Digestive System

Objectives:

Discuss the general functions and anatomy of the digestive tract

Describe the individual organs of the system, including a discussion of the gross and microscopic anatomy.

Digestive System

Muscular, hollow tube (= “digestive tract”)

+

Various accessory organs

consists of:

Function

ingestion

mechanical digestion

chemical and enzymatic digestion

secretion

absorption

compaction

excretion and elimination

The function of the system as a

whole is processing food in such a

way that high energy molecules can

be absorbed and residues

eliminated.

Individual parts

function in:

Muscularis

externa

Histological Organization

Tube made up of

four layers.

Modifications

along its

length as

needed.

1

2

3

4

The 4 Layers of the Gut

1) Mucosa

Epithelial cells – protection, absorption

2) Submucosa – made up of loose connective tissue contains submucosal plexus and blood vessels

3) Muscularis externa – smooth muscle, usually two layers -

outer layer: longitudinal

inner layer: circular

4) Serosa

outer layer, functions in protection

Ingestion

Ingestion is the first

step in the process

of digestion.

Ingestion means

that food is taken

into the mouth,

chewed, and

swallowed.

Oral Cavity

Also called the mouth, the oral cavity is the place where ingestion happens.

Hard and soft palates - form roof of mouth

Tongue - skeletal muscle

Salivary glands - three pairs

Teeth

Oral Cavity

Digestion starts here by two

means:

Mechanical – teeth tear,

shred, and grind food.

Chemical – enzymes in

saliva break down food

molecules such as

proteins and complex

sugars.

Structure of Teeth

Crown - exposed surface of tooth

Neck - boundary between root and crown

Enamel - outer surface

Dentin – bone-like, but noncellular

Pulp cavity - hollow with blood vessels and nerves

Root canal - canal length of root

Types and Numbers of Teeth

Dental succession

Deciduous (baby, milk) teeth - 20, replaced by

Permanent teeth - 32 teeth

Types and Numbers of Teeth

All teeth are formed

before milk teeth or

primary teeth are lost.

It is the action of adult

teeth moving into

place that causes

primary teeth to fall

out.

Three pairs of Salivary Glands

Salivary glands help with:

• digestion

• lubrication (swallowing)

• moistening (tasting)

They secrete enzyme-filled

saliva to help break down

food

Ingestion

The tongue is a

muscle that pushes

your food toward

teeth to be

mechanically

processed and

shapes your food into

small rounded pieces

to be swallowed.

Swallowing

As you swallow, your

tongue pushes the food to

the back of the mouth.

Since both air and food go

through the pharynx, a flap

of tissue called the

epiglottis covers the larynx

to prevent food from

travelling into the lungs