Growth Adaptations and Atrophy Quiz
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Questions and Answers

What cellular process is primarily responsible for the decrease in organ size during atrophy?

  • Neurogenesis
  • Hyperplasia
  • Apoptosis (correct)
  • Decreased blood supply

    • What is the main distinguishing feature of hypertrophy compared to hyperplasia?

  • Occurs in permanent tissues (correct)
  • Involves cellular division
  • Can occur in response to hormonal stimulation
  • Involves organelle reduction

    • Which type of growth adaptation involves the production of new cells from stem cells?

  • Hypertrophy
  • Metaplasia
  • Hyperplasia (correct)
  • Atrophy

    • What is a consequence of pathologic hyperplasia as mentioned in the content?

    <p>Development of dysplasia</p> Signup and view all the answers

    What mechanism is involved in the breakdown of cellular components during atrophy?

    <p>Ubiquitin-proteosome degradation</p> Signup and view all the answers

    In which scenario does metaplasia commonly occur?

    <p>Change in physical stress on an organ</p> Signup and view all the answers

    What is a notable exception regarding the risks associated with benign prostatic hyperplasia (BPH)?

    <p>It has no correlation with prostate cancer risk</p> Signup and view all the answers

    What type of cellular changes typically accompany hypertrophy in the uterus during pregnancy?

    <p>Hyperplasia and hypertrophy</p> Signup and view all the answers

    What type of cells does Barrett esophagus involve after metaplasia occurs due to acid reflux?

    <p>Nonciliated, mucin-producing columnar cells</p> Signup and view all the answers

    Which condition is described as a precursor to cervical cancer?

    <p>Dysplasia</p> Signup and view all the answers

    What is the nature of metaplasia in terms of cellular change?

    <p>It involves stem cell reprogramming to new cell types.</p> Signup and view all the answers

    What can result from persistent stress in metaplasia?

    <p>Progression to dysplasia and potentially cancer</p> Signup and view all the answers

    In vitamin A deficiency, which type of metaplasia occurs in the conjunctiva?

    <p>Stratified keratinizing squamous epithelium</p> Signup and view all the answers

    What term describes disordered cellular growth that often indicates precancerous conditions?

    <p>Dysplasia</p> Signup and view all the answers

    Which of the following conditions does NOT represent a type of metaplasia?

    <p>Cervical intraepithelial neoplasia</p> Signup and view all the answers

    What is the consequence if dysplasia goes unresolved?

    <p>Progression to carcinoma</p> Signup and view all the answers

    Hypertrophy results exclusively from an increase in cell number.

    <p>False</p> Signup and view all the answers

    Atrophy may occur due to decreased blood supply to an organ.

    <p>True</p> Signup and view all the answers

    Benign prostatic hyperplasia (BPH) is associated with an increased risk of prostate cancer.

    <p>False</p> Signup and view all the answers

    Metaplasia can occur in mesenchymal tissues, such as muscle, as seen in myositis ossificans.

    <p>True</p> Signup and view all the answers

    Barrett esophagus is an example of dysplasia resulting directly from normal squamous epithelial cells.

    <p>False</p> Signup and view all the answers

    Pathologic hyperplasia can lead to dysplasia, which may progress to cancer.

    <p>True</p> Signup and view all the answers

    Metaplasia typically involves the transformation of one type of muscle tissue into another.

    <p>False</p> Signup and view all the answers

    Vitamin A is not essential for the differentiation of epithelial surfaces, and its deficiency leads to metaplasia.

    <p>False</p> Signup and view all the answers

    Cells in permanent tissues undergo hyperplasia in response to increased physiological stress.

    <p>False</p> Signup and view all the answers

    Dysplasia can be reversed if the inciting stress is removed, but can progress to carcinoma if stress continues.

    <p>True</p> Signup and view all the answers

    Keratomalacia results from the transformation of the conjunctival epithelium into a non-keratinizing form due to vitamin A deficiency.

    <p>False</p> Signup and view all the answers

    The process of autophagy involves the breakdown of cellular components by lysosomes.

    <p>True</p> Signup and view all the answers

    Hypertrophy and hyperplasia can occur simultaneously in response to increased stress on an organ.

    <p>True</p> Signup and view all the answers

    The acid reflux from the stomach leads to the production of keratinizing squamous cells in Barrett esophagus.

    <p>False</p> Signup and view all the answers

    Dysplasia often arises from long-standing pathologic hyperplasia or metaplasia.

    <p>True</p> Signup and view all the answers

    Metaplasia is an irreversible cellular change that always leads to cancer.

    <p>False</p> Signup and view all the answers

    Explain how hypertrophy and hyperplasia can occur together during physiological stress.

    <p>Hypertrophy increases cell size while hyperplasia increases cell number, both activated by the same stressor, such as during pregnancy in the uterus.</p> Signup and view all the answers

    What role does apoptosis play in atrophy and how is it different from ubiquitin-proteosome degradation?

    <p>Apoptosis reduces cell number by programmed cell death, while ubiquitin-proteosome degradation breaks down specific cellular proteins without killing the entire cell.</p> Signup and view all the answers

    Discuss the relationship between metaplasia and the risk of developing dysplasia.

    <p>Metaplasia may lead to dysplasia if the stress causing the metaplastic change persists, potentially resulting in abnormal cell growth and increasing cancer risk.</p> Signup and view all the answers

    Describe the physiological changes that occur in cardiac myocytes due to systemic hypertension.

    <p>Cardiac myocytes undergo hypertrophy, increasing in size to cope with the elevated demands, without increasing cell number since they cannot undergo hyperplasia.</p> Signup and view all the answers

    What is the significance of autophagy in the context of atrophy?

    <p>Autophagy facilitates degradation of cellular components, allowing for recycling of nutrients and helping cells adapt to reduced stress or nutrient availability.</p> Signup and view all the answers

    How does benign prostatic hyperplasia (BPH) differ from other forms of hyperplasia in terms of cancer risk?

    <p>Unlike other forms of pathologic hyperplasia, BPH does not increase the risk of developing prostate cancer despite the enlarged gland.</p> Signup and view all the answers

    Explain the protective role of vitamins in preventing metaplasia in epithelial tissues.

    <p>Vitamins, particularly vitamin A, are essential for the differentiation and maintenance of epithelial tissue; their deficiency can initiate metaplastic changes.</p> Signup and view all the answers

    What defines pathologic hyperplasia and how can it progress if left unchecked?

    <p>Pathologic hyperplasia is an abnormal increase in cell number that can lead to dysplasia and potentially evolve into cancer if the inciting factors persist.</p> Signup and view all the answers

    What cellular adaptation occurs in Barrett esophagus due to acid reflux?

    <p>Metaplasia occurs, transitioning from nonkeratinizing squamous epithelium to nonciliated, mucin-producing columnar cells.</p> Signup and view all the answers

    What is the potential consequence of persistent cellular metaplasia?

    <p>Persistent metaplasia can progress to dysplasia and eventually lead to cancer.</p> Signup and view all the answers

    How can dysplasia theoretically be reversed?

    <p>Dysplasia can be reversed by alleviating the inciting stress or factor causing the cellular change.</p> Signup and view all the answers

    Which specific vitamin deficiency can lead to keratomalacia and what is its effect on epithelial tissue?

    <p>Vitamin A deficiency leads to keratomalacia, causing squamous epithelium to undergo metaplasia to a keratinizing form.</p> Signup and view all the answers

    Explain the role of stem cells in the metaplastic process.

    <p>Metaplasia involves the reprogramming of stem cells, which then differentiate into a new cell type better suited to handle stress.</p> Signup and view all the answers

    What phenomenon is exemplified by myositis ossificans?

    <p>Myositis ossificans is an example of metaplasia where connective tissue in muscle transforms into bone during healing.</p> Signup and view all the answers

    What is the relationship between metaplasia and cancer risk in Barrett esophagus?

    <p>Barrett esophagus, a form of metaplasia, significantly increases the risk of developing esophageal adenocarcinoma.</p> Signup and view all the answers

    Identify a notable exception of metaplasia that does not increase cancer risk.

    <p>Apocrine metaplasia of the breast is a notable exception, as it does not carry an increased risk for cancer.</p> Signup and view all the answers

    An increase in stress on an organ can result in growth adaptations such as ______.

    <p>hypertrophy</p> Signup and view all the answers

    During atrophy, the size of the organ decreases, typically due to decreased hormonal stimulation or ______.

    <p>nutrients</p> Signup and view all the answers

    Hyperplasia involves the production of new cells from ______.

    <p>stem cells</p> Signup and view all the answers

    Metaplasia involves a change in cell type often seen in response to changes in ______.

    <p>stress</p> Signup and view all the answers

    Pathologic hyperplasia can progress to ______ and potentially cancer if left unchecked.

    <p>dysplasia</p> Signup and view all the answers

    In cardiac myocytes, ______ occurs in response to systemic hypertension.

    <p>hypertrophy</p> Signup and view all the answers

    The mechanism behind the decrease in cell number during atrophy is ______.

    <p>apoptosis</p> Signup and view all the answers

    Benign prostatic hyperplasia (BPH) does not increase the risk for ______.

    <p>prostate cancer</p> Signup and view all the answers

    Barrett esophagus is a classic example of ______ due to acid reflux.

    <p>metaplasia</p> Signup and view all the answers

    Vitamin A deficiency can lead to metaplasia in the conjunctiva, resulting in ______.

    <p>keratomalacia</p> Signup and view all the answers

    Metaplasia occurs via reprogramming of ______ which then produce the new cell type.

    <p>stem cells</p> Signup and view all the answers

    Under persistent stress, metaplasia can progress to ______ and may eventually lead to cancer.

    <p>dysplasia</p> Signup and view all the answers

    Myositis ossificans is an example of metaplasia where connective tissue in muscle changes to ______.

    <p>bone</p> Signup and view all the answers

    The esophagus is normally lined by nonkeratinizing squamous epithelium, suited to handle ______.

    <p>friction</p> Signup and view all the answers

    Dysplasia is often a consequence of longstanding pathologic ______ or metaplasia.

    <p>hyperplasia</p> Signup and view all the answers

    Metaplasia can theoretically be ______ with the removal of the driving stressor.

    <p>reversed</p> Signup and view all the answers

    Match the following conditions with their associated cellular change:

    <p>Barrett esophagus = Metaplasia due to acid reflux Keratomalacia = Metaplasia due to vitamin A deficiency Adenocarcinoma of the esophagus = Possible progression from Barrett esophagus Myositis ossificans = Metaplasia of connective tissue to bone</p> Signup and view all the answers

    Match the following definitions with their corresponding terms:

    <p>Dysplasia = Disordered cellular growth Hyperplasia = Proliferation of cells often in response to stress Metaplasia = Reprogramming of stem cells to a different cell type Aplasia = Failure to develop or grow tissues</p> Signup and view all the answers

    Match the following features with their respective conditions:

    <p>Vitamin A deficiency = Can cause keratomalacia via metaplasia Barrett esophagus = Associated with chronic acid exposure Dysplasia = Can progress to carcinoma if stress persists Myositis ossificans = Involves connective tissue transforming to bone</p> Signup and view all the answers

    Match the following statements regarding metaplasia with their implications:

    <p>Reversible = Metaplasia can theoretically revert if stress is removed Persistent stress = Can lead to dysplasia and potentially carcinoma Stem cells role = Key in producing new cell types during metaplasia Example of metaplasia = Barrett esophagus as a response to acid reflux</p> Signup and view all the answers

    Match the following types of metaplasia with their specific causes:

    <p>Ciliated columnar to squamous = Chronic irritation of the respiratory tract Squamous to columnar = Gastroesophageal reflux disease Connective to osseous = Trauma-induced myositis ossificans Normal to keratinized = Vitamin A deficiency in the conjunctiva</p> Signup and view all the answers

    Match the following examples with the type of cellular adaptation they illustrate:

    <p>Endometrial hyperplasia = Example of pathologic hyperplasia leading to dysplasia Cervical intraepithelial neoplasia = Dysplastic change indicating precancerous status Barrett esophagus = Metaplastic change from squamous to columnar Keratomalacia = Metaplasia due to deficiency in vitamin A</p> Signup and view all the answers

    Match the following consequences with the conditions leading to them:

    <p>Chronic stress = Can lead to dysplasia Persistent metaplasia = Risk of progression to carcinoma Vitamin A deficiency = Causes keratomalacia in epithelial tissues Reversal of barrier = Removal of driving stressor may revert metaplasia</p> Signup and view all the answers

    Match the following cellular stressors with their related cellular adaptations:

    <p>Acid reflux = Metaplasia in Barrett esophagus Vitamin A deficiency = Keratinization in conjunctival epithelium Trauma = Myositis ossificans Chronic inflammation = Possible dysplasia development</p> Signup and view all the answers

    Match the following terms with their correct definitions:

    <p>Hypertrophy = Increase in cell size and/or number Hyperplasia = Increase in the number of cells Atrophy = Decrease in organ size due to loss of cells Metaplasia = Change in cell type in response to stress</p> Signup and view all the answers

    Match the following cellular processes with their descriptions:

    <p>Ubiquitin-proteosome degradation = Destruction of tagged cytoskeletal components Apoptosis = Programmed cell death leading to cell number decrease Autophagy = Breakdown of cellular components via lysosomes Gene activation = Initiation of protein synthesis in hypertrophy</p> Signup and view all the answers

    Match the following types of hyperplasia with their characteristics:

    <p>Endometrial hyperplasia = Can progress to dysplasia and cancer Benign prostatic hyperplasia = Does not increase risk of prostate cancer Pathologic hyperplasia = Occurs in response to abnormal physiological stimuli Physiologic hyperplasia = Occurs in normal tissues during development or repair</p> Signup and view all the answers

    Match the following conditions with their related cell responses:

    <p>Systemic hypertension = Cardiac myocyte hypertrophy Vitamin A deficiency = Conjunctival metaplasia Disuse = Muscle atrophy Pregnancy = Uterine hyperplasia and hypertrophy</p> Signup and view all the answers

    Match the following forms of cellular change with their examples:

    <p>Dysplasia = Can arise from pathologic hyperplasia or metaplasia Atrophy = Results from decreased nutrients or blood supply Hypertrophy = Adaptation of skeletal muscle to resistance training Metaplasia = Transformation of squamous epithelium to columnar in Barrett esophagus</p> Signup and view all the answers

    Match the following statements with their correct growth adaptations:

    <p>Hypertrophy only occurs in permanent tissues = Cardiac and skeletal muscle Hyperplasia can lead to increased cell size = Hypertrophy response in tissue stress Metaplasia is typically reversible = False, it can lead to dysplasia or cancer Atrophy involves only reduction in cell number = False, also involves decrease in cell size</p> Signup and view all the answers

    Match the following adaptations with their triggers:

    <p>Increased hormonal stimulation = Hypertrophy of breast tissue during pregnancy Decreased blood supply = Atrophy of muscle due to immobilization Chronic irritation = Metaplasia of respiratory epithelium Increased workload = Hypertrophy of the heart in athletes</p> Signup and view all the answers

    Match the following types of cellular adaptations with their forms:

    <p>Hyperplasia = Increased number of cells from stem cells Hypertrophy = Increased size of individual cells Atrophy = Reduction in both number and size of cells Metaplasia = Change from one differentiated cell type to another</p> Signup and view all the answers

    Study Notes

    Growth Adaptations

    • An organ will adapt to the physiologic stress placed on it
    • Increase, decrease, or change in stress leads to growth adaptations
    • Increase in stress can result in increased organ size via hypertrophy and hyperplasia
    • Hypertrophy is an increase in the size of cells
    • Hyperplasia is an increase in the number of cells via stem cell proliferation.
    • Hypertrophy involves increased gene activation, protein synthesis, and organelle production
    • Hyperplasia and hypertrophy typically occur together
    • Permanent tissues (cardiac, skeletal muscle, nerve) cannot make new cells and only undergo hypertrophy
    • Pathologic hyperplasia can progress to dysplasia and cancer
    • Exception: Benign Prostatic Hyperplasia does not increase risk for prostate cancer

    Atrophy

    • Decrease in stress causes decreased organ size. Decreased stress can be caused by decreased hormonal stimulation, disuse, or decreased nutrients/blood supply.
    • Occurs via decrease in cell size and number
    • Reduction in cell number occurs via apoptosis
    • Reduction in cell size occurs via ubiquitin-proteosome degradation of cytoskeleton and autophagy of cellular components
    • In ubiquitin-proteosome degradation, intermediate filaments of the cytoskeleton are tagged with ubiquitin and destroyed by proteasomes.
    • Autophagy of cellular components involves the generation of autophagic vacuoles that fuse with lysosomes whose hydrolytic enzymes breakdown cellular components

    Metaplasia

    • Change in stress causes a change in cell type
    • Most commonly involves a change of one epithelial type to another (squamous, columnar, urothelial)
    • Metaplastic cells are better able to handle the new stress
    • Example: Barrett esophagus (esophagus lining changes from squamous epithelial to columnar epithelial due to acid reflux)
    • Metaplasia is reversible with removal of the driving stressor.
    • Metaplasia can progress to dysplasia and eventually cancer
    • Example: Barrett esophagus can progress to adenocarcinoma of the esophagus
    • Exception: Apocrine metaplasia of the breast does not carry an increased risk for cancer
    • Vitamin A deficiency can also result in metaplasia
    • Example: In vitamin A deficiency, the conjunctiva of the eye undergoes metaplasia into stratified keratinizing squamous epithelium (keratomalacia)
    • Mesenchymal tissues can also undergo metaplasia
    • Example: Myositis ossificans (connective tissue within muscle changes to bone during healing after trauma)

    Dysplasia

    • Disordered growth of cells
    • Most often refers to the proliferation of precancerous cells
    • Example: Cervical intraepithelial neoplasia (CIN) is a precursor to cervical cancer
    • Often arises from long-standing pathological hyperplasia or metaplasia
    • Dysplasia is reversible with the removal of the inciting stress
    • If stress persists, dysplasia will progress to carcinoma (irreversible)

    Growth Adaptations

    • An organ in homeostasis with the physiologic stress placed on it.
    • Stresses can cause growth adaptations, which can result in an increase, decrease, or change in organ size.

    Hyperplasia and Hypertrophy

    • Increase in stress leads to an increase in organ size.
    • Hypertrophy is an increase in cell size, Hyperplasia is an increase in cell number.
    • Hypertrophy involves gene activation, protein synthesis, and production of organelles.
    • Hyperplasia involves production of new cells from stem cells.
    • Hyperplasia and hypertrophy often occur together (e.g., uterus during pregnancy).
    • Permanent tissues (e.g., cardiac muscle, skeletal muscle, and nerve) cannot make new cells and undergo hypertrophy only.
    • Pathologic hyperplasia can progress to dysplasia and cancer.
    • Benign prostatic hyperplasia (BPH) is an exception, it does not increase the risk for prostate cancer.

    Atrophy

    • Decrease in stress (e.g., decreased hormonal stimulation, disuse, or decreased nutrients/blood supply) leads to a decrease in organ size.
    • Atrophy is a decrease in cell size and number.
    • Decrease in cell number occurs via apoptosis.
    • Decrease in cell size occurs via ubiquitin-proteosome degradation of the cytoskeleton and autophagy of cellular components.
    • In ubiquitin-proteosome degradation, intermediate filaments of the cytoskeleton are "tagged" with ubiquitin and destroyed by proteosomes.
    • Autophagy of cellular components involves generation of autophagic vacuoles, which fuse with lysosomes whose hydrolytic enzymes breakdown cellular components.

    Metaplasia

    • A change in stress on an organ leads to a change in cell type.
    • Most commonly involves change of one type of surface epithelium (squamous, columnar, or urothelial) to another.
    • Metaplastic cells are better able to handle the new stresses.
    • Barrett esophagus is a classic example: the esophagus is normally lined by nonkeratinizing squamous epithelium, acid reflux from the stomach causes metaplasia to nonciliated, mucin-producing columnar cells, better able to handle the stress of acid.
    • Metaplasia occurs via reprogramming of stem cells, which then produce the new cell type.
    • Metaplasia is reversible with removal of the driving stressor.
    • Under persistent stress, metaplasia can progress to dysplasia and eventually result in cancer.
    • A notable exception is apocrine metaplasia of breast, which carries no increased risk for cancer.
    • Vitamin A deficiency can also cause metaplasia.
    • Vitamin A is necessary for differentiation of specialized epithelial surfaces such as the conjunctiva covering the eye.
    • In vitamin A deficiency, the thin squamous lining of the conjunctiva undergoes metaplasia into stratified keratinizing squamous epithelium. This change is called keratomalacia.
    • Mesenchymal (connective) tissues can also undergo metaplasia. Myositis ossificans is a classic example, where connective tissue within muscle changes to bone during healing after trauma.

    Dysplasia

    • Disordered cellular growth.
    • Often refers to proliferation of precancerous cells.
    • Often arises from longstanding pathologic hyperplasia or metaplasia.
    • Dysplasia is reversible, but if stress persists, it progresses to carcinoma (irreversible).

    Aplasia and Hypoplasia

    • No information regarding Aplasia and Hypoplasia is available in the provided text.

    Growth Adaptations

    • An organ in homeostasis with physiological stress placed on it.
    • Increased, decreased, or changed stress on an organ can lead to growth adaptations.

    Hyperplasia and Hypertrophy

    • An increase in stress leads to an increase in organ size.
    • Occurs via an increase in size (hypertrophy) and/or the number (hyperplasia) of cells.
    • Hypertrophy involves gene activation, protein synthesis, and production of organelles.
    • Hyperplasia involves the production of new cells from stem cells.
    • Hyperplasia and hypertrophy generally occur together (e.g., uterus during pregnancy).
    • Permanent tissues (e.g., cardiac muscle, skeletal muscle, and nerve) can only undergo hypertrophy.
    • Cardiac myocytes undergo hypertrophy, not hyperplasia, in response to systemic hypertension.
    • Pathologic hyperplasia (e.g., endometrial hyperplasia) can progress to dysplasia and eventually cancer.
    • Benign prostatic hyperplasia (BPH) is an exception and does not increase the risk for prostate cancer.

    Atrophy

    • A decrease in stress (e.g., decreased hormonal stimulation, disuse, or decreased nutrients/blood supply) leads to a decrease in organ size (atrophy).
    • Occurs via a decrease in the size and number of cells.
    • Decrease in cell number occurs via apoptosis.
    • Decrease in cell size occurs via ubiquitin-proteosome degradation of the cytoskeleton and autophagy of cellular components.
    • Ubiquitin-proteosome degradation involves tagging intermediate filaments of the cytoskeleton with ubiquitin and destruction by proteosomes.
    • Autophagy of cellular components involves generation of autophagic vacuoles that fuse with lysosomes, whose hydrolytic enzymes break down cellular components.

    Metaplasia

    • A change in stress on an organ leads to a change in cell type (metaplasia).
    • Most commonly involves a change of one type of surface epithelium (squamous, columnar, or urothelial) to another.
    • Metaplastic cells are better able to handle the new stress.
    • Barrett esophagus is a classic example.
    • The esophagus is normally lined by nonkeratinizing squamous epithelium.
    • Acid reflux from the stomach causes metaplasia to nonciliated, mucin-producing columnar cells (better able to handle the stress of acid).
    • Metaplasia occurs via reprogramming of stem cells, which then produce the new cell type.
    • Metaplasia is reversible with the removal of the driving stressor.
    • Treatment of gastroesophageal reflux may reverse Barrett esophagus.
    • Under persistent stress, metaplasia can progress to dysplasia and eventually result in cancer.
    • For example, Barrett esophagus may progress to adenocarcinoma of the esophagus.
    • Apocrine metaplasia of breast is an exception and carries no increased risk for cancer.
    • Vitamin A deficiency can also result in metaplasia.
    • Vitamin A is necessary for differentiation of specialized epithelial surfaces.
    • In vitamin A deficiency, the thin squamous lining of the conjunctiva undergoes metaplasia into stratified keratinizing squamous epithelium.
    • This change is called keratomalacia.
    • Mesenchymal (connective) tissues can also undergo metaplasia.
    • Myositis ossificans is a classic example in which connective tissue within muscle changes to bone during healing after trauma.

    Dysplasia

    • Disordered cellular growth.
    • Most often refers to proliferation of precancerous cells.
    • For example, cervical intraepithelial neoplasia (CIN) represents dysplasia and is a precursor to cervical cancer.
    • Often arises from longstanding pathologic hyperplasia or metaplasia.
    • Dysplasia is reversible with alleviation of inciting stress.
    • If stress persists, dysplasia progresses to carcinoma (irreversible).

    Aplasia and Hypoplasia

    • Agenesis refers to the complete failure of an organ to develop.
    • Hypoplasia refers to the incomplete development of an organ, resulting in a smaller than normal size.

    Growth Adaptations

    • Homeostasis: An organ maintains a balance with the physiologic stress placed on it.
    • Stress Changes: An increase, decrease, or change in stress can lead to growth adaptations.
    • Hyperplasia and Hypertrophy: An increase in stress leads to an increase in organ size.
      • Hypertrophy: Enlargement of individual cells due to increased gene activation, protein synthesis, and organelle production.
      • Hyperplasia: Increased number of cells due to production of new cells from stem cells.
      • Combined: Hyperplasia and hypertrophy often happen together, for example, in the uterus during pregnancy.
      • Permanent Tissues: Permanent tissues like cardiac muscle, skeletal muscle, and nerves cannot make new cells and only undergo hypertrophy. For example, cardiac myocytes hypertrophy in response to hypertension.
      • Pathologic Hyperplasia: Can lead to dysplasia and eventually cancer. A notable exception is benign prostatic hyperplasia (BPH), which does not increase the risk for prostate cancer.

    Atrophy

    • Decreased Stress: A decrease in stress, such as lowered hormonal stimulation, disuse, or reduced nutrients/blood supply, can lead to a decrease in organ size (atrophy).
    • Decreased Cell Number: Occurs through apoptosis.
    • Decreased Cell Size: Occurs through:
      • Ubiquitin-Proteosome Degradation: Intermediate filaments of the cytoskeleton are tagged with ubiquitin and destroyed by proteosomes.
      • Autophagy: Cellular components are broken down by autophagic vacuoles, which fuse with lysosomes containing hydrolytic enzymes.

    Metaplasia

    • Change in Cell Type: A change in stress on an organ can lead to a change in cell type (metaplasia).
      • Common Change: Often involves the transformation of one type of surface epithelium to another (e.g., squamous, columnar, or urothelial).
      • Adaptability: Metaplastic cells are better suited to handle the new stress.
    • Example: Barrett Esophagus:
      • Normal: The esophagus is lined with nonkeratinizing squamous epithelium, which can handle the friction from a food bolus.
      • Acid Reflux: Acid reflux from the stomach causes metaplasia to nonciliated, mucin-producing columnar cells, which are better able to tolerate acid.
    • Reversible: Metaplasia can be reversed by removing the source of stress. For example, treating gastroesophageal reflux might reverse Barrett esophagus.
    • Progression to Cancer: Under continued stress, metaplasia can progress to dysplasia and eventually cancer. For example, Barrett esophagus may progress to adenocarcinoma of the esophagus. A notable exception is apocrine metaplasia of the breast, which does not increase the risk for cancer.
    • Vitamin A Deficiency: Can lead to metaplasia.
      • Importance: Vitamin A is necessary for the differentiation of specialized epithelial surfaces like the conjunctiva covering the eye.
      • Keratomalacia: In vitamin A deficiency, the thin squamous lining of the conjunctiva undergoes metaplasia into stratified keratinizing squamous epithelium, leading to a condition called keratomalacia.
    • Mesenchymal Metaplasia: Connective tissues can also undergo metaplasia.
      • Example: Myositis ossificans, where connective tissue within muscle transforms into bone during healing after trauma.

    Dysplasia

    • Disordered Cellular Growth: Represents abnormal cell growth.
    • Precancerous Cells: Often refers to the proliferation of precancerous cells. For example, cervical intraepithelial neoplasia (CIN) is dysplasia and a precursor to cervical cancer.
    • Origin: Often arises from prolonged pathologic hyperplasia or metaplasia.
    • Reversible: Dysplasia can be reversed with the removal of the underlying stress. If stress persists, dysplasia progresses to carcinoma (irreversible).

    Aplasia and Hypoplasia

    • Aplasia: Complete absence of an organ or tissue due to failure of development.
    • Hypoplasia: Incomplete development of an organ or tissue, resulting in a smaller size.

    Growth Adaptations

    • Organs are in a state of equilibrium with the stress placed on them.
    • An increase, decrease, or change in stress can lead to growth adaptations.

    Hyperplasia and Hypertrophy

    • Increased stress results in an increase in organ size.
    • This increase occurs via an increase in cell size (hypertrophy) and/or cell number (hyperplasia).
    • Hypertrophy involves gene activation, protein synthesis, and the production of organelles.
    • Hyperplasia involves the production of new cells from stem cells.
    • Hyperplasia and hypertrophy often happen together.
    • Permanent tissues (e.g., cardiac muscle, skeletal muscle, and nerve) can only undergo hypertrophy, not hyperplasia.
    • Pathologic hyperplasia can progress to dysplasia and potentially cancer.
    • Benign prostatic hyperplasia is a notable exception and does not increase the risk for prostate cancer.

    Atrophy

    • A decrease in stress (e.g., decreased hormonal stimulation, disuse, or decreased nutrients/blood supply) leads to a decrease in organ size (atrophy).
    • Atrophy involves a decrease in cell size and number.
    • Apoptosis is responsible for the decrease in the number of cells.
    • Ubiquitin-proteosome degradation and autophagy of cellular components contribute to the decrease in cell size.

    Metaplasia

    • A change in stress on an organ results in a change in cell type (metaplasia).
    • Metaplasia most commonly involves a change in surface epithelial cell types.
    • Metaplastic cells are better suited to handle the new stress.
    • Barrett esophagus is a common example.
    • Metaplasia is reversible if the driving stressor is removed.
    • Metaplasia can progress to dysplasia and cancer under persistent stress.
    • Apocrine metaplasia of the breast does not increase the risk of cancer.
    • Vitamin A deficiency can also lead to metaplasia.
    • Connective tissues can also undergo metaplasia, as in myositis ossificans.

    Dysplasia

    • Dysplasia is characterized by disordered cellular growth.
    • It often refers to the proliferation of precancerous cells.
    • Dysplasia often arises from prolonged pathologic hyperplasia or metaplasia.
    • Dysplasia can be reversed by removing the inciting stress.
    • If stress persists, dysplasia progresses to carcinoma, which is irreversible.

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