Fundamentals of Pathology - Growth Adaptations

Fundamentals of Pathology - Growth Adaptations

Introduction to Growth Adaptations

  • The concept of homeostasis in relation to organs and physiological stress.
  • Example: The heart in homeostasis while pumping against systemic blood pressure.
  • When physiological stress increases, organs undergo growth adaptations to cope with the stress.
  • Importance of growth adaptations in examinations.

Overview of Growth Adaptations

  • Major types of growth adaptations: Hyperplasia and Hypertrophy.
  • Definition of Hyperplasia:
    • Increase in the number of cells, resulting in an increase in organ size.
  • Definition of Hypertrophy:
    • Increase in the size of individual cells, contributing to organ size increase.
    • Mechanisms of Hypertrophy:
    • Involves gene activation, protein synthesis, and production of organelles.

Hypertrophy Explained

  • Example: Uterus during pregnancy:
    • Undergoes both hyperplasia (increase in cell number) and hypertrophy (increase in cell size) to accommodate the developing fetus.

Permanent Tissues and Growth Adaptations

  • Permanent tissues that undergo hypertrophy only:
    1. Cardiac myocytes
    2. Skeletal muscle
    3. Nerve cells
  • Reason: They do not possess stem cells, thus hyperplasia cannot occur.

Case Study: Cardiac Hypertrophy

  • Example of thickened left ventricle vs. normal right ventricle.
  • Mechanism of change: Hypertrophy due to increased workload.

Pathologic and Physiologic Hyperplasia

  • Difference between pathologic and physiologic hyperplasia:
    • Pathologic Hyperplasia:
    • Caused by underlying pathological processes, potentially leading to dysplasia and cancer.
    • Example: Endometrial hyperplasia from prolonged estrogen exposure, can progress to endometrial carcinoma.
    • Physiologic Hyperplasia:
    • Occurs naturally without increased cancer risk, such as during pregnancy.

Atrophy

  • Definition of Atrophy:
    • Decrease in organ size due to decreased stress or demand on the organ.
    • Mechanisms:
    • Decrease in cell number through apoptosis.
    • Decrease in cell size through two pathways:
      • Ubiquitin Proteasome Degradation Pathway:
      • Mechanism for breaking down cytoskeletal components to reduce cell size.
      • Autophagy:
      • Cell consumes its own cellular components; involves formation of vacuoles that fuse with lysosomes for degradation.

Metaplasia

  • Definition of Metaplasia:
    • Change in cell type in response to stress, allowing for better handling of the new stress.
  • Commonly involves surface epithelial cells.
  • Example: Barrett's Esophagus:
    • Change of the lower esophagus from squamous to columnar epithelium due to acid reflux.
    • Columnar epithelium is more suited to handle acid exposure.
    • Histological images and distinctions with normal conditions.
    • Metaplasia is reversible upon removal of the stressor.
    • Risk factors: Barrett’s esophagus as a precursor to adenocarcinoma of the esophagus.
  • Exception: Apocrine metaplasia does not increase cancer risk, seen in fibrocystic breast changes.

Vitamin A Deficiency and Metaplasia

  • Relevance of Vitamin A deficiency:
    • Associated with night blindness and impaired immune function.
    • Vitamin A is crucial for maintaining specialized epithelial cells.
  • Example: Keratomalacia in vitamin A deficiency causes squamous epithelial cells to undergo metaplasia, resulting in thickening of the conjunctiva.

Myositis Ossificans

  • An example of metaplasia where skeletal muscle can form bone due to inflammation post-trauma.
  • Distinguishing from osteosarcoma:
    • Normal adjacent bone, clearly separated from pathological bone within muscle.

Dysplasia

  • Definition of Dysplasia:
    • Disordered growth often seen as a precursor to cancer; classically associated with CIN (cervical intraepithelial neoplasia).
  • Originates from long-standing pathologic hyperplasia or metaplasia.
    • Example: Endometrial hyperplasia leading to endometrial carcinoma, and Barrett's esophagus progressing to dysplasia and cancer.
  • Difference from cancer:
    • Dysplasia is reversible if stress is addressed, while carcinoma is irreversible.

Aplasia and Hypoplasia

  • Aplasia: Failure of tissue growth or organ development, e.g., congenital absence of a kidney.
  • Hypoplasia: Incomplete development or decreased number of cells, such as in Turner syndrome (streak ovary).