the central axis to
form the vasculature and skeletal components
what are the only excepts to the rule that all muscles derive from mesoderm
Sonic Hedgehog Gene
Where is it produced?
What axis does it pattern?
Mutations lead to
A/W
SHH –> responsible for making a protein called Sonic Hedgehog. This protein functions as a chemical signal that is essential for embryonic development of the forebrain (aka prosencephalon) and eyes (Separates eyes into 2)
mn: S for Sonic and Separation into 2
Mutations –> holoprosencephaly
commonest etiology: trisomy 13 (aka Patau syndrome)
Wnt 7 gene
Where is it produced?
What axis does it pattern?
Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb)
Dorsal Ventral Axis (i.e. it’s responsible for distally extending limbs in the right direction)
mn: 7 year olds “wanna be taller”
Homeobox (Hox) Genes
What does it do?
Mutations result in
Involved in segmental organization of embryo in craniocaudal direction
makes proteins called DNA binding transcription regulators
Hox mutations –> appendages in wrong location
HOX-D13 mutation causes polydactyly and syndactyly
teratogen that can mess w/ HOX gene = isotretinoin (excessive vit A)
FGF Gene
Where is it produced?
What does it do?
A/W?
- fibroblast growth factor
- Produced at apical ectodermal ridge
- Stimulates mitosis of underlying mesoderm, providing for lengthening limbs (mn: Fetus Growing Fingers)
- a/w achondroplasia/dwarfism
Week 2
“2 weeks = 2 layers”
Bilaminar disc with epiblast and hypoblast
N.B the hypoblast will eventually disappear
Week 3
3 weeks = 3 layers
bilaminar turns into Trilaminar disc (From dorsal to ventral, the three germ layers are ectoderm, mesoderm, and endoderm.) –> called gastrulation
- Primitive streak, notochord, mesoderm and its organization, and neural plate begins to form. somites begin to form
Week 3 - week 8
By week 4
Danger?
Embryonic Period, (somites form from mesoderm)
Organogenesis occuring
Extremely susceptible to teratogens
day 22–> neural tube formed
Day 0
Fertilization by sperm forms zygote initiating embryogenesis
Week 1
things that form during week one:
- Morula forms
- blastocyst /implantatoin of blasocyst
- trophoblast–> becomes placenta and fetal membranes –> secretes HcG
N.B. A morula is distinct from a blastocyst in that a morula (3–4 days after fertilization) is a mass of 16 totipotent cells in a spherical shape whereas a blastocyst (4–5 days after fertilization) has a cavity inside the zona pellucida along with an inner cell mass
Weeks 8-9
Start of fetal period
Fetal movement and fetus looks like a baby
Week 10
Genitalia have male/female characteristics
Gastrulation
What is established?
Starts with…
Process that forms the trilaminar disc
Establishes ectoderm, endoderm and mesoderm
Starts with epiblast invaginating to form primitive streak
What comes from Surface Ectoderm?
Adenohypophysis (Ant Pituitary from Rathke’s Pouch), Lens, Epithelial lining of oral cavity, Sensory organ of ear, Anal canal below pectinate line, Parotid, Sweat, and Mammary glands
Week 4
- “Four” –> “folding” of trilaminar disc (cranial to caudal as well as lateral folding)
- Neural tube formed by neuroectoderm and closes by week 4
- Heart begins to beat at week 4 (mn: 4 chambers of heart)
- upper and lower limb buds begin to form (mn: 4 weeks = 4 limbs)
What comes from Neuroectoderm?
Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland)
Retina, Optic Nerve, Spinal Cord
week 6 (GI development)
mn: the number 6 looks like a gut
midgut contents (i.e. intestines) herniate through umbilical cord –> rotates around SMA –> hernia reduces by 12th week
- failure to reduce –> simple omphalocele (n.b. if lateral embryonic folds fail, liver present in omphalocele –> “liver containing omphalocele”)
- failure of rotation –> malrotation pathologies:
- volvulus: small bowel twists around SMA –> ischemic damage
- obstruction (cecum ends up in mid upper abdomen, stretching the peritoneum causing Ladd bands which cause obstructions)
- left sided colon –> more of an anatomical variant than a pathology
Week 5
connection between midgut and yok sac narrows –> “yolk stalk” (aka “vitalline duct” or “omphalomesenteric duct”) –> disappears by week 9
if it persists–> Meckel’s diverticulum (outpouching at ilium d/t vitalline duct remnant) ; cysts or polyps
n. b. meckel’s diverticulum = most common congenital abnormality of GI tract
(mn: number 5 is V –> Vitalline duct)
What comes from Neural Crest Cells?
PNS (DRG, CN, Celiac ganglion, Schwann cells, ANS)
Melanocytes, Chromaffin Cells of adrenal medulla, Parafollicular (C) cells of thyroid, Schwann cells, Pia and Arachnoid, Bones of skull, Odontoblasts, Aorticopulmonary septum
Craniopharyngioma
Origin
Histo
Benign Rathke’s pouch rumor with cholesterol crystals and calcification
What comes from Mesoderm?
Muscle, Bone, Connective Tissue, Serous Lining of Body Cavities (Peritoneum), Spleen, CV Structures, Lymphatics, Blood, Wall of Gut Tube, Wall of Bladder, Urethra, Vagina, Kidneys, Adrenal Cortex, Dermis, Testes, Ovaries
Mesodermal Defects
“VACTERL”
Vertebral defects
Anal atresia
Cardiac defects
Tracheo-Esophageal fistula
Renal defects
Limb defects (bone and muscle)
What comes from Endoderm?
Gut tube epithelium (including anal canal above pectinate line)
Luminal epithelium derivatives (Liver, Lung, Gallbladder, Pancreas, Eustachian Tube, Thymus, Parathyroid, Thyroid follicular cells
week 18
fetal bones start making blood
Cleft lip results when
the maxillary prominence fails to fuse with the intermaxillary segment during the fifth-sixth week of embryonic development.
what are the TORCH infections
Revision to TORCH mnemonic → TORCHSZ
T toxoplasmosis
O Other: Parvovirus B19, pertussis
R rubella
C CMV
H HSV, HIV, HBV
S Syphilis
Z Zika, Zoster
fetal varicella syndrome p/w
limb hypoplasia, microcephaly, chorioretinitis. mother p/w chicken pox
chorioretinitis this is often described as a focal vitreous infiltrate appearing as “headlights in the fog”
Congenital CMV p/w
can cause jaundice, hepatosplenomegaly, and periventricular calcifications.
Congenital rubella infection characteristically causes
cataracts, sensorineural deafness, a “blueberry muffin” rash (purpuric lesions signify dermal erythropoiesis), PDA (murmur)
mn: RUmbling murmur in Rubella; Rubella –> Rubbing –> Public display of affection at a bakery–> PDA and bluberry muffin rash. They can’t hear (deafness) their order being called over the sound of the espresso machine (machine like murmur)
Congenital toxoplasmosis leads to
chorioretinitis, hydrocephalus, intracranial calcifications, microcephaly, and seizures. It is caused by an obligate intracellular protozoan, Toxoplasma gondii.
DHT induces the differentiation of the ______, _________, and ______
testosterone induces the differentiation of the ______, _________, and ______
DHT induces the differentiation of the penis, scrotum, and prostate
testosterone induces the differentiation of the epididymis, ductus (vas) deferens, and seminal vesicles.
what embryological event leads to tetralogy of fallot
Abnormal neural crest cell migration leads to anterior and cephalad deviation of the infundibular septum during embryologic development, resulting in a malaligned VSD and an overriding aorta
