Since you have taken up the job of nurturing a dog, you are required to be aware of how the body of your pet works.
In order to take proper care you are advised to gain some knowledge of the dog internal organ systems and how do they perform their functions.
If you are planning to keep a pet dog the following information on dog internal organ systems would be of great help for you.
Information of Dog Internal Organ Systems

• Dog Muscular System - There are mainly nine types of muscles that are located in the dorsal region, the head, neck, thorax, pelvic region, abdomen, trunk, tail and thoracic extremities.
  The muscular system of dog consists of mainly two types of muscles, voluntary and involuntary muscles.
  The voluntary muscles are usually attached to the bones of the limbs and so they are used for movement.
  The involuntary bones generally are associated with the vital life supporting organs like the heart, liver and such.
  Unlike voluntary muscles these types of muscles do not work according to the will of the animal.
  There is another kind of muscle that is responsible for controlling the whiskers and the hair of dog's coat.
  
• Dog Respiratory System - In dogs the oxygen enters the lungs through the nasal canals, larynx and the trachea.
  The right lung is bit larger than the left one.
  The entire lung cavity is separated from the abdomen by a thin membrane known as the diaphragm.
  
• Dog Digestive System - The digestive system turns the food into soluble material for the body to absorb.
  When the food is first taken in, it gets bind up with the saliva and travels down through the esophagus to the stomach.
  From the stomach the food travels to the intestines.
  In the intestines the food is filtered to absorb the nutrients and other essential components for the body.
  The small intestine is connected to the pancreas and the liver while the large intestine is connected to the anus of the dog.
  The left over food material gets excreted through the anus.
  
• Urinary System - The dog urinary system helps the body to get rid of the insoluble wastes.
  The excreted liquid gets stored in the bladder.
  When the bladder becomes full, the fluid is then excreted out though the urethra.
  

Apart from the above mentioned organ systems; dog organ system also consists of reproductive system.
There are also two anal glands located on either side of their anus.
They are primarily used for identifying the feces of other dogs.