The Digestive System

Chapter 23Anatomy of the Digestive

System – Part 1

Overview

• Organs:– Mouth, pharynx,

esophagus, stomach, small intestine, and large intestine

Overview

• Accessory Organs– Teeth, tongue,

gallbladder,, salivary glands, liver, pancreas

– Contribute to the breakdown of food

Imagine yourself

taking a bite of food….

• AKA: oral cavity or buccal cavity

• Opening oral orifice• Boundaries: – Lips anteriorly– Cheeks laterally– Palate superiorly– Tongue inferiorly– Continuous with oropharynx

posteriorly

The Mouth

• 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

The Lips (Labia) and Cheeks

• 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

The 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

Palate

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

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

• 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

Teeth - Types

• 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

Teeth - Regions

• 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.

Teeth - Cavities

Salivary Glands

• We see food or think of food Mouth starts to water saliva is released from the 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

Salivary Glands

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

• 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

Tongue

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

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.

• Filiform papillae– Smallest and most

numerous– Roughness that aids

in licking foods and provides friction for manipulating foods in mouth

– Aligned in parallel rows

– Whitish appearance

Tongue

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

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

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

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

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

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

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.

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