Chapter 37 DIGESTION AND NUTRITION

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

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

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.

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.

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

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

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.

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

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).

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

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.

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

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)

Stomach is site of: ] storage ] mechanical breakdown (muscle contraction) ] digestion (proteins) protein pepsin polypeptides ] minimal absorption (H 2 O, salts, some drugs, alcohol) Why doesn’t pepsin digest stomach? Mucus Stomach converts bolus into acid chyme.

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

Liver, gall bladder & pancreas empty secretions into duodenum. Liver - produces bile (emulsifies lipids) Gall bladder - stores bile Pancreas - produces pancreatic juice (H 2 O, bicarbonate ions, pancreatic amylase, trypsin, chymotrypsin, lipase & nuclease)

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 peptidases amino acids

] 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

6. Large Intestine (colon) - large 5- foot tube framing the small intestines. Note: ] cecum ] appendix ] rectum Colon contains large number of vitamin- producing bacteria [B 1, B 2, B 6, B 12, folic acid & biotin]

Large intestine is site of: ] absorption (H 2 O, salts, minerals & vitamins) ] elimination (feces) Feces consist of indigestible materials, bacteria & sloughed off intestinal cells. How would antibiotics affect normal colon function?

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

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

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.

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.

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

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

Good Nutrition = a balanced diet

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