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4.7 Tissue Repair
• When the body’s barriers are compromised, the inflammatory and immune responses are activated
• Repair starts very quickly• Repair is the function of the inflammatory process
© 2016 Pearson Education, Inc.
Steps in Tissue Repair
• Repair can occur in two major ways:– Regeneration: same kind of tissue replaces destroyed tissue, so
original function is restored– Fibrosis: connective tissue replaces destroyed tissue, and original
function lost• Step 1: Inflammation sets stage
– Release of inflammatory chemicals causes:• Dilation of blood vessels• Increase in blood vessel permeability
– Clotting of blood occurs
© 2016 Pearson Education, Inc.
Figure 4.12-1 Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
© 2016 Pearson Education, Inc.
Scab Blood clot inincised wound
Epidermis
Vein
Inflammatorychemicals
Migratingwhiteblood cell
Artery
Inflammation sets the stage:• Severed blood vessels bleed.• Inflammatory chemicals are released by
injured tissue cells, mast cells, and others.• Local blood vessels become morepermeable, allowing white blood cells, fluid,clotting proteins, and other plasma proteinsto seep into the injured area.
• Clotting occurs; surface exposed to airdries and forms a scab.
1
Steps in Tissue Repair (cont.)
• Step 2: Organization restores blood supply– Organization begins as the blood clot is replaced with granulation
tissue (new capillary-enriched tissue)– Epithelium begins to regenerate– Fibroblasts produce collagen fibers to bridge the gap until
regeneration is complete– Any debris in area is phagocytized
© 2016 Pearson Education, Inc.
Figure 4.12-2 Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
© 2016 Pearson Education, Inc.
Regeneratingepithelium
Area ofgranulationtissueingrowth
FibroblastMacrophage
Buddingcapillary
Organization restores the blood supply:• The clot is replaced by granulation tissue,
which restores the vascular supply.• Fibroblasts produce collagen fibers that
bridge the gap.• Macrophages phagocytize dead and
dying cells and other debris.• Surface epithelial cells multiply and
migrate over the granulation tissue.
2
Steps in Tissue Repair (cont.)
• Step 3: Regeneration and fibrosis effect permanent repair– The scab detaches– Fibrous tissue matures– Epithelium thickens and begins to resemble adjacent tissue– Results in a fully regenerated epithelium with underlying scar
tissue, which may or may not be visible
© 2016 Pearson Education, Inc.
Figure 4.12-3 Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
© 2016 Pearson Education, Inc.
Regenerated epithelium
Fibrosed area
Regeneration and fibrosis effectpermanent repair:
• The fibrosed area matures andcontracts; the epithelium thickens.
• A fully regenerated epithelium withan underlying area of scar tissueresults.
3
Regenerative Capacity of Different Tissues
• Tissues that regenerate extremely well include:– Epithelial tissues, bone, areolar connective tissue, dense irregular
connective tissue, blood-forming tissue• Tissue with moderate regenerating capacity:
– Smooth muscle and dense regular connective tissue
© 2016 Pearson Education, Inc.
Regenerative Capacity of Different Tissues (cont.)
• Tissues with virtually no functional regenerative capacity:– Cardiac muscle and nervous tissue of brain and spinal cord– New research shows cell division does occur, and efforts are
underway to coax them to regenerate better
© 2016 Pearson Education, Inc.
Clinical – Homeostatic Imbalance 4.3
• Scar tissue that forms in organs, particularly the heart, can severely impair the function of that organ– May cause the organ to lose volume capacity– May block substances from moving through organ– May interfere with ability of muscles to contract or may impair nerve
transmissions
© 2016 Pearson Education, Inc.
Clinical – Homeostatic Imbalance 4.3
• Scar adhesions may cause organs to adhere to neighboring structures, preventing normal functions
• Scarring can potentially cause progressive failure of the organ, particularly the heart
© 2016 Pearson Education, Inc.
Developmental Aspects of Tissues
• Primary germ layers– Superficial to deep: ectoderm, mesoderm, and endoderm– Formed early in embryonic development– Specialize to form the four primary tissues
• Nerve tissue arises from ectoderm• Muscle and connective tissues arise from mesoderm• Epithelial tissues arise from all three germ layers
© 2016 Pearson Education, Inc.
Developmental Aspects of Tissues
• Tissues function well through youth and middle age if given adequate diet and circulation and if wounds and infections are minimal
• As the body ages, epithelia thin, so they are more easily breached
• Tissue repair is less efficient• Bone, muscle tissues, and nervous tissues begin to atrophy• DNA mutations increase cancer risk
© 2016 Pearson Education, Inc.
Figure 4.13 Embryonic germ layers and the primary tissue types they produce.
© 2016 Pearson Education, Inc.
16-day-old embryo(dorsal surface view)
EctodermMesodermEndoderm
Epithelium(from all threegerm layers)
Inner lining ofdigestive system(from endoderm)
Nervous tissue(from ectoderm)
Muscle andconnectivetissue(mostly frommesoderm)