THE AGING PROCESS

All vital organs begin to lose some function as you age. Aging changes have been found in all of the body's cells, tissues and organs, and these changes affect the functioning of all body systems. Living tissue is made up of cells. There are many different types of cells, but all have the same basic structure. Tissues are layers of similar cells that perform a specific function. The various kinds of tissues group together to form organs.

There are four basic types of tissue:

• Connective tissue supports other tissues and binds them together. This includes bone, blood, and lymph tissues in addition to the tissues that give support and structure to the skin and internal organs.
• Epithelial tissue provides a covering. The skin and the linings of the various passages inside the body are made of epithelial tissue.
• Muscle tissue includes two types of tissue:
  • Striated muscles, such as those that that move the skeleton (also called voluntary muscle)
  • Smooth muscles, such as the muscles that surround the stomach
• Nerve tissue is made up of nerve cells (neurons) and is used to carry messages to and from various parts of the body. The brain is made of nerve tissue.

AGING CHANGES

Cells are the basic building blocks of tissues. All cells experience changes with aging. They become larger and are less able to divide and reproduce. Among other changes, there is an increase in pigments and fatty substances inside the cell (lipids). Many cells lose their ability to function, or they begin to function abnormally.                                                                                                                     

Waste products accumulate in tissue with aging. A fatty brown pigment called lipofuscin collects in many tissues, as do other fatty substances.         

 Connective tissue changes, becoming increasingly stiff. This makes the organs, blood vessels, and airways more rigid. Cell membranes change, so many tissues have more trouble receiving oxygen and nutrients and getting rid of carbon dioxide and wastes. Many tissues lose mass. This process is called atrophy. Some tissues become lumpy (nodular) or more rigid.                                           

 Because of cell and tissue changes, your organs also change as you age. Aging organs gradually but progressively lose function, and there is a decrease in the maximum functioning capacity. Most people do not notice this loss, because you seldom need to use your organs to their fullest capability.                          

Organs have a reserve ability to function beyond the usual needs. For example, the heart of a 20-year-old is capable of pumping about 10 times the amount that is actually needed to preserve life. After age 30, an average of 1% of this reserve is lost each year.  

The large, hollow organs of the digestive system contain muscle that enables their walls to move. The movement of organ walls can propel food and liquid and also can mix the contents within each organ. Typical movement of the esophagus, stomach, and intestine is called peristalsis. The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.

The first major muscle movement occurs when food or liquid is swallowed. Although we are able to start swallowing by choice, once the swallow begins, it becomes involuntary and proceeds under the control of the nerves.

The esophagus is the organ into which the swallowed food is pushed. It connects the throat above with the stomach below. At the junction of the esophagus and stomach, there is a ring like valve, called cardiac valve, closing the passage between the two organs. However, as the food approaches the closed ring, the surrounding muscles relax and allow the food to pass.

The food then enters the stomach, which has three mechanical tasks to do. First, the stomach must store the swallowed food and liquid. This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine. Another valve, called the pylorus prevents the movement of the food to the duodenum until it is ready.

Several factors affect emptying of the stomach, including the nature of the food (mainly its fat and protein content) and the degree of muscle action of the emptying stomach and the next organ to receive the contents (the small intestine). After the food moves from the duodenum, it is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine. The contents of the intestine are then mixed and pushed forward to allow further digestion.

Finally, all of the digested nutrients are absorbed through the intestinal walls. The waste products of this process include undigested parts of the food, known as fiber, and older cells that have been shed from the mucosa. These materials are propelled into the colon, where they remain, usually for a day or two, until the feces are expelled by a bowel movement.

Digestive System

The digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food.

Two solid organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system.

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.

Digestion involves the mixing of food, its movement through the digestive tract, and the chemical breakdown of the large molecules of food into smaller molecules. Digestion begins in the mouth, when we chew and swallow, and is completed in the small intestine. The chemical process varies somewhat for different kinds of food.