Warm-Up

Write down in correct sequence all the organs (at least 5) through which their food passes as it travels along the digestive tract. Then try to list any glands or organs that are found along the digestive tract, but through which food does not pass.

Human Digestive Human Digestive SystemSystem

Human Digestive System Digestion is the ability to process food in the body into a form

that can be absorbed and used or excreted.

Digestion involves three principle processes: Mechanical digestion: takes place in the mouth, your teeth

chew the food Chemical digestion: using chemicals to digest/ break

down food, this takes place in your mouth and stomach where acid and enzymes mix with the food.

Absorption: pulling nutrients out of the food, occurs in the small intestine

Structures

The GastrointestinaI tract (GI), also called the alimentary canal is the system of organs that take in food, digest it to extract nutrients and expels the waste. These organs are the mouth, pharynx, esophagus, stomach, small intestine and large intestine. Major Functions:

Ingestion Digestion Absorption Defecation or Excretion

Accessory organs: Organs that help with digestion but are not part of the digestive tract. These organs are the tongue, salivary glands, liver, gall bladder, and pancreas.

Human Digestive System Diagram

Villi

Mouth

Liver

Pharynx

StomachLarge Intestine

Small Intestine

Esophagus

Following the Trail

The process begins in the mouth. Chewing initiates mechanical breakdown of food

and is followed by secretion of saliva, which moistens and lubricates food for swallowing.

Saliva also contains amylases (enzymes), which start the chemical breakdown of carbohydrates.

The swallowing reflex begins in the pharynx and initiates rhythmic waves of smooth muscle contractions called peristalsis. Peristaltic contractions transport food to the

stomach and allow a person to swallow even if he/she are upside down.

Following the Trail II The stomach contains an extra layer of

muscle that aids in mechanically mixing and churning food into a semiliquid form called “chyme.” Chemical digestion begins with proteins

through the action of hydrochloric acid (HCl) and the enzyme, pepsin.

Only water and a few substances, such as aspirin and alcohol, are absorbed by the lining of the stomach.

Following the Trail III

As food enters the small intestine secretions from the liver, gall bladder and pancreas are added .

The small intestine completes digestion of food materials by absorbing nutrients into the blood stream

The lining of the small intestine consists of tiny folds or fingerlike projections, called villi, which, in turn, are covered by microvilli which increase surface area The villi contain capillaries and lymphatic

vessels for the absorption of nutrients Microvilli have brush border enzymes to

hydrolyze lactose and sucrose.

Cross-Section of small intestine Villi Microvilli

The large intestine does not contain villi and it plays no role in digestion Only water and vitamin K are

absorbed from the large intestine Undigested or unabsorbed food is

eliminated through the rectum and then anus.

Nutrition

Food materials are broken down to usable nutrients and absorbed into the bloodstream. They are used by the body for metabolism, building and repair Some nutrients are stored within the body

Nutrients include carbohydrates, proteins, lipids, vitamins, minerals and water.

Carbohydrates Must be broken down into monosaccharides Body’s main source of energy.

Nutrition II

Proteins Broken down to amino acids Supply the raw materials for growth and repair. The body requires 20 amino acids, 10 of which it cannot

make and must obtain Lipids are reduced to fatty acids and glycerol

They are used to make steroid hormones, cell membranes Store energy

Nucleic acids are reduced to nucleotides.DNA and RNAThe genetic material of all cells.

Where does each nutrient get broken down?

Carb-

Digestion

Protein Digestion

Nucleic Acid Digestion

Fat Digestion

Mouth, Throat, Esophagus

Polysacch. Into Disacch.

Stomach Polypepties into smaller proteins

DNA, RNA into nucleotides

Fat into glycerol, fatty acids and glycerides

Small Intestine

Disacch. Into Monosacch.

Small proteins into amino acids

Nucleotides into nitrogen base, sugar and phospate

What enzymes break down each nutrient?

Carb Digestion

Protein Digestion

Nucleic Acid Digestion Fat Digestion

Salivary amylase

(amylose is starch, a polysacch)

Peptidases

(amino acids are connected by “peptide” bonds)

Nucleotidases

(nucleotides are building block of DNA and RNA)

Bile salts and Lipase

(fats are made of lipids)

Nutrition III

Vitamins are organic molecules that aid in the regulation of body processes Vitamin C: healthy teeth, gums and

blood vessels; improves iron absorption and resistance to infection

Vitamin K: for normal blood clotting and synthesis of proteins found in plasma, bone, and kidneys

Water Required for metabolism and chemical

reactions within the body Transport of substances around the body Regulation of body temperature.

Approximately two-thirds of the body weight is water.

Cool Facts

Your intestines will grow to at least 25 feet as an adult. Be glad you're not a full-grown horse their coiled-up intestines are 89 feet long!

Food sloshing in the stomach can last 3-4 hours It takes 3 hours for food to move through the

intestine Food drying up and hanging out in the large

intestine can last 18 hours to 2 days! Americans eat over 2 billion pounds of

chocolate a year. In your lifetime, your digestive system may

handle about 50 tons!!