digestive

Here’s your in-depth study guide for Chapter 24: Digestive System from BIOL 133 Winter 2025 with all learning outcomes answered and content included. This is tailored for a high-difficulty exam—clear, detailed, and focused on critical understanding.

Chapter 24: Digestive System – Comprehensive Study Guide

I. Overview of Digestion and GI System

1.

What is the primary role of the digestive system?

• To break down (digest) food and absorb nutrients into the blood or lymph for cellular use.

2.

What is the GI tract and what does it include?

• A muscular tube open at both ends, including:
  

  • Oral cavity

  • Pharynx

  • Esophagus

  • Stomach

  • Small intestine (duodenum, jejunum, ileum)

  • Large intestine (cecum to rectum)

3.

What are accessory digestive organs?

• Organs that secrete substances to aid digestion but food doesn’t pass through them directly:
  

  • Teeth, tongue, salivary glands

  • Liver, gallbladder, pancreas

II. Digestive Processes

III. Oral Cavity and Teeth

1.

What are the functions and types of teeth?

• Functions: Mastication (chewing), speech, aesthetics

• Two dentitions:
  

  • Deciduous (20): Baby teeth; erupt ~6 months, lost by 6–12 years

  • Permanent (32): Includes molars and wisdom teeth

2.

What are the layers of a tooth?

• Enamel (96% CaPO₄, hardest substance, no cells)

• Dentin (70% CaPO₄, also acellular)

• Pulp: Contains CT, nerves, blood, lymph

IV. Salivary Glands and Saliva

1.

What are the 3 major salivary glands and their roles?

• Total: 1.5L saliva/day (99.4% water)

V. Tongue and Swallowing

1.

Tongue Functions

• Mechanical processing

• Assists swallowing & speech

• Contains sensors for taste, temp, touch

• Secretes lingual lipase (breaks down triglycerides)

2.

Swallowing (Deglutition)

• Begins voluntary, becomes reflexive (medulla)

• Stimulated by tactile receptors

• Occurs ~2400x/day

VI. Histology of the GI Tract

VII. Peritoneum and Folds

• Largest serous membrane

• Visceral (on organs) and parietal (on cavity wall)

• Folds:
  

  • Greater omentum (stomach)

  • Falciform ligament (liver → anterior wall)

  • Lesser omentum (liver → stomach)

  • Mesentery proper (SI)

  • Mesocolon (LI)

VIII. Motility: Peristalsis vs. Segmentation

IX. Stomach

1.

Functions

• Mechanically mixes food

• Begins protein digestion with pepsin

• Secretes gastric juice

• Regulates chyme entry to duodenum

2.

Cells of the Stomach

X. Liver, Gallbladder, and Pancreas

1.

Bile (from liver, stored in gallbladder)

• Emulsifies fats using bile salts (from cholesterol)

• Contains bilirubin (waste from heme)

• Bicarbonate buffer

2.

Pancreatic Juice

• Bicarbonate (neutralizes acid)

• Enzymes: trypsinogen, chymotrypsinogen, lipase, amylase, nuclease

• Activation: Enterokinase → Trypsin → Activates others

XI. Hormonal Regulation of Digestion

XII. Phases of Digestion

1. Cephalic Phase: Smell/sight triggers PSNS → gastric secretions

2. Gastric Phase: Stretch & chemoreceptors → ↑ gastric juice + motility

3. Intestinal Phase: CCK, GIP, Secretin ↓ gastric activity, ↑ pancreatic/bile secretion

XIII. Small Intestine

1.

3 Segments

• Duodenum: Short, receives chyme + secretions, many glands

• Jejunum: Long, lots of villi, nutrient absorption

• Ileum: Has Peyer’s patches, fewer villi

2.

Absorption Mechanisms

• Na+ cotransport for glucose, galactose, amino acids

• Facilitated diffusion for fructose and water

• Fatty acids → lymph via lacteals as chyle

• B12 requires intrinsic factor

• Fat-soluble vitamins (A, D, E, K) absorbed with fats

XIV. Large Intestine

• Absorbs water, Na+, vitamins (K, B5, B7, B9)

• Hosts gut bacteria that produce gas, indole, H2S, NH3

• Mass movements push feces; defecation reflex triggered by stretch

XV. Liver’s Role in Metabolism

1. Stores glycogen, vitamins, minerals

2. Kupffer cells destroy bacteria/RBCs

3. Nutrient interconversion (gluconeogenesis, lipogenesis)

4. Urea production (from amino acid catabolism)

5. Detoxifies drugs, alcohol, hormones

6. Produces plasma proteins and clotting factors

7. Regulates blood glucose, cholesterol, AA, FA levels

XVI. Nutrient Metabolism

Absorptive State (Fed)

• Insulin promotes:
  

  • Glucose uptake (→ glycogen or ATP)

  • Lipid formation

  • Protein synthesis

Postabsorptive State (Fasting)

• Glucagon, E, cortisol, GH:
  

  • Glycogenolysis

  • Lipolysis

  • Gluconeogenesis

  • Ketone production

XVII. Appetite Regulation

XVIII. Portal Circulation

• Nutrient-rich blood from GI → hepatic portal vein → liver

• Allows liver to regulate nutrients before systemic circulation

XIX. Fluid Balance in GI

• ~9L fluid enters GI tract/day

• Only 0.2L exits in stool

• Most absorbed in SI

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