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Questions and Answers
Which process describes the replacement of injured tissue with fibrous tissue?
Which process describes the replacement of injured tissue with fibrous tissue?
What type of cells in the nervous system are considered permanent cells and do not regenerate after injury?
What type of cells in the nervous system are considered permanent cells and do not regenerate after injury?
Which of the following is NOT a characteristic of stable cells?
Which of the following is NOT a characteristic of stable cells?
What is the first step in the bone healing process following a fracture?
What is the first step in the bone healing process following a fracture?
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What is formed during the bone healing process that acts as a temporary scaffold?
What is formed during the bone healing process that acts as a temporary scaffold?
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In the remodeling phase of bone healing, what primarily occurs?
In the remodeling phase of bone healing, what primarily occurs?
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What is a common feature of degenerative processes in the peripheral nervous system?
What is a common feature of degenerative processes in the peripheral nervous system?
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Which of the following tissues is most capable of regeneration after injury?
Which of the following tissues is most capable of regeneration after injury?
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What is the initial type of bone that forms in the granulation tissue during the healing process?
What is the initial type of bone that forms in the granulation tissue during the healing process?
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Which statement accurately describes the role of osteoclasts during osseous callus formation?
Which statement accurately describes the role of osteoclasts during osseous callus formation?
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What occurs during the remodeling stage of bone healing?
What occurs during the remodeling stage of bone healing?
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What is one consequence of poorly immobilized fractures?
What is one consequence of poorly immobilized fractures?
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In the peripheral nervous system, what is primarily responsible for regeneration after injury?
In the peripheral nervous system, what is primarily responsible for regeneration after injury?
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What pathological reaction in the peripheral nervous system can result from nerve injury?
What pathological reaction in the peripheral nervous system can result from nerve injury?
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Which complication may arise from non-union of a fracture?
Which complication may arise from non-union of a fracture?
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What is a characteristic of the central nervous system's response to neuronal destruction?
What is a characteristic of the central nervous system's response to neuronal destruction?
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What is the main characteristic of Wallerian degeneration in the peripheral nervous system?
What is the main characteristic of Wallerian degeneration in the peripheral nervous system?
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During axonal degeneration, what process initiates the degeneration?
During axonal degeneration, what process initiates the degeneration?
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What occurs during segmental demyelination in the peripheral nerve?
What occurs during segmental demyelination in the peripheral nerve?
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What typically results from an obstruction in the regeneration process of a peripheral nerve?
What typically results from an obstruction in the regeneration process of a peripheral nerve?
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What happens if the muscle sheath is intact after skeletal muscle injury?
What happens if the muscle sheath is intact after skeletal muscle injury?
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What is the outcome when skeletal muscle undergoes regeneration with a damaged sheath?
What is the outcome when skeletal muscle undergoes regeneration with a damaged sheath?
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What distinguishes cardiac muscle healing from that of skeletal muscle?
What distinguishes cardiac muscle healing from that of skeletal muscle?
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Which type of muscle is known to have limited regenerative capacity?
Which type of muscle is known to have limited regenerative capacity?
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Study Notes
Healing in Specialized Tissues - Nervous Tissue
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Peripheral Nervous System (PNS) undergoes three main types of degenerative processes:
- Wallerian degeneration: Occurs after axonal transection (caused by injuries like knife wounds, compression, traction, and ischemia). The axon and myelin sheath distal to the cut disintegrate up to the next node of Ranvier, followed by phagocytosis. Regeneration then occurs through axonal sprouting and Schwann cell proliferation from the proximal end.
- Axonal degeneration: Degeneration starts at the peripheral nerve ending and progresses backward toward the nerve cell body. The cell body experiences chromatolysis (breakdown of the Nissl substance), and axonal integrity is lost.
- Segmental demyelination: Loss of myelin between two consecutive nodes of Ranvier, leaving the axon segment exposed. Schwann cell proliferation leads to remyelination of the affected axon.
- Traumatic neuroma develops when axonal regeneration is obstructed by a hematoma or fibrous scar. The trapped axonal sprouts, Schwann cells, and fibroblasts form a mass.
Healing in Specialized Tissues - Muscles
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Skeletal muscle:
- When injured, muscle fibers retract but are held together by connective tissue.
- If the muscle sheath is intact, sarcolemmal tubes containing histiocytes (immune cells) appear along the endomysial tube, restoring properly oriented muscle fibers within 3 months. Example: Zenker's degeneration in typhoid fever.
- If the muscle sheath is damaged, an unorganized multinucleate mass and scar form, predominantly composed of fibrovascular tissue. Example: Volkmann's ischemic contracture.
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Smooth muscle:
- Limited regenerative capacity. Some smooth muscle can reappear in arterioles within granulation tissue.
- Extensive damage generally leads to scar tissue replacing the smooth muscle.
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Cardiac muscle:
- Damaged heart muscle is replaced by fibrous tissue.
- If the endomysium (connective tissue surrounding muscle fibers) remains intact (e.g., in the inner layer of the pericardium), some regeneration might occur.
Healing in Specialized Tissues - Bone
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Bone healing:
- Procallus formation: A soft tissue mass of granulation tissue and blood clot forms at the fracture site.
- Osseous callus formation: The procallus acts as a scaffold for the development of osseous callus, composed of lamellar bone. Osteoclasts remove woven bone, and calcified cartilage breaks down. Blood vessels and osteoblasts invade the area, laying down osteoid (unmineralized bone matrix) that eventually calcifies into lamellar bone.
- Remodeling: During lamellar bone formation, osteoblasts and osteoclasts work together to remodel the united bone ends, eventually making it indistinguishable from normal bone.
### Healing in Specialized Tissues - Bone Complications
- Fibrous union: May occur if bone immobilization is inadequate, resulting in a fibrous connection rather than a bony one. In some cases, a false joint (pseudoarthrosis) can develop at the fracture site.
- Non-union: Can occur if soft tissues are interposed between the fractured ends, preventing proper healing.
- Delayed union: Can occur due to various factors that hinder general wound healing, such as infection, poor blood supply, malnutrition, movement, and old age.
Healing in Specialized Tissues - Nervous Tissue (CNS and PNS)
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Central Nervous System (CNS):
- Nerve cells (neurons) in the brain, spinal cord, and ganglia cannot be replaced once destroyed. Axons of the CNS also do not regenerate significantly.
- Damaged neuroglial cells may proliferate, resulting in gliosis (scarring by astrocytes).
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Peripheral Nervous System (PNS):
- Peripheral nerves can regenerate, mainly due to proliferation of Schwann cells and fibrils from the distal end.
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Pathologic Reactions in the PNS:
- Degenerative processes leading to peripheral neuropathy.
- Formation of traumatic neuromas.
Healing (Regeneration & Repair)
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Healing - The body's response to injury, aiming to restore normal structure and function. It involves two main processes:
- Regeneration: Healing through proliferation of parenchymal (functional tissue) cells, often leading to complete restoration. Example: Epithelial tissue, liver.
- Repair: Healing through proliferation of connective tissue, resulting in fibrosis and scarring. Occurs in tissues that cannot regenerate parenchymal cells or when there is severe damage to both parenchymal tissue and the connective tissue framework.
- Chronic Inflammation: Can stimulate scar formation because inflammatory mediators like growth factors and cytokines promote fibroblast proliferation and collagen synthesis.
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Relationship of Parenchymal Cells with Cell Cycle:
- Labile cells: Cells that continuously divide (e.g., hematopoietic cells in bone marrow, epithelial cells). Regeneration is possible.
- Stable cells: Cells in a resting phase but can be stimulated to divide (e.g., liver, kidney, pancreas, thyroid). Regeneration is possible.
- Permanent cells: Non-dividing cells that cannot replicate (e.g., nervous system and cardiac muscle cells). Regeneration is not possible; only repair through fibrosis occurs.
Repair
- Repair is the replacement of injured tissue with fibrous tissue.
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Description
Explore the healing processes in nervous tissue, focusing on the dynamics within the Peripheral Nervous System (PNS). This quiz covers key degenerative processes such as Wallerian degeneration, axonal degeneration, and segmental demyelination. Test your understanding of how these processes impact nerve regeneration.
