The Digestive System

Cardiac Sphincter

After food passes into the stomach, a thick ring of muscle called cardiac sphincter closes the esophagus. This prevents the contents of the stomach from flowing back.

Peristalsis

Contractions of smooth muscles that provide the force that moves food through the esophagus toward the stomach.

Small Intestine

Digestive organ in which most chemical digestion and absorption of food takes place.

The Process of Digestion

During digestion, good travels through the mouth, esophagus, stomach, and small intestine. Mechanical digestion and chemical digestion are the two processes by which food is reduced to molecules that can be absorbed.

Villus

Fingerlike projection in the small intestine that aids in the absorption of nutrient molecules.

Esophagus

Tube connecting the mouth to the stomach.

Tongue

Your tongue moves food around so that it comes in contact with your teeth.

Epiglottis

a flap of cartilage at the root of the tongue, which is depressed during swallowing to cover the opening of the windpipe.

Mechanical Digestion

Physical breakdown of large pieces of food into smaller pieces.

Chemical Digestion

Process by which enzymes break down food into small molecules that the body can use.

Lipase

Released in pancreatic juices, and breaks down fat.

Peptic Ulcer

Stomach gland produces mucus, a fluid that lubricates and protects the stomach wall. If this protective layer fails, acids may erode the stomach lining and cause this sore.

Absorption From the Small Intestine

After leaving the duodenum, chyme moves along the rest of the small intestine. By this time, most of the chemical digestion has been completed. The chyme is now a rich mixture of small- and medium- sized nutrient molecules that are ready to be absorbed. Nutrient molecules are rapidly absorbed into the cells lining the small intestine. Most of the products of carbohydrate and protein digestion are absorbed into the capillaries in the villi. Most fats and fatty acids are absorbed by lymph vessels.

Mechanical Digestion in the Stomach

Alternating contractions of the stomach's three smooth muscle layers thoroughly churn and mix the swallowed food. The churning causes further breakdown of the chances of swallowed food and allows enzymes greater access to the food. Gradually a mixture with an oatmeal-like consistency called chyme is produced. After an hour or two, the pyloric valve, which is located between the stomach and small intestine, opens, and chyme begins to spurt into the small intestine.

Digestion in the Small Intestine

As chyme is pushed through the pyloric valve, it enters the duodenum. The duodenum is the first part of the small intestine, and it is where almost all of the digestive enzymes enter the intestine. Most of the chemical digestion and absorption of the food you eat occurs in the small intestine. As chyme enters the duodenum from the stomach, it mixes with enzymes and digestive fluids from the pancreas, the liver, and even the lining of the duodenum itself.

The Mouth

As you take a forkful of food into your mouth, the work of the digestive system begins.

The Liver and Gallbladder

Assisting the pancreas in fat digestion is the liver. The liver produces bile, a fluid loaded with lipids and salts. Bile is stored in a small pouch-like organ called the gallbladder. When fat is present in the duodenum, the gallbladder releases bile through a duct into the small intestine. Fats tend to glob together, which makes fat digestion by enzymes such as lipase difficult. Blue breaks up the globs of fat into smaller droplets that disperse in the watery environment of the small intestine. This action makes it possible for enzymes to reach the smaller fat droplets and break them down.

Amylase

Enzyme in saliva that breaks the chemical bonds in starches.

Pepsin

Enzyme that breaks down proteins into smaller polypeptide fragments.

Salivary Gland

Made by salivary glands in oral cavity and breaks down chemical bonds into starches.

Pepsin

Made in the stomach, and breaks down proteins.

What is the difference between mechanical digestion and chemical digestion?

Mechanical digestion prepares food for chemical digestion, chews and mixes with saliva, churning of food in the stomach, segmentation of intestines rhythmic local constrictions of intestine, causes mixing improves absorption. Chemical digestion breaks down complex food molecules into chemical building blocks, enzymes secreted into alimentary canal lumen.

Chyme

Mixture of enzymes and partially digested food.

Absorption and Elimination

Most nutrients from food are absorbed through the walls f the small intestine. The large intestine absorbs water and several vitamins and prepares waste for elimination from the body.

List the structures that food travels through during digestion and give the function of each.

The Oral Cavity, Teeth, Salivary Glands, The Pharynx, The Esophagus, The Stomach, The Small Intestine, Accessory Organs, The Liver and Gallbladder, The Pancreas, The Large Intestine, The Cecum, The Colon, The Rectum and Anal Canal.

Elimination

The concentrated waste material - the feces - that remains after most of the water has been removed passes into the rectum and is eliminated from the body through the anus. When something happens that interferes with the removal of water by the large intestine, you usually become aware of it right away. If not enough water is absorbed, a condition known as diarrhea occurs. If too much water is absorbed from the undigested materials, a condition known as constipation occurs.

Functions of the Digestive System

The digestive system converts food into small molecules that can be used by the cells of the body. Food is processed by the digestive system in four phrases - ingestion, digestion, absorption, and elimination.

How would the rate of digestion be affected if the various organs and glands did not release enzymes? Hint: You may wish to refer to Chapter 2 for a review of enzyme action.

The process would be slowed down, and it could cause possible infections.

Chemical Digestion in the Stomach

The stomach is a large muscular sac that continues the chemical and mechanical digestion of food. The lining of the stomach contains millions of microscopic gastric glands that release many substances into the stomach. Some of these glands produce hydrochloric acid. Other lands release enzymes called pepsin that is activated in and functions best in acidic conditions.

Teeth

The teeth are anchored in the bones of the jaw. Protected by a coating of enamel. The teeth do mucho f the mechanical work of digestion.

What impact do the folds and villi of the small intestine have on absorption?

The villi and microvilli, with their many folds, increase the surface area of the intestine and increase absorption efficiency of the nutrients.

Explain how nutrients are absorbed.

They need to be processed by the stomach and the small intestine before being absorbed through the intestinal wall.

Absorption From the Large Intestine

When chyme leaves the small intestine, it enters the large intestine, or colon. The large intestine is actually much shorter than the small intestine. The large intestine gets its name due to its diameter, which is much grater than the small intestine's diameter. The primary function of the large intestine is to remove water from the undigested material that is left. Water is absorbed quickly across the wall of the large intestine, leaving behind the undigested materials. Rich colonies of bacteria present in the large intestine produce compounds that the body is able to absorb and use, including vitamin K. When large doses of antibiotics are given to fight an infection, they can destroy these bacteria, and vitamin K, deficiency can occur.

Pharynx

the membrane-lined cavity behind the nose and mouth, connecting them to the esophagus.

The Esophagus

From the throat, the bolus passes through the esophagus into the stomach.

Pancreas

Just behind the stomach is the pancreas. A gland that serves three important functions. One Function - Is the produce hormones that regulate blood sugar levels. Second Function - It produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids. Third Function - The pancreas also produces sodium bicarbonate, a base that quickly neutralizes stomach acid as chyme enters the duodenum. The enzymes produced by the pancreas unlike those produced in the stomach, would be destroyed by strong acid, and therefore the sodium bicarbonate is necessary for digestion to proceed.

Stomach

Large muscular sac that continues the mechanical and chemical digestion of food.

Large Intestine

Organ in the digestive system that removes water from the undigested material that passes through it; also called colon.

Duodenum

The first part of the small intestine.

Saliva

The release of saliva is under the control of the nervous system and can be triggered by the scent of food.

Absorption from the Small Intestine

By the time chyme is ready to leave the small intestine, it is basically nutrient-free. Complex organic molecules have been digested and absorbed, leaving only water, cellulose, and other undigestible substances behind. As material leaves the small intestine and enters the large intestine, it passes by a small saclike organ called the appendix. In some mammals, the appendix processes cellulose and other materials. The only time humans notice their appendix is when it becomes clogged and inflamed, causing appendicitis. The remedy for appendicitis is to remove the infected organ by surgery - as quickly as possible - before it can rupture or break open.

What begins Chemical Digestion?

Chemical Digestion begins as digestive enzymes in saliva start the breakdown of complex carbohydrates into smaller molecules.

What begins Mechanical Digestion?

Chewing begins the process of Mechanical Digestion.

What cuts and tears into food?

Incisors, cuspids, and bicuspids.

Explain the function of the digestive system.

It is the break down of food into small, which are then absorbed into the body.