CHAPTER 21 Nutrition & Digestion Ingestion of Food Omnivore – ingests both plant & animals (humans) Herbivore – ingests only plants (cattle, deer, many.

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

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

Sect 21.2

Stages of Food Processing1. Ingestion–act of eating2. 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

•Saliva- buffers to protect teeth- salivary amylase – digestive enzyme that hydrolyzes starch

Oral Cavity

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

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

Sect 21.6

Heimlich Maneuver

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 21.8

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)

Sect 21.9

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 at the top of the stomach

• Prevents backflow into esophagus

• Pyloric sphincter is at the bottom of the stomach

• Regulates passage 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 producesdigestive enzymes & an alkaline solution rich in bicarbonate

Liver performs wide variety of functions:-bile salts that make fat moresusceptible to enzyme attack-gallbladder stores bile untilit is needed

LIVER

DUODENUM-1st 25 cm-Where acid chyme mixes w/bile and digestive enzymes-Follow along w/ Table on p. 438

Parts of the Small Intestine

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

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

Parts of Small Intestine (Jejunum & Ileum)

- 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)

- known as the lacteal

p. 439

•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

-Is about 1.5 m long & 5 cm in diameter-connected to small intestine at a T-shaped junction (a sphincter valve regulates movement)

Large Intestines - Colon

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

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

Sect 21.15

•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

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)

Sect 21.16

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!!

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)

Sect 21.18 & 21.23

Table on p.444

Nutrients (cont.)

•Minerals - chemical elements other than C, H, O, N

ex: Calcium, Iron, Phosphorus, Sodium

Table on p.445

Sect 21.19

•Food label provide important nutritional information about packaged foods

•choice of diet may reduce the risk of cardiovascular disease & cancer

- diets rich in saturated fats high cholesterol cardiovascular disease

Sect 21.21 & 21.24

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)