Vet Notes

Chapter: Animal Classifications

Classification is the process used by scientists to make sense of the 1.5 million or so different kinds of living organisms on the planet. It does this by describing, naming and placing them in different groups. As veterinary nurses you are mainly concerned with the Animal Kingdom but don’t forget that animals rely on the Plant Kingdom for food to survive. Also many diseases that animals are affected by are members of the other Kingdoms -- fungi, bacteria and single celled animals.

Naming Animals

Of course we know what a cat, a dog and a whale are but, in some situations using the common names for animals can be confusing. Problems arise because people in different countries, and even sometimes in the same country, have different common names for the same animals. For example a cat can be a chat, a Katze, gato, katt, or a moggie, depending on which language you use. To add to the confusion sometimes the same name is used for different animals. For example, the name "gopher" is used for ground squirrels, rodents (pocket gophers), for moles and in the south-eastern United States for a turtle. This is the reason why all animals have been given an official scientific or binomial name. Unfortunately these names are always in Latin. For example:

• Common rat: Rattus rattus

• Human: Homo sapiens

• Domestic cat: Felis domesticus

• Domestic dog: Canis familiaris

As you can see from the above there are certain rules about writing scientific names:

• They always have 2 parts to them.

• The first part is the genus name and is always written with a capital first letter.

• The second name is the species name and is always written in lower case.

• The name is always underlined or printed in italics.

The first time you refer to an organism you should write the whole name in full. If you need to keep referring to the same organism you can then abbreviate the genus name to just the initial. Thus Canis familiaris becomes C. familiaris the second and subsequent times you refer to it.

Classification of Vertebrates

As we have seen above the Vertebrates are divided into 5 groups or classes namely:

• Fish

• Amphibia (frogs and toads)

• Reptiles (snakes and crocodiles)

• Birds

• Mammals

These classes are all based on similarities. For instance all mammals have a similar skeleton, hair on their bodies, are warm bodied and suckle their young.

The class Mammalia (the mammals) contains 3 subclasses:

• Duck billed platypus and the spiny anteater

• Marsupials (animals like the kangaroo with pouches)

• True mammals (with a placenta)

Within the subclass containing the true mammals, there are groupings called orders that contain mammals that are more closely similar or related, than others. Examples of six mammalian orders are given below:

• Rodents (Rodentia) (rats and mice)

• Carnivores (Carnivora) (cats, dogs, bears and seals)

• Even-toed grazers (Artiodactyla) (pigs, sheep, cattle, antelopes)

• Odd-toed grazers (Perissodactyla) (horses, donkeys, zebras)

• Marine mammals (Cetacea) (whales, sea cows)

• Primates (monkeys, apes, humans)

Within each order there are various families. For example within the carnivore mammals are the families:

• Canidae (dog-like carnivores)

• Felidae (cat-like carnivores)

Even at this point it is possible to find groupings that are more closely related than others. These groups are called genera (singular genus). For instance within the cat family Felidae is the genus Felis containing the cats, as well as genera containing panthers, lynxes, and sabre toothed tigers!

The final groups within the system are the species. The definition of a species is group of animals that can mate successfully and produce fertile offspring. This means that all domestic cats belong to the species Felis domesticus, because all breeds of cat whether Siamese, Manx or ordinary House hold cat can cross breed However, domestic cats can not mate successfully with lions, tigers or jaguars, so these are placed in separate species, Felis leo, Felis tigris and Felis onca.

Even within the same species, there can be animals with quite wide variations in appearance that still breed successfully. We call these different breeds, races or varieties. For example there are many different breeds of dogs from Dalmatian to Chihuahua and of cats, from Siamese to Manx and domestic short-hairs, but all can cross breed. Often these breeds have been produced by selective breeding but varieties can arise in the wild when groups of animals are separated by a mountain range or sea and have developed different characteristics over long periods of time.

To summarize, the classification system consists of:

The Animal Kingdom which is divided into

• Phyla which are divided into

• Classes which are divided into

• Orders which are divided into

• Families which are divided into

• Genera which are divided into

• Species.

Keep Pond Clean Or Fish Get Sick are just two of the phrases students use to remind themselves of the order of these categories - on the other hand you might like to invent your own.

Chapter: Terminology 

Medical Terms are important to remember. This will make learning anatomy a little easier. The common terms are words that you need to know to talk to owners. 

Medical Terms

I have included just a few root words that will help you as you read the text and learn the anatomy.

Root Words

Common Anatomical Terms 

Common Anatomical Terms

Common Species Terms

Common Species Terms

Note about hybrid equine. Horses and donkey can cross breed and produce young. Those offspring are sterile. 

• A Hinny is a hybrid that is produced when a Jenny and Stallion cross breed. 

• A Mule is a hybrid that is produced when a Mare and a Jack cross breed.

• Chapter: Body Organization

  In this chapter, the way the cells of the body are organized into different tissues is described. You will find out how these tissues are arranged into organs, and how the organs form systems such as the digestive system and the reproductive system. Also in this chapter, the important concept of homeostasis is defined. You are also introduced to those pesky things -- directional terms. 

  Organization of Animal Bodies

  Living organisms move, feed, respire (burn food to make energy), grow, sense their environment, excrete and reproduce. These seven characteristics are sometimes summarized by the words MRS GREN functions of:

  Movement

  Respiration

  Sensitivity

  Growth

  Reproduction

  Excretion

  Nutrition

  Living organisms are made from cells which are organized into tissues and these are themselves combined to form organs and systems.

  Skin cells, muscle cells, skeleton cells and nerve cells, for example. These different types of cells are not just scattered around randomly but similar cells that perform the same function are arranged in groups. These collections of similar cells are known as tissues.

  There are four main types of tissues in animals. These are:

  • Epithelial tissues that form linings, coverings and glands,

  • Connective tissues for transport and support

  • Muscle tissues for movement and

  • Nervous tissues for carrying messages.

  Epithelial Tissues

  Epithelium (plural epithelia) is tissue that covers and lines. It covers an organ or lines a tube or space in the body. There are several different types of epithelium, distinguished by the different shapes of the cells and whether they consist of only a single layer of cells or several layers of cells.

  Connective Tissues

  Blood, bone, tendons, cartilage, fibrous connective tissue and fat (adipose) tissue are all classed as connective tissues. They are tissues that are used for supporting the body or transporting substances around the body. They also consist of three parts: they all have cells suspended in a ground substance or matrix and most have fibres running through it.

  Muscle Tissues

  Muscle tissue is composed of cells that contract and move the body. There are three types of muscle tissue :

  • Skeletal muscle 

  • Smooth muscle 

  • Cardiac muscle 

  Nervous Tissues

  Nervous tissue forms the nerves, spinal cord and brain. Nerve cells or neurons consist of a cell body and a long thread or axon that carries the nerve impulse. An insulating sheath of fatty material myelin usually surrounds the axon.

  Vertebrate Bodies

  We are so familiar with animals with backbones (i.e. vertebrates) that it seems rather unnecessary to point out that the body is divided into three sections. There is a well-defined head that contains the brain, the major sense organs and the mouth, a trunk that contains the other organs and a well-developed tail. Other features of vertebrates may be less apparent. For instance, vertebrates that live on the land have developed a flexible neck that is absent in fish where it would be in the way of the gills and interfere with streamlining. Mammals but not other vertebrates have a sheet of muscle called the diaphragm that divides the trunk into the chest region or thorax and the abdomen.

  Body Cavities

  In contrast to many primitive animals, vertebrates have spaces or body cavities that contain the body organs. Most vertebrates have a single body cavity but in mammals the diaphragm divides the main cavity into a thoracic and an abdominal cavity. In the thoracic cavity the heart and lungs are surrounded by their own membranes so that cavities are created around the heart - the pericardial cavity, and around the lungs the pleural cavity (See diagram 4.13).

  

  Diagram 4.13: The body cavities

  Organs

  Just as the various parts of the cell work together to perform the cell ’s functions and a large number of similar cells make up a tissue , so many different tissues can “cooperate” to form an organ that performs a particular function. For example, connective tissues, epithelial tissues, muscle tissue and nervous tissue combine to make the organ that we call the stomach . In turn the stomach combines with other organs like the intestines, liver and pancreas to form the digestive system (see diagram 4.14).

  

  Diagram 4.14 : Cells, tissues and organs forming the digestive system

  Generalized Plan of the Mammalian Body

  At this point it would be a good idea to make yourself familiar with the major organs and their positions in the body of a mammal like the rabbit. Diagram 4.15 shows the main body organs.

  

  Diagram 4.15 : The main organs of the vertebrate body

  Body Systems

  Organs do not work in isolation but function in cooperation with other organs and body structures to bring about the MRS GREN functions necessary to keep an animal alive. For example the stomach can only work in conjunction with the mouth and oesophagus (gullet). These provide it with the food it breaks down and digests. It then needs to pass the food on to the intestines etc. for further digestion and absorption . The organs involved with the taking of food into the body, the digestion and absorption of the food and elimination of waste products are collectively known as the digestive system .

  The 11 body systems

  • Skin

  • Skeletal System

  • Muscular System

  • Cardiovascular System

  • Lymphatic System

  • Respiratory System

  • Digestive System

  • Urinary System

  • Reproductive System

  • Nervous System

  • Endocrine System

  Homeostasis 

  All the body systems, except the reproductive system, are involved with keeping the conditions inside the animal more or less stable. This is called homeostasis . These constant conditions are essential for the survival and proper functioning of the cells, tissues and organs of the body. The skin, for example, has an important role in keeping the temperature of the body constant. The kidneys keep the concentration of salts in the blood within limits and the islets of Langerhans in the pancreas maintain the correct level of glucose in the blood through the hormone insulin . As long as the various body processes remain within normal limits, the body functions properly and is healthy. Once homeostasis is disturbed disease or death may result. 

• Chapter: Directional Terms

  In the following chapters the systems of the body in the list above will be covered one by one. For each one the structure of the organs involved will be described and the way they function will be explained.

  In order to describe structures in the body of an animal it is necessary to have a system for describing the position of parts of the body in relation to other parts. For example it may be necessary to describe the position of the liver in relation to the diaphragm , or the heart in relation to the lungs. Certainly if you work further with animals, in a veterinary clinic for example, it will be necessary to be able to accurately describe the position of an injury. The terms used for this are called directional terms .

  The most common directional terms are right and left . However, even these are not completely straightforward especially when looking at diagrams of animals. The convention is to show the left side of the animal or organ on the right side of the page. This is the view you would get looking down on an animal lying on its back during surgery or in a post-mortem. Sometimes it is useful to imagine ‘getting inside’ the animal (so to speak) to check which side is which. The other common and useful directional terms are listed below and shown in diagram 4.16.

  

  Diagram 4.16 : The directional terms used with animals

  Table

  Directional Terms

  Term	Definition	Example
  Dorsal	Nearer the back of the animal than	The backbone is dorsal to the belly
  Ventral	Nearer the belly of the animal than	The breastbone is ventral to the heart
  Cranial (or anterior)	Nearer to the skull than	The diaphragm is cranial to the stomach
  Caudal (or posterior)	Nearer to the tail than	The ribs are caudal to the neck
  Proximal	Closer to the body than (only used for structures on limbs)	The shoulder is proximal to the elbow
  Distal	Further from the body than (only used for structures on limbs)	The ankle is distal to the knee
  Medial	Nearer to the midline than	The bladder is medial to the hips
  Lateral	Further from the midline than	The ribs are lateral to the lungs
  Rostral	Towards the muzzle	There are more grey hairs in the rostral part of the head
  Palmar	The "walking" surface of the front paw	There is a small cut on the left palmar surface
  Plantar	The "walking" surface of the hind paw	The pads are on the plantar side of the foot

  Planes

  Planes are ways we divide the body. 

  Median plane divides the body into equal right and left halves. 

  Transverse plane divides the body into a front (head) and a back (rear). 

  Dorsal plane divides the body into back (dorsum) and belly (ventrum). 

  

  This dog is divided into right and left halves (median plane). Her right side is opposite your right side. 

   

  

  This dog is divided into: 1.  front and back (transverse plane) and 2. back and belly (dorsal plane).