Dogs are descendents of wolves that roamed wild over much of the world in ancient times. People have associated with dogs for thousands of years, originally domesticating them as beasts of burden and guard animals. Today, there are still many working breeds, and the service roles of dogs have greatly expanded to include assisting disabled individuals (for example, those with visual or hearing impairments), working with human law enforcement by sniffing out illegal drugs and other contraband, locating survivors in search-and-rescue missions, and even using their incredible sense of smell for early detection of cancer cells in human patients. Of course, the primary role of most dogs is that of loyal companion.
Choosing the dog that is right for you and your family is very important. The large variety of breeds means that dogs come in all sizes, shapes, and colors, and have a range of temperaments. Many dog breeds have been developed for specific purposes and behaviors. A mismatch can result in unnecessary stress and lead to behavioral problems, which can be difficult to correct.
In addition to feeding and exercising your dog, other aspects of general care are needed to keep your dog healthy throughout its life. These include routine veterinary care for vaccinations, parasite control, and dental care; grooming; and protection from household hazards.
Behavioral medicine is the scientific study of everything animals do, whether the animals are insects, birds, mammals, fish, or people. The field of animal behavior is concerned with understanding the causes, functions, development, and evolution of behavior. Behavior refers to the actions or reactions of an organism. Behavior is usually in relation to the environment, and is controlled by the endocrine and nervous systems. The complexity of animal behavior is related to the complexity of its nervous system. Generally, animals with complex nervous systems have a greater capacity to learn new responses and thus adjust their behavior.
Blood cells form and develop mostly in the bone marrow, that is, the tissue located in the cavities of bones. Blood performs a variety of important functions as it circulates throughout the body. It delivers oxygen and vital nutrients (such as vitamins, minerals, fats, and sugars) to the tissues. It carries carbon dioxide to the lungs to be exhaled and waste products to the kidneys and liver to be eliminated from the body. It transports hormones, which are chemical messengers, to various parts of the body, allowing those parts to communicate with each other. Blood also includes cells that fight infection and control bleeding.
The musculoskeletal system includes the bones, cartilage, muscles, ligaments, joints, tendons, and other connective tissue. It supports the body, permits movement, and protects the vital organs. Because many other body systems (including the nervous system, blood vessels, and skin) are interrelated, disorders of one of these systems may also affect the musculoskeletal system.
The nervous system is made up of the brain, spinal cord, and several different kinds of nerves that are found throughout the body. These create complex circuits through which animals experience and respond to sensations.
The digestive system includes all of the organs that are involved in taking in and processing food. It begins with the mouth and includes the esophagus, stomach, liver, pancreas, intestines, rectum, and anus.
The eyes of animals, including dogs' eyes, function much like yours. Animals also develop many of the same eye problems that people can have, including cataracts, glaucoma, and other problems. It is important for your dog to receive good eye care to protect its sight and allow it to interact comfortably with its environment.
The cardiovascular system includes the heart and the blood vessels (the veins and the arteries). The function of the heart is to pump blood. The right side of the heart pumps blood to the lungs, where oxygen is added to the blood and carbon dioxide is removed from it. The left side pumps blood to the rest of the body, where oxygen and nutrients are delivered to tissues, and waste products (including carbon dioxide) are transferred to the blood for removal by other organs (such as the lungs and kidneys). The heart is a hollow, muscular organ which, in mammals and birds, is divided into 4 chambers. The muscular tissue is called the myocardium. There are upper chambers on both the left and ride sides of the heart called the left and the right atria (the plural form of atrium). There are also 2 lower chambers called the left and right ventricles.
Hormones are chemical messengers that have many different functions. The effects of hormones in the body are wide-ranging and varied. Some familiar examples of hormones include insulin, which is important in the development of diabetes, and estrogen and progesterone, which are involved in the female reproductive cycle.
The immune system consists of a network of white blood cells, antibodies, and other substances that fight off infections and reject foreign proteins ( All.see table Specialized Cells and Molecules of the Immune System). In addition, the immune system includes several organs. Some, such as the thymus gland and the bone marrow, are the sites where white blood cells are produced. Others, including the spleen and lymph nodes, trap microorganisms and foreign substances and provide a place for immune system cells to collect, interact with each other and with foreign substances, and generate an immune response.
The urinary system or tract includes the kidneys, the ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube through which urine exits the body). The urinary system has several important functions. It gets rid of the waste products that are created when food is transformed into energy. It also maintains the correct balance of water and electrolytes (salts) within the body’s cells. Another key function is the production of hormones called erythropoietin and renin, which are important in maintaining healthy blood pressure, producing blood cells, and absorbing salt correctly. Finally, the urinary system processes vitamin D.
The respiratory system consists of the large and small airways and the lungs. When a dog breathes air in through its nose or mouth, the air travels down the trachea, which divides into the tubes known as the right and left bronchi, then into the smaller airways called bronchioles in the lungs. The bronchioles end in the small sacs called alveoli, where the barrier between the air and the blood is a thin membrane.
Metabolism refers to all processes in the body that break down and convert ingested substances to provide the energy and nutrients needed to sustain life. Foods, liquids, and drugs all generally undergo metabolic processes within the body. Many foods are complex materials that need to be broken down into simpler substances, which in turn become “building blocks” for the body to use as needed. For example, protein is broken down into amino acids, which are used in several metabolic reactions. Enzymes made by the body are needed for many metabolic processes to occur. Whenever the function of an enzyme is affected, a metabolic disorder can develop. Metabolic disorders are important because they affect energy production or damage tissues. They may be genetic (inherited) or acquired. Acquired metabolic disorders are more common and significant.
The reproductive system is the group of organs that produce offspring. In both males and females, the reproductive system is composed of primary sex organs and primary regulatory centers. The primary sex organs are the testes and genital tract in males and the ovaries, fallopian tubes, and uterus in females. The primary regulatory centers are in the brain (the pituitary gland and hypothalamus). They control the production of hormones that in turn influence the function of the primary sex organs.
The skin is the largest organ of your dog’s body. It provides a protective barrier against the environment, regulates temperature, and gives your dog its sense of touch. Depending on the species and age, the skin may be 12 to 24% of a dog’s body weight. The skin has 3 major layers: the epidermis or outermost layer, the dermis or middle layer, and subcutis or innermost layer. Other important parts of the skin include skin appendages (such as hair and claws) and subcutaneous muscles and fat.
There are many disorders that can affect multiple parts of the body. These may be caused by bacteria, viruses, poisonous or toxic substances in the environment, and other health hazards. Disorders affecting multiple body systems can also be inherited or develop while the animal is still in the womb. Diseases or conditions that involve multiple organ systems may also be described as systemic or generalized.