Ross & Wilson Anatomy and Physiology in Health and Illness (176 page)

Hashimoto’s disease (
p. 223
)

The body makes antibodies to thyroglobulin, leading to destruction of thyroid hormone, and hyposecretion of the thyroid.

Graves’ disease

The body makes antibodies to thyroid cells. Unlike Hashimoto’s disease, however, the effect of the antibodies is to stimulate the gland, with a resultant hyperthyroidism (
p. 222
).

Autoimmune haemolytic anaemia (
p. 69
)

In this, individuals make antibodies to their own red blood cells, leading to haemolytic anaemia.

Myasthenia gravis

This autoimmune condition of unknown origin affects more women than men, and usually those aged between 20 and 40 years. Antibodies are produced that bind to and block the acetylcholine receptors of neuromuscular junctions. The transmission of nerve impulses to muscle fibres is therefore blocked. This causes progressive and extensive muscle weakness, although the muscles themselves are normal. Extrinsic and eyelid muscles are affected first, causing
ptosis
(drooping of the eyelid) or
diplopia
(double vision), followed by those of the neck (possibly affecting chewing, swallowing and speech) and limbs. There are periods of remission, relapses being precipitated by, for example, strenuous exercise, infections or pregnancy.

Immunodeficiency

When the immune system is compromised, there is a tendency to recurrent infections, often by microbes not normally pathogenic in humans (
opportunistic infections
). Immunodeficiency is classified as
primary
(usually occurring in infancy and genetically mediated) or
secondary
, that is, acquired in later life as the result of another disease, e.g. protein deficiency, acute infection, chronic renal failure, bone marrow diseases, following splenectomy or acquired immune deficiency syndrome (AIDS).

Acquired immune deficiency syndrome (AIDS)

This condition is caused by the human immunodeficiency virus (HIV), an RNA retrovirus which produces the enzyme
reverse transcriptase
inside the cells of the infected person (host cells). This enzyme transforms viral RNA to DNA and this new DNA, called the provirus, is incorporated into the host cell DNA. The host cell then produces new copies of the virus that pass out into tissue fluid and blood and infect other host cells. When infected host cells divide, copies of the provirus are integrated into the DNA of daughter cells, spreading the disease within the body.

HIV has an affinity for cells that have a protein receptor called CD
₄
in their membrane, including T-lymphocytes, monocytes, macrophages, some B-lymphocytes and, possibly, cells in the gastrointestinal tract and neuroglial cells in the brain. Helper T-cells (
Fig. 15.3
) are the main cells involved. When infected their number is reduced, causing suppression of both antibody-mediated and cell-mediated immunity with the consequent development of widespread opportunistic infections, often by microbes of relatively low pathogenicity.

HIV has been isolated from semen, cervical secretions, lymphocytes, plasma, cerebrospinal fluid, tears, saliva, urine and breast milk. The secretions known to be especially infectious are semen, cervical secretions, blood and blood products.

Infection is spread by:

•
sexual intercourse, vaginal and anal

•
contaminated needles used:

    
–
during treatment of patients

    
–
when drug users share needles

•
an infected mother to her child:

    
–
across the placenta before birth (vertical transmission)

    
–
during childbirth

    
–
possibly by breast milk.

The presence of antibodies to HIV indicates that the individual has been exposed to the virus but
not
that a naturally acquired immunity has developed. Not all those who have antibodies in their blood develop AIDS, although they may act as carriers and spread the infection to others.

A few weeks after initial infection there may be an acute influenza-like illness with no specific features, followed by a period of two or more years without symptoms.

Chronic HIV infection may cause persistent generalised lymphadenopathy (PGL). Some patients may then develop AIDS-related complex (ARC) and experience chronic low-grade fever, diarrhoea, weight loss, anaemia and leukopenia.

When AIDS develops, the main complications are widespread recurrent opportunistic infections and tumours. Outstanding features include the following.

•
Pneumonia, commonly caused by
Pneumocystis jirovecii
(formerly
Pneumocystis carinii
), but many other microbes may be involved.

•
Persistent nausea, diarrhoea and weight loss due to recurrent infections of the alimentary tract by a wide variety of microbes.

•
Meningitis, encephalitis and brain abscesses may be recurrent, either caused by opportunistic microbes or possibly by HIV.

•
Neurological function may deteriorate, characterised by forgetfulness, loss of concentration, confusion, apathy, dementia, limb weakness, ataxia and incontinence (
p. 349
).

•
Skin conditions, often widespread, may occur, e.g. eczema, psoriasis, cellulitis, impetigo, warts, shingles and cold sores (see
Ch. 14
).

•
Generalised lymphadenopathy (
p. 134
).

•
Development of malignant tumours is not uncommon, because of the progressive failure of immunological surveillance as the virus destroys the T-cell population. Typical cancers include:

    
–
Lymphoma (
p. 135
)

    
–
Kaposi’s sarcoma, consisting of tumours under the skin and in internal organs (
p. 364
).

For a range of self-assessment exercises on the topics in this chapter, visit
www.rossandwilson.com
.

CHAPTER 16

The musculoskeletal system

Bone
380

Functions of bones
380

Types of bones
380

Bone structure
380

Microscopic structure of bone
381

Development of bone tissue
382

Bone markings
384

Healing of bone
384

Axial skeleton
385

Skull
386

Vertebral column
391

Thoracic cage
395

Appendicular skeleton
396

Shoulder girdle and upper limb
396

Pelvic girdle and lower limb
398

Joints
401

Fibrous joints
401

Cartilaginous joints
401

Synovial joints
401

Main synovial joints of the limbs
404

Shoulder joint
404

Elbow joint
405

Proximal and distal radioulnar joints
405

Wrist joint
406

Joints of the hands and fingers
406

Hip joint
407

Knee joint
408

Ankle joint
409

Joints of the feet and toes
409

Muscle tissue
409

Smooth muscle
409

Cardiac muscle
410

Skeletal muscle
410

Action of skeletal muscle
412

Principal skeletal muscles
413

Muscles of the face and neck
413

Muscles of the trunk
414

Muscles of the pelvic floor
416

Muscles of the shoulder and upper limb
417

Muscles of the hip and lower limb
418

Diseases of bone
421

Osteoporosis
421

Paget’s disease
421

Rickets and osteomalacia
421

Osteomyelitis
421

Developmental abnormalities of bone
422

Tumours of bone
422

Disorders of joints
422

Inflammatory joint disease (arthritis)
422

Traumatic injury to joints
423

Osteoarthritis (osteoarthrosis, OA)
424

Gout
424

Connective tissue diseases
424

Carpal tunnel syndrome
424

Diseases of muscle
424

Myasthenia gravis
425

Muscular dystrophies
425

Crush syndrome
425

Rotator cuff injury
425

ANIMATIONS