Atlas of plant and animal histology

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Glossary: E


Eccrine gland: it is a type of gland that releases its content directly into the skin surface.

♣ Animal organs: Sweat gland.

Ectoderm: it is one of three primary germ layers of animal embryos. Ectoderm is the germ layer that initially covers the embryo and gives rise to structures such as epidermis and the nervous system.

Elastic artery: aorta and pulmonary arteries, and their primary branches are called elastic arteries. They contain many elastic fibers in their thick walls, that allow to counteract the heart pumping pressure and recover their nomal diameter after an expansion. The tunica media is very thick and contains elastin, collagen and smooth muscle cells.

♣ Animal organs: Cardiovascular, Elastic artery.

Elastic cartilage: it is type of cartilage characterized by the abundant elastic fibers in the extracellular matrix. They provide elasticity and flexibility. Elastic cartilage is found in organs like ears.

♣ Animal tissues: Cartilage, Elastic cartilage

Elastic fiber: is is a type of fiber composed of proelastin, fibrillin and desmosin. Elastic fibers are abundant in the animal tissues under mechanical stress such as dermis and wall of large blood vessels. The role of elastic fibers is to recover the rest state of a tissue after stretching.

♣ Animal tissues: Connective proper .
♣ Animal organs: Cardiovascular.

Elastin: it is a protein found in the extracellular matrix of many animal tissues. Elastin associates with other proteins like fibrillin and desmosin to form the elastic fibers, which provide elasticity to structures like the skin and blood vessel walls. Elastine molecule contains long sequences of hydrophobic amino acids that makes the protein globular under aqueous environment. This feature lets elastin to recover the globular conformation after a mechanical stretch.

♣ Animal tissues: Connective proper tissue .

Encephalon: it is the rostral part of the central nervous system. The encephalon consists in telencephalon, hypothalamus, diencephalon, mesencephalon and rhomencephalon. The encephalon is covered and protected by the cranium. It develops high cognitive functions like thinking, emotions and memory, but also others more basic roles like controlling breathing and cardiac rhythm. It is also a key center of the endocrine system. The encephalon is known as brain.

Endocarp: (in plants) it is the inner layer of the pericarp. The pericarp is the fruit part that covers the seed, and the endocarp is the layer contacting the seed. The endocarp is the hardest part of fleshy fruits and it is made up of support cells like sclereids. However, the endocarp is the softest and juicy part in tomatoes and other fruits.

♣ Plant organs: Fruit , Orange .

Endodermis: (in plants) it is a layer of cells found in primary roots and other aerial parts of plants. Endodermis is made up of cells with primary cell walls containing suberin, which form belt-like thickenings called Casparyan band. In de deeper parto of the roots, endodermis functions as a filter for the incoming substances from the environment, such as water and minerals. These substances must cross the plasma membrane and cytoplasm of the endoermal cells to reach the vascular tissue.

Endoderm: it is one of the three primary germ layers during the embryo development. Endoderm is found in the inner parts of the embryo. For instance, the gut epithelium and gastric glands are derived from the endoderm.

Endolymph: it is the liquid that fills the cavities of the inner ear. It is the movement of the endolymph what is detected by receptors found in the semicircular canal ampullae and in the scala media of the cochlea.

♣ Órganos animales: Senses.

Endomysium: it is the layer of connective tissue that overlays each skeletal muscle cell.

♣ Animal tissues: Muscle tissue , Skeletal muscle.

endoneurium: it is the layer of connective tissue that wraps the myelinated and amyelinated axons in peripheral nerves.

Endosperm: (in plants) it is a storage tissue found in seeds that nurtures the embryo. The endosperm originates from cells of the embryonary sac (female gametophyte), although the mechanism is different in angiosperm and gymnosperms.

♣ Plant tissues: Parenchyma.
♣ Plant organs: Seed , Apple seed .

Endosteum: it is a thin layer of connective tissue covering the cavities of the bone marrow, bone trabeculae surfaces and the inner surface of the Harvesian canals of osteonic bone. In the endosteum, there are also messenchymal cells that function as bone cell progenitors and differentiate into osteoblasts.

♣ Animal tissues: Bone .

Endothelium: it is the layer of simple squamous epithelium that lines the inner surface of blood and lymphatic vessels.

♣ The cell: Membrane: carbohydrates.
♣ Cell types: Endothelial cell. .
♣ Animal organs: Cardiovascular.

Eosinophil: it is a type of granular leukocyte found in the blood and in other tissues, mostly in the connective tissue proper. Eosinophils show a nucleus with two prominent lobes. In the cytoplasm, many eosinophil granules can be visualized, so they contain basified material. These cells work against pathogens and infections, and they can abandon the blood stream and move through connective tissues.

♣ Animal tissues: Blood, Blood cells .
♣ Cell types: Eosinophil .

Ependyma: it is the layer of cells that line the surface of the brain ventricles and the central canal of the spinal cord. The cells that form the ependyma are known as ependymocytes, and sometime there are other cells like tanicytes. Cerebrospinal fluid fills the ventricles and the central canal.

♣ Animal tissues: Nervous tissue, Ependyma .
♣ Animal organs: Spinal cord .

Epidermal ridge: it is a projection from the epidermis of the animal skin toward the underlying dermis. Epidermal ridges are abundant in those regions of the body undergoing heavy mechanical stress, such as palms and soles.

♣ Animal organs: Integument, Thick skyn.

Epicarp: see exocarp

Epicotyl: (in plants) it is the part of the embryo above the insertion point of cotyledons. Epicotyl is the embryonary shoot: first internode, the shoot apical meristem and the leaf primordia.

♣ Plant organs: Seed.

Epidermis: (in animals) it is the stratified keratinized squamous epithelium that form the outer tissue layer of the skin. Epidermis is constantly renewing and performs many functions, such as protection against water loss, pathogens and mechanical insults. Hair, nails, feathers and horns are derived from epidermis.

♣ Cell types: Keratinocytes .
♣ Animal organs: Integument , Thin skin , Thick skin , Nail .

Epidermis: (in plants) it is the layer of cells that separates the inner plant tissues from the external environment. Epidermis is commonly made up of a monolayer of cells in those organs not showing secondary growth. Epidermal cells usually lack chloroplasts. The main function of epidermis is prevents water loos and protects against pathogen and mechanical damages. In roots, epidermis is responsible for the absorption of water and minerals. Stomata are cell structures that regulates the exchange of water and gases between the plant tissues and the external environment.

Epiphysis: (in bones) it is each of the ends of the large bones. Epiphysis mainly consists in trabecular bone surrounded by compact bone.

♣ Animal tissues: Bone

Epiglottis: it is a sheet-like cartilaginous structure found in the posterior part of the mammal tongue. During deglutition, epiglottis covers the glottis.

♣ Animal organs: Senses.

Epimysium: it is the layer of dense connective tissue that surrounds the skeletal muscles.

♣ Animal tissues: Muscle .

Epineurium: it is the layer of dense connective tissue that overlies the peripheral nerves.

♣ Animal organs: Peripheral nerve, Nerve .

Episperm: (or seed coat) it is the layer that wraps the embryo in the angiosperm seeds. Episperm consists in two layers: testa and tegmen. It derives from maturation of the embryo sac integument.

♣ Plant organs: Seed .

Eithelium: (or epithelial tissue) it is one of the four fundamental tissues of animals. The Epithelium is made up of cells arranged in layers. Epithelia are divided in two broad categories: covering and glandular. Epithelium forms polarized sheet with a basal domain in contact with the basal lamina and an apical domain facing the exterior of the body. In epithelial tissues, there are no blood vessels and little extracellular matrix.

Epithem: (in plants) it is a group of cells found in the hydathodes. Epithem cells are originated from parenchyma cells and connect the vascular bundle with the aquiferous stomata of the hydathode.

♣ Plant tissues: Glandular tissue.

Eponychium: it is a fold of the animal integument in the place where the nails begin to be formed. Nail matrix and root are located below the eponychium.

♣ Animal organs: Nail .

Erythrocyte: (red blood cell) it is the most abundant type of cell in the blood. Erythrocytes contain a high concentration of hemoglobin, protein that transports O2 y CO2 between tissues and the lungs. In mammals, erythrocytes lack nucleus and organelles, so they are sometimes not regarded as true cells. Erythrocytes show a biconcave shape with a diameter of about 7 µm. The proportion blood volume occupied by erythrocytes is known as hematocrit. In addition, glycoconjugates associated to the erythrocyte membrane are responsible for the blood types.

♣ The cell: Cell membrane.
♣ Cell types: Erythrocyte .
♣ Animal tissues: Blood, Blood cells .

Ethylene: (in plants) it is gas produced from plant metabolism. Ethylene is synthesized in any part of the body plant. It is particularly abundant in fruits during maturation. Ethylene is regarded as a phytohormone or plant hormone. As it is a gas, it can move through tissues by diffusion.

Excretion: it is the process by which cells or organisms get rid of waste material. It is sometimes difficult to distinguish between excretion and secretion because some excreted substances may be useful for the organism itself.

♣ Plant tissues: Gland tissue, Resiniferous canal.
♣ Animal organs: Excretory system.

Exine: it is the outer layer of the pollen grain.

♣ Plant organs: Seed.

Exocarp: (in plants) it is the outer layer of some fruits. Exocarp, or epicarp, is one of pericarp layers (together with the endocarp and mesocarp). It is the skin of fruits like mango and olive, but not in apples. The exocarp commonly consists in an epidemis and one or several underlying layers of parenchyma or collenchyma.

♣ Plant organs: Fruit , Apple, Orange .

Exocrine gland: es un tipo de glándula que libera sus productos a una superficie libre del cuerpo, como la piel o el epitelio de los tractos respiratorio y digestivo. Los productos suelen ser liberados por un conducto excretor. Las glándulas sudoríparas y la parte exocrina del páncreas son ejemplos de glándulas exocrinas.

External auditory canal: it is a duct of the external auditory system connecting the external environment and the tympanic membrane.

 ♣ Animal organs: Senses.

Extra-xilary fibers: (in plants) it is a type of cell that form the sclerenchyma. Extra-xilary fibers are found in the phloem (phloem fibers), in the cortex (cortical fibers) or around the vascular bundles (perivascular fibers).

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