1. Chapter 41 Campbell & Reece
Digestion
Chapter 41
Campbell & Reece

2. 49-1: Nutritional Requirements
Cells need:
Water
Carbohydrates
Lipids
Proteins
Nucleic acids
Vitamins-- Study Table 49-1 pg. 980
Minerals - Table 49-2 pg. 981

3. Nutrition involves the following steps:
Ingestion
Digestion
Absorption
Distribution
Digestion: the breakdown of ingested food materials into molecules that can be delivered to and utilized by the individual cells.
Can be both mechanical and chemical.
human anatomy tutorials, labeled with explanations (all systems) link

4. The “Gut” (Gastrointestinal Tract): Fig.49-2 pg. 983
Made of 4 layers (see pictures on page 985)
Mucosa: (innermost) -epithelial, connective, some smooth muscle
Submucosa: connective, nerve fibers, blood & lymph vessels
Muscularis Externa: muscle tissue (circular & longitudinal)
Serosa: outer covering of connective tissue

5. Peristalsis: coordinated contractions of circular muscles along digestive tract which move food along
Sphincters: thickened, heavy bands of muscle along tract that act as valves by contracting (closing) and relaxing (opening) to control of materials

6. The Oral Cavity: Initial Processing:
Mechanical Digestion
Tongue - swallowing (microscopic picture)
Teeth: “mastication” (chewing)
incisors- cutting, clipping
canines- tearing, stabbing
premolars- "bicuspids" 2 cusps (points)
molars- 4 or 5 cusps (for grinding)
Other Animals lack teeth, have alternatives:
rasping tongue: ex- snails, lamprey, frogs
grinding organ (gizzard): ex- birds, earthworms
Chemical Digestion (enzymatic hydrolysis): saliva, mucous
3 pairs of salivary glands and buccal glands in jaw: lubricates, softens food
Enzyme- salivary amylase for hydrolysis of starch into smaller sugar molecules; slightly alkaline (sodium bicarbonate)

7. The Pharynx & Esophagus: Swallowing
Swallowing: passage of food to the esophagus ----> stomach
begins as voluntary action (striated muscles in upper part of esophagus) lower portion involuntary (smooth muscle)= "peristalsis" Esophagus opens into Stomach
Abdominal cavity lined with peritonium / organs are suspended by mesentaries
(animation)

8. The Stomach: Storage & Liquefaction
…a collapsible, muscular, j-shaped bag with many folds and ridges
mucosal lining folds into gastric pits (microscopic picture)
lined with mucous-secreting epithelial cells
gastric glands secrete HCl and pepsinogen (precurser to pepsin)
pH between 1.5 & 2.5 (mucous barrier between acids + stomach lining )- ulcers?

9. Stomach acids, enzymes HCl:
kills bacteria loosens tissues for digestion converts pepsinogen to pepsin
Pepsin: breaks down proteins into smaller peptides
Semi-liquid mass "Chyme" moves to lower end of stomach => Pyloric Sphincter (takes about 4 hrs.)
Rate of leaving stomach = H2O,carbs, proteins, fat, protein/fat combo
The three phases of gastric secretion animation

10. The Small Intestine: Digestion and absorption
lined with VILLI ( microscopic fingerlike projections) and tiny microvilli on surface of epithelial cells
about 21 feet long (adult), total surface area about 300 m2
Digestion:
Duodenum- 1st 25 cm (10 inches)
most digestion takes place here;
receives several digestive juices/enzymes from ducts leading from ACCESSORY GLANDS (liver pancreas, gall bladder)

11. Accessory Glands neutralize stomach acids with alkaline secretions
produces several enzymes to chemically digest nutrients

12. The Pancreas
Enzymes made here enter the duodenum via the pancreatic duct
Amylase: continues starch digestion
Starchesdisaccharidesmonosaccharides
Trypsin: breaks down proteins  amino acids
Lipase: hydrolyzes fats

13. The Liver: an accessory gland
Bile-
produced by liver
stored in gall bladder
contains salts (emulsify fats)
sodium bicarbonate (neutralize pH to optimum 7 or 8)

14. Absorption of Nutrients:
food is absorbed through epithelial cells of intestinal mucosa into the bloodstream, for distribution to all cells
Active Transport: Monosaccharides, Dipeptides, Amino Acids
Diffusion: fatty acids
Lipids resynthesize into triglycerides, phospholipids (blood & lymph vessels), Cholesterol

15. The Large Intestine: Water Absorption & Elimination
The Large Intestine (colon)continues absorption of water, sodium, and other minerals (which begins in small intestine)
E. coli bacteria: makes Vit.K, amino acid synthesis
Appendix: vestigial organ (gastric caecum?)
Waste: "fecal matter"
water, bacteria, dead cells, indigestible matter (cellulose)
lubricated with mucus
temporary storage in rectum