Reversible Cell Injury

• what are the Ultrastructural changes of reversible cell injury?

  1. Plasma membrane alterations - blebbing, blunting, and loss of microvilli

  2. Mitochondrial changes - swelling and the appearance of small amorphous densities

  3. Accumulation of "myelin figures" in the cytosol c.o of phospholipids derived from damaged cellular membranes

  4. Dilation of the ER, with detachment of polysomes

  5. Nuclear alterations, with disaggregation of granular and fibrillary elements
• what are the features of reversibly injured cells?

  1) Generalized swelling of the cell and its organelles - blebbing of the plasma membrane, detachment of ribosomes from the endoplasmic reticulum (ER), and clumping of nuclear chromatin.

  2) Fatty change - occurs in organs that are actively involved in lipid metabolism (e.g., liver).

  
• what is the cellular response to chronic irritation

  metaplasia
• what is the cellular response to decreased nutrient supply or disuse

  atrophy
• what is the cellular response to increased hormones and GF?

  hyperplasia
• what is the cellular response to increase workload or demand?

  hypertrophy
• what is the Mechanism of Metaplasia

  maturecellswon'tbeconverted?

  either reprogramming of local tissue stem cells or, alternatively, colonization by differentiated cell populations from adjacent sites. In either case, the metaplastic change is stimulated by signals generated by cytokines, growth factors, and extracellular matrix components in the cells' environment.Metaplasia is pre‐malignant, if the insult persists, it can induce a malignant change in the metaplastic epithelium.
• where does metaplasia of squamous to columnar occur? why?

  Esophagus in chronic gastro-esophageal acid reflux disease.

  •The normal stratified squamous epithelium of the lower esophagus - cannot handle the acidity of reflux disease - undergoes metaplastic transformation to columnar epithelium - >Barrett's oesophagus

  can be precancerous and lead to development of adenocarcinoma of esophagus.
• what is the most common epithelial metaplasia?

  columnar to squamous ( in

  respiratory tract of smokers)Although the metaplastic squamous epithelium will survive better, the important protective functions of columnar epithelium are lost, such as mucus secretion and ciliary action.

  columnarcellslinedbycilia replaced
• what is Metaplasia?

  Definition: A reversible cell change, in which one differentiated cell

  type (epithelial/mesenchymal)is replaced by another cell type.
• what are the pathways for protein degradation?

  1. Ubiquitin - proteasome pathway:The degradation of cellular proteins occurs - Nutrient deficiency and disuse may activate ubiquitin ligases.

  2. Increased autophagy: increased numbers of autophagic vacuoles. Some cell debris within the autophagic vacuoles resist digestion and persist in the cytoplasm as membrane-bound residual bodies.
• what leads to atrophy?

  Atrophy results from decreased protein synthesis and increased protein degradation in cells. Protein synthesis decreases because of reduced trophic signals (e.g., those produced by growth receptors), which enhance uptake of nutrients and increase mRNA translation.
• what are examples of pathologic atrophy?

  - Loss of endocrine stimulation ( loss of estrogen in postmenopausal women) results in atrophy of

  endometrium, vaginal epithelium and breast.

  - A tumor compressing the surrounding normal tissue

  (due to compromised blood supply).
• what are examples of Physiologic atrophy?

  ‐Atrophy of embryonic structures like notochord and thyroglossal duct.

  - The decrease in the size of the uterus that occurs shortly after parturition.
• what is atrophy?

  reduction in the size of an organ or tissue due to a decrease in cell size and number.
• what induces hyperplasia?

  action of growth factors on cells, which leads proliferation of mature cells or on stem cells to produce new cells.
• true or false: Human papillomavirus(HPV) can cause hyperplasia leading to cancer

  true
• what is an example of Compensatory hyperplasia?


  part of the liver growing back
• which adaptive process does the bone marrow undergo during acute bleeding, hemolysis?

  hyperplasia
• during pregnancy why do the breasts change?

  Physiologic hyperplasia of breast and endometrium to increase its functional capacity
• during pregnancy the size of the uterus increases, why?

  due to Hypertrophy and hyperplasia
• what is Hyperplasia?

  increase in the number of cells in an organ or tissue in response to a stimulus.It occurs in cells capable of division.
• what are the stimuluses for hypertrophy?

  mechanical stress ( increase workload), agonists, growth factors leading to an Increased intracellular protein production

  
• in which type of cells does Hypertrophy happen?

  in Non dividing cells like

  ‐Skeletal muscle

  ‐Cardiac muscle
• what is Hypertrophy?

  increase in the size of cells that results in an increase in the size of the affected organ.
• what are the principal adaptive responses?

  • Hypertrophy

  • Hyperplasia

  • Atrophy

  • Metaplasia
• what are the changes that happen in an adapted cell?why?

  An adapted cell shows functional & morphologic changes. These changes make the cells able to sustain & live under physiologic stress or pathologic state Such changes are reversible - Upto a certain point
• what is adaptation?

  Adaptations are reversible changes in the size, number, phenotype, metabolic activity, or functions of cells in response to changes in their environment.
• what are the Cellular responses to stress and injurious stimuli?

  • Adaptations

  • Cell injury

  • Autophagy

  • Accumulation

  • Calcification

  • Aging
• what does a cellular response depend on?

  - The cell's ability to sustain, its nutrition & type and

  - The nature, duration and severity of stress
• What disturbs cells and causes cell injury?

  • O2 depletion

  • Physical agents

  • Chemicals and drugs

  • Infections

  • Immunologic reactions

  • Genetic Derangements (Mutation)

  • Nutritional deficiencies or over nutrition