Tissue Types Module

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Tissue Types Module

• ISOC

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Real mammalian cells (brain) - many sizes and
shapes
Image Wheater
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Basic methods of microscopy

• Method Used for seeing
• Light microscopy Tissues, cells,
• (LM) larger organelles
• Transmission electron Organelles,
• microscopy membranes,
• (EM or TEM) large molecules
• Scanning electron Tissues, cells,
• microscopy (SEM) organelles

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scale

• Light microscopy
• Most things measured in micrometres
• Micrometers (µm) - one millionth of a metre.
• Electron microscopy
• Most things measured in nanometres
• Nanometers (nm) - one thousand-millionth (10-9)
  of a metre. Note nano- 9

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scale

• Light microscopy
• -Cells 25 µm (range 6-100)
• -Nuclei 10 µm (5-20)
• -Red blood cell 8 µm
• Electron microscopy
• -Mitochondria 300 nm wide (200- 400) x
  3 µm (2-6)
• -Ribosomes 15 nm
• -Unit membrane (bilayer) 10 nm across

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Basic methods of microscopy

• Method Limit of resolution visualize
• Light microscopy 0.5 mm Tissues, cells,
• (LM) (best) larger organelles
• Transmission electron 0.1 nm Organelles,
• microscopy membranes,
• (EM or TEM)
• large molecules
• Scanning electron 10 nm Tissues, cells,
• microscopy (SEM) organelles
• 1 mm 1000 mm. 1mm 1000 nm

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The commonest stain Haematoxylin Eosin, H E

• Haematoxylin
• - a purple-blue basic dye.
• -stains acidic macromolecules DNA (hence
  nuclei), RNA, hence cytoplasm of cells with
  very many ribosomes (e.g. in glands) some
  proteins.
• Eosin
• - a pink acidic dye.
• - stains basic macromolecules muscle cell
  proteins, collagen (a major extracellular
  protein), cytoplasm of most cells.

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Example of section stained with H E
Small blood vessel
Cell nuclei are purple. E very flat nuclei in
blood vessel wall.
Image Wheater
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Cytoplasm (pink)
Nuclei (purple)
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Example where haematoxylin stains cytoplasm
Secretory cells of pancreas. These are in groups
like hollow balls (acini). Cytoplasm at outside
of acini (cell base) is purple. Why?...
Image Wheater
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Diagram of a secretory cell
Haematoxylin can stain cytoplasm because of
Rough endoplasmic reticulum at base of cell -
organelle with much RNA
Image Bloom Fawcett
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Immunostaining -Very specific.
Uses antibodies to pick out specific molecules.
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What is extracellular matrix?

• The part of a tissue that is outside the cells.
• Usually a gel-like ground substance strengthened
  by fibrous proteins

cell
Fibrous protein
Ground substance
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The 5 basic tissue types

• Tissue Nature Usual colour with H E
• Epithelium Sheets of cells. Purple. Cellular -
  many nuclei.(Barriers.)
• Connective Supports and Pale pink to white.
• tissue links other tissues Mostly extracellular
  matrix, usually.
• Blood Blood cells, plasma Red to pink
• Muscle Contractile tissues Bright pink
• Neural tissue Nerves Pale pink. Mostly
  cytoplasm, high lipid content (white).Central
  nervous Purplish. Many nuclei, ribosomes.system

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Epithelia

• epithelium cohesive sheet of cells.
• - It rests on a basement membrane, a thin, dense,
  mesh-like layer of extracellular matrix. This
  separates it from all other tissues, including
  its blood supply.
• - Epithelial cells are cohesive because joined
  to neighbours by continuous bands of
  junctional complexes.
• (See Ultrastructure session.)

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Epithelium (flat or squamous type) on basement
membrane
BM basement membrane
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Epithelial cells
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Classification of epithelia by cell shape

• Note that these classes merge into each other
• Squamous flat cells. Can be so flat that
  cytoplasm is invisible in sections.
• Cuboidal cell height is similar to width.
• Columnar cell height at least 2 x width.

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Classification of epithelia by layers

• Simple 1 layer of cells, all touching basement
  membrane.
• Stratified 2 or more layers of cells.
• Pseudostratified A kind of simple epithelium
  that looks stratified (pseudo-, false) because
  nuclei are at different levels however all cells
  touch basement membrane. (Found in the
  respiratory system.)
• Transitional A special kind of stratified
  epithelium found only in the excretory system
  not considered further this term.

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Simple squamous epithelium
BM basement membrane
Images Wheater
Face-on view.N nucleus.
E squamous epithelium
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Function of epithelia All epithelia form some
kind of barrier or containment. Simple
squamous epithelium is found where exchange
across the epithelium is important, e.g. -
lining of blood vessels, - lining of the
air-sacs of the lung.
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Simple cuboidal columnar epithelia
CuboidalRoundish nuclei
ColumnarSausage-shaped nuclei
Images Wheater
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FunctionsSimple cuboidal epithelia form
glands, the liver and much of the kidney. These
cells often secrete or transport fluids or
solutes.Simple columnar epithelia - like
cuboidal, but where wear and tear occurs -
reserve cells needed. E.g. intestines.
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Stratified (squamous) and pseudostratified
epithelium
Images Wheater
Stratified squamous (skin) - flat cells only in
upper layers
Pseudostratified - all cells touch base, but
nuclei at different levels
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FunctionsStratified squamous epithelium
Protection against friction, barrier to diffusion
or water loss - e.g. skin, oesophagus.Pseudostr
atified epithelium like an extreme form of
columnar epithelium - more reserve cells. E.g.
trachea.
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IMPORTANT POINTS

• Epithelia never contain blood vessels
• Epithelia are the tissues from which the most
  common cancers (carcinomas) develop

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Definition

• Connective tissues (CT) Function
• support tissue
• (not only mechanical)
• surround tissues
• Give the body form.
• Eg. Bone

Image Moore
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Image Moore

• Blood vessels and nerves reach tissues or organs
  that they supply via the CT.

muscle
Transverse section of arm
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Ridiculously oversimplified diagram of early
embryo
mesoderm
Most connective tissues in mammals develop from
the middle layer of the early embryo -mesoderm.
ectoderm endoderm
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What is extracellular matrix reminder?

• As the name suggests, its the part of a tissue
  that is outside the cells. (Latin, extra,
  outside).
• Usually a gel-like ground substance strengthened
  by fibrous proteins

cell
Fibrous protein
Ground substance
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• Unlike other tissue types, connective tissues
  typically contain a high ratio of extracellular
  matrix (ECM) to cells.
• ECM is secreted by cells, which are embedded in
  it.
• ECM varies for different tissues depending on
  their function. Examples of these different ECMs
  are-
• the hard part of bone, the tough part of
  fascia, the resilient part of cartilage.

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General components of ECMs

• Fibrous proteins, and
• Ground substance

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General components of ECMs

• Fibrous proteins, and
• Ground substance - a gel containing
• water, salts etc (tissue fluid) and
• 3 kinds of molecules containing carbohydrate
• a glycosaminoglycan or GAG,
• proteoglycans and
• glycoproteins

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So what are those?
1. GAGs (glycosaminoglycans) long unbranched
polysaccharide chains with disaccharide repeat
(XYXYXYXYXY. etc ) Only one GAG is found
unlinked to protein HYALURONAN. (Very large
molecule, abundant in many connective tissues.)
Image Alberts et al.
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• 2. Proteoglycans GAGs covalently linked to a
  protein core.

Image Alberts et al.
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• Proteoglycans can form enormous complexes.

Aggrecan aggregate
1µm
Actual (elec. microscopy) Images Alberts et al.
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• GAGs (and proteoglycans) attract positive ions
  (e.g. Na) as they are anionic (many negative
  charges).
• GAGs attract water by osmosis ? giving
  resilience (resistance to pressure) - e.g. in
  cartilage (much aggrecan).

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• 3. Glycoproteins
• They are proteins with polysaccharide chains
  attached, but no GAG chain.
• Lower carbohydrate content than proteoglycans.
• Various functions including providing fibrous
  webs for cell attachment and migration.

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Components of ECM

• Ground substance and
• Fibrous proteins

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Fibrous proteins

• These are proteins that aggregate together to
  form very long fibres, visible by light
  microscopy.
• There are just two kinds in ECM
• collagen fibres - providetensile strength
  (strength when pulled),
• and elastic fibres - provide elasticity.

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Collagen

• The most abundant extracellular protein
• 25 of all protein mass in mammals.
• Nearly pure in tendon.

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Type I collagen, the commonest type, forms
banded fibrils as seen by electron
microscopy.(L, longitudinal section T,
transverse.)
Fibril
Image Wheater
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Banded collagen fibrils aggregate into collagen
fibres it is these that can be seen with the
light microscope (NB this is still EM).
Fibre
Cell
Fibrils
Image Wheater
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This connective tissue has quite a lot of
collagen fibres.Collagen stains pink with HE.
The nuclei here (purple) are those of
fibroblasts, the basic cell type of connective
tissue, which make the collagen. The fibroblast
cytoplasm is pink and generally cannot be
distinguished from the collagen fibres.
Collagen fibres
Fibroblast nucleus
Ground substance
Image Wheater
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Elastin
Elastic fibre

• Form a random coil when relaxed
• straighten when pulled.
• covalently crosslinked together to make elastic
  fibres or sheets.

Single elastin molecule
Cross-link
Image Alberts et al.
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EVG stain (Elastic-Van Gieson) to show elastic
fibres

• This connective tissue in skin contains
• much collagen (red with EVG) and
• some elastic fibres (black/dark with EVG)

Elastic fibre
Image Wheater
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With HE, elastic fibres just stain pink like
collagen and cannot be distinguished. However,
sheets of elastin (as in the wall of this artery)
can be seen in transverse section as continuous
pink lines (E).
cell nucleus
Image Wheater
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Classes of CT

• Rigid (or skeletal)
• Soft (flexible supporting tissues)

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Rigid connective tissues

• Bone and cartilage are closely related
• most bone is formed from a cartilage model
  which develops first in the embryo.
• The bones of children still have some cartilage
  areas, as in the X-ray image.

Cartilage - transparent to X-rays
Image Moore
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• In both, it is the ECM that is hard or rigid.
• The strength of cartilage is provided by high
  concentrations of normal ECM components,
  especially collagens and proteoglycans.
• Bone ECM contains these too, plus the mineral
  hydroxyapatite (a calcium phosphate hydroxide).

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Both cartilage and bone contain cells that
secrete and maintain the ECM. These are
calledChondrocytes in cartilage,Osteocytes
in bone.
What makes this matrix?
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Cartilage, containing chondrocytes (HE)
Chondrocytes- Roundish or semicircular - often in
2s or 4s.
Matrix
Image Ross
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Bone, containing osteocytes (HE)
Osteocytes - generally single, oval, shrunken
(during preparation)
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Types of soft connective tissues

• Loose CT or areolar tissue
• A cushioning or filling tissue resilience with
  some strength.
• Dense CT - almost entirely made of collagen
  fibres
• Dense regular CT collagen fibres parallel
  (mainly tendons, ligaments). Very strong in one
  direction.
• Dense irregular CT fibres run in all directions
  (e.g. in skin, muscle sheaths). Strong in all
  directions.
• There are also intermediate forms.

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Loose connective tissue (stars)

bv


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Dense irregular connective tissue(in skin)
collagen fibres
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Dense regular connective tissue(tendon)
Tensile strength in one direction
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Cell types of soft CTs, functions

• Dense CT Fibroblasts only.

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Cell types of soft CTs, functions

• Loose CT
• (a) Resident cells (stationary)
• Fibroblasts secrete maintain the ECM.
• Adipocytes fat cells. Energy store, cushioning,
  electrical insulation (nerves).
• Macrophages phagocytic. Remove defunct cells
  matrix, foreign material organisms. Role in
  immune response.
• Mast cells role in inflammation (also in
  allergy). Derived from blood basophils.
• Plasma cells antibody production.
• Lymphocytes immune response.

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Cell types of soft CTs, functions

• (b) Transient cells (come go)
• Neutrophils defensive.
• Eosinophils defensive.

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Lymphocytes (arrow)
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Fat cells
N nucleus of fat cell, C blood
capillaries
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Mast cells (arrowheads) near blood vessel