Early Embryonic Development3cell, biology, pdf, book, medical, journal,

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Early Embryonic Development #3 Dr. Johnson Week 7, Monday 9/22/14 Lesson Objectives 1. Review gastrulation 2. Learn mechanism of neurulation 3. Learn neural crest derivatives 4. Describe etiology of DiGeorge syndrome 5. Define neural tube defects (NTDs) 6. Describe role of α-fetoprotein in prenatal diagnosis of NTDs 7. Describe different kinds of NTDs PART 1: Development of the CNS A. Consequences of Gastrulation 1. There are three primary germ layers established: a. Ectoderm forms outer surface and CNS b. Mesoderm forms CT, muscle, CV system and GU system c. Endoderm forms lining of gut tube 2. Basic body plan begins to unfold B. Early CNS 1. In early development, deep tissues beneath superficial layer on outer surface of embryo induce formation of mid-line neural plate 2. Neural plate expanded in cranial part-becomes brain 3. Neural plate narrow in caudal part-become spinal cord 4. Neural plate folds up into neural tube-neural crest leaves neuroepithelium-neural tubes sinks beneath surface of the body's 1

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Transcript of Early Embryonic Development3cell, biology, pdf, book, medical, journal,

Page 1: Early Embryonic Development3cell, biology, pdf, book, medical, journal,

Early Embryonic Development #3Dr. JohnsonWeek 7, Monday 9/22/14

Lesson Objectives1. Review gastrulation2. Learn mechanism of neurulation3. Learn neural crest derivatives4. Describe etiology of DiGeorge syndrome5. Define neural tube defects (NTDs)6. Describe role of α-fetoprotein in prenatal diagnosis of NTDs7. Describe different kinds of NTDs

PART 1: Development of the CNS

A. Consequences of Gastrulation1. There are three primary germ layers established:

a. Ectoderm forms outer surface and CNSb. Mesoderm forms CT, muscle, CV system and GU systemc. Endoderm forms lining of gut tube

2. Basic body plan begins to unfoldB. Early CNS

1. In early development, deep tissues beneath superficial layer on outer surface of embryo induce formation of mid-line neural plate

2. Neural plate expanded in cranial part-becomes brain3. Neural plate narrow in caudal part-become spinal cord4. Neural plate folds up into neural tube-neural crest leaves neuroepithelium-

neural tubes sinks beneath surface of the body's

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Page 2: Early Embryonic Development3cell, biology, pdf, book, medical, journal,

C. Neural Crest I1. Along dorsal midline of neural tube , neural crest cells exit the

neuroepithelium with an epithelial to mesenchymal transition…so this means that the neural crest cells will lose their epithelial qualities and will become more like Connective Tissues

2. These become widely dispersed throughout the body3. They differentiate into a highly diverse, pluripotent group of cells

D. Neural Crest II1. These cells make important contributions to nervous system, ex is

Schwann cells which originate from neural crest cells…they form the myelin of the Peripheral Nervous System neurons

2. Also these cells, form the dorsal roote ganglia, some CAN ganglia and numerous autonomic ganglia…note that the dorsal root ganglia consists of sensory neurons that originate in the body and extend toward the CNS

3. These cells make gut intrinsic innervation-myenteric plexus and submucosal plexus

4. NC make adrenal medulla5. NC makes part of the meninges surrounding CNS

E. Neural Crest III1. NC forms part of head mesenchyme, forming parts of facial bones, muscles

and ligaments and contributes to sclera of eye2. NC makes odontoblasts, dentin producing cells of teeth3. NC makes melanocytes, pigment producing cells in skin and elsewhere in

body

* Conotruncal septum is the opening between the pulmonary and systemic sections of the heart during development…made of NC cells

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F. DiGeorge Syndrome1. This disorder 22q11.2 Syndrome (deletion in #22)2. About 1/25003. Characterized by parathyroid aplasia (tetany and seizures), thymic aplasia

(decreased T cell function>opportunistic infections, ex oral thrush, subtle craniofacial anomalies(short philtrum, hypertelorism, microstomia), and cardiovascular anomalies

4. Results from abnormal migration and differentiation of neural crest cells

G. Neuroepithelium

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Page 4: Early Embryonic Development3cell, biology, pdf, book, medical, journal,

1. Primitive neural tube consists of highly proliferative, pseudostratified epithelium

2. Stem cells divide rapidly by mitosis, one daughter cell differentiates, other continues to divide

3. Some stem cells form neuroblasts, which differentiate into neurons 4. Other stem cells form glioblasts, which differentiate into glia

H. Wall of Neural Tube Thickens1. By repeated mitoses of stem cells, thickness of neuroepithelium increases

dramatically2. Thickening is large in spinal cord3. Thickening is even larger in brain

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Page 5: Early Embryonic Development3cell, biology, pdf, book, medical, journal,

PART 2: The Brain

A. General Info1. Cranial end of neural tube grows more rapidly than caudal end2. Cranial end forms brain, caudal end forms spinal cord3. Cranial end forms three primary brain vesicles,

prosencephalon(forebrain), mesencephalon(midbrain), and rhombencephalon(hindbrain)

B. Neural Tube Defects (NTDs)1. Common kind of congenital birth defects2. Typically caused by failure of neural tube closure and/or induction of bony

neural arches of spinal cord3. Range in severity from asymptomatic spina bifida occulta to devastating

and fatal anencephaly C. Etiology of NTDs

1. Multifactorial etiology-some genetic and some environmental-difficult to sort out

2. Higher incidence among Irish in Dublin3. Slightly lower incidence in Irish Americans in Boston4. Low incidence in African Americans in Boston5. Prenatal folic acid supplementation reduces incidence about 80%

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Page 6: Early Embryonic Development3cell, biology, pdf, book, medical, journal,

1. Spina Bifida Occulta: least severe, in this case there is bifida vertebrae, there is no herniation so no tugging/pulling of nerve tissue so skin forms instead of normal bony arch to protect spinal cord …will present with small hairy patch of skin under which the bifida vertebrae is present

2. Meningocele shows bulging3. Meningomyelocele the spinal cord forms in the CSF filled sac, pulling on

nervous tissue, severe neurodefecits4. Neural plate doesn’t close: Rachischisis so there is no neural tube

* The picture on the left shows the spinal cord which is exposed. Neuroectodem is degenerative so everything downstream of it will not work properly

* The image on th right shows that the occipatl bone does not form so large amount of nervous tissue herniating out

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* This is an anencephalic fetus…there is no brain just degenerated nervous tissue

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