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Chapter 3 The Human Body: From Food to
Fuel BIOL 103
Spring 2016
Today’s Topics
• Taste and Smell • GI Tract • DigesFon and AbsorpFon • AssisFng Organs • CirculaFon of Nutrients • Signaling Systems: Command, Control, and Defense – The Hormonal System – The Immune System
• Influences on DigesFon and AbsorpFon – Psychological, Chemical, Bacterial Influences
• NutriFon and GI Disorders
Taste and Smell: The Beginnings of our Food Experience
• Sight, smell, thought, taste, and sound – Can trigger a set of responses that prepare the digesFve tract to receive food
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The GastrointesFnal (GI) Tract
• OrganizaFon – Parts (mouth à anus)
• Mouth, esophagus, stomach, small intesFne, large intesFne, rectum
– Accessory organs 1. Salivary glands 2. Liver 3. Gallbladder 4. Pancreas
OrganizaFon of the GI Tract
• FuncFons: 1. IngesFon (the receipt and soXening of food) 2. Transport of ingested food 3. SecreFon of digesFve enzymes, acid, mucus,
and bile 4. AbsorpFon of end products of digesFon 5. Movement of undigested material 6. EliminaFon of waste material
OrganizaFon of the GI Tract
• Structural organizaFon of the GI tract: – Mucosa (innermost layer) • Glands and absorpFve 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 direcFon.
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Overview of DigesFon
• Mouth – Chewing à break food into smaller pieces – Saliva à lubricates the food à bolus
• Down the GI tract: – Physical movement • Peristalsis: push food down • Segmenta5on: move food forward and backward
Overview of Diges5on Which one is peristalsis? How about segmentaFon?
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DigesFve Enzymes in Chemical ReacFons Overview of DigesFon
• Chemical breakdown: (Bolus à Chyme) • Enzymes: proteins that catalyze (speed up) reacFons but are not altered in the process. – Examples: amylase, lipase, etc.
• Other secreFons: – Stomach Acid – Base – Bile – Mucus
Overview of AbsorpFon AssisFng Organs
1. Salivary glands – Moisten food – Supply enzymes
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AssisFng Organs
2. Liver – Produces bile – “Detox center” – “Chemical factory”: >500 chemicals as well as blood proteins, cholesterol, sugar
– “Dynamic warehouse”: stores hormones, cholesterol, minerals, sugar, etc.
AssisFng/Accessory Organs
3. Gallbladder – Stores and excretes bile
4. Pancreas – Secretes bicarbonate, digesFve enzymes – Secretes hormones (insulin and glucagon)
Puang it All Together: DigesFon and AbsorpFon
• Mouth – Enzymes • Salivary amylase acts on starch • Lingual lipase acts on fat
– Saliva • Moistens food for swallowing à bolus
Puang it All Together: DigesFon and AbsorpFon
• Esophagus – Transports food to stomach – Esophageal sphincter or cardiac sphincter • “Heartburn”
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Puang It All Together: DigesFon and AbsorpFon
• Stomach Enzymes: – Food in stomach triggers gastrin (hormone) sFmulates gastric secreFon of HCl and pepsinogen and movement
– Hydrochloric acid (HCl)/gastric acid 1. kills bacteria 2. prepares protein for digesFon – Pepsinogen (inacFve) à Pepsin (acFve)
– Pepsin: breaks down protein into smaller pieces – Gastric lipase: some fat digesFon – Intrinsic factor: binds to vitamin B12 to survive the journey through the acidic stomach
Puang It All Together: DigesFon and AbsorpFon
• Small intesFne (~10X) – Pyloric Sphincter – SecFons of small intesFne: • Duodenum • Jejunum • Ileum
– Main role: chemical digesFon and absorpFon
Puang It All Together: DigesFon and AbsorpFon
• Nutrient digesFon: – Acidic chyme in duodenum sFmulates release of two hormones by intesFnal mucosa: 1. Secre5n: – Goes to pancreas to release release bicarbonate – Goes to stomach to inhibit release of HCl, pepsinogen, and stomach moFlity
2. CCK (cholescystokinin): – Release pancreaFc enzymes (e.g. lipase) – Contract the gallbladder to release bile – Goes to stomach to reduce moFlity
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Puang It All Together: DigesFon and AbsorpFon
• Small intesFne – Completes absorpFon: • Folds, villi, microvilli expand absorpFve surface • Most nutrients absorbed here • Fat-‐soluble nutrients à lymphaFc system (lympha5c vessel in the intes5nal villus known as lacteals) • Water-‐soluble nutrients à bloodstream.
Puang It All Together: DigesFon and AbsorpFon
• Large IntesFne – Ileocecal valve – SecFons
• Cecum, colon, rectum, and anal canal
– DigesFon • PeristalFc movement is slow, taking 18-‐24 hours for material to travel
• Some bacterial acFvity (e.g. fiber digesFon)
Beans, Beans, Beans!
• Beans are made up of oligosaccharides (e.g. raffinose and stachyose), a component of fiber.
• They are ignored unFl they are met by 700+ species of bacteria in your large intesFne. – Bacteria digests these sugars à gases accumulate à flatulence
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Puang it All Together: DigesFon and AbsorpFon
• Large IntesFne: – AbsorpFon • Water • Na, K, Cl • Vitamin K (produced by bacteria)
– EliminaFon at anal sphincter • Feces: 60% solid (bacteria, dietary fiber, digesFve secreFons), 40% water
CirculaFon of Nutrients
• Vascular system – Veins and arteries – Carries oxygen and water-‐soluble nutrients to Fssues – Removes wastes
• LymphaFc system – Vessels that drain lymph – Carries fat-‐soluble nutrients – EmpFes into the bloodstream near the neck
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CirculaFon of Nutrients
• ExcreFon and eliminaFon – Once desFnaFon cells have used up the oxygen and nutrients, carbon dioxide and waste products are picked up by blood and transported to: 1. Lungs – Excrete water and carbon dioxide
2. Kidneys filter blood – Excrete waste; maintain water and ion balance
Summary of Diges5on and Absorp5on of Nutrients in the Human Body Review!!!
Signaling Systems: Command, Control, and Defense
• Nervous system – Regulates GI acFvity • Enteric nervous system: nerves located in the gut wall – “the brain”
• Autonomic nervous system: part of central nervous system that controls organ funcFon – Responses to sight, smell, thought of food by enhancing GI movement and secreFon – Parasympathe5c: “rest and digest”
Signaling Systems: Hormonal System
• Hormonal system – Hormones: chemical messengers from Fssues that travel in the bloodstream to target Fssue to cause an effect
1. Increases or decreases GI moFlity and secreFons 2. Influence your appeFte by sending messages to
your CNS
• Thus, your CNS and hormones work together to coordinate movement and secreFons of the GI tract.
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Influences on DigesFon and AbsorpFon
• Psychological influences – Taste, smell, and presentaFon of food
• Chemical influences – Type of protein you eat and the way it is prepared
• Bacterial influences – Hydrochloric acid kills most bacteria
NutriFon and GI Disorders
• Cons5pa5on (< 3x/week) – Hard, dry, infrequent stools – Reduced by high fiber, fluid intake, and exercise
• Diarrhea (> 3x/day) – Loose, watery, frequent stools – Symptom of diseases/infecFons à peristalsis – Can cause dehydraFon – Broth, tea, toast, and other low-‐fiber foods can help reduce diarrhea
NutriFon and GI Disorders • Diver5culosis – Pouches along colon develop as people age • 10-‐25% people à pouches become infected
– High-‐fiber diet reduces formaFon: • Low-‐fiber diet à harder stools à more pressure on colon à weak spots bulge outwards and form pockets
NutriFon and GI Disorders
• Heartburn/GERD – Chronic heartburn à GERD
– Reduced by smaller meals, less fat
– Smoking weakens the esophageal sphincter
– Being overweight oXen worsens symptoms
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NutriFon and GI Disorders
• Irritable Bowel Movement (IBS): disrupFve state of intesFnal moFlity with no known cause – Causes abdominal pain, diarrhea, or consFpaFon and cramps – Stress and certain foods aggravate the symptoms – Can usually be controlled by diet and lifestyle modificaFons • Stress management
NutriFon and GI Disorders
• Colorectal cancer: cancer in colon or rectum – Fiber-‐rich diet may reduce risk – 3rd leading cause of cancer-‐related deaths in the US – EaFng a lot of red meat and low fiber food can increase risks
• Gas – Most foods that contain carbohydrates can cause
NutriFon and GI Disorders
• Ulcers – Pain in the upper abdomen – Can cause nausea, vomiFng, loss of appeFte, and weight loss – Cause: Bacteria (H. pylori) and over-‐usage of NSAIDS (aspirin, ibuprofen)
NutriFon and GI Disorders
• Func5onal Dyspepsia: – Chronic pain in the upper abdomen not due to any obvious physical cause (such as inflammaFon of the esophagus, pepFc ulcer, or gallstones) – Treat with medicine and stress reducFon
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