GI Flashcards
What is mastication?
Why is mastication called physical digestion?
Mastication just means chewing. The teeth break food into smaller pieces, but the food itself doesn’t change—it’s just the same food in smaller pieces.
Because when you chew, you’re just breaking the food into smaller parts. No chemical bonds are broken, so it’s still the same food, just in tiny pieces.
What does the mandible do in chewing?
Why is physical digestion important?
The mandible is your lower jaw, and it moves when you chew. That movement helps your teeth grind food down into smaller pieces.
When you chew, you’re making food smaller, which makes it easier for your body to digest later. It helps enzymes do their job better.
What are the main structures in the oral cavity that help with digestion?
Teeth and salivary glands.
What are the three major salivary glands?
Are salivary glands paired?
The submandibular gland makes the most saliva, contributing around 75-80% of total saliva production.
The parotid gland produces a large amount of saliva, accounting for about 20-25% of total saliva production.
The parotid gland comes in second, making roughly 20-25% of saliva.
The sublingual gland makes the least saliva, contributing only about 2-3%.
Salivary glands are paired, with three on each side of the mouth.
What does saliva do to food?
What is chemical digestion, and how does it happen in the mouth?
How much saliva do we make daily?
Saliva moistens food, breaking it into smaller pieces and forming a soft ball called a bolus. This bolus is what you swallow down the pharynx into the esophagus.
Chemical digestion happens when chemical bonds in food are broken down. Amylase(淀粉酶) in saliva starts breaking down carbohydrates/starch into smaller sugars like disaccharides or monosaccharides.
We produce about 1.5 liters of saliva every day, which is about the same as drinking four cans of soda!
Polysaccharides
Carbohydrates
Disaccharides
Monosaccharides
Big, complex carbohydrate molecules made of many sugar units linked together. Think of them like a long chain of sugar blocks.
Example: Starch in bread and potatoes is a polysaccharide, glycogen
Sugars and starches that give us energy. They can be simple (like sugar) or complex (like starch).
Example: Rice, pasta, and fruit all have carbohydrates.
Smaller sugars made of two sugar units linked together. Your body needs to break them down further to use them for energy.
Example: Table sugar (sucrose) is a disaccharide.
Sucrose(蔗糖)= Glucose + Fructose; from sugarcane(甘蔗)
Lactose(乳糖): Glucose+ Galactose Lactose is the sugar in milk. Some people can’t digest it well because they lack lactase.
Maltose(麦芽糖): Glucose+Glucose When you chew bread for a long time, it starts tasting slightly sweet – that’s because enzymes in your saliva break starch into maltose!
The simplest sugars, made of just one sugar unit. Your body absorbs these directly for energy.
👉 Example: Glucose (in blood) and fructose (in fruit) are monosaccharides.
Maltose → mɔːl（像 “mall” 商场）+ toʊs
Sucrose → suː（像 “sue”）+ kroʊs
Lactose → læk（像 “lack” 缺乏）+ toʊs
Fructose → 两种发音：frʌk-toʊs（美式常见）或 fruːk-toʊs（某些地区发音）
What does the esophagus do?
The esophagus transports food from the oral cavity to the stomach. No metabolic changes happen during this process—it simply moves food down.
What types of muscles are found in the esophagus?
The esophagus has three types of muscle organization depending on location:
1️⃣ Proximal esophagus (top part, near the pharynx) – Lined with skeletal muscle, which allows voluntary control over swallowing.
2️⃣ Distal esophagus (lower part, near the stomach) – Made of smooth muscle, which is involuntary, meaning you have no conscious control.
3️⃣ Middle (mixed muscle region) – A mix of both skeletal and smooth muscle, transitioning from voluntary to involuntary control as food moves down.
👉 As you swallow, control shifts from voluntary (skeletal muscle) to involuntary (smooth muscle) to push the food (bolus) into the stomach.
What happens after you swallow food?
Where do we have voluntary and involuntary muscle control in digestion?
Peristalsis is an involuntary wave-like contraction of muscles that pushes food down the esophagus and through the entire GI tract until it reaches the end.
1️⃣ Swallowing (in the proximal esophagus) – Skeletal muscle allows you to voluntarily start swallowing.
2️⃣ Defecation (at the end of the GI tract) – Skeletal muscle lets you voluntarily control when you defecate.
Everything in between (esophagus, stomach, intestines) is controlled involuntarily by smooth muscle through peristalsis
After food goes through the small and large intestine, whatever is left moves into the rectum. Finally, the skeletal muscle at the anus allows voluntary control over defecation.
order of GI Tract– (The hollow organs that form the passage for food digestion and absorption.)
GI system = GI tract + digestive glands
Oral cavity-esophagus-stomach-small intestine-large intestine-rectum-anus
Digestive glands: Salivary glands, liver, gallbladder, pancreas
Salivary glands – Produce saliva with amylase for carbohydrate digestion
Liver – Produces bile to help digest fats
Gallbladder – Stores and releases bile
Pancreas – Secretes digestive enzymes (amylase, lipase, proteases) and bicarbonate
Proteases(蛋白酶)
📌 Proteases break down proteins into amino acids for absorption.
✅ 1️⃣ Pepsin（胃蛋白酶）
Produced by: Stomach (胃)
Active in: Stomach (胃)
Function: Starts breaking down proteins into smaller peptides in the acidic environment of the stomach.
✅ 2️⃣ Trypsin & Chymotrypsin（胰蛋白酶 & 胰凝乳蛋白酶）
Produced by: Pancreas（胰腺）
Active in: Small intestine（小肠）
Function: Further break down peptides into even smaller peptides and amino acids for absorption.
Amylase
✅ Breakdown of Carbohydrates (Carb Digestion Process)
📌 Carbohydrates are broken down into smaller sugars (such as maltose and glucose).
✅ Where does carbohydrate digestion occur?
Salivary amylase (from the salivary glands) – Starts carbohydrate digestion in the mouth by breaking down starch into smaller sugars.
Pancreatic amylase (from the pancreas) – Continues breaking down carbohydrates in the small intestine to produce even simpler sugars for absorption.
Lipase
Breakdown of Lipids (Fat Digestion Process)
📌 Lipids (fats) are broken down from triglycerides into glycerol and fatty acids for absorption.
✅ Where does fat digestion occur?
Lingual lipase (from the salivary glands) – Begins minimal fat digestion in the mouth.
Pancreatic lipase (from the pancreas) – Primarily breaks down fats in the small intestine, aiding in fat absorption.
The GI tract is composed of four main layers from the inner (closest to the food) to the outermost:
Mucosa – The innermost layer, directly in contact with the food (lumen).
2️⃣ Submucosa – Supports the mucosa with blood vessels and nerves.
3️⃣ Muscularis externa – Responsible for peristalsis and movement of food.
4️⃣ Serosa – The outermost protective layer.
Mucosa (黏膜层) – The Inner Lining
The mucosa is lined with epithelium, which forms the surface of the lumen (the hollow space inside the GI tract).
Epithelium – The topmost layer, involved in secretion, absorption, and protection.
Basement membrane – A thin layer that supports the epithelium.
Lamina propria(capillaries) – A loose connective tissue layer that sits below the basement membrane and provides structural support.
What types of epithelium are found in the GI tract, and how do they aid in protection and nutrient absorption?
The inner lining of the stomach, small intestine, and large intestine is made up of simple columnar epithelium, which helps with nutrient absorption.
✅ The esophagus is unique because its inner lining consists of stratified non-keratinized epithelium. This type of epithelium protects it from friction caused by food passage but does not harden like skin.
✅ Beneath the epithelial layer is a connective tissue layer called the lamina propria, which contains two important vascular systems:
Systemic capillaries – Absorb carbohydrates and amino acids, then transport them throughout the body.
Central lacteals – Specialized lymphatic vessels that absorb fats and transport them through the lymphatic system to the rest of the body.
In the GI tract, the epithelium is the layer that directly touches the food. Beneath it is the lamina propria, which provides blood supply and immune defense. If food reaches the lamina propria, that means the epithelium is damaged, like in an ulcer.”
