I am a Licensed Practical Nurse with five years' experience in this profession. I believe it is essential to go back to the basics in all things in order to really understand them. I am fascinated by how our bodies work and I hope I can get my readers to share my fascination. I hope we all learn new things and marvel again at the things we already know. This feature -- which includes a closing section on how disease affects the topic in question -- will run on The Cancer Blog on Wednesdays, and The Cardio Blog and The Diabetes Blog on Thursdays. [The contents in this post are for informational purposes only and should not be construed as medical advice or substitute for professional medical care.]
We looked at the cell in a series of six articles and now we are moving into the fascinating world of tissues. A tissue is a group of cells with similar structure and function. The tissue then contributes to the functioning of the organs in which it is found. Epithelial tissue exists at the body surface where it lines the skin and various organs such as the mouth, nose and other body cavities. It is also found at the lining of the respiratory, reproductive and urinary tracts. All blood vessels are also lined with epithelial tissue. Epithelial tissue is divided into different types.
The first type of epithelial tissue is the covering and lining epithelium. It forms the epidermis of the skin and the outer covering of some internal organs as well as the inner lining of blood vessels, ducts and body cavities. It is arranged by layers and cell shapes. The layers are: simple epithelium, stratified epithelium and pseudostratified columnar epithelium. The cell shapes are: Squamous, cuboidal, columnar and transitional.
Simple squamous epithelium: It consists of a single layer of flat cells that resembles a tiled floor. It is located in the lining of the blood vessels, lining of body cavities and part of the kidney tubules. Its functions are protection and absorption.
Simple cuboidal epithelium: The cuboidal shape of the cells in this tissue is obvious when the tissue is sectioned and viewed from the side. It is located in the secretory portion and ducts of some glands and part of the kidney tubules. Its functions are secretion and protection.
We looked at the cell in a series of six articles and now we are moving into the fascinating world of tissues. A tissue is a group of cells with similar structure and function. The tissue then contributes to the functioning of the organs in which it is found. Epithelial tissue exists at the body surface where it lines the skin and various organs such as the mouth, nose and other body cavities. It is also found at the lining of the respiratory, reproductive and urinary tracts. All blood vessels are also lined with epithelial tissue. Epithelial tissue is divided into different types.
The first type of epithelial tissue is the covering and lining epithelium. It forms the epidermis of the skin and the outer covering of some internal organs as well as the inner lining of blood vessels, ducts and body cavities. It is arranged by layers and cell shapes. The layers are: simple epithelium, stratified epithelium and pseudostratified columnar epithelium. The cell shapes are: Squamous, cuboidal, columnar and transitional.
Simple squamous epithelium: It consists of a single layer of flat cells that resembles a tiled floor. It is located in the lining of the blood vessels, lining of body cavities and part of the kidney tubules. Its functions are protection and absorption.Simple cuboidal epithelium: The cuboidal shape of the cells in this tissue is obvious when the tissue is sectioned and viewed from the side. It is located in the secretory portion and ducts of some glands and part of the kidney tubules. Its functions are secretion and protection.
Although cells synthesize many chemicals to maintain homeostasis, they are mainly devoted to synthesizing large numbers of proteins. Proteins are used as enzymes and as structural materials in the cells. Many proteins are retained in the cell for intracellular use. Some proteins are used to assemble cellular structures such as the plasma membrane, the cytoskeleton and other organelles. There are many specialized human proteins that are exported and function in cellular activities. For example, protein makes up the hormone insulin, the ligaments and tendons of joints, the hair, skin, and nails of the body.
One of the features of a cell is it's ability to reproduce independently. In somatic cell division, a cell undergoes a nuclear division called mitosis. Reproductive cell division is the mechanism that produces gametes. This process consists of a two step division called meiosis. 
With the exception of mature red blood cells, human cells have a nucleus and some, like skeletal muscle cells, have more than one. The nucleus is composed of three main parts, the nuclear envelope, the nucleolus and the chromatin.
We have discussed cell membranes (
Organelles
We start with the cell, because so much of what happens to us when we get sick, and how we get healthy again, can be explained by what happens on a cellular level. The cell is extremely complex and I will only touch on the basics in these posts, but at least we can have a rudimentary understanding.
Phospholipids (one of the three classes of membrane lipids) are formed into what is called a lipid bilayer. This occurs because it is amphiphilic (containing both hydrophobic and hydrophilic properties).The hydrocarbon tails of the molecule are hydrophobic (water repelling) and its polar head is hydrophilic (water loving). As the plasma membrane faces watery solutions on both sides, its phospholipids accommodate this by forming a phospholipid bilayer with the hydrophobic tails facing each other. Picture a row of heads facing the outside of the cell -- which contains water -- with the tails facing in and another layer of the heads facing the inside of the cell with the tails facing in.
