Chapter 2 Power Point

© 2016 Pearson Education, Inc.

Chapter 2 Lecture

Chapter 2:The Human Body:

Are We ReallyWhat We Eat?

Learning Outcomes

1. Compare and contrast the feelings of hunger and appetite, and the factors contributing to each.

2. Identify the relationship between the foods we eat and the structures and functions of our cells.

3. Name and state the function of each of the major organs of the gastrointestinal tract and the four accessory organs.


Learning Outcomes

4. Explain how the food you eat is broken down mechanically and chemically.

5. Identify the unique features of the small intestine that contribute to its ability to absorb nutrients.

6. Describe how the body eliminates food wastes.


Learning Outcomes

7. Discuss the causes, symptoms, and treatment of gastroesophageal reflux disease and peptic ulcers.

8. Distinguish between food intolerance and food allergy, and between celiac disease and non-celiac gluten sensitivity.

9. Compare and contrast diarrhea, constipation, and irritable bowel syndrome.


Why Do We Want to Eat What We Want to Eat?• Appetite: psychological desire to eat specific

foods• Some cravings, even when we're not hungry,

are due to appetite.• Hunger: physiological drive that prompts us to

eat nonspecific foods• Anorexia is a lack of appetite despite the

physical need for food.


Why Do We Want to Eat What We Want to Eat?• Signals that prompt us to eat:

• Hunger is detected by the hypothalamus–a region of the brain.

• Stomach cells sense emptiness or fullness.• Blood glucose levels trigger the release of

certain hormones.• The hypothalamus receives these hormone

signals to tell us if we are hungry.


Why Do We Want to Eat What We Want to Eat?


Why Do We Want to Eat What We Want to Eat?• Nerve Cells: particularly the ones lining the

stomach and small intestine that detect changes in internal pressure when the organ is empty or filled with food. These nerve cells relay that information to the brain's hypothalamus and contributes to sensations of hunger.


Why Do We Want to Eat What We Want to Eat?• Hormones: chemicals introduced by specialized

glands that enter the bloodstream and target organs in other parts of the body

• Some hormones, such as insulin and glucagon, stimulate food intake.

• Rising levels of glucose and responses from nerve cells produce feelings of satiety.


Why Do We Want to Eat What We Want to Eat?• Role of the amount and type of food

• Protein• Higher satiety (feeling of fullness) value

• Bulkiness• Amount of fiber and water within the food

• Solid food versus liquid food• Beverages tend to be less satisfying than solids


Environmental Cues Trigger Appetite

• Sensory data• Social cues• Cultural cues• Learned preferences


Environmental Cues Trigger Appetite


Are We Really What We Eat?

• Atoms: the smallest units of matter• Atoms bond to each other to form molecules.• Molecules: groups of atoms bonded in specific

configurations

• Example: water is H2O



• Molecules are the building blocks of cells.• Chemical reactions that join atoms and

molecules and break compounds apart are called metabolism.

• Cells: the smallest unit of life• Molecules that result from the digestion of food

are used to build the cells of the body.



• Cells join together to form tissues.• Tissue: group of cells acting together to perform

a common function• Examples: muscle tissue, nerve tissue

• Different tissues combine to form organs.



• Cell membrane: outer layer enclosing each cell of the body

• The cell membrane defines the cell's boundaries and acts as a gatekeeper.





• The cell membrane is semipermeable, allowing it to control the passage of materials into and out of the cell.

• The cell membrane encloses:• Cytoplasm, the liquid within the cell;

• Mitochondria and nucleus


What Happens to the Food We Eat?




Clink on the Digestion Absorption link separate from the power point.


• The food we eat undergoes three processes:• Digestion• Absorption• Elimination

• These processes occur primarily in the gastrointestinal (GI) tract.



• Digestion: the process of breaking large food molecules down into smaller molecules

• Digestion includes breaking food down:• Mechanically• Physically



• Digestion begins in the mouth.• Chewing is the mechanical digestion that

breaks food into smaller pieces.• Some chemical digestion takes place.

• Saliva contains amylase, an enzyme produced by the salivary glands.

• Salivary amylase begins the chemical digestion of carbohydrates.





• GI tract: series of organs arranged as a long tube• The GI tract includes:

• Organs such as the stomach and intestines• Sphincters, which are muscles that control the

passage of material from one organ to the next• Accessory organs, which assist digestion but

are not part of the GI tract




Click on the Enzymes link separate from the power point.


• Enzyme: a protein that induces a chemical change in another substance

• Enzymes speed up the rate of chemical reactions.• Digestion is dependent on many different

enzymes.


The Action of Digestive Enzymes


Some Digestive Enzymes and Their Actions


Digestion

• The epiglottis covers the opening to the trachea during swallowing.

• Food travels from the mouth to the stomach through the esophagus.

• Peristalsis is the muscular contractions moving food through the GI tract.


Chewing and Swallowing


The Esophagus and Peristalsis


Mechanical Digestion in the Stomach

• The gastroesophageal sphincter separates the esophagus from the stomach.

• Digestion in the stomach includes:• Extensive mechanical digestion, mixing food

with gastric juice to produce chyme• Chemical digestion of proteins and fats


Chemical Digestion in the Stomach

• Gastric juice contains:• Hydrochloric acid (HCl): to denature proteins

and activate pepsin• Pepsin: an enzyme to digest protein• Gastric lipase: an enzyme to digest fat• Mucus: to protect the stomach lining

• Chyme: semi-solid product of mechanical and chemical digestion in the stomach


The Stomach Mixes, Digests, and Stores Food


Most Digestion and Absorption Occurs in the Small Intestine• From the stomach, chyme is slowly released

through the pyloric sphincter to the small intestine.

• Most digestion and absorption occur in the small intestine.

• Absorption: the process by which molecules of food are taken from the GI tract into the body.


Most Digestion and Absorption Occurs in the Small Intestine


The Gallbladder and Pancreas Aid in Digestion• Accessory organs of the GI tract include:

• Liver: produces bile, which emulsifies fats• Pancreas

• Produces many digestive enzymes• Produces hormones involved in regulation of

metabolism

• Gallbladder: stores bile


Absorption Mechanisms


Click the Basic Absorption link for separate from the power point.

A Specialized Lining Enables the Small Intestine to Absorb Food• The lining of the GI tract has special structures

to facilitate absorption.• Villi are folds in the lining that are in close

contact with nutrient molecules.• The brush border is composed of microvilli,

which greatly increases the surface area.


Small Intestine Structure and Function







• The nutrient products of digestion are absorbed by villi lining the small intestine.

• The nutrients are picked up by blood and lymph and carried to all parts of the body.

• The liver plays a major role in processing, storing, and regulating the blood levels of the energy nutrients.




The Large Intestine

• Undigested food components move to the large intestine, where they mix with intestinal bacteria.

• In the large intestine:• Intestinal bacteria complete digestion • Material is stored 12–24 hours prior to

elimination• Water and some nutrients are absorbed


The Large Intestine


Probiotics

• Probiotic bacteria• Manufacture enzymes• Supply key nutrients• Produce certain vitamins• Degrade potential carcinogens• Oppose excessive inflammation• Need to consume daily


Prebiotics

• Prebiotic bacteria• Nondigestible substances that stimulate

growth of probiotics• Inulin is one example.


Disorders Related to Digestion

• Belching• Most common cause is swallowed air

• Flatulence• Normal body function• Partially digested carbohydrates• Olestra, sugar alcohols, and quorn



• The lining of the stomach is designed to cope with hydrochloric acid, but other regions of the GI tract are not.

• Heartburn is caused by hydrochloric acid in the esophagus.

• GERD, or gastroesophageal reflux disease, is painful, persistent heartburn.


The Mechanism of Heartburn and GERD



• Peptic ulcers are regions of the GI tract that have been eroded by HCl and pepsin.

• The bacterium Helicobacter pylori contributes to the production of both gastric and duodenal ulcers.

• Some peptic ulcers have been traced to use of nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen.



• Food intolerance is a group of GI symptoms associated with eating a particular food.

• Symptoms may include gas, pain, and diarrhea.• Lactose intolerance is an example.



• Food allergies: a response of the immune system caused by a particular food

• In some people, food allergies can be mild.• In others, food allergies can be quite severe and

require immediate medical attention.


Food Allergy Myths


Click the next slide for the video.


• Celiac disease is an immune system response to eating gluten, a protein found in wheat, rye, and barley.

• The immune response damages the villi in the small intestine, leading to decreased absorption of certain nutrients.

• Celiac disease is considered a genetic disorder. • Treatment involves a gluten-free diet although

there is no known cure.



• Non-celiac gluten sensitivity (NCGS)• The patient presents with symptoms but does

not have the genetic marker, antibodies, or intestinal damage associated with true celiac disease.



• Diarrhea:• Can be caused by infection of the GI tract,

chronic disease, food intolerances, stress, and bowel disorders

• Can lead to severe dehydration• Is more dangerous for infants and young

children



• Constipation:• Difficulty passing stools• Can be caused by the disruption of a person's

schedule, a change in diet, or certain medications

• May be treated by increasing fluid and fiber consumption



• Irritable bowel syndrome (IBS) is a disorder that interferes with normal colon function.

• Symptoms of IBS include:• Abdominal cramps and bloating• Either diarrhea or constipation

• IBS is more common in women than in men.
