quick study

### Digestive System Summary

#### Key Functions:

- Ingestion: Taking in food and liquids.

- Mechanical digestion: Physical breakdown (chewing, stomach churning).

- Chemical digestion: Enzymatic breakdown (proteins, carbs, fats).

- Absorption: Nutrients move into the blood or lymph.

- Defecation: Elimination of indigestible material.

#### Mechanical vs. Chemical Digestion:

- Mechanical digestion: Physical breakdown (e.g., chewing, peristalsis).

- Chemical digestion: Enzymes break down food molecules (e.g., carbs to sugars).

#### Digestive System Components:

- Alimentary canal (GI tract): Mouth → Anus (includes stomach, small and large intestine).

- Accessory organs: Salivary glands, pancreas, liver, gallbladder.

#### Peristalsis vs. Segmentation:

- Peristalsis: Wave-like muscle contractions that move food.

- Segmentation: Mixing contractions that help digestion and absorption.

#### 4 Layers of the GI Tract:

1. Mucosa: Secretes digestive enzymes, absorbs nutrients.

2. Submucosa: Contains blood vessels, nerves.

3. Muscularis externa: Controls peristalsis and segmentation.

4. Serosa: Outer layer, reduces friction.

#### Saliva:

- Composition: Water, mucus, enzymes (salivary amylase).

- Function: Moistens food, starts carbohydrate digestion.

#### Preventing Food from Entering the Nasal Cavity & Larynx:

- Soft palate blocks the nasal cavity.

- Epiglottis covers the larynx to prevent choking.

#### Gastric Gland Cells:

- Mucous cells: Secrete mucus to protect the stomach.

- Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor.

- Chief cells: Secrete pepsinogen (for protein digestion).

- Enteroendocrine cells: Secrete hormones like gastrin.

#### Small Intestine Modifications:

- Villi and microvilli: Increase surface area for nutrient absorption.

- Circular folds: Slow down chyme and increase absorption.

#### Pancreas, Liver, Gallbladder Roles:

- Pancreas: Secretes digestive enzymes and bicarbonate ions.

- Liver: Produces bile (for fat digestion).

- Gallbladder: Stores and releases bile.

#### Bicarbonate in Pancreatic Juice:

- Neutralizes stomach acid to create a proper pH for digestive enzymes.

#### Mucus in the Digestive Tract:

- Protects the lining of the GI tract from digestive acids and mechanical damage.

#### End Products of Digestion:

- Carbs: Simple sugars (glucose, fructose).

- Fats: Fatty acids and glycerol.

- Proteins: Amino acids.

#### Absorption:

- Blood capillaries: Absorb amino acids, sugars, and water-soluble vitamins.

- Lacteals: Absorb fatty acids and fat-soluble vitamins as chylomicrons.

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#### Digestive Tract Regions & Functions:

| Region | Main Function | Nutrients Digested | Enzymes Produced | Enzymes That Act Here |

|---------------------------|------------------------------|-------------------------|-----------------------------|------------------------------|

| Mouth | Ingestion, initial digestion | Carbohydrates | Salivary amylase | Salivary amylase |

| Stomach | Protein digestion, churning | Proteins | Pepsinogen (activated to pepsin) | Pepsin |

| Small Intestine (Lumen) | Digestion and absorption | Carbs, fats, proteins | Pancreatic enzymes (amylase, lipase, proteases) | Pancreatic enzymes, bile salts |

| Small Intestine (Brush Border) | Final digestion and absorption | Carbs, proteins, fats | Maltase, sucrase, lactase, dipeptidases | Brush border enzymes |

| Large Intestine | Water absorption, bacterial fermentation | Fiber, water | None | Bacterial enzymes |

#### Bile:

- Composition: Water, bile salts, cholesterol.

- Function: Emulsifies fats, aids in fat digestion and absorption.

#### What Cannot Be Digested?

- Cellulose (fiber): Not digestible by humans.

#### Vitamin Synthesis:

- Intestinal flora produce vitamin K and some B vitamins.

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This simplified guide highlights the main concepts of the digestive system, its anatomy, functions, and processes. Feel free to review each section as needed!