The dog is a mammal belonging to the order Carnivora their bodies have 11 systems similar to humans who belong to the primate order. The body is composed of several functional units called organ systems. Each organ system is a collection of organs that function together to perform a specific job to keep the body healthy. Tissues, and the microscopic units of tissues, the cells, are the building blocks of organs. Tissues include materials such as muscles, nerves and epithelia and connective tissues that bind the other tissues together.

Organ Systems:

1. Cardiovascular System includes the heart and blood vessels. The cardiovascular system performs the function of pumping and carrying blood to the rest of the body. The heart of all mammals contains four chambers. The upper left and right chambers are identified as the atrium, the lower left and right chambers are identified as the ventricles. Blood flows though the veins of a dogs body into the right atrium. Blood pools in the atrium until pumped into the right ventricle and is then pumped into a dogs lungs. Oxygen enters the blood from the lungs and carbon dioxide is expelled out of the blood into the lungs. The blood flows from the lungs into the left atrium where again pools before moving into the left ventricle. The left ventricle is capable of pumping blood through the entire cardio vascular system. Therefore the left ventricle muscle is the largest heart muscle, its function has the greatest effect on a dog’s cardiovascular health.

2. The lymphatic system includes the lymph nodes and lymph vessels. The lymphatic system is part of the immune system that helps the body fight off disease. The lymphatic system also works with the cardiovascular system to return fluids that escape from the blood vessels back into the blood stream.

3. Digestive System includes the mouth, teeth, salivary glands, esophagus, stomach, large intestine, small intestine, pancreas, liver and gall bladder. The digestive system absorbs and digests food and eliminates solid wastes from the body. A dogs mouth and teeth are designed to bit and tear off, their jaws are hinged allowing the opening and closing but not side to side movement, there is no need for a dog to chew. Healthy gums are firm and pink, black, or spotted, just like the dog’s skin. Young dogs have smooth white teeth that tend to darken with age. Puppies have 23 baby teeth and adults have around 42 permanent teeth, depending on the breed. As adult teeth come in, they push baby teeth out of the mouth. A dog’s saliva does not contain the digestive enzymes a human does and therefore does not assist in the digestive process. A dogs stomach contains a high level hydrochloric acid allowing them do digest large chunks of food. The liver is the largest organ in the canine body and consists of six lobes divided into three regions. Located in the forward part of the abdomen near the diaphragm, This organ receives nutrients through the portal vein and through the hepatic artery. Approximately one third of the blood flowing into the liver travels through the hepatic artery while approximately two thirds travels through the portal vein. While the nutrients that travel through the portal vein originate in the digestive tract, the blood entering the liver by the hepatic artery comes from the heart.

4. Integumentary Systemis the skin and fur that cover the animal’s body. The skin protects the underlying organs. The fur helps insulate against heat loss. Dogs and do not sweat through their skin. They only sweat from their footpads and nose. They lose water by panting rather than sweating.

5. Musculoskeletal System includes all the muscles, bones and joints. The mobility of dogs relies heavily on their synovial fluid. .Synovial fluid has two main functions: to aid in the nutrition of articular cartilage by acting as a transport medium for nutritional substances, such as glucose, and to aid in the mechanical function of joints by lubrication of the articulating surfaces. The fluid contains a high concentration of hyaluronic acid. Supplements containing the nutrients which aid a dogs joints and cartilage health can significantly improve a dogs mobility.

6. The respiratory system includes the mouth, nose, trachea, lungs and smaller airways (bronchi and bronchioles). The respiratory system is responsible for taking in oxygen and eliminating waste gases like carbon dioxide. Because dogs and cats do not sweat through the skin, the respiratory system also plays an important role in regulation of temperature.

7. The urogenital system includes the kidneys, ureters, urinary bladder, urethra and the genital organs of box sexes. The urinary system is responsible for removing waste products from blood and eliminating them as urine. The genital organs are involved in reproduction.

8. The nervous system includes the brain, spinal cord and all the nerves that communicate between tissues and the brain and spinal cord.

9. Endocrine System includes several glands that produce hormones. Hormones are substances that travel through the blood stream and affect other organs. Endocrine organs include the thyroid glands, parathyroid glands, adrenal glands and part of the pancreas. Hormones regulate many functions of an organism, including mood, growth and development, tissue function, and metabolism.
The thyroid gland — two small butterfly-shaped lobes located in the neck has a number of functions in dogs body, most importantly regulating a dog’s metabolism. Many dog health issues stem from the thyroid not functioning properly, the most common disorder of this gland is hypothyroidism, the thyroid gland is underactive, and unable to secrete enough thyroid hormone. This, in turn, decreases your dog’s metabolism. Overactive thyroid glands in the dog are rare and are usually associated with cancer. The hormones T3 and T4 produced by the thyroid are very basic and critical to almost all animal life.

10. Sensory System allow the animal to interact with its environment; sight, taste, smell and hearing. The ear has 3 major parts:
1 outer ear
2 middle ear
3 inner ear
The outer ear consists of the ear flap (also called the pinna) which can be upright (a prick ear) or floppy. The ear flap funnels sound into the ear canal. Unlike humans that have a very short ear canal, dogs have a long narrow ear canal that makes almost a 90 degree bend as it travels to the deeper parts of the ear.
The outer ear cannel is separated from the middle ear by a thin membrane called the eardrum or tympanic membrane. The ear drum is very fragile and can be damaged by ear disease or during ear cleaning. The middle ear consists of 3 small bones, an air filled cavity called the bulla and a thin tube (the eustachian tube) leading from the bulla to the back of the mouth.
The inner ear connects to the brain and contains nerves and centers for balance and hearing.

11. The hematopoietic system includes the bone marrow which is located inside the bones. Three types of blood cells are made in the bone marrow: white blood cells that fight infection, red blood cells that carry oxygen and platelets that are part of the blood clotting process.