Embryology Review - University of Arizona

Embryology Review - University of Arizona

Embryology Review Timeline: 0 to 3 weeks Day 0 to wk 3: all or none phase Insults to the fetus at this time will result in loss of embryo or will cause no damage. Day 0: fertilization (initiation of embryogenesis) Sperm + egg =zygote Up to wk1: blastocyst implantation By wk 2: bilaminar disk (2 germ layers: epiblast, hypoblast) 2 cavities: amniotic cavity, yolk sac

2 placental components: cytotrophoblast, syncytiotrophoblast Rule of 2s At this time, the mother will miss her period Timeline II: 3 to 10 weeks Wk3-8: Organogenesis (highest teratogen susceptibility)(90% of defects) By wk3: gastrulation: (rule of 3s) Primitive streak Notochord (becomes nucleus pulposus of intervertebral disks) Induces neural plate/neuroectoderm formation Mesoderm Neural PlateNeural Tube formation: folate deficiency causes spina bifida here 3 germ layers: endo, ecto and mesoderm

Wk 4 (day 28): heart beat (4 chambers), 4 limb buds, 4 branchial arches rule of 4s, but tongue, lungs, GI and diaphragm also begin formation then Week 4-6 is the critical period for TA, VSD, ASD, etc.) Wk 4-5: limb defect critical period Wk 5-6: cleft lip critical period Wk 5-7: gonad differentiation, kidney, bladder, rectum formation Wk 6-7: teeth/palate critical period Wk 8: fetal movement, fetus looks like a baby, critical period for formation of external genitalia Wk 10: Genitalia are recognizable as female/male The Timeline: Animated All-or-None Phase: <3wks

Organogenesis (3 to 8 weeks) Implantation of the Wk 6: palate and teeth BLASTOCYST into the Fertilization Wk 8: fetal movement uterus at up to 1 wk post Defect: external fertilization genitalia Wk 3 gastrulation:Week Rule of 2 :3s

rule of 2s 3 germ layers: ectoderm, mesoderm, *bilaminar disk of 2endoderm germ layers: epiblast and hypoblast Neural plate formation *2 cavities: amniotic cavity and yolk sac Defect: spina bifida closure of the neural *2(incomplete placental components: syncytiotrophoblasts, tube cytotrophoblasts

Wk 4: rule of 4s Wk 5: kidney, bladder, rectum This is when the mother will miss her period 4 limb buds, 4 and gonadal differentiation (5-7) branchial arches Defect: cleft lip (5-6) Heart beat Wk 10: Recognizable External Defects: heart (4-6), Genitalia limb (4-5) Timeline Quiz! How long after fertilization does the blastocyst

implant within the uterine wall? 1 week or less What structures does the embryo have at 2 weeks? Rule of 2s: a bi-laminar disk, 2 cavities, 2 placental components. Cavities: amniotic cavity and yolk sac. What is the significance of the All-or-None phase? Any teratogen exposure either does not affect the fetus or the fetus is lost. How long is the All-or-None phase? 3 weeks after

Timeline Quiz II ! What phase comes after the All-or-None phase? Organogenesis How long is Organogenesis? Weeks 3-8 (5-6 weeks) What percent of structural defects occur during weeks 3- 8? 90% What structures form during week 3? Rule of 3s: 3 germ layers: ecto, meso, endoderm.

Timeline Quiz III ! What is the defect associated with teratogens in week 3? Spina bifida (failure of closure of the neural tube) What structures form during week 4? Rule of 4s: 4 limb buds, 4 branchial arches What are the defects associated with weeks 4 and 5, and 4- 6? Wk 4-5: limb Wk 4-6: heart defects, including VSD, ASD, TA What structures form during week 5? Limbs, heart (still forming), and gonads, kidney, bladder and rectum.

Timeline Quiz IV ! What defect is associated with week 5? Cleft lip What structures form during weeks 6-7? Teeth and palate What happens in week 8? External genitalia differentiate, fetus moves and looks like a baby. Timeline Quiz V: Last One! What is the significance of week 10? External genitalia has differentiated to the point where one can determine whether ones baby is a boy or a girl. When do you first hear the fetal heartbeat? Week 4 (Day 28)(1 month)

When is the first fetal movement? Week 8 (Day 56) (2 months) Germ Layers Note: while this chart from the NIH has the yolk sac and amniotic ectoderm arising early, the boards books and Dr. Darnell want you to think about their derivation as follows: Yolk sac: endoderm and mesoderm Amnion: ectoderm and mesoderm

Presumably the extraembryonic germ layers later gain mesoderm. Germ Layers: Ectoderm Ectoderm Surface ectoderm Epidermis, epithelia of (skin, ear, eye and nose),hair and nails, lens of eye, enamel of teeth Adenohypophysis, mammary glands, sweat glands Neuroectoderm (Neural tube) CNS neurons, oligodendrocytes, astrocytes, ependymal cells Neurohypophysis, pineal gland Neural crest cells (also included initially in neuroectoderm) Autonomic (SNS/PNS) NS, dorsal root ganglia, Schwann cells

Odontoblasts (dentin and pulp of teeth), parafollicular C cells of the thyroid Melanocytes, adrenal medulla chromaffin + enterochromaffin cells Pia and arachnoid mater, skull bones except for the occiput, laryngeal cartilage Septum of truncus arteriosus that forms part of the ascending aorta and pulmonary trunk Germ Layers: Meso & Endoderm Mesoderm Dura mater, CT: perineal body, serous epithelia, blood vessels, lymphatics, blood, spleen Somites, muscle, bone, heart, kidneys, adrenal cortex, gonads Notochord (induces neuroectoderm formation from surrounding ectoderm)

Extraembryonic membranes Endoderm (GI tract/gut tube-pharynx, esophagus, stomach, sml and large intestines, cloaca) Lungs, liver, pancreas, thymus, parathyroid, thyroid follicular cells, lining of inner ear Lining of yolk sac and allantois Yolk sac remnant vitelline duct, Meckels diverticulum Extraembryonic Membranes Chorion and Amnion Ectoderm

Mesoderm Yolk Sac and Allantois Mesoderm endoderm Germ Layer Defects Mesoderm defects: (VACTERL) Defects: vertebral, anal atresia, cardiac, tracheo-esophageal fistula, renal, limb defects Ectoderm defects: hypophoic ectodermal dysplasia syndrome Neural crest cell (usually migration) defects: DiGeorge Syndrome/CATCH22/22q11 syndromes VSDs, defect in NC truncus arteriosus septation Neurofibromatosis Type 1 (NF1 gene, ch17) Caf au lait spots associated with PNS tumors Pheochromocytomas

Hirshsprungs disease Lack of neurons in colon, digestive defects Wardenburg syndrome Sensory neural deafness with GI defects (Hirshsprungs +) Germ Layers Quiz 1 of 5 The bilaminar disk epiblast differentiates into what embryonic germ layers? Ecto, meso, endoderm The hypoblast differentiates into what? Extraembryonic endoderm, which becomes part of the yolk sac. The yolk sac is made of hypoblast extraembryonic

endoderm and what other germ layer? Mesoderm. Germ Layers Quiz 2 of 5 The allantois is derived from what? Mesoderm and endoderm The Amnion is derived from which two germ layers? Mesoderm and extraembryonal ectoderm. The Chorion is derived from which two germ layers? Mesoderm and ectoderm. What are the three divisions of the embryonic ectoderm? Surface, neuroectoderm and neural crest cells. Germ Layers Quiz 3 of 5

Name five things derived from surface ectoderm? Skin, teeth enamel, hair and nails, eye lens Adenohypophysis and glands (mammary and sweat) From neuroectoderm? CNS: neurons, glia, ependymal cells, oligodendrocytes, pineal gland, neurohypophysis From neural crest cells? Peripheral nervous system: ganglia, neurons and Schwann cells Bones and membranes of the skull: pia, arachnoid mater (all except dura and the occiput bone) Septum of truncus arteriosus (separates pulmonary trunk from aorta Parafollicular C cells of the thyroid Odontoblasts: dentin and pulp of the teeth Adrenal medulla chromaffin cells Enterocromaffin cells Melanocytes of the skin

Germ Layers Quiz 4 of 5 Name at least 5 things that are derived from mesoderm. Bones, muscle, connective tissue, adrenal cortex, spleen, blood vessels, heart, kidneys, serous epithelia, gonads Name 5 things derived from endoderm. Lung, pancreas, GI tract, thymus, inner ear lining What germ layer is associated with VACTERL? Mesoderm Germ Layers Quiz 5 of 5!!!

What does VACTERL stand for? Vertebral Anal atresia Cardiac Tracheo-Esophageal fistula Renal Limb defects Name 4 defects associated with ectodermal dysplasia. CATCH22/22q11/DiGeorge syndromes Hirshsprungs disease Wardenburgs disease Neurofibromatosis Type 1 The Heart The process of heart formation

2 heart tubes form and combine to form one heart tube (mesoderm) The tube loops Blood originally enters from the bottom, but after folding enters at the top (r. atrium) Pump begins to work (heartbeat at day 22, the beginning of week 4)

Ventricle/Atria Formation Cardiovascular II Ventricular Septum development Muscular ventricular septum forms Interventricular foramen links ventricles Aorticopulmonary septum divides the truncus arteriosus into aortic and pulmonary trunks NC cell migration is crucial for this action

The MV septum fuses with the AP septum to form the membranous interventricular septum, which closes the interventricular foramen. Atrial Septation The septum primum forms first, allowing the right to left shunt. The septum secundum forms second, remaining as the foramen ovale after

the septum primum degenerates leaving only the valve seen here. The muscular septum Completed around wk 9. grows upwards to divide After birth, this is closed the interventricular due to decreased right foramen atrial pressure and The muscular septum increased left atrial eventually fuses with the pressure. membranous septum,

The remnant is the fossa which grows down from the ovalis. aorticopulmonary septum. Completed by about week 8. Cardiovascular III Atrial septal development Foramen primum narrows Septum primum grows towards the endocardial cushions Foramen secundum forms in septum primum

Maintains the Right to Left shunt Septum secundum begins to grow Permanent foramen ovale is part of the SS Septum primum degenerates, leaving the valve of the foramen ovale Cardio IV: Erythropoesis Erythropoesis 3-8wks: yolk sac 6-30wks: liver 9-29wks: spleen 28 wks +: bone marrow

Fetal hemoglobin is alpha-2-gamma-2 (not a2b2!) Cardio V: Circulation Umbilical vein blood is 80% O2 sat. Joins lower body venous blood after the fetal liver (ductus venosus) (65%o2) Umbilical artery blood has less (O2 sat. 57%) Still enough to supply lower body, but head gets the best blood 3 shunts (close at birth): Ductus venosus: conducts blood entering the fetus via the umbilical vein to the fetus IVC. Foramen ovale: conducts most of the oxygenated blood in the IVC (from the ductus venosus) to the left atrium/ventricle from the right

atrium. Ductus arteriosus: conducts blood from the pulmonary artery to the descending aorta. This is in large part deoxygenated blood from the SVCright atrium, ventricle. The Umbilical Cord Umbilical cord (Allantois gives rise to everything except yolk sac) Umbilical vein (into fetus) Umbilical arteries (2)(from fetal internal iliac arteries) Yolk sac-disappears by week 7 except for small vesicle

Gives rise to some of the umbilical cord Urachus Removes waste from fetal bladder to allantois Whartons Jelly: surrounds vessels and urachus, encapsulated by amniotic epithelium Cardio VI The first breath Lungs expand: decreased resistance in pulmonary vasculature

Decreases right atrial pressure and increases left atrial pressure Foramen ovale closes becomes fossa ovalis Increased o2decreased PGs, Ductus arteriosus closes Umbilical vein no longer contributes (also lowers RA pressure)becomes ligamentum teres hepatis and the superior vesicular aa. Portal sinus closes Ductus venosus closes, becomes ligamentum venosum Postnatal Derivatives Umbilical vein Ligamentum teres hepatis (falciform ligament) Umbilical arteries Medial umbilical ligaments

Allantois UrachusmediaN umbilical ligament Remnant of the allantois: urachal cyst or sinus Urachus: duct between bladder and umbiliacus Yolk sac Meckels diverticulum Postnatal derivatives II Ductus arteriosus Ligamentum arteriosum Ductus venosus Ligamentum venosum Foramen ovale Fossa ovalis Notochord

Nucleus pulposus of intervertebral disks Postnatal Derivatives III Truncus arteriosus Ascending aorta, pulmonary trunk Bulbus cordis Smooth parts of LV and RV Primitive ventricle Trabeculated parts of LV/RV Primitive atria Trabeculated left/right atria Postnatal Derivatives IV Left horn of sinus venosus (SV) Coronary sinus

Right horn of sinus venosus Smooth part of right atrium Right common cardinal vein SVC Right anterior cardinal vein SVC Endocardial cushions (NC derivatives) Separate the atria from the ventricles Heart Quiz! 1 of 3 How many heart tubes do we start with? 2 And then what happens? They join and fold forward, bunching into an atrium

and a ventricle, separated by cardiac cushions. When does the pump function? Beginning of week 4 How do the 2 ventricles form? The muscular septum joins the membranous septum to close off the interventricular foramen by week 8. Heart Quiz II of III How do atria form? The septum primum forms, leaving a hole called the foramen secundum. Then the septum secundum forms, leaving a hole called the foramen ovale. The septum primum degenerates (thins).

How does this right left shunt close after birth? Decreased right atria pressure and increased left sided pressure after the first breath causes the foramen ovale to be closed. What are two other shunts in the fetal circulation? Ductus venosus: umbilical vein to IVC Ductus arteriosus: pulmonary trunk to aorta Heart Quiz III of III What do the umbiliacaL arteries become after birth? Medial umbilical ligament.

What does the allaNtois become after birth? Median umbilical ligament What is a yolk sac remnant called? Meckels diverticulum, vitelline duct Summary: Cardiac Defects ASD, VSD, AV Canal and persistent truncus arteriosus are holes in the septa They cause LR shunts after birth, which result in right ventricular hypertrophy, pulmonary hypertension, and if severe, congestive heart failure/death Why are we looking? Sx: fatigue, failure to thrive Eisenmengers syndrome: R L shunt, results in cyanosis Eventual result of physiological response to LR shunt: pulmonary

hypertensionRV and RA hypertrophy. Solves the LR shunt by overcompensating: now blood flows RL without going to the lungs first! Dx: Look at the heart=echocardiography Tx: Holes in the heart=surgery Tetralogy of Fallot= actually 5 things: VSD, PDA, pulmonary stenosis, RV hypertrophy, overriding aorta Cardiovascular Defects ASD (Atrial-septal defect) If foramen ovale and foramen secundum are not staggered, they cannot be closed when pressure forces the septum primum and septum secundum together at birth.

The foramen ovale remains patent, blood shunts LeftRight This leads to Right sided atrial and ventricular hypertrophy, pulmonary hypertension and arrhythmias The hypertrophy minimizes the LR shunt Prevalence: 6/10,ooo, greater with Downs, trisomies, chromosomal aberrations Dx: echocardiography, systolic murmur with fixed S2 split Tx: surgery-insert occluding device or close hole More Cardio Defects VSD (Ventricular septal defect) Prevalence: 12/10,000 but represents 25% (1/4) of all cardiac defects. (Most common cardiac defect)

Results in LeftRight Shunt Results from any of the following Failure of fusion of the muscular and membranous ventricular septa Insufficient muscular septum Deficiency of the proximal conotruncal swellings Failure of the endocardial cushions to fuse Dx: echocardiography, audible murmur Sx: failure to thrive, fatigued baby, CHF (congestive heart failure) Tx: surgery Cardiac Defects III Persistent AV Canal

Often seen in Downs syndrome Failure of endocardial cushion fusion, leads to ASD and VSD Results in LR shunt Dx: echocardiography Sx: CHF (more severe), pulmonary hypertension(slightly less severe) Tx: Surgery Cardiac Defects IV Cotruncal defects Persistent truncus arteriosus (prevalence: 1/10,000) Conotruncal septa (NC cells) fails to form VSD plus no clear aorta/pulmonary trunk= lots of LR shunting after birth Dx: cyanosis at birth, systolic ejection murmur at left sternal border

Sx: pulmonary hypertensiondeath by age 2 Tx: surgery Transposition of the great vessels (prevalence: 5/10,000) Most common cause of death from cyanotic heart disease Results from failure of rotation of conotruncal septa, resulting in nonconnected pulmonary and systemic circulations. Dx: echocardiography Tx: surgery: requires PDA(give PGE2), ASD or VSD for survival of baby Cardiac Defects V Tetralogy of Fallot (~22q11 deletions) Prevalence: 10/10,000, increased with 22q11 deletion Unequal division of outflow tract= PDA plus

1. pulmonary stenosis 2.RV hypertrophy 3.VSD ( RV hypertrophy)(results in overriding aorta) 4.Overriding aorta The PDA lets blood from the aorta back into the pulmonary trunk. Patent ductus arteriosus Indomethacin helps close the DA Elevated prostaglandins can keep DA patent. (bad)

Drug related cardio defects LithiumEbstein anomaly- tricuspid valve is displaced in right ventricle, towards apex of heart The aorta is positioned over a VSD, so it receives blood from both ventricles A narrowing of the normal outflow tract of the right ventricle can be due either to increased muscular growth of the wall or

a secondary result from the VSDoverriding aorta The aortic and LV blood flowing back into the pulmonary/RV system results in RV hypertrophy and pulmonary hypertension = 5 things! PDA 1. Patent

ductus arteriosus: aortic blood flows back to pulmonary trunk! The VSD results from failure of fusion of the membranous and muscular septa and results in a LR shunt after birth. Cardiac Defects Quiz!

Describe the Tetralogy of Fallot. 5 : VSD, PDA, RV hypertrophy, pulmonic stenosis, overriding aorta What is the Ebstein anomaly and what causes it? Lithium causes a misplaced tricuspid valve What are common symptoms in a newborn with a heart defect? Fatigue, failure to thrive, possible cyanosis Name two types of cotruncal defects and differentiate between them. Persistent TRUNCUS arteriosus: failure of NC migration: no aorticopulmonary septa. Transposition of the great vessels: failure of rotation: septa makes right heart blood go to aorta. Tx: keep ductus arteriosus patent with PGE2. Both cotruncal defects present with cyanosis and are fatal if not surgically treated. The Lungs

Respiratory Diaphragm (mesoderm)(wk4) derived from Septum transversum Pleuroperitoneal folds Failure of pericardiopleural canal closure can result in diaphragmatic hernia Body wall Dorsal mesentery of esophagus (mesenchyme) Innervation: C3,4,5 keep the diaphragm alive Lungs bud from foregut endoderm at day 28/wk4 Secondary bronchial buds at day 30 Tertiary bronchial buds at day 38

Respiratory II-Diaphragm Esophageal mesenchyme Body wall Pleuroperitoneal membranes Septum transversum Respiratory development defects Congenital diaphragmatic hernia (prevalence: 4/10,000) incomplete diaphragm formation results in abdominal contents herniating into thorax

May result from lack of diaphragm muscle or failure to close of the left pericardioperitoneal canal Hypoplasia of thoracic organs(lungs, heart) Tx: surgery in utero (fatal at birth-scaphoid/hollowed abdomen) Respiratory Defects II Neonatal RDS(respiratory distress syndrome) Failure of surfactant production (<26wks at birth) Lungs cant inflate: sx: gasping, cyanosis, asphyxiation Tx: surfactant replacement

Pulmonary Hypoplasia Diaphragmatic herniation/insufficiency Uretric bud obstruction or other kidney loss Congenital hiatal hernia (limits urine production) Oligohydraminos (limits urine production) Lungs Quiz! What happens if there is a problem with kidney development? (to the lungs) Hypoplasia Why would a baby be born with not enough surfactant? Less than 26 weeks gestation (RDS) What 4 embryonic structures form the diaphragm? Septum transversum (mostly), body wall, pleuroperitoneal membranes (2),

esophageal mesenchyme From what and when do the lungs bud? The proximal foregut in week 4 (week of heartbeat) Digestive Tract GI Thyroid: late week 5 -buds down from the foramen cecum of the center of the tongue. Functional at wk 10-12 Pancreas- Ventral and dorsal buds fuse Ventral bud: head, main pancreatic duct Dorsal bud: body and tail, accessory pancreatic duct

Spleen-arises from dorsal mesentery Rotation of the GI tract(peritoneum fixes final position) 90 degrees counterclockwise Around the s. mesenteric artery as the gut tube extends into the belly stalk (physiologic herniation) Then, 180 degrees counterclockwise (starts at wk10) Gut reenters the abdomen, midgut being positioned on the left side (cecum, ascending colon) GI Blood supply Three gut divisions/Three unpaired arteries Foregut: stomach to first 1/3 of duodenum

Celiac artery Midgut: last 2/3 of duodenum to ascending colon Superior mesenteric artery Hindgut: transverse colon to rectum Inferior mesenteric artery GI Defects Tracheoesophageal fistula (part of mesodermal defects) Though endodermal, these are associated with mesodermal defects because mesoderm coats the gut tube and is, in part, responsible for

signals for growth/differentiation. Polyhydraminos, milk to the lungs and/or air to the stomach, asphyxiation/ drowning Thyroglossal Cyst/Sinus- the tube through which the thyroid descends remains patent and may fill with fluid. Pyloric stenosis: larger (more muscular)sphincter, smaller opening at opening to duodenum Sx: infant (2-6w) with non-bilious post prandial vomiting, failure to thrive Dx: palpable olive-sized mass in the epigastric region Increased prevalence in males, non-blacks (dominant polygenic inheritance) GI defects II

Annular pancreas: wraps duodenum, results from bilobed ventral pancreatic bulb Results in duodenal stenosis, gut malrotation, imperforate anus, polyhydraminos, pancreatitis/GI obstruction, jaundice Associated with Shh autosomal recessive -/-, Downs syndrome Dx: UGI, CT, Ab Xray or ultrasound Tx: bypass surgery Volvulus: torsion from malrotation or failure to be secured Increased risk in Duchennes muscular dystrophy Sx: bilious vomiting, pain, GI bleed, Results in acute obstruction with vessel/lymphatic compression, necrotic/stenotic bowel, venous engorgement

Dx: upper/lower GI study, X-rays Tx: surgery GI Defects III Meckels diverticulum (omphalomesenteric fistula, cyst or ligament from failure of regression of the vitelline duct remnant of the allantois) Rule of 2s: 2% of population, 2% of which have sx, 2x more males, dx: 2yrs old 2ft from ilium, 2 inches long, 2 types of abnormal lining In 2% of those that have it, presence of inappropriate gastric/pancreatic tissue causes self-digestion or adhesions Sx: peritonitis, appendicitis, ulcer, adhesions may lead to bowel obstruction Tx: treat infection, remove offending tissue (surgery)

Omphalocele 2.5/10,000 Persistent herniation of abdominal contents through umbilicus Gastroschisis: 1/10,000 herniation of abdominal contents through abdominal folds Due to failure of lateral body folds to fuse GI Quiz! Where and when do the thyroid form? Migrates down from the center of the tongue by week 12: Starts in late week 5. What does each pancreatic bud become in the adult pancreas? Ventral: Head and main pancreatic duct Dorsal: Body, tail and accessory pancreatic duct

What two rotations are necessary for healthy GI formation? 90 degrees counterclockwise, then 180 counterclockwise by wk10 GI Quiz II! What are the three arteries of the foregut and what parts do they supply? Foregut: celiac Midgut: s. mesenteric Hindgut: i. mesenteric artery

Name a GI defect associated with VACTERL mesodermal problems. Tracheoesophageal fistula, can result in polyhydraminos What's the difference between gastroschisis and omphalocele? Gastroschisis: prevalence 1/10,000, abdominal herniation through abdominal folds instead of the umbilicus with omphalocele, which is more common at 2.5/10,000. GI Quiz III Meckels diverticulum (yolk sac remnant) has what

characteristics? Rule of 2s: 2% of population, 2% of which have sx(adhesions, self digestion), 2x more males, dx: 2yrs old, 2ft from ilium, 2 inches long, 2 types of abnormal lining What is a thyroglossal cyst? A remnant of the path of the descent of the thyroid. What is pyloric stenosis? The pyloric sphincter wont let food out of the stomach What pancreatic defect is associated with a sonic hedgehog mutation? Annular pancreas Urinary and Genital

*see supplementary ppt for more detail on this system Urogenital formation Intermediate mesoderm divides cloaca into rectum and bladder, urethra and vagina (females) Intermediate mesoderm mesonephric ducts Uretric bud: kidney, ureters The rest of the mesonephric duct: Forms the trigone of the bladder Wolffian duct (males): Seminal vesicles, ductus deferens Paramesonephric ductsMullerian ducts: uterus, top of vagina, fallopian tubes

Sex determination (male: SRY gene initiates) Estrogen: male brain Testosterone: internal male genitalia DHT: external male genitalia Urogenital Defects Anal atresia (part of mesodermal defects)(see TE fistula) Incomplete partitioning Blind end rectum Urachal fistula, cyst, or sinus can result in urine from umbiliacus

Exostrophy of bladder Failure of penis formation in males Genital Defects XX male/XY female 1/20,000 Wnt4, Dax, SRY or receptor abnormalities Dx: karyotyping, physical exam Sx: infertility Tx: surgical correction often does not affect fertility Pseudohermaphroditism XY female with androgen insensitivity or MIF resistance Testes may become trapped in the broad ligament Other causes: CAH, mosiacism, 5a reductase deficiency Sx: infertility, gonadal tumors Tx: controversial surgery

More Genital Defects Potters syndrome/sequence (1/3000) No metanephros/kidney (renal agenesis) No urinepulmonary hypoplasia, limb deformities (sirenomelia/Mermaid syndrome), wrinkled skin, atypical facial features 100% fatal a few days after birth Horseshoe kidney (1/400) Renal fusion can increase risk of obstruction, stones, cancer Increased risk with Turners syndrome Usually Dxd at autopsy Even More Genital Defects Pelvic kidney (failure to migrate up) Cryptorchidism: failure of testes to descend~ with

increased rates of testicular cancer Hypospadius: urethra opens on the inferior aspect of the penis (Epispadius is above) Uterine anomalies: failure of fusion of the Mullerian tubes: bicornate, septated uterus Unicornate uterus Cervical atresia Sx: infertility GU Quiz! From what do the male reproductive ducts form? Wolffian ducts From what do the uterus and female reproductive ducts form?

Mullerian ducts What happens if the Mullerian ducts fuse improperly? Bicornate, unicornate uterus, cervical atresia From what does the bladder/rectum form? From intermediate mesoderm, which divides the cloaca into bladder and rectum GU Quiz II! What genetic changes can result in XX males or XY females? Wnt4, DAX, SRY or their receptor genes

Name two causes of pseudohermaphroditism Androgen insensitivity Mullerian Inhibiting Factor resistance What is Potters Syndrome? No kidney and look like a mermaid. But you die. How prevalent is horseshoe kidney? 1/400 The Brain and the Branchial Arches Nervous System Formation Day 18-21(wk3): Neural plate folds to form the neural tube

Alar plate(dorsal): sensory Basal plate(ventral): motor Neural Plate Neural tube Brain Expands in front to form telencephalon, diencephalon (forebrain Mesenchephalon (midbrain) Metencephalon, myelincephalon (pons, cerebellum, medulla) Craniofacial : Eye formation Pax6 gene in the optic placode, optic cup(retina), optic stalk Lens buds in Brain Development Prosencephalon(forebr

ain) Mesencephalon(midbrain) Rhombencephalon(hindbrai n) Telencephalon: cerebral cortex, caudate nucleus ,putamen, amygdala Diencephalon: thalamus, hypothalamus, retina

Mesencephalon : midbrain Metencephalon: pons, cerebellum Myelencephalon: medulla Craniofacial formation: Branchial Arches Branchial /Pharyngeal Arches (mesoderm) Begin developing at week 4 Ectoderm on outside, endoderm on inside Between arches, ectoderm contacts endoderm (pharyngeal membrane) Forms tympanic membrane (b/w BA 1 and BA 2)

Branchial arches/Pharyngeal arches Face: Muscles of the face, Palatine tonsil Tongue (1,3,4 BA) Ear The inner ear/Eustachian tube Incus, malleus and stapes Glands: Thymus, Parathyroid Parafollicular C cells of the thyroid Branchial Arch One: Mandibular Arch muscles of mastication tensor tympani tensor veli palatini maxilla

mandible (only as a model for mandible not actual formation of mandible) the incus and malleus of the middle ear Meckel's cartilage Innervation: Trigeminal nerve (V2 and V3) Blood: Maxillary artery Branchial Arch Two: Hyoid Arch Muscles of facial expression buccinator platysma stapedius stylohyoid Stapes of middle ear styloid process,

hyoid (lesser horn and upper part of body), Reichert's cartilage Innervation: Facial nerve (VII) Blood: Stapedial Artery Branchial Arch Three Stylopharyngeus Hyoid (greater horn and lower part of body) thymus inferior parathyroid gland Innervation: Glossopharyngeal nerve (IX) Blood: Common carotid/Internal carotid Branchial Arch Four cricothyroid muscle

all intrinsic muscles of soft palate including levator veli palatini thyroid cartilage epiglottic cartilage superior parathyroid gland Innervation: Vagus nerve (X),Superior laryngeal nerve Blood: Right side: subclavian artery Left side: aortic arch Branchial Arches 5 & 6 intrinsic muscles of larynx except the cricothyroid muscle cricoid cartilage

arytenoid cartilages corniculate cartilage Innervation: Vagus nerve (X),Recurrent laryngeal nerve Blood: Right side: pulmonary artery Left side: Pulmonary artery and ductus arteriosus Pharyngeal/Branchial Arches Endoderm PA-PP1tubotympanic (inside the future recesstympanic cavity of throat of the fetus)

middle ear, auditory/Eustachian tube PA-PP2 and PM2: ear forms -connects middle to palatine tonsil, infiltrated by pharynx lymphoid tissue during mo 3Pharyngeal Pouch 5 (week 12-20)

PA-PP3Dorsal- inferior parathyroid glands, must migrate to future location, source of PA-PP4ectopic parathyroid glands Dorsalsuperior gland parathyroid Ventral-Thymus glands Ventral- Ultimobranchial body/5th PA, migrates to thyroid, implants to form C/parafollicular cells of the 1 2

Mesoder The m first Ectoderm (neural pharyngeal arch tube) also gives rise to Pharyngeal cleft the incus and malleus of the Pharyngeal membrane middle ear Palatine Tonsils

Stapes Inferior parathyroid gland 3 Thymus gland Superior Parathyroid 4 Glands Ultimobranchial C cells of the thyroid body gland 6 Pharyngeal Arch

Craniofacial Development Defects Clefts Ear defects (wk 4-10) Conductive hearing loss (external or middle ear) Sensorineural hearing loss (inner ear, CN VIII, CNS) 150 genes implicated (50% environmental factors) Craniostenosis: abnormal fusion (early or late) of cranial sutures Frontal: Sagittal: tall head Lambdoid: broad head Coronal: bulging forehead Eye Defects Coloboma: pupil extends to the edge of the

iris Aphakia: no lens Aniridia: no iris Congenital cataracts (~rubella) Anophthalmia: no eye/eyes Strabismus: eyes are not aligned Neuro Defects Neural Tube Defects Failure to close Anencephaly: missing a portion of brain Spina bifuda occulta: brain exposed, herniating Holoprosencephaly (Cyclops) Forebrain does not divide to right/left hemispheres

Can get one eye, a nose above the eye, a single nare, a cleft palate, extra midline tooth Neuro Quiz! What does BA1 make? Incus and malleus, eustachian tubes, middle ear BA2? Stapes, palatine tonsil Ventral BA3? thymus Dorsal BA3? INFERIOR parathyroid glands Neuro Quiz II of II

Ventral BA4? Parafollicular C cells of the thyroid Dorsal BA4? SUPERIOR parathyroid glands What nerves innervate each arch? 1: V2/V3 (five), 2: VII(seven), 3: IX(nine), 4: X(ten) What are the 5 embyonic divisions of the nervous system? Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon Muscles and Bones

Musculoskeletal (somites) Limb patterning: 3 axes, outgrowth based on gradient of expression, apical ectodermal ridge Arm ahead of leg Homeobox genes, Shh Ear Bones Incus, malleus BA1 Stapes BA2 MS Somites II-The Tongue From Pharyngeal/Branchial arches 1,3,4 (wk 4) 1: anterior 2/3 From median tongue bud (tuberculum impar) and the lateral lingual swellings Innervation:

Sensory: lingual nerve, a branch of V3 (PA 1) Taste: CN VII, chorda tympani (PA2) 3: posterior 1/3 With 4th arch, forms the pharyngeal/hypobrachial eminence Innervation: Sensory and Taste: CN IX (PA3) 4: base of the tongue, innervated by CN X (PA4) Occipital somites (mesoderm) form muscles of tongue (intrinsic/extrinsic) (CN XII) Thyroid (ecto/endoderm) Originates at the foramen cecum at the center of the border between the

anterior and posterior tongue. Innervation: CN V, VII, IX, X, XII (ectoderm) Musculoskeletal defects Meromelia/Phocomelia: no leg between foot and hip Amelia: Missing limb Achondroplasia Split foot Syndactyly/Polydactyly Pataus syndrome (ch13) Omphalocele 2.5/10,000/Gastroschisis (when body wall closes behind intestines) 1:10,000 Weak abdominal wall allows herniation

Can result in bowel injury:malabsorption/obstruction Volvulus, reflux Tx: surgery MS Quiz! Which grows first from the limb buds, arm or leg? Arm What genes govern limb growth? Homeobox genes, Sonic hedgehog Which branchial arches contribute to the ear bones? BA1: incus, malleus BA2:stapes What chromosome is associated with the polydactyly of

Pataus syndrome? C13 MS Quiz II Which branchial arches form the tongue? 1,3 and 4 What part of the tongue does BA1 form? Anterior 2/3 What part of the tongue does BA3 form? Posterior 1/3 What part of the tongue does BA4 form? The base What forms the skeletal muscles of the tongue? Occipital somites (mesoderm)

MS Quiz III What nerve innervates the part of the tongue created by the first branchial arch? Sensory: lingual nerve, a branch of V3 (PA 1) Taste: CN VII, chorda tympani (PA2) What nerve innervates the part of the tongue created from the 3rd branchial arch? Sensory and Taste: CN IX (PA3) What nerve innervates the skeletal muscles of the tongue?

CN XII Teratogens and Genetics Teratogens and Genetics Increased risk during organogenesis (3 rd-8th wks) Common teratogens EtOH (FAS) Leading cause of congenital malformations pre and postnatal developmental retardation Microcephaly Facial abnormalities Limb dislocation Heart/lung fistulas

Mechanism: inhibition of cell migration (likely) Teratogens II Teratogens ACE- (Renal damage) Cocaine (Fetal addiction and abnormal development) DES (diethylstilbestrol) (Vaginal clear cell carcinoma) Iodide (Hypothyroidism, congenital goiter) Vitamin A/Retinoids Thalidomide (limb defects) Tobacco (preterm labor, ADHD, placental problems) ? Warfarin X-rays Anticonvulsants Fetal Infections

Genetics Uniparental disomy Double non-disjunctions results in two chromosomes from one parent only (none from other parent) Imprinting Phenotype dependent on whether gene was inherited from mom or dad (different methylation of germ cells) Example: single locus ch15 with only one allele active at a given time. (the other is inactivated by methylation) If the active allele is deleted, disease results. Prader-Willie (deletion of normal paternal allele 15q11-q13) Obesity, hypogonadism, hypotonia, infertility and mental retardation

Angelmans (Happy Puppet) syndrome (deletion of moms allele of 15q11-q13) Seizures, ataxia, speech impairment, inappropriate laughter, mental retardation Twinning Separate chorions and amnions 19% MZs, 58% DZ Fused but separate chorions and amnions 13% MZs, 42% DZ Single 1 chorion, 2 amnions 64% of MZs

1 chorion, 1 amnion 4% of Mza Most MZs share a chorion but not an amnion Most DZs have separate chorion and amnion Mosaicism: chimerism due to fusion of two embryos Teratogens and Genetics Quiz! What do monozygotic twins share that dizygotic twins dont? A chorion Name 5 abnormalities associated with FAS Microcephaly, lung/heart fistulas, developmental retardation, facial abnormalities

Whats Prader-Willie Syndrome? Congenital obesity, hypogonadism, mental retardation 15q11-13 DAD deletion Whats Angelman Syndrome? Happy Puppet Syndrome! 15q11-13 MOM allele deletion: seizures, ataxia, mental retardation, inappropriate laughing What is the difference between the effects of DAD/MOMs alleles called? Imprinting Summary Quiz!

Timeline Quiz When do you see the most structural defects? Wks 3-8 When do you get heart defects? Wk 4-6 When do you get limb defects? Wk 4-5 When do you get cleft lip/palate defects? Wk 5-7 When do you get external genitalia defects? Week 8 Germ Layers Quiz What ectodermal defect can occur in week 3? Spina bifida

What type of ectodermal dysplasia is associated with failure of neural crest cell migration? Hirschsprung disease, Wardenberg disease, Neurofibromatosis 1, CATCH22/DiGeorge syndrome. What mesodermal defects can occur? VACTERL What extraembryonic structures contain endoderm? Yolk sac and Allantois, with mesoderm Cardiovascular Quiz What forms the interventricular septum?

The muscular and membranous septa. When is the foramen ovale developed? By week 9 What is the Tetralogy of Fallot? A quintet of defects that center around a VSD and a PDA: overriding aorta, pulmonic stenosis, pulmonary hypertension. When would a PDA save the life of a child? When they have transposition of the great vessels Respiratory Quiz What's so bad about a congenital diaphragmatic hernia and how does this affect treatment?

Prevents complete formation of lungs and heart (hypoplasia of thoracic organs) and is fatal at birth unless surgery is performed in utero. When do the diaphragm and lung buds first form? Week 4 Why do premies often experience respiratory distress? Gastrointestinal Quiz

What are the rotations that the gut must complete and what happens if they dont rotate correctly? 90 counterclockwise followed by 180 counterclockwise or they get volvulus and can rupture What is annular pancreas? Pancreas wrapped around the duodenum What are the three arteries of the GI tract from stomach to colon? Celiac, S. mesenteric, I. mesenteric Genitourinary Quiz Urachal fistula can result in what unfortunate

occurrence in XYs? Failure of penis formation What germ layer forms the gonads and internal genitalia? Intermediate mesoderm What is pseudohermaphroditism? Phenotype(external) doesnt match gonads (internal) Name 5 causes of pseudohermaphroditism? 5a reductase deficiency, mosiacism, CAH, androgen insensitivity, MIF resistance

Neurological Quiz What is holoprosencephaly? Cyclops disease Name 3 eye defects. Aniridia: no iris Anopthalmia: no eye Aphakia: no lens Coloboma: pupil transverses iris. What is craniostenosis? Abnormal fusion of cranial sutures: weird shaped head. Name two types of hearing loss. Sensorineural (CNS/CN defect) Conductive(outer/middle ear defect can be BA defect) Branchial Arches Quiz

What does branchial arch one develop into? Incus, malleus, middle ear What nerve innervates it? CN V BA2? Stapes, palatine tonsil What nerve innervates it? CN VII BA3? Inferior parathyroid glands and thymus What nerve innervates it? CN IX BA4?

Superior parathyroid glands and thryroid C cells What nerve innervates it? CN X Musculoskeletal Quiz What nerves innervate the tongue? CN V3, VII, IX, XII What genes cause limb patterning? Homeobox, Shh When do the limbs bud? Wk 4 What do you call it when the limbs form wrong?

Amelia (no limb), Phoco/Meromelia (short limb) Syn/Polydactyly(extra digits) Teratogens/Genetics Quiz Describe Imprinting Fathers loss of allele has a different effect than mothers allele loss, due to differential methylation. Name 5 drugs that cause congenital defects Lithium-Ebstein anomaly ACE inhibitors Warfarin What's a difference in the surroundings of monozygotic twins v. dizygotic twins? What is uniparental disomy?

Getting two alleles from one parent and none from the other. Yay! You are done with Embryo!! Bibliography Podcast and ppt. First Aid Wikipedia Kaplan embryology http://amazingbeauty.org/embUNC/embUNC- heart.html (great embryo of the heart animations) http://www.med.unc.edu/embryo_images/unitwelcome/welcome_htms/contents.htm (images of all body system formation)

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