chapter 14

Chapter 14NUTRITION AND DIGESTION

The 4 Stages of Food Processing

1. Ingestion… in another word Eating.

2. DigestionIs the breakdown of food to small nutrient

molecules.

3. AbsorptionIs the uptake of the small nutrient molecules by

cells lining the digestive tract.

4. EliminationIs the disposal of undigested materials from

the food we eat.

1. The Digestive Tract

Digestion dismantles food particles for use by the body.

• Mechanical digestion

– Begins the process.

– Involves physical processes like chewing.

• Chemical digestion

– Is the chemical breakdown of food by digestive enzymes.

Chemical digestion proceeds via hydrolysis:

Which means that it involves chemical reactions that break down polymers into monomers using water in the process.

OH

H

monomer

H2Opolymer

Hydrolases

(enzymes that catalyze digestive hydrolysis reactions.)

The Human Digestive System

The Human Digestive System

The human digestive system consists of:

1. A digestive tube, the alimentary canal

2. Accessory organs that secrete digestive chemicals

Accessory organs

Salivary glands

Liver

Gallbladder

Pancreas

Alimentary canal

Oral cavityTonguePharynx

Esophagus

Stomach

Small intestineLarge intestineAppendixRectumAnus

A. The MouthThe mouth, or oral cavity functions in ingestion and the preliminary steps of digestion.

Saliva keeps the mouth moist. It contains enzyme salivary amylase which begins process of digesting starch

Comprised of skeletal muscles and Taste buds

The Teeth• 20 baby teeth• 32 adult teeth• Tooth divided into:

– Crown• Enamel• Dentin• Pulp

– Root• Dentin• Pulp

• Gingiva (gums)

enamel

dentinpulpgum

cementum

b.

periodontalmemb rane

root canal

jawbone

root

crown

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B. The Pharynx• Connects the mouth to the esophagus.

• Also opens to the trachea (respiratory tract). During swallowing, a reflex tips the epiglottis to close the windpipe entrance.

Not swallowing Swallowing started Swallowing finished

C. The Esophagus

• Is a muscular tube.

• Connects the pharynx to the stomach.

• Moves food down by peristalsis.

• Starts digestion of proteins

D. The Stomach• Can store food for several hours.

• 2 major functions: digestion and defense

How Does the Stomach Work?

The accidental shooting of a man in 1822 provided an opportunity for a doctor named William Beaumont to learn about the stomach’s many functions.

The hole was permanent and large enough that Beaumont could insert his entire forefinger into the stomach cavity.

What did he do to this poor man?

Rate of Digestion of different food:Beaumont tied different types of food (protein, fat, carb) to the end of a silk string and dangled the food through the hole into the stomach. Beaumont pulled out the string 1, 2, 3 and 5 hours later.

Stomach

Stomach acid

Fistula or tube

String

Food

Chemical Digestion in the Stomach

• This Churns food into a thick soup called acid chyme.

• The high acidity kills germs

•Normally empties in 2-6 hours

The stomach contains gastric juice made of strong acid, digestive enzymes, and mucus.

Stomach Ailments• Gastric ulcers

– Are erosions of the stomach lining.

– Are often caused by a bacterium named Helicobacter pylori, NOT stress.

• Heart burn– Nothing to do with the heart!

– Discomfort or pain caused by the stomach contents traveling up from the stomach up into the gullet (lower part of your esophagus). The gullet is not made to withstand acid and is irritated and inflamed when acid from the stomach travels up into it.

– Happens when you eat too much, wear tight clothes, bad posture….

E. The Small Intestine

• Longest part of the alimentary canal.

• Major organ for chemical digestion and absorption.

• Chemical Digestion in the Small Intestine: hydrolases break down food to monomers.

• Composed of 3 parts: 1. Duodenum (close to stomach)2. Jejunum (middle part)3. Ileum

Receives digestive agents from several organs.

The liver:

secretes bile, which helps digest fats.

The pancreas:

Secretes juice that neutralizes stomach acids into the duodenum.

Duodenum

Absorption of Nutrients

• It is not technically “in” the body yet.

• It must be absorbed.

Although food has been ingested,

Are parts of the small intestine specialized for absorption.

The jejunum and ileum

The intestinal wall contains villi and microvilli, which provide a large surface area for absorption.

Interior of intestine

VilliEpithelial cellsBlood vessels

Epithelial cell

Nutrient absorption

microvilli

F. The Large Intestine (and Beyond)

• shorter, but wider, than the small intestine.

1. The colon

– Makes up most of the length of the large intestine.

– Absorbs water, salt and some vitamins from the alimentary canal.

– Produces feces, the waste product of food.

2. The rectum

– Is the last 15 cm (6 inches) of the large intestine.

3. The anus

– Regulates the opening of the rectum.

Food processing takes place along the alimentary canal.

Ingestion

Digestion

Absorption

Eliminationhttp://video.about.com/ibdcrohns/Digestion.htm

G. Accessory Organs of Digestion

• Pancreas• Liver• Gallbladder

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bile

a.

pancreascommon hepatic duct

pancreatic duct

gallbladdercommon bile duct

duodenum

pancreaticjuice

The Pancreashttp://diabetes.emedtv.com/diabetes-video/what-does-the-pancreas-do-video.html

• Endocrine function (internal secretion)

– Insulin and glucagon

– Regulates blood glucose

• Exocrine function – pancreatic juice

(external secretion)

– Sodium bicarbonate: neutralizes the stomach acid

– Pancreatic amylase: starch digestion

– Trypsin: protein digestion

– Lipase: fat digestion

The Liver

– Largest gland in the body

– Lobules are the structural and functional units• Located between lobules

– A bile duct takes bile away– A branch of the hepatic artery brings O2 rich blood– A branch of the hepatic portal vein transports nutrients

from the intestines

• Each lobule has a central vein that enters a hepatic vein

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bile canals

bile duct

b.

branch ofhepatic artery

branch ofhepaticportalvein

central vein

Acts as a gatekeeper for the blood1.Removes poisonous substances and

detoxifies them2.Removes and stores iron and vitamins A, D,

E, K, and B12

3.Makes plasma proteins4.Regulates cholesterol5.Regulates blood glucose, stored as glycogen6.Produces bile

– Bilirubin – hemoglobin breakdown product– Bile salts – emulsify fat

The liver has many roles

The Gallbladder

• Liver produces 400-800 ml of bile each day

• Stores excess bile

• Water reabsorbed – thickens bile

• Secreted through common bile duct into duodenum via common bile duct

Digestive Enzymes

•Proteins that speed up specific chemical

reactions

•Break down carbohydrates, proteins,

nucleic acids, and fats

Human Nutritional Requirements

Nutrition

• Proper nutrition helps to maintain homeostasis.

• A balanced diet provides– Fuel energy for cellular work.– Building materials

to construct needed materials.

6 major classes of Nutrients1. Carbohydrates and fats

– Primary energy source

2. Proteins– Growth and development– Regulate metabolism (with vitamins and minerals)– Can be energy source

3. Water– Serves many important roles– Cells are 70-80% water

4. Vitamins and minerals

Physical activity: 30 min at least/day

A lot

little

Amount of food and proportion for each category

The more active you are the more you should eat. But the proportions should remain the same

Balancing Calories: - Enjoy your food, but eat less- Avoid oversized portions

Foods to Increase: - Make half your plate fruits and veg- Make at least half your grains whole grains- Switch to fat-free or 1% fat milk

Foods to reduce- Lower sodium- Drink water instead of sugary drinks

Any food made from wheat, rice, oats, cornmeal, barley or another cereal grain. Examples: Bread, pasta, oatmeal, breakfast cereals, tortillas, 2 subgroups: • Whole grains contain the entire grain kernel -- the bran, germ, and endosperm.

Examples: whole-wheat flour, Oatmeal, brown rice

GRAIN GROUP

2. Refined grains have been milled, a process that removes the bran and germ. This is done to give grains a finer texture and improve their shelf life, but it also removes dietary fiber, iron, and many B vitamins. Examples: white flour, white bread, white rice

VEGETABLE GROUP

OILS, FAT GROUPFats, oils and cholesterolUnsaturated vs saturated lipids:

• UNSATURATED = OILS •Liquid at room temperature•Found in vegetables and whole grains

• SATURATED = FATS•Solid at room temperature•Animal origin (butter, meat)•Associated with cardiovascular disease

Fats

That

Cause

Disease

• Plaques form in and block arteries– Contain cholesterol and saturated fats

• Cholesterol– Not soluble in blood, ie needs carriers, which are

low density lipoprotein (LDL) and high density lipoprotein (HDL)

– LDL (“bad” cholesterol) - transports cholesterol from the liver to cells

– HDL- (“good” cholesterol) - transports cholesterol away from arteries to the liver to make bile salts

Calories are a measure of the energy stored in your food. A measure of the energy you expend in daily activities. A kilocalorie is 1000 calories (The unit listed on food labels).

Food as Building Material

The cells of your body assemble polymers from the monomers found in food.

Essential nutrients are substances needed by the body that it cannot make itself.

A. Essential Amino Acids

There are 8 essential amino acids (needed to make proteins).– Different foods contain different ones.

B. Vitamins

• Are organic molecules required in the diet for good health.

• Vitamins are defined by their biological activity, not their structure.

• Function mostly as assistants to enzymes.

• http://www.youtube.com/watch?v=cqR2aYx2H3s&feature=related

Illnesses Due to Vitamin Deficiency

Rickets due to vitamin D deficiency

Pellagra dermatitis due to niacin deficiency

Bleeding of gums is a symptom of scurvy, a vitamin C deficiency

Recommended daily allowances (RDAs)

Minimal standards established by nutritionists for preventing nutrient deficiencies.

Male 19-242900 kcal/day

Female 19-242200 kcal/day

C. Minerals• Are inorganic substances required in the

diet (which means other than the 4 elements carbon, hydrogen, nitrogen and oxygen which are present in common organic molecules.)

• Example:• Calcium: construction of bones and teeth.

Osteoporosis can be counteracted by uptake of Ca2+

• Chloride (salt) water balance• Phosphorus: ATP, phospholipids, nucleic acids• Iron: hemoglobin synthesis• Magnesium: nerve and muscle contraction, protein

synthesis

D. Essential Fatty Acids

• Our cells make fats and other lipids by combining fatty acids with other molecules.

• Essential fatty acids are the fatty acids we cannot make from simpler molecules.

• They are involved in inflammation, cell signaling. Produce various hormones and plasma membrane of cells

• Example: Omega-3

E. Decoding Food

Labels

On food labels, the FDA requires:– The list of

ingredients– Key nutrition

facts

7. Nutritional Disorders

7. Nutritional Disorders

Nutritional dysfunction can cause severe problems.

• Malnutrition is a dietary deficiency of one or more of the essential nutrients.

• Protein deficiency is an example.

• Undernutrition is caused by inadequate intake of nutrients. Can cause anorexia.

• Obesity is an inappropriately high ratio of weight to height.

• The majority of Americans consume too many fatty foods.– This may be done to satisfy fat cravings.– These cravings may have an evolutionary

basis (sugar & fat give energy, good for reproduction, the brain wired us to like them).

• To some extent, a tendency toward obesity is inherited (Low metabolism could be an advantage in time of starvation, selection for such individuals).

Mutation in one gene caused this mouse to be overweight even if its diet was low in fat.

Eating Disorders• Bulimia nervosa

– Can coexist with either obesity or anorexia nervosa– Habit of binge eating and then purging

• Self-induced vomiting or use of a laxative

– Can be dangerous – abnormal heart rhythm, damage to kidneys, erosion of teeth

• Anorexia nervosa– Morbid fear of gaining weight– All the symptoms of starvation – death may result

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© Donna Day/Stone/Getty Images

•obsession about body shape and weight.

Persons with bulimia nervosa have

•recurrent episodes of binge eating: consuming a large amount of food in a short period and experiencing feelings of lack of control during the episode.

•increase in fine body hair, halitosis, and gingivitis.

Body weight is regulated by• a restrictive diet,• excessive exercise• purging (self-induced vomiting or misuse of• laxatives).

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Persons with anorexia nervosa have

Body weight is kept too low by

•a morbid fear of gaining weight; body weight no more than 85% normal.

•a distorted body image so that person feels fat even when emaciated.

•in females, an absence of a menstrual cycle for at least three months.

• a restrictive diet, often with excessive exercise.

• binge eating/purging (person engages• in binge eating and then self-inducesvomiting or misuses laxatives).

© Tony Freeman/PhotoEdit

28 years old - 59 pounds