Variations in Growth

Variations in Growth

1. Hyperplasia

   • increase in mass of an organ due to an increase in the NUMBER of its specialised constituent cells
     • Pubertal/Lactating breasts
     • Fibroadenosis of breast (benign)
     • Compensatory: increase in size to take over function of both organs
     • Reactive: pathological stimulus, physiological response

2. Hypertrophy

   • increase in mass of an organ due to an increase in the SIZE of its specialised cells
     • skeletal muscles of athletes
     • heart muscle of hypertensive patients
     • Smooth muscle undergoes a combination of hyperplasia and hypertrophy

3. Atrophy

   • decrease in mass of an organ due to a decrease in the size/number of its specialised cells
     • (Involution) uterus after menopause, testes in old age, thymus gland after childhood
     • hydronephrosis (pressure atrophy cased by urine obstruction), brain of a dementia patient, malnutrition

4. Agenesis

   • failure of an organ to develop at all from its primordia
     • anencephaly (lack of cerebrum), genesis of kidney (unilateral or bilateral), Amelia (no limbs - thalidomide)

5. Aplasia

   • sudden cessation of growth leading to decreased mass of tissue and defective development of the organ
     • thymus gland aplasia during childhood (T-cells result in immunodeficiency), Bone marrow aplasia (depleted blood cells result in aplastic anaemia)

6. Hypoplasia

   • tissue fails to attain full size
     • cryptorchidism (maldescended testes cause sterility), microcephaly (hypoplasia of brain causes neurological defects)

7. Metaplasia

   • fully differentiated adult cell changes into another more resilient but less specialised fully differentiated adult cell type (in response to chronic injury)
     • smokers airways (normal ciliated respiratory epithelium changes to stratified squamous epithelium), Gall bladder (gall stones - normal columnar epithelium changes to stratified squamous epithelium)

8. Dysplasia (occurs if metaplasia continues)

   • abnormal growth and differentiation with loss of regularity of cells, orientation and relationship to one another
     • Oral cavity (smoking, dentures), respiratory tract (smoking), cervix of the uterus (HPV)

9. Hamartoma

   • a focal overgrowth of normal cells in a tissue in which these cells ARE usually present
     • benign naevus (melanocytes proliferated - "mole"), haemangioma (blood vessels proliferated - "strawberry birthmark")

10. Choristoma (Ectopia)

    • a focal overgrowth of normal cells found in a tissue, in which these cells are NOT usually present
      • endometriosis (endometrial tissue outside the endometrium), adenomyosis (endometrial tissue in the myometrium)

11. Neoplasia

    • process that leads to the formation of an abnormal uncontrolled new growth of tissue, which has no coordinated useful function in the body
      • CLASSIFICATIONS
        • CLINICAL: describes the behaviour of the tumour and its effect on the patient
          • benign - margins are well defined with only local growth. Malignant - margins are poorly defined, neoplastic cells are growing into and destroying surrounding tissue
        • HISTOGENIC: describes the tissue origin of the tumour
          • bening tumours are give the suffix "-oma". Malignant epithelial tumours are given the suffix "carcinoma". Malignant mesenchymal tumours are given the suffix "sarcoma".
        • MORPHOLOGICAL: describes the appearance of the tumour
          • Scirrhous tumour: hard on palpation due to substantial collagenous stromal tissue. Encephaloid tumour: soft on Palatino due to little collagenous stromal tissue.