BME350 - L22

What are the three phases of digestion mentioned in the BME350 lecture?

The cephalic phase, gastric phase, and small intestinal phase.

The four main processes of the GI tract are digestion, absorption, secretion, and _____.

motility

What induces the responses seen in the cephalic phase of digestion?

Brain and nervous system activity, triggered by sensory information like sight and smell.

What is the function of the epiglottis during the swallowing reflex?

It prevents the food bolus from entering the respiratory tract.

What problem can occur if the esophageal sphincter is not fully contracted when the stomach is churning?

Acid can be squirted back into the esophagus.

What are the three main functions of the stomach during the gastric phase of digestion?

Storage of food, digestion into chyme, and protection against pathogens.

What protective mechanism is increased when the stomach is irritated by substances like aspirin or alcohol?

Mucus secretion is increased.

Name one factor that can cause a failure of the mucus-bicarbonate barrier in the stomach.

Gastrin-secreting tumors, NSAIDs, or Helicobacter pylori infection.

Where does most chemical digestion occur in the GI tract?

In the small intestine.

Into which part of the GI tract are pancreatic digestive enzymes secreted to facilitate chemical digestion?

The small intestine.

Where does the majority of nutrient absorption take place in the GI tract?

In the small intestine, specifically the duodenum and jejunum.

Where in the GI tract are water and ions primarily absorbed?

In the large intestine.

How is the surface area of the small intestine increased for absorption?

By the presence of finger-like villi, which have epithelial cells with a brush border.

Are digestion and absorption directly regulated processes?

No, they are not directly regulated but are influenced by motility and secretion.

Digestive enzymes that act in the stomach work best at an _____ pH, while enzymes in the small intestine work best at an _____ pH.

acidic; alkaline

What substance, secreted by the liver, disperses fats into fine droplets to increase surface area for digestion?

Bile.

Weight loss drugs like Ozempic are based on GLP-1, a hormone that mimics what natural bodily process?

It mimics the natural hormone to increase feelings of fullness, slow digestion, and reduce appetite.

What is the key difference between Ozempic/Wegovy and Mounjaro (Tirzepatide)?

Mounjaro is a dual agonist that targets both the GLP-1 and GIP hormone receptors.

What is a rare but serious inflammation of the pancreas that can be a side effect of some weight-loss drugs?

Pancreatitis.

Some weight-loss drugs can interfere with fat absorption, leading to what type of deficiency?

Vitamin deficiencies, specifically for fat-soluble vitamins.

Intestinal transport of carbohydrates is restricted to what form?

Monosaccharides.

Why can't humans digest cellulose?

Because humans lack the necessary enzyme to break it down.

What is the function of the enzyme amylase?

It breaks down long glucose polymers (like starch) into smaller glucose chains.

What is the primary source of energy for intestinal cells, allowing absorbed glucose to pass into circulation?

Intestinal cells use glutamine, not glucose, as their main source of energy.

Between plant and egg proteins, which is considered the most digestible?

Egg protein is the most digestible (85-90%).

A significant portion (30-60%) of protein in the intestinal lumen comes from what endogenous sources?

The sloughing of dead cells and protein secretions like enzymes and mucus.

How are enzymes that digest protein typically secreted into the GI tract lumen?

They are secreted as inactive proenzymes and are activated in the lumen.

What are the three primary products of protein digestion that can be absorbed by the small intestine?

Free amino acids, dipeptides, and tripeptides.

What happens to peptides that are absorbed into an intestinal epithelial cell?

They are either digested into amino acids by cytoplasmic peptidases or transported 'as is' into circulation.

How can the absorption of peptides larger than three amino acids lead to food allergies?

These peptides can act as antigens, stimulating the production of antibodies.

Why might delaying the introduction of allergenic foods to infants reduce the likelihood of allergies?

It allows the gut to mature, as the peptide absorption rate is very high in newborns and declines over time.

What is the name of the major allergenic protein in peanuts that is stable to the heat of cooking?

Ara h 1.

Studies have shown that early exposure (4 mo - 3 yo) of high-risk children to peanuts can lower food allergy risk by up to what percentage?

Up to 80%.

What form of lipid accounts for at least 90% of our dietary fat calories?

Triglycerides (TG).

What type of enzyme is responsible for the enzymatic digestion of fat?

Lipases.

Which dietary lipid can be absorbed without prior digestion?

Cholesterol.

How do fatty acids and monoglycerides cross the membrane of small intestine cells?

They move out of micelles and diffuse across the cell membrane.

How is cholesterol transported across the intestinal cell membrane?

It is transported on a specific, energy-dependent membrane transporter.

Where in the intestinal cell are monoglycerides and fatty acids resynthesized into triglycerides?

In the smooth endoplasmic reticulum (sER).

What is the role of colipase in fat digestion?

Colipase displaces some bile salts from the surface of fat droplets, allowing lipase to access and digest the fats.

What property of bile salts allows them to break down a coarse emulsion of fat into smaller, stable particles?

They are amphipathic, with a hydrophobic region that associates with lipids and a polar region that interacts with water.

What are micelles?

Small, disk-shaped particles composed of fatty acids, bile salts, monoglycerides, phospholipids, and cholesterol that deliver lipids to absorptive cells.

What are chylomicrons?

Particles formed when triglycerides combine with cholesterol and protein inside intestinal cells for transport.

Why are chylomicrons absorbed into the lymphatic system instead of the blood capillaries?

Their large size prevents them from crossing the basement membrane of the capillaries.

How are fat-soluble vitamins (A, D, E, K) absorbed?

They are absorbed in the small intestine along with fats.

How are water-soluble vitamins (C and B) absorbed?

They are absorbed by mediated transport.

In which specific part of the small intestine is Vitamin B12 absorbed?

The ileum.

Water absorption in the GI tract follows an _____ gradient created by _____ absorption.

osmotic; solute

Via what pump does Na+ leave the intestinal epithelial cell to enter the interstitial fluid?

The Na+-K+ ATPase pump.

Parietal cells in the stomach secrete acid into the lumen and absorb what substance into the blood?

Bicarbonate ($HCO_3^-$).

What is the 'alkaline tide'?

The phenomenon where blood leaving the stomach is less acidic due to the absorption of bicarbonate from parietal cells during acid secretion.

What is the primary function of the sodium bicarbonate ($NaHCO_3$) secreted by the exocrine pancreas?

It neutralizes the acidic chyme entering the small intestine from the stomach.

What is the underlying genetic defect in Cystic Fibrosis?

An inherited defect where the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) channel is defective or absent.

How does Cystic Fibrosis affect the digestive system?

Thick mucus clogs the pancreatic ducts, preventing digestive enzyme secretion into the intestine.

In the secretion of saline solution into the gut, what is the active step that drives the passive movement of Na+ and H2O?

The active secretion of chloride ions (Cl-) through the CFTR channel.

What type of cells in the GI tract secrete mucus?

Goblet cells.

What is the primary function of mucus in the GI tract?

To protect the GI mucosa and to lubricate the contents of the gut.