DIGESTIVE SYSTEM

UNFINISHED

6 Major Functions of Digestive System

Ingestion and Mastication, Propulsion and Mixing, Secretion, Digestion, Absorption, Elimination

Ingestion

Intake of solid or liquid food.

Mastication

Process by which the teeth chew food in the mouth.

Propulsion

Movement of food from one end of the digestive tract to the other.

Swallowing (Deglutition), Peristalsis Mass movements

Characteristics of propulsive movements

Mixing

Movement of food back and forth in the digestive tract, without forward movement.

24-36 hours

Time taken by food to travel the length of the digestive tract.

Secretion

Added to lubricate, liquefy, buffer, and digest the food.

Mucus

Secreted along the entire digestive tract, lubricates the food and the lining of the tract.

Digestion

Breakdown of large organic molecules.

Mechanical Digestion

Involves mastication and mixing of food.

Chemical Digestive

Accomplished by digestive enzymes.

Amylase

Enzyme involved in the digestive system.

Absorption

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

Intestines

Part of the digestive tract that has a lot of absorption.

Elimination

Process by which the waste products of digestion are removed from the body.

Digestive tract, Accessory digestive organs

Main groups involved in the digestive system (2)

Digestive tract

Continuous coiled hollow tube. (Alimentary canal)

Salivary glands, Teeth, Pancreas, Liver, Gallbladder

Accessory digestive organs

Mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine

Organs of the Alimentary canal.

Lips (Labia)

Protect the anterior opening of the mouth. Muscular structures formed mostly by the orbicularis oris muscle and connective tissue.

Keratinized stratified epithelium

Not a single layer and has keratin, which is the epithelium for skin.

Cheeks

Forms the lateral walls of the oral cavity. They consist of an interior lining of moist stratified squamous epithelium and an exterior covering of skin.

Buccinator muscle, Buccal fat pad

Substance of the cheek

Buccinator muscle

Flattens the cheeks against the teeth.

Buccal fat pad

Rounds out the profile on the side of the face.

Palate (Hard and Soft Palate)

The roof of the oral cavity. Separates the oral and nasal cavities and prevents food from passing into the nasal cavity during chewing and swallowing.

Hard Palate

Forms the anterior roof. (Bony part)

Soft Palate

Forms the posterior roof. Non-bony part, which consists of skeletal muscle and connective tissue.

Uvula

Posterior projection from the soft palate.

Fauces

Posterior boundary of the oral cavity which is the opening into the pharynx.

Palatine Tonsils

In the lateral wall of the fauces.

Vestibule

Space between lips externally and teeth and gums internally.

Oral cavity

Area contained by the teeth.

Tongue

Attached at hyoid and styloid processes of the skull, and by the frenulum. Its function is to move the food in mouth. Also participates in speech and swallowing.

Intrinsic muscles

Changes the shape (of the tongue)

Extrinsic muscles

Involves the protrusion or retraction of the tongue.

Terminal sulcus

Groove divides tongue into anterior 2/3 and posterior 1/3.

Anterior part

Papillae, some of which have taste buds.

Posterior part

No papillae and a few scattered taste buds.

Lymphoid tissue

Embedded in posterior surface.

Palatine tonsils

Located near the opening of the oral cavity into the pharynx.

Lingual tonsils

Located on the posterior surface of the tongue, which also places them near the opening of the oral cavity.

Tonsils

Lymphatic tissues that play an important role in the body immune mechanism.

Salivary Glands

Scattered throughout the oral cavity.

Parotid glands, Submandibular glands, Sublingual glands

Pairs of large, multicellular salivary glands (3)

Parotid glands

Largest. Located anterior to ears. Secretes serous fluid.

Parotid duct

Where serous fluid enters the parotid gland through. Adjacent to the 2nd upper molar.

Submandibular glands

Duct enters oral cavity on either side of frenulum. Mixed, mucinous and serous. Posterior half of inferior border of mandible.

Sublingual glands

Smallest. Primarily composed of serous demilunes and mucous acini. Mixed, but primarily mucous. Each has 10-12 ducts that enter the floor of the oral cavity.

Acinar glands

Branching glands with clusters of acini resembling grapes. They produce thin, serous secretions or thinker mucous secretions.

Location of small, coiled, tubular salivary glands

Deep to the epithelium of the tongue (lingual glands), in the palate (palatine glands), in the cheeks (buccal glands), in the lips (labial glands)

Saliva

Combination of serous and mucous secretions from various salivary glands. Composed of fluid and proteins.

Three main roles of saliva

Keeps the oral cavity moist for normal speech and suspension of food molecules, has protective functions, begins the process of digestion

Functions of saliva

Prevents bacterial infection, lubrication, contains salivary amylase, helps form bolus for deglutition, parasympathetic input causing salivary production, sympathetic stimulation leading to thick mucoid saliva

Lysozymes

Enzyme responsible for prevention of bacterial infection.

1-1.5 L/day of serous saliva

Secreted primarily by the parotid and submandibular glands, aiding the moistening function of saliva.

Teeth

Role is to masticate or chew food.

Deciduous (baby or milk) and Permanent teeth

Two sets of teeth

Deciduous teeth

20 teeth are fully formed by age two.

Permanent teeth

Replace deciduous teeth beginning between the ages of 6 to 12. Has a full set of 32 teeth in an adult person.

Masseter, Temporalis, Medial Pterygoids, Lateral Pterygoids

Main muscles of mastication (4)

Medial and Lateral Pterygoids

Produce lateral excursion when acting together.

Lateral Pterygoids

Opens the mouth.

Medial & Lateral Pterygoids and Masseter

Accomplish protraction and lateral and medial excursion of the jaw.

Temporalis

Retracts the jaw.

Masseter, Temporalis, Medial & Lateral Pterygoids

Muscles involved in tearing, crushing, and grinding food.

Incisors and Canines (Anterior teeth)

Primarily cut and tear food.

Premolars and Molars

Primarily crush and grind food.

Mastication reflex

Integrated in the medulla oblongata and controls the basic movements of chewing.

Incisors, Canines, Premolars, Molars

Classification of Teeth

Crown, Neck, Root

Regions of a tooth

Crown

Exposed part. Outer enamel. Dentin. Pulp cavity

Neck

Region in contact with the gum. Connects crown to the root.

Root

Periodontal membrane attached to the bone. Carries blood vessels and nerves.

Processes of the mouth

(1) Mastication of food, (2) Mixing masticated food with saliva, (3) Initiation of swallowing by the tongue, (4) Allowing for the sense of taste

Nasopharynx

Not part of the digestive system. Is lined with ciliated pseudostratified columnar epithelium.

Oropharynx

Posterior to oral cavity. Communicates with the nasopharynx superiorly, with the larynx and laryngopharynx inferiorly, and with the mouth anteriorly.

Laryngopharynx

Below the oropharynx and connected to the esophagus. Extends from the oropharynx to the esophagus and is posterior to the larynx.

Epiglottis

Covers opening of the larynx and keeps food and drink from entering the larynx.

Pharyngeal Constrictors

Are arranged like three stacked flowerpots, one inside the other.

Oropharynx and Laryngopharynx

Are lined with moist stratified squamous epithelium.

Pharynx

Serves as a passageway for air and food.

Longitude inner layer and Circular outer layer

Two muscle layers that propels food to the esophagus.

Peristalsis

Food movement is by alternating contractions of the muscle layers. Major means of moving food.

Esophagus

Runs from pharynx to stomach through the diaphragm. Conducts food by peristalsis (slow rhythmic squeezing).

Voluntary Swallowing

Bolus of food moved by tongue from oral cavity to pharynx.

Pharyngeal Swallowing

Controlled by swallowing center in medulla oblongata.

Soft palate elevates, upper esophageal sphincter relaxes. Elevated pharynx opens the esophagus. Food pushed into the esophagus by pharyngeal constrictors successive contraction from superior to inferior. Epiglottis is tipped posteriorly due to pressure of the bolus. Larynx elevated to prevent food from passing into larynx.

Esophageal Swallowing

Stretching of esophagus causes enteric NS to initiate peristalsis of muscles in the esophagus.

Mucosa, Submucosa, Muscularis externa, Serosa

Layers of the alimentary canal organs

Mucosa

Is the innermost layer. Has a moist membrane. Composed of surface epithelium, lamina propia (small amount of connective tissue), and small smooth muscle layer.

Submucosa

Just beneath the mucosa. Composed of soft connective tissue with blood vessels, nerve endings, and lymphatics.

Muscularis externa

Composed of smooth muscle, inner circular layer, and outer longitudinal layer.

Serosa

Is the outermost layer. Visceral peritoneum. This layer produces a serous fluid-producing cells, which acts as a lubricant inside the body.

Stomach

Located on the left side of the abdominal cavity. Acts as a storage tank for food. Site of food breakdown. Chemical breakdown of protein begins. Delivers chyme (processed food) to the small intestine.

Cardiac region (near the heart), Fundus, Body, Phylorus (funnel-shaped terminal end)

Regions of the stomach

Rugae

Internal folds of the mucosa. Functions to increase the surface area for absorption.

Lesser and Greater Curvature

External regions

Lesser Omentum, Greater Omentum

Layers of peritoneum attached to the stomach

Lesser Omentum

Attaches to the liver to the lesser curvature.