The Digestive SystemPurpose: to convert foods into simpler molecules that can be absorbed and

used by the cells of the body

Why is Digestion Important?

• When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nourishment.

• Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

• Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.

In other words…

• The purpose in your eating a Big Mac, other than simple hedonism, is to assimilate the nutrients it represents and make them available to build, repair and maintain your own tissues, as well as provide energy for studying and occasional other pursuits.

Let’s Break It Down…

• The digestive system it is a tube running from mouth to anus.

• This tube is like an assembly line, or more properly, a disassembly line.

• Its chief goal is to break down huge macromolecules (proteins, fats and starch), which cannot be absorbed intact, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tube, and into the circulatory system for dissemination around your body.

Components of the Digestive System

The Major Players• Mouth• Pharynx• Esophagus• Stomach• Small Intestine• Large Intestine

The Accessory Structures• Salivary Glands• Pancreas• Liver• Teeth• Tongue

All of these organs work together to carry out…

3 Fundamental Processes:

• Secretion: Delivery of enzymes, mucus, ions and the like into the lumen, and hormones into blood.

• Absorption: Transport of water, ions and nutrients from the lumen, across the epithelium and into blood.

• Motility: Contractions of smooth muscle in the wall of the tube that crush, mix and propel its contents.

The Path of Digestion

• Digestion begins in the mouth (oral cavity)– Food is broken down by chewing

(mechanical) and enzymes in the saliva (chemical)

– Teeth coated with enamel cut and tear food– Saliva contains the enzyme salivary amylase

(breaks down starch)– Food is turned into a soft ball called a bolus– Bolus travels from the mouth to the pharynx

(throat)

The Path of Digestion• Swallowing is a result of the combined effort

of the tongue and throat muscles• Epiglottis (small flap of connective tissue),

prevents food from going into the trachea (airway)

• Next, food travels Into the esophagus a.k.a. “food tube”

• Peristalsis squeezes food along into the stomach

Peristalsis

The Path of Digestion

• A ring of muscles called the cardiac sphincter closes the esophagus after food passes into the stomach– Ever had heartburn?

• Stomach continues chemical and mechanical digestion– Chemical: Glands release mucous, HCl,

pepsin (enzyme that breaks down protein)– Mechanical: Muscles contact and churn

contents into chyme (a thin watery liquid)

Liver, Gallbladder, & Pancreas

Liver, Gallbladder, & Pancreas

Liver• The liver performs numerous function

in the body including storing glucose, making proteins, and breaking down toxic substances.

• The liver produces bile, which is vital to digesting fats.

Liver, Gallbladder, & Pancreas

• Gallbladder– After the liver produces bile it travels

through a Y-shaped duct to the gallbladder.

– The gallbladder is a saclike organ that stores and concentrates bile.

– The gallbladder releases the bile through a common bile duct into the small intestine

Liver, Gallbladder, & Pancreas

• Pancreas– The pancreas is an organ that lies behind

the stomach. The pancreas serves two roles in its part in the digestive system.

• The first role it plays is to increase the pH of the stomach acid by producing sodium bicarbonate.

• The second role it plays is to secrete enzymes that help to further break down carbohydrates, proteins, lipids and nucleic acids.

The Path of Digestion

• The pyloric valve controls the one-way flow of chyme from the stomach to the small intestine

• Small intestine (named for its diameter) is about 6 meters long and is broken down into 3 sections– 1st: Duodenum– 2nd: Jejunum– 3rd: Ileum

The Small Intestine

• Most of the chemical digestion and absorption of food occurs here

• Villi- folded, finger-like projections of the inner surface of the small intestine absorb nutrient molecules

Large Intestine

• Once absorption is complete in the small intestine, peristalsis will move the remaining contents into the colon or large intestine.

• The colon has various sections, and all of these sections work together to finish the absorption of nutrients and water.

• The colon initiates contractions that move the material out of the body.

Large Intestine continued…

• As nutrients and water are absorbed from the matter in the colon, the matter solidifies into feces.

• Feces leave the body by passing through the rectum and the anal canal.

Carbohydrates, Proteins & Lipids

• The three nutrients needed by the body in the greatest amounts are carbohydrates, proteins, and lipids.– All of these nutrients are called organic

compounds, which are compounds that contain the elements carbon, hydrogen, and oxygen.

• An example of a carbohydrate is pasta; an example of a protein is chicken; and an example of a lipid is olive oil.

Nutrients

• Your body also needs –Vitamins

–Minerals

–Water