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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