Glossary: B
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
Bark: (in plants) see peridermis
Basal cell: (in taste buds) it is a type of cell found in the basal part of taste buds. Basal cells are located peripheral and near the basal lamina of taste buds, and they are supposed to be adult stem cells for renewing the other two types of taste bud cells: sensory cells and support cells.
Basal lamina: it is a type of extracellular matrix that is organized as a very thin layer separating the connective tissue from other tissues like epithelium and muscle cells. Type IV collagen, laminin, perlecan and entactin are abundant in the basal lamina, and form a net-like structure.
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,Basophil: It is a type of granular leukocyte found in the blood. Basophils contain one nucleus with 2 or 3 lobes. The nuclear lobes are closer to one another than those of eosinophils and neutrophils. Heterochromatin is abundant in the nucleus. There are many azurophilic granules in the cytoplasm stained with acidophilic dyes, so they get a bluish-purple color. In humans, basophils are smaller than eosinophils. The main function of basophils is to protect against pathogens because they can carry out phagocytosis. They can quite the blood stream and move through tissues. Basophils are the less abundant type of leukocyte in the blood.
.Berry: it is a type of fleshy fruit that may be formed by a cutinized exocarp and a fleshy mesocarp and endocarp. For example, tomato and watermelon.
Beta cell: it is a type of cell found in the Langerhans islets of the pancreas. Beta cells release the insulin hormone, which regulates the concentration of glucose in the blood.
Blade: (in plants) it is the larger par of the leaf, where photosynthetic parenchyma and most stomata are found. Most photosynthesis, transpiration and gas exchange are carried out by the blade. The shape and size of the blade is variable in the leaves of different plant species.
.Blind spot: (in the eye) it is the place of the retina through which the axons of the ganglion cells cross the photoreceptors layer. Thus, the blind spot lacks photoreceptors and therefore is a blind region of the retina. We are not awareness of this blind spot in our vision field because our brain "hide" it.
Blood: it is regarded as one of the specialized connective tissues. Blood consists in cells (erythrocytes and leukocytes), platelets and plasma. These components travel inside the blood vessels propelled by the heart and the body muscles. The function of the blood is to communicate the different parts of the body and distribute oxygen, carbon dioxide, nutritive substances, hormones, and waster substances. Cell involved in the immune responses travel as part of the blood.
Blood plasma: it is the liquid part of blood, where blood cells are immersed. Blood plasma is a complex liquid substance that is up to 55 % of the blood volume. It mostly consists of water, ions and proteins, but carbohydrates and lipids are also present. Blood plasma transport the nutrients and waste substances of tissues.
Bone canaliculi : they are ducts of the bone tissue that communicate neighbor bone lacunae, where osteocytes are found. Cellular extensions of osteocytes run inside these canaliculi that allow direct cell-cell communication.
.Bone labyrinth: it is the set of canals found in the head temporal bone that form the inner ear: the semicircular canals, vestibule and cochlea.
.Bone lamella: it is a layer or strip of bone extracellular matrix that can be observed in compact bone. Compact bone is made up of many bone lamellae. Bone lamellae are concentric in osteonic bone and organized in long paralell strips in non-osteonic compact bone. Osteocytes and bone canalliculi are visualized in bone lamellae.
Bone marrow: it is the gelatin-like tissue found in the cavities of bones. There are two types of bone marrow: red and yellow. Red bone marrow produce the cells of the blood. It is located in the cavities of the spongy bone and in medullary cavities of the diaphysis, where the red bone marrow is replaced by the yellow bone marrow. The yellow bone marrow is mostly composed of adipocytes.
,Bone tissue: it is a type of specialized connective tissue. Bone tissue is the major support tissue in vertebrate animals thanks to its hard and strong extracellular matrix. Bone tissue forms the bones that are the components of the skeleton. Osteocytes are typical cells of the mature bone. There are two main types of bone: compact and spongy. The spongy bone contain cavities with many cells mainly involved in hemopoiesis, which form the bone marrow.
Bone trabecula: it is the hard part of the spongy bone. Trabeculae are made up of bone extracellular matrix and osteocytes, organized in lamellas. Bone trabeculae are abundant in flat bones and epiphysis of large bones. Besides the supporting role, bone trabeculae limit the vascular lacunae that contain the hematopoietic cells of the bone marrow.
Bowman's gland: it is a type of gland found in the olfactory epithelium that releases mucous substances that cover the olfactory epithelium.
Bowman's membrane: it is a membrane found under the epithelium of the cornea (in the eye). Bowman membrane is a layer of tissue containing collagen, but not elastic fibers. Some mammals species lack this membrane.
.Bractea: modified leave associated to the basal part of the flower.
Brown fat: it is a type of adipose tissue made up of multilocular adipocytes (brown adipocytes), which contain many small lipid droplets in the cytoplasm. The brown color is a consequence of the high number of mitochondria in the adipocytes and blood irrigation. The main function of brown fat is to produce heat. Brown fat is most abundant during fetal and perinatal periods in mammals, but it is scarce in adults.
.Bulliform cell: it is a type of cell found in the leaves of some plants like monocot species. Bulliform cells are large epidermal cells that can modify their size by turgor pressure and then change the folding and unfolding of leaves depending on the environmental water availability.
Bundle sheath: it is a group of cells, usually sclerenchyma cells, that surrounds the primary vascular bundles. In the leaf, the bundle sheath consists of parenchyma cells.