Digestive System

The Central Nervous System

• The brain is the main switching area of the central nervous system
• The brain is divided into: Cerebrum (responsible for voluntary activities), Cerebellum (coordinates muscle movement and balance), and Brain Stem (consists of the pons and the medulla oblongata)
• The left half of the brain controls the right half of the body and vice-versa
• The human brain is more powerful and complicated than the world’s biggest computer
• The human body has over 100 billion neurons
• The brain can receive over 100,000 signals per second
• Messages whiz through the nerves at up to 270 mph

The Peripheral Nervous System

• Receives information from the environment and relays commands from the CNS to the organs and glands

The Endocrine System

• Regulates body activities, temperature, metabolism, development, and reproduction
• Maintains homeostasis and regulates other organ systems
• The body makes over 20 hormones, each with a different job to do
• Hormones can affect the way a person feels
• As a person ages, the body makes less of some hormones
• Major endocrine glands: hypothalamus, pituitary, thyroid, parathyroid, thymus, adrenal, pancreas, ovary (female), testis (male), and pineal

Glands and Hormones

• Pineal gland: produces melatonin, controls sleep and wake cycle
• Thyroid gland: produces thyroxine, controls appetite and metabolism
• Adrenal gland: produces adrenaline, deals with stressful situations
• Thymus gland: produces thymosin, involved in T-cell development (fight diseases)
• Ovary: produces estrogen, involved in female reproduction
• Testis: produces testosterone, involved in male reproduction

The Digestive System

• Function: to change food into simpler molecules that can be absorbed into bloodstream and used by the body
• Major organs: mouth, esophagus, stomach, small intestine, large intestine
• Mouth: where food enters the body
• Esophagus: muscular tube that connects throat to stomach, moves food down by squeezing (peristalsis)
• Stomach: muscular bag where chemical and mechanical digestion continue, food stays here ~4 hours, changes to chyme
• Small intestine: tube nearly 7 meters long where digestive juices from liver and pancreas are added, absorbs small nutrient molecules
• Large intestine: absorbs water from undigested food, where unabsorbed materials become more solid
• Rectum: where solid wastes (feces) are stored
• Anus: muscles control the release of solid wastes from the body

The Muscular System

• Function: movement
• Major muscle types: skeletal (attached to bones for voluntary actions), smooth (found in the digestive tract and blood vessels for involuntary actions), and cardiac (heart muscle cells are involuntary)
• Skeletal muscles work in opposing pairs
• Muscles can only pull – they cannot push
• Energy is stored in the muscles in a chemical called ATP
• Lactic acid is released when the muscles are overworked and lack O2, making the muscles hurt or ache
• Muscles are attached to bones by tendons
• The biggest muscles in the body are the gluteus maximus muscles (buttocks), but the muscle that can exert the most force is the masseter (jaw muscle)

The Respiratory System

• Major structures: lungs, nose, mouth, trachea
• Functions: moves air into and out of lungs, controls gas exchange between blood and lungs
• Bronchi branch to air sacs known as alveoli, where gas exchange occurs
• The respiratory system links to the circulatory system to provide cells with oxygen and remove carbon dioxide

The Excretory System

• Functions: removes cellular wastes from blood and the body
• Major structures: kidneys, urinary bladder, ureters, urethra, skin, lungs
• Wastes and water diffuse out of the blood into filters in the kidney. The kidneys form the liquid waste, URINE.