# Teaching Elementary School Health Education/Growth and Development/I Will Keep My Body Systems Healthy
## What Is A Body System?

A body system is a groups of organs that work together to perform a main body function.

## The Nervous System

A nervous system carries messages to and from the brain and spinal cord and all other parts of the body. It is composed of two divisions: central nervous system and the peripheral nervous system. The central nervous system consists of the brain and the spinal cord. The peripheral nervous system consists of the nerves that branch out from the central nervous system to the muscles, skin, internal organs, and glands.
The brain is a mass of nerve tissue that acts as the control center of the body. It has three major parts: the cerebrum, the cerebellum, and the brain stem.
The spinal cord is a thick column of nerve cells that extends from the brain down through the spinal column. It carries messages between the brain and body.
The nervous system is composed of cells called neurons. A neuron is a nerve cell that is the structural and functional unit of the nervous system. It consists of a cell body, an axon, and dendrites. An axon is an elongated fiber that carries impulses away from the cell body to the dendrites of another neuron. Dendrites are branching fibers that receive impulses and carry them to the cell body.
A reflex action is an involuntary action in which a message is sent to the brain via the spinal cord, is interpreted, and is responded to immediately.

## The Cardiovascular System

The cardiovascular system transports nutrients, gases, hormones, and cellular waste products throughout the body. The cardiovascular systems consists of blood, blood vessels, and heart.
The blood carries nutrients, oxygen, carbon dioxide, and cellular waste products to and from cells. The average adult has about ten pints of blood. Blood is composed of plasma and blood cells: red and white blood cells. Plasma is the liquid component of blood that carries blood cells and dissolved materials. Red blood cells transport oxygen to body cells and remove carbon dioxide from body cells. Red blood cells contain large quantities of hemoglobin (iron-rich protein). White blood cells attack, surround, and destroy pathogens that enter the body and prevent them from causing infection.
There are three major parts of blood vessels: arteries, veins, and capillaries. The arteries carry the blood away from the heart. A vein is a blood vessel that returns blood to the heart. A capillary is a tiny blood vessel that connects arteries and veins.
The heart is a four-chambered muscle that pumps blood throughout the body. The chambers are called the atria and ventricles. An atrium is one of the upper two chambers of the heart. A ventricle is one of the lower two chambers of the heart. A vena cava is one of two large veins that returns blood rich in carbon dioxide to the right atrium. The aorta is the main artery in the body. It branches into smaller arteries through which blood flows to all parts of the body.
Heart Rate is the number of times the heart contracts each minute. Pulseis the surge of blood that results from contractions of the heart. Blood pressure is the force of blood against the artery walls.

## Immune System

The immune system removes harmful organisms from the blood and combats pathogens. It is composed of lymph, lymph nodes, lymph vessels, thymus, and spleen.
Lymph is a clear liquid that surrounds body cells and circulates in lymph vessels. A lymph node is a structure that filters and destroys pathogens. The spleen is an organ on the left side of the abdomen that filters foreign matter from the blood and lymph.
'Immunity' is the body's resistance to disease-causing agents. An antibody is a special protein that helps fight infection.
The thymus gland is a gland that causes white blood cells to become T cells. A t-cell is a white blood cell that destroys pathogens. A B Cell is a white blood cell that produces antibodies.

## Respiratory System

The respiratory system provides body cells with oxygen and removes carbon dioxide that cells produces as waste. Air enters the respiratory system through the nose or mouth during inhalation. Mucus in the nasal passages and sinuses warms and moistens the air and traps dust particles and pathogens.
Air moves from the nose or mouth through the pharynx to the trachea. The pharynx is the throat. the epiglottis is a flap that covers the entrance to the trachea when a person swallows foods or beverages. The trachea is a tube through which air moves to the lungs.
The air then enters the bronchi which are two tubes through which air moves to the lungs. The lungs are the main organs of the respiratory system. The bronchioles are small tubes divided into alveoli. The alveoli are microscopic air sacs.

## Skeletal System

The skeletal system serves as a support framework, protects vital organs, works with muscles to produce movement, and produces blood cells. There are 206 bones in the skeletal system of an adult.
A bone is the structural material of the skeletal system. Periosteum is a thin sheet of outer tissue that covers bone. It contains nerves and blood vessels. Bone marrow is the soft tissue in the hollow center area of most bones where red blood cells are produced.
Cartilage is a soft, connective tissue on the ends of some bones. It acts as a cushion where bones meet. A ligament is a tough fiber that connects bones together. A joint is the point where two bones meet.

## Muscular System

The muscular system consists of muscles that provide motion and maintain posture. There are more than 600 muscles in the body. Muscles are divided into two major groups. A voluntary muscle is a muscle a person can control. An involuntary muscle is a muscle that functions without the person's control.
There are three types of muscles tissues in the body: smooth, skeletal, and cardiac. Smooth muscle is involuntary muscle tissue found in many internal organs. Skeletal muscle is muscle tissue that is attached to the bone. It helps your body move. Cardiac muscle is a unique kind of muscle tissue found only in the heart. It differs from other tissues in its structure. Its contractions are generated by nerve stimulation.
A tendon is tough tissue fiber that attaches muscle to bones.

## Endocrine System

The endocrine system consists of glands that control many of the body's activities by producing hormones. A gland is a group of cells, or an organ, that secretes hormones. A hormone is a chemical messenger that is released directly into the bloodstream.
The pituitary gland is an endocrine gland that produces hormones that control growth and other glands. It is located below the hypothalamus in the brain and is about the size of a pea. The pituitary hormones do the following:
* regulate the development of bones and muscles
* affect the reproductive organs
* affect the functioning of the kidney, the adrenal gland, and the thyroid glands
* stimulate the uterus to contract during childbirth
The thyroid gland is an endocrine gland that produces thyroxine. Thyroxine is a hormone that controls metabolism and calcium balance in the body. Metabolism is the rate at which food is converted into energy in body cells.
The parathyroid glands are endocrine glands that secrete hormones that control the amount of calcium and phosphorus in the body.
The pancreas is a gland that produces digestive enzymes and insulin. Insulin is a hormone that regulates the blood sugar level. If the person fails to produce enough insulin, a person develops diabetes mellitus. Diabetes , or diabetes millitus, is a disease in which the body produces little or no insulin.
The adrenal glands are endocrine glands that secrete several hormones, including adrenaline. Adrenaline is a hormone that prepares the body to react during times of stress or i an emergency. The two adrenal glands are located on the kidneys.
The ovaries are female reproductive glands that produce ova and estrogen. Ova are egg cells, or female reproductive cells.Estrogen is a hormone produced by the ovaries that stimulates the development of female secondary sex characteristics and affects the menstrual cycle.
The testes are male reproductive glands that produce sperm cells and testosterone. Testosterone is a hormone that produces the male secondary sex characteristics.

## Digestive System

The digestive system breaks down food into nutrients that can be used by the body. It allows nutrients to be absorbed by body cells and eliminates waste from the body. Digestion is the process by which food is changed so that it can be absorbed by the body's cells.
The mouth contains salivary glands that release saliva, which contains a chemical that begins the digestion of carbohydrates. Saliva is a fluid that helps soften food so that it can be swallowed more easily.
When food is swallows, it moves into the esophagus, a tube connecting the mouth to the stomach. Food passes to the stomach by the process of peristalsis, a series of involuntary muscle contractions.
The stomach is an organ that releases acids and juices that mix with the food and produces a thick paste called chyme.
The small intestine a coiled tube in which the greatest amount of digestion and absorption takes place.
The liver is a gland that releases bile to help break down fats, maintain blood sugar level, and filter poisonous wastes.
The gall bladder is an organ that stores bile.
The pancreas is a gland that produces digestive enzymes and insulin.
The large intestine is a tube extending from the small intestine in which undigested food is prepared for elimination from the body.
The rectum is a short tube at the end of the large intestine that stores wastes temporarily.
The anus is the opening to the outside of the body at the end of the rectum.

## Urinary System

The urinary system removes liquid wastes from the body and maintains the body's water balance. The organs of the urinary system are the kidneys, ureters, bladder, and urethra.
A kidney is an organ that filters the blood and excretes waste products and excess water in the form of urine.
A ureter is a narrow tube that connects the kidneys to the urinary bladder. The urinary bladder is a muscular sac that stores urine.
The urethra is a narrow tube extending from the urinary bladder to the outside of the body through which urine passes out of the body.

## Integumentary System

The integumentary system covers and protects the body and consists of skin, glands associated with the skin, hair, and nails. The skin is the largest organ in the body.
Melanin is a pigment that gives the skin its color and protects the body from ultraviolet rays of the sun.
The epidermis is the outer layer of skin cells. These cells are constantly shed and replaced. The dermis is a thick layer of cells below the epidermis that contains sweat glands, hair follicles, sebaceous (oil) glands, blood vessels, and nerves.
A sweat gland is a gland that helps the body get rid of wastes, such as salt. A sebaceous gland is a small oil-producing gland that helps protect the skin. Sebum is the oil produced by sebaceous glands.
A wart is a contagious growth that forms on the top layer of skin.
Ringworm is a skin condition that causes small, red, ring-shaped marks on the skin.
Keratin is a tough protein that makes up nails and hair. Hair is a threadlike structure consisting of dead cells filled with keratin.