Tissues And Tissue Types

Tissues and tissue types

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Tissues are:

• Collections of specialized cells and cell products organized to perform a limited number of functions 

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Histology = study of tissues

The four tissue types are: • Epithelial • Connective • Muscular • Nervous

Epithelial tissue 

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Layer of cells covering exposed body surfaces inside or outside • Skin • Linings of body cavities • Linings of any body opening • Linings of internal passageways Form barriers Form glands • Secretory structures from epithelium

Characteristics of epithelium Cellularity: composed of tightly bound, arranged cells Polarity: uneven distribution of materials in cells; one side always faces an opening; one side always attached to a basement membrane to adjacent tissue Attachment: one side always attached to membrane made by epithelium (basal membrane) & connective tissue underneath Avascularity: No blood vessels in epithelium Nourished by diffusion or absorption Regeneration Surface cells replaced continually by mitotic cells below

Epithelial function 1. Provide physical protection Protect from abrasion, dehydration,… 2. From a barrier for permeability Can give selective absorption or secretion Can be regulated & modified by stimuli, I.e., changed with need 3. Provide sensations: Epithelial cells deeply innervated w. sensory nerves Detect changes in environment & relay to body 4. Produce specialized secretions Glandular epithelium may be scattered in other epithelium

Classification of Epithelium 

Classified by arrangement of cells into layers • • •

simple = one cell layer thick stratified = many cell layers thick pseudostratified = single layer of cells where all cells don’t reach apical surface 

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nuclei at found at different levels so it looks multilayered

Classified by shape of surface cells • • • •

squamous =flat cuboidal = cube-shaped columnar = tall column transitional = shape varies with tissue stretching

Squamous

Simple squamous

In protected regions for absorption • Respiratory alveoli for gas exchange In regions to reduce friction • Linings of blood vessels & heart = endothelium • Serous membranes lining body cavities • Mesothelium = any simple squamous epithelium lining ventral body cavities

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Single row of cube-shaped cells, often with microvilli. • Absorption & secretion; produces mucus. Mammary and salivary glands.

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Single row of tall, narrow cells • vertically oriented, oval nuclei in basal half of cell Absorption & secretion; secretion of mucus Inner lining of GI tract

Keratinized Stratified Squamous

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Multilayered epithelium covered with layer of compact, dead squamous cells packed with protein keratin Retards water loss & prevents penetration of organisms

Nonkeratinized Stratified Squamous Epithelial layer

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Multilayered epithelium that lacks surface layer of dead cells forming abrasion-resistant, moist, slippery layer Found on tongue & vagina

Stratified Cuboidal Epithelium

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Two or more layers of cells; surface cells square Secretes sweat; ovarian hormones & produces sperm Found ovarian follicles & seminiferous tubules

Cuboidal Epithelia

Transitional Epithelium

Transitional Epithelium

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Multilayered epithelium with rounded surface cells that flatten when the tissue is stretched Stretches to allow filling of urinary tract Found in urinary tract -- urinary bladder

Muscle tissue  

Specialized for contraction Three types • Skeletal • Cardiac • Smooth

Muscle Tissue

Muscle Tissue

Muscle Tissue

Connective tissue functions  

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Establishing a structural framework Transporting fluids and dissolved materials Protecting delicate organs Supporting, surrounding and interconnecting tissues Storing energy reserves Defending the body from microorganisms

A Classification of Connective Tissues

Connective tissues contain  

Specialized cells Matrix • Composed of extracellular protein fibers and a ground substance

Connective tissue proper   

Contains varied cell populations Contains various fiber types A syrupy ground substance

Fluid connective tissue  

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Contains a distinctive cell population Watery ground substance with dissolved proteins Two types • Blood • Lymph

Supporting connective tissues    

Less diverse cell population Dense ground substance Closely packed fibers Two types • Cartilage • Bone

Connective tissue proper 

Contains fibers, a viscous ground substance, and a varied cell population • Fibroblasts • Macrophage • Adipocytes • Mesenchymal cells • Melanocytes • Mast cells • Lymphocytes • Microphages

Connective tissue proper  

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Classified as loose or dense Loose • Embryonic mesenchyme, mucous connective tissues • Areolar tissue • Adipose tissue • Reticular tissue Dense • Dense regular CT • Dense irregular CT

The Cells and Fibers of Connective Tissue Proper

Connective Tissue in Embryos

Adipose and Reticular Tissues

Dense Connective Tissues

Dense Connective Tissues

Dense Connective Tissues

Fluid connective tissues 

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Distinctive collections of cells in a fluid matrix Blood • Formed elements and plasma 

Red blood cells, white blood cells and platelets

• Arteries carry blood away, veins carry to the heart • Capillaries allow diffusion into the interstitial fluid 

Lymph

Formed Elements of the Blood

Supporting connective tissues  

Cartilage and bone support the rest of the body Cartilage • Grows via interstitial and appositional growth • Matrix is a firm gel containing chondroitin sulfate • Cells called chondrocytes • Cells found in lacunae • Perichondrium separates cartilage from surrounding tissues • Three types: hyaline, elastic and fibrocartilage

The Perichondrium and Types of Cartilage

The Perichondrium and Types of Cartilage

The Perichondrium and Types of Cartilage

Bone, or osseus tissue 

Has osteocytes • Depend on diffusion through canaliculi for nutrients

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Little ground substance Dense mineralized matrix Surrounded by periosteum

Bone