Biology | Animals » Animal tissues

Source: http://www.doksinet Animal  Tissues   There  are  four  types  of  tissues  found  in  animals:    epithelial  tissue,  connective  tissue,  muscle  tissue,  and   nervous  tissue.    In  this  lab  you  will  learn  the  major  characteristics  of  each  tissue  and  examine  various   types  of  each  tissue  under  the  microscope.         I.    Epithelial  Tissue     Epithelial  tissues  line  body  surfaces  and  cavities,  as  well  as  form  glands.    The  cells  of  the  tissue  are   closely  connected  to  each  other  via  cellular  junctions  and  because  epithelium  is  found  on  the  edges  of   organs,  it  has  two  distinct  surfaces.    The  apical  surface  is

 exposed  to  the  body  cavity  or  exterior,  while   the  basal  surface  is  adjacent  to  the  underlying  tissue  (see  the  figure  below).      Epithelia  contain  no  blood   vessels  (they  are  non-­‐vascular)  and  are  dependent  upon  the  underlying  connective  tissue  for  nutrients.             Epithelial  cells  can  be  one  of  three  shapes:    squamous  (flattened),  cuboidal,  or  columnar.    If  the   epithelium  consists  of  one  cell  layer  it  is  called  simple  epithelium.    Stratified  epithelium  has  more  than   one  layer.    The  combination  of  cell  shape  and  the  number  of  cell  layers  is  used  to  classify  epithelial   tissue.  (ie

 simple  columnar  epithelium  would  consist  of  a  single  layer  of  column  shaped  cells)    Cell   shape  in  stratified  epithelium  can  vary,  but  the  shape  of  the  cells  at  the  apical  surface  determines  the   name.     The  function  of  epithelial  tissue  varies  depending  on  its  location.    As  you  explore  the  types  of  epithelial   tissues  below,  think  about  how  the  structure  of  each  tissue  fits  its  function.       *Hint:    Many  of  the  slides  you  will  examine  contain  other  types  of  tissue  in  additional  to  epithelium.     Keep  in  mind  that  epithelial  tissues  line  either  the  outer  or  inner  surfaces  of  organs

 and  will  thus  be   found  on  the  edge  of  the  tissue.     Source: http://www.doksinet Simple  squamous  epithelium     Blood  vessels  (artery,  vein,  and  nerve  slide):    Simple  squamous  epithelium  comprises  the  inner  lining  of   blood  vessels,  where  it  provides  a  smooth  surface  that  reduces  friction  as  blood  travels  through  the   vessels.    The  blood  vessel  slide  shows  a  cross  section  of  an  artery  and  a  vein    The  wavy  lining  of  the   vessel  lumen  (interior)  is  simple  squamous  epithelium.               Lung  slide:    The  walls  of  lung  air  sacs  (alveoli)  are  also  composed  of  simple  squamous  epithelium.  

 Air   sacs  are  the  location  of  gas  exchange  between  the  air  and  blood.    How  does  the  structure  of  this   epithelial  type  allow  for  efficient  gas  exchange?  (hint:  the  gases  have  to  travel  through  the  epithelial   cells  to  move  between  the  air  and  the  blood)           Simple  cuboidal  epithelium   Simple  cuboidal  epithelium  (Kidney)  slide:  The  tubules  of  the  kidney  are  composed  of  a  single  layer  of   cuboidal  cells.    The  kidney  slide  shows  cross  sections  of  many  tubules,  all  of  which  are  lined  with  simple   cuboidal  epithelium.    These  cells  are  active

 in  absorption  and  secretion  of  various  substances  from  or   into  the  kidney  filtrate  (which  ultimately  becomes  urine).    Note  the  shape  of  the  epithelial  cells  and  the   centrally  located  nuclei.   Source: http://www.doksinet       Simple  columnar  epithelium   Duodenum/Small  intestine  slide:    The  intestinal  lining  is  a  simple  columnar  epithelium.    The  primary   function  of  these  cells  is  absorption  of  nutrients.    As  you  examine  the  slide,  note  the  large,  oval  shaped   nuclei  that  are  positioned  near  the  basal  edge  of  the  cells.    Also  note  the  large,  clear  goblet  cells  that  are   interspersed  in  the  epithelial

 layer.    These  are  glandular  cells  that  secrete  mucus  that  helps  protect  the   underlying  tissues.         Stratified  squamous  epithelium   Esophagus/stomach  slide:    Stratified  squamous  epithelium  consists  of  multiple  layers,  with  squamous   cells  at  the  apical  surface.      The  primary  function  of  this  type  of  epithelium  is  protection  Areas  subject   to  abrasion,  like  the  mouth,  esophagus,  and  skin,  have  stratified  epithelium.    Cells  at  the  apical  surface   can  be  scraped  away  (for  instance,  by  food  particles  traveling  down  the  esophagus),  but  the  layered   nature  of  the  epithelium  ensures  that  the  underlying  tissues  are

 protected.    Note  the  thick  layer  of   epithelium  on  the  esophagus  slide.    (*This  slide  also  contains  stomach  tissue,  which  has  a  simple   columnar  epithelium)   Source: http://www.doksinet       Keratinized  stratified  squamous  epithelium   Palmar  Skin  (Human  skin  corpuscle)  slide:    The  epidermis  (most  superficial  layer)  of  the  skin  is  composed   of  stratified  squamous  epithelial  cells  that  contain  large  quantities  of  the  protein  keratin.    Keratin  is  a   tough  fibrous  protein  that  offers  protection  from  abrasion  and  water  loss.    New  cells  are  produced  at   the  basal  surface  of  the  epithelium  and  are  gradually  pushed

 towards  the  apical  surface.    As  they  move   upwards,  they  become  filled  with  keratin  and  eventually  die,  forming  a  layer  of  dead,  keratin  filled  cells   on  the  apical  surface  of  the  epidermis.      Examine  the  palmer  skin  slide,  noting  the  entire  epidermis  and   the  layer  of  dead  cells  at  the  apical  surface.    The  dermis,  which  lies  deep  to  the  epidermis,  is  composed   of  connective  tissue.                 Compare  the  skin  and  esophagus  slide.    How  are  they  similar?    How  are  they  different?     II.    Connective  Tissue     Connective  tissues  vary  widely  in  their  form  and  function,  but

 they  are  all  characterized  by  the  presence   of  extracellular  matrix.      The  extracellular  matrix  is  nonliving  material  composed  of  protein  fibers  and   ground  substance.    The  protein  fibers  are  composed  of  collagen  (which  gives  strength)  or  elastin  (which   Source: http://www.doksinet gives  flexibility).    The  number  and  type  of  fibers  differs  between  the  various  types  of  connective  tissue   The  ground  substance  fills  the  spaces  between  the  cells  and  the  fibers.    It  contains  interstitial  fluid   (tissue  fluid)  and  large  polysaccharide  molecules.      The  consistency  of  the  ground  substance  can  vary   from  liquid  to

 gel-­‐like  to  a  solid.         *Hint:    Because  connective  tissue  consists  largely  of  extracellular  matrix,  the  cells  that  are  present  will   be  scattered  among  the  matrix  components.    For  most  of  these  slides  (adipose  tissue  is  an  exception),   you  will  not  see  cells  directly  adjacent  to  other  cells  as  they  are  in  epithelial  tissue.     Dense  connective  tissue   Palmar  Skin  (Human  skin  corpuscle)  slide:  The  layer  of  skin  that  lies  deep  to  the  epidermis  is  called  the   dermis  and  is  composed  of  dense  connective  tissue.    This  tissue  contains  densely  packed  bundles  of   irregularly  arranged  collagen  fibers.

   It  is  found  in  areas  of  the  body  that  are  subject  to  tension  from   many  different  directions.    Note  the  thick  layer  of  dense  connective  tissue  that  lies  deep  to  the   epithelium  on  the  skin  slide.    Nuclei  of  the  connective  tissue  cells  are  scattered  throughout  the  collagen   fibers.     Adipose  tissue  slide:    Adipose  tissue  consists  of  adipocytes,  or  fat  storage  cells.    It  functions  in  energy   storage,  insulation,  and  cushioning.    Small  pockets  of  adipose  tissue  can  be  found  all  over  the  body,  but   accumulates  under  the  skin  (subcutaneous  fat)  and  around  certain  organs,  such  as  the  kidneys.

   Unlike   other  connective  tissues,  it  has  very  little  matrix  and  the  cells  are  closely  packed  together.    Each  cell   contains  a  large  fat  droplet,  which  pushes  the  nucleus  to  the  side.    Note  the  clear  cytoplasm  and  the   peripherally  located  nuclei  of  the  fat  cells  in  the  slide.   Source: http://www.doksinet Hyaline  cartilage  slide:    Hyaline  cartilage  is  the  most  abundant  type  of  cartilage  in  the  body  and  is  found   in  the  rib  cage,  the  nose,  the  trachea,  and  the  ends  of  long  bones.    It  provides  structural  support  (but  is   more  flexible  than  bone)  and  has  cushioning  properties.      Hyaline

 cartilage  has  a  firm  matrix  with   abundant  collagen  fibers,  but  the  individual  fibers  cannot  be  seen  under  the  microscope.    When  viewed   under  the  microscope  the  matrix  an  amorphous  quality  (no  discernable  structures).    The  cells,  which  are   known  as  chondrocytes,  reside  in  small  cavities  within  the  matrix  called  lacunae.       Bone  tissue  slide:    Bone  tissue  forms  the  skeletal  system.    It  functions  in  structural  support,  protection,   and  mineral  (calcium)  storage.      The  extracellular  matrix  of  bone  tissue  contains  abundant  collagen   fibers  as  well  as  a  hard,  calcified  ground  substance.    Mature  bone  cells,

 called  osteocytes,  reside  in   cavities  within  the  matrix  called  lacunae.      As  bone  tissue  is  formed,  channels  remain  in  the  hardened   matrix  that  provide  passageways  for  blood  vessels  and  nerves.    The  larger  channels  are  called  central   canals  (Haversian  canals).    Bone  tissue  forms  in  rings  (lamellae)  around  these  canals,  creating  a  structure   called  an  osteon.    Examine  the  bone  tissue  slide,  noting  the  osteons  with  their  lamellae  and  bulls-­‐eye   like  central  canals.    The  lacunae,  which  contain  the  bone  cells,  are  visible  as  small  dark  patches  in  the   lamellae.         Source: http://www.doksinet III.  

 Muscle  Tissue     Muscle  tissue  is  specialized  for  contraction.    The  cells  are  elongated,  and  are  also  known  as  muscle   fibers.      They  contain  the  contractile  proteins  actin  and  myosin,  which  interact  to  shorten  and  elongate   the  cells.      There  are  three  different  types  of  muscle  tissue:    skeletal,  cardiac,  and  smooth    Examine   each  type  of  tissue  using  the  muscle  composite  slide.  (*The  skeletal  and  smooth  muscle  are  shown  as   part  of  organs,  so  they  are  not  the  only  tissue  present)     Skeletal  muscle  (muscle  composite  slide)   Skeletal  muscles  are  attached  to  bones,  and  contraction  of  these

 muscles  generates  body  movements   (limb  movement,  jaw  movement,  breathing,  etc.)    The  skeletal  muscle  fibers  are  long  and  cylindrical,   with  multiple  peripherally  located  nuclei.    The  cells  have  striations,  alternating  light  and  dark  bands  that   result  from  the  ordered  arrangement  of  actin  and  myosin  within  the  cell.           Cardiac  muscle  (muscle  composite  slide)   Cardiac  muscle  is  present  in  the  heart.    Cells  are  striated,  but  the  striations  are  much  less  obvious  than  in   skeletal  muscle  tissue.    The  cells  are  shorter  than  skeletal  muscle  fibers,  have  a  single  nucleus  and  are   often  branched.  

 Individual  cells  are  connected  via  gap  junctions  and  desmosomes    These  cellular   connections  are  visible  under  the  microscope  as  dark  bands  called  intercalated  disks.    These  cellular   communication  junctions  are  necessary  for  the  coordinated  beating  of  the  heart.       Source: http://www.doksinet Smooth  muscle  (muscle  composite  slide  &  artery/vein/nerve  slide)   Smooth  muscle  tissue  is  found  in  the  walls  of  hollow  organs,  such  as  the  gastrointestinal  tract,  blood   vessels,  and  the  urinary  bladder.    Contractions  of  these  muscles  propel  fluid  or  materials  through  the   organs  (i.e  food  through  the  GI  tract,  blood  through

 blood  vessels,  urine  pushed  out  of  bladder)         Smooth  muscle  cells  are  not  striated  (hence  the  name  “smooth”  muscle);  they  have  a  single  nucleus,   and  have  tapered  ends.    Examine  the  smooth  muscle  on  the  muscle  composite  slide  as  well  as  the  blood   vessel  slide.    In  blood  vessels  there  is  a  layer  of  smooth  muscle  deep  to  the  epithelial  layer    It  is  thicker   on  the  artery  than  on  the  vein,  but  can  be  seen  in  both.       IV.    Nervous  Tissue     Nervous  tissue  is  specialized  for  communication  and  composes  the  brain,  spinal  cord,  and  peripheral   nerves.    The  tissue

 consists  of  two  major  cell  types:    neurons  and  glial  cells    Neurons  communicate  with   each  other  via  electrical  and  chemical  signals.    They  have  nucleated  cell  bodies  and  two  types  of   elongated  cellular  processes:    dendrites  –  which  receive  signals,  and  axons  –  which  send  signals.         Glial  cells  are  the  support  cells  of  nervous  tissue.    There  are  several  different  types  with  various   functions,  including  maintaining  proper  ion  concentrations  in  the  fluid  surrounding  neurons,  generating   myelin  (an  insulating  material  that  surrounds  some  axons),  and  cleaning  up  debris.         Examine  the  slide  of

 nervous  tissue  (giant  multipolar  neuron  slide).    Note  the  large  neurons  with  their   elongated  cellular  processes  and  the  smaller,  more  numerous  glial  cells.