Pericytes and the Blood-Brain Barrier
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Questions and Answers

What is a characteristic function of precapillary sphincters in true capillaries?

  • They facilitate the exchange of gases and nutrients.
  • They maintain the structural integrity of the capillary.
  • They contract or relax to regulate blood entry. (correct)
  • They operate independently of metarterioles.

    • How does blood flow through capillaries when precapillary sphincters are closed?

  • Blood flow is halted completely in the capillary network.
  • Blood flows continuously into the capillaries.
  • Blood is diverted back to the arteries.
  • Blood flows directly from metarterioles to post capillary venules. (correct)

    • What role do tight junctions play in capillaries?

  • They support the rhythmic contraction of muscle fibers.
  • They regulate the permeability of the capillary walls. (correct)
  • They prevent the formation of basal lamina.
  • They promote nutrient absorption from surrounding tissues.

    • What structural feature is often observed in the nuclei of capillary cells?

    <p>They are typically curved to fit the tubular structure.</p> Signup and view all the answers

    What distinguishes the structural variation in capillaries across different organs?

    <p>Variations depend on the specific metabolic needs of the organs.</p> Signup and view all the answers

    What is the primary function of capillaries in the circulatory system?

    <p>They facilitate the exchange of nutrients and waste.</p> Signup and view all the answers

    Which type of capillary has pores that allow for increased permeability?

    <p>Fenestrated capillaries</p> Signup and view all the answers

    What is the average diameter of capillaries, which allows blood cells to transit one at a time?

    <p>4 to 10 μm</p> Signup and view all the answers

    What role do pericytes play in the structure of capillaries?

    <p>They assist in regulating blood flow and capillary stability.</p> Signup and view all the answers

    In which situation is blood flow to capillary beds maximally efficient?

    <p>When blood is shunted away by contracted sphincters.</p> Signup and view all the answers

    How is blood oxygenation characterized as it moves through the capillaries?

    <p>Blood enters well oxygenated and leaves poorly oxygenated.</p> Signup and view all the answers

    What is not a characteristic of continuous capillaries?

    <p>They contain large intercellular clefts.</p> Signup and view all the answers

    What is a common clinical condition associated with capillary dysfunction?

    <p>Diabetic microangiopathy</p> Signup and view all the answers

    Which characteristic is specific to fenestrated capillaries when compared to other types of capillaries?

    <p>They contain large perforations without diaphragms.</p> Signup and view all the answers

    What role do pericytes play in the maintenance of the blood-brain barrier?

    <p>They help maintain endothelial tight junctions.</p> Signup and view all the answers

    What is a consequence of the larger diameter of fenestrated capillaries?

    <p>Slower blood flow through the capillaries.</p> Signup and view all the answers

    What physiological change occurs in pericytes following tissue injury?

    <p>They proliferate and differentiate into smooth muscle cells.</p> Signup and view all the answers

    Which of the following organs does NOT typically contain fenestrated capillaries?

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

    In diabetic microangiopathy, what is the primary effect on capillaries?

    <p>Diffuse thickening of capillary basal laminae.</p> Signup and view all the answers

    How do fenestrated capillaries differ structurally from continuous capillaries?

    <p>They contain discontinuous endothelial cells with holes.</p> Signup and view all the answers

    What is a key function of capillaries in relation to pericytes?

    <p>Capillaries facilitate molecular exchange between blood and tissue fluid.</p> Signup and view all the answers

    What role do pericytes play in relation to fenestrated capillaries?

    <p>They provide structural support.</p> Signup and view all the answers

    Which of the following features allows fenestrated capillaries to be more permeable than continuous capillaries?

    <p>Large openings within the endothelial cells.</p> Signup and view all the answers

    How do pericytes respond to vasoactive agents like histamine?

    <p>By altering the permeability of the endothelial barrier.</p> Signup and view all the answers

    What type of vascular structure is often found along continuous capillaries and postcapillary venules?

    <p>Pericytes.</p> Signup and view all the answers

    Which cell type is included in the pericyte population and is vital for tissue regeneration?

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

    Fenestrated capillaries are primarily known for which of the following functions?

    <p>Selective filtration of plasma components.</p> Signup and view all the answers

    What is a major consequence of hyperglycemia on capillary function?

    <p>Reduced metabolic exchange across blood vessels.</p> Signup and view all the answers

    What structure is primarily disrupted in diabetic microangiopathy?

    <p>The capillary basal laminae</p> Signup and view all the answers

    What is the primary function of pericytes in relation to capillaries?

    <p>They regulate blood flow by dilating or constricting capillaries.</p> Signup and view all the answers

    What structural characteristic allows for greater exchange across endothelial layers?

    <p>Fenestrations in the endothelial cells.</p> Signup and view all the answers

    Which component do pericytes secrete that supports their function?

    <p>Extracellular matrix (ECM) components.</p> Signup and view all the answers

    What is a distinguishing feature of progressively larger collecting venules?

    <p>They contain a recognizable tunica media with smooth muscle layers.</p> Signup and view all the answers

    Which proteins are primarily found in the cytoskeletal network of pericytes?

    <p>Myosin, actin, and tropomyosin.</p> Signup and view all the answers

    How do pericytes interact with endothelial cells?

    <p>Through long cytoplasmic processes that partially surround them.</p> Signup and view all the answers

    What effect do pericytes have on the blood flow of red blood cells?

    <p>They regulate blood flow by contracting or dilating capillaries.</p> Signup and view all the answers

    Which statement accurately describes the relationship between pericytes and basal lamina?

    <p>Pericytes produce a basal lamina that can fuse with endothelial cells.</p> Signup and view all the answers

    Study Notes

    Capillaries Overview

    • Capillaries are the smallest blood vessels, with an average diameter of 4 to 10 μm and a wall thickness of only 0.25 μm.
    • They facilitate nutrient, waste, O2, and CO2 exchange through their endothelial structure.
    • Blood enters capillary beds in a pulsatile manner due to the contraction of precapillary sphincters.

    Types of Capillaries

    • Continuous Capillaries:

      • Composed of a single layer of endothelial cells forming a tube.
      • Characterized by tight junctions and few gaps, allowing selective permeability.

    • Fenestrated Capillaries:

      • Contain pores (fenestrations) around 80 nm in diameter, enhancing exchange capabilities.
      • Found in organs like the liver, spleen, some endocrine glands, and bone marrow.
      • Possess a discontinuous basal lamina and larger diameters (30-40 μm), which slow blood flow.

    • Discontinuous Capillaries:

      • Have large openings with a discontinuous endothelial layer, permitting maximal substance interchange.

    Pericytes

    • Mesenchymal cells located alongside continuous capillaries and postcapillary venules.
    • Involved in maintaining the endothelial blood-brain barrier within the CNS.
    • Regulate blood flow by contracting or dilating capillaries, with a significant role in tissue regeneration after injuries.

    Venules

    • Formed from the convergence of postcapillary venules into larger collecting venules.
    • As they increase in size, they develop tunica media with smooth muscle layers, termed muscular venules.
    • Facilitate the collection of blood from capillaries and act as sites for material exchange and white blood cell migration into tissues.

    Clinical Application

    • Diabetic Microangiopathy:
      • A consequence of hyperglycemia in diabetes leading to diffuse thickening of capillary basal laminae.
      • Impairs metabolic exchange, notably affecting the kidneys, retina, skeletal muscle, and skin.

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    Capillaries PDF - January 2021 Lecture Notes

    Description

    This quiz explores the role of pericytes within the central nervous system and their importance in maintaining the endothelial blood-brain barrier. It also discusses their functions, including collecting blood from capillaries and responding to vasoactive agents after tissue injuries.

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