Atlas of plant and animal histology

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Glossary: C

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Callose: it is a polysaccharide that covers the walls of plasmodesmata of sieve tubes of plants. The callose cylinder is laid between the plasma membrane and cell wall.

♣ The cell: Extracellular matrix.

Calyciform cell: (or globet cells) it is a type of cell found in some epithelia like the digestive and respiratory epithelia. Calyciform cells are unicellular intraepithelial glandular cells that release mucopolysccharides to the epithelial surface.

Calyptra: see root cap.

Calyx: (of plant flower) it is the group of sepals and petals of a flower.

♣ Plant organs: Flower .

Calyx: (of animal kideneys) it is the inner region of the animal kidneys that gathers the filtrated liquid produced first in the glomerolus of the kindey cortex, and then in the kidney medulla. In turn, kidney calyx drives the filtrate toward the kidney pelvis where ureteres collect the urine.

♣ Animal organs: Excretory system, Kidney .

Capillary: it is a blood vessel with a very small diameter, so small that sometimes is smaller than the size of a red blood cell. The exchange of molecules and gases between the blood and the tissues takes place in capillaries. This is possible because capillaries are composed of a layer of very thin endothelial cells and a basal lamina. Capillaries form large and complex nets that irrigate the organs of the body. This type of irrigation is called perfusion.

♣ Animal organs: Cardiovascular, Capillaries.

Capsule: it is a layer of connective tissue that wraps many organs of the body. The type of connective tissue depends on the organ where the capsule is found.

Carpel: it is a modified leave that form the pistil, or part of the pistil, of flowers. Pistil is the part of the flower that forms the female gametophyte, the macrospore or female gamete, and it is the place where fertilization takes place.

♣ Plant organs: Flower, Ovary , Fruit.

Cartilage: it is an elastic and resistant tissue composed of cells called chondrocytes and special extracellular matrix. Cartilage is a non-vascular tissue. The extracellular matrix contains collagen, elastic fibers, and sulfated glycosaminoglycans. Together with bones, cartilage is one of the main supporting tissues of animals. The extracellullar matrix composition is responsible for this supporting function. Cartilage is semirigid, provides form to many organs, and counteracts mechanical pressures and frictions at the bone joints. During embryo development, when the bone is not yet formed, cartilage is the main supportive tissue.

Casparian band: it is a structure of the cell wall found in the cells of the endodermis, which is found in plant roots. Casparian band is actually a deposition of suberin that form a impermeable barrier so that water and soluble substancias need to pass the endodermis layer by crossing the plasma membrane of endodermis cells. That is, thorugh a symplasty patway.

Cell junction: it is a protein complex found in the plasma membrane of many cells that establish cell-cell adhesion contacts or between cells and extracellular matrix. There are four main a cell junctions: tight junctions (zonula occludens), adherent junctions (macula adherens), desmosomes (zonula adherens) and hemidesmososmes.

Cellulose: it is a polysaccharide found in the cell walls of plant cells. Cellulose is the main component of cell walls. It provides support for organs and aerial parts of the plant body. A cellulose molecule is a long strand of many glucose units linked by beta 1-4 bounds. Cellulose strands make lateral electrical bonds between one another to form very compact cellulose fibrils, that together with pectins and hemicellulose form the cellulose fibers. The orientation of cellulose fibers on the cell surface determines the direction of cell grow, and therefore the growth of the plant organs.

♣ Plant tissues: Introduction, Support.
♣ Plant organs: Lignin.

Centroacinar cell: it is a type of cell found inside pancreatic acini. Centroacinar cells form the initial part of the ducts that collect the released products of the exocrine part of the pancreas. They are faintly colored with common staining techniques.

♣ Tejidos animales: Pancreas .

Cerominous gland: it is a type of gland found in the outer auditory canal. Cerominous glands release substances that mix with the sebaceous gland secretions, forming altogether the cerumen or earwax of the ear.

♣ Animal organs: Senses.

Chalaza: (in plants) it is the region of the embryonary sac that connects the funiculus with the nucella. Funiculus connects the embryonary sac with the placenta.

♣ Plant organs: Seed, Flower.

Chalazomgamy fertilization: (in plants) it is a type of fertilization where the pollen tube enter the ovary through the hilum and crosses the chalaza of the ovule.

♣ Plant organs: Seed.

Chlorenchima: see photosynthetic parenchyma.

Chloroplast: it is an organelle found in the photosynthetic eukaryote cells. Chloroplasts consist of two membranes that delimit the organelle, an inner space or stroma, and many cisterns in the stroma know as thylakoids. Thylakoids form stacks called granum (plural is grana). Chloroplasts are variable in size and shape depending on the cell type and plant species. The major function of chloroplasts is to carry out photosynthesis in thylakoid membranes, where I and II photosystem complexes containing chlorophyll are found. During evolution, chloroplasts have been proposed to be evolved from a cyanobacteria engulfed by ancient eukaryote cells. Those cyanobacteria became chloroplast by endosymbiosis.

♣ Plant organs: Leaf, Dicot leaf.

Chondroblast: it is a type of cell found during developing and formation of cartilage. Chondroblasts synthesize cartilage extracellular matrix and differentiate into chondrocytes, which produce the mature cartilage extracellular matrix.

♣ Animal tissues: Cartilage.

Chondrocyte: it is a type of cell found in cartilage. Chondrocyte is the mature cartilage cell and synthesize the extracellular matrix. When more than one chondrocyte are found in one lacuna they are called isogenous groups.

Chondrogenic cell: it is a type of precursor (undifferentiated) cell that differentiates into chondroblasts. Chondroblasts differentiated into chondrocytes, cells that form the mature cartilage. Chondrogenic cells can be found in the chondrogenic part to cartilage perichondrium.

♣ Tejidos animales: Cartilage, Hyaline cartilage .

Chondroitin sulfate: it is a sulfated glycosaminoglycon found in the extracellular matrix of many animal tissues. Chondroitin sulfate is bound to polypetide chains forming proteoglycans.

♣ Animal tissues: Cartilage, Bone.
♣ Animal organs: Senses.

Choroid: (in the eye; or choroidea coat) it is a layer of eye coats. Choroid is made up connective tissue and contains blood vessels. Choroid is part of the uvea.

♣ Animal organs: Senses.

Cilliary body: it is found behind the iris of the eye. Ciliary body performs two main functions: releases vitreous humor and changes the shape of the crystalline to focus the light on the retina. It links the ora serrata of the choroid to the root of the iris, and is connected to the crystalline by a ligament. The ciliary body shows ring shape, and, in transverse sections, looks like a triangle. It is divided in two components: pars plicata and pars plana. Pars plicata is located close to the crystalline lens and is organized in finger like structures known as ciliary processes, whereas pars plana shows a flattened form. The smooth muscle of the ciliary body is known as ciliary muscle, which controls accommodation by changing the shape of the crystalline lens to focus the light on the retina. The internal part of the ciliary body is dense connective tissue with abundant elastic fibers and blood vessels. The ciliary epithelium is made up of two layers, the inner one is pigmented and releases aqueous humor. The ciliary body, together with the iris, constitutes the uvea.

♣ Animal organs: Senses .

Ciliary epithelium: it is a type of epithelium found in the ciliary body of the eye. Ciliary epithelium is composed of two layers, the inner one is pigmented and produces the aqueous humor.

♣ Animal organs: Senses.

Ciliary ganglion: it is a ganglion of the parasympathetic system that innervates the pupil sphincter to decrease the eye pupil size.

♣ Animal organs: Senses.

Cillium: it is a filliform protrusion of the cell surface. Cilia are cell structures for cell movement and for sensing the environment. Most cilia can move and propel the cells if they are free or move the liquid near the cell surface when the cell is attached to other cells, as in epithelia. It is known that most cilia are also sensory structures. Cillia have been found in practically all cells studied so far. The main scaffold of cilia is called axonem, which is made up of microtubules and connexion proteins. Microtubules are parallel to the long axis of the cilium. There are 11 microtubules per cilium organized as 9 peripheral pairs and 1 central pair. Stereocilia are not a type of cilium, but are specialized microvilli.

Climacteric fruit: (in plants) it is a type of fruit with a very short maturation period. This period of time is called climacterium. Ethylene, a phytohormon, favors this process. Climacteric fruits are, for instances, tomatoes, pears and avocado.

♣ Plant organs: Fruit.

Cochlea: it is a spiraled duct found in the inner ear. The cochlea is connected with the vestibule. The vibrations of bones of the middle ear are transmitted across the vestibule and reach the cochlea. The Corti organ is found in the cochlea. It is a mecanoreceptor for detecting such vibrations and transform mechanical stimuli in electrical signals that are transmitted to the cochlear ganglion, and then to the encephalon for higher and associative processing.

♣ Animal organs: Senses.

Cochlear ganglion: see Corti's ganglion.

Collagen: it is the most abundant molecule of the animal kingdom and it is found in the extracellular matrix of all tissues. Collagen provides resistance against mechanical forces. It is made up of three amino acid chains that associate to form a helical structure. Combination of different amino acid chains gives 28 types of collagen molecules that may organize as fibers, nets, and anchoring elements. More than one type and specific proportions of collagen are found in the different animal tissues.

♣ Animal organs: Senses, Cardiovascular.

Collagen fiber: it is a macromolecular structure found in the extracellular matrix of animal tissues. Collagen fibers are composed of collagen molecules associated in bundles. Collagen types that associated to form bundles are I, II, III, V and XI. The main function of collagen fibers is to resist mechanical forces and therefore they are abundant in those tissues under heavy mechanical stress.

♣ Animal organs: Cardiovascular.

Colateral: (in plants) it is the organization of xylem and phloem in the vascular bundles or tissue. Collaterals can be open and closed.

♣ Plant tissues: Vascular .
♣ Plant organs: Primary stem.

Collenchyma: it is a type of plant tissue often found in growing shoots and leaves. It is not present in roots. Collenchyma cells are long and have primary cell walls showing irregular thickenings. Collenchyma provides stiffness and flexibility to the organ because their cell walls are resistant to mechanical forces. Collenchyma is usually found below the epidermis. There are four types of collenchyma regarding the cell wall thickenings: angular, laminar, lacunar and annular.

Collenchyma cell: it is a type of cell that forms the collenchyma tissue of plants. Collenchyma cells show a thick primary cell wall, with thickenings unequally distributed depending on the type of collenchyma. The thickenings allow cells to resist tensile forces and mechanical stress. Despite the thickness, collenchyma cells are able to become meristem cells since they have non-lignified primary cell walls.

Colloid: (in the pancreas) it is the accumulation of the products released by the follicular cells of the thyroid gland. Colloid occupies the interior of the thyroid follicles. It is mostly composed of thyroglobulin, a precursor protein for the synthesis of the thyroid hormones T3 an T4.

♣ Animal tissues: Thyroid .

Companion cell: (in vascular tissues of plants) it is a type of parenchymatic cell found in vascular tissues, xylem and phloem, and associated to the conducting cells. Companion cells are involved in nurturing conducting cells of the phloem, and they also participate in the loading and unloading of of both xylem and phloem conducting cells

Complex fruit: (in plants) it is a type of fruit develop for the ovary and other parts of the flower. For instance, apples and cucumber.

♣ Plant organs: Fruit .

Compound gland: it is a type of gland with branched excretory duct. Compound glands have secretory units releasing their products into different excretory duct branches, which finally drain to the main excretory duct.

Conducting elements: (in plants; or tracheary elements) they are the conducting cells of the xylem. There are two types: vessels elements and tracheids. They conduct the raw sap. Conducting elements show a thick, hard and lignified secondary wall, without cytoplasm, which is removed during differentiation. Vessels elements and tracheids can be distinguished at light microscopy because the secondary wall show annular, helicoidal, reticular and pitted thickenings.

♣ Plant tissues: Vascular tissue , Metaxylem.

Cone: (in the retina) it is a type of photoreceptor found in the eye retina. Cones are responsible for the perception of colors. Cones are distributed across the photoreceptor layer, but are more abundant in the fovea, where the light is focused.

♣ Animal organs: Senses.

Cork cambium:(or phellogen) it is a secondary meristem found inner to the bark of secondary stems. It is a cylinder or form several plates extending along the stem. The mitotic divisions of cork cambium cells are periclinal and produce bark to the exterior and pheloderm toward the interior of the stem.

♣ Plant organs: Stem, Dicot secondary stem.

Cornea: it is the outer part of the eye, in contact with the air. The cornea is a transparent structure involved in focusing the light that enters the eye and protects the eye surface. The optic properties of the cornea depend on the type and organization of the collagen fibers. It is avascular and therefore it is easily transplanted. The cornea is a layer of tissue consisting in 5 sublayers: corneal epithelium, Bowman's membrane, Stroma, Descement's membrane and endothelium. The corneal epithelium is the outer layer. It is squamous stratified epithelium with many nervous fibers, and a high regenerative capacity.

♣ Animal organs.: Senses.

Corneal epithelium: it is the outermost layer of the five layers that make up the cornea (in the eye). The corneal epithelium is squamous stratified, contains many nerve fibers, is very sensible, and shows a high capacity for regeneration. Laterally, the corneal epithelium is continuous with the conjunctiva epithelium.

♣ Animal organs: Senses.

Corolla: is the name of the set of petals of a flower

♣ Plant organs: Flower .

Cortical fiber: (in plants) it is a type of schlerenchyma cell found in the cortex of stems and branches, usually near the epidermis. They are also known as extra-xylary fibers because are outside the xylem. The main role of cortical fibers is mechanical support of the organ.

Corti's ganglion: (also known spiral or cochlear ganglion) it is a nerve ganglion found in the spiral part of the cochlea. Corti's ganglion is made up of neurons that send the nerve branch innervating the Corti's organ of the inner ear.

♣ Animal organs: Senses.

Cotyledon: it is a leaf primordial found in the embryo of plants. Cotyledons are the first leaves of the plant. Besides photosynthesis, cotyledons are storage organs for early plant development. The number of cotyledons in the embryo divide two broad group of plants: monocotyledonous (monocot) bears one cotyledon and dicotyledonous (dicot) plants have two cotyledons. The insertion point of cotyledons in the stem forms the first node of the stem.

♣ Plant organs: Seed .

Covering epithelium: it is the epithelial tissue that covers both the inner and outer surfaces of the body. Covering epithelium is specialized in protection and exchange of substances and gases, but not in secretion.

♣ Animal tissues: Covering epithelium .

Crystallin: it is a protein found in the eye crystallin. Crystallin account for most of the protein content and provides the optical properties of the crystalline.

♣ Animal organs: Senses.

Crystalline: (in the eye) it is a transparent and biconcave lens found just behind the pupil. Crystalline, together with the cornea, focus the incoming light on the retina. Fibers of the ciliary region determine the exact position and ciliary muscle cells bend the crystalline allowing a proper focus. In the anterior part of crystalline, there is an epithelium made up of cuboidal cells that disappear toward the edges. Thus, the majority of crystalline consists in cells called crystalline fibers. The capsule is a layer of tissue wrapping the crystalline. Crystalline fibers show a high content in crystallin protein, which is characteristic of this structure. Crystallin proteins are responsible for the optic properties of crystalline.

♣ Animal organs: Senses.

Cuticle: (in plants) it is a hydrophobic layer made up of waxes and cutin, which is the main component. Cuticle is laid in the cell wall of the epidermal free surfaces of the aerial organs of the plant body. It prevents water loss, it is thicker in plants of dry regions, inhibit gas exchange with the environment, and protects against pathogens.

♣ Plant tissues: Protection, Epidermis , Trichomes.

Cutin: (in plants) it is macromolecular complex that forms most of the epidermis cuticle of primary stems, leaves, flowers and fruits. Cutin is found in the free surface of the cell wall of epidermal cells. The amount, organization and composition of cutin depends on the plant organ. Cutin is composed of long fatty acids linked by ester bonds. It has a role in preventing the water loss and gas exchange between the plant and the environment. .

♣ Plant tissuesTejidos vegetales: Introduction, Epidermis.

Cytokine: it is a type of plant hormone (phytohormone). Cytokines are synthesized from andenins and stimulate the development of the body plant. They are synthesized in several parts of the plant, such as root apical meristems and in the developing seeds. Cytokines facilitate cell proliferation and inhibit aging and abscission. Their functions are carry out in collaboration with other plant hormones.

♣ Plant organs: Plant hormones.

Cytokinesis: it is the last stage of the cell division. The cytoplasm of the mother cell is strangled and divided in two, leading to two independent new cells. Cytokinesis is driven by actin filaments in animal cells and by microtubules in plant cells.

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