Review for the second hour exam, part two Origins of organs and tissues: Teeth Enamel (very hard outer layer of teeth) secreted by infoldings of stomodeal ectodermal epithelium Dentin (American spelling) or Dentine (British) (less hard, bone-like inner part of teeth) secreted by aggregations of neural crest ectodermal mesenchyme. Palate: palatal shelves: infoldings of sides of stomodeum: The palate separates the oral cavity from the nasal cavity (only in mammals) Thyroid Gland: formed by invaginations of anterior endoderm epithelium. Salivary glands: 3 pairs; the most anterior pair form as invaginations of the stomodeal ectoderm. The second and third pair of salivary glands form from invaginations of the anterior endodermal epithelium. Lungs: invaginations in the anterior endodermal epithelium. Liver: invaginations in the endodermal epithelium. Pancreas: invaginations in the endodermal epithelium. Kidney: metanephros; Posterior part of the intermediate mesoderm. Urine duct (Metanephric duct) Posterior intermediate mesoderm. Sperm Duct (=Vas Deferens) same as Pronephric Duct, Wolffian Duct (most anterior part of the intermediate mesoderm) Seminiferous Tubules of testis, develop from genital ridge (primordial germ cells crawl to the genital ridge from the yolk sac in mammals, from a crescent-shaped region of ectoderm anterior to the primitive streak in birds, from the endoderm in frogs, and from the most posterior cells of flies and nematodes, and from somewhere else in teleost fish! Sperm and oocytes develop only from primordial germ cells. Egg duct= oviduct : Müllerian duct; infolding in lateral plate mesoderm. Fallopian tubules develop from anterior end of Müllerian duct. Uterus: develop from middle and posterior parts of Müllerian duct. Many vertebrates have two uteruses; and this sometimes occurs as an abnormality ("birth defect") in humans. (Notice the analogy to formation of two hearts) Coelomic cavity: Lateral plate mesoderm Heart: Lateral plate mesoderm Skeletal muscles: Myotome of somites (paraxial mesoderm) Dermis (inner layer of skin): Dermatome of somites (paraxial mesoderm) Vertebrae: Sclerotome subdivisions of somites Nose (nostrils): Olfactory Placodes (thickenings and infolding of somatic ectoderm) Lenses of eyes: Lens Placodes (thickenings and infolding of somatic ectoderm) Otic Placodes (thickenings and infolding of somatic ectoderm) (inner ear -> semicircular canals, otoliths, "hair cells") Eustachian tube: first pair of gill slits = pharyngeal pouches Tonsils: second pair of gill slits = pharyngeal pouches Parathyroid gland: third and fourth pairs of gill slits = pharyngeal pouches Thymus: third and fourth pairs of gill slits = pharyngeal pouches Brain: Neural Tube Ectoderm Motor Nerves: Neural Tube Ectoderm Pigmented Retina: Neural Tube Ectoderm Neural Retina (of the eye): Neural Tube Ectoderm Optic Nerve: axons of ganglion cells of Neural Retina Sensory nerves: Neural crest ectoderm Post-ganglionic autonomic nerves: Neural crest ectoderm Melanocytes (or other pigment cells of the skin): Neural crest ectoderm Facial bones and muscles: Neural crest ectoderm Cloaca: proctodeum (invagination of posterior somatic ectoderm) Bladder: develops by separation of the anterior part of cloaca. Rectum: develops by separation of the posterior part of cloaca. Epidermis: Outer layer of the skin: Somatic ectoderm Hair, scales, feathers: Outer layer of the skin: Somatic ectoderm. Teleost fish scales are bones: Mesodermal