San Diego Mesa College 15
Upper Esophageal Sphincter & Epiglottis
Food passes through the upper esophageal sphincter into the esophagus.
The epiglottis, a cartilage flap, swings open and shut like a door.
Swallowing reflex triggers it to close, preventing food from entering the trachea.
Talking and breathing simultaneously can lead to choking if the epiglottis malfunctions.
Esophagus
The esophagus is essentially a long tube connecting the mouth to the stomach.
Sphincters
The lower esophageal sphincter (LES) controls the passage of food from the esophagus to the stomach.
It opens in a timed manner when food is present in the esophagus.
It remains closed otherwise, preventing the stomach's contents from refluxing (exceptions: dysfunction).
Stomach
Muscular organ with muscle fibers in various directions (laterally, horizontally).
Muscles churn and mix food.
Mixes food with gastric acid (hydrochloric acid) and enzymes (pepsin, gastric lipase).
Chyme Formation: Food transforms from a bolus to chyme.
Chyme = food mush + acid + enzymes.
Distinct from the food bolus due to the presence of acid and enzymes.
Gastric Emptying: Chyme moves from the stomach through the pyloric sphincter to the duodenum (upper small intestine).
Pyloric Sphincter
Regulates the release of chyme from the stomach into the duodenum.
Gastric Emptying
Typically takes 2-4 hours for the stomach to empty completely.
Factors Affecting Gastric Emptying (Motility)
Metabolic Rate: Higher metabolic rate = faster emptying.
Exercise: Mobility aids GI movement via gravity.
GI Irritants: Bowel irritation (e.g., spicy foods, bacterial overgrowth) increases motility.
Stimulants (Caffeine): Increase motility.
Motility Defined: The rate at which food moves through the gastrointestinal tract.
GLP-1 Agonists (e.g., Ozempic): Decrease motility, promoting a feeling of fullness.
Order of Eating
Emerging research suggests the order of food consumption impacts hunger and blood sugar spikes.
Decreased Motility: Leads to food staying longer in the stomach, decreasing hunger hormone (ghrelin) production.
Ghrelin: A hormone controlled by the stomach and fat levels, not directly by the pituitary complex.
Motility Factors
Increased Motility Causes:
Younger age
Higher metabolic rate
Exercise
Water intake
Decreased Motility Causes: Pain medications (Tylenol, ibuprofen) leading to constipation.
Fullness, Diet, and Dysfunction Questions
The digestive system is a source of common problems.
Order of Consumption and Blood Sugar Spikes
For diabetics or pre-diabetics, prioritize the order of food consumption.
Recommendation: Vegetables/fiber, then protein, then carbohydrates.
Fiber and Blood Sugar
Vegetables are primarily carbohydrates with low caloric density due to high water and fiber content.
Most vegetables contain insoluble fiber, which doesn't significantly mix with water.
Soluble Fiber Sources: Fruits, brown rice, quinoa, chia seeds (draws water into the GI tract).
Benefit of Fiber: Limits blood sugar spikes; protein has a similar effect.
Protein and Energy
Proteins are not a primary energy source; used for energy mainly during starvation/malnutrition.
Primary energy sources: carbohydrates and fats.
Fiber for Appetite
Fiber contributes to fullness by remaining in the GI system, signaling the brain and reducing ghrelin production.
Soluble fiber retains water, further contributing to the sensation of fullness.
Vegetable Consumption
Eating vegetables first expands the GI system due to water absorption, which can aid in managing sugar spikes.
Water Retention
Fiber, being a type of carbohydrate, helps retain water in the GI system, aiding normal bowel movements and appetite suppression.
Duodenum
The upper part of the small intestine.
Receives approximately 70% of the necessary digestive enzymes.
Pancreas
Enzymes secreted into the duodenum through the pancreatic duct.
Also secretes bicarbonate to neutralize acidic chyme, optimizing enzyme function by increasing the pH, since enzymes are sensitive to pH.
Gallbladder and Liver
The xbladder (biliary system) shares a duct with the pancreas, secreting bile into the duodenum.
Bile: Emulsifies fats and serves as an elimination route for cholesterol and detoxified substances.
The liver detoxifies substances and eliminates them either through the biliary system (GI tract) or the renal system.
Small Intestine
Following the duodenum are the jejunum and ileum.
Primary site for nutrient absorption and diffusion into the circulatory system.
High surface area (windy and squiggly structure) with microvilli and capillary beds.
Absorption of water, fatty acids, amino acids, glucose, and other monosaccharides.
Large Intestine
Called "large" due to its diameter, not length.
Main function: Desiccation or dehydration; reabsorption of water and salts.
Rectum
Leads to defecation.
Digestive Functions
Ingestion: Food intake into the system.
Propulsion: Movement of food from point A to B.
Mechanical Digestion: Physical breakdown (grinding, tearing, churning).
Chemical Digestion: Breakdown using enzymes or acid.
Absorption: Diffusion of nutrients from the intestine to the circulatory system.
Defecation: Elimination of fecal matter.
Ingestion
Happens primarily in the mouth.
Mouth
Mechanical digestion: Teeth shred and tear food.
Teeth: accessory structures.
Chemical digestion: Salivary amylase starts breaking down carbohydrates.
Esophagus
Movement of food from mouth to stomach only.
Stomach
Chemical digestion.
Mechanical digestion.
Propulsion.
Some absorption (e.g., alcohol).
Intestines
Small Intestine: All digestion processes.
Large Intestine:
Propulsion.
Mechanical digestion.
Water absorption.
Electrolyte absorption.
Absorption in the Stomach
Absorption starts in the mouth, then the stomach, followed by the small intestine.
Medications need to be designed to withstand the stomach's hostile environment.
First-pass metabolism: The liver processes substances absorbed from the stomach.
Medications with Food
Food can prevent reduced bioavailability of medication.
It can also mitigate nausea caused by medication irritating the GI lining.
Bioavailability: the proportion of a drug or other substance which enters the circulation when introduced into the body and so is able to have an active effect.
Ulcer
In the stomach, the mucus lining protects against acid, muscle, and protein.
Medications lead to denaturing, which causes damage and ulcers.
Carbohydrate Digestion
Saliva contains water () and salivary amylase.
Salivary Amylase
A key enzyme which cleaves glycosidic bonds, but doesn't function in the stomach due to pH.
Cuts bonds between individual sugars in a polysaccharide (or disaccharide, etc.).
Hydrolysis
This is where water helps in the process of hydrolysis.
Role of pH
The stomach has a pH of around 3-3.5, so salivary amylase denatures.
Pancreatic Amylase
Enters in the Duodenum.
Summary of Starchy Pasta
Contact with salivary amylase will break it into disaccharides.
Afterwards, pancreatic amylase will continue to break it down to monosaccharides.
Monosaccharides get absorbed or expelled. This breakdown needs amylase in TWO different sites because a polysaccharide is in long subunits of 10,000-30,000.
Digestion Recap
1. Taking pasta -> Addition of Water (aids in hydrolysis) and Salivary Amylase to break down to saccharides/Disaccharides.
2. Reaching the stomach -> Salivary Amylase denatures.
3. Then the introduction of Pancreatic Amylase happens, which cuts some more bonds.
4. Result: Monosaccarides -> Ready for absorption into the lumen of the System/Circulatory System.
Small Intestine
It has enzymes for lactose and Maltose.
Maltose --(Maltase, a brush border enzyme)--> Glucose.
Probiotic Health -- Good bacteria plays a role in breaking down some sugars (bacteria create gas as byproduct).
Fiber
A carbohydrate that enzymes cannot break down.
This leads to low calories, since it can't access the calories in it.
Antibiotics
Antibiotics: Bacteria in the Body grows resistant but affects the natural Biome and is killed, so food that's normally eaten might not be normal to eat.
Probiotic yogurt to replenish that biome.