Cells in the human Body:
This is the lesson we likely come across in the chapter of human anatomy and physiology.
If you are perceiving a degree in medicine or degree in science then this topic is important.
Human body has a number of cells and related tissues.
Since the Cell is the basic unit of any tissue, it decides the type, nature and function of the tissues.
A group of different types of cells form tissues in the human body and one or more types of tissues form organs.
These body organs working in a mutual manner form the organ systems.
If any tissue is damaged, it actually means the cells and cell structure in the organ is damaged. These damaged cells decides the fate of entire tissue i.e. either to recover or die.
Many cells have internal tendency to multiply and help in repair while few don’t have this property. Let’s see list of cells of human body with their functions.
Different Types of cells in the human body (based on tissue formation)
1.Bone cells (Osteocytes) They are the toughest body cell systems and are bound together by calcium and phosphate. As you knows they give strength, support and frame-work to the body by enclosing organs in skeletal system i.e bones.
2. Cartilage cells (chondrocytes)– These cells are similar to bone cells but the surrounding material is just loose and flexible compared to those of bone cells. Hence they are freely bendable. They are present in ear bone (hence ears are fold-able), in between large bones to help them bend and move freely like in between two ribs, spinal bones, joints etc.
3. Nerve cells: These cells features are, very long and have many branches at either ends. They never multiply in one’s life time. Once formed during fetus, they live till the entire life an individual. They are present all over the body and are sometimes as long as few meters long.
The human brain cells and are found in plenty in the brain and the spinal cord. They combine to form the nervous tissue.
These cells form covering layers of all the organs and hence are preset in skin, scalp, respiratory tract, in the buccal cavity surface etc. Ex: Skin cells, mucous cells.
5.Muscle cells: Also called as myocytes and are present in muscle tissue. They are rich in proteins actin and myosin, mostly long, large and have ability to contract and relax providing movements. They are of three types as skeletal, cardiac and smooth muscle cells.
- Skeletal muscles cells are attached to long bones and assist in their movement (by muscle contraction).
- Cardiac muscles cells are present only in heart muscle and responsible for heart beats.
- Smooth muscle cells are flexible yet, can contract and relax and are present in stomach, intestine, blood vessel walls (vascular tissue) etc. helping in the movement of food through the gut.
6 Secretory cell: These cells as name indicates are secretory in nature. They form glands and secrete something important ex; pancreatic cells which secrete insulin, glucagon, salivary gland secrete salivary amylase, sebaceous gland secrete oil on the skin etc.They are found in all secretory organs.
7. Adipose cells: These are fat cells and are storage in nature to store fat. Especially seen in the soles, palms, bums etc. They reduce friction to the body.
8. Blood cells: These cells include RBC’s, WBC, Thormbocytes etc. They are always motile and never stay in one place. They have limited life span and they never multiply to form new cells. Instead new cells are formed from other cells.
Types of cells in human body (based on their function)
Different cells and their functions help the body carry out many physiological functions. These cells include
Conductive cells: Nerve cells, muscle cells come under this category. They have internal ability to conduct an electric impulse from region to other distant region in the body.
Connective cells: Bone cells, blood cells come under this category. They help connect other cells and tissues.
Glandular cells: These cells secretory cells. They form glands like pancreas,salivary glands etc and help in the production of enzymes, hormones etc.
Storage cells: Adipose cells, some liver cells etc act to store materials like fat for later use. This fat is consumed in times of starvation and also in excess cold temperatures.
Supportive cells: These are the cells which are present as support to adjacent cells. Ex: Glial cells in the brain and spinal cord help provide nourishment to the nerve cells and also protect them from shocks and trauma.
Special type of cells: These are specialized cells with important functions in the body. They are
a) Sperms: These cells unlike others have haploid DNA (i.e. have only one set of chromosome). They are present only in the males after puberty. These cells have a tail which enables them to swim and move in the female uterus. They have an enzyme hayaluronidase which helps them penetrate through uterine tissue and reach into oocytes.
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b) Oocytes: Cells are haploid and present in adult female genital system. They are also haploid like sperms. They start to form after puberty and continue so till the stage of menopause. They accept sperm cells to form zygote (fertilized egg). This further grows in the uterus to form a baby.
c) Stem cells: These are basic cells or parent cells which can differentiate into any cell based on the requirement. These stem cells in human body are given so importance due to their promising role in treatment of disorders in future. See the article on stem cell types.
d) Rods & cones: These cells are in eye and have capacity to capture image color and light.
e) Ciliated cells: These cells are present as lining of respiratory tract, esophagus etc. and have a pointed thread like cilia which move in one particular direction to pass material.
Human tissue types are again dependent on the types of cells involved in their formation.
f) Blood cells: These are quite interesting cells and they are never attached to one another. Blood cells freely flow in the liquid blood. Some of them are not alive (RBC‘s) while others are alive and have varied shapes like WBC, platelets (spindle shape). Further these WBC’s are of different types. Of them macrophages have ability to eat (gulp) any foreign particle like bacteria in the body. Hence they are body defense cells.
Besides, there are cells which form covering tissue. These can be of different shapes, will ability to constrict, dilate, secrete and even absorb. Such cells are seen in the lining of intestine, stomach, lungs, nephrons etc. The examples include goblet cells, paneth cells etc.
Reference: Book-Essentials of Cell Biology.Albert Bruce.