Ross & Wilson Anatomy and Physiology in Health and Illness (26 page)

•
mild dysplasia
– the tumour cells retain most of their normal features and their parent cells can usually be identified

•
anaplasia
– the tumour cells have lost most of their normal features and their parent cells cannot be identified.

Encapsulation and spread of tumours

Most benign tumours are contained within a fibrous capsule derived partly from the surrounding tissues and partly from the tumour. They neither infiltrate local tissues nor spread to other parts of the body, even when they are not encapsulated.

Malignant tumours are not encapsulated. They spread locally by infiltration, and tumour fragments may spread to other parts of the body in blood or lymph. Some spreading cells may be phagocytosed but others lodge in tissues away from the primary site and grow into
secondary tumours
(metastases). Metastases are often multiple and
Table 3.3
shows common sites of primary tumours and their metastases.

Table 3.3 
Common sites of primary tumours and their metastases

Local spread

Benign tumours
enlarge and may cause pressure damage to local structures but they do not spread to other parts of the body.

Benign or malignant tumours may:

•
damage nerves, causing pain and loss of nerve control of other tissues and organs supplied by the damaged nerves

•
compress adjacent structures causing e.g. ischaemia (lack of blood), necrosis (death of tissue), blockage of ducts, organ dysfunction or displacement, or pain due to pressure on nerves.

Additionally
malignant tumours
grow into and infiltrate surrounding tissues and they may erode blood and lymph vessel walls, causing spread of tumour cells to other parts of the body.

Body cavities spread

This occurs when a tumour penetrates the wall of a cavity. The peritoneal cavity is most frequently involved. If, for example, a malignant tumour in an abdominal organ penetrates the visceral peritoneum, tumour cells may metastasise to folds of peritoneum or any abdominal or pelvic organ. Where there is less scope for the movement of fragments within a cavity the tumour tends to bind layers of tissue together, e.g. a pleural tumour binds the visceral and parietal layers together, limiting expansion of the lung.

Lymphatic spread

This occurs when malignant tumours grow into lymph vessels. Groups of tumour cells break off and are carried to lymph nodes where they lodge and may grow into secondary tumours. There may be further spread through the lymphatic system, and to blood because lymph drains into the subclavian veins.

Blood spread

This occurs when a malignant tumour erodes the walls of a blood vessel. A
thrombus
(blood clot) may form at the site and
emboli
consisting of fragments of tumour and blood clot enter the bloodstream. These emboli block small blood vessels, causing
infarcts
(areas of dead tissue) and development of metastatic tumours. Phagocytosis of tumour cells in the emboli is unlikely to occur because these are protected by the blood clot. Single tumour cells can also lodge in the capillaries of other body organs. Division and subsequent growth of secondary tumours, or
metastases
, may then occur. The sites of blood-spread metastases depend on the location of the original tumour and the anatomy of the circulatory system in the area. The most common sites of these metastases are bone, the lungs, the brain and the liver.

Effects of tumours

Pressure effects

Both benign and malignant tumours may compress and damage adjacent structures, especially if in a confined space. The effects depend on the site of the tumour but are most marked in areas where there is little space for expansion, e.g. inside the skull, under the periosteum of bones, in bony sinuses and respiratory passages. Compression of adjacent structures may cause ischaemia, necrosis, blockage of ducts, organ dysfunction or displacement, pain due to invasion of nerves or pressure on nerves.

Hormonal effects

Tumours of endocrine glands may secrete hormones, producing the effects of hypersecretion. The extent of cell dysplasia is an important factor. Well-differentiated benign tumours are more likely to secrete hormones than are markedly dysplastic malignant tumours. High levels of hormones are found in the bloodstream as secretion occurs in the absence of the normal stimulus and homeostatic control mechanism. Some malignant tumours produce uncharacteristic hormones, e.g. some lung tumours produce insulin. Endocrine glands may be destroyed by invading tumours, causing hormone deficiency.

Cachexia

This is the severe weight loss accompanied by progressive weakness, loss of appetite, wasting and anaemia that is usually associated with advanced metastatic cancer. The severity is usually indicative of the stage of development of the disease. The causes are not clear.

Causes of death in malignant disease

Infection

Acute infection is a common cause of death when superimposed on advanced malignancy. Predisposition to infection is increased by prolonged immobility or bedrest, and by depression of the immune system by cytotoxic drugs and irradiation by X-rays or radioactive isotopes used in treatment. The most commonly occurring infections are pneumonia, septicaemia, peritonitis and pyelonephritis.

Organ failure

A tumour may destroy so much tissue that an organ cannot function. Severe damage to vital organs, such as lungs, brain, liver and kidneys, are common causes of death.

Carcinomatosis

When there is widespread metastatic disease associated with cachexia, severe physiological and biochemical disruption follows causing death.

Haemorrhage

This may occur when a tumour grows into and ruptures the wall of a vein or artery. The most common sites are the gastrointestinal tract, brain, lungs and the peritoneal cavity.

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.

Section 2

Communication

CHAPTER 4

The blood

Plasma
56

Cellular content of blood
57

Erythrocytes (red blood cells)
57

Leukocytes (white blood cells)
61

Platelets (thrombocytes)
63

Erythrocyte disorders
66

Anaemias
66

Iron deficiency anaemia
66

Megaloblastic anaemias
67

Aplastic anaemia
67

Haemolytic anaemias
67

Acquired haemolytic anaemias
68

Normocytic normochromic anaemia
69

Polycythaemia
69

Leukocyte disorders
69

Leukopenia
69

Leukocytosis
70

Leukaemia
70

Haemorrhagic diseases
71

Thrombocytopenia
71

Vitamin K deficiency
71

Disseminated intravascular coagulation (DIC)
71

Congenital disorders
72

ANIMATIONS

4.1
Blood cell formation and functions
57

4.2
Red blood cells
57

4.3
Blood grouping
60

4.4
Haemolytic disease of the newborn
61

4.5
White blood cells
61

4.6
Platelets and clot formation
63

Blood is a fluid connective tissue. It circulates continually around the body, allowing constant communication between tissues distant from each other. It transports:

•
oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs for excretion

•
nutrients from the alimentary tract to the tissues, and cell wastes to the excretory organs, principally the kidneys

•
hormones secreted by endocrine glands to their target glands and tissues

•
heat produced in active tissues to other less active tissues

•
protective substances, e.g. antibodies, to areas of infection