Anatomy: Small Animal
Small Animal Anatomy
Welcome to small animal anatomy! We will be going through some of the major body systems of dogs and cats, such as the cardiovascular system, the musculo-skeletal system, the central nervous system, the digestive system and the respiratory system. An interesting fact about cat species is that on their tongue they have very hard structures called conical papillae. If a cat has ever licked you, it feels kind of like scratching, and these papillae are why. They are an adaptation to give cats the ability to lick meat off of bones!
The heart is the organ that pumps blood throughout the body. Blood flows through the heart in a specific direction. Deoxygenated blood returning from the body enters the heart via the cranial and caudal vena cava into the right atrium of the heart. Blood then moves through the right atrioventricular valve (also called the tricuspid valve) into the right ventricle of the heart. This blood is then pumped through the pulmonary valve into the pulmonary trunk. The blood in the pulmonary trunk goes to the lungs for oxygenation. Now that the blood is oxygenated, it flows back into the left atrium of the heart via the pulmonary vein. The blood then moves through the left atrioventricular valve (also called the mitral valve) into the left ventricle of the heart. This blood is then pumped through the aortic valve which will deliver this now oxygenated blood throughout the body, providing blood and oxygen that our bodies need to survive!
The pectoral girdle has no bony linkage to the body and is only attached by a group of muscles. Like humans, dogs also have a biceps muscle and a triceps muscle. The biceps muscle causes flexion at the elbow joint, while the triceps muscle causes extension. Fun fact: The triceps muscle is named so because it has three parts in humans. However, the dog’s triceps muscle has four parts.
Unlike the pectoral girdle, the pelvic girdle has a bony linkage to the axial skeleton via the femur and pelvis. Again, like humans, dogs have a group of muscles on the back of the leg called the hamstrings and on the front of the leg called quadriceps. The hamstrings cause flexion at the knee joint, while the quadriceps cause extension.
The canine skeleton is divided into two regions: the axial skeleton and the appendicular skeleton. The axial skeleton consists of the vertebral column and the rib cage. The appendicular skeleton consists of the pectoral girdle/limb and the pelvic girdle/limb. The vertebral column is a chain comprised of a varying number of vertebrae. Dogs have 7 cervical vertebrae, 13 thoracic vertebrae, 7 lumbar vertebrae, 3 sacral vertebrae, and 20-23 coccygeal vertebrae. The vertebral column has 3 functions: protection of the spinal cord, weight bearing and muscle insertion, and movement.
Look at this picture for an overview of some of the major bones in the dog!
The Central Nervous System
The central nervous system (CNS) consists of the brain and the spinal cord. The CNS controls most of the functions of the body including things like movement, planning and much more! The brain is the portion of the central nervous system that is contained within the skull. The cerebrum forms most of the brain and helps to perform the higher functions of the nervous system. It contains the frontal lobe, parietal lobe, temporal lobe and occipital lobe. The cerebellum is the part of the brain that moderates reflexes that coordinate voluntary movements
The brain is composed of the cerebrum, the cerebellum, and the brain stem. The cerebrum is composed of the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. It is covered with gyri and sulci in order to increase surface area. An enlarged cerebrum is unique to mammals and supports high level cognitive functioning. The cerebellum regulates motor movements. It coordinates voluntary movements such as posture, balance, coordination, and speech. This results in smooth and balanced muscular activity. The brain stem controls the flow of messages between the brain and the rest of the body. It also controls basic body functions like breathing, swallowing, heart rate, blood pressure, and consciousness.
The skull can be divided into three parts: the braincase, the facial bones, and the mandible. The braincase provides support and protection to the brain. The facial bones support the face, teeth, nasal, and oral cavities. The division between the braincase and the facial bones is at the levels of the orbits of the eyes. The mandible is also known as the lower jaw or the jawbone.
The inside of a dog’s stomach is divided into three sections: the fundus, the body, and the pylorus. The stomach also has large, linear folds called rugae. Rugae allow the stomach to stretch to accommodate large meals and help grip and move food during digestion.
The dog's digestive system consists of the same components as a human’s digestive system but is organized slightly differently. Food travels through the mouth into the esophagus and down the esophagus into the stomach. In the stomach food is broken down by proteins called enzymes. From the stomach, food moves into the small intestine. Despite its name, the small intestine is the largest part of the digestive tract. It is divided into three sections: the duodenum, the jejunum, and the ileum. It works with other organs in the digestive system to further digest food and absorb nutrients. From the small intestine, food moves into the large intestine, also known as the colon. The colon absorbs water and propels feces toward the rectum for elimination.
Small Animal Lung
Lungs consist of a right and left side. Different species vary in the numbers of lobes they have. The dog’s lungs are deeply lobated. There are four lobes on the right side, and two lobes on the left side. The right lung consists of the cranial lobe, the caudal lobe, the middle lobe, and the accessory lobe. The left lung consists of the cranial lobe and caudal lobe.
TEST YOUR KNOWLEDGE!!
Can you name the major bones in the dog skeleton below?
Test your Knowledge!
Can you remember the path that food takes through the body? Scroll up to check your answer!