A disease is any condition which disrupts the normal homeostatic processes of the body or any anomaly which alters normal body anatomy and physiology and is usually not the result of an external physical injury. Diseases can be caused by a wide range of etiological factors. These etiological factors may either be external or internal. Internal etiological factors usually arise from dysfunction in the immune system. This can be reduced immune function (immunocompromised states), increased immune reaction (hypersensitivity reactions such as asthma) autoimmunity or immunodeficiency. Diseases due to external factors usually arise from pathogenic agents such as parasites, bacteria, viruses and fungi. These diseases may affect one organ of the body such as the heart, lungs, skin or brain, in which case it is termed local, or may affect different organs at the same time, for example in shock due to systemic inflammatory response syndrome, in which case it is termed systemic.

Major Disease Classifications

Diseases are usually classified based on various factors. It is extremely important to classify these diseases. Not just is the classification necessary for diagnostic and therapeutic reasons, but it also aids in compiling important statistics on the etiology, prevalence and prognosis of diseases. For example, via the classification of diseases, it was made apparent that prevalence of lung cancer was beginning to increase by the numbers by the middle of the 20th century. Being aware of this, researchers decided to go on a search for the reason why lung cancer, which was once a rare form of cancer with very low prevalence, was beginning to go on the rise. It was later found that the rising incidence of lung cancer was attributed to the increased rate of cigarette smoking. Additionally, diseases are classified to get a good understanding of their pathogenesis.

As stated earlier, disease can be classified on different bases. The commonly used classifications of diseases are

  • Topographic classification: This involves classification of diseases based on topographic or systemic basis. In this category diseases are classified as respiratory diseases, neurological diseases, gynaecological diseases, immune system diseases, dermatological diseases and cardiovascular diseases.

  • Anatomic classification: This classification is based on the particular organ involved. In this category, diseases are classified as heart diseases, lung diseases and vascular diseases.

  • Physiological classification: This classification is based on the function of the body which has been affected.

  • Pathological classification: This classification is based on pathogenesis of the disease.

  • Etiological classification: This classification is based on the cause of the disease.

  • Epidemiological classification: This classification is based on the population or group of people which diseases affect.

It is important to note that one disease might fall into more than one disease classification. Various major subclasses of diseases will now be discussed below.

Gynaecological Conditions

Gynecological conditions are not just diseases but also any health concern pertaining to the female reproductive system. They include:

  • Disorders Pertaining to the Menstrual Cycle



*Heavy menstrual pain

  • Conditions that Require Family Planning:

*Contraceptive measures

*Advise on abortion


*Fertility problems

  • Papsmear abnormalities:

*Vaccination against human papilloma virus

*Routine papsmears.

  • General Gynaecological Disorders

*Polycystic ovarian disease

*Leiomyoma uteri (uterine fibroids)

*Uterine endometriosis


*Urinary tract infections

*Vagina skin disorders

*Acne vulgaris

*Congenital adrenal hyperplasia

  • Conditions Associated with the Outset of Menopause

*Postmenopausal symptoms

*Hormone replacement therapy

  • Disorders of the Pelvic Floor

*Weakness of the pelvic floor leading to conditions such as urinary incontinence and organ prolapse.

Neurological Disorders

Neurological disorders are disorders which affect the nervous system. This disorders affect cognition, memory and overall function. They are usually fatal and have poor prognosis. They include:

  • Vascular disorders such as cerebrovascular accident (shock) and intracranial hemorrhages such as subdural hemorrhage.

  • Diseases due to pathogenic microorganisms such as encephalitis, cerebral malaria, poliomyelitis and meningitis.

  • Anatomical disorders such as disc prolapse, muscle paralysis due to nerve degeneration, Bell’s palsy, Arnold-Chiari malformation and malignancy.

  • Physiological disorders such as seizures, fainting spells and neuralgia.

  • Biochemical disorders such as Wernicke encephalopathy.

  • Degenerative disorders such as Parkinson’s disease, Alzheimer’s disease and Huntington’s disease.

Dermatological Diseases

These include diseases that affect the skin. They include:

  • Inherited diseases such as: *Psoriasis: A condition caused by red inflammatory patches and scaly skin with bumps.

*Melanoma: Malignancy affecting the skin and is responsible for majority of deaths arising from skin cancers.

*Androgenetic alopecia: A condition characterized by minute growth of hairs on areas where hair growth should normally be prominent.

  • Acquired diseases are usually due to infections. These include:

*Tinea versicolor caused by Malassezia furfur

*Times nigra caused by Exophiala werneckii.

*Dermatophytoses caused by fungi of the genus Microphytum, Trichosporum and Epidermophytum.

*Candidiasis caused by Candida albicans.

*Sporotrichosis caused by Sporothrix schenckii



Cardiovascular Disorders

These include disorders affecting the heart and blood vessels. Cardiovascular disorders are among the leading causes of death worldwide. These disorders include:

  • Coronary heart disease

  • Arrhythmia

  • Stroke

  • Heart murmurs

  • Aneurysms

  • Cardiomyopathy

  • Rheumatic fever

  • Atherosclerosis

  • Arteriosclerosis

  • Hypertension

  • Hypotension

  • Carotid sinus syndrome

Immune System Disorders

These disorders affect the immune system. They include:

  • Hypersensitivity reactions:

*Type I hypersensitivity reactions such as asthma.

*Type II hypersensitivity reactions such as myasthenia gravis, autoimmune hemolytic anemia, Grave’s disease.

*Type III hypersensitivity reactions such as systemic lupus erythematosus and poststreptococcal glomerulonephritis.

*Type IV hypersensitivity reactions such as contact dermatitis.

  • Immunodeficiency diseases such as acquired immune deficiency syndrome caused by the human immunodeficiency virus.

Respiratory Diseases

Respiratory diseases are diseases which affect the respiratory system. They include:

  • Restrictive respiratory diseases:


*Myasthenia gravis

*Flail chest (broken ribs)

*Paralysis of diaphragm

*Pleural effusion


  • Obstructive respiratory diseases *Chronic bronchitis


*Cystic fibrosis *Laryngotracheobronchitis


*Chronic cough

Endocrine Disorders

These disorders affect the endocrine system. The endocrine system comprises the various endocrine glands responsible for the synthesis of endocrine hormones. Hormones are chemical messengers which carry out specific metabolic functions of the body. Thus, endocrine disorders often have metabolic consequences. They include:

  • Diabetes mellitus

  • Central diabetes insipidus

  • Hyperthyroidism and hypothyroidism

  • Hyperparathyroidism and hypoparathyroidism

  • Gigantism

  • Panhypopituitarism

  • Hypercortisolism

  • Hyperaldosteronism

Urinary System Disorders

These disorders affect the urinary system. The urinary system comprises the kidneys, urinary bladder, ureter and urethra. These disorders include:

  • Anuria

  • Oliguria

  • Nephrogenic diabetes insipidus

  • Renal failure

  • Glomerulonephritis

  • Urethral stricture

  • Urinary incontinence

  • Atonic bladder

  • Enuresis

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