Section 1, chapter 17: digestive system


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Section 1, chapter 17: digestive system

  1. 1. The Digestive System Section 1, Chapter 17
  2. 2. INTRODUCTION Digestion is the mechanical and chemical breakdown of food into forms that cells can absorb. • Mechanical Digestion – breaks down food into smaller pieces Chemical Digestion – decomposes food into smaller molecules • The digestive system consists of: • The alimentary canal – extends from mouth to anus • Accessory glands –secrete chemicals into the alimentary canal.
  3. 3. Figure 17.1 Organs of the digestive system.
  4. 4. THE ALIMENTARY CANAL • If stretched out, the alimentary canal is about 8 meters long. That’s 26 feet! • The alimentary canal (A.C.) wall has four distinct layers that differ from region to region.
  5. 5. STRUCTURE OF THE WALL • Mucosa – mucous membrane • Epithelial tissues on a bed of connective tissue (lamina propria). • Makes direct contact with the lumen • This layer absorb nutrients, secrete chemicals, and protect the underlying layers. • Submucosa – Beneath the mucosa • Loose connective tissue • Blood vessels, nerves, and lymphatic vessels • This layer nourishes the surrounding tissues, and carries away nutrients.
  6. 6. STRUCTURE OF THE WALL • Muscular – provides movements within the A.C. • Inner coat = transverse muscles: decrease the diameter of the A.C. • Outer coat = longitudinal muscles: shortens length of the A.C. • Serosa – serous membrane • Composed of visceral peritoneum in most places • Secretes serous fluid, which lubricates the A.C.
  7. 7. Figure 17.3 The wall of the small intestine, as in other portions of the alimentary canal, consists of four layers: An inner mucosa, a submucosa, a muscular layer, and an outer serous layer.
  8. 8. MOVEMENTS OF THE ALIMENTARY CANAL Muscles of the A.C. provide two basic movements: • Segmentation – mixing movement • Smooth muscles contract and relax, mixing foods with digestive juices. •Peristalsis – propelling movement • Smooth muscles contract in a wave-like motion pushing food through the alimentary canal. Figure 17.4 (b) segmentation mixes the contents of the small intestine. (c) Peristaltic waves move the contents along the canal
  9. 9. INNERVATION OF THE ALIMENTARY CANAL • Enteric Nervous System – subdivision of the ANS that innervates the alimentary canal. •Submucosal plexus – controls secretions •Myenteric plexus – controls gastrointestinal motility •Remember: • Parasympathetic impulses – increase activities of digestive system • Sympathetic impulses – inhibit certain digestive actions
  10. 10. THE MOUTH • The mouth: • Receives food • Mechanically breaks up solid particles using saliva • Prepares food for chemical digestion • This action is called mastication • The mouth also functions as an organ of speech, and sensory reception.
  11. 11. BOARDERS OF THE MOUTH • The cheeks form the lateral walls of the mouth • Buccinator muscle + buccal fat pad (gives form to cheeks) • The lips form the anterior boarder •Highly mobile structures that surround the mouth opening •Orbicularis oris skeletal muscle •Semitransparent epithelium, and a good blood supply makes the lips appear red. •Highly innervated by sensory receptors
  12. 12. THE TONGUE • The tongue is a thick, muscular organ that occupies the floor of the mouth and nearly fills the oral cavity when the mouth is closed Mucous Membrane – covers the surface of the tongue Lingual Frenulum – membranous fold, anchors the tongue to the floor of the mouth. Body – largely composed of skeletal muscle • Manipulate foods and aids in swallowing Root – posterior portion of the tongue • Anchored to the hyoid bone. • Covered with lingual tonsils Papillae – projections on the surface of the tongue. • Some provide friction, others house taste buds.
  13. 13. THE PALATE • The palate forms the roof of the oral cavity Hard Palate - bony roof of the mouth • Formed by the palatine bones and portions of the maxilla Soft Palate - Muscular arch Uvula – cone-shaped projection During swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity. Figure 17.7 Sagittal section of the mouth, nasal cavity, and pharynx.
  14. 14. THE TEETH Teeth are the hardest structures in the body •primary (deciduous) teeth numbering 20 •Usually erupt through the gums from age of 6 months to 2 years •secondary (permanent) teeth numbering 32 •Usually begin to erupt at 6 years • 3rd molars = wisdom teeth, which may erupt between 17-25 years of age Figure 17.8 This partially dissected child’s skull reveals primary and developing secondary teeth in the maxilla and the mandible.
  15. 15. TYPES OF TEETH Incisors- blade shaped teeth that bite or cut off large pieces of food Adult – 8 incisors Child – 8 incisors Canines- cone shaped teeth that grasp and tear food Adult – 4 canines Child – 4 canines Premolars – flattened surface for grinding food Adult – 8 premolars Child – 0 premolars Molars – flattened surface for grinding food Adult – 12 molars Child – 8 molars
  16. 16. TOOTH ANATOMY Enamel- Calcium salts; hardest structure in the body. Dentin- Living cellular tissue similar to bone. Pulp cavity- Filled with loose connective tissue, blood vessels, and nerves Crown- portion of tooth above the gums (gingiva) Root- portion of tooth below the gums (gingiva) Root canal – entrance into the pulp cavity Tooth attachments to the jaw Cementum – bone-like layer surrounding the root Periodontal ligaments – attaches the tooth to the jaw
  17. 17. DENTAL CARIES Microbes on the surface of teeth metabolize carbohydrates from foods left in the mouth. • Their acidic wastes dissolves and the destroys the enamel and dentin. • Dental caries form when the damage spreads to the underlying dentin. Figure 17A Actinomyces bacteria (falsely colored) clinging to teeth release acids that decay tooth enamel (1,250X)
  18. 18. SALIVARY GLANDS • Salivary glands secrete saliva •Saliva moistens the food, and begins the digestion of carbohydrates Three pairs of major salivary glands, include: Parotid glands – located anterior to the ear • A parotid duct enters the mouth opposite the second upper molars Submandibular glands – located on the floor of the mouth inside the jaw. Sublingual glands – located on the floor of the mouth, inferior to the tongue. •Many minor glands are also scattered throughout the mucosa of the tongue, palate, and cheeks
  19. 19. Figure 17.11 Locations of the major salivary glands.
  20. 20. SALIVARY GLANDS There are two types of secretory cells within the salivary glands: • Serous cells produce a watery fluid with digestive enzymes (salivary amylase) • Mucous cells secrete mucous • Parotid glands • Secrete clear watery, serous fluid • Rich in salivary amylase – begins the chemical digestion of carbohydrates •Submandibular glands • Secretes a mixed saliva with both serous fluid and mucus •Sublingual glands • Secrete primarily mucus
  21. 21. SALIVARY GLANDS End of Section 1, Chapter 17