Lecture # 16 CELL ADAPTATION - I Dr. Iram Sohail Assistant Professor Pathology College of Medicine Majmaah University OBJECTIVES • Definition of adaptation • Classification of adaptation • Mechanism of adaptation ADAPTATION • Adaptation is a reversible change in – Size – number – morphology – or function of cell in response to change in environment. Adaptation can be • Physiological • Pathological CLASSIFICATION OF ADAPTATION There are four types of adaptations 1. Hypertrophy 2. Hyperplasia 3. Atrophy 4. Metaplasia 1. HYPERTROPHY • Hypertrophy is an increase in the size of cell that results in increase in the size of organ. • Hypertrophy occurs in non-dividing cells. Mechanism Hypertrophy can be i. Physiological – Increased levels of estrogen during pregnancy causes enlargement of smooth muscles of uterus and eventually the whole uterus will enlarge. ii. Pathological • Heart enlargement in hypertension – Cardiac cell enlargement is caused by 2 types of signals a. Mechanical triggers – Such as stretch b. Trophic triggers • Increased production of growth factors, structural proteins, myofilaments ---- size & functional capacity of cell will increased. 2. HYPERPLASIA • Hyperplasia is the increased in the numbers of cells. • Occurs in dividing cells only. Hyperplasia can be physiologic or pathologic 1) physiologic: 1- hormonal (breast in pregnancy, endometrium: pregnancy) 2- compensatory : Hyperplasia that occurs when a portion of tissue is removed (resected liver can be restored after time by growth factors produced by remaining hepatocytes) 2) Pathologic: 1- Endometrial hyperplasia if balance between estrogen and progesterone is disturbed 2- Prostatic hyperplasia (dihydrotestosterone + estrogen) 3- Gyenecomastia (Estrogen) Mechanism Hyperplasia can be i. Physiological – Breast enlargement at puberty & during pregnancy. • The mechanism behind this type of hyperplasia is increased hormonal stimulation at puberty and during pregnancy causes increased in the number of breast cells. ii. Pathological • Endometrial hyperplasia in response to hormonal imbalance between estrogen and progesterone. 3. ATROPHY • Decrease in the size of cell (by the loss of cell substances) • Atrophy results in shrinkage of organ and also the function of organ will decrease. Causes • Decreased workload • Loss of nerve supply • Loss of blood supply • Inadequate nutrition • Loss of hormonal stimulation • Aging Mechanism • Decrease protein synthesis • Increase protein degradation • Autophagy (self-eating) – Starved cell eats its own components Renal atrophy Testicular atrophy Brain atrophy 4. METAPLASIA • One adult cell type is replaced by another cell type. • In metaplasia the metaplastic cell will be able to withstand the adverse environment. Mechanism • Genetic re-programming of stem cells • Example – In smokers, the normal ciliated columnar epithelial cells of respiratory tract are replaced by stratified squamous epithelium. Dysplasia: • Not truly adaptation • It is a pre-malignant disturbance of the cell proliferation, maturation and growth • The cells show: – Change in size, shape – Change in nuclei – Loss of organization – Increased mitotic activity • Seen in hyperplastic and metaplastic epithelium • May progress to cancer if stimulus not removed but it is a reversible change Cervical dysplasia Agenesis : • Is complete failure of development of an organ ( absent) – Kidney , Testis Hypoplasia : • Is the failure of development to reach normal mature size of organ Uterus, kidney, testes Aplasia : • Is complete cessation of multiplication of cells, which are in state of continuous multiplication to do their normal function – Bone Marrow cells ( radiation , drugs )