Chapter 41

Chapter 41 – Class Notes

Concept 41.1: Animal Diet Requirements

Animals Need 3 Things From Food

1. Chemical energy → Used to make ATP through cellular respiration.

2. Organic building blocks → Used to build proteins, nucleic acids, lipids, etc.

3. Essential nutrients → Nutrients the body cannot make and must obtain from food.

Essential Nutrients

• Essential amino acids → Humans need 8 (infants need 9, including histidine).

• Essential fatty acids → Used for membranes and signaling molecules.

• Vitamins

• Water-soluble: B vitamins, Vitamin C

• Fat-soluble: Vitamins A, D, E, K

• Minerals

• Iron → Hemoglobin

• Calcium → Bones

• Sodium & Potassium → Nerve and muscle function

Types of Diets

• Herbivores → Eat plants/algae.

• Carnivores → Eat animals.

• Omnivores → Eat both.

Many animals are opportunistic feeders and eat different foods if their normal food is unavailable.

Malnutrition

Occurs when the diet lacks enough nutrients or energy.

Examples:

• Protein deficiency → Poor growth and development.

• Vitamin deficiencies → Diseases and deformities.

• Undernourishment → Body burns stored fat first, then muscle proteins.

Folic Acid

• Vitamin B9

• Prevents neural tube defects during fetal development.

• Added to enriched grains in the U.S. since 1998.

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Concept 41.2: Food Processing

Four Stages of Food Processing

1. Ingestion → Taking food in.

2. Digestion → Breaking food into smaller molecules.

3. Absorption → Nutrients enter blood or lymph.

4. Elimination → Undigested waste leaves body.

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Feeding Mechanisms

• Filter feeding → Strains food from water (whales).

• Substrate feeding → Lives in food source (caterpillars).

• Fluid feeding → Sucks fluids (mosquitoes).

• Bulk feeding → Eats large pieces of food (humans).

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Types of Digestion

Mechanical Digestion

Physically breaks food into smaller pieces.

Examples:

• Chewing

• Grinding

• Churning

Chemical Digestion

Digestive enzymes perform hydrolysis to break:

• Carbs → Monosaccharides

• Proteins → Amino acids

• Lipids → Fatty acids + glycerol

• Nucleic acids → Nucleotides

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Digestive Systems

Intracellular Digestion

• Digestion inside food vacuoles.

• Seen in sponges.

Gastrovascular Cavity

• One opening acts as both mouth and anus.

• Seen in Hydra.

Alimentary Canal

• Complete digestive tract with mouth and anus.

• Allows one-way movement of food.

• Different organs specialize in different jobs.

Examples:

• Earthworms

• Birds

• Mammals

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Concept 41.3: Mammalian Digestive System

Accessory Organs

• Salivary glands

• Pancreas

• Liver

• Gallbladder

These release digestive secretions into the alimentary canal.

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Mouth

Functions:

• Mechanical digestion by teeth.

• Saliva moistens food.

• Salivary amylase begins starch digestion.

• Tongue forms a bolus for swallowing.

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Pharynx & Esophagus

• Swallowing prevents food from entering trachea.

• Food moves by peristalsis.

• Lower esophageal sphincter controls entry into stomach.

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Stomach

Functions:

• Stores food.

• Begins protein digestion.

• Produces chyme.

Gastric Juice Contains:

• HCl

• pH ≈ 2

• Denatures proteins.

• Kills bacteria.

• Pepsin

• Digests proteins.

• Mucus

• Protects stomach lining.

Cells

• Parietal cells → HCl

• Chief cells → Pepsinogen

• HCl converts pepsinogen → pepsin.

Food usually stays in the stomach 2–6 hours.

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Small Intestine

Longest digestive organ (~6 m).

Sections:

• Duodenum

• Jejunum

• Ileum

Most digestion and almost all nutrient absorption occur here.

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Digestion of Carbohydrates

• Mouth → Salivary amylase

• Small intestine → Pancreatic amylase

• Brush border enzymes → Monosaccharides

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Digestion of Proteins

• Stomach → Pepsin

• Pancreas → Trypsin & chymotrypsin

• Brush border enzymes → Amino acids

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Digestion of Nucleic Acids

Pancreatic nucleases digest DNA/RNA into nucleotides, which are further broken into:

• Sugars

• Bases

• Phosphates

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Fat Digestion

Bile (made by liver, stored in gallbladder):

• Emulsifies fats.

Pancreatic lipase

• Breaks triglycerides into fatty acids and monoglycerides.

Inside intestinal cells:

• Reassembled into triglycerides.

• Packaged into chylomicrons.

• Enter lacteals → lymph → bloodstream.

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Pancreas Functions

Produces:

• Digestive enzymes.

• Bicarbonate (HCO₃⁻) to neutralize acidic chyme.

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Hormones

Secretin

• Stimulates bicarbonate release.

CCK

• Stimulates pancreatic enzymes.

• Causes gallbladder contraction.

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Absorption

Villi and microvilli greatly increase surface area.

Absorption routes:

• Sugars & amino acids → Blood → Hepatic portal vein → Liver.

• Fats → Lacteals → Lymph → Blood.

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Large Intestine

Functions:

• Absorbs water.

• Compacts feces.

• Houses beneficial bacteria.

Structures:

• Cecum

• Colon

• Rectum

• Anus

Disorders

• Diarrhea → Too little water absorbed.

• Constipation → Too much water absorbed.

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Concept 41.4: Evolutionary Adaptations

Dentition

Teeth match diet.

Carnivores

• Sharp incisors

• Large canines

• Cutting molars

Herbivores

• Broad grinding molars

• Flat premolars

Omnivores

Humans have:

• Incisors

• Canines

• Premolars

• Molars

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Digestive Tract Adaptations

Carnivores:

• Short intestines.

• Expandable stomachs.

Herbivores:

• Long intestines.

• Large cecum or fermentation chambers.

Reason:

Plants contain cellulose, which is difficult to digest.

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Mutualistic Microbes

Gut bacteria:

• Produce Vitamin K, folate, and biotin.

• Help digest food.

• Support immune system.

• Form the microbiome.

Herbivores rely heavily on bacteria and protists to digest cellulose.

Examples:

• Cows → Rumen.

• Horses → Cecum.

• Rabbits → Practice coprophagy to recover nutrients.

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Concept 41.5: Regulation of Digestion, Energy, and Appetite

Hormones Controlling Digestion

Gastrin

• Released by stomach.

• Stimulates gastric juice.

Secretin

• Stimulates bicarbonate release.

CCK

• Stimulates pancreatic enzymes and bile release.

• Slows stomach emptying when fats are present.

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Energy Storage

Extra glucose is stored as:

• Glycogen (liver & muscles)

• Fat (triglycerides) in adipose tissue

Fat stores far more energy than glycogen.

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Blood Glucose Regulation

Insulin

Released by beta cells.

Functions:

• Lowers blood glucose.

• Increases glucose uptake.

• Promotes glycogen formation.

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Glucagon

Released by alpha cells.

Functions:

• Raises blood glucose.

• Breaks down glycogen.

• Releases glucose from liver.

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Diabetes Mellitus

Type 1

• Autoimmune destruction of beta cells.

• Little/no insulin.

• Requires insulin injections.

Type 2

• Insulin resistance.

• Strongly linked to obesity and inactivity.

• Makes up 90%+ of cases.

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Appetite Regulation

Ghrelin

• From stomach.

• Increases hunger before meals.

Leptin

• From fat tissue.

• Decreases appetite.

• Falls during dieting, making people hungrier.

Insulin

• Suppresses appetite after eating.

PYY

• Released from small intestine after meals.

• Reduces appetite.

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Chapter 41 Big Picture

• Animals need energy, building blocks, and essential nutrients.

• Food processing occurs in 4 stages: ingestion → digestion → absorption → elimination.

• The mouth, stomach, small intestine, and large intestine each have specialized digestive roles.

• Most digestion and nutrient absorption occur in the small intestine.

• Herbivores have longer digestive tracts and depend on mutualistic microbes to digest cellulose.

• Digestion is regulated by gastrin, secretin, and CCK.

• Blood glucose is maintained by insulin and glucagon.

• Appetite is regulated mainly by ghrelin, leptin, insulin, and PYY.