Digestion

Journey of a cheeseburger

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What is digestion?

• Digestion is the mechanical and chemical breakdown of food into usable molecules

• The Alimentary Canal (GI Tract) extends from the mouth to the anus with acessory organs (liver and pancreas)

• It is a 9 meter long tube

• Your entire body can be thought of as a tube within a tube.

• Movement through the tube is by wavelike motion called peristalsis

Peristalsis

(The British spelling of esophagus is “oesophagus”)

Major Parts and Function of the Digestive System:

• Mouth– Teeth begin digestion mechanically

• Chewing (“mastication”) breaks apart food• 2 sets of teeth

– Primary or “baby teeth” (20 in all)– Permanent teeth (32 in all)

• Incisors for cutting • Canines “fangs” for tearing• Premolars and molars for grinding

– Tooth has a crown and a root• Pulp contains the nerve and blood supply for

nutrients and waste removal

Tooth Diagram

Digestive System

– Saliva - begins chemical digestion of carbohydrates & secrete amaylase (digestive enzyme)

– Tongue - Pushes food back towards throat– Palate (hard and soft) - roof of oral cavity– Palatine tonsils - lymphatic tissue– Pharyngeal tonsils (adenoids) - lymphatic– Pharynx - connects nasal and oral cavities

Digestive system

• Esophagus - food passageway (heartburn is caused by the effects of gastric juice on the esophagus)

• Stomach - secretes gastric juices (pepsin, hydrochloric acid) which digest proteins and creates a paste of food called chyme.

• Pancreas - secretes pancreatic juice which helps digest carbs, fats, and nucleic acids and proteins.

Digestive system functions:

• Liver has many functions. The major are:– production of bile, which helps carry away

waste and break down fats in the small intestine during digestion

– production of certain proteins for blood plasma– production of cholesterol and special proteins to

help carry fats through the body– conversion of excess glucose into glycogen for

storage (This glycogen can later be converted back to glucose for energy.)

Digestive system functions:

• Liver functions (continued):– regulation of blood levels of amino acids,

which form the building blocks of proteins– processing of hemoglobin for use of its iron

content (The liver stores iron.) – conversion of poisonous ammonia to urea

(Urea is one of the end products of protein metabolism that is excreted in the urine.)

– clearing the blood of drugs and other poisonous substances

Digestive system functions:

• Liver functions (continued):– regulating blood clotting– resisting infections by producing immune factors

and removing bacteria from the blood stream– stores vitamin D

• Gall Bladder– Stores bile, releases through bile duct– Bile in the gall bladder can precipitate and form

solids or “stones”

Digestive System functions

• Small Intestine– Receives secretions from pancreas and

liver,completes digestion of nutrients in chyme, absorbs products of digestion through fingerlike projections called villi; transports residues to large intestine

– 3 major sections• Duodenum• Jejunum• Ileum

– Connected by mesentery which suspends these portions from abdominal wall

Digestive System Components

• Large Intestine– Absorbs water and electrolytes from chyme,

forms and stores feces– Cecum = beginning of large intestine– Appendix - small closed part, no longer serves a

digestive function, but contains lymphatic tissue– Colon - 4 sections

• Ascending colon, begins at cecum• Transverse colon• Descending colon• Sigmoid colon

Digestive System

• Rectum– Last part of large intestine

• Anus– Expels waste - two sphincter muscles guard

the anus (one under involuntary control ,the other, and final one, is under voluntary control)

Nutrients

• 4 major nutrients– Carbohydrates - supply energy (1 calorie per

gram)– Lipids - supply energy for cellular processes

and for building cells, stores energy (9 calories per gram)

– Proteins - control metabolic rates, clotting factors, keratin of skin and hair, source of energy (1 calorie per gram)

Vitamins

• Organic compounds required in small amounts for normal metabolic processes. Must come from foods.

• Vitamins A,C,D, and E appear to have anticancer effects. Most vitamins function as coenzymes to help an enzyme accomplish a function

• Fat soluble - A,D,E,K

• Water-Soluble - Thiamin, Riboflavin, C, Niacin, B6, Folate, B12, Biotin, Pantothenic acid

Vitamins

• A for healthy eyes, skin, bones and hormone synthesis

• C for collagen, detoxification

• Folate needed for DNA and RNA metabolism

• Niacin, Biotin, Thiamin needed for energy metabolism

Minerals

• Concentrated in bones and teeth

• Major minerals are calcium and phosphorous

• The body needs 7 - potassium, sulfur, sodium, chloride and magnesium in addition to trace amounts

• Fats and sugars have few minerals.

Minerals

• Phosphorus needed for bone and tooth formation

• Magnesium needed for bone, tooth, and enzyme formation

• Sulfur needed for cartilage, tendon, and proteins

• Sodium needed for nerve impulse transmission

• Potassium - nerve function

• Chloride - gastric juices and electrolyte balance

More Minerals

• Iron - for hemoglobin

• Iodine for thyroid function

• Fluoride - for bones and teeth

• Zinc for insulin, sperm production

• Selenium is an antioxidant

• Copper helps produce hemoglobin

• Chromium for energy metabolism

• Manganese and molybdenum are components of enzymes