Lecture_8_-_Integument

Kk 620 hg 613 mammary glands mammary glands arise

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Unformatted text preview: not considered to be homologous to reptilian scales. KK 6.20, H&G 6.13 Mammary Glands Mammary glands arise from ectoderm that descends along 2 folds or “milk lines” in the embryo. KK 6.22, H&G 6.14 Monotreme Keratin structures in mammals • • • • • • • hair, including sensory bristles pangolin scales (e.g. pangolin, armadillo) unguis (claws, nails, hooves) “true” horns (e.g. cow, antelope) rhinocerus horn baleen (baleen whales) quills (porcupine, hedgehog, echidna) echidna keratin horns bony imposters Teeth Teeth are also structures of the integument. They have fundamentally the same structure as the armour of ancient fishes and placoid scales of sharks. Teeth arise at the interface between the epidermis and the dermis. The epidermis produces the enamel from above, and the dermis produces the dentin from below. KK 6.32 Continuous formation of shark teeth. Mammalian Tooth Development Mammalian teeth also begin as a fold in the margin of the jaw, even though they are anchored in bone rather than integument. Special cells of the epidermis (ameloblasts) produce enamel, while odonoblasts from the dermis secrete dentine. Again, the tooth grows between epidermis and dermis. Neural crest contributes as well. KK 13.8, H&G 7.2...
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