The Digestive System

1. The Digestive System Chapter 23 Anatomy of the Digestive System – Part 1

2. Overview • Organs: • Mouth, pharynx, esophagus, stomach, small intestine, and large intestine

3. Overview • Accessory Organs • Teeth, tongue, gallbladder,, salivary glands, liver, pancreas • Contribute to the breakdown of food

4. Imagine yourself taking a bite of food….

5. The Mouth • AKA: oral cavity or buccal cavity • Opening  oral orifice • Boundaries: • Lips anteriorly • Cheeks laterally • Palate superiorly • Tongue inferiorly • Continuous with oropharynx posteriorly

6. The Lips (Labia) and Cheeks • Lips – orbicularis oris • Very large! Extend from bottom of nose to bottom of chin • Red margin – lipstick or kisses • Cheeks – buccinators • Both help to keep food between the teeth when we chew • Also play a role in speech • Labial frenulum – median fold that joins the internal aspect of lips to the gum

7. The Palate • Roof of the mouth • Hard palate • Palatine and maxillae bones • Rigid surface against which the tongue forces food during chewing • Soft palate • Posterior – arch shaped • Mobile fold formed mostly of skeletal muscle

8. Palate • Soft Palate • Uvula – projects down from the free edge of the soft palate • During swallowing both are drawn upwards closing off the nasopharynx and preventing foods/liquids from entering the nasal cavity • Try and breathe and swallow at the same time

9. Teeth • Teeth break and rip apart food • Increases surface area • Smaller pieces increases the surface area  enzymes in the saliva can get at the food easier  chemical breakdown of food takes place quicker

10. Teeth • 2 sets of teeth • Primary  baby teeth (20) • First teeth appear ~6 mo • Fall out b/t 6-12 years • Permanent  adult (32) • Absorb roots of baby teeth causing them to fall out • Usually all have erupted (except 3rd molars) by end of adolescence • Wisdom teeth (3rd molars)  erupt b/t 17-25 years

11. Teeth - Types • Incisors • Chisel-shaped • Cutting or nipping off pieces of food • Canines (cuspids/eyeteeth) • Conical or fanglike • Tear and pierce • Premolars (bicuspids) • Broad crowns and rounded cusps • Grinding or crushing • Molars • Broad crowns and rounded cusps • Grinding or crushing

12. Teeth - Regions • Crown • Exposed part of the tooth • Covered in enamel  a cellular, brittle material that bears the force of chewing. Hardest substance in the body. Can’t repair itself! • Root • Portion embedded in the jaw

13. Teeth - Cavities • Result from a gradual demineralization of enamel and underlying dentin by bacteria • Dental plaque (film of sugar, bacteria, etc.) adheres to teeth  bacteria dissolve trapped sugars  those produce acids, which dissolve the enamel.

14. Salivary Glands • We see food or think of food  Mouth starts to water  saliva is released from the salivary glands

15. Salivary Glands • Secrete saliva • Cleanses mouth • Dissolves food chemicals for tasting • Moistens food and aids in bolus formation • Contains enzymes that begin chemical breakdown of starchy foods • Three glands  parotid, submandibular, sublingual • Lie outside oral cavity and empty saliva into it

16. Composition of Saliva • Water  97 – 99.5% • Slightly acidic  pH 6.75-7.0 • Digestive enzyme  salivary amylase • Proteins  • Mucin – dissolved in water forms a thick mucus that lubricates the oral cavity • Lysozyme – inhibits bacterial growth in the mouth • IgA – antibodies, protection against microorganisms • Metabolic wastes  urea and uric acid

17. Tongue • Occupies most of the floor of the mouth and fills most of the oral cavity when mouth is closed • Composed of interlacing bundles of skeletal muscle fibers  during chewing grips and repositions food between the teeth

18. Tongue • Mixes food with saliva  forms bolus (“lump”) • Initiates swallowing  pushes bolus posteriorly • Helps to form consonants when we speak • Helps to keep food between the teeth by pushing the food against the hard palate

19. Tongue • Lingual frenulum – secures tongue to floor of mouth, limits posterior movements • Ankyloglossia (“fused tongue”) aka tongue-tied  when lingual frenulum is too short  limits movements of tongue so speech is distorted.

20. Tongue • Filiformpapillae • Smallest and most numerous • Roughness that aids in licking foods and provides friction for manipulating foods in mouth • Aligned in parallel rows • Whitish appearance

21. Tongue • Fungiform papillae • Mushroom-shaped • Scattered widely over the tongue surface • Have a reddish hue • House taste buds • Circumvallate (vallate) papillae • 10-12, large, located in a V-shaped row at that back of the tongue • House taste buds

22. Tongue • Foliate papillae • Pleatlike, located on the lateral aspects of the posterior tongue • House taste buds (only in infancy and early childhood) • Sulcus terminalis • Posterior to circumvallate papillae • Groove that distinguishes anterior and posterior tongue

23. Taste • For a chemical to be tasted it must dissolve in saliva, diffuse into the taste pore, and contact the gustatory hair. This causes a reaction from the nervous system that allows us to “taste” our food

24. Taste • Taste buds – sensory receptors for taste • Located mostly in the oral cavity ~10,000 • Most are on tongue. Few on soft palate, inner surface of cheeks, pharynx, and epiglottis • Most are found in papillae • Tops of fungiform papillae, sides of foliate papillae and circumvallate papillae

25. Taste • Taste qualities: sweet, sour, salty, bitter, and umami (“delicious”) • Most taste buds respond to 2 or more taste qualities and many substances produce a mixture of the basic taste sensations

26. Taste • Taste maps, although common, are inaccurate (sweet tip, salty and sour  sides, bitter  back, umami  pharynx • In reality, there are only slight differences in the localization of specific taste receptors in different regions of the tongue, all types of taste can be elicited from all areas that contain taste buds

27. Taste • Taste likes and dislikes have a homeostatic value • Umami guides intakes of proteins • A liking for sugar and salt helps satisfy the body’s need for carbohydrates and minerals. • Many sour, naturally acidic foods (lemons, tomatoes, oranges) are rich sources of vitamin C. • Many natural poisons and spoiled foods are bitter, our dislike for bitterness is protective.

28. Taste • Taste is 80% smell. When olfactory receptors are blocked, food is bland. • Mouth also contains thermoreceptors (temperature), mechanoreceptors (touch), and nociceptors (pain). The temperature and texture of foods can enhance or detract from their taste. Spicy or “hot” foods bring about their effects by activating the pain receptors in our mouth