Biology of Disease

be a feature of some diseases. Diseases may involve functional abnormalities
such as an inappropriate secretion of hormones. Examples of these include
the excessive production of thyroid hormones in hyperthyroidism or the
inadequate secretion of insulin in type 1 diabetes mellitus. Other functional
defects might include impaired nerve conduction and muscular contraction.

The term syndrome is often applied to describe certain diseases that are
characterized by multiple abnormalities that form a distinct clinical picture.
For example, Cushing’s syndrome (Chapter 7) occurs when an excess of the
hormone cortisol produces a combination of clinical features that include
hirsutism (excessive growth of facial hair), obesity, hypertension and
characteristic facial and body features.

Some diseases frequently present with complications, that is, new or
separate processes secondary to, and a consequence of, the initial disease.
Diabetic cataracts, retinopathy and nephropathy are all chronic or long-term
complications of diabetes mellitus.

The manifestations of a disease in a given person are not static and are affected
by compensatory mechanisms in the body as well as by environmental
influences and responses to treatment. Diseases often have a range of
manifestations and their presence and severity may vary from patient to
patient. In addition to differences between individuals, differences occur
within an individual at different stages of development, from infancy to old
age. Figure 1.5 outlines the key features of some diseases in terms of their
etiology, pathogenesis and manifestations.

Outcome of a Disease

Theprognosis of a disease is its likely outcome. Prognoses can vary considerably
between different diseases and, of course, can be influenced by treatment.
Hence when giving a prognosis, it is necessary to clarify if the disease is
following its natural course or whether there is, or needs to be, medical or
surgical intervention. A viral disease such as German measles (rubella) will
normally resolve of its own accord, whereas a broken leg or a heart attack
needs treatment. With some diseases, especially some cancers, patients may
go through a period of good health with a reduction or disappearance of the
symptoms and the disease is said to be in remission. However, a relapse may
occur with a return of the disease symptoms following this period of apparent
recovery. Diseases with a tendency towards remission and relapse include
acute lymphoblastic leukemia and ulcerative colitis (Chapters 17 and 11 ).

CHARACTERISTIC FEATURES OF DISEASES

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Figure 1.5 Characteristics of some diseases

showing relationship between etiology,

pathogenesis, morphological and functional

features and complications and sequelae.

mutation

(Chapter 15)

immune

reaction to

virus-infected

cells

(Chapter 4)

Pathogenesis

acute

inflammation

smoking tumor of the

lung

metastases

leading to

secondary

tumors

hepatitis B

virus

cirrhosis of

the liver

liver

failure

Local skin

infection

(Chapters 2

& 3)

Neoplasms,

for example

lung cancer

(Chapter 17)

Cirrhosis of

the liver

(Chapters 2

& 12)

Etiology

Morphological

and functional

features

Complications

and sequelae

local skin

infection

visible

Staphylococcus septicemia

aureus