Cells in a human body are of different types based on their structure and function.
Scientifically, a Cell is the basic unit of life.
A group of cells from a tissue and a group of tissues form an organ.
So, if an organ is damaged, it means the cells and cell structure in the organ are also damaged.
In fact, the damage can decide the fate of the entire tissue or organ. The cell death pathways decide if it recovers or dies instead.
Different Types of cells in the human body
For ease of learning, we will classify them based on the tissue they form or the function they perform.
Cells in the Human Body Based on the tissue they form
1. Bone cells
They are the most robust body cell systems and are bound together by calcium and phosphate. As you know, they give strength, support, and framework to the body by enclosing organs in the 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 (therefore 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 form the nervous system. They are longest cells of the body ranging up to 100 centimeters.
Its features are like they are very long, having many branches at either end. They never multiply or divide in one’s lifetime. Once formed during a fetus, they live until the entire life of an individual. They are present all over the body and are sometimes as long as a few meters long.
These cells are found in plenty in the brain and the spinal cord. They combine to form the nervous tissue.
4. Epithelial cell
These cells are very simple cells that form a covering of other cells.
They form covering layers of all the organs and hence are present in the skin, scalp, respiratory tract, in the buccal cavity surface, over the surface of the heart, etc. Ex: Skin cells, mucous cells.
They also form the essential structures like the nephrons in the kidney, which help infiltration of the blood.
5. Muscle cells
These cells are responsible for the movements of the body. They are also called myocytes and are present in the muscle tissues.
They are rich in proteins like actin and myosin, due to which they contract. They are mostly long, large and can provide movements to the body. They are three types the skeletal, cardiac, and smooth muscle cells.
- Skeletal muscle cells are attached to long bones and assist in their movements (by muscle contraction).
They are also called striated cells as they have bands or striations on them, as seen above (white and red bands). These bands are indicative of actin and myosin filaments, which help in contraction.
- Cardiac muscle cells are present only in the heart muscle and responsible for heartbeats.
These are also striated but have branches with others.
- Smooth muscle cells are flexible yet, can contract and relax and are present in the stomach, intestine, blood vessel walls (vascular tissue), etc. helping in the movement of food through the gut.
Muscle cells also store glucose due to which they generate energy and heat required by the body.
6 Secretory cells
These cells, as the name indicates, are secretory in function. They are present in the glands and secrete specific secretions containing enzymes or hormones.
a) Salivary gland cells called acini secrete saliva
b) Gastric cells present in the stomach secrete gastric juice.
7. Adipose cells
These are fat cells and are sites where fat is stored. Adipose cells are mainly seen in the soles, palms, bums, etc. They reduce friction to the body.
8. Blood cells
These cells include three basic types like
a) Red blood cells (RBC’s): These cells are called corpuscles and are not living in nature due to the absence of a nucleus in them. They are red-colored due to the presence of pigment hemoglobin. Their main role is to carry oxygen from the lungs to the tissues.
b) White blood cells (WBC’s): Unlike RBC’s, they have a nucleus and are living. But they are of five different types and play the main role in body defense against pathogens.
c) Thrombocytes (platelets). These cells are small of the three and are involved in the process of hemostasis, i.e., blood clot formation, to prevent bleeding due to injury.
These cells are always motile and never stay in one place. They have a limited lifespan before they are destroyed in the body. Unlike other cells, they never multiply to form new cells. Instead, new cells are formed from other cells.
Cell types based on their function
Different cells carry out distinct functions in the body like
Nerve cells, muscle cells come under this category. They have an inherent ability to conduct an electric impulse from one region to other distant regions 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 the 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 that 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.
The special type of cells: These are specialized cells with some crucial functions. They are
These cells, unlike others, have haploid DNA (i.e., have only one set of a chromosome). They are present only in males after puberty. These cells have a tail which enables them to swim and move in the female uterus. They have an enzyme hyaluronidase, which helps them penetrate through uterine tissue and reach into oocytes.
Cells are haploid and present in the 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 a zygote (fertilized egg). This zygote further grows in the uterus to form a baby.
c) Stem cells
These are primary cells or parent cells which can differentiate into any required cell-based. These stem cells in the human body are given so much importance due to their promising role in the treatment of disorders in the future. Have a glance at stem cell types.
d) Rods & cones
These cells are present exclusively in the retina of the eye. These cells contain photosensitive pigments that help to capture the light and convert it into a nerve impulse.
e) Ciliated cells
These cells are present as the lining of the respiratory tract, esophagus, etc., and have pointed threadlike cilia, which move in one particular direction to pass material.
f) Blood cells
These are quite interesting cells and they are never attached. 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 can eat (gulp) any foreign particle like bacteria in the body. Hence they are body defense cells.
g) Islets of Pancreas
These cells secrete pancreatic hormones like insulin and glucagon. There are a total of 5 types. Check out pancreatic cells for details.
These cells are present in the liver and constitute 80% of its mass. They are involved in the breakdown of toxins like drugs and other waste materials. The cells are large and many mitochondria and abundant endoplasmic reticulum to help in their function in the liver. Unlike other cells, they can regenerate.
i) Kupffer cells
These cells are located in the liver and are modified macrophage cells. They destroy the old and worn-out red blood cells in the liver.
J) Goblet cells
These cells are dispersed in the inner layer of the small intestine and they secrete mucus.
K) Paneth cells
Paneth cells are also found in the intestinal linings. They secrete anti-microbial proteins and help in defense against pathogens in the intestine.
L) Mesangial cells
These cells are found in the glomerulus of the nephron in between the capillary loop. These cells help to remove trapped residues so as to keep the filter free of clogging.
And guess how many cells are in the human body? There are 37 trillion cells in our body by an estimate.
Reference: Book-Campbell Biology.