Tissues, Organs, and Organ Systems - Biology

In response to infection, white blood cells multiply so that they can make antibodies against whatever it is your body is fighting off.

B-lymphocytes are the immune system's "memory"—once the body is attacked by a certain virus or bacteria, the body produces B-lymphocytes that can specifically recognize that disease. When the B-lymphocyte comes in contact with the disease (recognized by antibodies) it signals killer T-cells and helper T-cells to attack, and creates more antibodies to signal additional T-cells.

Natural killer cells destroy any cells of the human body that have become infected by an attacker.

Macrophages are a general clean-up cell that sweep up debris, old cells, and sometimes attackers via phagocytosis.

Killer and helper T-cells are both activated by B-lymphocytes

B cells make antibodies that are specific to antigens. Antibodies bind to antigens to tag them for destruction. Cytotoxic T cells recognize and bind antigens and destroy them immediately. Helper T cells recognize antigens presented by antigen-presenting cells such as dendridic cells, and bring them to the attention of B cells, stimulating the B cells to begin making lots of antibodies.

Innate immunity is defined as the general protection mechanisms from pathogens. Innate immunity will be present even when the body has not seen a specific pathogen. Antibodies are highly specific for one particular antigen, and only develop in the body after previous exposure to a pathogen. As a result, it is not considered innate. Instead, antibodies are considered a hallmark of adaptive immunity.

Physical barriers (like the skin), chemical barriers (like stomach acid), and non-specific immune cells (like phagocytes) help to protect against all pathogens, regardless of the type of pathogen or previous exposure.

Innate immunity is non-specific immunity linked to general defenses in the body. These immune defenses include inflammation and phagocytosis, which are not determined by the specific responses of B- or T-lymphocytes. Physical barriers, such as tight junctions in the skin and the acidity of the stomach and vaginal canal, also act as innate immune mechanisms.

Acquired and active immunity only result from a prior exposure to an antigen. Antibodies are produced by B-cells. Cell-mediated immunity involves the regulatory and cytotoxic activites of T-cells during the specific immune response. Humoral immunity is the term used to describe the protective activities of antibodies against infection by common microorganisms.

The innate immune system is a general defense against infections. Antibodies are very specific to the type of infection they can fight. Thus antibodies are considered specific defense.

Lymphocytes are part of the adaptive (specific) immune system, which monitors and dispatches in response to specific threats. The adaptive immune response utilizes antibody secretions from B-lymphocytes to target specific pathogens for elimination.

In contrast, the innate immune system is largely designed to prevent entry and propagation of non-specific pathogens. It is composed of barriers (such as skin and mucus linings) as well as non-specific immune cells (such as macrophages and natural killer cells).

The innate immune system is the part of your immune system that responds to threats almost immediately. It contains all the aspects which react to all threats and is generally seen as less complex than the adaptive immune system. The adaptive immune system includes aspects that respond to specific threats and develop memory to fight threats later on.

The endothelium is a form of squamous epithelium consisting of flat cells that line the blood and lymphatic vessels. Endothelial cells are metabolically active and produce compounds that relax vascular smooth muscle and inhibit the adhesion of platelets.

Adipose, or fat cells, are modified for long-term energy storage and are considered connective tissue. Cone cells are found in the eye and serve as light receptors for the nervous system. Stem cells can develop into more specifically differentiated daughter cells. Dendritic cells help T-cells respond to foreign antigens as part of the immune system.

An epithelia is a sheet of cells that are closely associated. Cells within an epithelium are polarized, indicating that the cells have a "direction". One side of the epithelium is called "apical" while the other side is "basal." The apical region is oriented toward a lumen, while the basal region is oriented toward a basement membrane associated with connective tissue. Cells within an epithelium are innervated, but not vascularized; therefore, they must receive signals through other methods of intercellular signaling, such as tight junctions.

The epidermis is composed of five layers of flattened epithelial cells. This stratified squamous epithelium allows the skin to be a barrier for the body and prevent pathogens and foreign materials from entering.

Stratified epithelium has multiple layers, and squamous epithelium is flattened.

Epithelium describes the inner and outer surfaces of the body including; the skin, colons, and the stomach. These surfaces have distinct upper and lower sides, are kept in place by connective tissue, and are made up almost entirely of cells. However, they are not supported by blood cells.

Nervous tissues such as the brain, spinal cord, and nerves function to transmit impulses for coordination, sensory reception, and motor actions. Epithelial tissue protects (skin), secretes (glands), absorbs (kidneys), and produces germ cells (embryo).

The primary function of epithelial tissue is to provide linings that separate the body from the external environment. Epithelial tissue lines blood vessels, the respiratory and digestive tracts, the excretory system, and composes the skins. Epithelial tissue also lines the ducts that connect the body to the exterior, such as those that allow the pancreas to secrete enzymes into the small intestine.

Epithelial tissue is avascular (does not have a blood supply); thus epithelial tissue is always found in close association with connective tissue that has a rich blood supply. Epithelial cells cover organs and are thus subject to lots of friction. As a result they are continually being renewed, and divide quickly. In particular, skin cells and the epithelium lining the digestive tract have a high rate of division.

Adipose tissue is the anatomical term assigned to fatty tissue. Keep in mind that adipose tissue is a type of connective tissue. Adipose tissue serves as an energy store, helps maintenain of core body temperature, and protects internal organs from damage caused by trauma. Epithelial tissue is responsible for covering body cavities, and comprising glandular tissue. Nervous tissue is responsible for receiving sensory input from the environment, integration of the sensory input, control of muscles and glands, maintenance of body homeostasis, and emotions/personality. Smooth and striated are subsets of muscle tissue: skeletal and cardiac muscle are striated, whereas smooth muscle is not.

Epithelial tissue forms membranes that cover the body, as well as lines body cavities and glands. Simple squamous epithelium consists of thin, flattened cells, that are one layer thick and allow for the easy movement of substances. This is especially important for gas exchange in the alveoli of the lungs and in the capillaries of the body. The minimal barrier provided by simple squamous epithelium allows molecules to easily diffuse across the membranes.

Stratified squamous epithelium is many layers thick and forms the skin and lining of mucous membranes. Simple cuboidal epithelium functions in absorption and secretion in the kidney tubules and salivary glands. Simple columnar epithelium forms a thick layer that lines the esophagus, stomach, intestines, and uterus. Pseudostratified columnar epithelium possess beating cilia and transport particles in the respiratory tract and reporductive system.

Keratinized stratified squamous epithelium makes up the outer layer of skin. Other types of epithelial tissues are found throughout the digestive and reproductive tracts, and other areas of the body.

Ciliated epithelium are located in the respiratory tract. There are hair-like processes, cilia, located on the surface that wave and function to sweep materials, such as mucous and dust, across the surface. Cuboidal epithelial calls are as high as they are wide. Cuboidal cells line the ducts of glands and organs and function in the absorption and transportation of substances. Squamous epithelial cells are flat and allow substances to freely move across their surface. These cells are located in the lungs and the kidneys. Stratified epithelial cells form layers, with mitosis taking place in the lowest layer. Skin is formed from stratified epithelial cells. Transitional epithelial cells adjust to mechanical changes such as stretching. This type of tissue is found only in the urinary system.