The Human Body: From Food to Fuel BIOL 103, Chapter 4.

The Human Body: From Food to Fuel

BIOL 103, Chapter 4

Today’s Topics• Taste and Smell• GI Tract• Digestion and Absorption• Assisting Organs• Circulation of Nutrients• Signaling Systems: Command, Control, and Defense– The Hormonal System– The Immune System

• Influences on Digestion and Absorption– Psychological, Chemical, Bacterial Influences

• Nutrition and GI Disorders

Taste and Smell: The Beginningsof our Food Experience

• Sight, smell, thought, taste, and sound– Can trigger a set of responses that prepare the

digestive tract to receive food

The Gastrointestinal (GI) Tract

• Organization– Parts (mouth anus)

• Mouth, esophagus, stomach, small intestine, large intestine, rectum

– Accessory organs• Salivary glands, liver,

gallbladder, and pancreas

Organization of the GI Tract

• Functions:1. Ingestion (the receipt and softening of food)2. Transport of ingested food3. Secretion of digestive enzymes, acid, mucus, and

bile4. Absorption of end products of digestion5. Movement of undigested material6. Elimination of waste material

Organization of the GI Tract

• Structural organization of the GI tract– Mucosa (innermost layer)

• Glands and absorptive cells

– Circular muscle and longitudinal muscle• Mix and move the food

– Sphincter: valve that controls the movement of food material so that it travels through the GI tract in only one direction.

Overview of Digestion

• Mouth– Chewing break food into smaller pieces – Saliva lubricates the food bolus

• Down the GI tract:– Physical movement• Peristalsis: waves of muscular contraction that helps

push food down the GI tract• Segmentation: a periodic muscle contractions in the

small intestine that move the content forward and backward.


• Chemical breakdown: – Bolus Chyme – Enzymes: are proteins that catalyze (speed up)

reactions but are not altered in the process.• Examples: amylase, lipase, etc.

– Other secretions: – Stomach Acid – Base – Bile – Mucus

Overview of Absorption

• 3 Main processes allow nutrients to be absorbed from GI tract blood/circulation– Passive Diffusion: movement of molecules through

cell membrane from high to low concentration gradient without energy use

– Facilitated Diffusion: movement of molecules through cell membrane from high to low concentration gradient with a help of a transport protein

– Active Transport: movement of molecules through cell membrane requiring both energy (ATP) and protein.

Overview of Absorption

Assisting/Accessory Organs1. Salivary glands

– Moisten food– Supply enzymes

2. Liver– Produce bile (fat emulsifier)– “Detox center:” filters toxins in blood kidney– “Chemical factory”: >500 chemicals

• Produce blood proteins, cholesterol, sugar– “Dynamic Warehouse”: stores hormones, cholesterol, minerals, sugar,

etc.3. Gallbladder

– Stores and excretes bile– Bile’s Enterohepatic circulation:

1. Liver Gallbladder Intestine Liver• Pancreas

1. Secretes bicarbonate, digestive enzymes2. Secretes hormones (insulin and glucagon)

Putting It All Together: Digestion and Absorption

• Mouth– Enzymes

• Salivary amylase • Lingual lipase

– Saliva• Moistens food for swallowing bolus

• Esophagus– Transports food to stomach– Esophageal sphincter (“cardiac sphincter”)

• “Heartburn”

Putting It All Together:Digestion and Absorption

• Stomach Enzymes:– Hydrochloric acid/gastric acid

1. kills bacteria2. prepares protein for digestion

1. breaks down 3D structure of protein2. Pepsinogen (inactive) Pepsin (active)

– Pepsin: breaks down protein into smaller pieces– Gastric lipase: some fat digestion– Gastrin (hormone) stimulates gastric secretion and

movement– Intrinsic factor is needed for vitamin B12 absorption.


• Small intestine (~10ft)– Pyloric Sphincter– Sections of small

intestine:• Duodenum • Jejunum• Ileum

– Nutrient digestion• Bicarbonate neutralizes

stomach acid• Pancreatic and intestinal

enzymes to digest carbohydrates, lipids, and proteins.


• Small intestine– Completes absorption:

• Folds, villi, microvilli expand absorptive surface– 600x fold increase/tennis court!

• Most nutrients absorbed here• Fat-soluble nutrients lymphatic

system (lymphatic vessel in the intestinal villus)

• Water-soluble nutrients bloodstream.


• Large Intestine– Ileocecal valve– Sections

• Cecum, colon, rectum, and anal canal

– Digestion• Peristaltic movement is

slow, taking 18-24 hours for material to travel

• Some bacterial activity (e.g. fiber digestion)

Beans, Beans, Beans!

• Beans are made up of oligosaccharides (e.g. raffinose and stachyose), a component of fiber.

• They are ignored until they are met by 700+ species of bacteria in your large intestine.– Bacteria digests these sugars gases accumulate

flatulence


• Large Intestine:– Absorption

• Water• Na, K, Cl• Vitamin K (produced by

bacteria)

– Elimination at anal sphincter• Feces: 60% solid (bacteria,

dietary fiber, digestive secretions), 40% water

Circulation of Nutrients

Vascular System• Veins and arteries• Water soluble nutrients are

absorbed into the capillaries of the intestines.

• Blood carries nutrients through portal vein to the liver before dispensing them through the body.

Lymphatic system• Vessels that drain lymph

(clear fluid formed in the spaces between cells)

• Fat soluble-vitamins are absorbed into lymph vessels in the intestine.

• Bypasses liver and delivers nutrients to veins in the neck enter blood


• Excretion and Elimination– Lungs• Excrete water and carbon dioxide (metabolic wastes)

– Kidneys filter blood• Excrete digestive wastes

– Urine: urea + salts + water

• Maintain water and ion balance

Summary of Digestion and Absorption of Nutrients in the Human Body

Signaling Systems:Command, Control, Defense

• Nervous system– Nerves carry info back and forth between tissues

and the brain using chemical signals known as neurotransmitters.

– The Central Nervous System (CNS) regulates GI activity in 2 ways:

1. Enteric nervous system: nerves located in the GI wall.2. Autonomic nervous system: part of CNS that controls

organ function.– Responses to sight, smell, thought of food by enhancing GI

movement and secretion


• Hormonal system– Hormones: chemical messengers that travel in the

bloodstream1.Increases or decreases GI motility and secretions2.Influence your appetite by sending messages to

your CNS.• Thus, your CNS and hormones work together

to coordinate movement and secretions of the GI tract.


• Immune System– Purpose: protects us from foreign invaders– Role of GI tract

• Immune Response– Macrophages: “big eaters” engulf and kill pathogens and old-

cells– Natural killer cells: attack virus-infected cells or cancerous cells

• Location of lymphoid tissues– Lymphocytes: white blood cells present in blood and lymph

» Some types produce antibodies – protein molecules that tag, neutralize, and help destroy bacteria/viruses or toxins.

Influences on Digestion and Absorption

• Psychological influences– Positive: Taste, smell, presentation of food– Negative: Stress, fear, depression

• Example: Stress activate autonomic NS reduced gastric secretion, reduced blood flow to stomach, inhibition of peristalsis upset stomach

• Chemical influences– Cooking protein changes + produce chemicals that may

influence digestion easier food digestion/absorption processes

• Bacterial influences– HCl acid kills most bacteria

• If lives food borne illnesses, gastritis, ulcer, etc.

Nutrition and GI Disorders

• Constipation (< 3x/week)– Hard, dry, infrequent stools– Reduced by high fiber, fluid intake, and exercise

• Diarrhea (> 3x/day)– Loose, watery, frequent stools– Symptom of diseases/infections peristalsis– Can cause dehydration– Broth, tea, toast, and other low-fiber foods can

help reduce diarrhea

Nutrition and GI Disorders• Diverticulosis

– Pouches along colon develop as people age • 10-25% people pouches become infected

– High-fiber diet reduces formation: • Low-fiber diet harder stools more

pressure on colon weak spots bulge outwards and form pockets

• Heartburn and GERD– Chronic heartburn GERD– Reduced by smaller meals, less fat– Smoking weakens the esophageal

sphincter– Being overweight often worsens symptoms


• Irritable Bowel Movement (IBS)– Causes abdominal pain, diarrhea, or constipation

and cramps– Stress and certain foods aggravate the symptoms• Examples: milk, beans, chocolate, alcohol

– Associated with reproductive hormones– Can usually be controlled by diet and lifestyle

modifications• Stress management


• Colorectal cancer: cancer in colon or rectum– 3rd leading cause of cancer-related deaths in the

US– Eating a lot of red meat and low fiber food can

increase risks– Fiber-rich diet may reduce risk:• Hypothesis: more fiber goes down the GI tract

faster, dilution of carcinogens in a bulkier stool, etc…• BUT, human/animal studies do not support those

theories.

Nutrition and GI Disorders• Ulcers– Pain in the upper abdomen

• Sore is in duodenum: duodenal ulcer• Sore is in stomach: gastric ulcer

– Can cause nausea, vomiting, loss of appetite, and weight loss

– Cause: Bacteria (H. pylori) and over-usage of NSAIDS (aspirin, ibuprofen)

• Functional dyspepsia– Chronic pain in the upper abdomen with no obvious

physical cause– Treat with medicine and stress reduction

Summary

The Human Body: From Food to Fuel BIOL 103, Chapter 4.

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Transcript of The Human Body: From Food to Fuel BIOL 103, Chapter 4.