Digestion

BMS Unit 4 Exam

A person is startled while driving and almost hits a deer. Predict the immediate effect on digestion and explain why.

Digestion decreases because sympathetic activation overrides parasympathetic “rest and digest,” reducing saliva, motility, and enzyme secretion

Why does mechanical digestion enhance chemical digestion at the molecular level?

It increases surface area, allowing enzymes more access to substrate for faster reactions

A patient lacks pancreatic enzyme secretion. Which macromolecule digestion is MOST impaired and why?

Fats, because pancreatic lipase is essential for efficient fat digestion

If glycosidic bonds are not broken, what happens to carbohydrate absorption?

Carbohydrates cannot be absorbed because only monosaccharides can cross the intestinal epithelium

Explain why proteins must be broken into amino acids before absorption.

Only amino acids can be transported across intestinal cells; intact proteins are too large

Food is swallowed but enters the nasal cavity. Which structure likely failed and why?

Soft palate failed to elevate, allowing food into nasopharynx

During swallowing, what prevents food from entering the lungs?

Epiglottis and laryngeal elevation close off the airway

A patient has weak peristalsis. Predict the effect on digestion.

Food transport slows or stops, leading to impaired digestion and possible blockage

Explain how peristalsis differs from simple gravity in moving food.

Peristalsis uses coordinated muscle contractions, allowing movement regardless of body position

Why does GERD cause a burning sensation in the chest?

Stomach acid reflux irritates the esophageal lining, which lacks protective mucus

A patient frequently eats spicy, fatty foods and drinks coffee. Explain the physiological link to GERD.

These factors relax the LES, increasing acid reflux into the esophagus

Why is saliva important even before food reaches the stomach?

It begins chemical digestion and lubricates food for easier swallowing

A decrease in saliva production increases risk of cavities. Explain the mechanism.

Less saliva means fewer lysozymes and less washing away of bacteria, leading to plaque and acid buildup

Why is the cephalic phase considered anticipatory regulation?

It prepares the digestive system before food arrives via neural signals triggered by sensory cues

Which phase of digestion would still occur if a person could not see or smell food?

Gastric phase, because it is triggered by food entering the stomach

Explain how the vagus nerve connects the brain to digestive activity.

It carries parasympathetic signals that stimulate secretion and motility in the GI tract

A person chews food very poorly. Predict the downstream effects.

Reduced surface area leads to less efficient enzyme action and slower digestion

Why is a bolus important for swallowing efficiency?

It forms a cohesive mass that can be easily moved through the esophagus

If the lower esophageal sphincter never opened, what would happen?

Food would not enter the stomach, causing backup in the esophagus

If the lower esophageal sphincter never closed, what would happen?

Chronic acid reflux (GERD) would occur

Why are enzymes specific to certain macromolecules?

Their active sites are shaped to bind specific substrates (lock-and-key mechanism)

Explain why fats require more complex digestion than carbohydrates.

Fats are hydrophobic and require emulsification and lipase action, unlike easily soluble carbohydrates

A person is sleeping with a bottle of juice in their mouth. Explain why this leads to “baby bottle caries.”

Sugar feeds bacteria, reduced saliva at night allows acid buildup, damaging enamel

Why is the GI tract technically “outside” the body?

Its lumen is continuous with the external environment until absorption occurs

What triggers the transition from gastric to intestinal phase?

Chyme entering the duodenum

A blockage in the esophagus prevents peristalsis from reaching the stomach. What symptoms might occur?

Difficulty swallowing and food accumulation in the esophagus

Why is mucus in saliva important?

It lubricates food, reducing friction and aiding swallowing

Explain why enzyme secretion increases during the cephalic phase even without food present.

Neural signals anticipate food intake and prepare the system for efficient digestion

A person cannot produce lysozymes. What is the likely consequence?

Increased bacterial growth in the mouth and higher risk of infection/cavities

Why can peristalsis move food even if you are upside down?

It relies on muscle contractions, not gravity

What branch of the autonomic nervous system controls digestion?

Parasympathetic nervous system (“rest and digest”)

What is the GI tract?

A tube from mouth to anuus where digestion occurs

Name the accessory digestive organs.

• Salivary glands (creates saliva)

• liver (creates bile + fat)

• gallbladder (stores bile)

• pancreas (releases digestive enzymes for small intestine)

What triggers the cephalic phase?

Thought, sight, smell, or taste of food

What happens during the gastric phase?

Food enters stomach → chyme forms

What happens during the intestinal phase?

Chemical digestion and nutrient absorption in small intestine

What nerve controls the cephalic phase?

Vagus Nerve

You are driving down the highway and narrowly miss hitting a deer. Which of the following biological processes would most likely occur because of your close encounter?

Increased sweat production

What triggers the intestinal phase?

By chyme moving into duodenum

Mastication will enhance enzymatic action by increasing the ___ of the ingested food.

Surface area to volume ratio

What are the determinants of Gastric Emptying?

• Volume (directly proportional)

• Osmotic Pressure (inversely proportional)

• Nutrient Density (inversely proportional)

• Particle size (inversely proportional)

• Viscosity (inversely proportional)

How is bolus moved toward the stomach?

Peristalsis - wave -like contraction of smooth muscles behind the bolus

A patient has damage to parietal cells. Predict two major digestive consequences.

Decreased HCl production (higher stomach pH) and impaired protein digestion due to lack of pepsin activation

Why does a higher stomach pH impair protein digestion?

Pepsinogen requires acidic conditions (HCl) to convert into active pepsin

A patient has excessive histamine release in the stomach. What happens to acid production?

HCl secretion increases because histamine stimulates parietal cells

Explain how gastrin indirectly increases HCl secretion.

Gastrin stimulates both parietal cells and ECL cells, which release histamine to further increase acid secretion

A drug blocks H2 receptors on parietal cells. What is the effect?

Reduced HCl secretion because histamine can no longer stimulate parietal cells

Why does acetylcholine increase stomach acid secretion?

It activates parasympathetic pathways that directly stimulate parietal cells

A patient has no mucus production in the stomach. Predict the outcome.

The stomach lining becomes damaged by acid, increasing risk of ulcers

Why is mucus critical despite the stomach being designed to handle acid?

It protects epithelial cells from being digested by acid and enzymes

Explain how HCl contributes to both digestion and defense.

It denatures proteins for digestion and kills ingested microorganisms

A patient cannot produce pepsinogen. What is the primary digestive issue?

Impaired protein digestion in the stomach

Why does stomach distension decrease ghrelin secretion?

Ghrelin signals hunger and is released when the stomach is empty, so stretching suppresses it

A patient eats a very high-fat meal. Predict the effect on gastric emptying.

Gastric emptying slows to allow more time for digestion

Why does increased viscosity slow gastric emptying?

Thicker contents reduce motility and require more mixing and dilution

A patient consumes a high-fiber soluble diet. Predict two physiological effects.

Slower gastric emptying and increased satiety

How does insoluble fiber help relieve constipation?

It increases stool bulk and speeds up transit through the colon

Why can soluble fiber help lower cholesterol levels?

It binds bile acids, reducing their reabsorption and lowering circulating cholesterol

A patient has rapid gastric emptying. What dietary change could slow it down?

Increase fiber, fat content, or viscosity of meals

Explain why large food particles delay gastric emptying.

They require more mechanical digestion before passing into the intestine

During vomiting, why must the lower esophageal sphincter relax?

To allow stomach contents to move upward into the esophagus

What is the role of reverse peristalsis in vomiting?

It moves intestinal contents backward into the stomach and up the GI tract

Why can chronic vomiting lead to cardiac issues?

Loss of electrolytes disrupts normal heart function

A patient frequently uses NSAIDs. Explain how this can lead to ulcers.

NSAIDs reduce protective mechanisms in the stomach, allowing acid to damage the lining

How does H. pylori contribute to ulcer formation?

It damages the mucosal lining, making it more vulnerable to acid

Why is the stomach able to mechanically digest food more effectively than the esophagus?

It has three muscle layers that create strong mixing waves

Explain how the bicarbonate buffering system in parietal cells supports acid secretion.

It generates H+ for secretion into the lumen while HCO3- enters the blood

Why does increased gastric pressure speed up gastric emptying?

Higher pressure pushes contents more quickly into the small intestine

A patient has reduced parasympathetic activity. Predict the effect on stomach function.

Decreased secretion of acid and enzymes and reduced motility

Why does the gastric phase amplify digestion compared to the cephalic phase?

It is triggered by actual food presence, increasing secretion and mechanical activity

A patient eats very low-fiber meals consistently. Predict long-term digestive effects.

Faster gastric emptying, reduced satiety, and increased risk of constipation

Explain why HCl inactivates many enzymes from food.

The acidic environment denatures proteins, including enzymes

A patient has impaired ECL cells. What happens to acid secretion?

It decreases because less histamine is available to stimulate parietal cells

Which of the following stomach secretions convert pepsinogen into pepsin?

HCl

As a bolus of food enters the stomach and causes distension, which of the following secretions will decrease?

Ghrelin

The rate of gastric emptying will be delayed by ___

A salty and low-fiber meal

What composes the mucosa of the small intestine?

Enterocytes

Why are villi helpful to the mucosa?

They increase surface area

What are enteroendocrine cells (EECs)?

Specialized enterocytes that release hormones

Describe the function of I cells

• Release cholecytokinin (CCK)

• Binds acinar cells in pancreas

• Acinar cells release pancreatic enzymes (Lipase, Amylase, Trypsin/Chymotrypsin)

Describe the function of S cells

• Release secretin

• Binds duct cells in pancreas

• Causes bicarbonate to be released into the small intestine to neutralize the acidic chyme

A mutation that decreases the release of cholecystokinin (CCK) will most likely result in impaired:

Fat breakdown

What type of organ is the pancreas?

An accessory organ of the digestive system with both endocrine and exocrine functions

What are the two functional divisions of the pancreas?

Endocrine (hormone secretion into the bloodstream) and exocrine (enzyme/bicarbonate secretion into the digestive tract).

Where are the endocrine cells of the pancreas located?

In the pancreatic islets (islets of Langerhans)

What do alpha cells of the pancreatic islets secrete?

Glucagon — raises blood glucose levels.

What do beta cells of the pancreatic islets secrete?

Insulin — lowers blood glucose levels

Where are the exocrine cells of the pancreas located?

They surround the pancreatic duct.

What are acinar cells and what do they secrete?

Acinar cells are exocrine cells that secrete pancreatic digestive enzymes: lipase, amylase, trypsin, and chymotrypsin.

What do duct cells of the pancreas secrete?

Bicarbonate — helps neutralize the acidic chyme entering the small intestine from the stomach.

What is the function of pancreatic lipase?

Breaks down fats (lipids) in the small intestine

What is the function of pancreatic amylase?

Breaks down starches (carbohydrates) into simpler sugars.

What are trypsin and chymotrypsin, and what do they digest?

They are proteases (protein-digesting enzymes) secreted by acinar cells that break down proteins in the small intestine

Cholecystokinin from I-cells in the SI binds what kind of cells in the pancreas?

Acinar, which release enzyme into duct that flows to the SI (Trypsinogen, Chymotrypsinogen, Amylase, Lipase)

Secretin from S-cells in the SI binds what kind of cells in the pancreas?

Duct cells, which release bicarbonate into duct that flows to the SI

What enzyme first breaks down carbohydrates, and into what?

Amylase breaks carbohydrates down into disaccharides.

How are disaccharides broken down to monosaccharides?

Transmembrane disaccharidases on the enterocyte surface cleave disaccharides into monosaccharides (e.g. glucose).

What enzymes begin protein digestion in the small intestine?

Trypsin and chymotrypsin break proteins down into small peptides.

What happens to monomers (monosaccharides and amino acids) after digestion?

They are transported across the enterocyte epithelium and absorbed into the blood

How is glucose moved into the enterocyte?

Apical by sodium-driven glucose cotransporter