Tissue: The Living Fabric - Humble ISD
Chapter 4 Tissue: The Living Fabric
Tissue: The Living Fabric
Individual body cells specialized
Tissues
Histology
Types of Primary Tissues
Epithelial tissue
Connective tissue
Muscle tissue
Nerve tissue
Studying Human Tissue: Microscopy
Tissue is fixed
Cut
Stained
Glandular Epithelia
Gland
One or more cells that makes and secretes an aqueous fluid called a secretion
Classified by
Site of product release—endocrine or exocrine
Relative number of cells forming the gland
unicellular (e.g., goblet cells) or multicellular
Endocrine Glands
Ductless glands
Secretions not released into a duct
Secrete (by exocytosis) hormones that travel through lymph or blood to their specific target organs
Target organs respond in some characteristic way
Exocrine Glands
Secretions released onto body surfaces (skin) or into body cavities
More numerous than endocrine glands
Secrete products into ducts
Examples include mucous, sweat, oil, and salivary glands
Unicellular Exocrine Glands
The only important unicellular glands are mucous cells and goblet cells
Found in epithelial linings of intestinal and respiratory tracts
All produce mucin
Dissolves in water to form mucus
Slimy protective, lubricating coating
Multicellular Exocrine Glands
Multicellular exocrine glands are composed of a duct and a secretory unit
Usually surrounded by supportive connective tissue
Supplies blood and nerve fibers
Extends into and divides gland into lobes
Classification of Multicellular Glands
By structure and type of secretion
Structure
Simple glands (unbranced duct) or compound glands (branched duct)
Cells tubular, alveolar, or tubuloalveolal
Type of secretion
Merocrine – most – secrete products by exocytosis as produced
Holocrine – accumulate products within then rupture
Apocrine – accumulates products within but only apex ruptures – controversy if exist in humans
Cell Junctions (add to diagram)
* Some cells "free"
* e.g., blood cells, sperm cells
* Some bound into communities
* Three ways cells are bound:
* Tight junctions
* Desmosomes
* Gap junctions
Covering and Lining Membranes (diagram)
Composed of at least two primary tissue types
An epithelium bound to underlying connective tissue proper
Are simple organs
Three types
Cutaneous membranes
Mucous membranes
Serous membranes
Tissue Repair
Necessary when barriers are penetrated
Cells must divide and migrate
Occurs in two major ways
Regeneration
Fibrosis
Steps in Tissue Repair (diagram)
Inflammation sets stage
Organization restores blood supply
Regeneration and fibrosis
Regenerative Capacity in Different Tissues
Regenerate extremely well
Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue
Moderate regenerating capacity
Smooth muscle and dense regular connective tissue
Virtually no functional regenerative capacity
Cardiac muscle and nervous tissue of brain and spinal cord
New research shows cell division does occur
Efforts underway to coax them to regenerate better
Developmental Aspects
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
[pic]
Aging Tissues
Normally function well through youth and middle age if adequate diet, circulation, and infrequent wounds and infections
Epithelia thin with increasing age so more easily breached
Tissue repair less efficient
Bone, muscle and nervous tissues begin to atrophy
DNA mutations possible ( increased cancer risk
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