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
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
Adherens
• dense layers of
proteins on inside
of membrane
• attach membrane
proteins to
microfilaments of
cell’s cytoskeleton
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 sheetsnot individually
Hemidesmosomes
• made of
proteins
• anchor cells
to basement
membrane
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
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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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 lumenapical 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
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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
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 squamouscuboidal & 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 sacacinar
• if secretory cells are found both
in tubular &acinar partstubuloacinar
• 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 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 suffixcyte
• 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 &
cells
Found-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-vocal cords &
ligaments which
connect vertebrae
Supporting Connective TissuesCartilage
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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
– resists compressions, absorbs shocks
– 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
formed elements
RBCs
WBCs
platelets
suspended in liquid matrixplasma 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
musclemuscularis 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 partlines 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
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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
• 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 &
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-axontransmits messages
• many smaller projectionsdendrites-receive
information
• Exocrine Gland Structure
– Unicellular
e.g. Goblet cell