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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 found at most apical part of cell join one cell tightly to a neighboring cell fuse 2 adjacent membranes with fibrous connections prevents passage of molecules & ions between cells if epithelium forms a tube space in tube is the lumen presence of tight junctions ensures that the contents of the lumen are isolated from the basolateral surfaces of the cell Adherens • dense layers of proteins on the inside of a membrane • serve to attach membrane proteins to the microfilaments of the cell’s cytoskeleton Desmosomes localized patches holding cells together allow tissues to resist mechanical stress resist twisting & stretching stabilize cell shapes most abundant in superficial skin layers links so strong that dead skin cells are shed in thick sheets-not individually Hemidesmosomes • made of proteins called • anchor cells to basement membrane Gap Junctions intercellular channels permit passage of ions & small molecules comprised of pore-like transmembrane proteins-connexons ions can flow through these junctions help coordinate functions such as cilia beating most abundant in cardiac & smooth muscle to 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 • • • • • CHARACTERISTICS OF ALL Cellularity EPITHELIA TISSUE – 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 a 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 • Neuroepithelium -epithelium with special sensory function • 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 – function in movement of fluids across and 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 all have same polarity typically fragile do not provide much protection against mechanical damage simple found only internally in areas of absorption or secretion Stratified – basal layer of cells rests on basement membrane – subsequent layers do not – stacked on top of the basal layer – cells of only the most superficial layer have a free surface – Stratified found in areas subjected to mechanical or chemical stresses such as the skin and lining of the mouth Cell Shapes • Squamous cells – flat & irregularly shaped – often so thin that the flattened nucleus bulges at the cell surface • Cuboidal cells – about as tall as wide – look like cubes or hexagonal boxes – nucleus is usually round & not flattened • Columnar cells – taller than they are wide – look like columns – nucleus usually is elongated and 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 where filtration or diffusion is a priority or where 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 • comprised of typically only 2 cell layers of cuboidal cells • not a great quantity found in the human body • only in large ducts of sweat and mammary glands Stratified Columnar • very rare • found where 2 other types of epithelia • some large ducts • in the pharynx, epiglottis, anus & urethra Pseudostratified Epithelium • looks like stratified columnar • appears layered but is not • all nuclei are at different levels but all cells rest on basement membrane but are not all same height • often contains cilia & goblet cells • found lining most of the 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 the 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 a single, unbranched duct • Compound –have a branched duct Exocrine Gland Classification • if duct & secretory part are of equal diameter- gland is tubular • If secretory cells form a sac glandacinar • if secretory cells of gland are found in both tubular &acinar parts it is tubuloacinar • 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 the body most diverse tissue type never exposed to outside environment highly vascularized-blood vessels are present (except cartilage and tendons) • All tissues are comprised of 3 basic components: – specialized cells – extracellular matrix • protein fibers • ground substance Functions • provides structural framework – binds muscle to bone, fat holds kidneys in place & fibrous tissues bind skin to underlying muscle • bone supports the body & cartilage supports ears, nose, trachea and bronchi. • provides protection for delicate organs such as brain & lungs • provides immune protection defending body from microorganisms • involved in transporting fluids & dissolved materials through the body • Allows movement – bones provide levers for body movement • important in storing energy & generating heat Cells • Each type of connective tissue has specialized cells at different stages of maturity • Juvenile cells actively secrete matrix – have the suffix blast • Mature cells have the suffix cyte • Destructive cells have the 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 consists of a 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 but arranged differently to form a tough, flexible branching framework. Classification of Connective Tissue • Embryonic – consists of mesenchyme & mucous types – found in embryo from the 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 and supports blood vessels and nerves and stores lipid • includes 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 • surrounds muscles, wraps blood vessels and glands • functions to absorb 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 the cell • organelles are squeezed to the side • serves as insulation • slows heat loss through skin • serves as a shock absorber around organs Reticular Connective Tissue • Reticular –consists of a network of reticular fibers & cells –found in 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 in vocal cords and ligaments which connect vertebrae Supporting Connective TissuesCartilage • • • • • • • • • • strong, flexible and 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 the knees, between pubic bones, around or in joints and tendons – resists compressions, absorbs shocks and 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 called formed elements RBCs WBCs-leukocytes, neutrophils, basophils, eosinophils, and lymphocytes – platelets – suspended in a liquid matrix called plasma which contains protein fibers important in blood clotting • Lymph – enters lymphatic vessels or small passageways that return it to cardiovascular system 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 the 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 (the lamina propia) • sometimes layer of smooth musclemuscularis mucosae • have absorptive, secretory & protective functions • help keep epithelial surfaces moist with a surface covered with mucus made by goblet cells Serous Membranes • line sealed internal parts such as ventral body cavities • composed of simple squamous epithelium resting on athin layer of areolar connective tissue • produce watery serous fluid • pleura lines pleural cavity and covers the lungs • peritoneum lines peritoneal cavity and covers internal organs • pericardium lines pericardial cavity covering the heart • each of these are thin, attached to body wall and to underlying organs • each can be divided into parietal partlines inner surface of cavity • and a visceral part which covers outer surface of organs Synovial Membranes • surround joint cavities • Joints are articulations for bones • allow for movement • surrounded by fibrous capsule consisting of areolar tissue with matrix of interwoven collagen fibers, proteoglycans & glycoproteins • space is 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 • • • • • skeletal muscle cells cannot divide new cells are made by division of satellite cells 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 and intercellular cement Ions move through gap junctions which coordinates contractions cells cannot divide once heart muscle is damagedcannot regenerate do not need nerve activity to contract pacemaker cells establish regular rate of contraction not under voluntary control striated involuntary muscle Smooth Muscle • cells are small, spindle shaped with tapering ends • contain actin & myosin but not arranged in striated fashion • cells are uninucleate • found in digestive & urinary organs, uterus & blood vessel walls • can divide after injury • not under voluntary control • called non-striated involuntary Nervous Tissue • consists of neurons (nerve cells) & neuralgia cells • specialized to detect stimuli, respond quickly & transmit information • each nerve cell has a soma or cell body • one long process-axon that transmits messages • many smaller projectionsdendrites that receive information • Exocrine Gland Structure – Unicellular e.g. Goblet cell
