Physiology: Salivary Gland and Saliva Formation

what are the 4 stages of food processing?

1. ingestion

2. digeation

3. absorption

4. egestion

what is ingestion?

taking in nutrients (proteins/amino acids, carbohydrates/glucose and fats/triglycerides)

what is digestion?

using physical and chemical means to break down complex organic molecules into smaller usable parts

what is absorption?

pulling in digested molecules into the cells of the digestive tract, then into the blood

what is egestion?

the removal of waste food materials (e.g. cellulose = fiber) from the body

what are the 3 phases of digestion?

1. cephalic (reflex) phase

2. gastric phase

3. intestinal phase

what is the cephalic (reflex) phase of digestion?

begins prior to food entry. Salivary gland secretion is the major component of the cephalic phase

what is the gastric phase of digestion?

Begins with the arrival of food in the stomach

what is the intestinal phase of digestion?

Begins as partially digested food enters the duodenum

cephalic phase: purpose

To prepare the body for a meal

cephalic phase: stimuli

Thoughts, site, sound, smell of food

cephalic phase: response

increase Parasympathetic Outflow

cephalic phase: effect

Salivation, gastric and pancreatic secretion and release of bile to the GI tract

how much liquid is ingested and secreted throughout the GI tract?

• 2 L ingested

• 7 L secreted into GI tract

what are some stimulants for secretion?

• Local effect of luminal contents

• Autonomic stimulation

  • Parasympathetic: usually increases

  • Sympathetic: usually decreases

• Hormonal and paracrine stimulation

which CNs are responsible for salivation?

VII and IX

which CNs are responsible for foregut outflow?

X

Oral homeostasis is dependent upon …?

saliva and its content of proteins

what are some positive regulators of saliva production?

• Thought of Food

• Smell of Food

• Sight of Food

• The Act of Chewing

• Nausea

what are some negative regulators of saliva production?

• Dehydration

• Sleep

• Fear

• Anticholinergic drugs

t/f; Reflex salivary flow occurs at a low 'resting' rate and for short periods during the day more intense taste or chewing stimuli evoke a ≥ ten-fold increases in salivation

true

what are some causes of xerostomia?

• Medications, especially anticholinergics

• Nerve damage

• Autoimmune destruction (Sjogren’s)

• Infection (HIV)

• Radiation

• Severe dehydration

what are some effects of xerostomia?

bicarbonate is essential in the GI tract for…?

• Buffering pH fluctuations

• Neutralizing gastric acid and providing optimal pH for digestive enzymes in duodenum

• Helps solubilize macromolecules (mucin, bile acids)

• HCO3- source: plasma, CA, GI lumen

what enzyme is involved in bicarbonate transport to/from blood circulation + lumen of small itntestine?

carbonic anhydrase

what are the 3 pairs of salivary glands that produce the majority of our saliva?

parotid, submandibular, and sublingual glands

what duct drains the parotid gland opposite to the upper second molar?

Stensen's duct

what duct drains the submandibular and some of the sublingual glands into the floor of the mouth near the frenulum of the tongue?

Wharton's duct

There are approximately ___ minor salivary glands in the mouth

600

Each salivary gland empties saliva into the ___

mouth

% salivary secretion is from the 3 major salivary glands

90%

Salivary Secretions from Acinar Cells include:

• alpha-amylase

• lipase

• mucin

• extracellular fluid (similar in ionic composition to plasma)

what is the function of alpha-amylase?

begins carbohydrate digestion and is inactivated by low pH

what is the function of lipase?

begins lipid digestion by converting triglycerides to fatty acids and monoglycerides

what is the function of mucin?

important in bolus formation and swallowing food being ingested

what do ductal cells do?

actively modify the ion content of saliva by absorption and secretion

t/f: Most salivary ductal cells express aquaporin (water) channels in their apical membrane.

false. The majority of salivary ductal cells do not express AQP channels and are impermeant to water. Without this feature it would be impossible to produce hypotonic saliva

______- condition (<Na+) of saliva entering the mouth aids the detection of salt in the diet

Hypotonic

Apical membrane (red) shows those cells expressing ______ channels

aquaporin (AQP, water)

t/f: Saliva in the ducts and mouth is hypotonic to plasma

true

Parasympathetic stimulation of the salivary glands results in …?

increased secretion of fluid and ions from the acinar and ductal cells

which nervous system controls the majority of salivary secretion?

PNS

t/f: Sympathetic stimulation of the salivary glands increase fluid, ion and protein secretion but is a minor contributor to increase in fluid volume

true

do GI hormones play a role in the regulation of salivary secretion?

GI hormones play NO role in the regulation of salivary secretion

Relative saliva contribution of the major salivary glands is as follows:

UNSTIMULATED

1) Submandibular gland=69%

2) Parotid gland=26%

3) Sublingual gland=5%

Relative saliva contribution of the major salivary glands is as follows:

STIMULATED

1) Parotid gland=69%

2) Submandibular gland=26%

3) Sublingual gland=5%

WHAT IS the most common disorder of the major salivary glands?

STONES (SIALOLITHS)

what are some diseases of the salivary gland?

• Stones (sialoliths)

• Bacterial infection (sialadenitis)

• Viral infection (ie. Mumps and flu)

• Sjögren's syndrome

• Benign pleomorphic adenomas

• Cancerous tumors

______ secretion is important in protecting the mouth from pH shifts and maintaining a pH neutral environment where amylase and lipase are active

Bicarbonate

what is responsible for the hypotonic saliva that enters the mouth?

The lack of aquaporin channels (AQP) in the apical membrane of most of the ductal cells

__________ stimulation of the salivary glands results in increased secretion of fluid and ions from the acinar and ductal cells.

Parasympathetic (Controls the majority of salivary secretion (volume))