Epithelial Tissues: Structure, Function, and Classification
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Lab Exercise 5 Epithelial and Connective Tissues Portland Community College BI 231
Tissues • Groups of cells similar in structure and function • Each tissue is then further subdivided into categories. • All organs are made of a combination of different tissues. • The four types of tissues • Epithelial • Connective • Muscle • Nerve
Epithelium • Covers all body surfaces, inside and out • Is anchored to connective tissue by a layer of glycoproteins and protein fibers called the basal lamina
Epithelial TissueDistinguishing Characteristics • Cellularity: Composed almost entirely of cells • Polarity: apical and basal surfaces (top and a bottom) • Attachment: Supported by connective tissue (basement membrane) • Avascular: Contains no blood vessels: obtains nutrients by diffusion • Regeneration: Rapidly replaces lost cells by cell division
Functions of Epithelia • Protection: Skin • Secretion: glands release secretions • Absorption: Uptake nutrients • Sensory: Taste buds • Filtration: In the kidneys
Classification of Epithelia • First name: • Simple: one layer • Stratified: more than one layer • Second name: • Based on the shape of the top layer of cells • Squamous (flat) • Cuboidal (square) • Columnar (rectangle) • Two additional categories • Transitional • Pseudostratified
Classification of Epithelia • Squamous • Cuboidal • Columnar
Simple Squamous Epithelium • Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm
Simple Squamous Epithelium • Top View
Simple Squamous Epithelium • Functions: • Diffusion • Alveoli in the respiratory system allows for exchange of O2 and CO2 • Filtration • Capillaries allow fluid and other substances out and holds blood cells and proteins in • Lubrication • Secretes lubricating substances in serosae
Simple Cuboidal Epithelium • Single layer of cube like cells with large, spherical central nuclei
Simple Cuboidal Epithelium • Functions: • Secretion • Glands such as the thyroid are composed of simple cuboidal epithelium and secrete hormones ect… • Absorption • In the kidney, the proximal convoluted tubule is composed of simple cuboidal epithelium and reabsorbs water and other nutrients from the filtered fluid
Simple Columnar Epithelium • Single layer of tall cells with oval nuclei toward the basal surface • Goblet cells are often found in this layer
Simple Columnar Epithelium • Functions • Secretion • Example: In the stomach, these cells secrete digestive enzymes • Absorption • Example: In the intestine, these cells absorb nutrients
Stratified Squamous Epithelium • Composed of several layers of cells • Top layer flat • Bottom layers any shape • Function in protection of underlying areas subjected to abrasion
Stratified Squamous Epithelium • Non-keratinized • Composed of several layers of cells • Top layer flat • Bottom layers any shape
Stratified Squamous EpitheliumNon-Keratinized • Functions • Physical protection against abrasion and pathogens • Non-Keratinized is associated with “moist” areas • Mouth • Throat • Esophagus • Anus • Vagina
Stratified Squamous EpitheliumKeratinized Looks “flakey” on the top
Stratified Squamous EpitheliumKeratinized • Functions • Physical Protection • Found only in the epidermis of the skin • Keratin is a protein that helps strengthen the cells against abrasion
Pseudostratified Columnar Epithelium • Single layer of cells with different heights; some do not reach the free surface • Nuclei are seen at different levels • May be ciliated (PCCE) or non-ciliated
Pseudostratified Columnar Ciliated Epithelium (PCCE) • Functions • Protection • Example: Lines the upper respiratory tract. The cilia sweep debris toward the throat • Secretion • Example: May contain goblet cells (unicellular glands) that secrete mucus
Transitional Epithelium • Several cell layers, basal cells are cuboidal • Apical cells are dome shaped when not stretched • Apical cells are flat when stretched • Only found in Urinary System • Functions: • Allows expansion and recoil after stretching
Transitional Epithelium Distended bladder Empty bladder
Stratified Cuboidal and Columnar • Typically two cell layers thick • Rare • Functions: • Secretion • Found in some sweat and mammary glands
Stratified Columnar Epithelium • Limited distribution in the body • To tell the difference between this and pseudostratified columnar, look at the nucleus. • The nuclei are lined up in a straight row • Function • Protection • Found in the pharynx, male urethra, lining some glandular ducts, and anus
Connective Tissue • 4 Types • Connective Tissue Proper • Bone • Blood • Cartilage
Connective Tissue Features • Specialized cells • Matrix: Nonliving material between the cells that makes up most of the volume (ground substance + fibers) • Extracellular fibers • Ground substance: Composed chiefly of interstitial fluid, cell adhesion proteins, and proteoglycans • Specific composition varies between tissues (Blood=fluid, Cartilage=gel like, Bone=Solid)
Connective Tissue Fibers • 3 types of fibers include collagen, elastic and reticular • Collagen Fibers:Fibrous protein molecules • Extremely tough • High tensile strength • Strongest type of fibers in connective tissue.
Connective Tissue Fibers • Elastic Fibers: Form branching networks • Elastin: a rubber like protein that allow it to act like a rubber band and snap back to its original shape after it is stretched • Reticular Fibers:Forming delicate networks • Fine collagenous fibers (with a different chemical structure) branch extensively • Surround small blood vessels and support soft tissue organs
Blast cells • Undifferentiated cells (blast = forming) • Fibroblasts- fount in loose and dense connective tissues (secrete matrix) • Chondroblasts in cartilage • Osteoblasts in bone • Hemocytoblasts in blood • ‘cytes’ are the mature forms
Cells of Connective Tissue Proper • Reticular cells: specialized fibroblasts found in reticular connective tissue • Macrophages: Scavenger cells that engulf pathogens or damaged cells • Adipocytes: Fat cells • Plasma cells: produce antibodies • Mast cells: Stimulate local inflammation: contain histamine and heparin • Leukocytes: WBC involved in immunity
Mesenchyme • Embryonic Connective tissue • Gel-like ground substance with fine protein fibers and immature cells; gives rise to all other connective tissues
Areolar Connective Tissue (Loose) • Gel like matrix • Contains all 3 fiber types • Functions: • Wraps and cushions organs • Holds and conveys tissue fluid • Locations: • Under epithelial tissues • Packages organs • Surrounds capillaries
Areolar Connective Tissue (Loose) Fibroblast Collagen fiber Macrophage Elastic fiber
Adipose Tissue (Loose) • Function: • Storage of lipid molecules • Insulation
