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Table of Contents


  1. The Skeletal System
  2. The Muscular System
  3. The Circulatory System
  4. The Respiratory System
  5. The Nervous System
  6. The Endocrine System
  7. The Urinary System
  8. The Digestive System
  9. The Reproductive System




appendicular skeleton

Autonomic Nervous System (ANS)

axial skeleton


Central Nervous System (CNS)


mechanical energy

parasympathetic nervous system

Peripheral Nervous System

sympathetic nervous system



A Simple Anatomy Lesson


indentThis is a short lesson on the anatomy of the human body. The body has nine major body systems working together to keep the body healthy. There are a lot of smaller and important systems in the body, but everyone should know the nine major ones well.

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The Skeletal System

Bones make up the Skeletal System. There are 206 bones in the body.

Three things bones do:

  1. move
  2. shape
  3. protect

This translates to:

  1. Bones help move.

  2. Bones give a body shape.

  3. Bones protect the body's organs.

All together they are called a skeleton. A skeleton has two parts. The two parts are axial and appendicular.

The axial skeleton is the head and trunk of the skeleton.

The appendicular skeleton is made up the body's arms and legs (limbs), or extremities


axial skeleton
the skeletal head and trunk

appendicular skeleton
the skeletal limbs

arms and legs
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The Muscular System

The body has more than 600 muscles. Muscles comprise the body's Muscular System.

The three types of muscles:

  1. striated
  2. smooth
  3. cardiac

  1. Striated muscle is attached to bones.

  2. Smooth muscle lines organs.

  3. Cardiac muscle works in the heart.

   Muscles produce movement, maintain posture, and relieve the tensions of structures in the body from activity. Muscles have cells that have the ability to contract. Some muscles you control, like when you move your arms or legs. Others you do not control, like when your heart beats. Muscles convert energy from a body's chemical reactions into mechanical energy.


mechanical energy
converted energy from a body's chemical reactions
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The Circulatory System

   The Circulatory System is made up of blood, blood vessels, and the heart. Blood vessels are veins and arteries. Also, there are very important smaller blood vessels called arterioles and capillaries.

The circulatory system carries oxygen to all the parts of the body.

The circulatory system carries blood and nutrients to make a body strong.

The circulatory system's veins carry blood toward the heart.

The circulatory system's arteries carry blood away from the heart.

   The heart pumps the deoxygenated blood to the lungs. The new oxygenated blood returns to the heart and it contracts, pumping blood out to the body. The direction of blood flow is controlled the heart valves.


large blood vessels
smaller blood vessels
a small artery
microscopic blood vessels


The Respiratory System

   The respiratory system is the body's system to breathe. The respiratory system is made up of the lungs and the windpipe, or the pharynx, larynx, and trachea. The nasal cavity, bronchi, and diaphragm are also part of the respiratory system. There are smaller organs called bronchioles and alveoli.

There are two lungs in the chest cavity, one on each side of the heart.

When you breathe in, you inhale oxygen.

When you exhale, you breathe out again and carbon dioxide is released into your lungs.



The Nervous System

The network of nerve cells in the body is called the nervous system.

The nervous system sends messages from one part of the body to another. Its main centers are the brain and the spinal cord. Together they are called the Central Nervous System.

The Autonomic Nervous System (ANS) which, together with the cranial and spinal nerves, directs the body functions that you do not control, like the heart beat. This system in the body is concerned with its regulation of activity of cardiac muscles, smooth muscles, and glands. It is divided into two parts called the sympathetic and parasympathetic systems.

The Peripheral Nervous System (PNS) is all parts of the nervous system outside of the central nervous system.


Central Nervous System (CNS)
the main centers of the nervous system, the brain and spinal cord
Autonomic Nervous System (ANS)
the two parts of the nervous system called the sympathetic and the parasympathetic systems
sympathetic nervous system
the part of the Autonomic Nervous System that is made of fibers which arise from the cell bodies (or the preganglionic fibers) in the thoracolumbar spinal cord (the thoracic and first three lumbar segments of the spinal cord); the postganglionic fibers are distributed to the heart, smooth muscle, and glands of the entire body
parasympathetic nervous system
the part of the Autonomic Nervous System that is made of fibers which arise from the cell bodies in the craniosacral part of the ANS; by these preganglionic fibers it innervates the heart, smooth muscle, and glands of head, neck, thoracic, abdominal, and pelvic viscera
Peripheral Nervous System
all the nerves and ganglia outside of the brain and spinal cord


The Endocrine System

The gland system in the body is called the Endocrine System.

Glands produce hormones. Hormones are chemicals that help other body systems to work. Glands are made up of the thyroid gland, pituitary gland, adrenal gland, part of the pancreas, and the gonads. It also includes the parathyroid and reproduction glands.

The endocrine system has a thyroid gland.

The pituitary gland is the master endocrine gland. Its other name is the hypophysis. It produces hormones that stimulate and regulate growth.

The endocrine system has an adrenal gland.

Part of the pancreas is within the endocrine system.

The endocrine system has gonads.

The endocrine system has a parathyroid.

The endocrine system has reproduction glands.



The Urinary System

   The kidneys and bladder make up the urinary system.

Two kidneys filter waste products from the blood. In other words, kidneys send waste and water to the bladder. When you have to urinate the bladder tells you by urging you to relieve yourself.



The Digestive System

The digestive system breaks down food into nutrients.
Nutrients are used by the blood.

The digestive system is made up of the mouth, esophagus, stomach, and intestines.

The digestive system has a mouth.

The digestive system has an esophagus.

The digestive system has a stomach.

The digestive system has intestines.

Chewing is a part of digestion and takes place in the mouth by the teeth. Food travels through the esophagus to the stomach. Most of the digestion takes place in the stomach and small intestine. The intestines are both small and large.



The Reproductive System

When humans grow to adulthood, they have a developed reproduction system. Bodies need this system to carry on the next generation, or to have babies.