EXPLANATIONS AND MEANINGS ABOUT WORDS AND EXPRESSIONS YOU WILL FIND IN THE TEXT OF MOL
| Acidophylic | A component of the cell or of the extracellular matrix that shows affinity to so called “acid” stains. They are usually structures or organelles that contain many proteins. Examples, the cytosol, mitochondria, collagen fibers. Examples of “acidic” stains and of stains that behave as such: eosin, floxin, orange G. |
| Afferent and efferent | An afferent structure (such as an artery or a nerve) reaches another structure or organ, carrying some substance, material or some information (e.g. blood, a nervous impulse). An efferent structure has the opposite meaning: it leaves an organ carrying out a fluid, an information (e.g. a hormone) or a nervous sensorial impulse. Lymph nodes, for example, receive lymph by afferent lymphatic vessels and send lymph away by efferent vessels. |
| Acinus | Acinus is one of the types of secretory units found in exocrine glands. It is spherical or ellipsoidal and composed of cone-shaped, columnar or cylindrical secretory cells. At the center of the acinus exists a narrow space, called lumen, often hard to visualize in sectons under the optical microscope. See also: secretory unit. |
| Apical (region or surface) | Used mainly regarding epithelial cells to indicate their region or surface oriented to or in contact with a cavity, often a lumen. The apical membrane refers to the plasma membrane of the cellular apical surface. This surface is also often called the free surface of the cell. See also<>Basal and Polarity. |
| Technical artifacts | Any artificial and involuntary modification or distortion introduced in the structure of cells and tissues during the procedures used to obtain hystologcal sections. |
| Avascular | A structure that does not directly receive blood vessels for oxygen and nutrients. It depends on the diffusion of these substances from neighbouring blood vessels. Most epithelia are avascular. |
| Basal (region ou surface) | As opposed to apical, refers to the base of a cell. Used often regarding epithelial cells, to indicate the cell region next to the basal membrane. This area of secretory cells has frequently a large amount of granular (or “rough”) endoplasmic reticulum, also called ergastoplasm. Basal membrane or surface is the region of the plasma membrane that covers the basal region of a cell. Be carefull not to confuse the basal plasma membrane with the extracellular basal lamina (also sometimes called basal membrane). This is an extracellular lamina composed of several macromolecules, such as collagens. See also Apical and Polarity. |
| Baso-lateral surface | Refers to cell surfaces situated in the basal and lateral regions of epithelial cells. The basal suface and the lateral surface of these cells are often continuous, hence the name. . |
| Basophylic | As opposed to acidophylic, a component of cells or of the extracellular matrix that shows an affinity to so called basic stains. Basophilic structures usually contain many acid components. Examples of basophilic structures: the nucleus, the nucleolus, the cartilagineous extracellular matrix. Examples of basic stains or stains that behave as such: hematoxylin, toluidine blue. |
| Excretory duct | A small duct or tubule that conducts the secretory product of exocrine glands from the secretory unit to the body surface or to an internal cavity of the body. |
| Endocytosis | Entry of small amouts of liquid into the cells by means of small vesicles formed at the cell surface. The vesicles are thereafter released from the cell surface and are transported along the cytoplasm and their content distributed in the cytoplasm. |
| Endothelium | A simple, one-layered squamous epithelium that covers the internal surface of blood and lymphatic vessels. |
| Stroma | Refers to the group of cells and extracellular matrix that support a tissue or organ, as opposite to the parenchyma of an organ. |
| Exocytosis | Exit of substances from a cell, by transfer across their plasma membrane or inside small cytoplasmic vesicles that fuse with the plasma membrane and lauch their contents into the extracellular space. |
| Mucous gland | A gland the secretes a viscous or sticky secretion, composed by large amounts of mucins. The cells of these glands usually show a faintly stained basophylic cytoplasm and darkly stained nuclei with very dense chromatin. These nuclei are placed next to the basal cell membrane. Their secretory units are single or often branched tubules (as opposed to the acinar secretory units, that are almost ever unbranched). |
| Serous glands | Glands characterized by a fluid secretion (as opposed to the mucous glands) and often composed mainly by proteins. Their cells stain well by acydophylic stains and contain secretory granules. In some of the serous glands (e. g. the pancreas) their basal cytoplasm stains strongly with basophylic stains. Their secretory units are usually acinar, not tubular. |
| Hilum | The region of the surface of an organ where blood and lymphatic vesels, nerves, excretory ducts and other structures (e.g bronchi) enter or leave the organ. |
| Basal lamina | A very thin extracellular layer of macromolecules that supports most epithelial cells and that also covers other structures such as muscle cells and nerve fibrils. Unless it is unusually thick (as it happens in some pathological conditions), the basal lamina can not be observed with a light microscope, only with electron microscopes. |
| Lamina propria | In the digestory, respiratory, urinary systems it refers to a layer of loose connective tissue that supports their surface epithelial lining. |
| Lumen | Is the central cavity of hollow organs and structures, such as the intestines (intestinal lumen), blood vessels and lymphatic vessels, secretory units of glands, excretory ducts, etc. |
| Mucosa or mucous membrane | The surface epithelium associated to connective tissue that line internally the surface of hollow organs of the digestory, respiratory and uro-genital systems. The connective tissue is also called lamina propria. Do not confuse with mucous glands. |
| Serosa or serosal membrane | Is formed by a very thin layer of flat epithelial cells, called mesothelial cells, placed over connective tissue. They line the large internal cavities of the body – pleural, peritoneal and pericardial cavities. Do not confuse with serous glands or serous acini. |
| Mesentery | A thin membrane formed by epithelial cells and connective tissue tnat binds most digestive organs to the internal abdominal wall. |
| Mesothelium | A very thin one-layered flattened epithelium that lines the serous membranes. See Serous membrane. |
| Metachromasia | The property of certain stains to colour structures in a different colour of the stain. This happens, for example, when a great amout of molecules of certain structures are arranged in specifical manners, for example in parallel. An example: toluidine blue stains the nuclei and the granular endoplasmic reticulum in blue, however stains the granules of mast cells in purple. |
| Microvilli | Short tubular finger-like expansions of the cell surface. Most cells own microvilli. They are very numerous in cells very active in absorption of substances, such as the cells that line the intestines. |
| Parenchyma | It refers to the functional part of an organ, as opposed to the stroma – the supportive structure of an organ. The parenchyma is formed by the goup of cells that exert the characteristic functionalities of an organ. For instance: the liver parenchyma is formed by hepatocytes; in the pancreas it is formed by exocrine and endocrine secretory cells. |
| Cortical region | Refers to the perypheral or superficial region of an organ. Cortex is a latin word for the bark of trees. |
| Medullary region | The latin word medulla means something inside or in the middle, and refers to the internal region of some structure or organ. |
| Polarity | This words means that the organelles of many cells (especially of epithelial cells) are distributed in such a way that they are specifically distributed in different areas of the cells. These different regions of the cells therefore execute different cellular functions. Polarized cells also show different features in their surface membranes. |
| Secretory unit | The smallest and basic functional unit, responsible for synthesising secretory products. They are present in most exocrine glands, especially of the digestory, respiratory and uro-genital systems. Each secretory unit is linked to a thin excretory tubulus or excretory duct, through which the secretory product is transported. Acini and mucous tubules are examples of secretory units. |