Digestive System (through esophagus)

Describe the boundaries of the mouth.

(oral or buccal cavity) is formed by the cheeks laterally, hard and soft palates superiorly, and the tongue inferiorly.

What are the two reasons that food is vital to life?

1. It provides the energy that drives the chemical reactions of the body cells. 2. It provides matter that is useful in building new tissues or repairing old ones.

palatal arches

Extending from the uvula are two muscular folds. Anteriorly, the palatoglossal arches extend to the base of the tongue. Posteriorly, the palatopharyngeal arches project to the anterior surface of the pharynx.

Name the four main layers of the GI tract.

In general, the wall of the GI tract, from esophagus to anus, has four main layers: 1. mucosa (mucous membrane) 2. submucosa 3. muscularis 4. serosa

What are the mesentery and the mesocolon?

In some areas, the peritoneum contains large folds that weave between the viscera and bind organs to the posterior wall, suspend-ing them within the abdominal cavity. The folds contain blood ves-sels, lymphatics, and nerves supplying the suspended organs. The mesentery surrounds the small intestine, and the mesocolon surrounds part of the large intestine.

Describe lysozyme.

Lysozyme is a nonspecific antimicrobial enzyme used to maintain some degree of cleanliness in the mouth.

Describe mucous in saliva.

Mucin mixed with water forms mucous. It is used to lubricate food so that it can be easily swallowed and to facilitate speech.

Describe ion in saliva.

Na+, K+, C-l, HCO3-, and HPO4-2 are the main ions found in saliva. They are used to activate salivary amylase and to buffer acidic foods, keeping salivary pH between 6.35 - 6.85.

function of the tongue

Once a rounded mass of chewed food, called a bolus, has been formed, the intrinsic muscles bow the tongue so that the bolus is moved from the front of the mouth, through the fauces, and into the oropharynx. The tongue is also used to alter sounds in the creation of speech

What are the basic components of saliva?

Saliva is composed of 99.5% water, used to dissolve foods, and 0.5% solutes.

Describe the chemical digestion that occurs in the mouth.

Salivary amylase enzymatically converts starch (a polymer [a chemical compound consisting essentially of repeating structural units] of glucose) into the disaccharide maltose (GLU-GLU). There is a lingual lipase, a lipid- digesting enzyme but its effects are very minor. Other dietary sugars, as well as proteins and fats, are unaffected chemically.

How is salivation controlled?

Salivation is completely under the control of the parasympa-thetic nervous system, via cranial nerves VII (facial) and IX (glossopharyngeal).

What does retroperitoneal mean?

Some organs of the abdominopelvic cavity lie between the parietal peritoneum and the muscular posterior abdominal wall. They are therefore said to be retroperitoneal.

Describe chemical stimuli.

Stimulation of taste buds by food components or the ingestion of irritants, working through the taste buds, initiates reflexive salivation.

Describe tactile stimuli.

Stimulation of touch receptors within the mouth and pharynx initiates reflexive salivation. (Think about holding a pencil in your mouth.)

Define swallowing.

Swallowing (deglutition) moves food from the mouth, through the pharynx and esophagus, to the stomach. It involves three phases and requires 4-8 seconds for solids, 1 second for liquids.

What are the accessory organs of the digestive system?

The accessory organs are those structures which are not a direct part of the GI tract, but which aid in the breakdown of food, either mechanically or by adding secretions to the material as it moves down the tube (teeth, tongue, salivary glands, pancreas, liver, and gallbladder).

Describe psychic stimuli.

The anticipation, sight, sound, smell, or memory of food, working through the cerebral cortex, initiates reflexive salivation. (think Pavlov).

Describe the epithelium of the mucosa.

The epithelium of the GI tract is in direct contact with the GI contents and is involved in protection, secre-tion of enzymes and hormones, and absorption of nutrients. From the stomach to the rectum, the epithelium is simple columnar. All other parts of the tract are stratified squamous.

Describe the function of the esophagus.

The esophagus plays no role in digestion other than as a conduit from the pharynx to the stomach, using peristalsis to move the food. There are no enzymatic secretions from the esophagus.

Describe the serosa.

The fourth, and outermost, layer of the GI tract is the serosa. This is a serous membrane composed of epithelium and connective tissue. It is also known as the visceral peritoneum

mucosa of the mouth

The inside of the mouth is lined with nonkeratinized stratified squamous epithelium

Describe the lamina propria

The middle layer of the mucosa is the lamina propria. This is a loose connective tissue rich in blood and lymphatic vessels and scattered lymphatic nodules.

Describe the mucosa/submucosa of the esophagus

The mucosa of the esophagus is nonkeratinized stratified squamous for abrasion resistance. The submucosa contains numerous blood vessels and mucous-secreting glands

Describe the mucosa by listing and describing its three components.

The mucosa, the inner lining of the tract, consists of three parts, listed from innermost to outermost. 1. epithelium 2. lamina propria 3. muscularis mucosa

Describe the muscularis of the esophagus.

The muscularis begins as skeletal muscle proximally, and grades into smooth muscle distally. The inner circular portions of the muscularis form the two sphincters of the esophagus

What are the two main groups of digestive organs?

The organs of the digestive system are divided into two main groups, the gastrointestinal (GI) tract (alimentary canal) and the accessory organs.

Differentiate between parietal peritoneum, visceral peritoneum, and the peritoneal cavity.

The parietal peritoneum lines the muscular wall of the abdominal cavity while the visceral peritoneum covers some of the organs as their serosa. The peritoneal cavity is the potential space between the two layers.

What is the peritoneum?

The peritoneum consists of a simple squamous epithelium called the mesothelium and an underlying connective tissue layer. It is divided into two layers with a potential space between them.

Describe the submucosa.

The second major level of the GI tract is the submucosa, a loose connective tissue that binds the mucosa to deeper structures. It is highly vascular and contains autonomic ganglia of the parasympathetic system, and may contain some exocrine glands that secrete into the gut.

Describe the muscularis mucosa.

The third layer of mucosa is the muscularis mucosae, a thin layer containing the smooth muscle cells arranged circumferentially around the tube. It throws the mucosa into folds that increase its surface area. This is particularly true in the stomach.

Describe the muscularis.

The third layer of the GI tract is the muscularis, generally consisting of inner circular and outer longitudinal smooth muscle. This muscle is responsible for GI motility (movement of food through the gut).

innervation of the tongue

The tongue muscles, both intrinsic and extrinsic, are innervated by cranial nerve XII, the hypoglossal nerve.

Describe the sphincters of the esophagus.

There are two esophageal sphincters. The upper esophageal sphincter lies at the point where the esophagus exits from the laryngopharynx. The lower esophageal (gastroesophageal) sphincter lies at the distal end of the esophagus, at its junction with the stomach. They are normally closed and open only in response to the deglutition reflex.

Describe the mechanical digestion that occurs in the mouth.

Through chewing (mastication), food is reduced to a soft, shredded, and ground moist mass. This mass is shaped by the combined action of the cheeks, tongue, and teeth into a flexible bolus that can be easily swallowed.

Describe the gross anatomy of the esophagus.

a muscular, collapsible 10-inch long tube that lies posterior to the trachea. It begins at the inferior end of the laryngopharynx, passes through the mediastinum anterior to the vertebral column, pierces through the diaphragm at the esophageal hiatus, and ends at the stomach.

hard palate

anterior portion of the roof of the mouth. It is formed by the two maxillae and the two palatine bones. It also serves as the floor of the nasal cavity

Describe the pharyngeal stage of swallowing.

begins when tactile receptors in the oropharynx are stimulated by the presence of the bolus. The sensory information is carried to the deglutition center of the medulla. From the deglutition center, motor information via cranial nerves IX, X, XI causes contraction of the pharyngeal constrictors, contraction of the soft palate, and contraction of the laryngeal muscles. As a result, food is moved down the pharynx to the esophagus, the soft palate blocks access to the nasal cavity, and the larynx is pulled up against the epiglottis, blocking access to the trachea.

Describe the esophageal stage of swallowing.

begins when the bolus is pushed into the proximal end of the esophagus. In response, the upper esophageal sphincter relaxes and the bolus moves into the esophagus. Stretch of the esophagus initiates reflexive peristalsis, a wavelike contraction of the esophageal muscularis that pushes the bolus of food to the stomach. At the distal end of the esophagus, the gastroesophageal sphincter (lower esophageal sphincter) is reflexively opened and the bolus is pushed into the stomach. The gastroesophageal sphincter immediately closes.

Describe lingual lipase.

enzyme in saliva but is not active in saliva because it needs a slightly more acidic pH- slightly active in stomach, digests fats

Describe salivary amylase.

enzyme is used to initiate carbohydrate chemical digestion by catalyzing the breakdown of starch (a polymer of glucose) to the disaccharide maltose (glucose-glucose).

location and structure of the tongue

forms the floor of the oral cavity. The tongue itself is com-posed of interlacing skeletal muscles, called the intrinsic muscles, covered by stratified squamous epithelium.

Name and give a brief definition for each of the five basic processes of digestion.

ingestion -- taking food and drink by mouth movement of food -- passage of food through the gastrointestinal tract by peristalsis digestion -- breakdown of foodstuffs absorption -- passage of simple molecules from the digestive tract into either blood or lymph defecation -- elimination of indigestible substances from the system

Name and give a brief description for each of the two types of digestion.

mechanical digestion -- various movements specific for a particular organ that moves and churns food, breaking it down mechanically. chemical digestion -- consists of a series of catabolic reactions that break down the foodstuffs enzymatically

fauces

oral cavity itself extends from the gums and teeth, to the fauces, the passageway posterior to the palatopharyngeal arches that open into the oropharynx

extrinsic muscles of the tongue

originate outside the mouth and insert into the tongue's base. They are used to move the tongue side-to-side and in-and-out, and to help maneuver food and shape it within the mouth.

parotid salivary glands

paired parotid glands are located inferior and anterior to the ears, between the skin and masseter muscle. They empty their secretions into the mouth via the parotid (Stensen's) ducts that open into the vestibule of the mouth opposite the upper second molars.

sublingual salivary glands

paired sublingual glands are located superior to the submandibular glands just under the mucosa of the floor of the mouth. They empty via a number of small ducts directly into the floor of the oral cavity proper

submandibular salivary glands

paired submandibular glands are located just inside the mandible and beneath the base of the tongue on either side. They empty via the submandibular (Wharton's) ducts on either side of the lingual frenulum, opposite the two lower central incisors.

soft palate

posterior portion of the roof of the mouth. It consists of skeletal muscle covered by mucous mem-brane. Hanging from the middle of its free border is the uvula, a cone-shaped muscular process

Name the three types of stimuli that initiate salivation.

psychic, chemical, tactile

Name the four basic solutes or solute groups in saliva.

salivary amylase, ions, mucous, lysozyme

buccal salivary glands

small glands located in the mucous membrane of the mouth itself. They are responsible for keeping the mouth and pharynx moist, even when food is not in the mouth.

vestibule

space bounded externally by the cheeks and lips and internally by the gums and teeth

Describe the voluntary stage of swallowing.

the bolus of food is forced to the back of the mouth and into the oropharynx by the movement of the tongue upward and back against the palate. (cranial nerves V, VII, XII)