DIGESTION AND NUTRITION

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Slide 1 :

Chapter 37 DIGESTION AND NUTRITION

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Why must certain organisms consume food? To obtain energy & raw materials required for growth, repair, and maintenance of the body.

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Often classify consumers based on what they eat. Carnivore - animals Frugivore - fruits & berries Herbivore - plants Insectivore - insects Omnivore - plants & animals Detritivore - nonliving organic matter

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Consumers process food in stages: ?Ingestion - intake of food. ?Mechanical breakdown - physically cutting food into smaller pieces. ?Digestion - chemically breaking food particles into small molecules (monomers). ?Absorption - cellular uptake of monomers. ?Elimination - ridding the body of undigested material.

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A. Digestive Diversity 1. Types of Digestion Intracellular digestion - occurs within a cell’s food vacuoles. Extracellular digestion - occurs outside cells; usually within a cavity or tube connected with the outside world.

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Why must digestion occur in some type of compartment (food vacuole, gastrovascular cavity, stomach)?

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Digestive systems may have one or two openings. Opening serves as both mouth & anus. Separate mouth & anus; food travels in 1 direction.

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2. Digestive System Adaptations Digestive systems are adapted to an animal’s diet. Insectivores & Carnivores - tend to have short, simple digestive tracts; cecum is greatly reduced or absent.

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Herbivores - tend to have long, complex digestive tracts; cecum is prominent. Exception is giant panda - herbivore with a short digestive tract.

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B. Human Digestive System Consists of gastrointestinal tract (mouth, pharynx, esophagus, stomach, small intestine & large intestine) and accessory structures (salivary glands, pancreas, liver & gall bladder).

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1. Mouth Site of: ingestion mechanical breakdown (teeth) digestion (carbohydrates) starch [polysaccharide] salivary amylase maltose [disaccharide]

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2. Pharynx - passageway for air & bolus; opens into larynx & esophagus. What structure ensures that bolus enters esophagus? 3. Esophagus - muscular tube leading to stomach. Bolus is pushed down esophagus by peristalsis.

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4. Stomach - muscular J-shaped sac. Structure 4 regions (cardia, fundus, body, pylorus) lower esophageal sphincter pyloric sphincter rugae

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Stomach mucosa (lining) contains gastric glands consisting of: mucus cells - secrete mucus parietal cells - secrete HCl chief cells - secrete pepsinogen pepsinogen + HCl ? pepsin (active enzyme)

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Stomach is site of: storage mechanical breakdown (muscle contraction) digestion (proteins) protein pepsin polypeptides minimal absorption (H2O, salts, some drugs, alcohol) Why doesn’t pepsin digest stomach? Mucus Stomach converts bolus into acid chyme.

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5. Small Intestine - muscular 23-foot tube (duodenum, jejunum, ileum). Intestinal mucosa: has a large surface area (circular folds, villi, microvilli) produces several enzymes: - carbohydrases - peptidases

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Liver, gall bladder & pancreas empty secretions into duodenum. Liver - produces bile (emulsifies lipids) Gall bladder - stores bile Pancreas - produces pancreatic juice (H2O, bicarbonate ions, pancreatic amylase, trypsin, chymotrypsin, lipase & nuclease)

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Small intestine is site of: mechanical breakdown (segmentation) digestion (carbohydrates, proteins, lipids & nucleic acids) starch pancreatic amylase maltose disaccharides carbohydrases monosaccharides polypeptides trypsin chymotrypsin peptides peptides peptidases amino acids

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absorption (monosaccharides, amino acids, monoglycerides, fatty acids, nucleotides) Absorbed materials enter circulatory system. fat globules + bile ? small fat droplets fat droplets lipase monoglycerides + fatty acids RNA & DNA nuclease nucleotides

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6. Large Intestine (colon) - large 5-foot tube framing the small intestines. Note: cecum appendix rectum Colon contains large number of vitamin-producing bacteria [B1, B2, B6, B12, folic acid & biotin]

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Large intestine is site of: absorption (H2O, salts, minerals & vitamins) elimination (feces) Feces consist of indigestible materials, bacteria & sloughed off intestinal cells. How would antibiotics affect normal colon function?

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Fats (3-6 hours) Proteins (?3 hrs) Carbs (1-2 hrs)

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C. Human Nutrition Nutrients are chemical substances in food that are required for growth, maintenance & repair. Essential nutrients - must be ingested; body cannot synthesize. Nonessential nutrients - can be synthesized if not ingested. Essential nutrients vary among species.

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Humans cannot synthesize 9 amino acids. meats contain all 9 vegetables contain some, but not all Strict vegetarians must eat certain vegetables in combination to obtain all 9 essential amino acids.

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1. Macronutrients (energy nutrients) Nutrients required in large amounts; can be broken down by cellular respiration to supply energy (ATP). Carbohydrates - cell’s major energy source. Proteins - required to make enzymes, hemoglobin, antibodies & some hormones. Lipids - required to make cell membranes & some hormones; needed for insulation & absorption of fat-soluble vitamins.

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The amount of energy a macronutrient releases is measured in kilocalories (kcal). Which macronutrient yields the most energy (ATPs) per gram? Lipids Lipids ? 9 kcal/gram Carbohydrates & Proteins ? 4 kcal/gram

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2. Micronutrients Nutrients required in small amounts. Vitamins water-soluble vitamins: B’s & C fat-soluble vitamins: A, D, E & K Minerals Bulk minerals: calcium, chloride, sodium, magnesium, phosphorus, potassium & sulfur Trace minerals: chromium, cobalt, copper, fluorine, iodine, iron, manganese, selenium & zinc

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Good Nutrition = a balanced diet

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Poor Nutrition Primary nutrient deficiencies - caused by an inadequate diet. Marasmus - lacking all nutrients. Kwashiorkor - lacking protein in diet. Anorexia nervosa - self imposed starvation. Bulimia - eating followed by purging. Secondary nutrient deficiencies - caused by a metabolic abnormality. Celiac disease - genetic condition in which nutrients cannot be absorbed from small intestine.

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