Chevromist: Canine Anatomy

Dogs are classed as mammals. This means that, like humans, they give birth to live young, which the females feed with milk and care for until they are old enough to look after themselves.

Dogs are also omnivores, which means that they can survive on meat and/or vegetable based diets. In the wild, dogs and their canine relatives are predators – often hunting in packs to provide food for the group. As pack animals, body language is very important for communication, so a dog’s anatomy has adapted to the role as both hunter and member of the pack.

The skeleton
• Provides the internal supporting structure for the body, especially the spine, hind limbs and fore legs.

• Protects delicate internal organs.
o The skull protects the brain and other sensory organs such as the eyes.
o The pelvis protects lower abdominal organs such as the uterus.
o The vertebrae (spine) protect the nerves that form the spinal cord.
o The ribs protect all the organs of the chest such as the heart and lungs.

• Enables movement. When the muscles that are attached to the bones around a joint contract, the bones move and the joints bend. It is the strength of the muscles in the dog’s hind limbs that allows them to jump high and chase prey.

• Produces blood cells.

• Stores important minerals such as calcium and phosphorus.

Although dogs have roughly the same number of bones as humans, they are shaped differently and have become specially adapted to meet their needs as predators. Strong jaws and limbs enable them to hunt large or small prey, whilst their tails are important in helping them to stay balanced – as well as aiding communication.

The skin
The skin actually forms the largest organ of an animal’s body. The skin is mainly responsible for protecting the body from infection, physical damage and the loss of heat and water.

A dog’s skin is covered in hair – although some dogs are bred to be hairless. Hair also helps to keep the dog’s body warm and to prevent damage to the skin. It can also react to the presence of a threat by standing on end, making the dog appear larger.

Some parts of the skin or hair have evolved to perform particular functions.

• The feet are covered by pads of skin that is much thicker than the skin on the rest of the body.

• The whiskers are longer and thicker than normal hairs, and are very sensitive to touch. Apart from the face, they are found on several places on the body and provide dogs with information about their surroundings.

The senses

Dogs have excellent hearing and can detect noises well beyond the range of human ears, although some breeds have better hearing than others. The shape and orientation of a dog’s ears vary, depending on the breed and what it was bred to do. Wolves, thought to be the ancestors of the domestic dog, have relatively large ears that they can move around. This allows them to pinpoint the origin of faint sounds. The ears also work with the brain to help maintain balance.

A dog’s vision has become well adapted to the function of hunting, particularly of small, fast-moving animals. The field of vision will vary depending on the breed. A greyhound, for example, has a greater field of vision than a Pekingese, whose eyes are set more forward facing in the skull. Although it is commonly thought that dogs see only in black and white, the latest thinking suggests otherwise. The structure of their eyes, and the fact they are natural daytime hunters, leads many canine experts to believe that dogs have full colour vision, albeit that they are probably better with some colours than others. Behavioural tests seem to show that dogs are most sensitive to red and can also distinguish green and yellow.

Scent is very important to dogs and their sense of smell is very highly developed, far more so than that of humans. Dogs use scents for various functions including marking territory, recognising other animals, and communicating with other dogs. Smell is detected by nerve endings in the nose and interpreted by the brain.

Compared to humans, a dog’s sense of taste is not very highly developed. The tongue is covered in taste buds allowing dogs to detect tastes that are sour, bitter salty, and sweet.

The respiratory system
The respiratory system carries air from the nose to the small chambers in the lungs (called ‘lung alveoli’). It is responsible for warming and filtering the air and transporting it to the lungs, where oxygen is taken in by the body and exchanged with carbon dioxide that gets breathed out.

The cardiovascular system
The cardiovascular system is made up of the heart, veins and arteries, as well as smaller blood vessels. It is responsible for the transport of blood in the body, carrying oxygen, nutrients, blood cells and waste products to where they are needed. Blood is also important for maintaining body heat.

The urinary system
The primary function of the urinary system is to control the body’s water balance and remove toxins. The kidneys filter the blood and remove excess water and toxins, which are then passed into the bladder and stored until the dog urinates. Chemicals in the urine can be used as a method of scent communication between dogs.

The digestive system
The digestive system is responsible for the intake of food into the body, breaking it down and absorbing all the nutrients before expelling indigestible food and other waste products from the body. Digestion starts in the mouth, where dogs take in food and begin to chew. Their teeth are specially adapted to the role of hunter, with large, sharp canines developed for grabbing prey. As omnivores, they also use the flatter back teeth to chew their food.

The reproductive system
Male dogs have two testicles. In an uncastrated male, they should descend into the scrotal sac by the time the puppy is 8 to 10 weeks of age. With adults, they will sit between the hind legs. Females, meanwhile, mature any time from 6 months old and come onto ‘heat’ every 6 to 12 months. This is usually be triggered by external factors, such as the season.

The nervous system
This is responsible for carrying messages from the body to the brain via nerves and the spinal cord. The brain is responsible for controlling all the processes in the body, from breathing to temperature control. The endocrine system The endocrine system consists of several glands that produce hormones. These glands include the thyroid gland, the pancreas and the ovaries and testicles.

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