The San Diego State University Histology Project

Eccrine (EHK-rihn) A type of sweat gland that functions in the maintenance of body temperature.

Ectoderm (EHK-to-derm) One of three primary germ layers in the developing embryo. It gives rise to the nervous system and to the epidermis and its derivatives.

Efferent arteriole (EHF-er-ehnt awr-TER-ee-ol) An arteriole that transports blood away from the glomerulus of a nephron (in the kidney).

Efferent ductules (DUHK-tyoo-ehlz) Small coiled tubes that transport sperm from the rete testis to the epididymis.

Elastic cartilage A type of cartilage (connective tissue) that contains large numbers of elastic fibers in a more opaque matrix. It is present in the external ear, and in parts of the larynx.

Elasticity (ee-lahs-TIH-sih-tee) The physiological property of tissue to return to its original shape after extension or contraction.

Embryo (EHM-bree-o) In the human, it is the developing organism during its first eight weeks of life following fertilization.

Enamel (ee-NAHM-ehl) The hardened outer covering on the crown of a tooth.

Endochondral ossification (ehn-do-KOHN-drawl ohs'-ih-fih-KA-shuhn) The development of bone such that bone tissue forms in replacement of hyaline cartilage.

Endocrine gland (EHN-do-krihn gland) One of two main categories of glands, in which the products are secreted into the extracellular space and transported by the bloodstream. Also called ductless glands.

Endocytosis (ehn'-do-sih-TO-sihs) The active process of bulk transport of material into a cell. It includes phagocytosis and pinocytosis.

Endoderm (EHN-do-derm) One of the three primary germ layers in an embryo, it begins as the inner layer and later forms the organs of the alimentary canal and the respiratory tract.

Endometrium The innermost layer of the uterine wall. The endometrium undergoes changes in response to female hormones, resulting in a 28-day cycle involving menstruation during which much of the endometrium is sloughed off to be rebuilt again.

Endomysium (ehn'-do-MI-see-uhm) The deepest layer of connective tissue associated with a muscle. It surrounds individual muscle fibers.

Endoneurium (ehn'-do-NYOO-ree-uhm) The deepest layer of connective tissue associated with a nerve. It surrounds individual nerve fibers (myelinated axons of neurons).

Endoplasmic reticulum (ehn'-do-PLAHZ-mihk reh-TIHK-yoo-luhm) (ER) A cytoplasmic organelle that consists of a series of tubules with a hollow center. It functions in the transport of cellular products (smooth ER), and as a site for protein synthesis (if ribosomes are attached, called rough ER).

Endosteum (ehn-DO-stee-uhm) A membrane lining the medullary cavity within a bone and containing osteoblasts and osteoclasts.

Endothelium (ehn'-do-THEE-lee-uhm) A layer of simple squamous epithelium lining the inside of blood vessels and the heart chambers.

Eosinophil (ee'-o-SIHN-o-fihl) A type of granulated white blood cell characterized by a cytoplasm that accepts the eosin stain.

Ependymal (eh-pehn-DI-mahl) cells A type of neuroglial cells in the brain that line the ventricles. Also called ependymocytes.

Epicardium (ehp'-ih-KAWR-dee-uhm) The thin outer layer of the heart wall. Also called the visceral pericardium.

Epidermis (ehp'-ih-DERM-ihs) The superficial layer of skin composed of stratified squamous epithelium.

Epididymis (ehp'-ih-DIHD-ih-mihs) An organ in the male reproductive system that consists of a coiled tube located within the scrotum.

Epiglottis (ehp'-ih-GLOHT-ihs) A part of the larynx that consists of a leaf-shaped piece of hyaline cartilage that forms a movable lid over the opening into the trachea, called the glottis.

Epimysium (ehp'-ih-MI-zee-uhm) The outer layer of connective tissue associated with muscle, it surrounds the whole muscle. Also called deep fascia.

Epineurium (ehp'-ih-NYOO-ree-uhm) The outermost layer of connective tissue associated with a nerve. It surrounds the whole nerve.

Epiphyseal (ehp'-ih-FIHZ-ee-awl) line A line of calcified bone visible in a section through bone that is the remnant of the epiphyseal plate.

Epiphyseal plate A region of cartilage between the epiphysis and diaphysis that produces lengthwise growth of a bone.

Epiphysis (eh-PIHF-ih-sihs) The end of a long bone that contains spongy bone tissue.

Epithelial (ehp'-ih-THEE-lee-awl) tissue One of four primary tissue types, it is characterized by a close arrangement of cells with little intercellular material. Also called epithelium.

Eponychium (ehp'-o-NIHK-ee-uhm) A narrow region of stratum corneum at the proximal end of a nail. Also called cuticle.

Erythrocyte (eh-RIHTH-ro-sit) A synonym for red blood cell.

Esophagus (eh-SOHF-aw-guhs) A tubular segment of the alimentary canal between the pharynx and the stomach.

Excretion (ehk-SKREE-shuhn) The process by which metabolic waste materials are removed from a cell, a tissue, or an entire body.

Exocrine (EHK-so-krihn) gland One of two main categories of glands, in which the products are released into ducts that transport them to the body surface or into body cavities.

Exocytosis (ehk'-so-sih-TO-sihs) The active cellular process by which materials are transported out of a cell and into the extracellular environment.

External auditory canal The epidermal-lined tube of the external ear extending from the auricle to the tympanic membrane. It passes through the hole in the temporal bone called the external auditory meatus.

External ear The outer part of the ear, which consists of the appendage known as the auricle, the external auditory canal, and the tympanic membrane.

Extracellular environment (ehk'-strah-CEHL-yoo-lawr ehn-VI-rohn-mehnt) The body space outside the plasma membrane of cells.

Extracellular fluid (ECF) The fluid outside the plasma membrane of cells, including interstitial fluid and blood plasma.

Fascia (FAWSH-ee-aw) A sheet or band of dense connective tissue that structurally supports organs and tissues. Deep fascia surrounds muscle, and superficial fascia separates the skin and muscle layers.

Fascicle (FAWS-ih-kuhl) A bundle of skeletal muscle fibers (cells) that forms a part of a muscle.

Fat A lipid compound formed from one molecule of glycerol and three molecules of fatty acids. It is the body's most concentrated form of energy, and also serves to insulate from external temperature changes. It is stored within cells comprising adipose tissue.

Fetus (FEE-tuhs) The early developmental stage from eight weeks after fertilization to the time of birth.

Fibrin (FI-brihn) An insoluble protein in the blood that is formed from fibrinogen and is required for blood clotting.

Fibrinogen (fi-BRIHN-o-jehn) A large plasma protein that plays an important role in blood clotting: it is converted to fibrin by thrombin.

Fibroblast (FI-bro-blahst) A large cell in connective tissue that manufactures much of the extracellular material.

Fibrocartilage A type of cartilage (connective tissue), which is distinguished from other cartilages by the small size and numbers of chondrocytes and lacunae, differential staining, and close resemblance to dense regular connective tissue. It is found in the intervertebral discs.

Fibrous tunic The outer wall of the eyeball that is composed of dense connective tissue, it contains the sclera and the cornea.

Flagellum (flaw-JEHL-uhm) A single, long extension of a cell composed of protein filaments to provide mobility. In human cells, it is found only in sperm cells.

Fovea centralis (FO-vee-aw cehn-TRAWL-ihs) The region of the retina that consists of cone cells but no rod cells, it is the area of highest visual acuity (sharpness of vision).

Frontal plane A plane that extends in a verticle direction dividing the human body into front (anterior) and back (posterior) portions. Also called the coronal plane.

Fundus A large, expanded compartment within the stomach that serves as a temporary storage area for ingested food material.

Gallbladder (GAWL-blahd-er) A small saclike organ located beneath the liver that stores bile.

Gamete (gah-MET) A sex cell. It may be male (sperm cell) or female (oocyte).

Ganglion (GANG-lee-ohn) A cluster of neuron cell bodies located outside the central nervous system.

Gastric (GAHS-trihk) gland Any one of several types of glands in the stomach mucosa that contributes to the gastric juice.

Germinal (JER-mih-nawl epithelium A layer of epithelial cells covering the ovaries.

Gestation (jehs-TA-shuhn) The period of development prior to birth.

Gland A specialization of epithelial tissue to secrete substances. It may consist of a single cell or a multicellular arrangement.

Glandular epithelium A type of epithelial tissue whose primary function is secretion, and is the prominent tissue forming endocrine and exocrine glands.

Glomerulus (glo-MEHR-yoo-luhs) One of many specialized capillary networks located in the kidney cortex, each of which is encapsulated by a Bowman's capsule. It is part of the kidney nephron, and is the site of kidney filtration.

Goblet cell A unicellular gland often in the shape of a goblet that secretes mucus. Also called a mucus cell.

Golgi apparatus (GOL-jee ahp'-ah-RAHT-uhs) A cellular organelle characterized by a series of flattened, hollow cisternae. It serves as a site of anabolic activities.

Gonad (GO-nahd) An organ that produces gametes and sex hormones. In the male it is the testes, and in the female it is the ovaries.

Graafian follicle: A mature ovarian follicle that contains a single oocyte. The Graafian follicle secretes the female hormone estrogen. Following ovulation, it changes form to become the corpus luteum, which produces progesterone.

Gray matter Nerve tissue in the brain and spinal cord that contains neuron cell bodies, dendrites, and nonmyelinated axons, and therefore appears gray or non- white in color.

Gustation (guhs-TA-shuhn) The sense of taste.

Gustatory organ A special sensory organ that contains chemoreceptors providing the sense of taste, or gustation. Also known as taste buds, they are mainly located on the tongue and embedded within papillae.

Hair A threadlike outgrowth of the skin that is composed of columns of keratinized cells.

Hair follicle A cluster of epithelial tissue surrounding the root of a hair where the hair originates.

Haversian system (see osteon).

Heart The hollow muscular organ within the thoracic cavity that propels blood through the circulatory network.

Hematocrit (hee-MAHT-o-kriht) The percentage of red blood cells in a sample of blood, which is determined by centrifuging the sample and measuring the red blood cell volume relative to other blood components.

Hematopoiesis (heem'-ah-to-poy-EE-sihs) The production of blood cells in the red bone marrow. Also called hemopoiesis.

Hemoglobin (HEE-mo-glo-bihn) A complex protein in red blood cells involved in the transport of oxygen and carbon dioxide.

Hemolysis (hee-MOHL-ih-sihs) The bursting of a red blood cell resulting from disruption of the plasma membrane by toxins, freezing or thawing, or exposure to a hypotonic solution.

Hemostasis (hee'-mo-STA-sihs) The stoppage of bleeding.

Hepatic (heh-PAHT-ihk) Pertaining to the liver.

Hepatocytes Liver cells.

Histology (HIHS-toh-lo-jee) The microscopic study of tissues.

Horizontal plane A plane that extends perpendicular to the length of the body dividing it into superior and inferior portions. Also called transverse plane.

Hormone (HOHR-mon) A substance secreted by endocrine tissue that changes the physiological activity of the target cell.

Hyaline cartilage A type of connective tissue that contains chondrocytes embedded within lacunae, both of which are surrounded by a dense, semitranslucent matrix of collagen fibers and glycosaminoglycans. Hyaline cartilage is found in tracheal and bronchial walls, the costal cartilages, the nose, and the larynx.

Hyperplasia (hi'-pehr-PLA-zee-aw) An increased production and growth of cells beyond normal limits.

Hypertonic (hi'-pehr-TOHN-ihk) The state of a solution having a greater concentration of dissolved particles than the solution it is compared to.

Hypertrophy (hi'-PEHR-tro-fee) The abnormal enlargement or growth of a cell, tissue, or organ.

Hypodermis (hi'-po-DEHRM-ihs) The area of the body between the dermis of the skin and skeletal muscle.

Hyposecretion (hi'-po-see-KREE-shuhn) The diminished secretion of a product by a gland.

Hypothalamus (hi'-po-THAHL-aw-muhs) The small, inferior portion of the diencephalon in the brain. It functions mainly in the control of involuntary activities, including endocrine gland regulation, sleep, thirst, and hunger.

Hypotonic (hi'-po-TON-ik) The state of a solution having a lower concentration of dissolved particles that the solution it is compared to.

Ileum (IHL-ee-uhm) The distal segment of the small intestine.

Inferior (ihn-FER-ee-or) A directional term describing a location further from the head than something else.

Infundibulum (ihn'-fuhn-DIHB-yoo-luhm) The narrow connection between the hypothalamus of the brain and the pituitary gland. Also, the funnel-shaped distal end of the uterine tube that opens near an ovary.

Integumentary (ihn-tehg'-yoo-MEHN-tar-ee) Pertaining to the skin and its accessory organs.

Intercalated disk (ihn-ter'-kaw-LA-tehd dihsk) A transverse thickening of a cardiac muscle cell's sarcolemma at its boundary with an adjacent cell. It aids in the conduction of an impulse from one cardiac cell to another.

Intercellular (ihn'-tehr-SEHL-yoo-lar) environment The area between cells.

Internal (ihn-TER-nawl) A directional term describing a location deep to the surface of the skin relative to something else.

Interstitial cells (ihn'-ter-STIH-shuhl) Cells in the testes located between seminiferous tubules that secrete testosterone. Also called cells of Leydig.

Interstitial fluid (ihn'-tehr-STIH-shuhl FLOO-ihd) The portion of extracellular fluid that fills the tissue spaces between cells. Also called tissue fluid and intercellular fluid.

Intervertebral disk (ihn'-tehr-VEHR-teh-brahl disk) A cartilaginous joint that consists of a pad of fibrocartilage located between two adjacent vertebrae.

Intestinal gland (ihn-TEHS-tihn-awl glahnd) A tubular gland in the mucosa of the small intestine that secretes digestive enzymes. Also called crypt of Leiberkuhn.

Intracellular (ihn'-traw-SEHL-yoo-lar) environment The space within a cell.

Intracellular fluid (ICF) The fluid within cells.

Intramembranous ossification (ihn'-trah-MEHM-braw-nuhs ohs'-ih-fih-KA-shuhn) The development of bone from fetal connective tissue membranes.

In vitro (ihn VEE-tro) Outside the body, such as in a culture bottle.

In vivo (ihn VEE-vo) Inside the living body.

Iris (I-rihs) A part of the vascular tunic of the eye. It is located on the anterior side of the eyeball and is composed of smooth muscle fibers that regulate the amount of light entering the eye. The iris is the colored part of the eye surrounding the pupil.

Islet of Langerhans (I-leht of LANG-er-hawnz) One of numerous clusters of endocrine cells within the pancreas.

Isotonic solution A solution that contains an equal amount of solutes relative to another.