Chapter 15The Digestive System

Day 1

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

Introduction

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

Intro Cont.

Alimentary Canal

Muscular tube, roughly 8 meters in length Structure of the Wall

4 layers Mucosa Membrane Submucosa Muscular Layer Serosa

General Characteristics

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

Mucosa Membrane

Made up of loose connective tissue, glands,

blood vessels, lymphatic vessels, and nerves Nourishes surrounding tissues and carries

away absorbed materials

Submucosa 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

Muscular 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

Serosa Layer

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

Movements of the Tube

Receives food and begins digestion by

mechanically breaking up solid particles and mixing them with saliva Mastication

Mouth

Cheeks

Form lateral walls of mouth Lips

Contain sensory receptors that judge temp. and texture of food

Cheeks and Lips

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

Tongue

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

Palate

Two Sets Primary Teeth-deciduous

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-17-25 years with wisdom teeth

Teeth

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

Teeth Cont.

Secrete saliva that helps moisten and bind

food particles Begins chemical digestion by enzyme amylase Helps cleanse the mouth and teeth

Salivary Glands

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

Salivary Secretions

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

Major Salivary Glands

Submandibular

Gland Located on

floor of mouth Secretes both

mucous and serous fluid

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

Major Salivary Glands

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

Pharynx-The Crossroads

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

Pharynx Cont.

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

Swallowing Mechanism

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.

Esophagus

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?

Review Questions