Embryology (Endo and Repro) Flashcards
Thyroid development
- ) Thyroid diverticulum arises from floor of primitive pharynx and DESCENDS into neck
- ) Connected to tongue by thyroglossal duct –>may persist as pyramidal lobe
- ) Most common ectopic thyroid site is tongue (lingual thyroid)
Thyroglossal duct
- ) Foramen cecum is normal remnant of thyroglossal duct
2. ) May persist as thyroglossal duct cyst – anterior midline neck mass that moves with swallowing
Fetal adrenal gland
Inner active fetal zone
Outer adult zone - secretes cortisol (lung maturation, surfactant production) during late gestation under control of fetal pituitary and placenta (ACTH, CRH)
Sonic hedgehog
- ) A/P axis patterning; produced at base of limbs in ZPA
2. ) Involved in CNS development; mutation can cause holoprosencephaly (forebrain does not form 2 hemispheres)
Wnt-7
D/V axis patterning; produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb)
FGF gene
Produced at apical ectodermal ridge; stimulates mitosis of underlying mesoderm –>limb elongation
Hox genes
DNA-binding TFs that regulate morphogenesis; involved in segmental organization of embryo in craniocaudad direction; mutation –>appendages in wrong locations
Fetal development: day 0
Fertilization by sperm forming zygote, initiating embryogenesis
Fetal development: within week 1
hCG secretion begins after implantation of blastocyst
Fetal development: within week 2
Bilaminar disc (epiblast, hypoblast) **2 weeks = 2 layers
Fetal development: within week 3
Gastrulation –>trilaminar disk **3 weeks = 3 layers
Epiblast invaginates to from primitive streak, notochord, mesoderm + organization, neural plate
Fetal development: weeks 3-8
Neural tube formed by neuroectoderm and closes
Organogenesis
Extremely susceptible to teratogens
Fetal development: within week 4
Heart begins to beat
Upper and lower limb buds begin to form **4weeks = 4 limbs
Fetal development: week 8 (start of fetal period)
Fetal movement, fetus looks like a baby
Fetal development: week 10
Genitalia have male/female characteristics
Surface ectoderm derivatives
Epidermis Rathke's pouch (ant. pit) Lens and cornea Inner ear sensory organs Nasal, oral, and olfactory epithelium Salivary, sweat, mammary glands
Neuroectoderm (neural tube) derivatives
Brain and spinal cord
Posterior pituitary
Pineal gland
Retina
Neural crest derivatives
Autonomic, sensory, and celiac ganglia Adrenal medulla Pia and arachnoid mater Melanocytes Schwann cells Aorticopulmonary septum Endocardial cushions Branchial arches (bones & cartilage) Skull bones
Mesoderm derivatives
Paraxial mesoderm Muscles (skeletal, cardiac, smooth) Bones & cartilage Connective tissue Cardiovascular system and blood Lymphatics Serosal linings Spleen (foregut mesentery) Wall of gut tube Adrenal cortex
Intermediate mesoderm
Kidney & ureters
Internal genitalia
Endoderm derivatives
Middle ear Lung Thymus Thyroid follicular cells Parathyroids GI tract Liver Pancreas Bladder and urethra
Errors: agenesis
Absent organ due to absent primordial tissue
Errors: aplasia
Absent organ despite primordial tissue
Errors: deformation
Extrinsic disruption; occurs after the embryonic period
Errors: hypoplasia
Incomplete organ development; primordial tissue present
Errors: malformation
Intrinsic disruption; occurs during the embryonic period (weeks 3-8)
Teratogen timing of effect
Before week 3: all or nothing effects
Weeks 3-8: most susceptible
After week 8: growth and function affected
Teratogen: ACEi
Renal damage
Teratogen: Alkylating agents
Absence of digits, multiple anomalies
Teratogen: Aminoglycosides
CN VIII toxicity (ototoxicity)
Teratogen: Carbamazepine
NTDs, craniofacial defects, fingernail hypoplasia, developmental delay, IUGR
Teratogen: DES
Vaginal clear cell adenocarcinoma, congenital Mullerian anomalies
Teratogen: Folate antagonists
NTDs
Teratogen: Lithium
Ebstein’s anomal (atrialized RV)
Teratogen: Phenytoin
Fetal hydantoin syndrome: microcephaly, dysmorphic craniofacial features, hypoplastic nails and distal phalanges, cardiac defects, IUGR, mental retardation
Teratogen: Tetracyclines
Discolored teeth
Teratogen: Thalidomide
Limb defects (flipper limbs)