Download Connective Tissue

Tissues
-four primary tissue types:
1. Epithelial
2. Connective
3. Muscle
4. Neural
-however: all tissues in the body develop from three germ layers
1. ectoderm - epithelial + neural
2. mesoderm - connective + muscle + some epithelial
3. endoderm – organs + some epithelial
Epithelial Tissue
= lining epithelium & glands
•lining epithelium = line body surfaces and cavities
• glandular epithelium = secretion
•multiple functions of epithelial tissue:
1. protection (chemical and physical) – e.g. from
dehydration,
pathogens
2. synthesis – e.g. hormones, vitamins
3. regulation - e.g. body temperature, transport via
permeability
4. excretion - e.g. wastes
5. absorption – e.g. nutrients
6. immune response
7. detection – detection of extracellular signals
Epithelial characteristics
1. Cellularity
2. Polarity
3. Attachment
A. to each other
B. to connective tissue
4. Avascularity
5. Regeneration
Epithelial tissue characteristics
1. Cellularity: epithelial tissues are composed almost entirely of cells held
together by cell junctions
-very little to no extracellular matrix
2. Polarity: epithelial cells possesses an exposed surface that faces the exterior
or into the lumen of an organ - apical face
-also has an attached base which is anchored to other tissues (usually a
connective tissue - basal face
-the organelles are not uniformly
distributed in epithelial cells
Epithelial characteristics
3. Attachment: in many animals, epithelial tissues are attached to underlying tissues
via the basement membrane
-BM is produced by the basal
surface of the cells & connective
tissue - comprised of
collagen type IV and laminin
-the BM is comprised of two layers:
a. closest to epithelial cell = basal lamina
(glycoproteins, laminin and actin)
-acts as a barrier to transport from underlying
tissue into the epithelium
b. furthest from the epithelial
cell = reticular lamina
-collagen IV bundles produced by the
underlying connective tissue cells
-provides a strong connection to the
connective tissue
Epithelial characteristics
characteristics
Epithelial
1. Tight junctions: lipid portions of plasma
membranes are bound together by interlocking
membrane proteins forming a complex just
underneath the apical face
-very tight union - prevents passage of water and
solutes between the two cells
3. Attachment: also form extensive connections between each other
Epithelial characteristics
characteristics
Epithelial
2. Gap junctions: two cells held together
by protein called connexons
-connexons grouped together as
hexamers
-act as channels linking adjacent cells
-materials can freely move between
the two cells when the connexons open
-passage of materials helps to coordinate
the activities of the two cells
e. g beating rhythm of cilia
3. Desmosomes: comprised of
1.a protein plaque that links to the cytoskeleton of
the cell (via keratin)
-made up of a protein called desmoplakin
2.cellular adhesion molecules/CAMs known as
cadherins (desmoglein and desmocollin)
-the CAMs link protein “plaques” from
adjacent cells to one another
-require calcium to work
-several types of desmosomes known: belt, hemi,
button
-hemidesmosome: attaches the cell to the
basement membrane of the tissue
-link to a basement membrane protein = laminin
Epithelial characteristics
4. Avascularity: do not contain blood vessels
-must obtain nutrients via diffusion or absorption
5. Regeneration: damaged cells are replaced through differentiation of
stem cells located deep within the tissue
-rate of renewal depends on rate of cell death
-stem cells = germinative cells
-these cells are found closest to the basement membrane
-migrate towards the surface and differentiate
Classification of Epithelia
• catagorizing epithelial tissue types
A. # of layers
simple = 1 layer
stratified = multiple
**pseudo = 1 layer
B. Cell shape
columnar
cuboidal
squamous
Simple Epithelium
-relatively thin
-cells have the same polarity - nuclei are generally aligned
-very fragile - cannot provide mechanical/physical protection
-line internal compartments
-relatively permeable - absorptive surfaces, secretion, filtration
Stratified Epithelium
-thicker due to multiple layers
-found in areas subject to mechanical and chemical stress
e.g. skin, mouth
-tougher than simple epithelia
-organelles do not align
Pseudostratified Epithelium
-appears to be stratified
-yet the basal surface of every cell contacts basement membrane
-apical surface of some cells possess cilia
-other cells within the epithelium secrete mucus – goblet cells
-found lining absorptive organs
e.g. respiratory epithelium
Squamous Epithelium
-tile-like cells - cells are thin, flat and
irregular in shape
-cells interlock like tiles
-very difficult to see from the side due to
their thinness
-simple squamous - most delicate tissue
in the body
-found in protected regions where
absorption occurs
-many types: mesothelium - lines
ventral body cavity
(i.e. abdomen)
endothelium - lines
heart and vessels
SIMPLE SQUAMOUS
Squamous Epithelium
-stratified squamous – found where
mechanical stresses are severe
e.g. epidermis of the skin
e.g. lining of the oral cavity, anal canal
-cells on exposed surfaces may contain
keratin - an intermediate filament
protein that reduces water loss and
provides strength = keratinized
epithelium
-non-keratinized epithelium is tough
but must be kept moist
STRATIFIED SQUAMOUS - KERATINIZED
STRATIFIED SQUAMOUS - KERATINIZED
Transitional Epithelium
-a stratified squamous epithelium that permits stretching
-located in walls of the bladder, renal pelvis and the ureters
e.g. bladder wall - when empty the epithelium looks as if it has several
layers
-actual number of layers can be seen upon distension
TRANSITIONAL
Cuboidal Epithelium
-cells are cubes
-nucleus is large, round and in the center of the cell
-simple cuboidal: regions of secretion, absorption and excretion
e.g. kidney tubules – absorption of salts and water, excretion of wastes
e.g. pancreas & salivary glands - buffers & enzymes
e.g. thyroid follicles - thyroid hormones
SIMPLE CUBOIDAL
SIMPLE CUBOIDAL
Cuboidal Epithelium
-stratified cuboidal: relatively rare
-ducts of sweat glands and mammary glands
Columnar Epithelium
-height is greater than their width
-nuclei is close to the BM and can be more oval shape
-simple columnar: provides some protection but is mainly for absorption and
secretion
-often possess microvilli at their exposed apical faces
e.g. lining of the small intestines – i.e. absorptive cells
Simple columnar epithelium
microvilli
wandering lymphocytes
-usually involved in secretion and absorption
-located in the gallbladder, larger ducts of exocrine glands, gastric pits of stomach
-basally located nuclei aligned with one another
-frequently the apical face is modified with cellular extensions
e.g. microvilli – intestinal lining = brush border
-short-lived cells – replaced every 4 to 5 days
-frequently found with Goblet cells (intestine and stomach)
Columnar Epithelium
-stratified columnar: relatively rare
-two to multiple layers
-only outer layer contains truly columnar cells
-protection role
Stratified columnar epithelium
Columnar Epithelium
-pseudostratified columnar: only a single layer because the basal
face of every cell contacts the basement membrane
-nuclei are at varying levels - appearance of multiple layers
-exposed apical surface typically bears cilia
e.g. respiratory epithelium
Pseudostratified
-these tissues are generally ciliated
Connective Tissue
• binds structures together
•e.g. dense and elastic connective tissues
• provides support
•e.g. bone, reticular tissue
• fills cavities
•e.g. adipose tissue, loose areolar tissue
• produces blood
•e.g. bone marrow
• protects organs & structures
•bone and cartilage
Connective Tissue
•components: matrix + cells
-matrix: non-cellular support material
-comprised of extracellular protein fibers
e.g. 1. collagen fibers (white) – type I
2. elastic fibers (yellow)
3. reticular fibers – collagen type III
4. fibronectin
-plus a ground substance = water + sugars, proteoglycans and glycoproteins
-cells: secrete the matrix
-most basic kind of connective tissue cell = fibroblast
-some have become very specialized and make a very specialized matrix
e.g. osteoblasts of bone
Connective Tissues
-cell types possible in connective tissue:
A. fibroblasts: immature cell type found in basic connective tissues like areolar
tissue, reticular tissue, dense connective tissues
-secrete the extracellular matrix
-secrete main component of matrix = collagens
-also produce hyaluronan = glycosaminoglycan (sugar) that gives the
ground substance a viscous quality
-also produce the other components of the ground substance
e.g. proteoglycans
B. adipocytes: main cellular component of adipose tissue
-more specialized type of fibroblast – fat storage
-fill with lipid upon maturation
-found in adipose tissue and areolar tissue
C. melanocytes: synthesize and secrete melanin
-dark, brown pigment that absorb light
-found in areolar tissue
Connective Tissues
D. Macrophages (Fixed): engulf damaged and dead cells by phagocytosis
-immune cell
-derived from monocytes
E. free macrophages: wander rapidly through the connective tissue
-called monocytes when circulating in blood
F. mast cells: another immune cell
-synthesize and secrete histamine - inflammation response
-synthesize and secrete heparin - inflammation response
G. lymphocytes - immune cells (T and B cells)
-differentiate into plasma cells (type of B cells) - antibodies
-differentiate into T cell subtypes - assist B cells
Connective tissue Matrix fibers: collagen, reticular and elastic
1. Collagen fibers: long, straight and unbranched fibers made of CN type I
-very concentrated and dense in tendons and ligaments
-long chains of collagen protein subunits forming a triple helix
-these helices are wound together - “rope” or a bundle = fibril
-fibrils are then stacked together = collagen fiber
-triple helix – three subunits = 2 alpha 1 chains + 1 alpha 2 chain
e.g. CNI - 2 chains of CNIa1 and one chain of CNIa2
-there are nineteen types of collagen in the body = 80-90% are CNI, CNII
& CNIII
Connective tissue: fibers
2. Reticular: made of collagen type III
-2 collagen III alpha1 + 1 collagen III alpha2 subunits = reticular fiber
-reticular fibers interact in a different way – crosslinked to form a 3D network
rather than bundles like collagen type I
-thinner than collagen type I fibers - more flexible
-reticular fibers often have carbohydrates associated with them
-abundant in the walls of hollow organs
-form a supportive stroma (3D network) that supports the functional
cells of these organs
3. Elastic: primarily made up of the proteins fibrillin & elastin
-branching and wavy in appearance
Classification
The way I organize Connective
tissues
•
•
•
•
Loose – areolar, fat & reticular
Dense – dense (regular, irregular), elastic
Supportive – bone & cartilage
Fluid – blood
Embryonic: first to appear = mesenchyme
-derived from mesoderm germ layer
-cells are star-shaped
-matrix - fine protein filaments
-Mucus connective tissue - jelly-like, many regions of embryo
Loose connective tissues: types
1. Areolar tissue
-cells:mainly fibroblasts, spaced far apart
-matrix: sparse collagen fibers, elastic fibers, mostly ground substance
-cushions structrures and can be distorted due to loose organization
e.g. subcutaneous tissue found beneath the dermis
2. Adipose tissue = fat
-cells = adipocytes (fat storing fibroblasts) – derived from pre-adipocytes
-stores triglycerides as a single fat droplet
-matrix: collagen IV – surrounds the individual adipocytes
-cushions joints and organs, stores energy, insulates, secretes hormones
-two types: white and brown (heat production)
-found in the subcutaneous layer under the dermis
liposuction: suction assisted lipoplasty
-removal of SQ fat
3. Reticular:
-thin collagen fibers (reticular fibers) in a 3D network
-supports walls of certain organs
e.g. liver, spleen
Dense connective tissues: types
-most of the tissue is densely packed extracellular matrix fibers of
collagen type I
-often called collagenous tissue or fibrous tissue
-type types: 1) dense regular - dense, elastic
e.g. tendons, ligaments
2) dense irregular - interwoven meshwork or fibers
-e.g. dermis of skin, perichondrium of joints
and periosteum of bone
1. Dense Regular :
-cells: few fibroblasts
-matrix: multiple, closely packed collagen I fibers PLUS a fine network
of elastic fibers
-very well organized matrix
e.g. tendons, ligaments
2. Dense Regular & Irregular:
-cells: few fibroblasts
-matrix: collagen I fibers PLUS a fine network of elastic fibers with very
little organization
e.g. dermis of the skin
Dense irregular tissue
2. Elastic:
-yellow, elastic fibers in parallel or branching networks
-walls of larger vessels, airways, hollow organs
Supportive Connective tissues: types
-cartilage & bone
1. Cartilage:
-cells = chondrocytes
-matrix = collagen II fibers embedded in a gel-like
ground-substance
-ground substance - water + proteoglycans
-proteoglycans – core protein (aggrecan) +
sugars
called glycosaminoglycans
e.g. chondroitin sulfate, glucosamine
-functions in support, attachment, protection
-in developing child - model for future bone
development
(endochondral bone)
- is an avascular tissue - produces anti-angiogenic
chemicals
(inhibits growth of blood vessels)
-therefore diffusion is the main mode of transport
Proteoglycan
-3 types: 1) Hyaline - most common
- “glassy” ECM of collagen II and ground substance
- ends of bones, within joints (synovial, articular),
- end of nose, supports respiratory passages
- when at the ends of bones in a synovial joint = synovial or
articular
2. Elastic - flexible cartilage
-elastic fibers embedded within the ECM
- external ears and parts of larynx
3. Fibrocartilage - very tough -> collagen I fibers within the ECM
- shock absorber
e.g. intervertebral discs
meniscus of the knee
Supportive Connective tissues: types
2. Bone = osseous tissue
-most rigid connective tissue
-cells = osteoblasts, osteocytes
-matrix = collagen type I, proteoglycans, other specialized bone proteins
-secreted by osteoblasts – as an unmineralized matrix = osteoid
-mineralized as the OBs mature into osteocytes
-osteocytes are found in lacunae
-matrix is laid in concentric circles = lamellae
-if lamellae surrounds a central canal = Osteon
-two types of bone – when the matrix classified by histology
1. Compact - shaft of long bones, outer layer of short, flat
and irregular bones
-very dense appearing bony matrix
-matrix is made up of units called osteons
2. Spongy - ends of bones, middle layer of short, flat
and irregular bones
-thin bars or “plates” (called trabeculae) of bone
separated by irregular spaces filled with red marrow
-lighter than compact – yet stronger
Fluid Connective tissue: Blood
-cells suspended in a fluid matrix = plasma
-plasma ~ 55% blood volume
-inorganic salts
-organic substances - e.g. sugars, proteins
-cells: 1) RBCs - biconcave, disc-shaped
-contains hemoglobin - 4 globin proteins
+ heme group (iron)
2) WBCs - fight infection
= leukocytes
- many types: a. monocytes/macrophages
b. lymphocytes - T and B cells
c. basophils - histamine
d. neutrophils - 1st at infection
e. eosinophils - allergic response
3) platelets - blood clotting response
Muscular Tissue
•specialized for contraction
•very distinct organelles within the cells
•3 types
•1. skeletal – voluntary muscle
•2. cardiac – involuntary muscle
•3. smooth – involuntary muscle
3 types of Muscle tissue:
1) striated/skeletal – voluntary nervous control
-repeating banding patterns of actin & myosin = striated
appearance
-mature muscle cells = muscle fibers
- very long, multi-nucleated cells – made from fusion of
myoblasts
-muscle cells/fibers cannot divide – but new cells form from
differentiation of myogenic stem cells = satellite cells
-attached to bones via tendons
2) cardiac - involuntary control
- only found in heart
-cells are striated but uni-nuclear =
cardiomyocytes
-incapable of dividing – PLUS there are
no satellite cells
-therefore damaged heart muscle
cannot be regenerated
-cardiomyocytes are connected end to end by
intercalated discs
-these discs are areas of communication between
cardiocytes through gap junctions
-the discs also help channel the forces of contraction
3) smooth – involuntary control
-lines blood vessels, airways and organs
-control their own rate of contraction
through action of pacemaker cells
-nervous system can also control
contraction
-slow, sustained contraction
-non-striated, spindle shaped cells single nucleus
-capable of division and can regenerate
damaged tissue after injury through
simple division ???
SMOOTH
DENSE
-you could confuse dense irregular connective tissue and smooth muscle – so
be careful!!
-there are more cells/nuclei in smooth muscle
Neural Tissue (Nervous Tissue)
•specialized for the conduction of electrical impulses from one body
region to another
•two types of neural cells:
1) neurons
2) glial cells
1) glial cells: e.g. astrocytes, oligodendrocytes, microglia, Schwann cells
-supportive function to neurons
-differ depending whether they are found in the CNS or PNS
2) neuron:
- cell body (soma), dendrites, axon with axon terminals and synaptic end
bulbs
-therefore the neuron has polarity
-capable of generating an electrical signal = action potential
-dendrite receives and/or generates the action potentail
-axon - conducts the nerve impulse
-forms a synapse with another neuron or a muscle cell