THE EXTRACELLULAR MATRIX
The extracellular matrix (ECM) is the material that surrounds animal cells. The ECM is useful in producing a variety of structures (like bone, tendons, shells of molluscs.) Not only does it have a structural role, but it can also regulate the behaviour of its inhabited cells. The ECM is abundant in connective tissue. Connective tissue can be either loose or dense (the ECM is present in both.) The spaces around the cells are filled with hydrated polysaccharide glycosaminoglycans, which are often linked to proteins to form a proteoglycan gel.
The extracellular matrix holds several important roles: it influences the survival development, migration, shape, proliferation and function of the cells within it.
Molecules of the ECM are produced locally (meaning they are secreted by fibroblasts in loose connective tissues, by osteoblasts and chondroblasts in bone/cartilage).
What are glycosaminoglycans? (GAGs)
They are chains of repeated units. These repeated units are negatively charged disaccharides that form linear chains and attract cations (sodium.) The attraction of cations causes large amounts of water to be sucked into the matrix (highly useful.) Most can be linked to proteins to form proteoglycans. Both are synthesised in, and secreted by, cells in the ECM.
What is the cytoskeleton? Components that work together to perform particular functions.
The cytoskeleton consists mainly of actin filaments and microtubules and plays an important role in cell movement, shape, growth, division, and differentiation, as well as in the movement of organelles within the cell. All eukaryotic cells have a cytoskeleton.
What is epithelial tissue?
Layers of epithelial cells that are packed together to carry out different functions. These are:
Protection, selective barriers, filtration, secretion, absorption and excretion. Protection involves waterproof casing (the skin), selective barriers are used to control the movement of substances into and out of the body and filtration involves the kidneys. Filtering systems need epithelia to maximise the absorption of substances that need to be filtered, this ensures we have the substances we need in our body and we excrete what we do not need.
Epithelial tissue can be classified in different ways. We firstly have squamous epithelium; these cells are very thin and lay at the surface of blood vessels. There is cuboidal epithelium which cover cells of the ovary and kidney tubules. Cuboidal shapes are those which produce wiggly lines, this extends surface area to maximise secretion. Lastly there is columnar epithelium which can be found on the lining of the gastrointestinal tract (GIT.)
Cell layers can be described in certain ways:
We firstly have simple. Simple layers are just one layer of epithelium. Pseudostratified epithelium is one layer that appears like there is several. Lastly there is stratified epithelium, this is two layers.
What is connective tissue?
Fibrous protein structures joined together to bind, support, strengthen, protect, insulate and compartmentalise. The tissue is one of the most abundant, with a wide distribution.
What is muscle tissue?
Elongated muscle fibres (myocytes) work together to perform muscular function. These functions are movement and locomotion, maintenance of posture, controlled movement and thermogenesis.