Red Blood Cells

Red blood cells perform the most important blood duty. A single drop of blood contains millions of red blood cells which are constantly traveling through your body delivering oxygen and removing waste. If they weren't, your body would slowly die.

Red blood cells are red only because they contain a protein chemical called hemoglobin which is bright red in color. Hemoglobin contains the element Iron, making it an excellent vehicle for transporting oxygen and carbon dioxide. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As the blood passes through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bond with the tissue's carbon dioxide or other waste gases, transporting it away.

Over time, the red blood cells get worn out and eventually die. The average life cycle of a red blood cell is 120 days. Your bones are continually producing new blood cells, replenishing your supply. The blood itself, however, is re-circulated throughout your body, not being remade all of the time.

Since the human body is continually making more blood, it is safe for healthy adults to donate blood. The blood is then stored for use in emergency situations. Initially after giving blood, the donor may feel some momentary lightheadedness due to the loss of oxygen-rich red blood cells and blood sugar. The body quickly stabilizes itself. In humans, mature red blood cells are flexible biconcave disks that lack a cell nucleus and most organelles. White Blood Cells

White blood cells (WBCs), or leukocytes, are a part of the immune system and help our bodies fight infection. They circulate in the blood so that they can be transported to an area where an infection has developed. In a normal adult body there are 4,000 to 10,000 (average 7,000) WBCs per microliter of blood. When the number of WBCs in your blood increases, this is a sign of an infection somewhere in your body.

Here are the six main types of WBCs and the average percentage of each type in the blood: Neutrophils - 58 percent Eosinophils - 2 percent Basophils - 1 percent Bands - 3 percent Monocytes - 4 percent Lymphocytes - 4 percent

Neutrophils are the one of the body's main defenses against bacteria. They kill bacteria by actually ingesting them (this is called phagocytosis). Neutrophils can phagocytize five to 20 bacteria in their lifetime. Neutrophils have a multi-lobed, segmented or polymorphonuclear nucleus and so are also called PMNs, polys or segs. Bands are immature neutrophils that are seen in the blood. When a bacterial infection is present, an increase of neutrophils and bands are seen.

Eosinophils kill parasites and have a role in allergic reactions.

Basophils are not well understood, but they function in allergic reactions. They release histamine (which causes blood vessels to leak and attracts WBCs) and heparin (which prevents clotting in the infected area so that the WBCs can reach the bacteria).

Monocytes enter the tissue, where they become larger and turn into macrophages. There they can phagocytize bacteria (up to 100 in their lifetime) throughout the body. These cells also destroy old, damaged and dead cells in the body. Macrophages are found in the liver, spleen, lungs, lymph nodes, skin and intestine. The system of macrophages scattered throughout the body is called the reticuloendothelial system. Monocytes stay in the blood for an average of 10 to 20 hours and then go into the tissues, where they become tissue macrophages and can live for months to years. Neutrophils and monocytes use several mechanisms to get to and kill invading organisms. They can squeeze through openings in blood vessels by a process called diapedesis. They move around using ameboid motion. They are attracted to certain chemicals produced by the immune system or by bacteria and migrate toward areas of higher concentrations of these chemicals. This is called chemotaxis. They kill bacteria by a process calledphagocytosis, in which they completely surround the bacteria and digest them with digestive enzymes. Skin Cells

The skin often mirrors the health of the whole body. The skin is the largest organ of the body and is as indispensable as the body's other major organs. A radiant clear complexion begins with proper nutrition, efficient digestion and assimilation of nutrients by the body and regular elimination. The skin consists of four distinct layers: the epidermis, the basement membrane zone, the dermis and the subcutaneous layer. The skin is an ever-changing organ that contains many specialized cells and structures. The skin functions as a protective barrier that interfaces with a sometimes-hostile environment. The skin is the ultimate vessel for the human body; it receives and transports, accepts and expels according to the body's needs. It is container, defender, regulator, breather, feeler, and adaptor. But success in these roles is not accomplished automatically. As sturdy as it is, the skin requires attention and maintenance to function properly. Without such care, the complex organization of the skin breaks down, making it and the body it protects susceptible to injury and disease. Epidermis The epidermis is the outermost layer and is a microscopic 0.2 mm (8/1000 inch) thick on the face. Thesurface consists of dead cells which are in the process of flaking away and new ones which are growing to take their place. Between the epidermis and dermis lies the basal layer, where new epidermal cells are formed and progress to the surface. It takes approximately twenty-eight days for a new cell to reach the top. Dermis The dermis is usually 1.8 mm (7/1000) thick. It is composed of a fibrous protein called collagen, elastin, which makes the skin supple, and a network of blood vessels, nerves, oil and sweat glands, pores and hair follicles. The function of the skin are as follows:  Physical barrier against friction and shearing forces  Protection against infection, chemicals, ultraviolet irradiation, particles  Prevention of excessive water loss or absorption  Ultraviolet-induced synthesis of vitamin D - Sensible exposure to sunlight synthesizes the production of vitamin D through interaction with ergosterol, a naturally occurring fat found in the skin. Vitamin D absorption helps metabolize calcium and phosphorous, which is important to bone and tooth health.  Temperature regulation - It is also very involved in maintaining the proper temperature for the body to function well.  Sensation (pain, touch and temperature)  Antigen presentation/immunological reactions/wound healing Bone Cells The creation and oversight of bone growth and repair takes a well organized group of specialized bone cells to keep the body healthy and strong. Starting as mesenchymal stem cells, the cells of the bone are developed into one of three main structures, osteoblasts, osteoclasts or osteocytes. Osteoblasts Osteoblasts are the bone cells that create and form new bone. Consisting of a single nucleus, the osteoblast is created in the bone marrow of the body. Osteoblasts binds together to form bone material called osteoid. Osteoid is made up of a mixture of protein and collagen. Once in place, the osteoblasts facilitate the retrieval of minerals such as calcium to form the outer surface of the bone. Osteoclasts Osteoclasts are also produced in the bone marrow and have a similar structure to white blood cells. Instead of producing bone like the osteoblast, osteoclasts dissolve the bone and in the process send calcium into the bloodstream. Unlike the osteoblast, osteoclasts are large cells that combine with other cells during their production. This means that most osteoclast structures have multiple nuclei. Osteocytes Osteocytes have a similar cell structure as osteoblasts, as they are created from osteoblast cells. As osteoblasts create new bone structure, some are transformed into osteocytes and remain underneath the newly created bone surface. This allows the osteocyte to branch out long connectors that allow the osteocytes to communicate with other nearby bone cells. These cells also have the unique ability to sense damage to the bone, and activate osteoclasts and osteoblasts to work to dissolve the affected area and create new bone

Muscle Cells

The two principal functions of muscle are to produce movement and to maintain posture. These functions are achieved by adjusting the length and tension of muscle. In other words, muscle works by contracting. Therefore, when we look at the structure and function of muscle, we see that muscle is designed to contract. There are three basic types of muscle in the human body: skeletal muscle (also called striated muscle), cardiac muscle (the muscle of the heart) and visceral muscle (also called smooth muscle). Skeletal muscle is the most abundant type of muscle. It attaches to bone and so is important in producing movements in our joints and maintaining our posture. Under the microscope, skeletal muscle cells look like long fibres and have a striped (striated) appearance (figure 1). Skeletal muscle cells also have many mitochondria and more than one nucleus. Sometimes special terms are applied to the organelles in muscle cells. For example, the cell membrane is called the sarcolemma, and the cytoplasm is called the sarcoplasm. A network that looks like the endoplasmic reticulum is called the sarcoplasmic reticulum. We generally think of skeletal muscle as being under voluntary control. Cardiac muscle is the muscle of the heart. Under the microscope, cardiac muscle cells also appear striated, however the striations are not as well organized as in skeletal muscle. Cardiac muscle cells are often branched, so that one cell forms connections with several of its neighbours (figure 2). The activity of cardiac muscle is controlled to a large degree by the autonomic nervous system. We generally think of cardiac muscle as being involuntary. Visceral muscle is the muscle which lines our blood vessels and internal organs. Under the microscope, visceral muscle cells do not have the obvious striations of skeletal or cardiac muscle. Hence, it is called smooth muscle. Visceral muscle cells are often relatively short, and usually they each have only one nucleus. We generally think of visceral muscle as being involuntary.

Sperm Cells

Sperm cell is the male reproductive cell that carries the male portion of chromosomes, DNA or hereditary information to be fused with the female egg, or ovum. In humans and many other animal sperm cells, the sperm carries various amounts of hereditary information inside the cell's nucleus. In plants, the sperm cell is much smaller and the sperm nucleus is produced inside pollen. There are also various ways in which sperm can be transmitted to the egg for fertilization. Sperm can be sent to the female egg through sexual intercourse, or through asexual reproduction, meaning the sperm is sent to the egg on the wind, or transmitted by another animal such as birds, bees or other insects. Structure of a Sperm Cell The sperm cell is composed of three main parts: the head, midpiece and tail. The head, with a cap, or acrosome, containing enzymes near the tip, contains the nucleus and all hereditary information needed to successfully reproduce once the sperm cell has fertilized an egg. The head is also used to penetrate the egg. The midpiece contains various pieces of mitochondria which are essential for the sperm to successfully survive on its journey to the female egg. The flagellating tail propels the sperm cell, moving as quickly as possible to reach the egg. Human sperm cells are approximately 10 microns in length, whereas many plant or flower sperm cells can be less than four microns long. In addition, a male animal or plant will often produce hundreds or even thousands of sperm at a time for each time they try to fertilize an egg. Components of a Sperm Cell The nucleus, located on the head of the sperm cell, contains all of the necessary components for successful reproduction. In human and animal sperm, the nucleus contains various amounts of DNA and chromosomes that fuse together with similar DNA and chromosomes inside the female egg once the sperm has successfully fertilized the egg. Sperm cells have a limited life span. In humans they can survive up to three days inside the female reproductive system; however many of them die off very quickly, sometimes within a few minutes, or a few hours.

Fat Cells

While it may seem fitting to think of fat cells as lazy globs that take up room in the body, this is actually not the case. In fact, an article published in the "Washington Post" describes fat cells as "extraordinarily dynamic, complex and influential entities that affect a staggering array of crucial bodily functions." Clearly, fat cells do more than most of us realize. Warmth Fat cells, which are categorized as either brown or white, form a thick layer of insulation around the entire body. Brown cells in particular serve to produce heat for keeping the body warm. According to a "USA Today" article by Nanci Hellmich, scientists once thought these brown cells were found only in babies. However, these cells have since been found in adults as well, though in much smaller quantities than the widespread white cells. Protection In addition to providing insulation, fat cells serve to surround and protect vital organs and tissues, like the heart, kidneys, intestines, lymph nodes and genital organs. They also exist between the joints to prevent the bones from rubbing together. Storage A primary function of white fat cells is to store extra fats received from digested food. Ideally, these fats are saved for later and turned into energy for the purpose of exercising. When these fat stores are not depleted, the cells become larger and larger as the body continues to store fat. Obesity occurs when the body has stored more fat than is healthy. Regulating Body Functions Fats work to regulate the amount of energy that is burned during a given activity. If the fat cells receive signals that the body needs more fuel, they will metabolize some of their stored fat into energy for the body. Fat cells also help control the immune system, kicking it into high gear when the body is being threatened by a disease. When the fat cells are small, they produce a hormone known as andiponectin, which serves to regulate blood sugar and help prevent heart disease. However, enlarged fat cells do not produce this hormone, which is why many people who are overweight develop diabetes and heart disease. Smoothing Fat fills the sharp angles between the muscles and bones, giving the body a smoother, more attractive appearance. Fat cells, combined with hormonal and genetic factors, determine the size and shape of a person's body.

Nerve Cells

A nerve cell, or neuron, is the basic unit of the nervous system. It transmits information to and from the brain. The structure of a neuron allows the transmission to be quick. Types There are several types of nerve cells, including multipolar, bipolar and pseudounipolar. They can be classified as motor, sensory or interneurons. Function Motor neurons send information away from the central nervous system (CNS). Sensory neurons send information toward the CNS. Interneurons send information between motor and sensory neurons. Structure Nerve cells consist of a cell body, axon and dendrites. The cell body contains the nucleus and other cellular compartments. The axon is long and surrounded by a layer of fat. The dendrites are branches from the cell body. Features Axons carry information away from the cell body. Dendrites carry information toward the cell body. The cell body processes information and maintains the nerve cell by producing proteins. Transmission The space between nerve cells is called the synapse. For information to cross the synapse, chemicals are released from one nerve cell and interact with the next nerve cell.