Fertilized egg

Fertilized egg

1. morula

   • ICM
     • Epiblast
       • Extraembryonic mesoderm: form vascualture of placenta and umbilical cord
         • Connecting stalk. Forms umbilical cord with mesoderm forming its vasculature
       • Amniotic membrane (extraembryonic ectoderm): surrounds the amnion cavity forming in the epiblast layer
       • Primitive streak (day 14 in caudal half)
         • 3 germ layers
           • Endoderm
             • Digestive tract (epithelium and glands)
               • Foregut
                 • Oral cavity, pharynx, larynx, respiratory system, oesophagus, stomach, duodenum (until bile duct), liver, pancreas, gall bladder, bile duct
                 • Supplied by celiac trunk artery
               • Midgut
                 • Supplied by superior mesentric artery
                 • Small intestine (after bile duct), caecum, appendix, ascending colon, most of transverse colon
               • Hindgut
                 • Supplied by inferior mesenteric artery
                 • remaining large intestine, urinary bladder, most of urethra
             • Accsessory organs
               • Kidney
               • Lungs
               • Pancreas
               • Liver
               • Gall bladder
           • Mesoderm
             • Notochord No BMP
             • Paraxial mesoderm
               • Somites (40/44-38)
                 • Sclerotome: Induced by SHH
                 • Mytotome
                   • Epaxial
                   • Hypaxial
                 • Dermatome
             • Intermediate mesoderm
             • Lateral plate mesoderm
               • Splanchopleuric (endoderm)
                 • Connective tissue and smooth muscle of the digestive tract
                 • Fuse above and below gut forming the ventral and dorsal mesentery. Only dorsal mesentery persists, whereas ventral coelom fuse, only retained near the stomach as Septum Transversum
               • Coelom (cavity)
                 • Body cavities of abdomen
               • Somatopleuric
           • Ectoderm
             • Neural plate: cuboidal epithelium turns into columnar epithelium
               • Neural tube: neural plate folding and fusing along the midline, as notochord induce apical constriction
                 • Brain: CNS
                 • Neural pituitary
                 • Spinal cord
                   • Divided into 9 distinct layers, each containing neurons with a specialised function
                 • Motor neurons
                   • Somatomotor: skeletal muscle/voluntary
                   • Autonomic: smooth + cardiac muscle
                     • Parasympathetic: rest & digest
                     • Sympathetic: fight & flight
                     • Enteric: gut
                 • Retina
             • Outer ectoderm
               • Epidermis
               • Hair
               • Nails
               • Sebaceous glands
               • Olfactory epithelium
               • Mouth epithelium
                 • Anterior pituitary
                 • Odontoblasts
                 • Cheek epithelium
               • Lens + cornea
             • Neural crest cells (pluripotent stem cells)
               • Cranial
                 • Odontoblasts
                 • Schwann celsl
                 • Connective tissue and skeletal contributions (along with some paraxial mesoderm) to the face
               • Vagal
                 • Enteric NS
               • Trunk
                 • Melanocytes
                   • Migrate torso-laterally into ectoderm
                 • Adrenomedullary cells (epinephrine producing medulla cells of the adrenal gland)
                   • Migrate ventro-laterally though anterior half of somite
                 • Sensory (Dorsal root ganglia)
                   • Remain in sclerotome
                   • Each dorsal root ganglia is composed of 3 neural crest populations: neural crest opposite the anterior portion of somite, one from each adjacent region opposite the posterior portions of somites.
                   • Specialized for a distinct modality of sense
                     • Somatosensory: senses onto body, eg. hot, light touch
                     • Viscerosensory; viscera/organs, homeostasis
                     • Special sesnory: ears, nose, eyes etc.
                 • Automomic ganglia
                   • Migrate towards the aorta
               • Lumbo-sacral
                 • Enteric NS
         • Germ cells
       • Primitive node (anterior to streak)
         • Notochord
         • Prechordal plate: loose population of cells (of mesoderm and ectoderm) that underlies the developing forebrain
     • Hypoblast
       • Heusers membrane (extraembryonic endoderm): turn blastocoel into yolk sac
   • Trophoblast
     • Blastocoel: pumps Na into ICM (morula-->blastocyst)
     • Cytotrophoblast
     • Syncytiotrophoblast (multinucleated syncytium) Forms upon implantation starting day 6
       • Function: - Implantation, Differentiate chorion, immunosupression, endocrine gland (release hCG)