NOTES ON VETERINARY PATHOLOGY

Definition

Pathology is defined as the science of disease. Pathology is derived from the two words Patho and logy. Patho means disease and logy means the study . A disease can be defined as inability to perform physiological functions at normal levels when  provided with nutrition and other environmental requirements are provided at adequate levels. It can also be defined as any abnormality of the body which is harmful to the animal. Pathology deals mainly with the cause of the disease and the changes produced in the body as a result of diseases . It is also concerned with how the disease is started(pathogenesis) ,the tissues or organs affected by the disease ,the nature of the damage caused  by the disease (pathogenicity), the effect of the disease on the life of the animal and the possible outcome of the disease(prognosis). The symptoms and the pathology of the disease depends  largely on the tissues and organs affected by the disease. Diseases are usually as a result of abnormal changes in the body. Disease causing agents when they enter the body, usually  inflict various damages to the tissues of the body .Some of the damages caused by disease causing agents are puncturing of the blood vessels leading to the escape of  blood from the vessels(haemorrhage).Other disease causing agents produce toxins which may cause irritation to the tissues of the body leading to inflammation. Some of the toxins may kill the cells they come in contact with leading to death of cells (necrosis). Pathology basically seeks  to identify abnormal changes in the body  and making use of them  to recognise or diagnose  diseases.

Pathology is concerned with both dead and living animals. In dead  animals, pathology  is concerned mainly  with finding the causes  of death and in living animals to diagnose diseases so that  they  can be treated controlled or prevented.

Importance of pathology

1.         To find the causes of death  in dead animals.

2.        To diagnose diseases in living animals.

3.         Pathology is made use of  in research into diseases, disease reporting ,disease surveillance and monitoring and all investigations into diseases

4.        Pathology helps to lead a healthy disease free lives.

BRANCHES OF PATHOLOGY

There are four branches of pathology:

1.         Gross Pathology.

2.        Histopathology.

3.         Clinical pathology.

4.        Applied or Special pathology.

Gross pathology

This branch of pathology deals with abnormal changes that can be seen with the naked eye like lesions seen  at post mortem examinations.

Histopathology :            This branch of pathology deals  with abnormal changes that are so small that they cannot be seen with the naked but only with the aid of a microscope example examination of the brain tissues for negri-bodies in rabies infection.

PATHOLOGY

Clinical pathology:       This branch of pathology deals with abnormal changes in body fluids like blood, serum, urine, milk ,saliva  and cerebro-spinal fluid.

Special  /Applied  Pathology :         This branch of pathology deals  with specific diseases and their characteristic lesions

TERMINOLOGIES;

Pathogenic: disease causing

Non-pathogenic :not causing disease.

Lesion:  an  abnormal change in the tissue  produced by a disease.

Pathognonomic:  This is a term applied to a sign or a lesion of a disease which is so characteristic  to the disease and on whose presence the disease is diagnosed and in its absence the disease cannot be diagnosed e.g. the enlargement of the bursa of Fabricius in Gomboro disease is pathognonomic for the disease.

Leucopenia :means decrease in the number of white blood cells below normal.

Leucocytosis :increase in the number of W.B.C .above normal.

Pan:  A prefix meaning all e.g. panleucocytosis means increase in all the types of WBC.

Suffix -aemia at the end of a word means it is referring to the blood e.g. hypoalbuminaemia means decrease albumin level in the blood .

Suffix-nuria the end of a word means it is referring to the urine e.g. albuminuria means the presence of albumin in the urine.

Oligo-means absence or lacking e.g.  oliguria means lack of urine.

The prefix a at the beginning of a word means absence e.g.  anuria meaning absence of urine.

Hypo means below normal

Hyper means above normal

Leuco is a prefix meaning white and when it is used in pathology it is referring to white blood cells.

Tachycardia- this means increased heart rate.

Bradycardia- this means decreased heart rate.

CAUSES OF DISEASES IN ANIMALS

A disease may be defined as the inability of the body to perform normal physiological functions given the right nutritional and environmental conditions. Disease can also be described as any abnormality of the body which is harmful to the animal .

Causes of diseases can be classified into two main groups;

1.         Living agents

2.        Non-living agents

Living things as causes of diseases

Living agents are living plants and animals who invade the tissues of animals basically to obtain their food but in the process cause various damages to their bodies leading to diseases and death.

Types of the living things are viruses, bacteria, Rickettsia organisms, protozoan organisms, fungi, worms, ticks, flies, fleas, mites and lice.

Pathogenicity of bacteria and viruses;

Bacteria and viruses are the main causes of diseases and death in animals mainly because of the fact that they can multiply to large numbers in a very short time. Their physical presence cause irritation to the tissues leading to inflammation. Some of these viruses and bacteria produce toxins harmful to  the cells that come into contact with them leading to inflammation and necrosis. As they multiply in the cells they disrupt the functions of the cells leading to abnormal functions and therefore diseases. Some viruses like the rabies virus leave deposites called inclusion bodies in the cells in which the multiply which disrupt the normal function of the cell  leading to disease. Bacteria and viruses that live and multiply in the bloodstream damage the blood vessels leading to escape of blood ( haemorrhages).

Pathogenicity of fungal agents

They mainly attack the skin and the appendages. Others attack internal organs like the lungs and  uterus causing inflammation. Fungi also grow in food substances and produce toxins in them so when the food is eaten the toxin affect the tissues of the body leading to disease.

Pathogenicity of worms

Their physical presence especially if present in large numbers cause irritation to the GIT leading to inflammation. The immature stages of certain worms like ascarid worm can pass through the walls of the intestine and attack other internal organs leading to diseases. Migration of larvae of ascarid worm through the liver tissues causes haemorrhages in the liver and hepatitis. Other worms like the haemonchus and hook worm of dogs suck the blood of the animal leading to anaemia, shock and death.

Pathogenicity of protozoan organisms: These are unicellular animals. They commonly invade the blood stream of animals where they attack the red  blood cells, destroying them leading to anaemia, jaundice and death. These protozoan organisms include trypanosomes, babesia, anaplasma and theirelia. They  multiply in ticks or flies who therefore serve as vectors  and the parasites are transmitted when the tick or fly sucks blood. Other protozoan organism like the Eimeria that causes coccidiosis attack and destroys the intestinal lining leading to haemorrhages into the intestine and death. The coccidian organism also attacks the liver in rabbits.

Pathogenicity  flies

Flies cause disease by sucking the blood of animals thereby predisposing them to anaemia. Others like the Glossina(tsetsefly) transmits the causative agent of trypanosomiasis(trypanosomes).

Pathogenicity of ticks.

Ticks sucks the blood of animals predisposing them to anaemia. They also transmit the causative agents of diseases eg the causative agent of heartwater,  Cowdria ruminantum is transmitted by the Amblyoma tick. The causative agents of Babesiosis(Babesia spp), Anaplasosis(anaplasma spp) and Theileriosis(Theileria spp)are transmitted by ticks. Ticks also cause irritation to the skin leading to dermatitis and loss of condition of the animal.

Pathogenicity of lice, fleas and mites

These ecto-parasites cause itching to the animal causing the animal to scratch its body against fixed objects leading to dermatitis and loss of condition of the animal and fall in production of eggs and milk. They also suck blood leading to anaemia. 

Non-living agents of disease

These include the following factors

1.         Physical agents

2.        Chemical agents

3.         Nutritional

4.        Genetic factors

5.         Environmental factors

 Physical factors.   These include such things like trauma (a blow) cuts, excessive heat and cold applied directly to the body. These factors produce damages  to the tissues of the body leading to diseases.

Chemical factors.  These are chemical substances from plant and animal sources which damage the tissues of the body in various ways leading to diseases and death. These poisonous substances get into the body by ingestion when it is taken inadventely as food  or as drug over dose. These toxins may also get into the body through skin application as acaricides.

Nutritional factors.           Diseases can also be caused by lack of certain necessary nutrients in the diet  which are essential for the normal function of the body. Their absence in the feed leads to malfunctioning of the body ; e.g. lack of iron in the diet leads to anaemia.

Genetic factors.       Some diseases can be passed on from parents to offspring through the genetic materials(genes) which determine certain traits of the offspring. If the genetic material is defective, the offspring will automatically be disease e.g. hydrocephalon, hairlessness dwarfism hereditary blindness and deafness in dogs.

Environmental factors.  this include such factors like excessive cold which predisposes the animal to pneumonia. Others are excessive heat, poor hygiene, pollution of water bodies with toxic wastes, overcrowding which leads to rapid spread of diseases.

SIGNS OF DISEASE IN ANIMALS

Sick animals show certain signs when they are diseased .Some of these signs are not specific to a particular disease but a general sign of ill-health .Some of these unspecific signs  of disease are;

 Isolation. A sick animal tends  to isolate itself from the rest of the group. When they are moving in a herd it would be found lagging behind or show exercise intolerace.

Dullnes. The normal instinct of a health animal is to move away when being approached, but a sick animal will not move away or do so sluggishly.

Inappetence. A healthy animal will rush to food when it is provided. Therefore indifference to food or refusal to eat is a sure sign of ill-health.

Fall in egg and milk production.

This is a sign that the animal may be sick and should be investigated.

Ceasation of rumination. Ruminants in some cases stop ruminating when they are sick.

Poor hair coat. The hair coat of a healthy animal should be smooth and shinny. Therefore rough and poor hair coat may be a sign of a disease.

Unthriftiness. Poor growth or animal  inability to reach market size or come into production at the normal time may indicate sickness.

Specific signs  of specific of specific diseases should be dealt with when treating such diseases in medicine

GENERAL SIGNS OF DISEASES OF THE BODY SYSTEMS

The digestive system. Diseases  affecting the  digestive system normally show as diarrhoea, abdominal pains, vomiting  and refusal to eat. The diarrhoea may be foul smelling, containing frank blood or occult blood or mucus. Diarrhoea is due to increased peristalysis  which is an attempt by the body to flush out what is causing the problem. Vomiting is also an attempt by the body to get rid of irritant. Severe diarrhoea leads to dehydration and loss of electrolytes which are the causes of death in diarrhoea cases.

Respiratory system. Diseases of the respiratory system are manifested by

Difficulty in breathing -laboured breathing

Increased respiratory rate

Abnormal respiratory sounds

Nasal discharges

Coughing

Exercise intolerance -lagging behind the flock.

The nervous system. Signs of diseases of the nervous system are circling ,lateral deviation of the head, convulsion, rolling of the eyes  torticollis and generally change in behaviour.  

Reproductive system. The signs of diseases of the reproductive system are abortions, barreness, infertility.

Any disease or stress affecting a pregnant animal may result in abortion.

Musculo-skeletal system. Diseases  affecting this system will manifest as lameness. 

GENERAL PATHOLOGY

INFLAMMATION

Definition:            Inflammation is the reaction of the tissue to an injury, an irritant or a foreign body. An irritant in this context can be any foreign substance that gains  entry into the body. This includes pathogenic living agents like bacteria, virus, fungi agents, worms and non-living things like trauma, bullets,  stones or thorns that get stuck into the flesh of the body, needle pricks, cuts,  burns and harmful substances like poisons .

These foreign substances, irritants and injuries of the body , provoke a series of complex chain reactions resulting in what is called inflammation.

Inflammation is basically part of the body’s defence system since the vascular and cellular responses  of the body are aimed at bringing the body s defensive weapons like the white blood cells, antibodies and other bactericidal substances  into contact with the irritant. By so doing,  the irritant is destroyed thereby ,preventing it from doing  more injuries and  stopping the spread of the irritant. Inflammation aims at repairing the damages caused by the irritants and restoring the tissues and the body as a whole  to normalcy.

Inflammation is denoted by the suffix ‘’tis’’  at the end of the organ inflamed.

ORGAN OR TISSUE	INFLAMED
Peritoneum Intestine  Conjunctiva Lungs Liver Kidney Muscle Brain Uterus Oviduct Mouth Stomach Middle ear Joint Testes Heart Lymph node Gum Artery Pharynx Bone marrow Brain and meningis Penis Urinary bladder Bone Vein Spinal cord	Peritonitis Enteritis. Conjunctivitis Pneumonia Hepatitis Nephritis Myositis Encephalitis Metritis Salpingitis Stomatitis Gastritis Otitis-media Arthritis Orchitis Myocarditis Lymphadenitis  Gingivitis Arteritis Pharyngitis Osteomyelitis Encephalomyelitis Balanitis Cystitis Osititis Phlebitis Myelitis

Causes of inflammation

Pathogenic living agents.  These are the most important causes of inflammation. They include such agents as viruses, bacteria ,fungi agents protozoan organisms, worms,  mites ,lice ,ticks and flies.

Poisons: poisons from plant , chemical and animal  sources are major causes of inflammation.

Physical agents . Things  like cuts ,burn,  a blow(trauma) and any injury to the tissues will provoke  an inflammation response.

Foreign substance.  Any foreign substance that gains entry into the tissues will provoke  an inflammation response since the body will recognise it  as not part of the body and will attempt remove it  leading to inflammation. This include things like thorns, stones ,bullets  pins, e.t c.

Cardinal signs of an acute inflammation;

There are five signs of an acute inflammation:          These are

1.         Redness

2.        Heat

3.         Swelling

4.        Pain

5.         Loss of function.

The redness is due to  the blood vessels in the area of inflammation becoming more numerous as a result of vasodilatation and the blood vessels being packed  with red blood cells.

The heat at the site of inflammation is due to more blood which is pumped to the area.  The blood contains the heat of the body and therefore the area becomes hot.

The swelling is due to excess fluid which is pumped to the site of the inflammation to dilute the toxins of the irritant.

The pain experienced at the site of inflammation is due to pressure exerted on nerve endings at the site by the accumulating fluid. The loss of function of the   inflamed  organ is due to the pain  experienced at the site of the inflammation.

The mechanism of inflammation

When a tissue of the body is attacked by a pathogenic agent,  the following processes are set into motion immediately at the area.

1.         Dilation of blood vessels.  The blood vessels in the area become bigger. The number of capillaries in the area also increase and the area  become grossly reddened(hyperaemia).

2.        Increased permeability of the blood vessels of the area. The blood vessels in the area become more permeable to allow large molecular substances like antibodies which normally are not permeable to pass through them to the site of the pathogen to fight  it.

3.        Migration and emigration of W.B.C.

White blood cells converge from all over the body to the area of the pathogen and they are able to pass through the walls of the capillaries by means of amoebic action to engulf  the pathogen by a process called Phargocytosis

Gross appearance of an inflamed organ:

1.         The inflamed  organ is reddened.

2.     There are  exudates present at the site(an exudates is the fluid that seeps out of an inflamed organ).  Its composition depends on the type of inflammation. It  usually consists of the irritant ,W.B.C .,R.B.C. ,injured  and dead cells ,water, protein and antibodies. The function of the exudates is to dilute the irritant and decrease it  action, to wash it  away to  effect healing.

3.     The inflamed organ is usually swollen due to the accumulation of fluid.

                     Histological appearance of an inflamed organ

1.         Infiltration of the site by large number of W.B.Cs.   Large numbers of white blood wells are seen at the site of inflammation. Therefore the presence of large numbers of W.B.C. in a tissue is indicative that the organ is inflamed.

2.        Hyperaemia. The blood vessels of the area becomes numerous and are   packed with R.B.Cs.

3.         The offending irritant may be found at the site of inflammation.

4.     There is  exudates present  at the site.

White blood cells  and the roles  they play in inflammation.

The white blood cells of the body  are

1.         Neutrophils.

2.        Lymphocytes.

3.         Eosinophils.

4.        Basophils

5.         Monocytes(macrophages).

Neutrophils.  They migrate from the blood vessels into the tissue and engulf bacteria by Phargocytosis .They are the first to reach the site of inflammation and are therefore seen in acute infections. They  are said to be the first line of defence .They are found in pus and are seen in large numbers in acute purulent infections in response to pyogenic bacteria

 

Lymphocytes

They appear late in infections and are therefore seen in chronic infections

They fight infections by antibody production.

Eosinophils.   Their number increase in certain worm infections .Their specific role in fighting infections are not known.

Basophils.    They contain histamine which are secreted during allergic infections.

Monocytes:  They are seen in chronic infections. When they migrate from the blood stream into the tissues they  increase in size and are called macrophaphages.

        Classification of inflammations;

Inflammation are classified according to the predominant constituent of the exudates into the following;

1.         Serous Inflammation

2.        Fibrinous

3.         Purulent.

4.        Haemorrhagic

5.         Catarrhal

Serous inflammation.           In this type of inflammation the exudates is made up of predominantly  serous exudates  which is a clear albuminous  fluid.

Fibrinous  inflammation.  Here the exudates contain large amount of fibrinogen. The exudates appears like yellowish jelley  like material.

Purulent inflammation.       Here the exudates is made up mainly of purulent exudates consisting of pus which is creamy-yellow in colour and vary in consistency from  watery to semi-solid. Pus consist of large amount of dead and living neutrophils together with necrotic cells. Purulent inflammations are caused by pyogenic  bacteria An abscess is an example of a purulent  inflammation. An abscess is a circumscribed collection of pus in the tissues of the body. A  phlegmon is also a collection of pus but it is not  localised but scattered throughout  the  tissue particularly the subcutaneous tissue(syn.cellulites).

Haemorrhagic inflammation.  In this case the exudates is made up mainly of red blood cells. Grossly the exudates looks like clotted blood .It is seen in diseases like anthax, blackleg and coccidiosis.

Catarrhal inflammation:.  Here the exudates is made up mainly of mucus secreted by epithelial cells of the area of inflammation .Grossly the  exudates appear as a clear-slimy liquid dripping from the nostrils of animals suffering from P.P.R ,  and pneumonia

Classification of inflammation based on duration of inflammation:

Inflammation is also classified according to the duration of the inflammation into the following:

Hyperacute.             In this case the inflammation arise suddenly progresses very rapidly and ends in the death of the animal within a few hours(sudden death) e.g. in anthrax.

Acute.  Here inflammation arises suddenly and progresses quickly and ends in a few days terminating in either death or recovery.

Subacute.  In this case the inflammation lasts a few months.

Chronic.  In this case the inflammation begins slowly progresses slowly and indefinitely and may last for years e.g. tuberculosis.

N/B. The two classifications may be combined to describe an inflammation as e.g. an acute purulent pneumonia  and an acute muco-purulent pneumonia.

Effects  of inflammation .     After  an inflammation the affected tissue is either healed  or die (necrosis).

NECROSIS

Necrosis is the death of a cell or a group of cells of an organ in a living animal.

Normally necrosis follows inflammation  since the cells affected by the inflammation may recover or die . However an injured cell may die without first showing inflammation.

Causes of Necrosis;

Infectious agents. Like viruses bacteria, fungal agent  etc. These agents produce toxins which kills  cells  nearest to them in the organ.

Poisons.         Poisons are toxic substances that have the ability to kill cells of the body  when they come into contact with them.

Cutting off the blood supply to the cells.  All cells of the body need continuous  supply of oxygen ,nutrients and the removal of metabolic waste products. These functions are accomplished  by the blood so that when the blood supply is cut off the cells which are supplied by the cut blood vessel would die. This type of necrosis is seen in burdizor castration.

Loss of nerve supply.  the nerves facilities the function of the blood vessels and it is observed that when the nerve supply to an organ is damaged the blood vessels are unable to function  leading to the death of the cells being supplied by the nerve.

Mechanical and thermal injuries: These include such things like trauma  a blow applied to an area of the body which may cause the cells of the area to rupture or destroy the internal arrangement  of the cell to an extend that the cell is not able to carry out its normal metabolic functions and therefore dies. Strong heat or radiation  applied to the cells will cause the coagulation of the protoplasm within the cell leading to the inability to perform normal metabolic activities leading to the death of the cell.

Pressure, If pressure is applied directly to the cells of an organ for a long time the cells in the area will die.

Microscopic changes in the cell during necrosis

Changes in the nucleus

Pyknosis

The nucleus is decreased in size but more rounded.  It is black or nearly so

The pyknotic nucleus is homogeneous lacking  nucleolus, chromatin granules and lack internal structures of a normal cell. The nucleus is disintegrated (karyorrhexis) into tiny fragments.

Karyolysis

This is the dissolution of the nuclear material. When completed the nucleus is not seen in the cell.

Changes in the cytoplasm

1.      Unusually acidophilic; The cytoplasm takes acid  stains which is red (eosin); The cytoplasm is deeper red than normal.

2.     Cytoplasmolysis

3.     The cytoplasm becomes less and less dense and finally disappears.

The cell as a whole will show

a.   loss of outline; complete loss of cell outline.

b.  Loss of differential staining; the cell loses the normal colour when stained

c.   Absence of cells; Empty spaces  are seen within the organ. 

       Gross appearance of a necrotic area:

Loss of normal colour: The dead tissue is normally paler than the living cells. Where the necrotic contains a lot of blood the area looks blackish.

Loss of normal strength:  The area easily tears when small pressure is applied.

Bad odour:   Putrefaction from the dead cell will produce bad smell from the area.

Empty space or a depression  within  the organ as a result of loss of cells may be seen.

Zone of inflammation; the necrotic area is usually surrounded by a whitish zone of inflammation.

Types of necrosis

1.         Coagulative necrosis

2.        Caseous necrosis

3.         Liquetactive necrosis

4.        fat necrosis

5. Zenkers necrosis

1.   Coagulative necrosis

grossly the necrotic area looks greyish, whitish, firm(Cooked) and often depressed. This type of necrosis is seen in fibrinous inflammation.

2.Caseous necrosis

Grossly the necrotic area looks like cottage cheese; yellowish or whitish in colour,dry, firm but without cohesive strength so that the necrotic tissue can be easily separated into granular fragments with a blunt instrument. This type of necrosis is seen in tuberculosis which has a caseous necrotic center.

3.Liquefactive necrosis

Here the necrotic cells are liquefied and grossly looks like loss of cells within the organ filled with fluid.

4. Fat necrosis

this type of necrosis is seen in fat tissues like the omentum. In this process the fatty acid react with  metallic ion like Ca, Na to form soap. The affected area looks shinny,whitish and later become opaque and solid

5.Zenkers necrosis

This is seen in striated muscles where the affected muscle looks whitish or pale swollen and shinny.

The outcome of necrosis

The tissues of a necrotic area may be got rid off or transformed into the ff

1.         Liquefaction of the dead cells and the removal of the fluid via the blood  and lymphatic systems

2.        Liquefaction of the dead tissues into a cysts-(a cyst is a cavity filled with a clear fluid).

3.         Liquefaction of the dead tissues and the formation of an abscess

4.        Gangrene formation: The necrotic tissues may be invaded by putrefactive bacteria leading to a gangrene.

5.         Encapsulation:        The area may be walled off by the formation of a thick fibrous tissue surrounding the necrotic area.

6.        Calcification:           In some cases the wall surrounding the necrotic area may be further be reinforced  by the addition calcium salt  e.g. in bovine tuberculosis.

7.         Replacement by scar tissue leading a scar at the place.

8.        Regeneration:          The formation of new cells like those that have died to replace the dead cells by the remaining cells.

DEGENERATION

Degeneration is a  chemical change developed within a cell as a result of an injury to the cell. The affected cell develop chemical changes or abnormalities in the cell which makes it less able to perform its normal functions and is also in danger of dying.  Degeneration can be said to be a step before necrosis where the cell has been injured  but the injury is not enough to kill the cell.

The affected cells  may recover or progress to necrosis

INFILTRATION:            In some cases, after the injury of a cell ,the cell will allow some foreign substances  to enter the cell giving rise to infiltration.  Infiltration can therefore be said to be a change in the chemical composition of the cell as a result of entry of foreign substances into the cell.

 Types of degeneration;

1.         Cloudy degeneration(cloudy swelling).

2.        Hydropic degeneration

3.         Fatty degeneration.

4.        Mucus and mucin degeneration

5.         Mucoid degeneration

6.        Hyaline degeneration.

Infiltrative changes are    1.  Amyloid infiltration.    2. Glycogen infiltration

Miscellaneous cellular changes are

1.Gout

2.Calcification

3.Pigmentation.

PATHOLOGY OF GROWTH;

Atrophy.

Hypertrophy.

Hypoplasia.

Tumours.

ATROPHY

Definition: This is  the shrinking of an organ from its normal size to less than its normal size. Atrophy may result from either a decrease in the number of constituent cells or a decrease in the sizes of the component cells.

Gross appearance of an atrophied organ:

1.      Smaller in size

2.     Harder.

3.     More fibrous.

Causes of atrophy:

1.      Damage to the nerve trunk supplying the organ; If the nerve trunk supplying a muscle is cut off the muscle will not be able to contract  or receive normal blood supply because the nerves  are essential for normal function of the blood vessels e.g. radial nerve paralysis leads to atrophy of the leg in man and dogs.

2.     Loss of blood supply to the  organ; When the blood supply to an organ is cut off ,the cells affected will die  leading to the organ becoming smaller.

3.     Starvation and malnutrition; During starvation, adipose tissue, muscle and grandular tissues are consumed to produce energy.

4.     Disuse atrophy .Generally organs tend to grow bigger when used continuously  and decrease in size when not used for along time.

5.     Prolong pressure from out side on an organ can lead to the shrinkage of the organ e.g.  in chronic orchitis the testes is observe to decrease in size

6.     Old age (physiological atrophy) this is due to cells becoming depleted  as a result of death  of some of the cells of the organ. Decrease in size of the uterus after parturition.

HYPERTROPHY

Hypertrophy refers to the increase in size of an organ from its normal size to more than its normal size. The increase in size is entirely due to the enlargement of the existing cells. There is no increase in the number of cells.

Types of hypertrophy and their causes:

There are 3 types

1.         Physiological hypertrophy; In this case the increase in size is due to normal body demand; e.g. the increase in size of the uterus during gestation in order to accommodate the growing foetus, the enlargement of the mammary gland at the approach of lactation, increase in the thickness of the muscle  following  continuous exercise and work demand.

2.        Compensatory Hypertrophy ;This is seen  in some paired organs like the kidney, testes, ovaries, where after the damage or the removal of one, the other pair enlarges in order to perform the functions of the two organs  as previously.

3.         Adaptive hypertrophy; here the increase in size of the organ is due to some pathological condition affecting the organ. e.g. the enlargement of the heart in some heart diseases and in  chronic anaemia. Enlargement of the spleen(splenomegaly) is seen in certain disease conditions  like trypanosomiasis.

Hyperplasis: This is  the abnormal enlargement

 of an organ due to increase in the number of cells of the organ.

Hypoplasia; This is the failure of an organ to develop to its normal size. The cause is usually congenital.

TUMOURS,CANCERS,NEOPLASMS

A tumour is a swelling resulting from new growth of cells within the organ. Tumours are denoted by the suffix -OMA  at the end of a word. e.g. adenoma, granuloma, carcinoma, pappiloma.

Characteristics of a tumours

1.         The tumour cells grow continuously  without control

2.        The tumour cells resemble the healthy cells of the organ.

3.         There is no orderly arrangement of the tumour cells.

4.        They serve no useful function, others may produce hormones in excessive amounts leading to disease e.g. ovarian tumour may lead to excessive production of oestrogen leading to nymphomania condition.

Classification of tumours:   2 Types:

1.         Benign tumours. These class of tumours do not normally  cause deaths. They grow slowly pressing or pushing neighbouring organs aside but not invading or destroying them. The seldom ulcerate through the skin. A benign tumour may later become malignant.

2.        Malignant tumours These class of tumours normally cause death. They grow and spread rapidly infiltrating and destroying neighbouring tissues. They are liable to ulcerate when superficial. They spread through the blood and lymphatic systems giving rise to secondary tumours.

Differences between Malignant and Benign tumours:

Malignant tumours:

             MALIGNANT TUMOURS                             BENIGN TUMOURS

Infiltrative: it grows and pierces into Nearby tissues and organs destroying Them in the process	Non-infiltrative: it pushes nearby organs Aside but does not pierce or destroy them
Not capsulated and therefore tend to be  Infiltrative and invasive.	Encapsulated: it normally has a well defined fibrous connective tissue capsule To prevent it from infiltrating nearby organs
Tendency to ulcerate through the skin and the mucus membrane.	Does not ulcerate
Metastasis Malignant tumours tend to spread to distant organs by means of metastasis. In this process a piece of the tumour mass breaks off and it is carried by the blood and the lymphatic routes to distant organs to start a new tumour. Benign tumours do not metastasis	There is no metastasis

Causes of tumours;

1.         Viral:  Some group of viruses are known to cause tumour(oncorna viruses).

2.        Parasites:      Spirocerca lupi which invades the walls of the oesophagus ultimately lead to tumour formation.

3.         Carcinogens:            these are substances that cause tumours.