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Goddard Veterinary Group
Wanstead Veterinary Hospital
84 New Wanstead
Wanstead
London E11 2SY |
Tel: +44 (0) 20
8989 7744
Fax: +44 (0) 20 8532 2821 |
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Skeletal System
The skeleton is the framework for all warm-blooded animals. It supports our body, allows us to move, protects organs (e.g. brain and spinal cord), helps maintain our mineral levels and also is involved in producing both red and white blood cells.
Our animal's skeleton can be divided up into three parts:
skull, spine (vertebral column), ribs and breast bone (sternum): collectively known as the axial skeleton
the bones of the front and back legs; collectively known as the appendicular skeleton
bones that develop within tissue and are not directly connected to the main framework are grouped together as the splanchnic skeleton. This includes small bones found in the penis and at the back of the knee.
Most bones are joined together with a joint. Some of these joints allow little or no movement, e.g. fused joints of the bones in the skull. Others allow movement of those associated bones, e.g. ball and socket joint found in hip or a hinge joint found in the elbow.
Joints found in the knee for example allow a lot of movement and contain a special shock absorbing fluid known as synovial fluid.
The stability of joints are improved by:
ligaments, which attach bone to bone, e.g. cruciate ligaments found in the knee
tendons, which attach bone to muscle, e.g. Achillies tendon found at the hock
bone surfaces that are well contoured to fit perfectly together.
Attached to this framework of bones is an intricate mass of skeletal muscles. These are known as voluntary muscles as your pet controls the use of these muscles, e.g. biceps and triceps muscles found above the elbows.
Other types of muscle exist in the body, which are under involuntary control. One type is smooth muscle. These include muscles in the stomach and gut and those found in the respiratory system, e.g. diaphragm and the muscles found between the ribs. The other type is cardiac muscle a specialist type of muscle which rhythmically contracts.
 The above diagram is reproduced from 'Veterinary Nursing' 2nd Edition, edited by D.R.Lane and B.Cooper, 1999 - with the kind permission of Butterworth-Heinemann and the BSAVA. This diagram may not be downloaded and/or stored electronically or in hard copy without the express permission of Butterworth-Heinemann and BSAVA.
Heart and Circulatory System
This is your pet's transport system. It comprises a powerful active pump called the heart and an intricate system of tubes or blood vessels, called arteries, veins and capillaries.
The blood within these vessels contains:
red blood cells, involved in gas exchange
white blood cells, involved in defence
platelets, which are cell fragments involved in the clotting process
plasma, the fluid part of blood and contains water, salts, protein, digested food stuffs, hormones, enzymes, antibodies and waste products.
The circulation connects to every tissue and cell in the animal's body and is responsible for transporting oxygen, nutrients and hormones, helping with the body's defence system, providing the necessary ingredients for clotting, helping regulate heat, helping remove waste products and carrying water.
Principally the heart consists of two pumps fused together; each has two chambers (atrium and ventricle) and several valves to prevent back-flow. Blood flows through the heart and around the body as follows:
Deoxygenated blood (blood with a low level of oxygen) enters the right side of the heart from the rest of the body. This is then pumped to the lungs.
Gas exchange takes place in the lungs.
Oxygenated blood (blood with a very high level of oxygen) enters the left side of the heart. This side is very muscular as it pumps blood to the rest of the body.
The heart is supplied both by electrical and chemical messages from the nervous system. Within the muscular walls of the heart are its own electrical centres and associated nerves. One of these is the heart's natural pacemaker; this sends impulses through the heart to make it beat rhythmically, whereby both the right and left atrium contract together then the right and left ventricle contract together.
 Lymphatic System
This system is responsible for:
returning excess fluid back into the circulation
filtering bacteria and foreign material out of the circulation producing white blood cells
transporting digested food, in particular fat, from the walls of the small intestine via lacteals. These are small lymphatic capillaries which are found in the walls of the small intestine.
Lymphatic vessels pass through special filters called lymph nodes so that bacteria can be removed and the new white blood cells can be collected. Eventually the contents will be emptied into the bloodstream.
There are many lymph nodes in the animal's body and these may swell up if the animal has an infection or cancer.
The spleen and tonsils are also part of the lymphatic system. The spleen stores red blood cells, makes lymph cells, breaks down expired red blood cells and eats up bacteria and other foreign material from the circulation. The tonsils, situated at the back of the animal's mouth, may become enlarged during an infection.
Respiratory System
This system enables your pet to breathe, it allows gas exchange between your pet and the environment. The respiratory and the circulatory system work together to ensure that your pet has the correct amount of oxygen and carbon dioxide in its body. The rate at which your pet breathes and the rate at which its heart beats are altered to keep the levels within the normal range.
Air is pulled in through the nose (or mouth if the animal is panting), down the back of its throat into a special tube called the trachea. This trachea then branches into two bronchi that pass into the left and right lungs. These bronchi continue to branch out, getting smaller and smaller. Actual gas exchange happens at the very tip of these branches in microscopic air sacs called alveoli. These are covered with many blood capillaries. It is here that fresh air and therefore oxygen is absorbed into the animal's blood stream and 'old air' is passed out all within one breath.
There are two types of blood capillaries that surround the air sacs.
Blood leaving the air sac capillaries will be enriched with oxygen and is called oxygenated blood. This blood will then be carried to the heart.
Blood coming into the air sac capillaries having given up most of its oxygen to the body's tissues. This is termed deoxygenated blood.
Red blood cells carry oxygen around the body in a specially designed red pigment called haemoglobin.
Most of this system is contained within the thoracic cavity. This is normally an airtight cavity.
During inspiration the diaphragm and the muscles situated between each rib contract. A decrease in pressure draws air into the lungs. Expiration follows as the muscles relax and the pressure is increased. This is mainly a voluntary movement and also involves the use of the nervous system.
 The above diagram is reproduced from 'Veterinary Nursing' 2nd Edition, edited by D.R.Lane and B.Cooper, 1999 - with the kind permission of Butterworth-Heinemann and the BSAVA. This diagram may not be downloaded and/or stored electronically or in hard copy without the express permission of Butterworth-Heinemann and BSAVA.
Nervous System
This is the body's communication system receiving information from both outside and inside the animal's body. There are two parts:
the central nervous system which is made up of the brain and spinal cord
the peripheral nervous system which contains nerves that the animal can control (voluntary) and those that it can not (involuntary)
The voluntary nerves allow us to eat and move
Involuntary nerves control and regulate body functions, e.g. respiration and heart
Messages can either be carried electrically or chemically. The nervous system is responsible for the electrical impulses which travel along a pathway of nerves. These electrical messages will quickly affect the heart, bones, joints, organs and tissues. Chemical messages in the form of hormones are released into the animal's blood stream and will travel more slowly to their 'target' organ where they will act. The animal's body has built in reflex actions. These allow an automatic and very rapid response without which its survival may be affected, i.e. the flight, fright, fight and flee response.
Digestive System
We are what we eat! Food and water is needed for every living thing to survive. Our bodies are made up of millions of cells each with a basic requirement for water and energy (derived from food).
Like us our animals first need to tear up and swallow their food. This passes down a long tube called the oesophagus into the stomach. Breakdown of this food starts as it is mixed with various enzymes and hydrochloric acid. It then enters the gut (intestines) to be mixed with more enzymes. The soluble parts of digested food are absorbed through the small intestine walls into the blood supply or into the lymphatic system. The solid indigestible parts, e.g. fibre, pass into the large intestine where most of the water is resorbed and expelled out of the body as faeces, a process called defecation.
The liver is the largest organ in the body. Some of its blood supply is derived from the small intestine so that it processes many products of digestion. It is responsible for storing and filtering blood, regulating sugar, fats and proteins and storage of many vitamins and minerals.
The pancreas is also involved in digestion as it produces many of the digestive enzymes used in the small intestine. It also produces hormones, including insulin which is vital for controlling sugar levels in the body.
Urinary System  The main function of this system is to conserve water and for the excretion and removal of waste products from the body. This is an essential and continuous process because if allowed to build up the waste can become toxic to the body.
The kidneys are responsible for filtering out unwanted or excess materials and conserving products that the body needs, e.g. they will conserve water, salts and sugars, or add any of these to the urine which are in excess.
As the urine is formed it is collected and passed down the ureter to be stored in the collection bag called the bladder. When this starts to become full the animal will contract its bladder muscle and expel the urine down the urethra and outside into its environment.
Reproductive System
Reproduction is needed for the creation of more individuals. In our pets it requires a sexual process between a male and female animal of the same species.
Reproduction takes place with special cells produced by the reproductive organs. The ovaries produce eggs and are also involved in producing hormones to maintain all the reproductive functions. The testicles produce sperm and sperm fluid to provide support and nutrition. It is also involved in producing the male hormone testosterone.
Mammals go through the process of fertilisation and development within the female reproductive system. Birds and reptiles have a small degree of internal development as eggs are produced. After the egg is laid, development will take place inside the egg.
The female usually has the greatest role to play during mammalian reproduction. First an egg(s) or ova are produced in the ovaries which travel down the fallopian tubes where they wait to be fertilised by sperm during mating or copulation. Following this the egg moves into uterine horns where it is implanted in its wall. Once the foetus is ready to be born a process called parturition moves it into the uterus. From there it enters the cervix (this is a natural barrier from the external environment and only opens during mating and birth) into the vagina and is passed out into the environment through the vulva.
 Many mammals including the dog, cat and rabbit have a breeding cycle. This is when the female is said to be 'on heat' or 'in season'. Males are able to detect a member of the same species in season by the female's behaviour and the scent or pheromones given off. Different species are in season at different times of the year, depending on the day length and age of the animal. Dogs tend to come into season every six months. Cats and rabbits tend to come into season from spring to autumn.
The male reproductive system consists of a pair of testes protected by a scrotum. Both sperm and sperm fluid are transported from the testes by a tube, known as the vas deferens. As this joins the urethra more fluid and nutrition are added to the sperm from the accessory sex gland(s) e.g. the prostate gland. From here it enters the urethra the end of which is enclosed within the muscular organ know as the penis. This organ is placed into the female reproductive tract where its sperm and associated fluids are expelled during mating. The urethra and penis is shared with the urinary system.
 Endocrine System
This is a group of glands (including thyroid and adrenal glands, pancreas, ovaries and testicles) within the body that produce chemical messages called hormones. These hormones are carried in the blood to their target organ or tissue, linking this system to the nervous system. An important endocrine gland called the pituitary gland, found at the base of the brain, is the master gland which controls the whole of this system.
The pituitary gland acts on:
the thyroid and adrenal glands
reproductive system as it assists in the development of the egg or sperm, maintains pregnancy, allows birth of young and enables milk production
urinary system as it prevents excess water loss
The thyroid gland regulates growth, body development and the animal's metabolism. Attached to it is the parathyroid gland which regulates the body's calcium and phosphorus levels in both blood and bones.
Adrenal gland functions include regulation of the growth, development of bones and muscle, regulation of body water, forming antibodies, helping deal with stress and controlling metabolism of the products from the digestive tract.
As part of the digestive tract the pancreas is responsible for regulating the body's glucose and produces insulin.
The ovaries produce hormones responsible for the oestrus cycle and the preparation of the uterus during pregnancy.
The testes produce testosterone to enable the animal to breed.
Exocrine System
This system comprises of different organs whose products are not transported by the blood stream. This includes salivary and mammary glands, sweat and scent glands found in the skin. The stomach, part of the pancreas and the cells within the walls of the small intestine, all have exocrine functions as they produce digestive enzymes which are excreted into the digestive system.
Saliva is produced by pairs of salivary glands. Within the saliva is a very small amount of digestive enzyme which starts to chemically breakdown the food. The saliva helps to moisten the food so that it can be broken up by the teeth and digestive enzymes further down in the tract. Its secretion is stimulated by the sight and smell of food.
The skin has many functions including helping to prevent water loss, storage of fat and control of body temperature. It is also involved in the production of vitamin D, (which is required for the absorption of calcium from the digestive system). As a sense organ it responds to touch, temperature, pressure and pain; these messages are sent to the brain via the nervous system.
The skin is made up of a number of layers. The top layer is called the epidermis and is made of many dying and dead skin cells, which are constantly being shed. Sweat or sebaceous glands are found in the dermis layer of the skin and produce sebum. This is an oily substance that helps to seal the skin against water loss and act as a bacterial barrier. Sweat glands also function as a scent gland as they produce certain odours, e.g. pheromones used during mating. Scent glands are also found on either side of the anus as anal glands; these assist as a chemical message left for other animals to detect their presence as it is secreted during defecation.
Mammary glands are modified sweat glands. They contain special tissue that is activated during pregnancy, at the end of which the mammary secretion milk is formed. This is controlled by hormonal changes.
 Sense Organs
These organs collect stimuli which is sent to the nervous system and is interpreted by the brain. These organs are capable of receiving information from inside and outside of the body. They include the eye, ear, tongue and nose.
The eye is a very delicate organ, which allows the animal to see. It contains a transparent cornea and lens, which act to focus the image rather like a camera. At the back of the eye is the light sensitive retina, which is filled with 'rods and cones'. These are the light sensors which enable the animal to see black and white and a small selection of colours. Light entering the eye is controlled by a diaphragm called the iris. This gives the eye colour, e.g. brown, blue, green or red. Its centre makes up the black central spot known as the pupil.
 The ear is involved with the animal's hearing, its balance and is used to detect a change in the animal's body position. It is divided into three parts:
the outer part is used for collecting sound, the pinna and external canals
the middle part transmits the vibrations collected through a series of minute bones (malleus, incus and stapes) to the window of the inner part
the inner part then receives a series of sound waves. This is then translated to nerves and is then sent to the brain for processing.
Smell is as important to animals as eyesight is to humans. Animals use it for the detection of food and information about other animals. This can be used in combination with the taste sensation to gain a larger picture. Taste is formed from mucus membrane cells in the mouth and on the tongue. Together taste and smell stimulate the production of saliva in readiness to receive food and stimulate the digestive system.
The above diagram is reproduced from 'Veterinary Nursing' 2nd Edition, edited by D.R.Lane and B.Cooper, 1999 - with the kind permission of Butterworth-Heinemann and the BSAVA. This diagram may not be downloaded and/or stored electronically or in hard copy without the express permission of Butterworth-Heinemann and BSAVA.
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