tissue level of organization. 4 basic tissue types epithelial connective muscle nervous
TRANSCRIPT
TISSUE LEVEL OF ORGANIZATION
4 BASIC TISSUE TYPES
• Epithelial
• Connective
• Muscle
• Nervous
Cell Connections
• Tight Junctions
• Adherens
• Desmosomes
• Hemidesmosomes
• Gap Junctions
Tight Junctionsmost apical part of cellfuse 2 adjacent membranes
with fibrous connectionsprevents 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
Desmosomeslocalized patches
holding cells together
allow tissues to resist twisting & stretching
stabilize cell shapesmost abundant in
superficial skin layers
links so strong that dead skin cells are shed in thick sheets-not individually
Hemidesmosomes• made of
proteins
• anchor cells to basement membrane
Gap Junctionsintercellular 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 lumen-
apical 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• Simple
– each cell rests on basement 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 sac-acinar• if secretory cells are found both in
tubular &acinar parts-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 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 suffix-cyte• 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 & cellsFound-spleen, lymph nodes & liver
Dense Connective TissueDense 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 cartilages-perichondrium & bones-periosteum
– forms thick, fibrous capsule around internal organs such as liver, kidney and spleen
Elastic Connective Tissuecontains great many elastin fibers
give tissue flexibility
found-vocal cords & ligaments which connect vertebrae
Supporting Connective Tissues-Cartilage
• 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 Tissues-Bone
• 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 matrix-
plasma 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-axon-transmits messages
• many smaller projections-dendrites-receive information
• Exocrine Gland Structure– Unicellular
e.g. Goblet cell