Cellular Adaptations & Injury.pdf

Cellular Adaptations  Cell specificity and homeostasis Each cell has a specific function Genetic setup Machinery and metabolic pathways Cell’s specific function The concept of homeostasis - equilibrium with external environme...

Cellular Adaptations  Cell specificity and homeostasis Each cell has a specific function Genetic setup Machinery and metabolic pathways Cell’s specific function The concept of homeostasis - equilibrium with external environment - maintenance of dynamically stable internal machinery - input orchestrated with output  Concept of adaptation External disturbances - Physiologic - pathologic changes in cell machinery new steady state counteract external changes escape from cell injury preserve viability  Cellular adaptations Reactions induced by: - physiological stimuli - pathological stimuli. Aim: to escape cell injury The adaptive responses include: 1.Atrophy 2.Hypertrophy 3.Hyperplasia 4.Metaplasia 5.Dysplasia  Hypertrophy An increase in the size of cells resulting in increase in the size of the relevant organ. It is caused either by increased functional demand or by specific hormonal stimulation. Hypertrophy can be physiologic or pathologic. Physiological e.g. - athletes - mechanical workers - uterus in pregnancy (+ hyperplasia) Pathological e.g. - LVH in systemic hypertension Athletes as an example of muscular hypertrophy  Uterine hypertrophy in pregnancy On the left is a normal uterus showing the normal mass of smooth muscle in its wall. On the right is a uterus from a pregnant women, in which the striking increase in mass of smooth muscle is evident. At cellular level this is due to both hyperplasia and hypertrophy of uterine smooth muscle.  Normal Vs hypertrophied uterine smooth muscle cells A B A. Small spindle-shaped uterine smooth muscle cells from a normal uterus. Compare this with (B) large, plump hypertrophied smooth muscle cells from a gravid uterus (same magnification). A 51-year-old male has a blood pressure of 150/95 mm Hg. If this condition remains untreated for years, which of the following cellular alterations will be seen in the heart? (A) Atrophy (B) Hyperplasia (C) Metaplasia (D) Hemosiderosis (E) Hypertrophy Comparison between normal heart (left) & hypertrophied heart (right)  Define hyperplasia. Give examples.  Hyperplasia Increase in the number of cells in an organ or tissue leading to an increase in its size. Hyperplasia and hypertrophy closely related; often occur together  Physiological and pathological HP Physiological hyperplasia : 1. Hormonal: Uterus in pregnancy. 2. Compensatory: Following partial liver resection Pathological hyperplasia: 1. Excessive hormonal stimulation: Estrogen induced endometrial hyperplasia 2. The effect of growth factors on target cells: e.g. Viral warts  Endometrial hyperplasia The prominent folds of endometrium in this uterus (opened to reveal the endometrial cavity) are an example of hyperplasia. The hyperplasia involves both endometrial glands and stroma.  Verruca vulgaris (Viral warts) Multiple papules with rough, pebble-like surfaces at infection sites.Define atrophy.Give examples  Atrophy Decrease in the size of the cell ↓organ or tissue size (atrophic) It is an adaptive response Causes of atrophy 1. Decrease workload (e.g. immobilization of a limb) 2. Denervation (e.g. in poliomyelitis) 3. Ischemia 4. Under nutrition (e.g. Starvation) 5. Loss of endocrine stimulation (e.g. postmenopausal endometrial atrophy) A. Normal brain of a young adult. B. Atrophy of the brain in an old male with atherosclerotic disease. Atrophy of the brain is due to aging and reduced blood supply. Note that loss of brain substance narrows the gyri and widens the sulci. The meninges have been stripped from the right half of each specimen to reveal the surface of the brain.  B A A. Is a normal testis. B. Atrophic testis Bilateral atrophy may complicate chronic alcoholism, hypopituitarism, atherosclerosis, chemotherapy or radiation, and severe prolonged illness..Define metaplasia.Give examples  Metaplasia Replacements of one mature cell type by another mature cell type Also represent a reversible adaptive response Examples 1. Squamous metaplasia of the - laryngeal and bronchial respiratory epithelium in heavy smokers - urothelium in the urinary bladder in bilharziasis 2. Columnar metaplasia of lower esophageal squamous epithelium in gastro-esophageal reflux disease. Metaplasia of normal columnar (left) to squamous epithelium (right) in a bronchus Barrett esophagus: Metaplastic transformation (arrow) of the normal esophageal stratified squamous epithelium (Lt) to mature columnar epithelium