Cell Turnover and Morphogenesis
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Questions and Answers

Which of these tissues is classified as labile?

  • Bone marrow (correct)
  • Cardiac muscle
  • Endocrine glands
  • Liver
  • What is the main difference between embryonic stem cells and tissue stem cells?

  • Embryonic stem cells are found in the inner mass of the blastocyst while tissue stem cells are found within differentiated tissues.
  • Embryonic stem cells can give rise to any cell in the body while tissue stem cells can only produce cells that are constituents of that particular tissue.
  • Embryonic stem cells have a virtually limitless self-renewal capacity while tissue stem cells have a limited self-renewal capacity.
  • All of the above. (correct)
  • Which of these tissues is considered to be permanent?

  • Liver
  • Neurons (correct)
  • Skin
  • Bone
  • Which of these locations is NOT a source of adult stem cells?

    <p>The heart (C)</p> Signup and view all the answers

    Which of these is NOT a characteristic of labile tissue?

    <p>Cells are not readily replaced when lost (B)</p> Signup and view all the answers

    Which type of growth is characterized by an increase in the size of individual cells?

    <p>Auxetic growth (A)</p> Signup and view all the answers

    What is the primary function of cellular differentiation?

    <p>To develop a specialized function or morphology. (C)</p> Signup and view all the answers

    Which of the following is the best example of multiplicative growth?

    <p>An increase in the number of cells during embryonic development. (A)</p> Signup and view all the answers

    What is the key characteristic of morphogenesis?

    <p>The development of structural shape and form. (A)</p> Signup and view all the answers

    What process involves the selective expression of genes to produce a cell with a specialized function?

    <p>Cell differentiation (D)</p> Signup and view all the answers

    What two processes does morphogenesis involve?

    <p>Growth, differentiation and movement of cells. (A)</p> Signup and view all the answers

    Which of the following is a physiological condition that can increase cell proliferation?

    <p>Menstrual cycle changes in endometrial tissue (D)</p> Signup and view all the answers

    How can cell growth be achieved in a tissue context?

    <p>By increasing the rate of the cell cycle or shortening it. (B)</p> Signup and view all the answers

    What is the primary role of the G1/S checkpoint in the cell cycle?

    <p>To monitor the integrity of DNA before replication (C)</p> Signup and view all the answers

    Which of the following correctly describes the cell cycle phase where DNA is synthesized?

    <p>S phase (D)</p> Signup and view all the answers

    What happens if DNA damage is beyond repair during the cell cycle?

    <p>The cell undergoes apoptosis or senescence (D)</p> Signup and view all the answers

    Cyclins and CDKs interact to regulate what aspect of the cell cycle?

    <p>Cellular proliferation (D)</p> Signup and view all the answers

    Which of the following correctly defines asymmetric division of stem cells?

    <p>One daughter cell differentiates while the other remains undifferentiated (B)</p> Signup and view all the answers

    What is the function of cyclin-dependent kinase inhibitors (CDKIs)?

    <p>To broadly inhibit CDKs activity (D)</p> Signup and view all the answers

    How do CDKs acquire their ability to phosphorylate proteins?

    <p>By forming complexes with cyclins (D)</p> Signup and view all the answers

    What is the primary purpose of maintaining cell populations?

    <p>To ensure accurate DNA replication and division (B)</p> Signup and view all the answers

    Flashcards

    Embryonic Stem Cells

    Present in the inner mass of the blastocyst, they have virtually limitless self-renewal capacity and can differentiate into any cell type in the body.

    Tissue (Adult) Stem Cells

    Found within differentiated tissues, they can only produce cells that are constituents of that particular tissue.

    Labile Cells

    Cells that continuously proliferate throughout life, having a short lifespan and rapid turnover. They are susceptible to the toxic effects of radiation and drugs due to their high turnover rate.

    Stable Cells

    Cells that divide very infrequently under normal conditions but can be stimulated to divide rapidly when cells are lost.

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    Permanent Cells

    Cells that do not persist long into postnatal life and cannot be replaced when lost.

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    Growth

    The process of increasing size due to the synthesis of specific tissue components.

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    Multiplicative Growth

    An increase in the number of cells through cell division (mitosis). This is how tissues expand during early development.

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    Auxetic Growth

    An increase in the size of individual cells. An example is skeletal muscle getting bigger.

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    Differentiation

    The process by which a cell develops a specialized function or structure, becoming different from its parent cell.

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    Morphogenesis

    A complex process of developing a structural shape and form during embryogenesis (early development). This involves growth, differentiation, and cell movement.

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    Cell Proliferation

    The process of cell division, which contributes to development, tissue maintenance, and replacing lost cells.

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    Apoptosis

    The process of programmed cell death, a natural and controlled way for cells to die.

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    Microenvironment Signals

    Signals from the surrounding environment that either promote or inhibit cell proliferation.

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    Cell Cycle

    The process by which cells replicate and divide, consisting of a sequence of events and phases. Ensures accurate DNA replication, coordinated synthesis of cellular components, and equal distribution of both to daughter cells.

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    G1 (Gap 1) Phase

    Phase in the cell cycle where the cell grows and prepares for DNA replication. Ensures cell size and resources are sufficient before moving to the next phase.

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    S (Synthesis) Phase

    Phase in the cell cycle where the cell's DNA is replicated. Ensures all genetic material is duplicated accurately.

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    G2 (Gap 2) Phase

    Phase in the cell cycle where the cell continues to grow and prepares for division. Ensures everything is ready before the cell splits.

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    M (Mitosis) Phase

    The process of cell division, where one parent cell divides into two identical daughter cells. Ensures the accurate distribution of duplicated chromosomes

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    G1/S Checkpoint

    A critical point in the cell cycle that ensures all DNA is intact and undamaged before committing to DNA replication. Prevents errors from accumulating.

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    G2/M Checkpoint

    A critical point in the cell cycle that ensures accurate DNA replication is complete before the cell divides. Prevents errors from being passed on to new cells.

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    Stem Cells

    Undifferentiated cells capable of self-renewal and differentiation into multiple cell types. Essential for tissue repair and development.

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    Study Notes

    Cell Turnover

    • The presentation is on cell turnover, detailing growth, differentiation, and morphogenesis, as well as cell cycle, stem cells, and tissue types.
    • The presentation was given by Dr N Buthelezi, Department of Anatomical Pathology, on 20/01/2025.

    Growth, Differentiation and Morphogenesis

    • Growth is the increase in size due to tissue synthesis.
    • Types of growth include:
      • Multiplicative: Increase in cell number via mitosis, occurs in all tissues during embryogenesis.
      • Auxetic: Increase in individual cell size (e.g., skeletal muscle).
      • Accretionary: Increase in intercellular components (e.g., bone, cartilage).
      • Combined: A combination of the above types.
    • Differentiation is the development of a cell's specialized function or morphology, distinguished from its parent cell.
    • Gene expression is selective during differentiation, producing cells with specialized functions.

    Morphogenesis

    • Morphogenesis is a complex process creating the form and structure of organs (e.g., limbs, facial features).
    • It involves growth and differentiation, cell movement relative to each other, and apoptosis to remove unwanted structures during embryogenesis.

    Maintaining Cell Populations

    • Cell proliferation is essential for:
      • Development
      • Maintaining steady-state tissue homeostasis
      • Replacing dead/damaged cells
    • Cell population size depends on proliferation rate and apoptosis (cell death).
    • Cell proliferation can be stimulated by physiological or pathological conditions.
    • Physiological examples include endometrial tissue changes during the menstrual cycle or thyroid tissue during pregnancy.
    • Pathological examples include after cell death or tissue injury.

    Cell Cycle

    • The cell cycle is a series of events leading to cell division.
    • Phases include:
      • G1: Presynthetic growth phase
      • Restriction point
      • G1/S checkpoint
      • S: DNA synthesis
      • G2: Premitotic growth phase
      • G2/M checkpoint
      • M: Mitosis

    Cell Cycle Regulation

    • The cell cycle is controlled by activators (cyclins) and inhibitors (CDKIs):
      • Cyclins
      • Cyclin-dependent kinases (CDKs)
      • Cyclin-dependent kinase inhibitors (CDKIs)
    • CDKs phosphorylate proteins, controlled by cyclin levels, which wax and wane.

    Cell Cycle Checkpoints

    • Checkpoints ensure cells with genetic imperfections do not replicate.
    • G1/S checkpoint monitors DNA integrity before replication.
    • G2/M checkpoint ensures accurate genetic replication before mitosis.
    • Damaged DNA beyond repair triggers apoptosis or senescence.

    Cyclin-Dependent Kinase Inhibitors

    • p21 (CDKN1A), p27 (CDKN1B) and p57 (CDKN1C) broadly inhibit CDKs.
    • p15 (CDKN2B), p16 (CDKN2A), p18 (CDKN2C) and p19 (CDKN2D) selectively affect CDK4 and CDK6.

    Stem Cells

    • Stem cells are undifferentiated, able to differentiate into various cell types.
    • Properties include:
      • Self-renewal: Maintain stem cell pool.
      • Asymmetric division: One daughter cell differentiates, the other remains undifferentiated, maintaining self-renewal capacity.
    • Types of stem cells:
      • Embryonic stem cells (most undifferentiated, present in the inner mass of the blastocyst, virtually unlimited self-renewal capacity, totipotent - can differentiate into any cell type).
      • Tissue (adult) stem cells (found within differentiated tissues, produce cells specific to that tissue, protected within stem cell niches).
        • Labile: Continuously proliferate in postnatal life, short lifespan, rapid turnover (e.g., hematopoietic cells, skin, lining cells of the digestive tract).
        • Stable: Divide infrequently under normal conditions but can rapidly divide when cells are lost (e.g., liver cells, endocrine glands, bone, renal tubules).
        • Permanent: Active stem cells do not persist long into postnatal life, cells cannot be replaced when lost (e.g., neurons, cardiac muscle cells, photoreceptors).

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    Description

    This quiz explores the concepts of cell turnover, growth, differentiation, and morphogenesis. It covers various types of growth, the role of stem cells, and the cell cycle, providing a comprehensive understanding of tissue formation and specialization. Perfect for students in anatomical pathology or related fields.

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