Embryology Flashcards
Endoderm derivatives
Epithelial lining of:
GI tract, trachea, bronchi, lungs, liver, urinary bladder
Other:
thyroid, parathyroid, thymus
Mesoderm derivatives
Muscles
Bone
Dermis
Connective tissue
Kidneys
Spleen
Cardiovascular structures
Blood
Gonads
Ectoderm derivatives
Surface ectoderm: epidermis, sailvary glands, sweat glands, mammary glands
Neuroectoderm: CNS, retina
Neural Crest: ANS, dorsal root ganglia, cranial nerves, melanocytes, Schwann cells, adrenal medulla, bones of skull (pharyngeal arches)
Organizing center
Instructs differentiation of cells
Ex: Primitive Node (anterior of primitive streak in humans, controls gastrulation; equivalent to Spemann’s organizing center in other animals), Isthmus Organizer (in midbrain-hindbrain isthmus; required for cerebellum development)
Fertilization sequence of events
Secondary oocyte (in metaphase II) released from ovary –>sperm digest corona radiata –> one sperm penetrates zona pellucida –> block to polyspermy –> secondary oocyte completes meiosis II to make fertilized ovum and second polar body –> egg and sperm undergo rapid DNA synthesis –> nuclear membranes dissolve –> first mitosis
Blastocyst
Created when fluid enters morula
Trophoblast: Outer sphere of cells
Embryoblast/Inner Cell Mass: cluster of cells on one inside edge of trophoblast
Embryoblast/Inner Cell Mass
Gives rise to entire embryo
Epiblast: surrounds amniotic cavity; gives rise to entire body; (columnar cells); where primitive streak forms and gastrulation eventually occurs
Hypoblast: upper surrounding of exocoelomic cavity/primitive yolk sac (cuboidal cells)
Trophoblast
Cytotrophobalst: cells divide and go outward to syncitiotrophoblast and fuse/lose cell membranes
Syncitiotrophoblast: no cell boundaries; secretes HCG; forms lacunae
How does the embryo hijack the mother’s physiology?
Trophoblast secretes HCG to sustain the corpus luteum which secretes progesterone to sustain endometrium
After about 8 weeks, the placenta takes over progesterone production
Placenta previa
An ectopic pregnancy where blastocyst implants too close to cervix and hemorrhaging occurs around 7 months (however can still have viable fetus)
3 ways twinning can occur
1) Split at 2 cell stage: 2 amniotic cavities, 2 chorionic cavities, 2 placentas (RARELY happens)
2) Split at early blastocyst: 2 amniotic cavities, 1 chorionic cavity and 1 placenta
3) Split at late blastocyst: 1 amniotic cavity, 1 chorionic cavity, 1 placenta
Sirenomelia
Cells moving into primitive streak lose steam at the end and fail to gastrulate properly, giving fused limbs (mermaid limbs)
Sacrococcygeal teratoma
Caused by primitive streak persistence; tumor has bits of every germ layer; most common in female fetuses
When are embryos most vulnerable to insult?
3-8 weeks
This is when body plan/organ systems are formed
Axial mesoderm
Notochord
Paraxial mesoderm
Somites create sclerotome (bone and cartilage of vertebral column), myotome (skeletal muscles), dermatome (dermis)
Intermediate mesoderm
Kidney
Lateral plate mesoderm
Creates mesothelial/serous membranes (peritoneum, pericardium, lung pleura); splits into two divisions and coelomic cavity forms in between them
Parietal/Somatic mesoderm: body wall
Visceral/Splachnic mesoderm: surrounds endodermal organs
Extraembryonic mesoderm
Anybody know what this turns into?
How does the neural plate begin to form?
Notochord induces it to
Forebrain
(Procephalon)
Telencephalon: oflactory nerve
Diencephalon: optic nerve
Midbrain
(Mesencephalon)
Cranial nerve III (occulomotor)
Hindbrain
(Rhombencephalon)
8 Rhombomeres
Cranial nerves IV to XII
Foregut
Epithelium of…
Pharyngeal pouch derivatives: thyroid, parathyroid, thymus, tonsils
Esophagus
Trachea
Lung buds
Stomach
Liver
Gall bladder
Pancreas
Duodenum
Midgut
Epithelium of…
Posterior duodenum
Small intestine
Transverse colon (part of it)
Hindgut
Epithelium of…
Colon
Rectum
Urinary bladder
Prostate
Urethra
Examples of epithelial-mesenchymal transition
1) Gastrulation at primitive streak
2) Neural crest migration
3) Lateral plate forming mesothelium lining of peritoneum (mesenchymal TO epithelial…opposite!)
4) Note: also happens in cancer invasion when cells detach from each other and attach to basement membrane
When does basic organogenesis of the fetus complete?
End of 1st trimester
Most sensitive to teratogens during 1st trimester
Fetus’ genetalia differentiated
14 weeks
When does surfactant secretion begin and why is that relevant?
24 weeks
Note: at ~26 weeks (beginning of 3rd trimester) CNS matured enough to support rhythmic breathing so after this point, viable fetus can be born
Morphogen gradient responsible for dorsal-ventral axis
BMP
High on ventral side (induces epidermis and lateral plate–most ventral)
(BMP signals through protein kinase receptor that activates Smad TFs)
Genes responsible for anterior-posterior axis
Hox genes
How do chordin and noggin act?
BMP antagonists that bind BMP and stop it from signaling
Act on dorsal side to inhibit BMP
Hox gene vs. Homeodomain vs. Homeobox
Hox: gene
Homeodomain: structural motif in the protein that can bind to DNA
Homeobox: DNA that encodes the homeodomain
How does retinoic acid affect Hox gene transcription?
RA activates Hox gene transcription by binding receptor and translocating into nucleus
RA sequentially activates Hox gene expression: anterior to posterior
Retinoic acid teratogenesis
Hox genes not usually expressed in most anterior pharyngeal arch (containing rhombomeres 1 and 2) but excess RA causes Hox expression there
Causes cleft palate, micrognathia, etc
RU 486
Progesterone receptor antagonist
Used in first months of pregnancy, but not after because at that point placenta is making progesterone, and can’t block that
Malformation
Results from abnormal formation of a structure (usually during embryogenesis)
Deformation
Results from impact of mechanical forces on normally-formed structure (usually during fetal period)
Disruption
Results from destruction of previously normally formed structure
Dysplasia
Results when normal structures are made out of abnormal tissues
