A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Labyrinth: (related to senses) it is a system of channels and chambers that form the inner ear. There is bone labyrinth and a membranous labyrinth. The bone labyrinth consists in semicircular canals, vestibule and cochlea. Membranous labyrinth is inside the bone labyrinth. Bone and membranous labyrinth are involved in body balance and perceiving sounds.
Lacuna: (in cartilage) it is the cavity where chondrocytes are located surrounded by extracellular matrix. Chondroblasts release extracellular matrix during differentiation. As they become chondrocytes, the extracellular matrix forms a cavity with the cells inside. Cartilage lacunae are typically observed in the hyaline cartilage.
Lacuna: (in bone) it is a cavity where osteocytes are located surrounded by extracellular matrix. Bone lacunae are formed during osteoblasts maturation. Bone lacunae located close enough are connected by bone canliculi, that are channels with osteocytes cellular extensions inside.
Lacunar collenchyma: (in plants) it is a type of collenchyma characterized by large extracellular spaces. Primary cell walls of lacunar collenchyma cells show thickenings that delimit those extracellular spaces.
Lamellar collenchyma: (in plants) it is a type of collenchyma with cells showing primary cell wall thickenings oriented parallel to the surface of the organ. For instance, in the stem, the thickenings are parallel to the stem surface. There are extracellular spaces in the lamellar collenchyma, but not so large as in the lacunar parenchyma. The lamellar collenchyma is also known as tangential collenchyma.
Langerhans cell: it is a type of cell found in the epidermis of animals. Langerhans cells perform immunity roles as antigen presenting cells.
Langerhans islet: it is a group of cells found in the pancreas that forms the endocrine part of this organ. There are many of them in the pancreas. Langerhans islets release hormones, such as insulin by beta cells and glucagon by alpha cells.
Lateral meristem: see secondary meristem.
Laticiferous: (in plants) it is a type of cell that synthesizes and stores latex.
Leaf: (in plants) it is the organ of plants specialized in performing photosynthesis. Generally, a leaf consists in a petiole, which is a stalk connecting the leaf to the stem, and a blade, which is the largest part. The blade contains the photosynthetic parenchyma (mesophyll) with many chloroplasts. Stomata are found in the epidermis of leaves and regulate the exchange of water and gases between the plant and the environment. There are great variability in leaf shape and size depending on the plant species and environmental variables.
Leaf primordium: (in plants) it is a group of cells derived from the stem apical meristem that proliferates and differentiates into a leaf.
Lens fiber: it is a type of cell found in the eye lens. Lens fibers are called fibers because they are very long cells (up to 10 mm) and a few micrometers in thickness. They contain a high amount of proteins and the so-called crystalline protein is the most abundant. The optical properties of the lens depends on lens fibers.
Lenticelle: (in plants) it is a structure found in stems showing secondary grow. Lenticelles allow the exchange of gases between the inner living tissues of the stem and the exterior air.
Leukocyte: it is a type of cell found in the blood. Leukocytes are colorless, unlike the red erythrocytes. Leukocytes are a diverse group of cells that form the defense system of the organism. There are two types of leukocytes: granular (neutrophils, acidophils, and basophils) and agranular (lymphocytes and monocytes). Leukocytes are also known as white cells.
Liber: (in plants) it is the phloem of stem and root. See phloem.
Lignin: (in plants) it is carbohydrate polymer very large and complex that can be found in the plant cell wall. Lignin provides strength and hydrophobicity to the cell wall. This is important in the xylem cell walls because xylem is the main support of plant organs and also is a vascular tissue for conducting water and minerals.
Loose connective tissue: it is a type of connective tissue widely distributed in animals. The loose connective tissue is not a very specialized tissue. It shows few fibroblasts and disorganized extracellular matrix. The function of the loose connective tissue is to facilitate the feeding of other tissues and the communication between each other..
Lymph: it is the aqueous solution that fills the lymphatic vessels. The lymph is similar to blood plasma, and contains proteins, fatty acids and salts. It is originated from the interstitial liquid of tissues. Unlike blood, there are no erythrocytes in the lymph, but leukocytes may be observed.
Lymphatic system: it is a group of organs and vessels conducting a liquid known as lymph. The lymphatic vessels drain the tissue extracellular fluid. The lymphatic system influences the immune system and hematopoiesis.
Lymphatic vessel: it is a type of duct in animals for conducting the lymph. Lymphatic vessels are made up of layers of connective tissue with smooth muscle cells, that are thicker as the vessel diameter increases. As veins, lymphatic vessels have valves to prevent the re-flux of lymph.
Lymphocyte: it is a type of cell found in the blood and other tissues. Lymphocytes are the agranular leukocytes. They show a rounded nucleus that occupies the majority of the cell. Lymphocytes can exit the blood stream and travel through tissues. The immune defense is the main role of lymphocytes. They synthesize the immunoglobulins.
Lysogeny: (in plants) it is a mechanism for producing aeriferous parenchyma. During lysogeny, the large empty spaces between cells are generated by cell death.
Locule: (in plants) it is the chamber of the ovule of the flower that contains the female gametophyte, which in turn contains the egg.
Lunula: it is the crescent-shape white area observed in the growing region of the nails.