Tissues

No, I'm not going to be talking about tissues as in Kleenex and Sorbent, but rather tissues as in the tissues that make up the human body. (That was probably already pretty obvious, but I consider playing the role of Captain Obvious to be one of the aspects of my "job" here on this blog.)

There are four kinds of tissues in the human body: epithelial, connective, muscular and nervous. The different kinds of tissues are similar in that a tissue is made up of a group of similar cells and some intercellular material (called the matrix). Now that we've looked at the similarities, let's look at the differences:

Epithelial Tissue

What it does: Epithelial tissue, or epithelium, is used to cover body surfaces (e.g. skin) and line body cavities and ducts (e.g. in the small intestine). Its functions include absorption, secretion and protection, depending on the location of the tissue in the body.
Examples: Skin, lining of small intestines, secretory tissue of glands etc.
Structure: The cells are closely joined. Very little matrix between cells. Cells are classified according to their shape- cube-shaped cells are called cuboidal cells, column-shaped ones are called columnar cells, and so on. In some places there is only a single layer of cells (simple epithelium), while in other places there are multiple layers of cells (stratified epithelium). The epithelium is attached to a membrane of connective tissue, which is located beneath the epithelial cells.
Miscellaneous stuff: Cells in the glandular epithelium secrete stuff such as sweat, saliva, enzymes, hormones and so on. Sometimes the gland is only one cell, while sometimes a gland is comprised out of clusters of cells. Exocrine glands secrete stuff outside the body, or onto a body lining. Endocrine glands, on the other hand, secrete their products directly into the blood or into the tissue fluid.

Connective Tissue

What it does: Connective tissue binds and supports the other tissues of the body. There are many different types, including loose connective tissue, dense connective tissue, adipose tissue, cartilage and bone (bone has already been mentioned on this blog in my post about the skeleton) and blood. Each kind of connective tissue has different functions: loose connective tissue supports and connects other tissues; dense connective tissue does pretty much the same thing (as far as I can see) but it's stronger, making it more suited for joining tendons to bones and so on; adipose tissue cushions vital organs and restricts heat loss; and cartilage provides structural support while still providing some flexibility. (Bone and blood have been discussed in their respective posts.)
Examples: Blood, bones, cartilage (bet you didn't see those three coming, did ya?), fat (adipose tissue), tendons (dense connective tissue), fibrous membranes around various organs (also dense connective tissue) etc.
Structure: Loose connective tissue is made up of fibres and cells in a semi-fluid matrix. Dense connective tissue has large numbers of fibres, which give the tissue great strength, with cells scattered in between. Adipose tissue consists of cells that contain large globules of fat with the cytoplasm forming a thin layer on the outside. Cartilage has fibres embedded in a firm matrix which also contains spaces for the cartilage cells. Bone, as mentioned in my post about the skeleton, has inorganic salts in its matrix, increasing rigidity and strength. Blood consists of a whole bunch of cells separated by a matrix called plasma (see my post about blood for more details).

Muscular Tissue

What it does: Muscle fibres (long, thin muscle cells) are able to contract, causing movement. They can also be stretched, and are elastic enough to return to their original length after stretching. There are three types of muscular tissue: skeletal muscle, cardiac muscle and smooth muscle. (You can read more about skeletal muscle here.)
Examples: Hmm do I really have to say? Biceps, triceps, quadriceps, hamstrings, the gluteus maximus, etc. etc. etc. (there are over 600 skeletal muscles alone, don't expect me to list all of them). Cardiac muscle is found in the walls of the heart (w00t), and smooth muscle is found in the walls of many internal organs (blood vessels, bladder, uterus, alimentary canal etc.).
Structure: Structure of skeletal muscle can be found in my main post on muscles, but here's a quick overview anyway: skeletal muscle is made up of a series of parallel cylindrical muscle fibres that are up to several centimetres long. Each fibre contains several nuclei located on the edges. Skeletal muscle is also called striated muscle, as the thick and thin filaments (myosin and actin, respectively) give a striped appearance under a microscope. Cardiac muscle has cross-striations like skeletal muscle, but unlike skeletal muscle, cardiac muscles branch to form a network. Smooth muscle (or non-striated muscle) does not have striations, and is made up of long cells with tapering ends that fit into each other. Smooth muscle cells each have one nucleus in the centre of the cell (as opposed to skeletal muscle fibres, which have several nuclei around the edges of the cell).
Miscellaneous Stuff: Skeletal muscle is also called voluntary muscle as these muscles can only be contracted voluntarily. Smooth muscle (and presumably cardiac muscle as well) is known as involuntary muscle as it can't be contracted voluntarily.

Nervous Tissue

What it does: Contains neurons (nerve cells), which receive and transmit messages to the body.
Examples: Brain, spinal cord, nerves
Structure: The neurons in the tissue have a cell body which contains the nucleus as well as one or more strands of cytoplasm that extend from the cell body. There are several different types of neurons, as well as several other kinds of cells that help to support and nourish the neurons, but apparently all that is discussed in the Year 12 book. Boo!