Digestive System

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Ingestion

Ingestion

Solid or liquid food usually through mouth

Digestion

Breakdown of large organic molecules into smaller molecules that can be absorbed

Absorption

Movement of molecules out of the digestive tract and into the blood or lymphatic system

Elimination

Removal of undigested material such as fiber from the food and other waste products from the body

Feces

Undigested materials such as fiber from food and other waste products from the body are eliminated as

Divisions of Digestive System

Digestive/Gastrointestinal Tract and Specific Associated Organs

Organs of the Digestive System

Oral Cavity

Pharynx

Esophagus

Stomach

Small Intestine

Large Intestine

Anus

Layers of the GI Tract

Mucosa

Submucosa

Muscularis

Serosa/Adventitia

Mucosa

Innermost layer; Mucus Membrane

Submucosa

Thick layer that contains nerves, blood vessels, and small glands

Muscularis

Made of an inner and outer layer of smooth muscle

Serosa

Outermost layer; made of peritoneum

Anatomy of Oral Cavity

Lips

Cheek

Tongue

Palate

Tonsils

Teeth

Salivary Glands

Lips

Also called labia; protects interior opening

Cheek

Forms lateral walls of the mouth; Helps in forming words during speech

Buccinator

Flattens cheek against teeth

Tongue

Attached to the posterior part of the oral cavity; Functions in moving food in the mouth; Helps in speech

Palate

Separates oral cavity and nasal cavity; Prevents food from passing into the nasal cavity during chewing and swallowing

Parts of the Palate

Hard Palate

Soft Palate

32

Teeth in Normal Adult

20

Primary Teeth

Major Pairs of Salivary Glands

Parotid

Submandibular

Sublingual

Parotid Gland

Largest salivary gland

Submandibular Gland

Produces serous secretion

Sublingual Gland

Produces mucus secretions

Saliva

Contains salivary amylase the breaks down starch into simple sugars

Lysozyme

Lyses bacterial cell membrane; antimicrobial agent in food

Mucin

A proteoglycan that gives a lubricating quality to the secretions of the salivary glands

ANS

Salivary gland secretion is primarily regulated by the

Pharynx

Connects mouth with esophagus

Parts of Pharynx

Nasopharynx

Oropharynx

Laryngopharynx

Oropharynx and Laryngopharynx

Only parts of the pharynx that carry food downs to the esophagus

Esophagus

Extends from the pharynx to the stomach

25cm

Length of esophagus

Anterior, Posterior, Mediastinum

The esophagus lies ________ to the vertebrae and ______ to the trachea within the P __________

Regions of Esophagus

Upper esophageal sphincter

Lower esophageal sphincter

2/3

____ of the esophagus is made of skeletal muscle

Phases of Deglutition

Buccal Phase

Pharyngeal Phase

Esophageal Phase

Buccal Phase

Voluntary; Oral transit phase

Tongue

Moves the bolus to the oropharynx

Pharyngeal Phase

The bolus is pushed through the pharynx and into the esophagus;

Movement of the bolus stimulates receptors in the oropharynx which stimulates the soft palate and uvula to close off the nasopharynx and the epiglottis to seal off the larynx which prevents the bolus from entering the respiratory system.

Esophageal Phase

The upper esophageal sphincter relaxes to allow the bolus to enter the esophagus and contracts to reduce backflow into the pharynx

Peristalsis

A wave of involuntary light contractions of the circular longitudinal smooth muscles of the esophagus

Muscularis layer:

Outer longitudinal layer

Middle circular layer

Inner oblique layer

Stomach

Is Eolined with simple columnar epithelium

Epithelial Cells in the Stomach

Surface Mucus Cells

Mucous Neck Cells

Parietal Cells

Endocrine Cells

Chief Cells

Surface Mucous Cells

produces mucus that Muprotects the stomach lining

Mucous Neck Cells

produce mucus that lubricates the epithelial cells; protects the stomach walls from the acidic chyme

Parietal Cells

produce hydrochloric acid and intrinsic factor

Hydrochloric Acid

keeps the stomach acidic and this pH (2.0) must be maintained to kill microorganisms and activate the enzyme, pepsin

Intrinsic Factor

Is needed for the absorption of vitamin B12 (for DNA synthesis RBC production) from the small intestine

Endocrine Cells

produce regulatory chemicals

Chief Cells

produce pepsinogen (precursor of pepsin)

Stomach Secretions from other gastric glands

o Mucus o Hydrochloric acid o Intrinsic factor o pepsin

Chyme

Mixture of food and stomach secretions

Bolus

Folds in the stomach when it is empty

True

Approximately 2L of gastric secretions are produced each day

False

When there is an decrease of gastric secretions it results to heartburn or burning sensation in the chest (caused by overconsumption of caffeine or alcohol or fatty food or when you lie down after you eat)

Gastric Secretions

Regulated by both nervous and hormonal mechanisms

Three phases of Gastric Secretion

cephalic phase

gastric phase

intestinal phase

20 seconds

Movement in the stomach occurs every

Movements in the Stomach

move chyme through the digestive tract, made by smooth muscle contractions in the stomach wall, move chyme toward the pyloric sphincter

Types of Stomach Movement

Mixing Waves

Peristaltic Wave

Mixing Waves

relatively weak contractions that mix food with stomach secretions to form chyme F

False

In mixing waves, the solid part of the chyme is pushed toward the pyloric sphincter while liquid part is pushed back toward the body of the stomach

Peristaltic Wave

stronger contractions that push the chyme toward and through the pyloric sphincter

False

In peristaltic wave, a few milliliters of fluid chyme is forced through the pyloric sphincter into the jejunum

True

Most of the chyme is forced back to the stomach to further mix in peristaltic wave

Small Intestine

Approximately 3 meter long; Major site of digestion and absorption

Parts of the Small Intestine

• Duodenum

• Ileum

  • Jejunum

Cell Types in the Small Intestine

Absorptive

Goblet

Granular

Endocrine

Absorptive Cells

have microvilli and absorb digested food

Goblet Cells

produce protective mucus

Granular Cells

protect the epithelium against bacteria

Endocrine Cells

produce hormones

Modifications that increase small intestine surface area

Circular Folds

Villi

Microvilli

Circular Folds

formed by mucosa and submucosa and do not disappear when filled with food

Secretions of Small Intesine

Mucus

Ions

Water

Small Intestine Secretions

lubricate and protect the intestine from the acidic chyme and action of digestive enzymes.; keep the chyme in the small intestine in a liquid form to facilitate the digestive process.

enzymes

The epithelial cells in the walls of the small intestine have ________, bound to their free surfaces that are significant in the final steps of digestion.

Peptidase

Protein-digesting enzyme

Disaccharidase

Disaccharide-digesting protein

Maltose

broken downby Disaccharidases into the monosaccharide, glucose.

Peristaltic Contractions

proceed along the length of the intestine for variable distances and cause the chyme to move along the small intestine.