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Chapter 3 The Human Body: From Food to

Fuel BIOL 103

Today’s Topics

•  Taste and Smell •  GI Tract •  DigesDon and AbsorpDon •  AssisDng Organs •  CirculaDon of Nutrients •  Signaling Systems: Command, Control, and Defense –  The Hormonal System –  The Immune System

•  Influences on DigesDon and AbsorpDon –  Psychological, Chemical, Bacterial Influences

•  NutriDon 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 digesDve tract to receive food

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The GastrointesDnal (GI) Tract

•  OrganizaDon –  Parts (mouth à anus)

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

–  Accessory organs 1.  Salivary glands 2.  Liver 3.  Gallbladder 4.  Pancreas

OrganizaDon of the GI Tract

•  FuncDons: 1.  IngesDon (the receipt and soWening of food) 2.  Transport of ingested food 3.  SecreDon of digesDve enzymes, acid, mucus,

and bile 4.  AbsorpDon of end products of digesDon 5.  Movement of undigested material 6.  EliminaDon of waste material

OrganizaDon of the GI Tract

•  Structural organizaDon of the GI tract: – Mucosa (innermost layer) • Glands and absorpDve 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 direcDon.

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Overview of DigesDon

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

•  Down the GI tract: – Physical movement • _____________________: push food down • _____________________: move food forward and backward

Overview of Diges4on Which one is peristalsis? How about segmentaDon?

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DigesDve Enzymes in Chemical ReacDons Overview of DigesDon

•  Chemical breakdown: (Bolus à _____________) •  Enzymes: proteins that catalyze (speed up) reacDons but are not altered in the process. –  Examples: amylase, lipase, etc.

•  Other secreDons: –  Stomach Acid –  Base –  Bile – Mucus

Overview of AbsorpDon AssisDng Organs

1.   Salivary glands – Moisten food – Supply enzymes

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AssisDng 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.

AssisDng/Accessory Organs

3.   Gallbladder – Stores and excretes bile

4.   Pancreas – Secretes __________________, digesDve enzymes – Secretes hormones (_________ and _________________)

Puang it All Together: DigesDon and AbsorpDon

•  Mouth – Enzymes • _______________acts on starch • ______________________acts on fat

– Saliva • Moistens food for swallowing à bolus


•  Esophagus – Transports food to stomach – Esophageal sphincter or cardiac sphincter •  “Heartburn”

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Puang It All Together: DigesDon and AbsorpDon

•  Stomach Enzymes: –  Food in stomach triggers gastrin (hormone) sDmulates gastric secreDon of HCl and pepsinogen and movement

– Hydrochloric acid (HCl)/gastric acid 1.  kills bacteria 2.  prepares protein for digesDon – Pepsinogen (inacDve) à Pepsin (acDve)

–  _________: breaks down protein into smaller pieces –  _____________________: some fat digesDon –  Intrinsic factor: binds to vitamin B12 to survive the journey through the acidic stomach


•  Small intesDne (~10W) –  Pyloric Sphincter –  SecDons of small intesDne: •  Duodenum •  Jejunum •  Ileum

– Main role: chemical digesDon and absorpDon


•  Nutrient digesDon: – Acidic chyme in duodenum sDmulates release of two hormones by intesDnal mucosa: 1.   Secre4n: – Goes to pancreas to release release bicarbonate – Goes to stomach to inhibit release of HCl, pepsinogen, and stomach moDlity

2.   CCK (cholescystokinin): – Release pancreaDc enzymes (e.g. lipase) – Contract the gallbladder to release bile – Goes to stomach to reduce moDlity

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•  Small intesDne –  Completes absorpDon: •  Folds, villi, microvilli expand absorpDve surface • Most nutrients absorbed here •  Fat-‐soluble nutrients à lymphaDc system (lympha4c vessel in the intes4nal villus known as lacteals) • Water-‐soluble nutrients à bloodstream.


•  Large IntesDne –  Ileocecal valve –  SecDons

•  Cecum, colon, rectum, and anal canal

–  DigesDon •  PeristalDc movement is slow, taking 18-‐24 hours for material to travel

•  Some bacterial acDvity (e.g. fiber digesDon)

Beans, Beans, Beans!

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

•  They are ignored unDl they are met by 700+ species of bacteria in your large intesDne. – Bacteria digests these sugars à gases accumulate à flatulence

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•  Large IntesDne: –  AbsorpDon • Water •  Na, K, Cl •  Vitamin K (produced by bacteria)

–  EliminaDon at anal sphincter •  Feces: 60% solid (bacteria, dietary fiber, digesDve secreDons), 40% water

CirculaDon of Nutrients

•  Vascular system – Veins and arteries – Carries oxygen and water-‐soluble nutrients to Dssues – Removes wastes

•  LymphaDc system – Vessels that drain lymph – Carries fat-‐soluble nutrients – EmpDes into the bloodstream near the neck

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CirculaDon of Nutrients

•  ExcreDon and eliminaDon – Once desDnaDon 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 Diges4on and Absorp4on of Nutrients in the Human Body Review!!!

Signaling Systems: Command, Control, and Defense

•  Nervous system – Regulates GI acDvity •  Enteric nervous system: nerves located in the gut wall – “the brain”

• Autonomic nervous system: part of central nervous system that controls organ funcDon – Responses to sight, smell, thought of food by enhancing GI movement and secreDon – Parasympathe4c: “rest and digest”

Signaling Systems: Hormonal System

•  Hormonal system – Hormones: chemical messengers from Dssues that travel in the bloodstream to target Dssue to cause an effect

1.  Increases or decreases GI moDlity and secreDons 2.  Influence your appeDte by sending messages to

your CNS

•  Thus, your CNS and hormones work together to coordinate movement and secreDons of the GI tract.

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Influences on DigesDon and AbsorpDon

•  Psychological influences – Taste, smell, and presentaDon of food

•  Chemical influences – Type of protein you eat and the way it is prepared

•  Bacterial influences – Hydrochloric acid kills most bacteria

NutriDon and GI Disorders

•  Cons4pa4on (< 3x/week) – Hard, dry, infrequent stools – Reduced by high fiber, fluid intake, and exercise

•  Diarrhea (> 3x/day) – Loose, watery, frequent stools – Symptom of diseases/infecDons à peristalsis – Can cause dehydraDon – Broth, tea, toast, and other low-‐fiber foods can help reduce diarrhea

NutriDon and GI Disorders •  Diver4culosis –  Pouches along colon develop as people age •  10-‐25% people à pouches become infected

–  High-‐fiber diet reduces formaDon: •  Low-‐fiber diet à harder stools à more pressure on colon à weak spots bulge outwards and form pockets


•  Heartburn/GERD –  Chronic heartburn à GERD

–  Reduced by smaller meals, less fat

–  Smoking weakens the esophageal sphincter

–  Being overweight oWen worsens symptoms

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•  Irritable Bowel Movement (IBS): disrupDve state of intesDnal moDlity with no known cause – Causes abdominal pain, diarrhea, or consDpaDon and cramps – Stress and certain foods aggravate the symptoms – Can usually be controlled by diet and lifestyle modificaDons • Stress management


•  Colorectal cancer: cancer in colon or rectum – Fiber-‐rich diet may reduce risk – ____ leading cause of cancer-‐related deaths in the US – EaDng a lot of red meat and low fiber food can increase risks

•  Gas – Most foods that contain carbohydrates can cause


•  Ulcers – Pain in the upper abdomen – Can cause nausea, vomiDng, loss of appeDte, and weight loss – Cause: Bacteria (H. pylori) and over-‐usage of NSAIDS (aspirin, ibuprofen)


•  Func4onal Dyspepsia: – Chronic pain in the upper abdomen not due to any obvious physical cause (such as inflammaDon of the esophagus, pepDc ulcer, or gallstones) – Treat with medicine and stress reducDon

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