2The 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.
3Mechanical DigestionDigestion includes the mechanical and chemical breakdown of food into nutrientsMechanical digestion begins when the teeth cut and grind food.The tongue also aids in mechanical digestion
4Chemical DigestionSaliva is produced by the salivary glands to begin chemical digestion of food.Salivary amylase is the chemical in saliva that begins the chemical digestionThe pharynx is an open area that begins at the back of the mouth, and serves as a passageway for both air and food.
5food is then forced from the pharynx into the esophagus.
6The 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.
7This process forms a mixture called chyme. MechanicalChemicalThe 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.This process forms a mixture called chyme.
8The other organs that help digestion are the liver, gallbladder, and pancreas.
9The Liver The liver produces bile, which is vital to digesting fats. It also stores glucose, makes proteins, and breaks down toxic substances.
10Gall BladderThe gallbladder is a saclike organ that stores and concentrates bile.The gallbladder releases the bile through a common bile duct into the small intestine.
11Pancreas 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
12Small IntestineThe chyme from the stomach will further break down in the small intestine.Absorption occurs mostly in the small intestine.
13Once 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.
15The 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.
17The second division is the peripheral nervous system that sends information to and from the central nervous system.
18Somatic 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.
19Somatic system also relays the signals in reflexes. Reflexes are involuntary and often self-protective movements. An example is the patellar, or knee- jerk, reflex.
20Autonomic Nervous System The autonomic nervous system controls internal body conditions by regulating smooth muscles in blood vessels and organs.
21Two SubdivisionsThe 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.
23The BrainCerebrum- largest part of the brain, divided into two hemispheresThe two hemispheres are divided into four lobes: the frontal, parietal, temporal, and occipitalThrough years of study scientists have determined how and where various functions are localized in the brain.