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Download cells - Doctor Jade Main
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TISSUE LEVEL OF ORGANIZATION 4 BASIC TISSUE TYPES • Epithelial • Connective • Muscle • Nervous Cell Connections • Tight Junctions • Adherens • Desmosomes • Hemidesmosomes • Gap Junctions Tight Junctions most apical part of cell fuse 2 adjacent membranes with fibrous connections prevents passage of molecules & ions between cells if epithelium forms tube space in tube is-lumen presence of tight junctions ensures that contents of lumen are isolated from basolateral cell surfaces Adherens • dense layers of proteins on inside of membrane • attach membrane proteins to microfilaments of cell’s cytoskeleton Desmosomes localized patches holding cells together allow tissues to resist twisting & stretching stabilize cell shapes most abundant in superficial skin layers links so strong that dead skin cells are shed in thick sheetsnot individually Hemidesmosomes • made of proteins • anchor cells to basement membrane Gap Junctions intercellular channels permit passage of ions & small molecules comprised of pore-like transmembrane proteins-connexons help coordinate functions such as cilia beating most abundant in cardiac & smooth muscle coordinate muscle cell contraction Epithelial Tissue • • • • flat sheets of contiguous cells line body surfaces & cavities cover every exposed surface skin & all passageways that communicate with the outside world – Digestive – Reproductive – Urinary – Respiratory • • • • • EPITHELIA TISSUE CHARACTERISTICS Cellularity – made almost entirely of cells – packed together tightly with little extracellular space Polarity – cytoplasmic components of cells not evenly distributed – cells have one exposed face either to external world or to a lumenapical surface and basal surface which faces underlying connective tissue Attachment – bottom row of cells bound to basement membrane Avascularity – no direct contact of epithelial cells with blood vessels – nutrition comes via diffusion or absorption from underlying tissues Regeneration – able to repair and renew themselves – stem or germinative cells are found in deepest layer of epithelium near basement membrane FUNCTIONS • physical protection – protect underlying cells from abrasion, dehydration and destruction • control permeability – anything entering or leaving the body must cross an epithelium • provide sensation – some detect environmental changes & relay information to nervous system • produce special secretions – primary function of glandular epithelium Specializations of Apical Surface • Microvilli – finger-like projections – increases surface area 20X – specialized for absorption & secretion • Cilia – longer with larger diameter – beat in coordinated fashion – movement of fluids across & through epithelia Classification of Epithelia • cell shape • arrangement of cell layers Arrangement of Layers • Simple – one layer of cells • Pseudostratified – one layer that looks like several layers • all cells attach to basement membrane • Stratified – several layers of cells stacked on top of each other • Function & Classification of Epithelia – each cell rests on basement Simple – – – – – – – • membrane one surface faces either lumen or outside world cells are thin same polarity typically fragile do not provide much protection against mechanical damage found only internally absorption or secretion Stratified – basal layer of cells rests on basement membrane – subsequent layers do not – stacked on top of basal layer – cells of only most superficial layer have free surface – found in areas subjected to mechanical or chemical stresses • skin & lining of mouth Cell Shapes • Squamous – flat & irregularly shaped – often so thin that flattened nucleus bulges at cell surface • Cuboidal – about as tall as wide – look like cubes or hexagonal boxes – Nucleus-usually round & not flattened • Columnar cells – taller than wide – look like columns – Nucleus-usually elongated & found in long axis of cell • Transitional cells – go from squamouscuboidal & back again – all organs to change shape TYPES OF EPITHELIA Simple Squamous • one layer of squamous cells • delicate • found in protected regions • filtration or diffusion • slick, slippery surfaces are needed to reduce friction • substances can move quickly through Simple Cuboidal • one layer of cuboidal cells • specialized for secretion & absorption • found in secretory portion of glands • some cells may have a dense border of microvilli • found in kidney tubules, pancreas & salivary glands Simple Columnar • one layer of columnar cells • found where absorption & secretion take place • small intestine • in small intestine epithelium has goblet cells which secrete mucus to protect and lubricate • found with cilia in oviducts & respiratory tract Stratified Squamous • several layers of squamous cells • surface cells look squamous • lower ones appear more cuboidal or columnar • found where body experiences severe mechanical stresses • cells are worn away quickly • replaced rapidly by mitosis in lower layers • outer layer of the skin- epidermis – here mechanical stress and dehydration of the superficial layers is aided with keratin • skin is said to be keratinized • Non-keratinized stratified squamous epithelium – found in mouth, pharynx & esophagus Stratified Cuboidal • typically only 2 cell layers of cuboidal cells • not a great quantity found in • human body • large ducts of sweat & mammary glands Stratified Columnar • rare • found where 2 other types of epithelia meet • large ducts • in pharynx, epiglottis, anus & urethra Pseudostratified Epithelium • looks like stratified columnar • appears layered but is not • nuclei are at different levels but all cells rest on basement membrane • not all same height • often contains cilia & goblet cells • found lining most of respiratory tract Transitional Epithelium • multi-layered • goes from cuboidal squamous and back again • thicker, multilayered epithelium • found in bladder • tolerates great deal of stretching • surface cells are more muffin-shaped • cells are rounded when organ is not filled and flattens as organ fills Glanduar Epithelia • Gland – cell or organ that secretes substances for use elsewhere in the body or releases them for elimination from body – composed primarily of epithelia tissue • Endocrine – ductless – release hormones into interstitial fluid – regulate or coordinate activity of other tissues, organs & organ systems • Exocrine – ducted – release secretions into passageways or ducts which empty onto the skin or other epithelial surfaces – produce enzymes & perspiration Exocrine Gland Classification • Unicellular • Multicellular • Simple –have single, unbranched duct • Compound –have branched duct Exocrine Gland Classification • if duct & secretory part are equal in diameter-gland is tubular • if secretory cells form sacacinar • if secretory cells are found both in tubular &acinar partstubuloacinar • Exocrine Gland Structure – Unicellular – Multicellular • Secretory sheets • Tubular • Alveolar (Acinar) • Tubuloalveolar Merocrine Glands • most common • sweat & mucus secreting • release products via exocytosis Apocrine Glands • product accumulates in apical tip • pinched off to secrete • rest of gland repairs itself Holocrine glands • entire cell becomes packed with secretory product • cell bursts releasing secretion and in so doing kills the cell • further secretion depends on replacement of gland cell • sebaceous or oil glands associated with hair follicles Connective Tissue • • • • widely spread throughout body most diverse tissue type never exposed to outside environment highly vascularized-blood vessels are present (except cartilage & tendons) • comprised of 3 basic components: – specialized cells – extracellular matrix • protein fibers • ground substance Functions • structural framework – binds muscle to bone, fat holds kidneys in place & fibrous tissues bind skin to underlying muscle • supports the body • protection for delicate organs such as brain & lungs • immune protection defending body from microorganisms • transports fluids & dissolved materials through body • movement – bones provide levers for body movement • stores energy & generates heat Cells • each type of connective tissue has specialized cells at different stages of maturity • Juvenile cells actively secrete matrix – have suffix blast • Mature cells have suffixcyte • Destructive cells have suffix clasts • prefix is different for different types of connective tissues • Cartilage-chondro • Bone-osteo • Blood-hemo Protein Fibers • Collagen fibers • long, straight, unbranched & very strong – each fiber-bundle of fibrous protein subunits wound together like strands of rope • Elastic fibers • contain elastin – able to stretch & recoil without damage • Reticular fibers • fine collagen fibers – made of same protein subunits as collagen – arranged differently forming a tough, flexible branching framework Classification • Embryonic – mesenchyme & mucous types – found in embryo from third gestational month to birth – tissue from which all connective tissue originates • Mature – Loose – Dense – Cartilage – Bone – Liquid Loose Connective Tissue • packing material • fills spaces between organs, cushions & stabilizes cells in organs & supports epithelia • surrounds & supports blood vessels and nerves & stores lipid • areolar, adipose & reticular Areolar Connective Tissue • consists of an open framework • ground substance accounts for most of its volume • forms soft-pliable-packing material around tissues – muscles, blood vessels & glands • absorbs shock • loose organization allows it to distort without damage • presence of elastic fibers makes it able to return to original shape • forms layer separating skin from deeper structures Adipose Tissue • composed mainly of adipocytes • little matrix • cells have large vacuoles filled with fat • fat droplet compresses cytoplasm around edges of cell • organelles are squeezed to side • insulation • slows heat loss through skin • shock absorber around organs Reticular Connective Tissue consists of network of reticular fibers & cells Found-spleen, lymph nodes & liver Dense Connective Tissue Dense regular – collagen fibers regularly arranged in parallel – forms ligaments which connect bone to bone & tendons which connect muscle to bones • Dense irregular – collagen fibers found in irregular arrangements forming interwoven meshworks – provides strength & support for areas subjected to stress from many directions – found in skin where it gives strength to lower layer – forms sheath around cartilagesperichondrium & bones-periosteum – forms thick, fibrous capsule around internal organs such as liver, kidney and spleen Elastic Connective Tissue contains great many elastin fibers give tissue flexibility found-vocal cords & ligaments which connect vertebrae Supporting Connective TissuesCartilage • • • • • • • • • • strong, flexible found throughout the body Matrix firm gel containing chondroitin sulfate which forms complexes with proteinsproteoglycans cells are chondrocytes found in chambers or lacunae avascular, blood cells do not grow into it three types : hyaline, elastic and fibrocartilage. Hyaline – covers ends of long bones – matrix consists of closely packed collagen fibers which makes it tough & flexible – found connecting ribs to sternum, nasal cartilages, respiratory tract and as a cover in opposing bone surfaces in joints such as the knees & elbows. Elastic cartilage – like hyaline-more elastin fibers making it flexible and resilient – epiglottis & ear pinna Fibrocartilage – looks like dense regular connective tissue – matrix dominated by collagen fibers-densely interwoven making it durable, tough & more compressible than other cartilages – found as intervertebral discs – menisci of knees, between pubic bones, around or in joints and tendons – resists compressions, absorbs shocks – prevents bone to bone contact Supporting Connective TissuesBone • osseous tissue • support & protection, fat storage and blood cell formation • small amount ofground substance • Matrix-like cartilage but more rigid because of calcium salt-CaPO4 – remainder is collagen fibers – Ca salts make tissue hard & brittle – Collage fibers make it strong & flexible • Bone cells are called osteocytes – found in lacunae – organized around blood vessels that branch through the matrix – osteocytes communicate with each other & blood vessels by canaliculi Fluid Connective Tissue • Blood – – – – – – contains blood cells formed elements RBCs WBCs platelets suspended in liquid matrixplasma which contains protein fibers for blood clotting • Lymph Membranes • physical barriers composed of epithelia & supported by connective tissue • cover & protect other tissues • 4 types: – Mucous – Serous – Cutaneous – Synovial Cutaneous Membranes • cover body surface • largest membrane in body – skin – stratified squamous epithelium + layer of areolar connective tissue reinforced by underlying dense connective tissue • thick, relatively water proof & usually dry Mucus Membranes • line cavities in communication with outside • mucosa consists of two to three layers • an epithelium • an areolar connective tissue layer (lamina propia) • sometimes layer of smooth musclemuscularis mucosae • absorptive, secretory & protective functions • help keep epithelial surfaces moist with mucus made by goblet cells Serous Membranes • line sealed internal parts such as ventral body cavities • simple squamous epithelium resting on thin layer of areolar connective tissue • produce watery serous fluid • pleura lines pleural cavity and covers lungs • pericardium lines pericardial cavity covering heart • each can be divided into parietal partlines inner surface of cavity • and visceral part-covers outer surface of organs Synovial Membranes • surround joint cavities • Joints-articulations for bones • allow for movement • surrounded by fibrous capsule consisting of areolar tissue with matrix of interwoven collagen fibers, proteoglycans & glycoproteins • space filled with synovial fluid Muscle Tissue • • • • specialized for movement & contraction 3 types: skeletal, cardiac and smooth all contract alike but have different internal organizations Skeletal muscles have cells called fibers – long & thin – multinucleated often containing several hundred nuclei – striated or striped due to repeating groups of cellular proteins actin and myosin-responsible for contraction • cells contract when stimulated by nerves • under voluntary control • can be called striated voluntary muscle Cardiac Muscle • • • • • • • • • • found only in the heart striated like skeletal & arranged same uninucleate-may have 1-5-centrally located nuclie Cardiocyte-smaller than skeletal m. cell connected to one another via darkened bands between themintercalated discs • special areas locked together by desmosomes, gap junctions & intercellular cement Ions move through gap junctions which coordinates contractions do not need nerve activity to contract pacemaker cells establish regular rate of contraction not under voluntary control striated involuntary muscle Smooth Muscle • Cells-small, spindle shaped with tapering ends • contain actin & myosin-not arranged in striated fashion • cells are uninucleate • found in digestive & urinary organs, uterus & blood vessel walls • not under voluntary control • non-striated involuntary Nervous Tissue • consists of neurons (nerve cells) & neuralgia cells • specialized to detect stimuli, respond quickly & transmit information • each nerve cell has soma or cell body • one long process-axontransmits messages • many smaller projectionsdendrites-receive information • Exocrine Gland Structure – Unicellular e.g. Goblet cell
