Glossary: V
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
Vacuole: it is a cellular organelle found in plant cells, and much less abundant in animal cells. There are vacuoles with different sizes and functions depending on the cell type and differentiation process. Commonly, plant cells contain a large vacuole that fills most of the cytoplasm and functions as store and water pressure regulator. Vacuoles may contain degradation enzymes.
Vagus nerve: (nerve X) it is a peripheral nerve that gathers information from several regions, such as taste buds of larynx and epiglottis.
.Vascular cambium: it is a secondary meristem that produces vascular tissues: secondary xylem and secondary phloem. New secondary xylem cells are placed in the inner surface of the meristem, and secondary phloem cells in the outer surface. This organization is the result of periclinal divisions of the vascular cambium cells.
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Gymnosperm secondary stem.
Vascular fiber: (in plants)(o perivascular fiber) it is a sclerenchyma cell wrapping the xylem and phloem in vascular bundles. Since vascular fibers are not in the xylem, they belong to the extra-xilary fibers group.
.Vascular plant: (in plants) it is the group of plants with tissues specialized in conducting substances along the plant body. These tissues are the vascular tissues: xylem and phloem.
Vascular tunic: (or uvea) it is the middle tunic of the eye.
Vasa vasorum: it is the set of blood vessels that irrigate the walls of the larger blood vessels.
Vegetative nucleus: (in plants) it is one of the haploid nuclei found in the pollen grain. The vegetative nucleus is responsible for the formation of the pollinic tube.
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.Vegetative peripheral nervous system: it is the set of nervous elements that carry information from viscerae and inner organs to the central nervous system and those coming from the central nervous system that innervate the smooth muscles of the inner organs. These are non-voluntary movements.
Vein: (in plants) it is each of the vascular bundle of the leaf blade. The organization of veins may be in parallel, as many monocot plants, or branched and reticulated, as in most dicot plants.
.Vein: it is a type of blood vessel that conducts the blood from the capillary network toward the heart (excepting the portal veins that drive the blood between two organs). Histologically, veins consist in a tunica intima, tunica media and tunica adventitia.
Venous valve: it is formed by folds of the vein wall that prevent the blood to flow in the opposite direction when it is impulsed by gravity or by a smaller pressure.
Ventral root: (in animals) it is a fascicle of nerves that exits the spinal cord ventrally (the anterior part). Ventral roots largely carry motor information to the muscle cells to produce body movements. There are as many ventral roots as spinal cord segments.
Ventricle: (in the brain) it is a type of cavity in the brain (encephalon) that contains the cerebrospinal fluid. There are 4 ventricles: 2 lateral ventricles (I and II) in the cerebral hemispheres, another (III) in the mesencephalon and the last one (IV) in the rhombencephalon. Ventricles are communicated between each other and with the central canal of the spinal cord.
Ventricle: (in the heart) it is a type of cavity of the heart. The contraction of the wall of the ventricle impulses the blood toward the arteries and through the body. There are two ventricles: left ventricle and right ventricle.
Venula: it is a type of vein with small diameter. Venules are divided in postcapillary venules, that get the blood from the capillaries, and muscle venules that connect the postcapillary venules with the veins. The diameter of venules ranks from 0.1 mm (postcapillary venules) to 1 mm (mucular venules). The three tunicae: intima, media and adventitia, can be observed in the muscular veins.
Vessel: (in plants)see trachea.
Vessel element: (in plants) it is a type of cell found in the xylem, a component of the vascular tissue. Vessel elements are aligned in long tubes called vessels or tracheae. Raw sap is conducted through the vessels elements via simplast. Communication between contiguous vessel elements is done through their transversal cell walls, and with other cells by the lateral pit areas.
.Vestibular ganglion: it is a type of ganglion found in the cochlear branch of the vetibulo-cochlear nerve, located outside the inner ear. There are two vestibular ganglia that have cellular processes innervating the receptors in the labyrinth and vestibule of the inner ear. Thus, they carry balance-related information.
Vestibular labyrinth: it is the part of the inner ear encompassing the semicircular canals, sacule and utricle.
.Vestibular system: it is the set of structures that keeps the balance of the body by sensing and processing the movement and gravity. The vestibular system sensory cells are found in the inner ear.
Vestibular window: (or oval window) it is an oval opening of the bone of the ear system that transmits the stape vibrations to the labyrinth of the inner ear.
Vestibule: it is the cavity of the inner ear connected with both the semicircular canals and the cochlea. The vestibule is divided into two subcavities: the sacule and the utriculum.
Vestibulochoclear nerve: (nerve VII; or statoacoustic nerve) it is the nerve that carries information from the inner ear. Vestibulochoclear nerve has two branches: one innervating the labyrinth and vestibule receptors, and another innervating the choclear receptors. The neurons that send these axons are also divided in two ganglia: the vestibular ganglion and the Corti ganglion (also known as spiral or choclear ganglion).
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.Visceral peripheral nervous system: see vegetative peripheral nervous system.
Vitreous body : it is a gel that fills the cavity between the crystalline and the retina. Vitreous body is a gel-like structure showing transparency similar to the glass. It is made up of an aqueous solution containing types II and XI collagen and hyaluronan. It also contains some scattered cells called hyalocytes.
Vitreous humor: it is the substance found between the crystalline and the retina of the eye. The vitreous humor is released by the ciliary body.
.Volkmann's canal: it is a type of canal found in the osteons of the compact bone of some animal species. Volkmann's canals laterally connect neighbor Harvesian canals, allowing blood vessels to branch, reach other Harvesian canals, and irrigate the bone tissue between Harvesian canals.
.Vomeronasal organ: (or Jakobson organ) it is a sensory structure found in the oral cavity of some vertebrate species. The function of the vomeronasal organ is not completely clear yet, but it is suggested that it recognizes pheromones and other airborne large molecules, such as those that indicate potential preys.
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