Nutrition and Digestion Chapter 21

Obtaining Food All animals eat other organisms Herbivores: eat autotrophs Carnivores: eat other animals. - meat eating plants Omnivores: eat plants and animals Animals differ in how food is ingested Suspension feeders: filter food from water Substrate feeders: eat through a substrate Fluid feeders: sucking fluids Bulk feeders: ingest large pieces of food, using various ‘utensils’

Processing Food Ingestion: act of eating Digestion: breaking down food into small, absorbable molecules Mechanically broken into pieces Chemical breakdown catalyzed by enzymes that add H2O Occurs in compartments so only food, not self, is digested Absorption: cells in GI tract take up digestion products Transported in blood to wherever needed Excess intake converted to fat for storage Elimination: undigested material passes out GI tract

Understanding Food Processing Chemical Breakdown 4 main stages

Comparative Compartmentalization Gastrovascular cavity Alimentary canal

Digestive Cycle Food ingested into a mouth opening Pushed into a pharynx or throat Passes through an esophagus to a secondary structure Crop: pouch like organ to soften and store food Stomach and gizzard: churn and grind food; some storage Food chemically digested and nutrients absorbed in the intestines Undigested materials exit via the anus

Human Digestive System Accessory glands in the alimentary canal secrete digestive juices through ducts Moved through the canal by peristalsis, alternating waves of contraction and relaxation of smooth muscles Passage regulated by sphincters

The Mouth Mechanical breakdown and mixing of food w/ saliva Teeth chew, cut, smash, and grind the food Easier to swallow and expose to enzymes Incisors bite chunks, canines tear, and molars grind Chemical digestion starts w/ saliva, a glycoprotein that protects the mouth and lubricates food Sight and smell can stimulate before food continues it Salivary amylase for carb digestion, bicarbonate to neutralize, and mucins to lubricate Tongue is a muscle that manipulates food, allows taste, and forms a food bolus Pushed back into the pharynx

The Esophagus Pharynx has esophagus and trachea, or windpipe Esophagus closed so air can enter larynx, voice box, then into lungs Tongue pushes bolus which relaxes sphincter and closes epiglottis over larynx Bolus passes and pharynx returns for breathing Esophagus is a muscular tube that is voluntarily controlled at the top, peristalsis continues the length of Lined with stratified squamous Length varies with species

The Stomach Prevents need for constant feeding Stores and mixes food Secretes gastric juices (pH=2) of mucus, enzymes, and acid Breaks food, kills bacteria and microbes 3 cell types produce Peristaltic contractions transforms bolus into acidic, nutrient-rich chyme Sphincter controls release to small intestine Small amounts at regular intervals

Gastric Juices Cells in gastric glands produce Mucous cells: lubricate and protect lining Parietal cells: produce H+ and Cl- ions to form HCl Coverts pepsinogen to pepsin Chief cells: secrete pepsinogen Pepsin increases pepsinogen production = positive feedback Pepsin starts digesting proteins by splitting polypeptide chains Secretion as pepsinogen and mucus prevents digestion of stomach lining Epithelium regularly replaced

Controlling Digestion Sight, smell, and/or taste of food signals brain Brain signals stomach to start producing gastric juices Stomach produces hormone gastrin in presence of food Enters circulatory system and reenters stomach wall Stimulates more gastric juice production Increase in acidity inhibits gastrin so less juices produced Protects stomach lining

Digestive Ailments Acid reflux Gastric Ulcers Backflow of chyme into esphogeal opening Pepcid AC, Zantec, and Prilosec slow or limit acid production Gastric Ulcers Corrosive effect of gastric juices due to lack of mucus Helicobacter pylori results in localized loss of protection Mild inflammation from WBC’s attack H. pylori Can reach a point where a hole develops

Small Intestine (SI) Enzymes Pancreas produces enzymes and bicarbonate solution Protein degradation Buffer to neutralize chyme Liver produces bile to emulsify fats Gall bladder stores bile All mix in the duodenum

Small Intestine Digestion Carbs started in the oral cavity Proteins started in the stomach Fats undigested until duodenum All finished by duodenum, rest of SI for absorption

Small Intestine Absorption SI has huge surface area as a result of folding Large circular folds Small finger-like villi Each villi covered with epithelial cells containing microvilli Absorption via diffusion or against [gradients]

Liver’s Role Key in regulating metabolism Direct transport of nutrients from SI and LI Removes excess glucose from blood and converts to glycogen to store in liver cells Coverts substances into new, essential proteins E.g plasma proteins for blood clotting Modifies and detoxifies substances in blood before they reach the heart Converts toxins to inactive products to be released in urine Excess can cause damage

Large Intestine (LI) also called the colon, joins SI at a T-shaped junction Blind pouch on one end = cecum with attached appendix Absorbs water from alimentary canal leaving solids behind Solidifies as moves along colon via peristalsis to produce feces containing indigestible plant fibers and prokaryotes Rectum stores feces until elimination Two sphincters, a voluntary and an involuntary one, control Water reclamation inhibited = diarrhea Peristalsis too slow, excess water reabsorbed = constipation

Comparative GI tracts Length of GI tract often related to diet Herbivores and omnivores longer Herbivores lose many nutrients to feces Recycle feces to regain Ruminants have 4 chambered stomachs Regurgitate food from 1 to another = chew cud

Nutritional Needs All animals, regardless of diet, have the same Fuel to power all activities Organic molecules to build own molecules Essential nutrients or substances that can’t be self made Must obtain from food Combinations of 4 major biological molecules

Essential Nutrients 4 classes Essential fatty acids: most diets provide ample Essential amino acids: 8 of 20 AA’s needed for proteins Can’t be stored, deficiencies effect others Meat, eggs, milk, and cheese provide all in correct amounts Vitamins and minerals Undernourishment: diet chronically deficient in calories Common during drought, war, anorexia nervosa Malnourishment: long term diet absence of 1+ essential nutrient More common, can be obese

Vitamins and Minerals Vitamin: an organic nutrient that must be obtained from diet, but required in minute amounts Tiny amounts, but serious complications when deficient Excess can be problematic too Water-soluble excess excreted in urine (Vitamin C and B’s) Fat-soluble excess build up in fat (Vitamins A, D, E, and K) Minerals: simple inorganic nutrients needed in small amounts Many are components of various enzymes and vertebrate processes Bone growth, ATP, and hemoglobin

Grocery Shopping Vegetarians need to make sure a variety of foods eaten to ensure adequate nutritional requirements Mexican diet of corn tortillas and beans Vitamin and mineral supplements aim to guarantee RDA’s Levels are debated, at least can be wasteful, worst harmful Food label ingredients listed most to least amounts Look for high fructose corn syrup Food serving size and energy content (calories) % of nutrients related to disease

Health and Obesity Overnourishment: consuming more food energy than needed for normal metabolism Now recognized as a major global health problem In the US 30% obese, 35% overweight, can start at 15 Inheritance is 1 known factor in addition to lifestyle Leptin findings not applicable to humans Leptin is produced by adipose tissues; high levels should inhibit loss of body fat stimulate Defective leptin gene in mice = severe obesity, injection of leptin reverses Gene not in obese humans

Comparative Feeding Hydra (Phylum Cnidaria) uses tentacles to catch prey and bring it close to the entrance of the gastrovascular cavity. Annelids take food into a mouth down a short esophagus into the crop and then the gizzard. - crop: pouch-like organ where food is stored and softened. - gizzard: muscular pouch (stomach) where food is churned.

Arthropods (chelicerates and mandibulata) use a crop to store food Arthropods (chelicerates and mandibulata) use a crop to store food. The midgut contains gastric pouches whereby nutrients are absorbed. The hindgut functions as a “large intestine” whereby water is absorbed and waste products are compacted. Aves have three separate chambers for food processing. - crop, stomach and a gravel filled gizzard (grinding seed)