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Embryo2010
| Question | Answer |
|---|---|
| Name the three axes that determine the body plan. | Dorsal-ventral, cranial/rostral-caudal, left-right |
| How is dorsal-ventral determined? | At blastocyst formation (4-5days): the side of the inner cell mass facing the blastocoele will become ventral |
| Name the stages of embryonic development. | Pregenesis, early cell divisions, embryogenesis, organogenesis, phenogenesis |
| Pregenesis | Formation of germ line and gametes to the moment of fertilization |
| Early cell divisions | From conception (0wks) to 1.5wks: cleavage, blastogenesis, when implantation into the uterine wall is complete |
| Embryogenesis | Gastrulation - form three germ layers, and neurulation - form nervous system |
| Organogenesis | Genesis of organ system primordia |
| Phenogenesis | "Fine tuning" of development generating traits constituting family resemblance and racial affiliation (fetal period) |
| How is rostral-caudal determined? | By the appearance of the prochordal plate(14days): prochordal plate forms at head end, primitive streak forms at tail end and elongates toward prochordal plate |
| How is left-right determined? | During gastrulation during formation of three primordial cell layers(15-16days): cells left and right of the mesoderm express different proteins (first visible with looping of heart) |
| Normal variant, major anomaly, minor anomaly | Normal variants - >4% of the population, least significant, major anomaly - carries medical, surgical, or cosmetic consequences, minor anomaly - benign |
| Disruption, deformation, malformation, dysplasia | Classifications of single anomalies: Extrinsic: Disruption-impacts normally developing structure, Deformation-developing structure is constrained in space. Intrinsic: Malformation-defective primordia, Dysplasia-deffective tissue surrounding primordia |
| Sequence, syndrome, association | Sequence - cascade of events resulting from single primary malformation or disruption, sporadic Syndrome - multiple primary anomalies (major and minor) due to similar cause, genetic Association - multiple major anomalies with similar embryonic timing |
| Ovulation | Ovarian follicles contain oocytes suspended in the middle of meiosis from fifth month of fetal life to ovulation. Follicle ruptures and becomes corpus luteum - secretes progesterone to maintain uterine lining |
| Fertilization | Sperm induces oocyte to complete meiosis, restoring diploid, cleavage of zygote, pre-implantation diagnosis if in-vitro |
| Morula | Enters uterine cavity (4days) |
| Blastocyst | Hollowed out morula, consisting of outer trophoblast and inner cell blast (becomes embryo, source of embryonic stem cells), side facing blastocyst becomes ventral surface, implants in uterine wall (6days) |
| Bilaminar disk | Formed by inner cell mass (8days), a portion fuses to become prochordal plate - location of mouth, determines rostro-caudal axis |
| Amniotic cavity | Forms dorsal to bilaminar disk |
| Yolk sac | Forms ventral to bilaminar disk |
| Gastrulation | Embryo becomes three-layered structure (3-4wks), primitive streak (caudal end) and primitive node (cranial end) form. Mesoderm forms in the middle of primitive streak: ectoderm faces amniotic cavity, endoderm faces yolk sac |
| Ectoderm is the precursor to... | Skin(epidermis), hair, nails, teeth, nervous system |
| Mesoderm is the precursor to... | Muscle, skeleton, dermis |
| Endoderm is the precursor to... | Gut, respiratory lining |
| Neural tube development | Notochord(mesoderm) induces neural plate(ectoderm) to form, folds into neural crest then closes to become neural tube. Neural plate-brain and spinal cord, neural tube lumen-cerebral ventricles and spinal canal, neural crest-spinal ganglia and PNS |
| Describe the development and contents of the head fold. | Mouth, heart, foregut. These and septum transversum(diaphragm) are moved caudal to developing brain. Foregut. |
| Describe the development and contents of the tail fold. | Cloacal membrane(anus), allantois and connecting stalk(umbilical cord) are moved to ventral surface. Hindgut. |
| Describe the development and contents of the lateral folds. | Pinch off yolk sac and internal cavity for pleural, pericardial, and peritoneal cavities. Midgut. |
| Placenta | Develops from chorionic villi(removed for CVS) initially surrounding embryonic sac |
| Mechanism of mefipristerone | Inhibits progesterone receptor and endometrial thickening and vacsularization preventing implantation, terminates <7wk pregnancy |
| Early miscarriage | Failure of implantation in first two weeks |
| Ectopic pregnancy | Implanation other than in uterine wall |
| Anencephaly and myelomeningocoele | Neural tube defects: A - failure of rostral neuropore to close, brain is exposed M/spina bifida - failure of caudal neuropore to close, exposed spinal nerve tissue |
| Sacrococcygeal teratomas | Tumors at base of spinal column with ecto/meso/endo-dermal tissue from failure to degenerate primitive streak |
| Folding of the heart | Head fold brings heart caudal to oropharyngeal membrane, lateral folds brings left and right lobes of cardiac together in the midline ventral to foregut |
| Heart tube | U-shaped, two lobes fuse with left and right openings at rostral and caudal ends. Rostral openings connect to dorsal aortas (right later degenerates), aortic arches connect tube to dorsal aortas. Caudal end connects with sinus venosus |
| Embryonic arterial and venous connections to heart | Aortic arches become carotids, right subclavian, ductus arteriosus, ascending aorta. Sinus venosus drains umbilical vein, vitelline vein(yolk sac), and cardial veins. |
| Looping for atria and ventricles | As the heart tube elongates it forms a loop which brings ventricle caudal and atria cephalad |
| Endocardial cushions | Grow from the juncture of atrium and ventricle and partition heart into left and right canals |
| Partitioning of the atria | Septum primum and septum secundum grow down dividing atrium into left and right halves. Foramen ovale in septum secundum allows oxy blood to flow to left atrium in fetus |
| Partitioning of the ventricles | Muscular interventricular septum grows up dividing ventricle into left and right halves. Endocardial cushion grows down to meet it forming membranous septum. |
| Partitioning of the arterial outflow tract | Foramen ovale - oxy blood from placenta through right atrium to left atrium (feeds head) Ductus arteriosus - shunts blood from pulmonary artery to aorta bypassing lungs (feeds body) |
| Atrial septal defects | Persistence of foramen ovale, failure of septum primum/secundum to close, abnormal growth of endocardial cushions |
| Endocardial cushion defects | Produces atrio-ventricular defect, common in Down syndrome, abnormal mitral and tricuspid valves and blood from left and right halves mix |
| Patent ductus arteriosus | Persistence of ductus arteriosus, blood shunts from aorta to pulmonary artery and overloads lungs, common in premature infants |
| Ventricular septal defects | Incomplete formation of interventricular septum. Membranous VSD most common - faulty growth of endocardial cushion cells. Muscular VSD - faulty growth of interventricular ridge. Blood from LV goes to RV, overloads lungs, decreases blood |
| Persistent truncus arteriosis | Failure of spiral septum to develop, aorta and pulmonary artery not separated. Mixed oxy/deoxy blood in aorta and lungs exposed to high pressure |
| Transposition of the great vessels | Failure of septum in truncus arteriosus to spiral properly. Blood from right ventricle goes to aorta and body while blood from left ventricle goes to pulmonary artery and lungs |
| Origin of urogenital ridge | Intermediate mesoderm during lateral folding |
| Three primordial kidney structures | 1. pronephroi in cervical region 2. mesonephroi in midsection 3. metanephroi in caudal area (kidneys) |
| Origin of the adult kidney | Forms from metanephroi near the sacrum but then ascend due to caudal growth |
| Origin of the urinary bladder | Forms from ventral portion of cloaca (urogenital sinus) and allantois (degenerates to median umbilical fold). Hindgut-derived. |
| Differentiation of the indifferent gonad | Primary sex cords extend from urogenital ridge. Develops into ovary unless influence of Y chromosome and SRY transcription factor (testis) |
| Wolffian v. Mullerian ducts | Mesonephric ducts become Wolffian ducts - epididymus and vas deferens in male. Paramesonephric (Mullerian) ducts - uterus, vagina, oviducts in female. Prevented in males by Mullerian Inhibiting Factor secreted by testis |
| Differentiation of external genitalia | In the absense of testosterone, female genitalia develop |
| Potter sequence | Faulty development of metanephric diverticulum leading to abnormal or absent kidneys bilaterally (renal agenesis) leading to decreased amniotic fluid |
| Horseshoe kidney | Fusion of lower poles of kidney produce U-shaped kidney, remains in pelvis |
| Exstrophy of the bladder | Faulty mesodermal migration to ventral abdominal wall leading to protrusion of the bladder and ureters with splaying pelvic bones |
| Androgen insensitivity syndrome | Defective androgen receptors - Y chromosome males have female external genitalia |
| What are the adult structures derived from foregut? | Pharynx, lungs, esophagus, stomach, proximal duodenum, liver, biliary tree, pancrease |
| What are the adult structures derived from midgut? | Most of the duodenum, small intestine, cecum, large intestine up to middle of transverse colon |
| What are the adult structures derived from hindgut? | Remaining large intestine, rectum up to superior portion of anal canal, epithelium of urinary bladder, most of urethra |
| Development of liver and pancreas | Bud off from the caudal part of the foregut |
| How does the midgut move during development? | As it elongates it herniates into the umbilical cord and rotates around the superior mesenteric artery, and later returns to the abdomen |
| What are the blood supplies of the foregut, midgut, and hindgut? | Foregut - celiac artery Midgut - superior mesenteric artery Hindgut - inferior mesenteric artery |
| How is the hindgut partitioned into the rectal and urinary tracts? | A septum grows and divides the cloaca into a urogenital sinus and a rectal canal |
| Duodenal atresia | Lack of recanalization of the duodenum |
| Biliary atresia | Incomplete connections of bile canaliculi with hepatic and common bile ducts |
| Omphalocoele | Protrusion of abdominal contents through umbilical hernia |
| Midgut volvulus | Faulty midgut rotation leading to twisting of jejunum or ileum on its mesentery obstructing the blood supply |
| Meckel diverticulum | A pouch at the point where the yolk sac joined the midgut, maybe with vascular and gastric tissue leading to ulcers and bleeding |
| Hirschprung disease | Faulty migration of ganglion cells into the distal large intestine causing a narrowed segment with abnormal movements/obstruction |
| Imperforate anus | Persistence of anal membrane, or faulty development of urorectal septum (rectum may be connected to bladder/urethra/vagina) |
| How is the respiratory tree derived from the foregut? | Respiratory tract buds off foregut (4wks) as laryngotracheal diverticulum. Mesenchyme surrounds diverticulum forming lung bud. |
| How is the laryngotracheal tube divided from the esophagus? | Tracheoesophageal folds from foregut fuse to form tracheoesophageal septum dividing laryngotracheal tube from esophagus. |
| Describe the branching of the bronchial tree. | Lung bud < two bronchial buds=primary bronchi < secondary bronchi and bronchioles (until 24-26wks) < terminal saccules (26-28wks) can exchange some air = alveoli (32wks) full air exchange but need pulmonary surfactant to prevent collapse |
| How is the chest cavity divided from the abdominal cavity? | Septum transversum, a band of mesodermal tissue, lies between future thoracic cavity and yolk sac. Pleuroperitoneal folds from dorsal sides fuse with ventral septum forming diaphragm and dividing thoracic and abdominal cavities. |
| Respiratory distress syndrome | Due to extreme prematurity (before 26wks), without enough surfactant, surface tension collapses alveoli |
| Pulmonary hypoplasia | Decreased amniotic fluid or compression of the lungs can stunt lung development and decrease lung capacity |
| Esophageal atresia | Blind-ended esophagus due to faulty tracheoesophageal septum cutting off esophagus from foregut |
| Congenital diaphragmatic hernia | A posterior gap in diaphragm allows intestines to enter chest and restrict lung development, occur most often on the left (form and fuse later) |
| Tracheoesophageal fistula | Faulty separation of trachea and esophagus due to incomplete development of tracheoesophageal folds and septum |
| How do the brain and spinal cord develop from the neural tube? | Anterior portion of neural tube develops into three primary brain vesicles which divide into five secondary vesicles. Forebrain/telencephalon become cerebral hemispheres. The more caudal part of neural tube becomes spinal cord. |
| What does neural crest develop into? | PNS - spinal dorsal root ganglia and sympathetic nervous system |
| Origins of the eye | Forebrain - retina, overlying ectoderm - lens, mesoderm - choroid and sclera |
| Origins of the ear | Ectoderm on the side of the head thickens at first branchial groove to form otic placodes which invaginate forming inner ear. Middle and outer ear formed from pharyngeal pouches. |
| Origins of the branchial arches and pharyngeal pouches | Formed (4wks) when mensenchymal neural crest cells migrate into neck area. Each arch is covered by ectoderm on outside and endoderm on inside. Pouches line the inner surface of the arches and are located between each pair of arches |
| Describe the development of the face. | From branchial arches and pharyngeal pouches. First arch - maxilla, mandible, muscles of mastication, CN V. Second arch - facial muscles, CN VII. Forebrain induces frontonasal prominence (nose and upper face) |
| Describe the development of the palate. | Front of the (primary) palate - fusion of frontonasal prominences. Secondary palate - fusion of palatal shelves along the walls of the pharynx as they elevate above the tongue |
| Congenital hydrocephalus | Blocked flow of cerebrospinal fluid, often by failure of the neural tube lumen to stay open. Dilation of ventricles and enlarged head. |
| Holoprosencephaly | Defect in prosencephalon differentiation, can lead to underdeveloped forebrain, hypopituitarism, midline cleft palate, cebocephaly, cyclopia |
| Lissencephaly | Failure of cerebral neurons to migrate to brain's surface, smooth brain with underdeveloped sulci and gyri |
| Pierre Robin sequence | First arch anomaly - maldevelopment of jaw, which interferes with tongue decent, which results in a cleft soft palate |
| Hemifacial microsomia (Goldenhar syndrome) | First and second arch anomaly - small jaw and external ear anomaly, often unilateral. Goldenhar - with ocular, vertebral, cardiac, and urinary tract anomalies |
| DiGeorge anomaly | Small jaw, hypoparathyroidism, hypocalcemia, absent thymus with immune defects, interripted aortic arch |
| Cleft lip | Failure of maxillary and nasal prominences to fuse, often lateral. |
| Cleft palate | Anterior cleft - faulty development of primary palate and improper fusion of primary palate with lateral palatine processes (shelves). Posterior - abnormal fusion of lateral palatine processes. |
| Differentiation of somites into three layers | Dermatome - dermis Myotome - muscles of the trunk Sclerotome - vertebra and ribs |
| Origin and fate of mesenchyme | From undifferentiated mesoderm, can become fibroblasts (connective tissue), chondroblasts (cartilage), osteoblasts (bone), myoblasts (muscle) |
| Developmental origin of membranous bones | (skull and jaw) form directly from mesenchyme |
| Developmental origin of enchondral bones | (long bones of limbs) form from cartilage matrix |
| Developmental origin of limbs | Limb buds |
| Name the three axes that determine limb development. | Proximal-distal, Ventral-dorsal, Preaxial-postaxial (thumb-pinkie) |
| Describe the mode of formation of the bones of the hand. | Apoptosis in the flat plates causes formation of 5 digital rays |
| Ectrodactyly | aka lobster claw deformity, defect in middle digital rays |
| Syndactyly | aka mitten hand, defect in formation of apoptotic centers in developing digital ray |
| Polydactyly | extra digit (usually ulnar side), extra apoptotic centers in developing hands |
Created by:
amc319
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