Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 41.3 Organs Specialized for Sequential Stages of Food Processing Form the Mammalian Digestive System
Overview of Digestion
- Digestion is the breakdown of food into absorbable molecules.
- Two types:
- Mechanical digestion: physical breakdown (e.g., chewing)
- Chemical digestion: enzymatic breakdown into monomers
- Enzymes break down:
- Proteins → amino acids
- Polysaccharides/disaccharides → monosaccharides
- Fats → glycerol and fatty acids
- Nucleic acids → nitrogenous bases, sugars, phosphates
Compartmentalization of Digestion
- Most animals digest food in specialized compartments to avoid self-digestion.
- Intracellular digestion: occurs in food vacuoles (e.g., sponges)
- Extracellular digestion: in compartments like stomach or gastrovascular cavities
The Mammalian Digestive System
- Alimentary canal: the full digestive tube from mouth to anus
- Accessory glands: salivary glands, pancreas, liver, gallbladder—secrete digestive fluids and enzymes
1. Oral Cavity
- Teeth break down food mechanically
- Salivary amylase starts digesting starch
- Mucus lubricates food; buffers protect teeth
- Tongue forms food into a bolus for swallowing
2. Pharynx and Esophagus
- Pharynx connects mouth to both esophagus and trachea
- Epiglottis prevents food from entering the airway during swallowing
- Peristalsis moves food down the esophagus via muscle contractions
3. Stomach
- Stores food and begins protein digestion
- Secretes gastric juice:
- HCl: lowers pH to ~2, kills microbes, denatures proteins
- Pepsin: active enzyme that digests proteins
- Partially digested food becomes chyme
Protection of the Stomach
- Mucus protects the stomach lining
- Parietal cells secrete H⁺ and Cl⁻ separately to form HCl in the lumen
- Chief cells release pepsinogen, activated by HCl into pepsin
- Rapid cell division renews the stomach lining every few days
In a Nutshell
The mammalian digestive system uses compartmentalized organs and enzymatic activity to transform food into absorbable nutrients. Mechanical breakdown, chemical hydrolysis, and protective adaptations work in concert to ensure that digestion is efficient and safe for the animal’s body.