UNIT 9 GPT

What is another name for the digestive system?

The gastrointestinal tract.

What is the main function of the digestive system?

To efficiently extract nutrients from ingested food.

Which macronutrients are focused on in this digestive system study?

Proteins, carbohydrates, and lipids.

How are macronutrients chemically digested?

By enzymes secreted into the digestive tract that break them into smaller absorbable units.

What mechanical processes aid chemical digestion of macronutrients?

Chewing and stomach grinding muscle activity.

What is the main goal of the digestive tract?

To absorb as much of the ingested nutrients as possible.

Why must secretion, digestion, and motility be coordinated in the digestive system?

To allow for maximal nutrient absorption.

What problems arise from improper motility in the digestive tract?

Digestive issues from motility being too fast or too slow.

What defensive roles does the digestive tract play?

Protects the body from harmful pathogens, toxins, and foreign substances from food and drink.

Name two reflexes that aid defense in the digestive system.

Vomiting reflex and increased intestinal motility causing diarrhea.

Besides reflexes, how else does the digestive system protect the body?

Protective secretions help shield the internal environment from external pathogens.

What are accessory organs in the digestive system?

Organs that do not contact food directly but secrete substances like saliva, enzymes, and bile into the digestive tract.

Which organs directly contact ingested food?

Oral cavity, esophagus, stomach, small intestine, and large intestine.

Are salivary glands considered digestive tract organs or accessory organs?

Accessory organs (they don’t contact food directly).

Name three accessory organs other than salivary glands.

Liver, gallbladder, and pancreas.

What important secretions do salivary glands produce?

Saliva.

What does the liver secrete for digestion?

Bile.

Where is bile stored before entering the digestive tract?

Gallbladder.

Into which part of the digestive tract do liver, gallbladder, and pancreas secretions enter?

The small intestine.

What are the four key digestive processes that occur throughout the digestive tract?

Digestion, secretion, motility, and absorption.

Define digestion in the digestive system context.

The breakdown of food into smaller pieces mechanically and chemically.

What is mechanical digestion?

Physically making food smaller (e.g., chewing).

What is chemical digestion?

Breaking chemical bonds in food molecules via enzymes.

What is secretion in the digestive system?

Release of substances by cells into the lumen or blood, including enzymes, acid, water, mucus, bicarbonate, and hormones.

What is an exocrine secretion?

Secretions released into the lumen, like enzymes and acid.

What is an endocrine secretion in the digestive system?

Hormones secreted into nearby blood vessels, not into the lumen.

What is a paracrine secretion?

Secretions from epithelial cells that affect nearby cells without entering blood or lumen.

What is motility?

Coordinated muscle movements moving food through the digestive tract.

How can motility aid digestion beyond moving food?

Some motility patterns help mechanically break down food, e.g., chewing and stomach churning.

What is absorption?

Movement of food particles from the lumen through epithelial cells into the blood or lymph.

What is the lumen?

The hollow central tube of the digestive tract where food passes.

What are the four tissue layers of the digestive tract?

Mucosa, submucosa, muscularis externa, and serosa.

What does the mucosa layer do?

Faces the lumen, contacts food, contains epithelial cells that secrete and absorb.

What is special about the epithelial cells in the mucosa?

They vary between organs and perform secretion and absorption.

What connects the mucosa to the muscularis externa?

The submucosa.

What important structures are found in the submucosa?

Blood vessels and the submucosal plexus (part of enteric nervous system).

What does the muscularis externa consist of?

Two layers of smooth muscle: circular and longitudinal.

What plexus is located in the muscularis externa?

The myenteric plexus (part of the enteric nervous system).

What additional muscle layer does the stomach have?

An oblique muscle layer.

How does circular muscle contraction affect the digestive tract?

It narrows the tube diameter.

How does longitudinal muscle contraction affect the digestive tract?

It shortens the length of the tube.

What is the serosa?

The outer protective connective tissue layer continuous with the mesentery.

What is the enteric nervous system (ENS)?

A network of neurons in the digestive tract layers that controls digestion autonomously.

Where are the neuron bodies of the ENS found?

In the submucosal plexus (submucosa) and myenteric plexus (muscularis externa).

How does the ENS compare in size to other parts of the nervous system?

It has as many neurons as the spinal cord, more than any other peripheral organ.

Does the ENS require input from the central nervous system (CNS) to function?

No, it can function autonomously but is modulated by CNS inputs.

What functions do the myenteric plexus neurons serve?

Coordinate muscle contraction and relaxation for motility patterns.

What functions do the submucosal plexus neurons serve?

Stimulate epithelial secretion and act as sensory neurons detecting lumen contents and stretch.

How do submucosal neurons detect the composition of the lumen?

They sense whether contents are liquid or solid and the presence of nutrients like lipids and carbohydrates.

Which nervous systems innervate the ENS?

Parasympathetic and sympathetic branches of the autonomic nervous system.

How does input from the autonomic nervous system affect the ENS?

It modulates digestive tract activity but the ENS can work independently.

What is the starting point of digestion?

The mouth (oral cavity) is the beginning point of digestion.

Does significant macronutrient absorption occur in the oral cavity?

No, almost no absorption of macronutrients occurs here.

What starts in the mouth related to digestion?

Mechanical breakdown of food begins in the mouth.

What is saliva mostly composed of?

Saliva is mostly water.

Besides water, what important components does saliva contain?

Proteins, ions (sodium, chloride, bicarbonate), mucus, and digestive enzymes (salivary amylase, lingual lipase).

What is the function of bicarbonate in saliva?

It helps neutralize any acid present in food.

What role does mucus in saliva serve?

Lubricates the mouth.

What proteins in saliva help protect the teeth?

Specific proteins in saliva protect teeth from bacteria and acid.

How many pairs of salivary glands mainly produce saliva?

Three pairs of exocrine glands produce most saliva.

What is the structure of the salivary glands’ duct system?

Many small ducts converge into fewer larger ducts, ending in a main duct.

Do all salivary glands produce the same type of saliva?

No, each gland produces slightly different saliva compositions.

What does the parotid gland secrete?

A watery saliva rich in salivary amylase and lingual lipase.

Where is the parotid gland located?

On the upper side of the oral cavity.

What does the submandibular gland secrete?

A thicker saliva with more mucus and less enzyme content.

Where is the submandibular gland located?

Underneath the mandible (jawbone).

What does the sublingual gland secrete?

A mucusy saliva with almost no enzymes.

Where is the sublingual gland found?

Underneath the tongue.

How does saliva secretion vary with activity?

During active eating, parotid glands produce enzyme

What is mastication?

Mastication is the mechanical digestion through chewing, breaking food into smaller pieces.

Why is chewing important if not for nutrient absorption?

It breaks food down so it can be swallowed without getting stuck.

Which organ is most important for mechanical digestion?

The stomach.

What enzyme in saliva breaks down amylose?

Salivary amylase.

What enzyme in saliva digests lipids, and when does it become active?

Lingual lipase; it activates in the acidic environment of the stomach.

What is the pH dependence of salivary amylase and lingual lipase?

Salivary amylase works in the mouth’s pH; lingual lipase activates in the acidic stomach.

What are the motility patterns in the oral cavity?

Chewing (mastication) and swallowing.

What is swallowing?

A motility pattern moving food from oral cavity to esophagus, consisting of voluntary and involuntary phases.

Describe the voluntary phase of swallowing.

The individual controls how long to chew and voluntarily pushes the bolus to the back of the oral cavity.

What triggers the pharyngeal stage of swallowing?

The sensation of the bolus at the pharynx triggers involuntary swallowing reflexes.

What happens during the pharyngeal stage?

The nasopharynx is closed by the soft palate; the epiglottis covers the trachea; upper esophageal sphincter relaxes.

What happens during the esophageal stage of swallowing?

Peristalsis pushes the bolus down the esophagus; the lower esophageal sphincter relaxes to allow passage into the stomach.

What is the bolus?

Food mixed with saliva, softened for swallowing.

Why is lubrication important for the bolus?

Lubrication helps the bolus move smoothly down the esophagus.

What muscles coordinate to push the bolus down the esophagus?

Circular and longitudinal esophageal muscles.

Is gravity required for moving the bolus through the esophagus?

No, peristalsis moves the bolus independent of gravity.

What is peristalsis?

A coordinated wave of muscle contractions that propels the bolus downward.

What is secondary peristalsis?

A stronger wave of contractions to push a bolus that has become stuck.

What role do sensory neurons play in swallowing and peristalsis?

They detect bolus location and trigger swallowing reflexes and peristalsis.

What sphincters are involved in swallowing?

The upper esophageal sphincter and the lower esophageal sphincter.

What is the function of the upper esophageal sphincter?

It opens to allow the bolus from the pharynx into the esophagus.

What is the function of the lower esophageal sphincter?

It opens to allow the bolus to enter the stomach.

What macronutrients are absorbed in the oral cavity?

Minimal absorption; some glucose and small non

Why is nutrient absorption minimal in the oral cavity?

Because the mouth has few absorptive cells and most food needs further digestion.

How is glucose absorbed in the oral cavity?

Via glucose carriers expressed in oral epithelial cells.

What is the clinical relevance of sublingual absorption?

Some medications are designed for sublingual absorption due to rapid uptake of small non

What is the main function of the stomach in digestion?

The stomach acts as a reservoir for food before it enters the intestines for absorption.

What are the two curvatures of the stomach and their locations?

The greater curvature is on the left side (left of the body), and the lesser curvature is on the right side.

What is the fundus of the stomach?

The upper portion of the stomach that first receives the bolus.

What is receptive relaxation in the stomach?

The stretching of the fundus in response to the incoming bolus.

What happens to the bolus as it moves from the fundus to the body and antrum?

It becomes liquefied by coordinated muscular contractions and mixes with gastric juices.