1. The Digestive System Day 1
Chapter 15
The Digestive System
Day 1

2. Introduction Covers 186 square meters Digestive System:
Made up of the alimentary canal which extends from the mouth to anus
Includes:
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, recturm, and anus
Accessory Organs:
Salivary glands, liver, gallbladder and pancreas
Covers 186 square meters

3. Intro Cont.
Digestion:
The chemical and mechanical breakdown of foods and the absorption of the resulting nutrients by cells.
Mechanical Digestion
Breaks large pieces into smaller ones without altering the chemical composition
Chemical Digestion:
Breaks food into simpler chemicals

4. General Characteristics
Alimentary Canal
Muscular tube, roughly 8 meters in length
Structure of the Wall
4 layers
Mucosa Membrane
Submucosa
Muscular Layer
Serosa

5. Mucosa Membrane
Made up of epithelium, connective tissue and small amounts of smooth muscle
Contains folds or tiny projections that extend into the passageway called LUMEN
Increase absorptive surface are
Secrete mucus and digestive enzymes
Protects tissues beneath it and
carries on secretion and absorption

6. Submucosa Layer
Made up of loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves
Nourishes surrounding tissues and carries away absorbed materials

7. Muscular Layer Produces movements of the tube
Contains two types of smooth muscle
Circular Fibers
Contraction causes decrease in tube’s diameter
Longitudinal Fibers
Contraction leads to shortening of tube

8. Serosa Layer Outer covering Also called visceral peritoneum
Protect underlying tissues and secrete serous fluid which moistens and lubricates tube’s outer surface
Allows other organs in abdominal cavity to slide freely against one another

9. Movements of the Tube Two types of motor movements Mixing Movements
Caused by smooth muscle contracts rhythmically
Segmentation: alternately contracting and relaxing the smooth muscle in nonadjacent segments
Occurs in stomach
Propelling movements
Peristalsis: wavelike motion that pushes contents of tube ahead
Occurs in esophagus and intestines

10. Mouth
Receives food and begins digestion by mechanically breaking up solid particles and mixing them with saliva
Mastication

11. Cheeks and Lips Cheeks Lips Form lateral walls of mouth
Contain sensory receptors that judge temp. and texture of food

12. Tongue Fills oral cavity
Responsible for mixing food with saliva and moving food towards pharynx during swallowing
Papillae
Rough projections on tongue that provide friction to help handle food
Lingual Frenulum
Connects tongue to floor of mouth
Lingual Tonsils: Posterior portion
Lymphatic tissue

13. Palate Forms roof of oral cavity Anterior portion-hard palate
Muscular posterior portion-soft palate
Uvula
Cone-shaped projection in back of mouth
Palatine Tonsils and Pharyngeal Tonsils-adenoids
Masses of lymphatic tissues that protect the body against infection
Commonly removed

14. Teeth Two Sets Primary Teeth-deciduous Secondary Teeth 20
Erupt though gums in regular
intervals from 6 months-2-4 years
of age
Usually shed in the same
order they erupted
Secondary Teeth
Push primary teeth out of sockets 32
Erupt 6 years years with wisdom teeth

15. Teeth Cont. Role in digestion Begin mechanical digestion by breaking
food into smaller pieces
Increases surface area of food to allow
for digestive enzymes to work more effectively
Parts to a tooth
Crown-projects beyond gum
Root-below gums
Neck-portion where crown and root meet
Enamel-glossy white, covers crown, consists of calcium salts, hardest substance in body, never replaced when damaged
Dentin-bulk of tooth beneath enamel
Pulp-contains blood vessels, nerves, and connective tissue
Root Canals -area where blood vessels and nerves reach pulp
Cementum-bonelike material that helps attach tooth to jaw
Periodontal Ligament -contains blood vessels and helps attached tooth to jaw

16. Salivary Glands
Secrete saliva that helps moisten and bind food particles
Begins chemical digestion by enzyme amylase
Helps cleanse the mouth and teeth

17. Salivary Secretions Each gland has two types of secretory cells
Serous
Produce a watery fluid that includes digestive enzyme salivary amylase
Enzyme splits carbohydrates
Mucous
Secretes thick liquid called mucus
Binds food particles and lubricates food during swallowing
Saliva is produced just by thinking of good foods
Saliva stops production in the presence of unpleasant smells or tastes

18. Major Salivary Glands Three Pairs Parotid Glands largest
Lies anterior and somewhat inferior to ears
Found between skin, cheeks, and masseter muscle
Secretes clear, water fluid that is rich in amylase

19. Major Salivary Glands Submandibular Gland Located on floor of mouth
Secretes both mucous and serous fluid

20. Major Salivary Glands Sublingual glands Smallest
On the floor of mouth inferior to the tongue
Secretes primarily mucous type making their secretions thick and stringy

21. Pharynx-The Crossroads
Cavity posterior to mouth which leads to esophagus
Do not digest food but functions in swallowing
Connects nasal and oral cavities with the larynx and esophagus

22. Pharynx Cont. Three parts:
Nasopharynx-communicates with nasal cavity and provides a passageway for air during breathing, auditory tube connects to nasopharynx
Oropharynx-posterior to soft palate and inferior to nasopharynx, allows food and air to pass through
Laryngopharynx- inferior to oropharynx, passage way to esophagus

23. Swallowing Mechanism 3 Stages
1. Food is mixed with saliva, tongue rolls mixture into a mass called bolus, forces bolus into oropharynx
2. Once food reaches oropharynx, swallowing reflex kicks in (See steps on Page 409)
3. Peristalsis transports food into esophagus and on to the stomach

24. Esophagus
Straight, collapsible tube about 25 cm long that allows food to pass from mouth to stomach
Mucous glands are scattered throughout
Lower Esophageal Sphincter/Cardiac Sphincter
Closes the entrance to stomach preventing contents from regurgitating into esophagus.
Peristaltic waves allow food to enter stomach.

25. Review Questions Which organs constitute the digestive system?
Describe the wall of the alimentary canal.
Name the two basic types of movements in the alimentary canal.
How does the tongue function as part of the digestive system?
Where are the tonsils located?
How do primary teeth differ from secondary teeth?
Describe the structure of a tooth.
Explain how a tooth is attached to the bone of the jaw.
What is the function of saliva?
What stimulates salivary glands to secrete saliva?
Where are the major salivary glands?
Describe the regions of the pharynx.
List the major events of swallowing.
What is the function of the esophagus?