BI 103 Lecture Notes: Chapter 30 Nutrition and Digestion

I. Nutrition

A) Functions of nutrients

1. Energy to fuel cell metabolism

2. Building blocks to construct complex molecules

3. Molecules to assist in metabolic reactions

B) Nutrient Classifications

1. Carbohydrates; primary energy source, stored as glycogen

2. Lipids: efficient energy storage and building blocks

3. Proteins (9 essential amino acids: not synthesized by body

4. Minerals

5. Vitamins (water soluble and fat soluble)

II. Digestion

A) Tasks of the digestive system

1. Ingestion 2. Mechanical breakdown 3. Chemical Breakdown

4. Absorption 5. Elimination

B) Processes of Human Digestion

1. Breakdown of food begins in mouth

a) mechanical breakdown: teeth (incisors, canines, molars)

b) Chemical breakdown: saliva has amylase

2. Esophagus conducts food to stomach

a) peristalsis: Rhythmic contractions of smooth muscle in tubes

3. Stomach

a) Stores food

b) Mechanically breaks down food : segmentation movements: churning

c) Chemically breaks down food: HCl and Pepsin (protease)

d) Food becomes chyme (thick, acidic liquid)

e) only water, alcohol, some medications absorbed from stomach

4. Small Intestine (longest part of digestive system)

a) Chemical Digestion

1. Pancreas: Pancreatic juice

a) bicarbonate & Enzymes: amylase, lipase, proteases

2. Liver: Bile

a) stored in gall bladder

b) contains bile salts that assist in breakdown of fats

b) Absorption

1. Large surface area to absorb nutrients

a) Villi: finger like projections

b) microvilli: projections off villi of cell membrane

2. Blood vessels and lacteals (lymph vessels) run up villi

a) site of active transport into the body

b) fats travel through lymph system to circulatory system

5. Large intestine (colon and rectum)

a) Absorption: water, vitamins and some electrolytes

b) Contain bacteria which produce some vitamins (B and K)

c) elimination: indigestible material: feces

c) Control of digestion

1) Nervous system: food stimuli activates digestive system (saliva, HCl secretion)

2) Endocrine system (see table 30-6 in text for details)

a) Gastrin b) Secretin c) Cholecystokinin