Lecture 10 - Connective (support) tissue and extracellular matrix Flashcards
Connective tissue (support) functions
Tissues that provide…
General structure
Physical and metabolic support for more specialised tissues
Mechanical strength
Fills spaces in the body and provides cushioning
Three general properties of connective tissue
Tensile strength
Collagen - most abundant protein in the body and provides a key role in giving strength
Elasticity
Elastin - protein that is also made up of fibres, more elastic than collagen
Volume
Ground substance - mixture of various different molecules that come together to form a ground substance, made up of lots of different molecules that allow it to bind water and create volume
Collagen
Tensile strength
Collagen - most abundant protein in the body and provides a key role in giving strength
Elastin
Elasticity
Elastin - protein that is also made up of fibres, more elastic than collagen
Ground substance
Volume
Ground substance - mixture of various different molecules that come together to form a ground substance, made up of lots of different molecules that allow it to bind water and create volume
Classifying connective tissue
Connective tissue proper
Cartilage
Bone
Blood
Connective tissue proper - loose
Open, loose structure
Lots of ground substances that allows it to have space
areolar
reticular
Adipose
Connective tissue proper - areolar (loose)
Strong yet cushioning
Underlies epithelium, forms lamina propria (lamina propria is below the basement membrane and is made up of areolar tissue)
Connective tissue proper- reticular (loose)
Reticular fibres (supportive mesh) Supportive organs More delicate reticular fibre network and provides a supportive mesh within some of our organs
Connective tissue proper - adipose (loose)
Adipose (sometimes classified separately)
Adipocytes
Made up of adipocytes and in contrast to other loose connective tissue types within a section of adipose tissue the majority of what we see is adipocytes, the actual adipose support cells because they get really filled up with adipose droplets within them
Important tissue in energy storage and utilisation
White = stores energy
Brown = thermoregulation
Brown because it is very mitochondrically rich so it has a high thermoregulatory capacity which is used to burn energy, babies have high brown adipose tissue and over the first few years it is converted to white adipose tissue
White adipose
stores energy
Brown adipose
thermoregulation
Brown because it is very mitochondrically rich so it has a high thermoregulatory capacity which is used to burn energy, babies have high brown adipose tissue and over the first few years it is converted to white adipose tissue
Connective tissue - dense
Greater proportion of fibres
Dense connective tissue proper
regular
irregular
Connective tissue - regular (dense)
Parallel fibres (mainly type I collagen) Find collagen fibres in parallel which provides strength in one particular direction so find it in things like ligaments and tendons E.g. ligaments, tenldons
Connective tissue - irregular (dense)
Non-parallel fibres - provides strength in lots of different directions
e.g. in dermis
Dermis of the skin and connective tissue times
Papillary dermis is loose
Reticular dermis is dense - can see lots of collagen (stained pink with H&E) and that they are not lying parallel so not much white space and instead lots of pink staining
Cartilage types
Hyaline
Fibrocartilage
Elastic cartilage
Hyaline cartilage
Makes up the end of bones and the rings of our trachea
Smooth, translucent
Few collagen fibres
ECM made up of collagen and ground substance and have chondrocytes which are the support cell of cartilage
Semirigid due to its structure
Fibrocartilage
Relatively more collagen fibres than hyaline cartilage
Many collagen fibres
e.g. cartilaginous joints, menisci of knee joint
Same support cells of chondrocytes
Kind of a cross between dense connective tissue and cartilage
Elastic cartilage
Elastin and collagen fibres
Elastin provides elasticity
e.g. ear
Bone
Collagen containing extracellular matrix but ECM becomes calcified - osteoblasts secrete minerals that allow the ECM to become calcified and therefore become very hard and within the calcification of the extracellular matrix, we have osteoclasts which are mature support cells from osteoblasts where they basically become inactive and frozen within this matrix
Compact bone and cancellous bone
Compact bone
Compact bond - typically around the outside of bone, provides a lot of strength
Cancellous bone
Cancellous bond, forming the trabecular (criss cross structure)
Layout depends on the stress/weight bearing nature of the bone for the trabecular
Support cells
Derived from embryological tissue mesenchyme - all support cells of connective tissue are ultimately linked to the embryonic mesenchyme tissue origin but there we can think of them as diverging and producing different types fo support cells which go on to make our different connective tissues
Produce ECM components
Note = fibroblasts are very versatile cell types and can actually fo on to make osteoblasts and chondroblasts and adipocytes
Matrix key features
Mature connective tissue has predominant ECM with sparse cellular component
Matrix characteristics crucial to functions performed by tissue
Connective tissue proper matrix components - quite a high percentage of cushioning ground substance particularly in our connective tissue, can find both collagen and elastin
Ground substance is found in the spaces between fibres
Connective tissue proper = jelly-like matrix
Different tissue = different matrix
Different tissue =
different matrix
Connective tissue proper matrix components
quite a high percentage of cushioning ground substance particularly in our connective tissue, can find both collagen and elastin
Ground substance is found
in the spaces between fibres
Connective tissue ECM
Support cells secrete ECM (excrete proteins and molecules that make up the ECM)
Mature tissue has predominant ECM with sparse cellular component
Characteristics of ECM crucial to function of tissue
Cell is connective tissue adhere to extracellular materials rather than other cells
Components of the ECM
ground substance
Fibrillar proteins
Adhesion proteins
Ground substance elements
Structural glycoproteins
Glycosaminoglycans (GAGs) - very long unbranching polysaccharides, chains of two different sugars repeating in a very long line
Proteoglycans - proteins that covalently bond to GAGs
Both of these join together and because of their nature they can bind to water, salt, collagen proteins and other things in the matrix that makes a big matrix structure
Ground substance binds to water, salts, collagen proteins, other molecules to make a massive matrix structure
Fibrillar proteins elements
Fibres provide strength or elasticity
Collagen and elastin
Adhesion proteins elements
Link fibres, ground substance and cells together
Links everything together
Glycosaminoglycans (GAGs)
Long unbranched polysaccharide chains
Hyaluronic acid (hyaluronate) most common GAG Long linear molecules of two repeating sugar molecules
Other GAGs (e.g. Dermatan sulphate) attach to via hyaluronic acid as proteoglycans
Carboxyl groups and sulphate groups help to make the GAGs negatively charged which makes them hydrophilic which ultimately makes the get like substance because they attract lots of water which is making the cushioning
Proteoglycans and glycosaminoglycans (GAGs)
Form the ground substance
Volume and compression resistance - together makes a big branched structure and the interaction with each other and other things listed means that this branching structure is going to create volume and compression resistance
Interact with: Each other With water and salts Collagen And other fibres and molecules
Fibrillar proteins
Add strength/elasticity to tissue
Collagen
Forms fibrils, fibres and sheets, gives tensile strength
Many types - different functions in different tissue types
Most abundant protein in the human body
Found in most support tissues
Secreted by fibroblasts
Stains pink in H&E
Many different types based on amino acid composition, produced by different genes (different amino acids composition for different fibres depending on the type of collagen
28 types
Type I = ~90% of collagen in the body. Makes up ligaments, tendons, bone, skin
Type II = cartilage
Type III = reticular tissue (forms reticular fibres)
Type IV = basement membrane
Elastin
Forms fibres or sheets, allows stretching and elastic recoil
Produced by fibroblasts
Abundant in blood vessels, skin, lungs, elastic cartilage
Elastin protein comprised of short-segments
Covalently bound to each other to allow stretching and relaxing
Fibrillar proteins - collagen
Forms fibrils, fibres and sheets, gives tensile strength
Many types - different functions in different tissue types
Most abundant protein in the human body
Found in most support tissues
Secreted by fibroblasts
Stains pink in H&E
Many different types based on amino acid composition, produced by different genes (different amino acids composition for different fibres depending on the type of collagen
28 types
Type I = ~90% of collagen in the body. Makes up ligaments, tendons, bone, skin
Type II = cartilage
Type III = reticular tissue (forms reticular fibres)
Type IV = basement membrane
Fibrillar proteins - elastin
Forms fibres or sheets, allows stretching and elastic recoil
Produced by fibroblasts
Abundant in blood vessels, skin, lungs, elastic cartilage
Elastin protein comprised of short-segments
Covalently bound to each other to allow stretching and relaxing
How many collagen types are there?
28
Type I collagen
~90% of collagen in the body. Makes up ligaments, tendons, bone, skin
Type II collagen
cartilage
Type III collagen
reticular tissue (forms reticular fibres)
Type IV collagen
basement membrane
Collagen structure
Collagen is a series of twisted protein fibres
Fibres are banded under the electron microscope due to the overlap between the triple helices (different overlap of different helices)
(Pink single strand in image) - This is the thing that is directly coming out of the ribosomes, it is the thin alpha chain of collagen and three f these alpha chains will come together to make a triple helices which wind together and adds a lot of strength in one direction and this occurs at the endoplasmic reticulum and then these triple helices can move out of the support cell and then in the ECM can come together to make these collagen fibrils and fibres and the size of these fibres will differ depending on the connective tissue type we find it in and the collagen type
Adhesion glycoproteins function and types
Mediate interactions between cell cytoskeleton and extracellular matrix (help everything basically stick together in the matrix)
fibronectin
laminin
Fibronectin
Dimeric glycoprotein - made up of 2 different dimers and it can also have sugar groups coming off it
Binds collagen, proteoglycans and cells - binding sites for support cells, for collagen, for proteoglycans (proteoglycans which are making up the ground substance)
Binds collagen to integrins on cell surface
Laminin
Binds multiple components of the ECM (collagen binding, cell binding, proteoglycan binding)
Form sheets that make up basement membrane
Binds cells to basement membranes (via integrins, integrins are the proteins that connect our cells to the extracellular matrix)
Binds to integrins
Cell matrix adhesion mechanisms
Junctions between cells and ECM are important in maintaining structural integrity
Focal adhesions - bind cells to the ECM
Hemidesmosomes - attach epithelial cells to the basement membrane
Integrin proteins are important for both types of junction
How do cells anchor to ECM?
Matrix - GAGs and proteoglycans
Structural fibres - collagen and elastin
Adhesive glycoproteins - fibronectin and laminin
Transmembrane receptors - intern
Focal adhesions attach cells to …
ECM - integrin molecules interact with other proteins on both sides of the lipid layer, integrins pass through the membrane and connect to the actin cytoskeleton within the cell. Support cells bind to ECM via focal adhesions
Hemidesmosomes
Modified desmosomes
Basal surface of cell
Anchor to basement membrane
Bind to cytokeratin
Main transmembrane protein - integrins
How do cells anchor to the basement membrane? - stationary epithelial cells bind to ECM via hemidesmosomes (electron dense plaque region on electron microscope)
Hemidesmosomes attach cells to basement membrane
Integrins passes through the cell membrane and is anchoring into the basement membrane at the laminin adhesive glycoproteins
Integrins are linked to
Intracellular intermediate filaments (cytokeratin) via an electron dense plaque)
The basement membrane by anchoring to filaments composed of laminin
What do hemidesmosomes bind to?
Cytokeratin
Main transmembrane protein of hemidesmosomes
Integrins
Integrins are linked to … (hemidesmosomes)
Intracellular intermediate filaments (cytokeratin) via an electron dense plaque)
The basement membrane by anchoring to filaments composed of laminin
The constiuents of the ECM determines
the properties of the tissue, the matrix is made up of molecules made by the support cells
