Cheeks and Lips

The cheeks form the lateral walls of the mouth. They consist of outer layers of skin, pads of subcutaneous fat, muscles associated with expression and chewing, and inner linings of moist, stratified squamous epithelium.

Because cheek cells are easily removed, for many years biology laboratory classes have had students collect them and use them to study cell structure. More recently, similar "cheekbrush tests" have been developed to identify carriers of certain inherited disorders. The patient simply swishes a brush on the inside of the cheek; then the doctor sends the brush to a laboratory. Here, cheek cells are removed from the brush, and the DNA is extracted and analyzed for the presence of gene variants, such as those that cause cystic fibrosis.

The lips are highly mobile structures that surround the mouth opening. They contain skeletal muscles and sensory receptors useful in judging the temperature and cm

Artery

Mesentery 4

Serosa

Circular fold

Longitudinal muscle

Circular muscle

Serosa

Circular fold

Tissue Layers The Alimentary Canal

Microvilli

Goblet cell

Nucleus

Simple columnar epithelium

Microvilli

Goblet cell

Nucleus

Simple columnar epithelium

Muscular

Nerv^ ^^^^ ^_ longitudinal miisc|e |ayer plexuses Serosa

Figure 17.3

The wall of the small intestine, as in other portions of the alimentary canal, includes four layers: an inner mucosa, a submucosa, a muscular layer, and an outer serosa.

Figure 17.3

The wall of the small intestine, as in other portions of the alimentary canal, includes four layers: an inner mucosa, a submucosa, a muscular layer, and an outer serosa.

Layer

Composition

Function

Mucosa Submucosa

Muscular layer

Serosa

Epithelium, connective tissue, smooth muscle Loose connective tissue, blood vessels, lymphatic vessels, nerves

Smooth muscle fibers arranged in circular and longitudinal groups

Epithelium, connective tissue

Protection, secretion, absorption Nourishes surrounding tissues, transports absorbed materials Movements of the tube and its contents

Protection, lubrication

Blood Vessels Tube

Movement of food

(a) Mixing movements occur when small segments of the muscular wall of the alimentary canal rhythmically contract. (b) Peristaltic waves move the contents along the canal.

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