Fundamentals of Medicine, Causes of Disease | Science & Technology for UPSC CSE PDF Download

• Etiology: Etiology is the study of the causation of disease. It may be intrinsic (within the body) or extrinsic (outside the body).
• Pathology: Pathology deals with the study of diseases and their causes.
• Homeostasis: The mechanism by which the body is kept in equilibrium is known as Homeostasis.
• Predisposing Causes: These are those that make the person susceptible to the disease and are also known as remote, distant or preparatory causes.
• Pathogenesis: The mechanism by which the causes produce disease.
• Symptoms or Signs is the outward manifestations of the patient suffering from disease while alive.
• The lesion is the alteration in the structure, detectable macroscopically by the naked eye or microscopically.
• The incubation period is the time that elapses between the action of a cause and the manifestation of disease.
• Prognosis is the estimation of the probable severity and outcome of the disease. 
• Morbidity is the percentage of deaths among the population affected by a disease. 
• An autopsy is seeing with one's own eyes. Also known as necropsy.
• A biopsy is an examination of tissues received from the living body.

Causes of Disease

Etiological Factors

The disease-causing agents can be classified as follows:

I. Genetic or Inherited Causes: These causes are transmitted to the offspring through the germplasm.

• Lethal factors: Some factors cause death in utero or after birth death
• Sublethal factors: Those factors which are inherited and interfere with the function of the body but do not cause death.
• Defects that are inherited errors in structure or function

Cryptorchidism: The condition in which one or both testicles do not descend to the scrotal sac and remain in the abdominal cavity. The testicle is complete or partial non-functional in this condition.

Webbed digits: Web-like structures are present in between the digits.

Webbed Digits

II. Non-genetic or Non-inherited Defects: These causes do not transmit through the germplasm.

Anomalies: Developmental defect affecting an organ or part of the body.

1. Disturbances in the development

2. Arrest of development

• Agenesia or aphasia: Complete absence of a body part. Agenesia renale—when there is no Kidney in the body.
• Hypoplasia: Reduction in size of a body part.
• Atresia: Closer of the lumen of a hollow organ or duct - Atresia ani (closure of ana opening)
• Fissure: Inability to fuse the part on the median line.
• Fusion of paired organs: Horseshoe kidney.

3. Excessive Development

• Congenital hypertrophy: Increase in the size of the organ. Example: Ventricular hypertrophy is the hypertrophy of the myocardium of the ventricle.
• Increase in number - Example: Polydactyla is the presence of supernumerary digits on the hands or feet.