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Chapter 26

ANAT100 Chapter 26: Module10: Digestive System

Anatomy and Cell Biology
Course Code
ANAT 100
Leslie W Mac Kenzie

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Module 10: Digestive System
10.1 Digestive System I
includes organs that ingest the food, transport ingested material, digest material into smaller
usable components, absorb necessary digested nutrients into bloodstream, and expel waste
products from the body
Components of the digestive system:
1. Digestive tract (alimentary canal): mouth, oral cavity, pharynx, esophagus, stomach, small
intestine, large intestine, anus
form a continuous tube from the mouth to the anus
contraction of muscle in the GI tract wall propels materials through the tract
2. Accessory digestive organs: teeth, tongue, salivary glands, liver, biliary ducts and gall bladder,
not part of GI tube, but often develop as outgrowths from and connect to the GI tract
assist the GI tract in the digestion of material
Oral Cavity (mouth): entrance to the GI tract; initial site of mechanical digestion (via
mastication) and chemical digestion (via an enzyme in saliva) ; 2 distinct regions:
Oral cavity proper: lies central to the alveolar processes of the mandible and maxillae
Vestibule: space between the cheeks or lips and the gums
Palate: forms roof of oral cavity and acts as a barrier to separate it from the nasal cavity
Hard palate: hard and bony anterior two-thirds
Soft palate: soft, muscular posterior one-third
Uvula: conical median projection; extending inferiorly from the posterior part of
the soft palate
Tongue: accessory digestive organ that is formed primarily from skeletal muscle and
covered with stratified squamous epithelium
manipulates and mixes ingested materials during chewing and helps compress the
materials against the palate to turn them into a bolus
also performs important functions in swallowing
Frenulum: thin, vertical mucous membrane attaching tongue to floor of oral
Extrinsic - main movements
Intrinsic - alter shape
Papillae: small projections covering superior (dorsal) surface of tongue
Taste buds: some papillae contain taste buds: can be seen in histological stain
Salivary Glands: salivary glands collectively produce and secrete saliva, a fluid that
assists in the initial activities of digestion; three pairs located external to oral cavity
Parotid: anterior and slightly inferior to the ear, partially overlying masseter
muscle; largest glands; Serous fluid
Submandibular: inferior to the body of the mandible; Serous and mucous fluid
Sublingual: inferior to the tongue and internal to the oral cavity mucosa.
extends multiple tiny sublingual ducts that open onto the inferior
surface of the oral cavity, posterior to the submandibular duct papilla.
Mucous fluid
muscous cells: secrete mucin, which forms mucus upon hydration

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serous cells: secrete a watery fluid containing ions, lysozyme, and salivary
Teeth: responsible for mastication, the first part of the mechanical digestion process
Deciduous (20): 2 incisors, 1 canine (cuspid) , 2 molars in each half jaw
Permanent (32): 2 incisors, 1 canine (cuspid), 2 premolars (bicuspids), 3 molars
in each half jaw
incisors: shaped like a chisel, one root, designed for slicing food
canines (aka cuspids) : pointed tip for puncturing and tearing food
premolars (aka bicuspids):fat crowns w/ prominent ridges (cusps) to
crush and grind materials, one or two roots
molars: thickest, large, broad, flat crowns, three or more roots, adapted
for grinding and crushing ingested materials
Tooth structure:
Alveolus (socket)
Gingiva (gum)
exposed crown, one or more root and constricted neck
roots fit into dental alveoli: sockets w/in alveolar processes
Dentin: forms primary mass of tooth, comparable to bone
Enamel: forms crown of tooth, hardest substance in body composed
primarily of calcium phosphate crystals
Pulp cavity: at centre of tooth, contains connective tissue called pulp
Periodontal ligament: bind roots to alveolar processes together w/ roots
and dental alveoli to form gomphosis joint
Cementum: ensheathes root of tooth
Pharynx: common space used by both the respiratory and digestive systems
nonkeratinized stratified squamous epithelial lining of the oropharynx and the
laryngopharynx provides protection against the abrasive activities associated with
swallowing ingested materials
nasopharynx: superiormost region of the pharynx, posterior nasopharynx wall
also houses a single pharyngeal tonsil (tonsils: lymphoid tissue)
oropharynx: middle region, immediately posterior to the oral cavity; lymphatic organs in
oropharynx provide “first line of defense” against ingested or inhaled foreign materials
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