Anatomy and Physiology - Tissues - Quick Guides | Anatomy and Physiology

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Study GuideAnatomy and Physiology–Tissues1.Epithelial TissueWhat is Epithelial Tissue?Epithelial tissue (epithelium)is a type of tissue made ofclosely packed cells. It forms thecoverings and liningsof many parts of the body.These cells are usually arranged like a “sheet,” and they protect body surfaces and control whatpasses in and out.1.1Main Characteristics of EpitheliumEpithelial tissue has some special features:1. Cells are tightly packedThe cells are close together withvery little spacebetween them.This means there isvery little intercellular material.2. Epithelium has no blood vessels (Avascular)Epithelium isavascular, which means itdoes not contain blood vessels.So how does it get nutrients and remove wastes?Bydiffusionfrom nearbyconnective tissue.3. It has two surfacesEpithelium has:•afree (apical) surface→ faces outside the body or inside a body cavity•abasal surface→ rests on connective tissueBetween the epithelium and connective tissue, there is a thin supportive layer called thebasementmembrane.

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Study Guide1.2Types of Epithelial TissueThere aretwo major typesof epithelium:1. Covering and lining epitheliumThis type:•covers the outside surface of the body•lines internal organs and body cavities2. Glandular epitheliumThis type forms glands andsecretes substanceslike hormones or enzymes.Covering and Lining EpitheliumCovering/lining epithelium is classified usingtwo important features:1) Cell Shape2) Number of Cell Layers1) Classification by Cell ShapeA. Squamous cells•Flatand thin•Their nucleus is near the upper surface•They often look like afried egg(flat with a bulge in the middle)B. Cuboidal cells•Cube-shaped or hexagon-shaped•Have acentral, round nucleus•Main functions:osecretion (example: sweat)oabsorption (example: digested food)

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Study GuideC. Columnar cells•Tall cells•Oval nucleus located near thebasement membrane•Functions:oprotect underlying tissueoabsorptionSome columnar cells may have:•microvilli→ tiny surface extensions that increase surface area for absorption•cilia→ help move substances like mucus (example: in respiratory tract)D. Transitional cellsThese cells can change shape:•may look flat or tall•they stretch or compress depending on body movement2) Classification by Number of Cell LayersA. Simple epithelium•Single layerof cellsB. Stratified epithelium•Many layersof cells•Usually provides strong protectionC. Pseudostratified epithelium•Actuallyone layer, but cells have different heights•This makes it look like it hasmultiple layersHow Epithelial Tissues are NamedEpithelial tissues are named using:

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Study Guide1.number of layers2.cell shape(and sometimes cilia)Example:•Simple squamous epithelium= one layer of flat cells•Pseudostratified columnar ciliated epithelium= one layer of columnar cells, differentsizes, with ciliaImportant point:Stratified epithelium is named by the shape of the top (outermost) layer only.So even if inner layers are cuboidal/columnar, the name depends on the outer layer.

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Study GuideFigure1.Types of epithelial tissues.Glandular EpitheliumGlandular epithelium forms glands that make and release useful substances.

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Study GuideThere aretwo main types of glands:1. Endocrine Glands (No Ducts)Endocrine glands releasehormones directly into the bloodstream.Example:•Thethyroid glandreleasesthyroxin•Thyroxin travels through the blood and increases themetabolic rateof body cells2. Exocrine Glands (Have Ducts)Exocrine glands release their products intoducts (tubes), which carry the secretion to the epithelialsurface.Examples of exocrine secretions:•sweat•saliva•milk•stomach acid•digestive enzymes1.3Exocrine Glands: Classification by StructureExocrine glands can be classified based on how they are built.

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Study GuideFigure2.Exocrine glands can be classified as simple or compound with either a tubular oralveolar structure.Structural classification terms1. Unicellular vs Multicellular•Unicellular gland= single-celled gland•Multicellular gland= many cellsA multicellular gland includes:•agroup of secretory cells•aductfor carrying secretions out2. Branched“Branched” means thesecretory cellsare arranged in branches.3. Simple vs CompoundThis depends on theduct, not the secretory part:•Simple gland→ duct doesnotbranch•Compound gland→ ductbranches

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Study Guide4. Tubular vs Alveolar (Acinar)This describes the shape of the secretory part:•Tubular gland→ secretory portion forms a tube•Alveolar (acinar) gland→ secretory portion forms a round, sac-like shape1.4Exocrine Glands: Classification by FunctionExocrine glands are also classified byhow they release their secretions.Figure3.Exocrine glands can be classified according to their function.1. Merocrine GlandsInmerocrine glands:•secretions leave the cell byexocytosis•the cell stays intactExample:•Goblet cellsin the trachea releasemucusby exocytosis

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Study Guide2. Apocrine GlandsInapocrine glands:•a portion of the cell (the top/apical part) breaks off•this portion contains the secretion•the rest of the cell remains and continues workingExample:•Lactiferous glandsreleasemilkthis way3. Holocrine GlandsInholocrine glands:•the entire secretory cell fills with product•the whole celldisintegrates•cell contents + cell debris are released togetherExample:•Sebaceous glandsreleasesebum•sebum helpslubricate the skinKey TakeawaysEpithelium = tightly packed cells that cover surfaces and form glandsAvascular = no blood vessels (diffusion from connective tissue)Basement membrane = between epithelium and connective tissueClassified by:•cell shape (squamous, cuboidal, columnar, transitional)•layers (simple, stratified, pseudostratified)

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Study GuideGlands:•endocrine → hormones into blood•exocrine → secretions into ductsExocrine glands:•structure (simple/compound, tubular/alveolar)•function (merocrine, apocrine, holocrine)2.Quiz: Epithelial Tissue1. QuestionA group of organized __________ working together forms __________. An organized group of thelatter work together to form __________.Answer Choices• tissues; organs; cells• organs; cells; tissue• cells; tissue; organsCorrect Answercells; tissue; organsWhy This Is CorrectThe body is organized in levels:1.Cellsare the smallest living units.2.Groups of similar cells formtissues.3.Different tissues work together to formorgans.Example: Muscle cells → muscle tissue → heart (organ)

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