Nutrition Notes

Nutrition--process by which organisms obtain and utilize their food

2 Parts:

1. ingestion- taking in of food

2. digestion- mechanical and chemical breakdown of food so that it can be absorbed and used by the body cells

Autotrophs- self feeders-make their own food ex. green plants

Heterotrophs- other feeders-depend upon other organisms for their food

nutrients- substances in food that organisms can use

micronutrients- nutrients needed in small amts. by an organism

exs. vitamins (used as coenzymes to help enzymes) and minerals (involved with many metabolic processes)

macronutrients- nutrients needed in large amts. by an organism

exs. fats (used for energy storage, protection, insulation, and part of cell membranes), proteins (used for energy, growth and repair, and cell membranes), carbohydrates (used for energy or energy storage), and water (universal solvent)

** Water, vitamins, and minerals are small molecules that can be absorbed without digestion. (hydrolysis)

** Large molecules like carbohydrates (starches), lipids, and proteins require digestion.

Carbohydrates (sugars and starches) should constitute 50% of the energy for the body. They provide the major source of energy for the body.

Carbohydrates are found in fresh fruits and vegetables as well as whole grains.

Complex carbohydrates provide a source of nondigestible materials which increase the amount of ROUGHAGE (also called "fiber"--stimulates the muscles of the alimentary canal or food tube)

calorie -- used to measure the energy in foods

Obviously the calorie value of different types of food varies.

** Nutritional requirements, including energy (caloric needs), vary with the human:

1.) body weight

2.) age

3.) activity level

4.) sex

5.) natural body efficiency

** Fats contain more potential energy per each unit of their mass then any other major nutrient.

MECHANISM FOR CHEMICAL DIGESTION

Hydrolysis--the splitting of large, insoluble molecules into small, soluble molecules with the addition of water

** In organisms, this process is regulated by hydrolytic (digestive) enzymes and is illustrated by the following:

1. Maltose + water ----> simple sugars (glucose for instance)

2. Proteins + water ---> amino acids

3. Lipids + water ---> 3 fatty acids + glycerol

** In a similar fashion, polysaccharides such as starch, are completely hydrolyzed to simple sugars.

Human digestive tract = GI (gastrointestinal) tract = alimentary canal

-- consists of a continuous one way food tube and accessory organs

peristalsis- slow, rhythmic muscular contractions that push food through the GI tract

Mouth- ingests food

Oral cavity- contains the tongue, teeth, and salivary gland openings

Teeth- function in the mechanical breakdown of food which increases the surface area of the food thus improving enzyme action

Salivary glands- secrete the digestive fluid saliva

2 Fcts. of Saliva:

1. Provides lubrication for the (chewed food)

2. Contains the digestive enzyme amylase that begins the digestion of starch..

Tongue--acts as a plunger to push food back into the throat (pharynx)

Secretion of saliva is stimulated automatically. (conditioned reflex)

Esophagus--10 inch long muscular tube--its muscular walls move food from the mouth to the stomach by peristalsis

Stomach--J-shaped, saclike, muscular churn which mixes the partially chewed food with gastric juice

Gastric juice--components and their functions

1. Water--solvent

2. Mucus--lubrication

3. Hydrochloric acid (HCl)--makes food acidic (pH=2)--thus allowing the enzyme pepsin to function

4. Pepsin--gastric protease which begins the digestion of proteins in the stomach

Pyloric sphincter--muscular valve between the stomach and the small intestine regulating the passage of the partially digested mass

** Food is usually held 2-4 hours in the stomach.

Small intestine:

--a 20-25 foot long twisted tube of small diameter (about 1 inch)

--lined with enzyme secreting intestinal glands

--does most of the chemical digestion

--protein, carbohydrate, and lipid chemical digestion is finished here

--accessory structures, the gall bladder and the pancreas, empty their secretions into the SI

LIVER--largest body organ--has many functions --digestive function is to make bile

Gall bladder--small bile storage sac beneath the liver

Bile duct--carries bile from the gall bladder to the S.I.

Bile emulsifies lipids--breaks their droplets down into smaller particles.

Pancreas--located near the small intestine--pancreatic juice is carried to the SI by the pancreatic duct

** Pancreatic juice digests all major nutrient types.

Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

Intestinal glands--line the small intestine secreting intestinal juice --aid the completion of digestion in the small intestine

--intestinal juice contains enzymes to breakdown proteins, fats, and carbohydrates

(Absorption in the SI)

Much absorption is thought to occur directly through the wall without the need for special adaptations.

villi--microscopic fingerlike projections on the SI wall--increase the surface area for nutrient absorption -- contain a capillary and a lymph vessel called a lacteal

Large Intestine

--averages 6 feet in length--2.5 inches in diameter

--sometimes called the colon

--appears as an inverted U surrounding the SI

appendix--not needed in human digestion--at the beginning of the LI

** Undigested food and water enter the large intestine where water is absorbed. Strong peristaltic action forces feces out through the rectum and the anus.

defecation--the removal of feces

The Human Digestive System (diagram)

Some Digestive Homeostais Disorders)

1. Ulcers--open sores in the lining of the stomach or the small intestine generally associated with some kind of irritant or bacterial infection

2. Constipation--condition in which the feces are evacuated infrequently and with difficulty --results from sluggish peristalsis that allows excess water to be removed from the feces (fecal material hardens) --may result from insufficient roughage in the diet

3. Diarrhea--opposite of constipation --associated with intestinal disturbances frequently caused by infections or stress --prolonged diarrhea may result in severe dehydration of body tissues

4. Appendicitis--infection and inflammation of the appendix

5. Gallstones--small hard particles made of cholesterol which form and collect in the gall bladder --may block the bile duct causing pain and discomfort --treated by surgical removal of the gall bladder