Cells in the Musculoskeletal System
Blood Cells
Red Blood Cells
Known for their bright red color, red cells are the most rich cell in the blood, accounting for about 40-45 percent of its volume. The shape of a red blood cell is a biconcave disk with a flattened center – in other words, both faces of the disc have shallow bowl-like indentations.
Production of red blood cells is controlled by erythropoietin, a hormone produced primarily by the kidneys. Red blood cells start as immature cells in the bone marrow and after approximately seven days of bulid up are released into the bloodstream. Unlike many other cells, red blood cells have no nucleus and can easily change shape, helping them fit through the various blood vessels in your body. However, while the lack of a nucleus makes a red blood cell more flexible, it also limits the life of the cell as it travels through the smallest blood vessels, damaging the cell’s membranes and depleting its energy supplies. The red blood cell survives on average only 120 days.
Red cells contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbon dioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their color from the hemoglobin.
White Blood Cells
White blood cells protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of your blood.
The most common type of white blood cell is the neutrophil, which is the “immediate response” cell and accounts for 55 to 70 percent of the total white blood cell count. Each neutrophil lives less than a day, so your bone marrow must constantly make new neutrophils to maintain protection against infection. Transfusion of neutrophils is generally not effective since they do not remain in the body for very long.
The other major type of white blood cell is a lymphocyte. There are two main populations of these cells. T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors. Lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials.
Platelets
Unlike red and white blood cells, platelets are not actually cells but rather small fragments of cells. Platelets help the blood clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur. This results in the formation of a fibrin clot, which covers the wound and prevents blood from leaking out. Fibrin also forms the initial scaffolding upon which new tissue forms, therefor promoting healing.
A higher than normal number of platelets can cause unnecessary clotting, which can lead to strokes and heart attacks; however, thanks to advances made in antiplatelet therapies, there are treatments available to help prevent these potentially fatal events.
Known for their bright red color, red cells are the most rich cell in the blood, accounting for about 40-45 percent of its volume. The shape of a red blood cell is a biconcave disk with a flattened center – in other words, both faces of the disc have shallow bowl-like indentations.
Production of red blood cells is controlled by erythropoietin, a hormone produced primarily by the kidneys. Red blood cells start as immature cells in the bone marrow and after approximately seven days of bulid up are released into the bloodstream. Unlike many other cells, red blood cells have no nucleus and can easily change shape, helping them fit through the various blood vessels in your body. However, while the lack of a nucleus makes a red blood cell more flexible, it also limits the life of the cell as it travels through the smallest blood vessels, damaging the cell’s membranes and depleting its energy supplies. The red blood cell survives on average only 120 days.
Red cells contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbon dioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their color from the hemoglobin.
White Blood Cells
White blood cells protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of your blood.
The most common type of white blood cell is the neutrophil, which is the “immediate response” cell and accounts for 55 to 70 percent of the total white blood cell count. Each neutrophil lives less than a day, so your bone marrow must constantly make new neutrophils to maintain protection against infection. Transfusion of neutrophils is generally not effective since they do not remain in the body for very long.
The other major type of white blood cell is a lymphocyte. There are two main populations of these cells. T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors. Lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials.
Platelets
Unlike red and white blood cells, platelets are not actually cells but rather small fragments of cells. Platelets help the blood clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur. This results in the formation of a fibrin clot, which covers the wound and prevents blood from leaking out. Fibrin also forms the initial scaffolding upon which new tissue forms, therefor promoting healing.
A higher than normal number of platelets can cause unnecessary clotting, which can lead to strokes and heart attacks; however, thanks to advances made in antiplatelet therapies, there are treatments available to help prevent these potentially fatal events.
Bone Cells
There are three special types of cells that are found only in the bone. These cell names all start with "OSTEO" because that is the Greek word for bone.
Osteoclasts
Osteoclasts are large cells that dissolve the bone. They come from the bone marrow and are related to white blood cells. They are formed from two or more cells that fuse together, so the osteoclasts usually have more than one nucleus. They are found on the surface of the bone mineral next to the dissolving bone.
Osteoblasts
Osteoblasts are the cells that form new bone. They also come from the bone marrow and are related to structural cells. They have only one nucleus. Osteoblasts work in teams to build bone. They produce new bone called "osteoid" which is made of bone collagen and other protein. Then they control calcium and mineral deposition. They are found on the surface of the new bone.
When the team of osteoblasts has finished filling in a cavity, the cells become flat and look like pancakes. They line the surface of the bone. These old osteoblasts are also called linning cells. They regulate passage of calcium into and out of the bone, and they respond to hormones by making special proteins that activate the osteoclasts.
Osteocytes
Osteocytes are cells inside the bone. They also come from osteoblasts. Some of the osteoblasts turn into osteocytes while the new bone is being formed, and the osteocytes then get surrounded by new bone. They are not isolated, however, because they send out long branches that connect to the other osteocytes. These cells can sense pressures or cracks in the bone and help to direct where osteoclasts will dissolve the bone.
Osteoclasts
Osteoclasts are large cells that dissolve the bone. They come from the bone marrow and are related to white blood cells. They are formed from two or more cells that fuse together, so the osteoclasts usually have more than one nucleus. They are found on the surface of the bone mineral next to the dissolving bone.
Osteoblasts
Osteoblasts are the cells that form new bone. They also come from the bone marrow and are related to structural cells. They have only one nucleus. Osteoblasts work in teams to build bone. They produce new bone called "osteoid" which is made of bone collagen and other protein. Then they control calcium and mineral deposition. They are found on the surface of the new bone.
When the team of osteoblasts has finished filling in a cavity, the cells become flat and look like pancakes. They line the surface of the bone. These old osteoblasts are also called linning cells. They regulate passage of calcium into and out of the bone, and they respond to hormones by making special proteins that activate the osteoclasts.
Osteocytes
Osteocytes are cells inside the bone. They also come from osteoblasts. Some of the osteoblasts turn into osteocytes while the new bone is being formed, and the osteocytes then get surrounded by new bone. They are not isolated, however, because they send out long branches that connect to the other osteocytes. These cells can sense pressures or cracks in the bone and help to direct where osteoclasts will dissolve the bone.
Muscle Cells
There are three basic muscle cell types: the striped, or striated, skeletal muscles that move the bones; the smooth, involuntary muscles that line the blood vessels, stomach, digestive tract, and other internal organs; and the cardiac muscles, which are a cross between the smooth and the striped muscles.
On a basic level, all three muscle cell types are quite alike. If one were to slice through a muscle diagonally, he would find that it resembles a telephone cable. Inside is a bundle of smaller cables, and each bundle surrounds still smaller ones.
Type One
The first and largest bundle is made up of muscle fibers in which there are nerves, blood vessels, and connective tissue. Each fiber is built up from smaller strands called myofibrils, and each myofibril contains interlaced filaments of muscle proteins. Nerve impulses bring about muscle contraction and contraction causes fiber shortening so light and dark fibers become closer together. As contraction of the muscle ends, fibers relax and normal muscle length is once again attained. Specifically, cardiac muscles, found only in the heart, power the action that pumps blood throughout the body.
Type Two
The smooth muscles meanwhile surround or are part of the internal organs. They are concerned with the movements of organs, such as the contractions of the uterus during childbirth. Many parts of the body contain these smooth muscles. Smooth muscle is made up of long, spindle-shaped cells. In most hollow organs, these cells are arranged in bundles organized in an outer longitudinal layer and an inner circular layer. Both cardiac and smooth muscles are called involuntary muscles, because they cannot be consciously controlled.
Type Three
The third of the types of muscles are called skeletal muscles. These carry out voluntary movements and are what ache after exercise. Skeletal muscles are the body's most abundant tissue, comprising about 23% of a woman's body weight and about 40% of a man's body weight.