1.        Acidophilic Structures that stain with eosin, a negatively charged dye that stains pink to red. Acidophilic tissue componenets have a net positive charge such as proteins (NH2+). Examples of acidophilic components: mitochondria (due to membrane proteins), Lysosomes (due to enzymes) erythrocytes (hemoglobin), collagen fibers, secretory vacuoles that contain proteins, and cytosolic proteins.
2.        Acrosome A modified lysosome at the tip of the head of a sperm which contains lytic enzymes (hyaluronidase in mammalian sperm) which digest the outer surface of the egg and allow the sperm to inject its haploid DNA. The release of these enzymes is called the acrosome reaction and is triggered when a spermatozoon binds to a secondary oocyte.
3.        Actin A filamentous protein (42 kD) involved in muscle contraction in both smooth and striated muscle. It is the main constituent of the thin filaments of muscle fibers. Actin also makes up the microfilaments that form part of the cytoskeleton. Actin filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits. This is known as globular or g-actin.
4.        Adventitia The outermost connective tissue layer of any hollow organ not covered by a serosa. An adventitia plus a mesothelium makes a serosa.
5.        Afferent Moving or carrying inward or toward a central part, such as an afferent arteriole, which carries unfiltered blood toward the glomerulus. (see efferent for more examples)
6.        Aldehyde fuchsin A stain that produces violet staining of elastic fibers, mast cell granules, gastric chief cells, beta cells of the pancreatic islets.
7.        Ampulla A dilated portion of a tubular structure, e.g. the ampulla of Vater (major duodenal papilla) or the ampulla of the oviduct.
8.        Anaphase The stage of mitosis or meiosis beginning with the separation of sister chromatids (or homologous chromosomes) followed by their movement towards the poles of the spindle.
9.        Anisocytosis A condition where the red blood cells are unequal in size, evident on blood smear. This condition could be due to low vitamin B12, folic acid and iron.  Anisocytosis often involves a mixture of macrocytes (abnormally large cells) and microcytes (abnormally small cells) in the same sample.
10.    Annulus A ring like structure, e.g. the annulus fibrosus of D23an intervertebral disc.
11.    Anterograde Moving or extending forward (antonym: retrograde).  Anterograde transport in a neuron involves transport away from the neuronal cell body and toward the peripheral processes
12.    Antrum A general term for cavity or chamber within a certain organs or sites in the body. The antrum of the stomach (gastric antrum) is a portion before the outlet which is lined by mucosa which does not produce acid.  Also the antrum in secondary & tertiary ovarian follicles.
13.    Apical Relating to or located at the tip (an apex). The apical membrane of a cell is the part that lines the luminal surface (antonym: baso-lateral membrane).
14.    Apocrine Form of secretion in which some portion of the cell is shed along with the secretory product. example: the secretion of lipid droplets by cells of the lactating mammary gland. The fat drople lacks a membrane when it is in the cytoplasm, but leaves the cell by budding from the apical plasma membrane, taking with it a piece of the membrane.
15.    Apoptosis Programmed cell death as signaled by the nuclei or external factors in normally functioning human and animal cells when age or state of cell health and condition dictates. This active process requires metabolic activity by the dying cell, which is characterized by cleavage of the DNA into fragments that give a so called laddering pattern on gels. Cells that die by apoptosis show margination of chromatin, nuclear blebbing fragmentation into membran-bounded apototic bodies that are phagocytosed by macrophages or neighboring cells. These do not usually elicit an inflammatory response. Apoptosis is distinct from necrosis where dying cells break open, and the intracellular components trigger an inflammatory reaction. 
16.    Arcuate Curved like a bow. Examples include the median/medial/lateral arcuate ligaments of the diaphragm, the arcuate line of the transversalis fascia and arcuate vessels of kidney.
17.    Atrophy A wasting away, a diminution in the size of a cell, tissue, organ or part.
18.    Autocrine Secretion of a substance, such as a growth factor, that stimulates the secretory cell itself. One example is interleukin-2 release by T cells, which induces the proliferation of the same T cell as well as other T cells.
19.    Autophagy Removal of cytoplasmic components, including membrane bounded organelles, by digesting them within secondary lysosomes (autophagic vacuoles). Mechanism: A region of cytoplasm becomes surrounded by primary lysosomes which fuse with one another to form a double membrane around the cytoplasmic region. The lysosomal enzymes are initially limited to the space between the two membranes. The inner membrane breaks down, giving the enzymes free access to the enclosed region of cytoplasm. 
20.    Axon A long process of a neuron, that carries efferent (outgoing) action potentials from the cell body towards target cells. Axons can be identified by the presence of an axon hillock (tapering region between a neuron's cell body and its axon that is pale-staining because it lacks Nissl bodies). 
21.    Axoneme The 9+2 arrangement of microtubule (9 doublets + a pair of complete microtubules) that forms the core of a cilium or flagellum
22.    Basal In morphologically polarized epithelial cells, the surface closest to the basement membrane.
23.    Basal body The structure from which a cilium develops.  Has 9 triplets of microtubules, similar to the arrangement in a centriole.
24.    Basal lamina Terminology varies from book to book. We consider a basal lamina to be an electron dense layer visible by EM that lies between an epithelium and connective tissue layer and helps bind the two together. The basal lamina and the reticular lamina form the basement membrane. The basal lamina (or lamina densa) is produced by epithelial cells and contains type IV collagen. The reticular lamina is formed by the connective tissue cells and contains reticular fiber of type III collagen. Between the epithelial cells and the basal lamina lies a pale-staining layer (the lamina lucida or lamina rara).
25.    Basophilic Tissue components tah carry a net negative charge and therefore bind positively charged dyes such as hematoxylin. Basophilic tissue components include DNA, RNA (PO4) Proteoglycans, and GAGs (SO4, CO2). Examples of basophilic structures include: nucleus, nucleolus, and ribosomes.
26.    Best's carmine A stain used for the demonstration of glycogen in tissues.
27.    Bouin's A common fixative for light microscopy. It includes formalin, acetic acid and picric acid.
28.    Brush border The densely packed microvilli on the apical surface of, for example, the cells of the proximal tubules of the nephron.
30.    Canaliculus Literally a little channel or canal. In bone: canaliculi radiate from lacuna. House cytoplasmic processes of osteocytes.
In liver:  labyrinthine intercellular spaces 1-2 um in diameter called bile canaliculi conduct bile between hepatocytes to the periphery of classical lobules.
In parietal cells: deep invaginations of the apical plasmalemma form intracellular canaliculi lined by microvilli. These increase the surface area of the apical plasma membrane, across which HCl secretion occurs.
31.    Centriole Small cylindrical structures composed of nine microtubule triplets; they constitute the core of the microtubule organizing center (MTOC)  in the centrosome 
32.    Centrosome A zone of cytoplasm usually located near the nucleus that contains the Golgi apparatus and a pair of centrioles (Wheater, Figs. 1.9b & 1.25). Also called the cytocentrum. Sometimes distinguishable by LM (Wheater, Fig. 1.9c) because the organelles it contains stain poorly with H&E.
33.    Chromophil Characterized by secretory granules having high affinity for histological dyes. In the pituitary there are 2 types of chromophils: acidophils & basophils.
Acidophils: abundant in pars distalis of pituitary. Include somatotrophs (somatotropin) stimulated by SRH and inhibited by somatostatin, and mammotrophs (prolactin) involved in lactation.
Basophils:  In pars distalis and pars intermedia. Include corticotrophs (ACTH, LPH) stimulated by CRH, thyrotrophs (TSH) stimulated by TRH and inhibited by presence of T4 and T3 in blood, and gonadotrophs (FSH, LH) stimulated by GnRH and inhibited by gonadal hormones.
34.    Chromophobe Cells whose cytoplasm does not take up stain readily. Located in pars distalis. Possibly degranulated chromophils. Include folliculostellate cells which make up a large portion of cells in pars distalis.  
35.    Cilium Motile hair-like projections that emanate from the surface of certain epithelial cells. Specialized function in propelling mucus and other substances over the surface of epithelium via rapid wave'like oscillations.

Core of cilium contains a complex of uniformly arranged microtubules called the axoneme. The axoneme is composed of two centrally placed microtubules (central sheath) surrounded by nine doublets of microtubules (connected by nexin) (9+2). Movement is powered by dynein which has ATPase activity and transiently attaches to specific sites on the protofilaments in adjacent doublets, sliding them toward the tip of the cilium. Nexin restrains the sliding motion causing the bending of cilia. 
36.    Clathrin A protein involved in intracellular vesicular transport. Clathrin triskelions (protein complexes with a three-armed structure) coat the cytoplasmic aspect of certain cytoplasmic membranes such as the trans golgi network, causing the coated parts of the membrane to bud off as a vesicle. Example: formation of lysosomes in the trans golgi network where mannose-6-phosphate is bound. The clathrin-coated pit deepens to form a vesicle (lysosome) which then loses its clathrin coat and can then fuse (and release its contents) to a late endosome.
Clathrin coats are used in many other types of vesicles. Different receptor binding sites are coupled to clathrin via different intermediary proteins called adaptins
37.    Connexon A gap junction is made up of many connexons. A connexon is a cylindrical structure that consists of six copies of the transmembrane protein connexin. Connexons are aqueous pores through the plasma membrane. Paired connexons in neighboring cell membranes form hydrophilic channels that permit the passage of ions, amino acids, cAMP, etc., directly from the cytosol of one cell to the cytosol of the other. Connexons are regulated by pH and Ca2+ (high pH/low Ca2+ opens connexons). 
38.    Constitutive Continuous and without regulation, as in constitutive vs. regulated secretion.
39.    Cortex A histologically distinct region located at the periphery of an organ. Examples include renal cortex, suprarenal cortex, thymic cortex.
40.    Crista Folds of the inner mitochondrial membrane. Cristae greatly increase the surface area where theelectron transport chain and ATP synthase are located. Numerous cristae therefore indicate a high energy requirement in that cell.
Mitochondria of steroid-secreting cells have tubular cristae whereas most other cells have cristae organized in shelves.
41.    Cumulus Cumulus literally means "hill."  Thus "cumulus oophorus" is the hill that carries the egg.
42.    Cytokinesis Stage in cell division where division of cytoplasm occurs. Cleavage furrow begins in late anaphase but cytokinesis is best characterized in telophase.

Polar microtubules are surrounded by a contractile ring composed of actin and myosin filaments attached to the membrane. Constriction of the ring is followed by depolymerization of the remaining spindle microtubules separating the two daughter cells. Separation of the daughter cells induces the disassembly of the mitotic apparatus, concluding cytokinesis. 
43.    Cytosol Water and the inorganic and organic chemicals suspended in it that make up the bulk of the cytoplasm. All cytoplasmic organelles are surrounded by the cytosol. Cytoplasm = cytosol + cytoplasmic organelles + cytoplasmic inclusions (e.g., lipid droplets, glycogen).
44.    Demilune Demilune means "half moon," i.e. shaped like a crescent moon. A serous demilune is a half-moon shaped group of serous cells associated with the outer surface of a mucous acini (e.g., in submandibular and sublingual glands). 
45.    Dendrite Processes specialized for receiving stimuli from sensory cells, axons, and other neurons. Often multibranched. 
46.    Desmosome One of the three components of junctional complex between epithelial cells (other two are the  zonula occludens and zonula adherens). Also occur in epithelia & muscle as individual desmosomes that are not part of a junctional complex.
47.    Diapedesis Process by which leukocytes leave the bloodstream by migrating between the endothelial cells of the blood vessels to enter the connective tissue spaces where they perform their major functions. 
48.    Diaphysis Shaft of a long bone 
49.    Dyad Present near Z-line of cardiac muscles, composed of a T-tubule and a terminal cisternae of the sarcoplasmic reticulum. Important in excitation-contraction coupling
50.    Dynein Microtubule-associated protein responsible for moving vesicles along the microtubules in retrograde transport. Ciliary dynein forms arms associated with each microtubules doublet in the axoneme. The ATPase activity of the dynein slides one doublet relative to the next during ciliary movement.
51.    Dysplasia A disordered pattern of growth, most often encountered in epithelia. May involve loss of cell orientation, variation in cell size and shape, and increased numbers of mitotic cells that are  often found in unusual locations within the epithelium.
52.    Efferent Leading away from. Examples: 1) Functionally, the PNS is divided into a sensory (afferent) component, which receives and transmits impulses to the CNS for processing, and a motor (efferent) component, which originates in the CNS and transmits impulses to effector organs throughout the body.  2) Afferent lymphatic vessels deliver lymph into the lymph nodes, while efferent lymphatics carry lymph away from the node after it has passed through it.
53.    Endocrine A gland that lacks a duct and secretes into surrounding connective tissue, where the hormone is picked up by the bloodstream. Does not secrete into a lumen or onto the body surface. E.g., Adrenal (suprarenal) glands, thyroid, enteroendocrine (DNES or diffuse neuroendocrine system) cells.
54.    Endocytosis Process whereby a cell ingests macromolecules, particulate matter, and other substances from the extracellular space.
55.    Endomitosis Process whereby the DNA replicates without subsequent division of the nucleus or the cell; instead, ithe cell becomes larger and the nucleus becomes polyploid, as much as 64 N, sometimes more.  Megakaryoblasts undergo endomitosis prior to platelet formation.  
56.    Endomysium Composed of reticular fibers and an external lamina (basal lamina), surrounds each muscle cell.
57.    Endoneurium The innermost layer of the three connective tissue investments of a nerve. It surrounds individual nerve fibers and consists mainly of collagen fibrils.
58.    Epineurium Outermost layer of the three connective tissue investments covering a nerve. It surround the entire nerve, usually binding multiple fascicles together. It consists of dense irregular connective tissue, sometimes associated with adipose tissue.
59.    Epiphysis Articular end of long bone.
60.    Euchromatin Active form of chromatin where genetic material of the DNA molecule is uncoiled and is either being replicated or being transcribed into RNA. Euchromatic areas of a nucleus are pale-staining by LM or EM. 
61.    Exocrine Secreting into a lumen (e.g. the stomach) or onto the body surface, usually via a duct.
62.    Exocytosis Release of material from the cell by fusion of a membrane-bounded vesicle with the plasma membrane
63.    Fibrillin Widely distributed connective tissue protein that forms the microfibril on which elastin is laid down to form elastic fibers. Absence of these microfibrils results in formation of elastic sheets (lamellae) rather than elastic fibers.
64.    Formalin A 37% aqueous solution of formaldehyde. The most common fixative agent used in light microscopy.
65.    Fundus The rounded end of a hollow organ farthest from the outflow opening. e.g. fundus of stomach, gall bladder, and uterus.
66.    GAG (Glycosaminoglycan) Negatively charged, long, unbranched, rod-like chains of repeating disaccharides that  have the capability of binding large quantities of water. GAGs associate with a core protein to form proteoglycans.
67.    Ganglion A general term for a group of nerve cell bodies located outside the central nervous system, occasionally applied to certain nuclear groups within the brain or spinal cord, for example basal ganglia. 
68.    Glutaraldehyde A dialdehyde used as a fixative, especially for electron microscopy. By its interaction with amino groups (and others) it forms cross links between proteins. 
69.    Glycocalyx Also called the cell coat. The fuzzy layer, seen by electron microscopy, on the outer surface of the plasmalemma. Especially prominent on enterocytes of the intestine & proximal tubules of the kidney. It is rich in proteoglycans, glycolipids, and glycoproteins.  A thick glycocalyx may be visible by LM after special staining (e.g. PAS)
70.    Haustra Large intestine sacculations maintained by taeniae coli.
71.    Hemidesmosome Membrane junctions that anchor epithelial cells to the basement membrane in simple, stratified and pseudostratified epithelia. Also provide anchoring sites for the intermediate filaments of the cytoskeleton.
72.    Herring body A dilation along an axon in the posterior lobe of the pituitary caused by the presence of groups of secretory granules that contain oxytocin or vasopressin
73.    Heterochromatin A condensed, inactive form of chromatin that stains dark in LM or EM. Located mostly in the periphery of the nucleus.
74.    Heterophagy Digestion within a cell of an exogenous substance phagocytosed from the cell's environment. Involves fusion of phagosome with lysosomes
75.    Hilum (Hilus) A depression or fissure where vessels, nerves and/or ducts enter or leave a bodily organ.
76.    Holocrine Form of secretion in which the whole cell is shed from the gland, usually after becoming packed with the main secretory substance. In mammals, sebaceous glands are one of the few examples. 
77.    Hyaline Clear, transparent, glassy, granule free, as for example hyaline cartilage, hyaline membrane disease of the lung, and the hyaline zone at the front of a moving amoeba. 
78.    Hyperplasia The increase in size of a tissue or organ due to increase in the total number of cells present, e.g. development of the female breast at puberty due to replication duct epithelium. Contrast with hypertrophy.
79.    Hypertrophy The enlargement or overgrowth of an organ or part due to an increase in cell size. May occur along with hyperplasia, as in the pregnant uterus where smooth muscle cell size and cell number both increase.
80.    Integrin Family of transmembrane proteins that attach internally to the cytoskeleton and which also anchor a cell to glycoproteins in the extracellular matrix (laminin, collagen, fibronectin) or on another cell's surface (e.g. intercellular cell adhesion molecules such as ICAM-1).
81 Intermediate filament Structural cytoskeleton fibers of intermediate size (~10nm diameter), between microtubules and actin filaments, formed by polymers of various alpha-helical rod-shaped proteins.  Found in many places, including hair, nails, and skin (keratins); muscle Z-disks (desmin); and cell nuclear envelopes (lamins). Unlike microfilaments and microtubules, IFs are extremely stable (they do not 'cycle' or 'treadmill') and their assembly does not require hydrolysis of ATP or GTP.
82.    Intima Innermost, as in tunica intima, the innermost layer of blood and lymphatic vessels composed of a simple squamous endothelium and the immediately surrounding (underlying) connective tissue.
83 Isogenous Literally means "having exactly the same (iso-) genes (-genous)". Having the same developmental origin; i.e. arising from the same tissue or cell. For example, clusters of 2-4 (or more) chondrocytes that arose (by mitosis) from the same chondrocyte are known as isogenous groups.
84 Keratin Family of durable intermediate filamentous proteins produced but not secreted by epithelial cells; keratin production may be enhanced/induced in response to local wear and tear (e.g. in the vocal cords). Keratins are the primary protein constituents of hair, nails, and the stratum corneum of the epidermis.
85.    Kinesin Family of ATP-powered motor proteins that transport attached vesicles/particles along microtubules in an anterograde (towards the +-pole) direction.  (cf. dynein)
86.    Lacteal  Lymphatic vessel at the core of an intestinal villus that conveys lipids in chyle (chylomicron-bearing fluid); the name lacteal derives from the fluid's 'milky' appearance. 
87.    Lacuna ('Little lake') - a small space, cavity, or depression. Chondrocytes are chondroblasts that have become trapped by matrix into a lacuna; similarly, osteoblasts become known as osteocytes when they entrap themselves in a lacuna surrounded by bone matrix.  (Also recall from embryology that the maternal-blood-filled vascular spaces surrounding the villi in the placenta develop by the fusion of smaller spaces called lacunae.)
88.    Lamina propria Layer of loose (areolar) connective tissue underlying the epithelium of a mucous membrane
89.    Laminin Extracellular matrix glycoprotein found in the upper (lamina lucida) layer of all basal laminae.  Has integrin-, heparan-sulfate- , and dystroglycan-binding domains that allow cells to anchor themselves to the basal lamina. Laminin also binds to the type IV collagen molecules of the lower (lamina densa) layer of the basal lamina, which are themselves involved in securing the basal lamina to the underlying lamina reticularis
90.    Lamins Group of intermediate filament proteins that form the nuclear lamina on the inner surface of the nuclear envelope. Phosphorylation of lamins leads to breakdown of the nuclear lamina in mitosis. Dephosphorylation leads to binding of chromosomes to vesicles derived from the nuclear membrane, and fusion of these vesicles to reconstitute the nuclear envelope.
91.    Lipofuchsin Yellowish-brown pigment that accumulates in residual bodies (old lysosomes) in long-lived cells; e.g. in liver, kidney, adrenal, cardiac muscle, and/or ganglion cells of older people. Believed to be the oxidized lipid-containing residues of lysosomal digestion.
92.    Macula Macula means "spot", e.g. macula adherens (a desmosome) or macula densa
93.    Media The intermediate layer of blood vessels, composed mostly of smooth muscle cells oriented concentrically around the lumen i.e., tunica media
94.    Medulla The inner portion of an organ i.e., medulla of hair follicle, medulla of lymph nodes, medulla of thymus, medulla of suprarenal gland, medulla of kidneys. Compare with cortex.
95.    Melanin Manufactured by melanocytes of skin & hair; made from tyrosine via a series of reactions progressing through 3,4-dihydroxyphenylalanine & dopaquinone in melanosomes
96.    Melanosome Oval vacuoles derived from Golgi found in melanocytes; site of melanin synthesis; tyrosine is transported into melanosomes where tyrosinase and other enzymes convert tyrosine to melanin 
97.    Merocrine Also called eccrine. Describes a types of secretion where only secretory product is lost from the cell, usually by fusion of secretory vacuole with plasma membrane. Example: parotid gland. Neither the cell membrane nor cytoplasm becomes a part of the secretion.
98.    Mesenchyme An embryonic form of connective tissue containing multipotent mesenchymal cells, extensive ground substance and few fibers.  Not always derived from mesoderm, but usually is.
99.    Mesothelium Simple squamous epithelium of mesodermal origin. It lines the peritoneal, pericardial and pleural cavities.
100.            Metachromasia The situation where a stain when applied to cells or tissues gives a color different from that of the stain solution; i.e., toluidine blue staining mast cell granules reddish purple. Metachromasia usually occurs when a basic stain binds to a polyanion in the specimen so that dye molecules are close enough for interactions to occur between them.
101.            Metaphase Classically the second phase of mitosis or of meiosis. In this phase the chromosomes align themselves on the equator of the mitotic spindle
102.            Metaplasia The change in the type of adult cells in a tissue to another normal form but one that is not usually found in that location.  i.e., pseudostratified ciliated columnar epithelium of the bronchi of heavy smokers can undergo squamous metaplasia, transforming it into stratified squamous epithelium
103.            Metastasis The transfer of disease from one organ or part to another not directly connected with it. It may be due either to the transfer of pathogenic microorganisms (for example, tubercle bacilli) or to transfer of cells,  as in malignant tumors. The capacity to metastasize is a characteristic of all malignant tumors. Often involves transport of cells via lymphatics or blood vessels.
104.            Microtubule Cytoplasmic tubule, 25nm outside diameter with a 5nm thick wall. Made of tubulin heterodimers packed in a three start helix (or of 13 protofilaments looked at another way) and associated with various other proteins (MAPs, dynein, kinesin). Microtubules of the ciliary axoneme are more permanent than cytoplasmic and spindle microtubules.
105.            Microvillus Small finger-like cytoplasmic projections emanating from the free surface of the cell into the lumen. Microvilli are one mechanism for increasing cell surface area. Very prominent on some cell (e.g., enterocytes), but present to some extent on most cell types.
106.            Mucous Secreting a slimy or mucigenous substance; as the mucous gland. But note that a mucous membrane doesn't have to secret mucus.  Mucous membrane is a synonym for a mucosa.
107.            Mucus The secretory product of mucous glands.  A vicous mixture of highly hydrated glycoproteins.
108.            Nebulin A long nonelastic protein; 2 molecules of nebulin are wrapped around the entire length of each actin thin filament in striated muscle, further anchoring it in the Z disk & ensuring the maintenance of the specific array in the sarcomere. Nebulin may help regulate the length of the thin filament in developing muscle.
109.            Necrosis Cell death resulting from injury to the cell; in necrosis, the injured cell swells & bursts, cell contents that are toxic to other cells are released into surrounding tissues, & inflammation ensues
110.            Neurofilament Intermediate filaments 10nm in diameter found in axons of nerve cells
111.            Nissl body A mixture of free polysomes interspersed among short stacked cisternae of RER; especially prominent in large motor neurons
112.            Node of Ranvier Interruptions that occur in the myelin sheath at regular intervals along the length of the axon, exposing the axon; each node indicates an interface between the myelin sheaths of  2 different Schwann cells located along the axon
113.            Nucleolar organizer Loops of DNA that transcribe ribosomal RNA. They are located in the acrocentric chromosomes 13-15 and 21; secondary constrictions of the chromosomes where the nucleoli are found in interphase; Since these loci actively transcribe rRNA late into Prophase, they are less coiled and folded, causing them to appear thinner, "constricted," when viewed cytologically with a microscope at metaphase. 
114.            Oil red O Stains lipid red
115.            Osmium Osmium tetroxide stains unsaturated lipids dark brown or black (also acts as a lipid fixative)
116.            Osteoid Thin noncalcified layer of bone matrix separating osteoblasts (as well as osteocytes) from mineralized matrix.  Consists mainly of collagen type I and other less abundant proteins.
117.            Osteon (aka Haversian  system). Consists of an Haversian canal with its surrounding concentric lamellae of bone. Includes osteocytes in lacunae between successive lamellae, and canaliculi that interconnect the lacunae with one another and with the Haversian canal. 
118 Paracrine The target cell is located in the vincinity of the signaling cell so that the mediator secreted by the signaling  cell travels to the target cell via diffusion rather than in the blood.  
119.            Parenchyma The tissue that makes up the essential or specialized part of an organ as opposed to the supporting tissue (stroma).
120.            Parietal 1. Of or relating to the walls of a part or cavity; 2. Parietal Cells are stomach secretory cells which produce HCl and intrinsic factor 
121.            Pedicel The foot-process of a podocyte that is associated with the outer surface of glomerular capillaries in the kidney. Forms part of the blood-urine filtration barrier. 
122 Perinuclear cisterna The space which separates the inner and outer nuclear membranes. It is continuous with the lumen of the RER cisternae.
124.            Periodic acid-Schiff Staining technique which stains glycogen and most carbohydrate-rich molecules magenta. Used to demonstrate basement membranes, g;ycocalyx, glycogen, etc.
125.            Periosteum Except at synovial articulations, bone is covered on its external surface with a periosteum which consists of an outer layer of dense fibrous connective tissue and an inner cellular layer containing osteoprogenitor (osteogenic) cells .
126.            Peroxisome Small (0.2-1.0 um in diameter), spherical to ovoid membrane-bounded organelles that contain many oxidative enzymes that produce hydrogen peroxide (toxic to cells). Also contain catalase, which breaks down hydrogen peroxide. Function in catabolism of long-chained fatty acids (beta oxidation), forming acetyl coenzyme A as well as hydrogen peroxide by combining hydrogen from the fatty acids with molecular oxygen. Also involved in alcohol metabolism, especially in liver.
127.            Phagocytosis The process of engulfing large particulate matter, such as microorganisms, cell fragments and cells (e.g. defunct red blood cells). Is usually performed by specialized cells known as phagocytes. The most common phagocytes are the white blood cells, the neutrophils and the monocytes. When such monocytes leave the bloodstream to perform their task of phagocytosis, they become know as macrophages.
128 Pinocytosis Transport of small substances in and out of the cell via vesicles
129 Plasmalemma The plasma membrane of a cell.
130.            Plica 1. A fold or folded part; especially : a groove or fold of skin; 2. Plicae circulares: folds in the small intestines (esp. in the jejunum). Each plica involves both mucosa and submucosa, and carries many villi on its lumenal surface.
131.            Polysome One mRNA molecule associated with several ribosomes that are in the process of translating it. 
132.            Proteoglycan When sulfated GAGs form covalent bonds with a protein core, they form a family of macromolecules known as proteoglycans, many of which occupy huge domains. Abundant for example in the matrix of hyaline cartilage.
133.            Pseudostratified An epithelium in which all cells are in contact with the basement membrane, but not all reach thefree lumenal surface of the epithelium.
134.            Pyknosis The characteristic of cell death where DNA has been enzymatically degraded and the nucleus has become shrunken, heterochromatic and irregular in shape.
135.            Retrograde Transport in a reverse or backward direction, e.g., from axon to soma in a neuron. Items returned to the cell body from the axon include protein building blocks of neurofilaments, subunits of microtubules, soluble enzymes, and materials taken up by endocytosis. 
136.            Ruga All the gastric regions display rugae, which are folds of mucosa and submucosa that disappear in the distended stomach.  It permits expansion of the stomach as it fills with food and gastric juices.
137.            Sarcolemma The muscle cell plasma membrane
138.            Sarcomere The region between 2 successive Z lines. Considered the contractile unit of skeletal and cardiac muscle.
139.            Sarcoplasmic reticulum Muscle cells' smooth endoplasmic reticulum. Forms the terminal cisternae that are part of the triads & diads in striated muscle. Releases calcium into the sarcoplasm to make contraction possible, and also pumps calcium back into the SR cisternae to terminate a contraction.
140.            Sebaceous Glands that secrete an oily substance known as sebum in a holocrine fashion. Sebum maintains the suppleness of the skin. They are found throughout the body excepts for the palms of hands, soles of feet, and sides of feet inferior to the hairline.
141.            Septum Sheets of connective tissue that subdivide an organ (usually incompletely) into smaller compartments
142.            Serosa Outer layer of an organ that consists of connective tissue and a mesothelium. Organs with a serosa can be found in all body cavities- peritoneal, pleural, or pericardial. 
143.            Serous Serous glands secrete a watery fluid that is often rich in enzymes. Contrast with mucous glands, which produce a highly viscous secretion.
144.            Sinusoid Wide, highly permeable capillaries in certain organs of the body including bone marrow, liver, spleen and certain endocrine glands.
145.            Soma The central portion of a neuron where the nucleus and perinuclear cytoplasm are located; also called cell body or perikaryon
146.            Squamous Composed of single or stratified layer of tightly packed, flat, low profile polygonal cells. Centrally placed bulging nucleus in each cell. 
147.            Stereocilium Long branching microvilli found only in the epididymis, vas deferens, and on the sensory hair cells of the cochlea.
148.            Striated border Microvilli represent the striated border of the intestinal absorptive cells.
149.            Stroma The elements that surround and support the parenchyma of an organ. Usually composed of connective tissue.
150 Synapse Site where nerve impulses are transmitted from a presynaptic cell (neuron) to a postsynaptic cell (another neuron, muscle cell, or cell of a gland)
151.            Syncytium A multinucleated protoplasmic mass formed by the fusion of previously separate cells, e.g. skeletal muscle or syncytiotrophoblast.
152.            Teniae coli (Taeniae coli) Three thick smooth muscle bands of the outer longitudinal layer of muscularis externa of the colon. Teniae coli are one of the three characteristic features that distinguish large intestine from small (teniae, haustra & epiploic appendages).
153.            Terminal bar LM equivalent of a junctional complex (zonula occludens, zonula adherens, and desmosome). Looks like a very small black dot between lateral plasma membranes of neighboring epithelial cells near their apical end.
154.            Terminal cisterna Regions of the sarcoplasmic reticulum adjacent to T tubules from which Ca2+ is released when striated muscle is activated
155.            Terminal web Network of actin microfilaments just beneath the cell surface. Stabilized by spectrin. In many epithelial cells the microfilaments that form the core of microvilli insert onto the terminal web, and the terminal web in turn inserts on the zonula adherens.
156.            Titin Large, linear, elastic protein; four molecules anchor a thick filament between the two Z disks of each sarcomere in striated muscle
157.            Trabecula Literally "a beam." An elongated finger-like projection, often composed of connective tissue and forming part of the stroma of an organ (spleen, lymph node). In the heart trabeculae carneae are composed of cardiac muscle rather than connective tissue.
158.            Transcytosis Transport of water-soluble molecules greater than 11 nm in diameter from the adluminal plasmalemma to the abluminal plasmalemma or vice versa by pinocytotic vesicles; used by endothelial cells of capillaries, by enterocytes tranporting secretory IgA, etc.
159.            Triad T tubule flanked by two terminal cisternae of striated muscle sarcoplasmic reticulum
160.            Tropomyosin Part of thin filaments in striated and smooth muscle myofibrils that interacts with actin.  Prevents interaction of actin and myosin in relaxed muscle.
161.            Troponin Associated with tropomyosin and actin on the thin filament in striated muscle; confers Ca2+ sensitivity; 1-1 relationship with tropomyosin; absent in smooth muscle
162.            Tubulin Localized in centrosome. Is the main protein component of microtubules.
163.            Tunica A coat; ex: tunica intima/media/adventitia of blood vessels
164.            Unilocular Having a single droplet or cavity; ex: unilocular fat cell (forms white adipose tissue)
165.            Vasa recta Capillaries from efferent glomerular arterioles that extend into the medulla and wrap around the limbs of Henle's loop and the collecting tubule in a hairpin-like shape; descending limb = arteriolae rectae; ascending limb = venae rectae; essential to urine concentration
166.            Vasa vasorum Small arteries that enter blood vessel walls and branch profusely to serve the cells located in the tunica media and tunica adventitia; more prevalent in walls of veins
167.            Villus Finger-like projections found on thelumenal lining of the small intestine; serves to increase the absorbing surface. Consists of a core of lamina propria covered by epithelium. 
168.            Vimentin Type III intermediate filament protein of the cytoskeleton; found in cells of mesenchymal origin (fibroblasts); secures periphery of Z disks/lines of neighboring myofibrils to each other
169.            Visceral Relating to or affecting one or more internal organs. Compare with parietal.
170.            Wright's A type of Romanovsky stain used for differential staining of blood cells; pink=erythrocytes, eosinophil granules; purple=leukocyte nuclei, basophil granules; blue=cytoplasm of monocytes and lymphocytes
171.            Z line Line formed where actin filaments attach between two sarcomeres; electron-dense by EM; divides each myofibril into contractile units (sarcomeres) arranged end-to-end
172.            Zenker's Zenker's fixative=rapid fixative useful light microscopy. Based on a mixture of formalin and mercuric chloride.
173.            Zona pellucida Translucent, elastic, noncellular layer surrounding the ovum; present in unilaminar and multilaminar primary follicles, secondary follicles, and graafian follicles
174.            Zymogen Inactive precursor of an enzyme, particularly a proteolytic enzyme; contained in secretory vesicles
175.            Extra-  Prefix meaning "outside of"
176.            Inter- Prefix meaning 'between'
177.            Intra- Prefix meaning 'within'
178.            -itis Suffix meaning 'inflammation'
179.            Para- Prefix for "along side of"
180.            -penia Suffix for insufficiency (e.g. Leukopenia = insufficiency of white blood cells)
181.            -philia Suffix for 1.) affinity for (e.g. Eosinophilia, an affinity for eosin)  2.) an abundance of (e.g. Eosinophilia, an abnormally high number of eosinophils in the blood)
182.            -phobia Suffix for fear of or aversion toward (e.g. hydrophobia)
183.            Sub- Prefix meaning "below"