Transcript Chapter 21
CHAPTER 21 Nutrition & Digestion Ingestion of Food • Omnivore – ingests both plant & animals (humans) • Herbivore – ingests only plants (cattle, deer, many aquatic species) • Carnivore – ingests animals (lions, sharks, hawks, spiders) Sect 21.1 Sect 21.2 Methods of Ingestion •Suspension feeders – extract food particles suspended in water •Substrate feeders – live in or on their food source & eat their way through •Fluid feeders – suck nutrient rich fluids from their living hosts •Bulk feeders – use tentacles, claws, or jaws & teeth to kill & eat their prey Stages of Food Processing 1. Ingestion–act of eating 2. Digestion – breaking down food (polymers) into molecules (monomers) small enough for the body to absorb 3. Absorption – cells lining the digestive tract take up (absorb) small nutrient molecules 4. Elimination – undigested material passes out the digestive tract,… (a chance to get some reading done) Human Digestive Tract Oral Cavity • Saliva - buffers to protect teeth - salivary amylase – digestive enzyme that hydrolyzes starch Sect 21.5 Oral Cavity (cont.) • Teeth – cut, smash, grind solid food - incisors: bite off food - canines: tear loose a piece of food - premolars & molars: grind, crush the piece of food •Tongue – used to taste & to manipulate food while we chew – helps shape food into a ball called a bolus Sect 21.6 Pharynx • Region commonly known as the throat • An intersection that leads either to the esophagus or trachea • As we swallow, the larynx (voice box) moves upward & tips the epiglottis (flap of cartilage) over the opening of the trachea Heimlich Maneuver Sect 21.8 Esophagus • Conducts food from the pharynx down to the stomach • Peristalsis – wavelike contraction of the smooth muscles of the digestive tract that squeezes the bolus down to the stomach (sect 21.4) Sect 21.9 Stomach • Highly elastic and can stretch to accommodate about 2 L of food & liquid • Rugae are ridges or folds in lining to allow for expansion • Gastric glands - release gastric juice (breakdown of protein begins) Gastric Juice Contents • Mucus – coats & lubricates stomach lining • HCl – acid that breaks apart the food • Pepsinogen – inactive form of the enzyme pepsin - HCl converts pepsinogen into pepsin (pepsin breaks down proteins into smaller chains) Stomach (cont.) • Contraction of the muscles in stomach wall aid chemical digestion - contents of stomach are churned every 20 seconds - mixture is called acid chyme Sphincter Valves on Stomach • Cardiac sphincter is • Pyloric sphincter is at the top of the at the bottom of stomach the stomach • Prevents backflow • Regulates passage into esophagus of chyme into small intestine Stomach (cont.) • Takes about 2-6 hours to empty the stomach of a meal • Mucus coats stomach & protects it from the corrosive effects of digestive juices Stomach Ulcers • Gastric ulcers are open sores that develop on stomach wall • Some ulcers develop from too much pepsin &/or acid, or too little mucus • Some ulcers develop from bacterial infections that cause a loss of mucus & damage the stomach lining Sect 21.10 Small Intestine • Most of the chemical digestion of macromolecules in food take place • Nutrients are absorbed into the blood Sect 21.11 Pancreas Pancreas produces digestive enzymes & an alkaline solution rich in bicarbonate LIVER Liver performs wide variety of functions: -bile salts that make fat more susceptible to enzyme attack -gallbladder stores bile until it is needed Parts of the Small Intestine DUODENUM -1st 25 cm -Where acid chyme mixes w/bile and digestive enzymes -Follow along w/ Table on p. 438 Carbohydrate Enzymes • Pancreatic amylase – hydrolyzes starch into a disaccharide • Different disaccharidases – are specialized to hydrolyze different disaccharides - maltase, sucrase, lactase Protein Enzymes • Trypsin & Chymotrypsin – break polypeptides into smaller chains • Carboxypeptidase & Aminopeptidase – splits off one amino acid at a time working opposite ends of the polypeptide • Dipeptidase – hydrolyzes fragments only 2 or 3 amino acids long Nucleic Acid Enzymes Nucleases – hydrolyze nucleic acids into their component nucleotides What are nucleic acids? What is a nucleotide? Fat Enzymes • Fats are 1st coated w/bile salts to keep them separated from one another - known as emulsification • Lipase then breaks down fat droplets into fatty acids & glycerol Parts of Small Intestine (Jejunum & Ileum) Specialized in absorbing nutrients, wrinkles w/in the small intestine give it a large surface area, wrinkles are covered by small, fingerlike projections called villi - each villus has tiny surface projections called microvilli - microvilli extend into the interior of the intestine •Tiny lymph vessels extend directly into core of the villus along w/the capillaries (lymph vessels & capillaries pick up nutrients) p. 439 - known as the lacteal •Capillaries that drain nutrients away from the villi converge into larger blood vessels, which eventually lead to the liver •the liver converts many nutrients into new substances that the body needs Large Intestines - Colon -Is about 1.5 m long & 5 cm in diameter -connected to small intestine at a T-shaped junction (a sphincter valve regulates movement) Sect 21.12 •One arm of the T is a blind pouch cecum - appendix (a small fingerlike projection of the cecum) has a minor contribution to immunity - appendix is prone to infection itself •Function of the colon is to reabsorb water •if water used during digestion is not reclaimed, severe dehydration would result •wastes are called feces •feces are stored in the rectum until they can be eliminated Sect 21.15 Healthful Diet • ATP • energy content in food is measured in Kilocalories (1 kcal = 1000 calories) • BMR (basal metabolic rate) - about 1300 - 1800 cal a day - minimal numbers, any activity consumes kcal in addition to BMR •Fad diets are often ineffective & harmful •balanced diet is adequate amounts of all nutrients •Recommended Dietary Allowance (RDA) for nutrients - minimal standards Sect 21.20 Sect 21.16 Essential Nutrients • The body cannot make 9 of the 20 amino acids needed to make proteins - must be obtained from the diet and cannot be stored in excess - meat & animal by-products (eggs, milk, cheese) Undernourished- deficient calories Malnourished- missing essential nutrients Vegetarian Diet - cannot make all aa - must eat more than 1 type of plant - beans & corn together Nutrients (cont.) • Most of the required fatty acids are made from simpler molecules • some must be obtained from our diet NOT A PROBLEM!! Sect 21.18 & 21.23 Nutrients (cont.) • Vitamin - organic nutrient that is essential but required in small amounts - coenzymes (catalytic functions) - water soluble vitamins (B, C) - fat soluble vitamins (A, D, E, K) Table on p.444 Sect 21.19 Nutrients (cont.) • Minerals - chemical elements other than C, H, O, N ex: Calcium, Iron, Phosphorus, Sodium Table on p.445 •Food label provide important nutritional information about packaged foods Sect 21.21 & 21.24 •choice of diet may reduce the risk of cardiovascular disease & cancer - diets rich in saturated fats high cholesterol cardiovascular disease Cholesterol • Low-density lipoproteins - have a tendency to cause blocked blood vessels & high blood pressure (found in saturated fats) • High-density lipoproteins - may decrease the risk of vessel blockage (found in unsaturated fats)