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What is the order of appearance of the 3 axes?

1. dorso-ventral, 2. rostro-caudal, 3. Left-Right (medio-lateral)

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describe dorso-ventral axis development:

occurs in blastocyst @ 4-5 days post-fertilization. side of inner cell mass facing blastocoele becomes ventral. Amniotic cavity forms @ 8 days over dorsal surface.

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describe rostro-caudal axis development

@ 14 days, prochordal plate develops (rostral). primitive streak forms at caudal end @ 15 days & elongates rostraly.

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describe left-right axis development

@ 15-16 days, cells in primitive streak form mesoderm (different protein expression on left vs. right). looping of heart @ 22-24 days = visible asymmetry.

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Major Stages of Development

1. Pregenesis (prior to fertilization), 2. Early Cell Divisions (0 - 1 1/2 weeks), 3. Embryogenesis (1 1/2 - 4 weeks, 4. Organogenesis (4-8 weeks), 5. Phenogenesis (8-38 weeks), Postnatal Maturation

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Developmental Origin of Gametes

develop from primordial germ cells arising in the yolk sac wall @ 4 weeks. oocytes are produced in 5th month (fetal period)

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Pre-Embryonic Period

0-1 1/2 weeks (when implantation in uterine wall is complete). Cleavage, bilaminar disc. Zygote (cells called Blastomeres) -> Morula (3-4 days) -> Blastocyst

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Determining Fetal Age

menstruation = 14 days after peak fertility. Age of fetus = 2 weeks + date of last period.

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Embryonic Period

1 1/2 - 8 weeks. (1-4 mm). implantation of blastocyst -> gastrulation (3 germ layers)-> neurulation (neural plate)-> trilaminar disc -> cylindrical embryo->organogenesis (heart beat, limb buds, 0.4-3 cm)

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Fetal Period

8-38 weeks. 3.5-35 cm. differentiation & growth of organ primordia, lung branching, facial definition. 10 weeks = external genitalia.

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Postnatal Period

neonatal = 0-4 weeks post-birth: ductus closure, liver maturation, closing of patent ductus, lung expansion, liver metabolism, gain 0.5 oz/day. 13 months - puberty = childhood. Puberty - 18 years = adolescence. 18-death = adulthood.

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Infantile Period growth rate

gain 0.5 oz/day until 1 month, double birth weight @ 5 months, triple birth weight at 1 year.

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What % of couples are infertile?

15% cannot conceive after trying for 6 months

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What % of pregnancies end in spontaneous abortion or stillbirth?

20% are miscarried (spontaneous abortion) / 4 % end in still birth (death after veal viability @24 weeks).

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Deformities occurring during 1/12 - 4 weeks

= embryonic. during blastogenesis, gastrulation & neurulation. VATER syndrome. vertebral/anorectal/tracheo-esophageal fistula/ radial & renal defects.

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Embryonic period deformities

single/multiple anomalies. miscarriage/malformed infant

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Organogenesis abnormalities

5-8 weeks post-fertilization. singular deformaties affecting single organ (e.g. congenital heart defect/spina bifida)

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defects during the fetal period

abnormalities = subtle defects e.g. single palmar crease & normal variants e.g. stork-bite hemangioma. insult = immature lungs, growth retardation, limb deformation (e.g. arthrogryposis), porencephalic cyst in brain due to disrupted cerebral vasculature.

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types of anomalies

isolated/single (usually sporadic), multiple (usually genetic), sequence or syndrome (single cause -> multiple primary anomalies. random). abnormal = defective vs. normal (e.g. birth marks). major = requires medical intervention vs. minor = <4% of people.

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Extrinsic singular anomalies

Disruption = normal development disrupted by dugs/amniotic band constriction/blood vessel clotting or hemorrhage. Deformation = space constraints limit growth (e.g. clubfoot)

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Intrinsic singular anomalies

Malformation = primordial structure is abnormal from genesis (e.g. polydactyly, holoprosencephaly). Dysplasia = tissue surrounding primordium fails to grow (e.g. in adhoncroplasia, limbs are short due to defective cartilage growth)

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Associations

multiple major anomolies that have similar embryonic timing but no known cause(e.g. VATER @ 20-25 days of development). Few minor anomalies (e.g. small face, prominent occiput, clenched fists)

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Sequence vs. Syndrome

Sequence = isolated defect. singular causative anomaly/mechanical factor. Syndrome = multiple defects. no known initiating factor.

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Malformation vs. Dysplasia

malformation = morphological defect resulting from intrinsic anomaly. Dysplasia = disorganization of cells into tissues (e.g. hemangioma).

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Blastomeres

produced by cleavage divisions, pluripotent

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pre-implantation testing

8-16 cell stage, remove single cell for genetic testing.

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morula

same size as the ovum, enters the uterus 4 days post-fertilization

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blastocyst

outer trophoblast layer (invades uterus -> chorion & placenta) & inner cell mass (forms embryo: ventral = inner, dorsal = outer. pluripotent stem cells). forms bilaminar disk @ 8 days (amniotic cavity = dorsal to disk/ yolk sac = ventral to disk)

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prochordal plate

2 layers of blastocyst bilayer plate fuse --> prochordal plate determines location of mouth, anterior-posterior axis of the embryo, head development

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Gastrula

3-4 weeks. primitive streak & primitive node induce migration into mesoderm layer. cells facing amniotic cavity -> ectoderm. cells facing yok sac -> endoderm. ecto & endoderm remain connected @ oropharyngeal membrane (-> mouth) & cloaca membrane (->anus)

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3 tissue layers

ectoderm -> skin, hair, nails, nervous system. mesoderm -> muscle & skeleton. endoderm -> gut & respiratory lining.

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notochord

appears cephalad to the primitive node in the gastrula, provides rigid axis for embryo (mesoderm). induces overlying ectoderm -> neural plate

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neural tube

formed by the folding of the neural plate. progenitor of the CNS. open at rostral & caudal ends (neuropores). lumen ->cerebral ventricles & spinal canal.

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neural crest

= derived from ectoderm cells @ apex of dorsal fold in the neural plate as it forms the neural tube. -> mesenchyme (connective tissue, muscle, bones of face & skull) & spinal ganglia & support cells, melanocytes, adrenal medulla

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limb buds

-> bones & muscles of limbs

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Landmarks on Day 20

axial/intermediate/lateral somites form, GI/mouth/anus/urinary tract(allantois) progenitors form, cardiac tube forms.

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primitive streak

formed @ gastrulation (week3-4). cells migrate along to form mesoderm. shrinks, degenerates into structure @ base of spine, & disappears end of week 4.

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landmarks on week 4

mouth, heart & septum transversum (precursor to diaphragm) fold ventral so that mouth is most rostral. allantois, connecting stalk, & cloacal membrane move ventrally. lateral fold -> yolk sac pinched off, gut/pleural/pericardial/peritoneal cavities form.

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chorionic villi

form from outer trophoblast cell layer of blastocyst. surround embryonic sac. portion under embryo -> placenta. remainder -> chorionic sac.

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spontaneous abortion causes

failure of implantation (morula/blastocyst) w/in 2 weeks of fertilization (mistaken for normal period). 10-15% of pregnancies.

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RU486 (Mefipristone)

inhibits progesterone R. prevents normal implantation (endometrial thickening & vascularization). effective before 7 weeks after last period. 96% effective in terminating pregnancy when taken w/prostaglandins.

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Ectopic Pregnancy

1 in 180-250 pregnancies (higher risk = older mom or low socioeconomic status). venereal disease scarring + tubal inflammation = predisposing factor.

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Anencephaly

Faulty closure of rostral neuropore

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myelomeningocele (spina bifida)

Faulty closure of the caual neuropore -> mass of tangled spinal nerve tissue on back. usually paralysis below the defect.

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sacrococcygeal teratomas

ectoderm (hair), mesoderm (cartilage), & glandular (endoderm) tissues. normally degenerates @ end of week 4. non-malignant.

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early heart development

E20 lateral mesoderm -> u-shaped primordium -> folds together w/2 conotruncal aortic rostral & 2 atrial caudal outlets. heart elongates & loops to bring ventricle caudal & atria cephalad.

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development of internal heart divisions

endocardial cushions ->left & right canals. septum primum -> left & right atrium (flap over foramen ovale). septum secundum helps divide atrium. muscular interventricular septum grows up from apex. membranous septum grows down from endocardial cushions.

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embryonic heart inputs & outputs

inputs = sinus venosus, umbilical/vitelline/cardinal veins. outputs = conotruncal region (bulbus cordis & truncus arteriosus)-> aortic sac -> branchial arches -> dorsal aortas

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spiral septum (aorticopulmonary)

divides pulmonary trunk from aorta. from ridges from walls of bulbus cordis & truncus arteriosus (conotruncal region)

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atrial septal defect

1. persistence of foramen ovale (usually asymptomatic). 2. failure of septum primum/secundum to close completely (extreme = common atrium). 3. abnormal growth of endocardial cushions-> persistent ostium primum w/cleft mitral valve = ostium primum defect.

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atrio-ventricular septal defect

severe failure of endocardial cushion fusion (common in Down syndrome) = severly abormal mitral & tricuspid valves = atrioventricular canal/endocardial cushion defect.

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patent ductus arteriosus

common in premature infants. lungs are overloaded with fluid.

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ventricular septal defect

membranous/muscular VSD. Severe = single ventricle. lungs overloaded when blood from left ventricle -> right ventricle. work stress -> heart failure.

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persistent truncus arteriosus

when spiral septum fails to develop. mixed O2 in aorta + lungs overpressured.

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transposition of the great arteries

when aorticopulmonary septum of truncus arteriosus doesn't spiral. right ventricle -> systemic. left ventricle -> lungs.

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renal development

intermediate mesoderm-> pro/meso/meta-nephroi (cervical->caudal). metanephric diverticulum/ureteric bud-> ureter, renal pelvis/calices/collecting tubule. metanephroic mesoderm-> glomeruli & collecting tubules. kidneys start excreting urine @ 9 weeks.

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bladder development

ventral cloaca & allantois -> urogenital sinus ->bladder & urethra.

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genital development

primary sex cords from urogenital ridge -> undifferentiated gonad (SRY -> testis). mesonephric ducts -> Wolffian ducts (epididymus & vas deferens). paramesonephric ducts -> Mullerian -> uterus/vagina/oviducts (Mullerian Inhibiting Factor prevents).

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renal agenesis = Potter syndrome

due to faulty development of metanephric diverticulum -> low fetal urination & oligohydramnios + anbormal facial features, lax skin, club feet + abnormal lung development & hypoplasia. death x multiple anomaly.

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horseshoe kidney

fusion of kidneys @ lower pole. prevent ascent of kidneys by inferior mesenteric artery. common w/Turner syndrome.

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Exstrophy of the bladder

faulty mesodermal migration to ventral abdominal wall -> bladder protrudes & pelvic bones splay.

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Exstrophy of the cloaca

similar to exstrophy of the bladder + urorectal septum does not form. (faulty mesoderm migration)

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androgen insensitivity syndrome

testes + testosterone but female external genitalia. Mullerian Inhibiting Factor -> no true uterus & oviduct.

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gut development

gut tube suspended by dorsal & ventral mesenteries. ventral degenerates, dorsal provides neurovascular path to distal fore,mid,& hindgut.

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derivatives of the foregut

pharynx, lungs, esophagus, stomach, proximal duodenum, liver, biliary tree, pancreas.

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derivatives of the midgut

midgut herniates into umbilical cord & rotates around superior mesenteric artery -- later returns to abdomen. most of duodenum, small intestines, cecum, colon up to transverse (areas supplied by superior mesenteric artery)

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derivatives of the hindgut

colon (after transverse), rectum, bladder epithelium, urethra. cloaca connects w/allantois. septum divides cloaca into urogenital sinus & rectal canal, -> anal membrane & urogenital membrane of cloaca. anal membrane ruptures= anus open to amniotic cavity.

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duodenal atresia/stenosis

duodenal canal normally closes in week 5-6 & reopens in week 8. with duodenal atresia, it never reopens. presents w/vomiting. double-bubble in X-ray of abdomen. common in Down Syndrome.

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Biliary atresia

incomplete connections of bile canaliculi to hepatic & common bile ducts. children present with hyperbilirubinemia (severe jaundice).

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Omphalocele

protrusion of abdominal contents through hernia (covered w/thin membrane). persistence of normal midgut hernia that should reenter.

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midgut volvulus

midgut twists too much in development, cuts off blood supply, can cause small intestine necrosis.

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ileal diverticulum

= Meckel diverticulum. pouch remains where yolk sac joined midgut. may retain vascular & gastric tissue. bleeds.

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Hirschprung disease

faulty migation of ganglion cells into distal colon causing narrowed aganglionic segment.

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Imperforate anus

membranous anal atresia = persistence of anal membrane that usually perforates at 8 weeks. anorectal agenesis = faulty development of urorectal septum (fistulas w/bladder/vagina/urethra may be present)

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respiratory tract early development

branches off of primitive foregut (week 4) = laryngotracheal diverticulum. mesenchyme surrounds. tracheoesophageal folds fuse -> tracheoesophageal septum. lung bud branches into 2 primary bronchi

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respiratory tract later development

lungs grow until 26 weeks, terminal saccules ->28 weeks, immature alveoli -> 32 weeks (capable of function), alveoli continue to develop for several years

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diaphragm development

septum transversum= between future thoracic cavity & yolk sac, partly separates thoracic from abdominal cavity. pleuroperitoneal folds from dorsum fuse w/ventral septum transversum -> diaphragm. left side fuses later than right.

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respiratory distress syndrome

infants born before 26 weeks may not have enough alveoli/surfactant

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pulmonary hypoplasia

decreased lung capacity with tachypnea, respiratory distress. caused by decreased amniotic fluid or lung compression (e.g. diaphragmatic hernia)

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esophageal atresia

blind esophagus caused by posterior deviation of the tracheoesophageal septum. frequently associated w/tracheoesophageal fistula

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tracheoesophageal fistula

faulty separation of the trachea & esophagus. "h" type = mild, food inhaled into lungs. severe = blockage of trachea/esophagus via esophageal atresia.

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congenital diaphragmatic hernia

posterior gap in diaphragm allows intestines to enter chest & restrict lung development. usually on left. high mortality rate, cannot be surgically corrected.

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secondary brain vesicles

HINDBRAIN: myelencephalon = medulla & 4th ventricle, metencephalon = pons, cerebellum, 4th ventricle. MIDBRAIN:mesencephalon = midbrain, aqueduct. FOREBRAIN: Diencephalon = Thalamus, 3d ventricle, telencephalon = cerebrum, lateral ventricles.

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eye development

retina = from forebrain. lens placodes (ectoderm), choroid & sclera (mesoderm).

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inner ear development

ectoderm (from otic placodes).

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skin layers of the head

ectoderm -> epidermis. mesoderm -> dermis.

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branchial arches, about

(=pharyngeal arches). end of week 4. from mesenchymal neural crest in neck + mesoderm. layered w/ecto & endoderm. 4 arches visible w/grooves (5 & 6 rudimentary), 1 aortic arch per branchial arch. pharyngeal pouch b/tw each arch (inner side).

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branchial arch derivatives

1: maxilla, mandible, mastication muscles & trigeminal nerve. 2: facial muscles & facial nerve. pharyngeal pouches -> middle ear.

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facial development

frontonasal prominence induced by forebrain development -> nose & upper face (fuse to form primary palate). palatal shelves on walls of pharynx -> 2ndary palate. 1st pharyngeal pouch -> middle ear. prominences @ sides of 1st branchial groove -> outer ear.

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palate development

primary (anterior) from fusion of frontonasal prominences. secondary from palatal shelves (walls of pharynx). shelves initially oriented caudally, but rotate ventrally above developing tongue & fuse.

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congenital hydrocephalus

caused by abnormal closure of the neural tube -> CSF buildup in brain & head enlargement. severe conditions -> brain atrophy. can be caused by X-linked recessive mutation.

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holoprosencephaly

defective prosencephalon differentiation can -> arrhinencaphaly, or undeveloped prosencephalon w/1 ventricle. mild= cleft palate. severe= ceocephaly (primate-like nose), hypotelorism (narrow-set eyes), cyclopia (single eye + proboscis instead of nose)

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cleft palate

ANTERIOR= due to abnormal primary palate development or its abnormal fusion w/lateral palatine processes (shelves). POSTERIOR= abnormal fusion of lateral palatine processes.

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lissencephaly

smooth brain w/no sulci & gyri. failure of cerebral neurons to migrate properly.

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Pierre Robin sequence

1st branchial arch anomaly -> small mandible, protruding tongue through palatal shelves w/out fusion. cleft soft palate & tongue protruding over jaw (glossoptosis)

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hemifacial microsomia

small mandible & unilateral external ear anomalies.

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Goldenhar syndrome

similar to hemifacial microsomia + extra tissue over sclerae, cleft eyelids, absent cervical & thoracic vertebre, scoliosis, cardiac septal defects (tetralogy of Fallot), urinary tract anomalies.

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DiGeorge anomaly

small jaw, hypoparathyroidism, hypocalcemia, absent thymus (+ immune defects), interrupted aortic arch (coarctation of aorta). can be sporadic or caused by deletion of 22q11. multiple branchial arch developmental abnormalities.

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cleft lip

CLEFT LIP: lateral = failure of maxillary & nasal prominences to fuse. midline = rare, usually due to arrhinencaphaly/holoprosencaphaly.

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axial vs. appendicular skeleton

axial = vertebrae, ribs, sternum. appendicular = shoulder, pelvis, & limbs.

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paraxial, intermediate, & lateral mesoderm

paraxial= lateral & ventral to neural tube-> somites, skin/muscle/bones of trunk. intermediate mesoderm= more lateral-> urogenital system. lateral mesoderm= more lateral-> pleural/pericardial/peritoneal membranes, heart, spleen & blood-forming tissues.

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somite development

paraxial mesoderm -> dermatome, myotome, sclerotome of trunk. mesoderm -> mesenchyme (pluripotent) -> fibro-, chondro-, osteo-, & myoblasts.

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bone development

from paraxial mesoderm -> somites. membranous bones (e.g. skull/jaw) from mesenchyme. echondral bones (e.g. long limb bones) from chondroblasts (cartilage matrix). vertebrae from osteoblasts, ribs grow from vertebrae. skull from somites & neural crest.

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limb development

arm limb buds appear prior to leg. long bones have ends (epiphysis), necks (metaphysis), & shafts (diaphysis). primary ossification centers= in diaphyses (fetal). 2ndary ossification= in epiphyses (postnatal). muscles= from mesenchyme surrounding bones.

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limb axes

proximal-distal (from apical epidermal ridge @ end of limb bud), dorso-ventral, preaxial-potaxial (e.g. thumb -> pinky).

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ectrodactyly

lobster claw, due to bilateral defects of middle digital rays (2-4). may be associated w/Ectrodactyly-Ectodermal Dysplasia-Clefting syndrome OR as isolated anomaly or non-genetic birth defect.

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syndactyly

digit fusion -> mitten hand. defects in apoptosis of digit rays. may be associated w/Apert Syndrome w/ Craniosynostosis, defects in FGFR2, or isolated congenital anomaly.

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polydactyly

extra digits, usually ulnar(postaxial polydactyly) due to extra apoptotic centers. may be associated w/trisomy 13, Smith-Lemli-Opitz Syndrome (defect in cholesterol synthesis), or isolated anomaly. most common in African Americans.

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Events in Week 1 of Development

Fertilization, Cleavage, Morula, Implantation

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Events in Week 2 of Development

Bilaminar Disc, Placental Circulation, Axes

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Events in Week 3 of Development

Primitive Streak, Notochord, Neural Plate, Neural Groove, Somites

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Events in Week 4 of Development

Trilaminar Disc -> cylindrical embryo, Heart Beats, Neural folds fuse, Neuropores, Branchial Arches, Eye/Ear primordia, Limb Buds

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Events in Week 5 of Development

Nasal Pits, Optic Cup, Hand/Foot Plates, Cerebral Vesicles

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Events in Week 6 of Development

Upper lip, Digits defined, Palate

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Events in Week 7 of Development

Eyelids, Primitive Genitalia

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Events in Week 8 of Development

Arms bend @ elbows, primordia of all organs present

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cleft lip

midline cleft lip= holoproencephaly. lateral= failure of frontonasal prominence fusion.

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