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Early embryonic development (Day 0 - 10)
Early fetal development (Weeks 1 - 10)
Within week 1
hCG secretion begins around the time of implantation of blastocyst
Within week 2
Inner cell mass divides into bilaminar disc that is composed by 2 layers (Epiblast and Hypoblast). Two cavities form: the amniotic cavity and yolk sac form
Within week 3
Gastrulation forms trilaminar embryonic disc.
Cells from epiblast invaginate causing primitive streak, forming the endoderm, mesoderm, ectoderm.
Notochord arises from midline mesoderm; overlying ectoderm becomes neural plate.
Weeks 3–8 (embryonic period)
Neural tube formed by neuroectoderm and closes by week 4.
Extremely susceptible to teratogens.
Heart begins to beat.
Upper and lower limb buds begin to form.
Fetal cardiac activity visible by transvaginal ultrasound.
Fetal movements start.
Genitalia have male/female characteristics. Baby's sex is able to be determined.
Anterior Pituitary (Adenohypophysis) from Rathke pouch
Lens of eye and Cornea
Epithelial linings of nasal and oral cavity
Sensory organs of ear
Anal canal below the pectinate line
Parotid (salivary), sweat and mammary glands
Neural tube (neuroectoderm)
Brain (CNS neurons, oligodendrocytes, astrocytes, ependymal cells) and spinal cord
Posterior Pituitary (neurohypophysis)
Neural Crest (see Picmonic-made Picmonic for derivatives)
Neural Crest Derivatives
CA MOTEL ASS
Craniofacial Structures (skull)
Arachnoid and Pia Mater
Enterochromaffin (Adrenal Medulla)
Spiral Septum (Aorticopulmonary Septum)
Serous linings of body cavities (eg, peritoneum)
Spleen (derived from foregut mesentery)
Wall of gut tube
Notochord arises from midline mesoderm. Notochord induces ectoderm to form neuroectoderm (neural plate). Its only postnatal derivative is the nucleus pulposus of the intervertebral disc.
Gut tube epithelium (including anal canal above the pectinate line)
Most of urethra and lower vagina (derived from urogenital sinus, the lower 2/3rds)
Heart-lung fistulas and holoprosencephaly in most severe form
Mechanism is failure of cell migration
VSD, PDA, ASD, tetralogy of Fallot
Dizygotic (“fraternal”) twins arise from 2 eggs that are separately fertilized by 2 different sperm (always 2 zygotes) and will have 2 separate amniotic sacs and 2 separate placentas (chorions).
Monozygotic (“identical”) twins arise from 1 fertilized egg (1 egg + 1 sperm) that splits in early pregnancy.
The timing of cleavage determines chorionicity (number of chorions) and amnionicity (number of amnions).
1º site of nutrient and gas exchange between mother and fetus.
Inner layer of chorionic villi.
Outer layer of chorionic villi
Synthesizes and secretes hormones, eg, hCG (structurally similar to LH; stimulates corpus luteum to secrete progesterone during first trimester).
Lacks MHC-I expression causing a decreased chance of attack by maternal immune system.
Derived from endometrium.
Maternal blood in lacunae.
Umbilical arteries (2)—return deoxygenated blood from fetal internal iliac arteries to placenta
Umbilical vein (1)—supplies oxygenated blood from placenta to fetus; drains into IVC via liver or via ductus venosus.
Single umbilical artery (2-vessel cord) is associated with congenital and chromosomal anomalies.
Umbilical arteries and vein are derived from allantois.
In the 3rd week the yolk sac forms the allantois, which extends into urogenital sinus.
Allantois becomes the urachus, a duct between fetal bladder and umbilicus.
Total failure of urachus to obliterate leads to urine discharge from umbilicus.
Partial failure of urachus to obliterate; fluid-filled cavity lined with uroepithelium, between umbilicus and bladder.
Can lead to infection, adenocarcinoma.
Slight failure of urachus to obliterate leads to outpouching of bladder.
7th week—obliteration of vitelline duct (omphalomesenteric duct), which connects yolk sac to midgut lumen.
Vitelline duct fails to close causing meconium discharge from umbilicus.
Details in other Picmonic
Results from a partial closure of the vitelline duct, with the patent portion open at the umbilicus
vitelline duct cyst
Forms if peripheral portions of the vitelline duct (connected to the ileum and umbilicus) obliterate, but the central part remains
This cyst is connected with the ileum and abdominal wall by fibrous bands
Aortic arch derivatives
Develop into arterial system
Part of maxillary artery (branch of external carotid).
Stapedial artery and hyoid artery
Common Carotid artery and proximal part of internal Carotid artery.
On left, aortic arch; on right, proximal part of right subclavian artery.
Proximal part of pulmonary arteries and (on left only) ductus arteriosus.
recurrent laryngeal nerve
Right recurrent laryngeal nerve loops around right subclavian artery
Left recurrent laryngeal nerve loops around aortic arch distal to ductus arteriosus
568 Branchial (Pharyngeal) Apparatus and Branchial Cleft Derivatives
Branchial (pharyngeal) apparatus
Composed of branchial clefts, arches, pouches
Branchial clefts—derived from ectoderm. Also called branchial grooves
Branchial arches—derived from mesoderm (muscles, arteries) and neural crest (bones, cartilage)
Branchial pouches—derived from endoderm
Clefts = ectoderm
Arches = mesoderm + neural crest
Pouches = endoderm
Branchial cleft derivatives
1st cleft develops into external auditory meatus
2nd through 4th clefts form temporary cervical sinuses, which are obliterated by proliferation of 2nd arch mesenchyme
Persistent cervical sinus leading to branchial cleft cyst within lateral neck, anterior to sternocleidomastoid muscle. Immobile during swallowing
Pharyngeal Arch Derivatives: 1st Arch
Muscles of Mastication
Tensor Veli Palatini
Anterior Belly of the Digastric
Treacher Collins Syndrome
Pharyngeal Arch Derivatives: 2nd Arch
Lesser Horn of Hyoid
Muscles of Facial Expression
Posterior Belly of Digastric
Congenital Pharyngocutaneous Fistula
Pharyngeal Arch Derivatives: 3rd Arch
Greater Horn of Hyoid
CN IX (Glossopharyngeal)
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