BIO 107 - The Oral Cavity, Pharynx and Esophagus

Which digestive-related structures are part of the oral cavity?

• Lips and cheeks

• The palate

  • hard palate

  • soft palate

    • uvula

• Oral Mucosa

• Tongue

• Salivary glands

• Teeth

Which specific type of epithelium lines the oral cavity?

Non keratinized stratified squamous which protects it from abrasion/friction (Oral Mucosa)

What is the function of the soft palate and uvula?

It rises reflexively to close off the nasopharynx when we swallow and projects downward from the free edge of the soft palate

What is the tongue composed of and what does it aid with?

Skeletal muscle covered with mucous membrane

• Maneuvering food for chewing

• Shaping the food into a rounded mass (bolus)

• Forcing the food to the back of the mouth for swallowing

What are several functions of the tongue that are specific to digestion?

1. Mechanical digestion by compression, abrasion, distortion

2. Manipulation to assist in chewing and to prepare the food for swallowing

3. Sensory analysis by touch, temp, taste receptors

4. Secretion of mucins (mucus) and the enzyme lingual lipase

What is the function of the enzyme lingual lipase?

It’s substrate is triglycerides and it produces free fatty acids and mono- and diglycerides

• initiates fat digestion

Name the 3 major salivary glands:

• Parotid salivary gland

• Sublingual salivary gland

• Submandibular salivary gland

What is the name of the secretion from the salivary glands?

Saliva

Which salivary glands produce and release the enzyme salivary amylase?

Parotid glands

What happens once food enters the mouth?

Saliva secretion increases

What is the function of salivary amylase?

It’s substrate is polysaccharides and it produces disaccharides and trisaccharides

• initiates carbohydrate digestion in the mouth by breaking down starches into simpler sugars

What are the major functions of saliva?

1. Moistening and softening of food → bolus

2. Digestion of starch (salivary amylase)

3. Taste - saliva dissolves food so we can taste it

4. Defense - lysozyme

What is the composition of saliva (“juice”)?

• Water (99.5%): provides a medium for dissolving foods so they can be tasted and for initiating digestive reactions

• Solutes (0.5%)

What is the main ingredient in saliva?

Water (99.5%)

What ions are present in saliva?

• ions

• dissolved gases

• organic substances

Which organic substances are present in saliva?

• salivary amylase

• mucus - lubrication of food/bolus

• lysozyme - antibacterial enzymes

How do the parasympathetic and sympathetic nervous systems regulate salivation?

PNS increase salivation and SNS decreases salivation (dry mouth)

Name several other stimuli for salivation:

• touch and taste of food

• smell, sight, sound, or memory of food (psychological activation of the glands)

• ingesting irritating foods

What is the major contribution of the teeth to digestion?

Mechanical digestion (breakdown) via the process of mastication (chewing)

• it grinds the food

Give specific examples of mechanical digestion that occur in the mouth:

• the tongue manipulates food

• the teeth grind food

• food is mixed with saliva

• food molecules begin to dissolve in the water in saliva

• mastication → food is reduced to a bolus which can be easily swallowed

What 2 enzymes contribute to chemical digestion?

Salivary amylase and Lingual lipase

Give specific examples of chemical digestion that occur in the mouth:

Salivary amylase (polysaccharides) concerts starches to maltose, maltotriose, and alph-dextrans

• they still cannot be absorbed by small intestine

Lingual lipase

• initiates the digestion of dietary triglycerides into fatty acids and monoglyceride

• BUT it is not very effective because bile is needed for fat digestion (absorption)!

When the food bolus is first swallowed, where does it pass from?

The mouth

What is the pharynx composed of?

Skeletal muscle and lined by mucus membrane

What is the contribution of the pharynx to digestion?

It helps with deglutition (swallowing)

What specific type of muscle makes up the muscularis externa layer of the pharynx?

Skeletal muscle

Define the term “deglutition”:

It means swallowing

Where is the deglutition center located?

Medulla oblongata and lower pons of the brain stem

What stimulates the receptors in the oropharynx?

The bolus of food that was created in the mouth

What sends impulses to the deglutition center?

The oropharynx

What do the returning impulses cause the soft palate and uvula to do?

It causes them to move upward and close off the nasopharynx

What happens to the larynx, epiglottis and respiratory passages during deglutition?

The larynx is pulled forward and upward the tongue: therefore, the epiglottis moves backward and downwards and seals off the respiratory passages

When does the respiratory passageway reopen and breathing resumes?

Once the bolus has entered the esophagus

Is swallowing a voluntary or involuntary act?

Swallowing is initiated voluntarily in the mouth and after that is controlled by the involuntarily reflex coordinated by the deglutition center

Name the 3 stages of swallowing:

1. Voluntary stage (buccal/oral)

2. Pharyngeal stage

3. Esophageal stage

What are the events of the voluntary stage (buccal/oral)?

• The bolus moves into the oropharynx

• Swallowing starts when the bolus is forced to the back of the oral cavity and into the oropharynx by the movement of the tongue upward and backward against the palate

• This act activates the receptors that initiate the swallow reflex

What are the events of the pharyngeal stage?

• The involuntary passage of the bolus through the pharynx into the esophagus

• The respiratory passageway closes, and breathing is temporarily interrupted

• This stage includes relaxation of the UES and LES

What are the events of the esophageal stage?

• The involuntary passage of the bolus through the esophagus into the stomach

Define the term “Dysphagia”

It means difficulty/discomfort with swallowing

What does oropharyngeal dysphagia specifically refer to?

Difficulty transferring food from oropharynx to esophagus

What are 2 possible causes of oropharyngeal dysphagia?

• mechanical obstruction

• neuromuscular conditions

What does esophageal dysphagia specifically refer to?

Difficulty passing food through the esophagus into the stomach

What are 2 possible causes of esophageal dysphagia?

• altered esophageal peristalsis

• failure of LES to relax

What is the esophagus?

A collapsible muscular tube that lies posterior to the trachea. It takes a relatively straight course through the thorax (chest cavity) and pierces through the diaphragm to enter the abdomen and joins the stomach.

What is the contribution of the esophagus to digestion?

• Moves food and liquids from the mouth to the stomach through peristalsis

• Secretes mucus for lubrications

• Uses sphincters to prevent backflow

Which type of epithelium lines the esophagus?

Non keratinized squamous epithelium (mucosa)

In which wall layer are esophageal glands located?

In the submucosa layer

What substance is released by esophageal glands? What is the benefit of this secretion?

• Mucus is produced and released by the esophageal glands.

• The lubrication reduces friction and makes it easier for food to go down smoothly during swallowing

Which specific types of muscle are part of the muscularis externa of the esophagus?

The top 1/3 is skeletal muscle and the middle & last 1/3 is smooth muscle

Why is the most superficial layer of the wall of the esophagus called adventitia and not serosa?

This is because it is above the diaphragm (which divides the chest and abdominal cavity)

Name the 2 psychological sphincters associated with the esophagus, and state where they are exactly located:

Upper Esophageal Sphincter (UES)

• located at the junction of the pharynx and the esophagus, around the level of the cricoid cartilage

Lower Esophageal Sphincter (LES - cardiac Sphincter)

• located at the junction of the esophagus and the stomach, just above the gastroesophageal junction at the diaphragm

What are involved in the opening and closing of the esophageal sphincters?

Pressure changes

What des the UES act as?

A sphincter (valve)

What muscle is the UES made up of?

Skeletal muscle

What muscle is the LES made up of?

Smooth muscle - between the esophagus and the stomach!

• @ rest it is contracted (closed)

What is the significance of the UES and LES being physiological sphincters?

They are not as well-defined as sphincter muscles, but they work by constricting and relaxing

• pressure changes are involved in opening and closing

The LES is closed when:

Constricted

THE LES is open when:

Relaxed

Food is pushed through the esophagus via what?

Peristalsis

What is peristalsis?

The series of coordinated muscular contractions and relaxations are repeated in a wave that actively pushes the food towards the stomach

Peristalsis in the smooth muscle segment of the esophagus is under the direct control of what?

The Autonomic Nervous System (ANS)

What happens after swallowing?

A peristaltic wave begins at the upper esophagus and proceeds sequentially towards the stomach

What happens prior to contraction in peristalsis?

The pressure in the esophagus is 0 (equal to atm P). When each segment of the esophagus contracts, its pressure increases and then decreases back to 0

Each sequential contraction moves what along the esophagus?

Bolus

How is the peristaltic activities of the esophagus related to the opening of the LES?

When the peristaltic wave is initiated, the LES relaxes and the press in the LES falls to 0

• the LES remains open until the bolus can be pushed into the stomach

What does the esophagus secrete? (the only secretion by the esophagus)

Mucus

What does the esophagus transport?

Food to the stomach

Mucus is NOT an:

Enzyme

At which process are digestive enzymes NOT produced and absorption DOES NOT take place?

In the digestive process of the esophagus

What is LES relaxation?

The approach of the bolus triggers the opening of the LES (via relaxing it) and the bolus continues into the stomach

What happens when the bolus is swallowed?

The relaxation of the LES is closely coordinated with the peristaltic movements that moved the bolus through the esophagus

What simultaneously happens when the peristaltic wave is initiated in the esophagus?

The LES simultaneously relaxes

The combined activity of what plays a role in coordinating this peristalsis and sphincter relaxation?

The vagus nerve and enteric nervous system (ENS)

Define the clinical condition GERD:

It is when the LES does not close properly and the stomach contents reflux into the esophagus!

What are some common symptoms/signs of GERD?

• Heartburn

• Regurgitation

• Non-cardiac chest pain

• Sore throat

How do changes in pressure play a role in the movement of the bolus down the esophagus?

There are coordinated pressure changes that help with the movement of bolus down the esophagus

• at rest UES is contracted (high pressure) to prevent air from entering the esophagus

  • LES is also usually contracted to prevent reflux

• UES relaxes (pressure drops) which allows the bolus into the esophagus

  • when bolus is swallowed, relaxation (opening) of the LES coordinated with peristaltic movements

Relaxed LES → Open (bolus can pass into the stomach).

Contracted LES → Closed (blocks reflux of stomach contents).

The UES is contracted when:

Closed (blocks reflux of stomach contents)

The LES is relaxed when:

Open (bolus can pass into the stomach)