Question

Discuss Morphology of cells and the factor it plays in general function and structure. Select two different cells and discuss the difference between various cells and the role these cells play in specific disease processes.

Answer 1

Humans are made up of trillions of cells — the basic unit of life on earth. In this article, we explain some of the structures found in cells and describe a few of the many types of cell found in our bodies.

Cells can be thought of as tiny packages that contain minute factories, warehouses, transport systems, and power plants. They function on their own, creating their own energy and self-replicating — the cell is the smallest unit of life that can replicate.

However, cells also communicate with each other and connect to create a solid, well stuck-together animal. Cells build tissues, which form organs; and organs work together to keep the organism alive.

Robert Hook first discovered cells in 1665. He gave them their name because they resembled the cella (Latin for "small rooms") where monks lived in monasteries.

Inside the cell

Different cell types can look wildly different, and carry out very different roles within the body.

For instance, a sperm cell resembles a tadpole, a female egg cell is spherical, and nerve cells are essentially thin tubes.

Despite their differences, they often share certain structures; these are referred to as organelles (mini-organs). Below are some of the most important:

A simplified diagram of a human cell.

Golgi apparatus - Mitochondrion - Cytoskeleton Centrosome Membrane Cytoplasm Vesicle hun Ribosome - Nucleolus Nucleus Lysosome Smooth endoplasmic reticulum Rough endoplasmic reticulum

Nucleus

The nucleus can be thought of as the cell's headquarters. There is normally one nucleus per cell, but this is not always the case, skeletal muscle cells, for instance, have two. The nucleus contains the majority of the cell's DNA (a small amount is housed in the mitochondria, see below). The nucleus sends out messages to tell the cell to grow, divide, or die.

The nucleus is separated from the rest of the cell by a membrane called the nuclear envelope; nuclear pores within the membrane allow through small molecules and ions, while larger molecules need transport proteins to help them through.

Plasma membrane

To ensure each cell remains separate from its neighbor, it is enveloped in a special membrane known as the plasma membrane. This membrane is predominantly made of phospholipids, which prevent water-based substances from entering the cell. The plasma membrane contains a range of receptors, which carry out a number of tasks, including being:

• Gatekeepers: Some receptors allow certain molecules through and stop others.
• Markers: These receptors act as name badges, informing the immune system that they are part of the organism and not a foreign invader.
• Communicators: Some receptors help the cell communicate with other cells and the environment.
• Fasteners: Some receptors help bind the cell to its neighbors.

Cytoplasm

The cytoplasm is the interior of the cell that surrounds the nucleus and is around 80 percent water; it includes the organelles and a jelly-like fluid called the cytosol. Many of the important reactions that take place in the cell occur in the cytoplasm.

Lysosomes and peroxisomes

Both lysosomes and peroxisomes are essentially bags of enzymes. Lysosomes contain enzymes that break down large molecules, including old parts of the cells and foreign material. Peroxisomes contain enzymes that destroy toxic materials, including peroxide.

Cytoskeleton

The cytoskeleton can be considered the scaffolding of the cell. It helps it maintain the correct shape. However, unlike regular scaffolding, the cytoskeleton is flexible; it plays a role in cell division and cell motility — the ability of some cells to move, such as sperm cells, for instance.

The cytoskeleton also helps in cell signaling through its involvement in the uptake of material from outside the cell (endocytosis) and is involved in moving materials around within the cell.

Endoplasmic reticulum

The endoplasmic reticulum (ER) processes molecules within the cell and helps transport them to their final destinations. In particular, it synthesizes, folds, modifies, and transports proteins.

The ER is made up of elongated sacs, called cisternae, held together by the cytoskeleton. There are two types: rough ER and smooth ER.

Golgi apparatus

Once molecules have been processed by the ER, they travel to the Golgi apparatus. The Golgi apparatus is sometimes considered the post office of the cell, where items are packaged and labeled. Once materials leave, they may be used within the cell or taken outside of the cell for use elsewhere.

Mitochondria

Often referred to as the powerhouse of the cell, mitochondria help turn energy from the food that we eat into energy that the cell can use — adenosine triphosphate (ATP). However, mitochondria have a number of other jobs, including calcium storage and a role in cell death (apoptosis).

Ribosomes

In the nucleus, DNA is transcribed into RNA (ribonucleic acid), a molecule similar to DNA, which carries the same message. Ribosomes read the RNA and translate it into protein by sticking together amino acids in the order defined by the RNA.

Some ribosomes float freely in the cytoplasm; others are attached to the ER.

Cell division

Cell division is ongoing for our entire life.

Our body is constantly replacing cells. Cells need to divide for a number of reasons, including the growth of an organism and to fill gaps left by dead and destroyed cells after an injury, for instance.

There are two types of cell division: Mitosis and meiosis.

Mitosis

Mitosis is how most of the cells in the body divide. The "parent" cell splits into two "daughter" cells.

Both daughter cells have the same chromosomes as each other and the parent. They are referred to as diploid because they have two complete copies of the chromosomes.

Meiosis

Meiosis creates sex cells, such as the male sperm and female egg cells. In meiosis, a small portion of each chromosome breaks off and sticks to another chromosome; this is called genetic recombination.

This means that each of the new cells has a unique set of genetic information. It is this process that allows genetic diversity to occur.

So, in brief, mitosis helps us grow, and meiosis makes sure we are all unique.

Cell Types

When you consider the complexity of the human body, it is no surprise that there are hundreds of different types of cell. Below is a small selection of human cell types:

Stem cells

Stem cells are cells that are yet to choose what they are going to become. Some differentiate to become a certain cell type, and others divide to produce more stem cells. They are found in both the embryo and some adult tissues, such as bone marrow.

Bone cells

There are at least three primary types of bone cell:

• Osteoclasts, which dissolve bone.
• Osteoblasts, which form new bone.
• Osteocytes, which are surrounded by bone and help communicate with other bone cells.

Blood cells

There are three major types of blood cell:

• red blood cells, which carry oxygen around the body
• white blood cells, which are part of the immune system
• platelets, which help blood clot to prevent blood loss after injury

Muscle cells

Also called myocytes, muscle cells are long, tubular cells. Muscle cells are important for a huge range of functions, including movement, support, and internal functions, such as peristalsis — the movement of food along the gut.

Sperm cells

These tadpole-shaped cells are the smallest in the human body.

They are motile, meaning that they can move. They achieve this movement by using their tail (flagellum), which is packed with energy-giving mitochondria.

Sperm cells cannot divide; they only carry one copy of each chromosome (haploid), unlike the majority of cells, which carry two copies (diploid).

Female egg cell

Compared with the sperm cell, the female egg cell is a giant; it is the largest human cell. The egg cell is also haploid so that the DNA from the sperm and egg can combine to create a diploid cell.

Fat cells

Fat cells are also called adipocytes and are the main constituent in adipose tissue. They contain stored fats called triglycerides that can be used as energy when needed. Once the triglycerides are used up, the fat cells shrink. Adipocytes also produce some hormones.

Nerve cells

Nerves cells are the communication system of the body. Also called neurons, they consist of two major parts — the cell body and nerve processes. The central body contains the nucleus and other organelles, and the nerve processes (axons or dendrites) run like long fingers, carrying messages far and wide. Some of these axons can be over 1 meter long.

Muscle cell Disorders:

Common primary muscle disorders include inflammatory myopathies, including polymyositis, which is characterized by inflammation and progressive weakening of the skeletal muscles; dermatomyositis, which is polymyositis accompanied by a skin rash; and inclusion body myositis, which is characterized by progressive muscle

There are a number of common neuromuscular disorders, according to Dr. Robert Schabbing, chief of neurology at Kaiser Permanente in Denver.

Common primary muscle disorders include inflammatory myopathies, including polymyositis, which is characterized by inflammation and progressive weakening of the skeletal muscles; dermatomyositis, which is polymyositis accompanied by a skin rash; and inclusion body myositis, which is characterized by progressive muscle weakness and wasting. Other common disorders are muscular dystrophies and metabolic muscle disorders, he said. Muscular dystrophy affects muscle fibers. Metabolic muscle disorders interfere with chemical reactions involved in drawing energy from food.Neuromuscular junction disorders impair the transmission of nerve signals to muscles, Schabbing noted.

The most common neuromuscular junction disorder is myasthenia gravis, which is characterized by varying degrees of weakness of the skeletal muscles. Schabbing said. "There are many types of peripheral neuropathies that can be secondary to other medical conditions, such as diabetes, or due to a variety of other causes, including toxins, inflammation and hereditary causes," he said.

Motor neuron disorders affect the nerve cells that supply muscles, Schabbing said. The most recognizable motor neuron disease is amyotrophic lateral sclerosis, or ALS, commonly known as Lou Gehrig's disease.

Blood cell Disorders:

A blood cell disorder is a condition in which there’s a problem with your red blood cells, white blood cells, or the smaller circulating cells called platelets, which are critical for clot formation. All three cell types form in the bone marrow, which is the soft tissue inside your bones. Red blood cells transport oxygen to your body’s organs and tissues. White blood cells help your body fight infections. Platelets help your blood to clot. Blood cell disorders impair the formation and function of one or more of these types of blood cells.

Red blood cell disorders

Red blood cell disorders affect the body’s red blood cells. These are cells in your blood that carry oxygen from your lungs to the rest of your body. There are a variety of these disorders, which can affect both children and adults.

Anemia

Anemia is one type of red blood cell disorder. A lack of the mineral iron in your blood commonly causes this disorder. Your body needs iron to produce the protein hemoglobin, which helps your red blood cells (RBCs) carry oxygen from your lungs to the rest of your body. There are many types of anemia.

• Iron deficiency anemia: Iron deficiency anemia occurs when your body does not have enough iron. You may feel tired and short of breath because your RBCs are not carrying enough oxygen to your lungs. Iron supplementation usually cures this type of anemia.
• Pernicious anemia: Pernicious anemia is an autoimmune condition in which your body is unable to absorb sufficient amounts of vitamin B-12. This results in a low number of RBCs. It is called “pernicious,” meaning dangerous, because it used to be untreatable and often fatal. Now, B-12 injections usually cure this type of anemia.
• Aplastic anemia: Aplastic anemia is a rare but serious condition in which your bone marrow stops making enough new blood cells. It can occur suddenly or slowly, and at any age. It can leave you feeling tired and unable to fight off infections or uncontrolled bleeding.
• Autoimmune hemolytic anemia (AHA): Autoimmune hemolytic anemia (AHA) causes your immune system to destroy your red blood cells faster than your body can replace them. This results in you having too few RBCs.
• Sickle cell anemia: Sickle cell anemia (SCA) is a type of anemia that draws its name from the unusual sickle shape of the affected red blood cells. Due to a genetic mutation, the red blood cells of people with sickle cell anemia contain abnormal hemoglobin molecules, which leave them rigid and curved. The sickle-shaped red blood cells can’t carry as much oxygen to your tissues as normal red blood cells can. They may also become stuck in your blood vessels, blocking blood flow to your organs.

Thalassemia

Thalassemia is a group of inherited blood disorders. These disorders are caused by genetic mutations that prevent the normal production of hemoglobin. When red blood cells do not have enough hemoglobin, oxygen doesn’t get to all parts of the body. Organs then do not function properly. These disorders can result in:

• bone deformities
• enlarged spleen
• heart problems
• growth and developmental delays in children

Polycythemia vera

Polycythemia is a blood cancer caused by a gene mutation. If you have polycythemia, your bone marrow makes too many red blood cells. This causes your blood to thicken and flow more slowly, putting you at risk for blood clots that can cause heart attacks or strokes. There is no known cure. Treatment involves phlebotomy, or removing blood from your veins, and medication.

White blood cell disorders

White blood cells (leukocytes) help defend the body against infection and foreign substances. White blood cell disorders can affect your body’s immune response and your body’s ability to fight off infection. These disorders can affect both adults and children.

Lymphoma

Lymphoma is a blood cancer that occurs in the body’s lymphatic system. Your white blood cells change and grow out of control. Hodgkin’s lymphoma and non-Hodgkin’s lymphoma are the two major types of lymphoma.

Leukemia

Leukemia is blood cancer in which malignant white blood cells multiply inside your body’s bone marrow. Leukemia may be either acute or chronic. Chronic leukemia advances more slowly.

Myelodysplastic syndrome (MDS)

Myelodysplastic syndrome (MDS) is a condition affecting the white blood cells in your bone marrow. The body produces too many immature cells, called blasts. The blasts multiply and crowd out the mature and healthy cells. Myelodysplastic syndrome may progress either slowly or quite fast. It sometimes leads to leukemia.

Platelet disorders

Blood platelets are the first responders when you have a cut or other injury. They gather at the site of the injury, creating a temporary plug to stop blood loss. If you have a platelet disorder, your blood has one of three abnormalities:

• Not enough platelets. Having too few platelets is quite dangerous because even a small injury can cause serious blood loss.
• Too many platelets. If you have too many platelets in your blood, blood clots can form and block a major artery, causing a stroke or heart attack.
• Platelets that don’t clot correctly. Sometimes, deformed platelets can’t stick to other blood cells or the walls of your blood vessels, and so can’t clot properly. This can also lead to a dangerous loss of blood.

Platelet disorders are primarily genetic, meaning they are inherited. Some of these disorders include:

Von Willebrand disease

Von Willebrand disease is the most common inheritedbleeding disorder. It is caused by a deficiency of a protein that helps your blood clot, called von Willebrand factor (VWF).

Hemophilia

Hemophilia is probably the best-known blood clotting disorder. It occurs almost always in males. The most serious complication of hemophilia is excessive and prolonged bleeding. This bleeding can be either inside or outside your body. The bleeding can start for no apparent reason. Treatment involves a hormone called desmopressin for mild type A, which can promote release of more of the reduced clotting factor, and infusions of blood or plasma for types B and C.

Primary thrombocythemia

Primary thrombocythemia is a rare disorder that can lead to increased blood clotting. This puts you at higher risk for stroke or heart attack. The disorder occurs when your bone marrow produces too many platelets.

Acquired platelet function disorders

Certain drugs and medical conditions can also affect the functioning of platelets. Be sure to coordinate all your medications with your doctor, even over-the-counter ones you choose yourself. The Canadian Hemophilia Association (CHA) warns that the following common drugs may affect platelets, especially if taken long-term.

• aspirin
• nonsteroidal anti-inflammatory (NSAIDs)
• some antibiotics
• heart drugs
• blood thinners
• antidepressants
• anesthetics
• antihistamines

• Plasma cell disorders

  There are a large variety of disorders that affect the plasma cells, the type of white blood cells in your body that make antibodies. These cells are very important to your body’s ability to ward off infection and disease.

  Plasma cell myeloma

  Plasma cell myeloma is a rare blood cancer that develops in the plasma cells in the bone marrow. Malignant plasma cells accumulate in the bone marrow and form tumors called plasmacytomas, generally in bones such as the spine, hips, or ribs. The abnormal plasma cells produce abnormal antibodies called monoclonal (M) proteins. These proteins build up in the bone marrow, crowding out the healthy proteins. This can lead to thickened blood and kidney damage. The cause of plasma cell myeloma is unknown.