TISSUE LEVEL OF ORGANIZATION

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TISSUE LEVEL OF ORGANIZATION
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4 BASIC TISSUE TYPES

• Epithelial
• Connective
• Muscle
• Nervous

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Cell Connections

• Tight Junctions
• Adherens
• Desmosomes
• Hemidesmosomes
• Gap Junctions

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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

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Adherens

• dense layers of proteins on inside of membrane
• attach membrane proteins to microfilaments of
  cells cytoskeleton

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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 sheets-not individually

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Hemidesmosomes

• made of proteins
• anchor cells to basement membrane

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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

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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

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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

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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

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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

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Classification of Epithelia

• cell shape
• arrangement of cell layers

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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

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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

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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 squamous?cuboidal back again
• all organs to change shape

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TYPES OF EPITHELIA
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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

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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

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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

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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

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Stratified Cuboidal

• typically only 2 cell layers of cuboidal cells
• not a great quantity found in
• human body
• large ducts of sweat mammary glands

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Stratified Columnar

• rare
• found where 2 other types of epithelia meet
• large ducts
• in pharynx, epiglottis, anus urethra

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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

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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

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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

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Exocrine Gland Classification

• Unicellular
• Multicellular
• Simple
• have single, unbranched duct
• Compound
• have branched duct

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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

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• Exocrine Gland Structure
• Unicellular
• Multicellular
• Secretory sheets
• Tubular
• Alveolar (Acinar)
• Tubuloalveolar

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Merocrine Glands

• most common
• sweat mucus secreting
• release products via exocytosis

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Apocrine Glands

• product accumulates in apical tip
• pinched off to secrete
• rest of gland repairs itself

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Reticular Connective Tissue

• consists of network of reticular fibers cells
• Found-spleen, lymph nodes liver

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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 cartilages-perichondrium
  bones-periosteum
• forms thick, fibrous capsule around internal
  organs such as liver, kidney and spleen

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Elastic Connective Tissue

• contains great many elastin fibers
• give tissue flexibility
• found-vocal cords ligaments which connect
  vertebrae

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Supporting Connective Tissues-Cartilage

• strong, flexible
• found throughout the body
• Matrix? firm gel containing chondroitin sulfate
  which forms complexes with proteins?proteoglycans
• 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

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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

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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

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Membranes

• physical barriers composed of epithelia
  supported by connective tissue
• cover protect other tissues
• 4 types
• Mucous
• Serous
• Cutaneous
• Synovial

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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

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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 muscle?muscularis
  mucosae
• absorptive, secretory protective functions
• help keep epithelial surfaces moist with mucus
  made by goblet cells

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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 part?lines
  inner surface of cavity
• and visceral part-covers outer surface of organs

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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

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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

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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 them?intercalated 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

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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

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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

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• Exocrine Gland Structure
• Unicellular

e.g. Goblet cell