Alimentary System Question And Answers

Question 1. Development of tongue.
Answer:

• Development of the tongue starts in the fourth week of intrauterine life
• The medial most parts of the mandibular arches proliferate to form two lingual swellings.
• These lingual swellings are partially separated from each other by another swelling called tuberculum impair.
• These are derived from 1st branchial arch.

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• Another midline swelling, hypobranchial eminence is derived from mesoderm of the second, third, and part of the fourth arch.

• It is sub-divided into cranial and caudal part.
• The anterior two-thirds of the tongue is formed by fusion of
  1. The tuberculum impair and
  2. The two lingual swelling.
• The posterior one-third of the tongue is derived from the cranial part of the hypobranchial eminence.
• The posterior-most part of the tongue is derived from the fourth arch.
• The musculature of the tongue is derived from the occipital myotomes.
• Taste buds are formed in relation to the terminal branches of the innervating nerve fibres.
• Nerve supply of the tongue depends on the its developmental derivation.
• Anterior two-third of the tongue is supplied by lingual branch of mandibular nerve which i branchial arch.
• Posterior one third is supplied by the glossopharyngeal nerve, nerve of third branchial arch.
• Posterior most part is supplied by the superior laryngeal nerve, nerve of the fourth branchial arch.

Question 2. Give a detailed account of development of milk teeth.
Answer:

• By the sixth week of development of basal layer of the epithelial lining of the oral cavity forms dental
  lamina.
• This lamina gives rise to 16 localized thickened buds called enamel organs.
• The enamel organ grows downwards assuming a cup-shaped appearance which is occupied by dental papilla.
• This stage is described as cap stage.
• The cells of the enamel organ lining the papilla become columnar called ameloblasts.
• Mesodermal cells of the papilla form a continuous epithelium-like layer called odontoblast.
• The remaining cells form the pulp.
• The developing tooth now looks like a bell.
• Amelobasts lay down enamel while odontoblasts lay down dentin.
• Odontoblasts in the root region lay down dentin.
• The dentin is covered by mesenchymal which lay down cementum.
• Outside it, mesenchymal cells from the periodontal ligament.

Question 3. Structure of tooth (labelled diagram only)
Answer:

Question 3. Enumerate congenital anomalies of teeth.
Answer:

• Anodontia – absence of teeth.
• Supernumerary teeth – extra number of teeth.
• Abnormal teeth.
• Gemination – fusion of two/more teeth.
• Precocious – early eruption of teeth.
• Delayed eruption of teeth.
• Ectopic eruption of teeth.
• Improper formation of enamel and dentin.

Question 4. Development of oral mucosa.
Answer:

• The oral cavity is derived partly from the ectoderm and partly from the endoderm.
• The anterior part of the oral cavity is derived from the ectoderm while tongue, epiglottis and pharynx are derived from the endoderm.
• The vestibular lamina separates from the primary epithelial band at about 6 weeks.
• Degeneration of the cells in the central part of this process leads to the formation of labial and buccal sulcus.
• The tongue is separated from the rest of the mandibular process by linguo-gingival sulcus.
• The alveolar process of the upper jaw is separated from the upper lip and cheek by labio-gingival sulcus appears laterally to the linguo-gingival sulcus.