Human Cells are of different types based on their structure and function.
A Cell is the basic unit of life, and a group of them forms tissues, and further, a group of tissues forms an organ.
Thus human cells are designed by nature to meet the end anatomy and physiological requirements.
Different Types of Human Cells by Structure
Structurally Cells are of various kinds like
1. Bone cells
- These cells, unlike others, are the hardest of the body cells.
- The presence of calcium and phosphate material binds them together.
- They provide structural shape, strength, and movement to the body.
- Forming bone cages, they help enclose and protect essential organs like the brain, heart, lungs, eyes, etc.
2. Cartilage cells (Chondrocytes)
- These cells are part of the cartilage bones in the body.
- They are similar to bone cells, but due to binding material, they form flexible elastic tissue.
- The matrix around these chondrocyte cells is loose and flexible compared to those of bone cells.
- Hence, the cartilage tissue can be freely bent, as in the external ear.
- They form the ear pinna, knee caps, and intervertebral discs and are also present in between large bones to help them move freely, like in between two ribs, spinal bones, and joints.
3. Nerve cells
- These cells are part of the nervous system.
- Some of these cells are the longest cells of the body, ranging up to 100 centimeters in length.
- Structurally, they are long, with many branches at either end.
- Unlike other cells, they never undergo cell division or multiply during their lifetime.
- Once formed during the fetus stage, they live until the entire life of an individual.
- They are present all over the body and extend to the superficial and deeper parts of the body.
- These cells are found in plenty in the brain and the spinal cord. They combine to form the nervous tissue.
4. Epithelial cells
- These cells form surface-covering tissues.
- They are of different shapes and sizes, like cuboidal, flattened, columnar, etc.
- They can be found as covering layers for all the organs and as inner linings.
- They are present in the skin, scalp, respiratory tract, digestive tract, over the surface of the heart, and more.
- Ex: Skin cells, mucous cells.
- They also form essential structures, like the nephrons in the kidney, that help in the filtration 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 and large and can provide movements to the body.
- They are three types of muscle cells, viz., 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 with ease.
- They are present in the stomach, intestine, and blood vessel walls (vascular tissue), helping in the movement of food through the gut.
- Muscle cells also store glucose, by which they generate the body’s energy and heat.
6 Secretory cells
- These cells, as the name indicates, are secretory in function.
- Their size is comparatively large, and they are mostly present in the glands.
- They 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 spread in a loose areolar matrix to form adipose tissue.
- Adipocytes are large and filled with large fat globules, due to which the nucleus is pushed to one side.
- These cells of adipose tissue are mainly seen in the soles, palms, and bums below the skin.
Their main function is
- To store energy (as fat)
- Prevent heat loss from the skin.
- Maintain body temperature,
- Reduce friction due to contact with hard surfaces.
8. Blood cells
These cells include three basic types like
a) Red blood cells (RBCs): 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 primary role is to carry oxygen from the lungs to the tissues.
b) White blood cells (WBCs): Unlike RBCs, they have a nucleus and are living. They are of five different types and play a prominent role in body defense against pathogens.
c) Thrombocytes (platelets). These cells are the 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 and muscle cells come under this category. They have an inherent ability to conduct an electric impulse from one region to other distant body areas.
Bone cells and blood cells come under this category. They help connect other cells and tissues.
These cells are secretory. They form glands like the pancreas, salivary glands, etc., and help produce enzymes, hormones, etc.
Adipose cells, some liver cells, store materials like fat for later use. This fat is consumed in times of starvation and excess cold temperatures.
These are the cells that are present as support to adjacent cells.
Ex: The Glial cells present in the brain and spinal cord nourishes the nerve cells and 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 with 23 chromosomes (i.e., have only one set of a chromosome).
- They are present only in males after puberty in the seminal vesicles.
- These cells have a tail that enables them to swim and move in the female uterus.
- They also release an enzyme hyaluronidase, which helps them penetrate through uterine tissue and reach the oocytes.
- Cells are haploid and present in the adult female genital system.
- They are also haploid, like the 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 parent cells that can differentiate into any other body cell when required.
- These stem cells have gained prominence due to their promising role in the treatment of diseases.
d) Rods & cones of eyes
- These cells are present exclusively in the retina of the eye.
- They contain photosensitive pigments that help to capture the light and convert it into a nerve impulse.
e) Ciliated cells
- These cells are present in the lining of the respiratory tract and esophagus and have threadlike cilia, which move in one particular direction.
- Their movement helps in the movement of food from the buccal cavity into the stomach and phlegm and other wastes out of the respiratory tract.
f) Blood cells
- These are quite interesting cells as they are freely moving in the body. Blood cells freely flow in the liquid blood.
- Some of them are not alive (RBCs), while others are alive and have varied shapes like WBC and platelets (spindle shape).
- Further, these WBCs 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 the 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 with many mitochondria and abundant endoplasmic reticulum to help in liver function.
- Unlike other body cells, they are the only ones that 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 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.
- They help to remove trapped residues to keep the filter free of clogging.
Frequently Asked Questions and Answers.
How many cells are present in the human body?
By an estimate, there are 37 trillion cells in our body.
Are there any significant differences between animal and human cells?
How many chromosomes are in a human Somatic cell?
Somatic cells are normal body cells, and it has 46 chromosomes.
Are human cells prokaryotic or eukaryotic?
Human cells are eukaryotic in nature. They have a well-defined nucleus.