WARM-UP
1. (Ch. 40) What is the principle of
countercurrent exchange?
2. (Review) What are the 4 classes of
macromolecules?
3. (Ch. 41) You eat a piece of candy. List the
structures it passes through as it travels through your alimentary canal.
4. Where does most of the digestion of the candy
What you need to know:
1.
Major compartments of alimentary
canal (organs)
2.
Digestive glands: salivary, pancreas,
liver, gall bladder
Essential Nutrients
: required by cells,
obtained through food
• Four classes of essential nutrients:
– Essential amino acids (8) – Essential fatty acids
– Vitamins (13) - fat-soluble, water-soluble – Minerals
Dietary Deficiencies
• Undernourished: diet is deficient in calories, not
enough energy
• Malnourishment is the long-term absence from
the diet of 1+ essential nutrients
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The main stages of food processing:
1. Ingestion: eating
2. Digestion: breakdown of food into small molecules
– Mechanical (chewing, grinding)
– Chemical (enzymes)
3. Absorption: cells take up nutrients
4. Elimination: pass undigested materials from digestive system
Figure 41.5
Mechanical
digestion Chemical digestion (enzymatic hydrolysis)
Nutrient molecules enter body cells
Undigested material
Elimination Absorption
Digestion Ingestion
Bulk Feeders
Suspension Feeders and Filter Feeders
Fluid Feeders
Baleen
Feces Caterpillar
Substrate Feeders
Digestive Compartments
• Most animals process food in specialized compartments
• Intracellular: digestion of food inside cells by food vacuoles
– Ex. phagocytosis, pinocytosis, sponges
• Extracellular: food broken down outside of cells
– Gastrovascular cavity (simple) or alimentary canal (complex)
Intracellular Digestion: Sponges
Extracellular Digestion
• Compartments are outside of the animal’s body
• Gastrovascular cavity: simple animals; single-opening, two-way digestion (food in, waste out)
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• Alimentary canal: more complex, one-way tubes with mouth and anus
Specialized organs for digestion in humans
• Digestive system = alimentary canal + glands
• Glands = salivary glands, pancreas, liver, and gallbladder
Q: Can you name the organs of the human alimentary canal in order?
• Peristalsis: push food through rhythmic
contractions of muscles in the wall of the canal
• Sphincters: valves regulate the movement of
material between compartments
Digestion of Macromolecules:
• Mouth = carbs
• Stomach = proteins
• Small Intestine = carbs, proteins, fats, nucleic acids
• Oral cavity: mechanical, chemical digestion
• Salivary glands: saliva lubricates food
• Teeth chew food into smaller particles
• Salivary amylase: breakdown glucose polymers
• Saliva contains mucus, a viscous mixture of
water, salts, cells, and glycoproteins
• Pharynx: back of throat
• Epiglottis: flap of cartilage, covers trachea when
swallowing
• Esophagus: food tube (pharynx stomach)
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Tongue
Pharynx
Glottis Larynx
Bolus of food
Epiglottis up
Esophageal sphincter contracted Esophagus
To lungs To stomach Trachea
Tongue
Pharynx
Glottis Larynx
Bolus of food
Epiglottis up
Esophageal sphincter contracted Esophagus
To lungs To stomach Trachea
Tongue Pharynx Glottis Larynx Bolus of food Epiglottis up Esophageal sphincter contracted Esophagus
To lungs To stomach Relaxed
Digestion in the Stomach
• The stomach stores food and secretes gastric
juice, which converts a meal to acid chyme
• HCl: pH 2, kill bacteria & denature proteins
• Pepsin: enzyme (protease) that hydrolyze proteins into smaller peptides
– Pepsinogen (inactive) pepsin (active) by HCl
• Mucus: protects lining of stomach
• Gastric ulcers: lesions in the lining, caused mainly by bacterium Heliobacter pylori
Digestion in the Small Intestine
• SI = major organ of digestion and absorption
– Duodenum: first section, digestive juices, major chemical digestion
• Digestive juices:
– Pancreas: bicarbonate (basic), trypsin & chymotrypsin (proteases); lipase (fats);
amylase (carbs)
– Bile: made in liver, stored in gall bladder
• Emulsify fats (make smaller droplets)
Figure 41.12-1
Carbohydrate digestion
Polysaccharides Salivary amylase
Smaller
polysaccharides Maltose Oral cavity,
Figure 41.12-2
Protein digestion
Small polypeptides Proteins
Pepsin Carbohydrate digestion
Polysaccharides Salivary amylase
Smaller
polysaccharides Maltose
Figure 41.12-3
Fat digestion Nucleic acid digestion
Protein digestion Fat (triglycerides) DNA, RNA Nucleotides Pancreatic nucleases Pancreatic lipase
Glycerol, fatty acids, monoglycerides Small peptides
Pancreatic carboxypeptidase Smaller
Fat digestion Nucleic acid digestion
Protein digestion Fat (triglycerides) DNA, RNA Nucleotides Pancreatic nucleases Pancreatic lipase
Absorption in the Small Intestine
• Villi and microvilli increase surface area
• Villi capillaries hepatic portal vein liver
heart
• Liver: distribute nutrients, detox, glucose storage (glycogen)
Absorption in the Large Intestine
• LI = colon
• Function = compact waste,
reabsorb water
• Cecum: pouch where SI & LI meet, ferment plant material
– Appendix = extension of cecum, role in immunity
• Rectum: end of LI, feces stored until elimination
Evolutionary adaptations of vertebrate digestive
systems correlate with diet
• Dentition: teeth correlate with diet
• Herbivores: longer alimentary canal, longer
cecum
Mutualistic Adaptations
• Many herbivores have fermentation chambers,
where mutualistic microorganisms digest cellulose (ruminants)
Homeostatic Mechanisms
• Vertebrates store excess calories as glycogen in
the liver and muscle cells, and as fat in
adipose tissue
• Overnourishment can lead to obesity
• Leptin: hormone that suppresses appetite
