Transcript cells - Doctor Jade Main

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
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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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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
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Function & Classification of
Epithelia
– each cell rests on basement
Simple
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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 squamouscuboidal & 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
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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
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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 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
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strong, flexible and 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 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
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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
musclemuscularis 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 partlines 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
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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
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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
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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 and
intercellular cement
Ions move through gap junctions which
coordinates contractions
cells cannot divide
once heart muscle is damagedcannot
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