Digestive System & Nervous System

The process of breaking down food into molecules the body can use is called digestion.

Digestion occurs in the gastrointestinal tract, or digestive tract, which is a long tube which begins at the mouth and winds through the body to the anus.

Digestion includes the mechanical and chemical breakdown of food into nutrients

• Mechanical digestion begins when the teeth cut and grind food.

• The tongue also aids in mechanical digestion

Mechanical Digestion

Saliva is produced by the salivary glands to begin chemical digestion of food.

Salivary amylase is the chemical in saliva that begins the chemical digestion

The pharynx is an open area that begins at the back of the mouth, and serves as a passageway for both air and food.

Chemical Digestion

food is then forced from the pharynx into the esophagus.

The stomach is an organ involved in both mechanical and chemical digestion.

It is located in the upper left side of the abdominal cavity, just below the diaphragm.

This process forms a mixture called chyme.

Mechanical Chemical

The stomach has three layers of smooth muscle—a circular layer, a longitudinal layer, and a diagonal layer.

These muscles churn the food within the stomach and help to carry out mechanical digestion.

Gastric fluid carries out chemical digestion in the stomach.

Gastric fluid is a liquid that is secreted by the gastric glands in the stomach.

Hydrochloric acid within the gastric fluid helps dissolve food and minerals and keep bacteria at bay.

The other organs that help digestion are the liver, gallbladder, and pancreas.

The Liver

The liver produces bile, which is vital to digesting fats.It also stores glucose, makes proteins, and breaks down toxic substances.

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.

Gall Bladder

Pancreas• The pancreas has two roles in digestion

• 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.

It is also responsible for secreting the hormones insulin and glucagon

The chyme from the stomach will further break down in the small intestine.

Absorption occurs mostly in the small intestine.

Small Intestine

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

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

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

Nervous System

The nervous system includes two major divisions.

The first division is the central nervous system and is made up of the brain and the spinal cord.

The brain is the control center of the nervous system.

The spinal cord carries nerve signals between the body and the brain.

The second division is the peripheral nervous system that sends information to and from the central nervous system.

Somatic Nervous System

The somatic nervous system contains motor neurons that control the movement of skeletal muscles.

The somatic system is considered voluntary, but can operate without conscious control.

Somatic system also relays the signals in reflexes.

Reflexes are involuntary and often self-protective movements. An example is the patellar, or knee-jerk, reflex.

Autonomic Nervous System

The autonomic nervous system controls internal body conditions by regulating smooth muscles in blood vessels and organs.

The sympathetic division prepares the body when activated by physical or emotional stress.

For example, pupils dilate and heart rate increases.

The parasympathetic division controls the internal environment during routine conditions.

For example, pupils constrict and heart rate decreases.

Two Subdivisions

Cerebrum- largest part of the brain, divided into two hemispheres

The two hemispheres are divided into four lobes: the frontal, parietal, temporal, and occipital

Through years of study scientists have determined how and where various functions are localized in the brain.

The Brain