Unit 1

• Tissue is the assemblage of similarly specialized cells united in performing a specific function. Tissue is composed of cells and an extracellular matrix (ECM)
• A cell can: Self replicate, synthesise macromolecules for their own structure, synthesise and secrete molecules allowing them to interact with their environment, receive, process and send signals to environment, obtain energy, digest substances from environment or own components, carry out catabolic processes, breathe anaerobically and aerobically and move
• Shape of a cell is mediated by its function. IT depends on the cytoskeleton. Can vary due to tension of adjacent cells, nutrition, hormonal stimulation or external pathogens. Cells are usually spherical, flat, cubic, prismatic or star shaped
• Epidermis and mucosa have ?

  flat cells
• Intestine cells are?

  Spherical
• Hepatocytes and thyroid cells are?

  Cuboidal
• Plant cells are?

  Polyhedral
• Red blood cells or erythrocytes are?

  Biconcave or oval
• Myocytes or muscle cells are?

  Elongated or fusiform
• Neuron cells are?

  Stellae
• Sperm cells are?

  Filiform
• The female ovule cell is?

  Spherical
• Size of cell is mediated by function. The smaller cells would include lymphocytes and the larger ones would include neurons.
• The ECM is made up of macromolecules which support the cell, contain fluid that transports nutrients to the cells, it carries away waste as secretory products. Cells produce ECM locally. During development cells and their associated matrix become functionally specialised. Organs are formed by an orderly combination of the tissues. Precise arrangement allows for the functioning of each organ and then the organism as a whole
• The four different types of tissue are epithelial, connective, muscle and nervous
• Parenchyma: cells responsible for organ function
• Stroma: cells with a supporting role
• Epithelial cells have a small amount of ECM, they are found lining the surface of body cavities and organs. Made up of aggregated polyhedral cells
• Connective tissue has an abundant amount of ECM. It protects and supports tissue/organs. Made up of several types of fixed and wandering cells
• Muscle tissue has a moderate amount of ECM. It causes strong contractions and body movements. Made up of elongated contractile cells
• Nervous tissue has a very small amount of ECM. It is responsible for transmitting nerve impulses and is made up of elongated cells with extremely fine processes
• Method of preparing cell for observation: Fixation is the use of formaldehyde and glutaraldehyde to preserve cell structure. These chemicals react with the amine group NH2 of proteins preventing their degradation by common proteases. Next the cell is dehydrated by being put into solutions of increasingly higher concentration of ethanol. Dehydration is essential for the embedding within hydrophobic paraffin. Next Xilol is used to remove excess ethanol as ethanol should not be heated with paraffin.
• Method of preparing cell for observation: Once a cell has been Fixated, Dehydrated and Cleared infiltration occurs. Infiltration is the process of adding the cell to paraffin or plastic resin. Paraffin is used often for light microscopy while resin can also be used for electron microscopy. At room temperature paraffin is solid so it is heated to about 52-60 degrees. Once introduced into cell sample, it is put onto a cassette and onto a cold table, which leads to colidifying and embedding. This is done to prevent damage to the cell and for long term preservation.
• Cutting of paraffin, done by microtome. paraffin can be cut to less than 1 um while plastic resin to around 1 - 5 um. Electron microscopy requires sections of less than 1um, so resin usually used for this. Slides 3 - 10 um thick for light microscopy. Once cut, paraffin slides are put into cold water (20-30 degrees) to prevent folding.
• Staining of the cell occurs after fixation, dehydration, clearing, infiltration and embedding
• The regular sectioning methods include the use of ethanol which remove lipids and stop enzyme activity.. When trying to look at adipose tissue, freeze with liquid nitrogen instead of using ethanol. This method allows to see enzymatic essays and structures that contain lipids. After liquid nitrogen, the samples are fixed and sliced using a cryostat resulting in thick 30um slides. Difficult to maintain and expensive as must be kept in temperatures below -80
• For observing hard tissue, Decalcification must be carried out. This can be done with 5-10% nitric acid treatment for days/weeks, 90% dormic acid treatment for a week or EDTA tratment for weeks. This causes tooth enamel to be removed
• Due to decalcification and removal of enamel, another method had to be developed to observe it. The tooth is submerged in acrylic resin and then cut using a tungsten knife and then filed with arkansas stone to obtain slides of 30um. No stain is used here
• Stains are acidic or basic compounds which form electrostatic (salt) linkages with ionizable radicals from macromolecules in tissues
• Nucleic acids with net negative charge have an affinity for basic dyes making them basophilic. Basic dyes include toluidine blue, alcian blue, methylene blue and hematoxylin
• Cationinc (positively charged) components such as proteins stain with acidic dyes making them acidophilic. Acidic dyes include orange G, acid fuchsin and eosin.
• Neutral components aren't dyed with acidic or basic dyes instead being dyed with giemsa stain
• Metachromasia is where certain basic dyes react with components leading to the change of colour. The presence of polyanions within the tissue causes this to happen. An example of this is toluidine blue
• The presence of what type of ions causes the reaction of basic dyes leading to metachromasia?Give an example of one of these basic dyes

  polyanions, toluidine blue
• Hematoxylin and eosin are the most common stain. Hematoxylin stains DNA, RNA rich cytoplasm, matrix of cartilage and nuclei (purple/dark blue) and eosin acts as a counterstain for cytoplasm and collagen (pink).
• Masson's trichrome is a stain that colours nuclei, cytoplasm and collagen. Called trichrome as it stains three colours
• Silver stain is used to stain nerves
• Cresyl violet stains reticular fibres and cell bodies of neurons in spinal chord
• Periodic acid Schiff stains polysaccharides and other carbohydrate rich tissue purple. When this stain is modified it is called feulgen and is specifically used to stain DNA. Periodic Acid Schiff stain is also used for staining hiphae and fungi spores
• Trichrome stains include mallory, masson, gomori and van gieson