Nobody knows the exact number of cells in a human body, but it is estimated to be around 50 to 75 trillion and if lined up end-to-end, they could circle the earth more than two times. Each specialized cell makes different parts of the body, such as neurons which carry messages throughout the nervous system by an electrical process. Red blood cells carry oxygen through the body, and the brain has approximately 100 billion cells. Cardiac muscle cells, also known as (myocardiocytes) are specialized striated tissues found only in the heart. The lungs are spongy organs made up from epithelial tissue called alveolar. All parts of the body are made from cells (the basic building blocks of all living things). Cells form tissue (the part of an organism containing a large number of cells that have a similar structure and function). Tissues form organs (a collection of tissue jointed in a structural unit to serve as a common function). Organs make up the body system (structures that work together as one unit).
Cells have many parts and are enclosed by a protective coating consisting of lipids and proteins, called the plasma membrane which holds the parts of the cell inside which are called organelles (a Latin term for little organs). The plasma membrane (also called the nuclear envelope) have specialized channels which allow necessary nutrients to pass into and out of the cell.
The nucleus controls all cell activity and stores the majority of genetic material. Chromosomes are the thread like structure made up of protein and a single molecule called deoxyribonucleic acid (DNA) which makes each living creature unique and each cell contain 23 pair. Each structure of chromosome keeps DNA tightly wrapped around spool-like proteins called histones. Changes in the number of chromosomes can result in serious problems such as leukemia, cancer, or birth defects such as Down syndrome. It is very important that this copied material have correct structure.
Cytoplasm is the viscous gel-like substance where most cellular activities occur. It is eighty percent water, surrounds the nuclear envelope and suspends all organelles, and is usually clear in color. It contains enzymes, fatty acids, sugars, and amino acids to nourish the cells.
The endoplasmic reticulum (ER) functions as the packaging system. It consists of a network of flattened sacks and extended branching tubules that selectively transports and manufactures molecules between the lumen (spaces in the ER) and cytoplasm.
The ribosomes (a Greek word meaning body) serve as the primary site to form specific essential proteins for cell growth and to control the cells reaction to chemicals. They can freely float in the cytoplasm or attach themselves to the endoplasmic reticulum.
The mitochondria also referred to the power house of the cell, because it generates most of the cells chemical energy in the form of adenosine triphosphate (ATP) and produces hundreds and thousands of ATP molecules every minute. These molecules range in diameter from 0.5 to 1.0 micrometers and have its own independent genome.
The golgi apparatus contain compartments called cisternae, which contain different proteins and enzymes manufactured by the ER. They are modified to add or remove sugars and then packaged for transport to various locations within the cell. A typical cell can produce about 30,000 different proteins. If there are defects in this organelle, the affects can result in congenital glycosylation disorders, some forms of muscular dystrophy, and may contribute to diabetes, cancer, and cystic fibrosis
Lysosomes act as the cell’s recycling center and waste disposal. Powerful enzymes inside these cells break down worn-our organelles and ship their building blocks to the cytoplasm. There they are used to build new organelles. Lysosomes also dismantle and recycle proteins, lipids, and other molecules.
Most researchers concentrated on one particular cell or cell part to study and do research on. Cell biology has now branched out in many different directions. Developmental biologists focus on the formation and development of human egg cells. Molecular genetics determine the order of nucleotides in DNA strands and map the location of genes on chromosomes. Evolutionary microbiologists study the single-celled creatures that lived on earth millions of years ago and many medical researchers also study cells. No one can predict all the amazing things that will be learned in the future, but studying the cell for future progress is very important process for understanding humans and other creatures which inhabit our world.