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21 Reproductive
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.
Organogenesis.
Extremely susceptible to teratogens.
Week 4
Heart begins to beat.
Upper and lower limb buds begin to form.
Week 6
Fetal cardiac activity visible by transvaginal ultrasound.
Week 8
Fetal movements start.
Week 10
Genitalia have male/female characteristics. Baby's sex is able to be determined.
Ectoderm derivatives
ECTODERM
Surface ectoderm
Epidermis
Anterior Pituitary (Adenohypophysis) from Rathke pouch
Lens of eye and Cornea
Epithelial linings of nasal and oral cavity
Sensory organs of ear
Olfactory epithelium
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)
Pineal gland
Retina
Neural Crest
Neural Crest (see Picmonic-made Picmonic for derivatives)
Neural Crest Derivatives
CA MOTEL ASS
Craniofacial Structures (skull)
Arachnoid and Pia Mater
Melanocytes
Odontoblasts
Tracheal Cartilage
Enterochromaffin (Adrenal Medulla)
Laryngeal Cartilage
All Ganglia
Schwann Cells
Spiral Septum (Aorticopulmonary Septum)
2 mins
Mesoderm derivatives
Muscle
Bone
Connective tissue
Serous linings of body cavities (eg, peritoneum)
Spleen (derived from foregut mesentery)
Cardiovascular structures
Lymphatics
Blood
Wall of gut tube
Upper vagina
Kidneys
Adrenal cortex
Dermis
Testes
Ovaries
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.
Endoderm 563
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
Twinning
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).
Placenta
1º site of nutrient and gas exchange between mother and fetus.
Fetal component
Cytotrophoblast
Inner layer of chorionic villi.
Syncytiotrophoblast
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.
Maternal component
Decidua basalis
Derived from endometrium.
Maternal blood in lacunae.
Umbilical cord
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.
Urachus
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.
Patent urachus
Total failure of urachus to obliterate leads to urine discharge from umbilicus.
Urachal cyst
Partial failure of urachus to obliterate; fluid-filled cavity lined with uroepithelium, between umbilicus and bladder.
Can lead to infection, adenocarcinoma.
Vesicourachal diverticulum
Slight failure of urachus to obliterate leads to outpouching of bladder.
Vitelline duct
7th week—obliteration of vitelline duct (omphalomesenteric duct), which connects yolk sac to midgut lumen.
Vitelline fistula
Vitelline duct fails to close causing meconium discharge from umbilicus.
Meckel diverticulum
Details in other Picmonic
VItelline Sinus
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
1st
Part of maxillary artery (branch of external carotid).
2nd
Stapedial artery and hyoid artery
3rd
Common Carotid artery and proximal part of internal Carotid artery.
4th
On left, aortic arch; on right, proximal part of right subclavian artery.
6th
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
Cartilage
Meckel's Cartilage
Mandible
Malleus
Incus
Sphenomandibular Ligament
Muscles
Muscles of Mastication
Tensor Tympani
Tensor Veli Palatini
Anterior Belly of the Digastric
Mylohyoid
Nerves
CN V2
CN V3
Conditions
Treacher Collins Syndrome
3 mins
Pharyngeal Arch Derivatives: 2nd Arch
Cartilage
Reichert's Cartilage
Stapes
Styloid Process
Lesser Horn of Hyoid
Stylohyoid Ligament
Muscles
Muscles of Facial Expression
Stapedius
Stylohyoid
Platysma
Posterior Belly of Digastric
Nerves
CN VII
Conditions
Congenital Pharyngocutaneous Fistula
2 mins
Pharyngeal Arch Derivatives: 3rd Arch
Cartilage
Greater Horn of Hyoid
Muscles
Stylopharyngeus
Nerves
CN IX (Glossopharyngeal)
Arteries
Common Carotid
Internal Carotid
1 min
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