Download INTRODUCTION CELL BIOLOGY

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CELL BIOLOGY
INTRODUCTION
Cells are the structural and functional units of all living organisms, primarily formed from the elements carbon, oxygen,
hydrogen, and nitrogen. They not only function as individual units, but also as a part of larger structures, namely
tissues and organs, where they communicate with other cells, forming co-ordinated functional units.
New cells are created by cell division. Once divided, they differentiate into cells specialized for their purpose. These
qualites allow them to respond to the body's constantly changing internal and external environments.
The human body is composed of many different types of cell, which are generally classified by size, shape, and function.
Cells contain numerous small structures called organelles, which carry out specific functions; different cells have
different complements of organelles depending on the ultimate function of the cell. There are two main types of cell,
germ cells, and somatic cells; germ cells consist of the sperm in the male, and oocyte in the female, and somatic cells
include all other cells in the body.
Some of the main types of cell are described in the table below.
TYPES OF CELL
Somatic cells
Epithelial cell
Epithelial tissue forms many of the linings and coverings in the body. Epithelial cells have many
functions, including acting as a protective surface, secretory surface, or as an absorptive surface,
regulating the movement of substances into and out of the body. Epithelial cells vary in shape
depending on their function and location.
Blood cells
Red blood cells, or erythrocytes, are the most common type of blood cell. These cells bind oxygen
in the lungs, and carry it to tissues throughout the body, where it is exchanged for the waste product
carbon dioxide.
White blood cells, or leukocytes, function by identifying, capturing, and eliminating invading
pathogens, or foreign particles. There are many types of white blood cell, including neutrophils,
eosinophils, basophils, monocytes, and lymphocytes.
Bone cell
Osteoblasts are bone-producing cells present in bone marrow and other connective tissues. They
synthesize and secrete collagen fibers, and other organic components, which are used to build the
extracellular matrix of bone tissue and initiate calcification.
Fibroblast cell
Fibroblasts are large, flat, branching support cells present in most connective tissue. They secrete
fibers including collagen, and some of the ground substance component of the extracellular matrix.
These are used to provide the structural framework for tissues. Fibroblast cells also play in important
part in skin wound healing.
Muscle cells
Skeletal muscle cells are found attached to the skeleton via tendons, or through a connective tissue
sheet called an aponeurosis. Skeletal muscle is under voluntary control and is able to contract,
respond to stimulation from the nervous system, stretch beyond its normal resting length, and revert to
its original resting length.
Smooth muscle cells are found in the walls of internal organs, blood vessels, and the intrinsic
(internal) muscles of the eye. Smooth muscle tissue is involuntary. It helps to propel and expel liquid
within and from the body, allows peristalsis that aids in digestion, and helps to regulate the diameter of
blood vessels.
Nerve cell
Nerve cells, or neurons, are the main functional cells of the nervous system. They have long
extensions that are sensitive to external stimuli, allowing them to respond to, and communicate
information through, electrical and chemical signals.
Germ cells
Sperm cell
Found in the male, approximately 300 million spermatozoa or sperm cells are made in the testes per
day. Sperm cells are uniquely designed and have a number of important features, which enable them to
travel to and fertilize an ovum.
Ovum
Found in the female, approximately one oocyte, or immature gamete, is released from the ovary each
month during the ovulation process. During the course of each month, the oocyte will travel down the
uterine tube until it encounters a sperm cell. If a sperm cell enters the oocyte, fertilization occurs. At
this stage, the oocyte is now called an ovum. Within minutes, the sperm and ovum nuclei fuse to form
a zygote.
Cells have a variety of different functions. The components of each cell determine its size, shape and function.
Some of the most important functions of a cell are described in the table below.
FUNCTIONS OF THE CELL
Protection and There are number of cells that help to protect and support the body. Epithelial cells, such as those
support
found in the skin, provide a protective surface, preventing foreign particles from invading the body.
Communication The nervous system contains a vast network of specialized neurons that act as a communication
system: perceiving, relaying, and conveying information in pathways throughout the body.
Energy
Energy released during cellular metabolism enables cellular activities, such as synthesis,
production
contraction, and heat production to occur.
Movement
Some cells, such as skeletal muscle cells, are able to facilitate movement of the body by
contracting and relaxing in response to stimulation from the nervous system.
Inheritance
The sex cells, namely sperm cells and oocytes, are responsible for providing inherited genetic
information.
Transport
Many cells facilitate the transport of substances within the body. For example, red blood cells bind
oxygen in the lungs, and carry it to tissues throughout the body. It can then be exchanged for the
waste product carbon dioxide.