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a thin layer of tissue that covers a surface, lines a cavity, or divides a space or organ. adj., adj mem´branous.
alveolar-capillary membrane (alveolocapillary membrane) a thin tissue barrier through which gases are exchanged between the alveolar air and the blood in the pulmonary capillaries. Called also blood-air barrier and blood-gas barrier.
alveolodental membrane periodontium.
arachnoid membrane arachnoid.
basement membrane a sheet of amorphous extracellular material upon which the basal surfaces of epithelial cells rest; it is also associated with muscle cells, Schwann cells, fat cells, and capillaries, interposed between the cellular elements and the underlying connective tissue. It comprises two layers, the basal lamina and the reticular lamina, and is composed of Type IV collagen (which is unique to basement membranes), laminin, fibronectin, and heparan sulfate proteoglycans.
basilar membrane the lower boundary of the scala media of the ear.
Bowman's membrane a thin layer of basement membrane between the outer layer of stratified epithelium and the substantia propria of the cornea.
Bruch's membrane the inner layer of the choroid, separating it from the pigmented layer of the retina.
cell membrane plasma membrane.
decidual m's (deciduous m's) decidua.
Descemet's membrane the posterior lining membrane of the cornea; it is a thin hyaline membrane between the substantia propria and the endothelial layer of the cornea.
diphtheritic membrane the peculiar false membrane characteristic of diphtheria, formed by coagulation necrosis.
drum membrane tympanic membrane.
epiretinal membrane a pathologic membrane partially covering the surface of the retina, probably originating chiefly from the retinal pigment epithelial and glial cells; membranes peripheral to the macula are generally asymptomatic, while those involving the macula or adjacent to it may cause reduction in vision, visual distortion, and diplopia.
extraembryonic m's those that protect the embryo or fetus and provide for its nutrition, respiration, and excretion; the yolk sac (umbilical vesicle), allantois, amnion, chorion, decidua, and placenta. Called also fetal membranes.
false membrane a membranous exudate, such as the diphtheritic membrane; called also neomembrane.
fenestrated membrane one of the perforated elastic sheets of the tunica intima and tunica media of arteries.
hemodialyzer membrane the semipermeable membrane that filters the blood in a hemodialyzer, commonly made of cuprophane, cellulose acetate, polyacrylonitrile, polymethyl methacrylate, or polysulfone.
Henle's membrane fenestrated membrane.
high efficiency membrane a hemodialyzer membrane that has clearance characteristics that increase progressively with increases in dialysis blood flow rates; this usually implies that the membrane is not a high flux membrane.
high flux membrane a hemodialyzer membrane that has a high permeability to fluids and solutes and thus a high rate of clearance of fluids and solutes composed of large molecules.
hyaline membrane
1. a membrane between the outer root sheath and inner fibrous layer of a hair follicle.
3. a homogeneous eosinophilic membrane lining alveolar ducts and alveoli, frequently found at autopsy of infants that were preterm. See also hyaline membrane disease.
hyoglossal membrane a fibrous lamina connecting the undersurface of the tongue with the hyoid bone.
impaired oral mucous membrane a nursing diagnosis approved by the North American Nursing Diagnosis Association, defined as disruptions of the lips and soft tissue of the oral cavity. Changes in the integrity and health of the oral mucous membrane can occur as a characteristic of such medical disorders as periodontal disease, uncontrolled diabetes mellitus, oral cancer, and infection with herpes. Chemical irritants such as alcohol and tobacco can also adversely affect the oral mucous membrane, as can mechanical trauma due to broken teeth, poorly fitting dentures, and endotracheal intubation. Other etiologic factors include dehydration, mouth breathing, poor oral hygiene, radiation to the head or neck, and antineoplastic agents.

Preventive measures that can help maintain the health and integrity of the oral mucosa will depend on the cause. Routinely brushing and flossing the teeth during the day and at bedtime can help avoid dental caries and periodontal disease. Some patients may need instruction in the proper procedure for cleaning the teeth and removing debris and plaque, or they may need assistance in devising ways to cope with physical disabilities that make good oral hygiene difficult for them. Patients who are unconscious or unable to perform self-care activities should have mouth care as often as needed to keep the mouth clean and moist and avoid aspiration of debris and infectious microorganisms. Adequate hydration and a lip lubricant can help avoid alterations in the oral mucosa and promote comfort.
limiting membrane one that constitutes the border of some tissue or structure.
mucous membrane the membrane covered with epithelium that lines the tubular organs of the body.
Nasmyth's membrane primary cuticle.
nuclear membrane
1. either of the membranes, inner and outer, comprising the nuclear envelope.
olfactory membrane the olfactory portion of the mucous membrane lining the nasal fossa.
placental membrane the membrane that separates the fetal from the maternal blood in the placenta.
plasma membrane the membrane that encloses a cell; it is composed of phospholipids, glycolipids, cholesterol, and proteins. The primary structure is a lipid bilayer. Phospholipid molecules have an electrically charged “head” that attracts water and a hydrocarbon “tail” that repels water; they line up side by side in two opposing layers with their heads on the inner or outer surface of the membrane and their tails in the core, from which water is excluded. The other lipids affect the structural properties of the membrane. Proteins embedded in the membrane transport specific molecules across the membrane, act as hormone receptors, or perform other functions.
Reissner's membrane the thin anterior wall of the cochlear duct, separating it from the scala vestibuli.
membrane of round window secondary tympanic membrane.
Scarpa's membrane tympanic membrane, secondary.
semipermeable membrane one permitting passage through it of some but not all substances.
serous membrane the membrane lining the walls of the body cavities and enclosing the contained organs; it consists of mesothelium lying upon a connective tissue layer and it secretes a watery fluid.
synovial membrane the inner of the two layers of the articular capsule of a synovial joint; composed of loose connective tissue and having a free smooth surface that lines the joint cavity.
tympanic membrane see tympanic membrane.
tympanic membrane, secondary the membrane enclosing the round window; called also Scarpa's membrane.
unit membrane the trilaminar structure of all cellular membranes (such as the plasma membrane, nuclear membranes, mitochondrial membranes, endoplasmic reticulum, lysosomes) as they appear in electron micrographs. The biochemical structure is a lipid bilayer.
virginal membrane hymen.
vitelline membrane the external envelope of an ovum.
vitreous membrane
2. hyaline membrane (def. 1).
4. a delicate boundary layer investing the vitreous body.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


1. A thin sheet or layer of pliable tissue, serving as a covering or envelope of a part, as the lining of a cavity, as a partition or septum, or as a connection of two structures. Synonym(s): membrana [TA]
2. Synonym(s): biomembrane
[L. membrana, a skin or membrane that covers parts of the body, fr. membrum, a member]
Farlex Partner Medical Dictionary © Farlex 2012


1. Biology
a. A thin, pliable layer of tissue covering surfaces or separating or connecting regions, structures, or organs of a living organism.
b. A semipermeable layer that bounds a cell or an organelle, typically consisting of lipids and proteins.
2. Chemistry A thin sheet of natural or synthetic material that is permeable to substances in solution.

mem′bra·nal (-brə-nəl) adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A thin layer of tissue covering a surface, lining a body cavity or dividing a space or organ.

Molecular biology
(1) A phospholipid mono- or bilayer which forms a hydrophobic barrier around and within cells.
(2) A sheet of nylon, nitrocellulose or similar material used to create a template for a gel for Southern blots, Northern blots or Western blots.

A popular term for the amniotic sac, see there.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


A very thin layer of tissue covering a surface, lining a body cavity, or dividing a space or organ
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


1. A thin sheet or layer of pliable tissue, serving as a covering or envelope, the lining of a cavity, a partition or septum, or a connection between two structures.
Synonym(s): membrana [TA] .
2. Synonym(s): biomembrane.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(mem'bran?) [L. membrana, parchment]
1. A thin, pliable layer of tissue that lines a tube or cavity, covers an organ or structure, or separates one part from another.
2. A very thin sheet of polymer, ceramics, glass, or metal.
Enlarge picture

alveolocapillary membrane

The structures and substances through which gases must pass as they diffuse from air to blood (oxygen) or blood to air (carbon dioxide), including the alveolar fluid and surfactant, cell of the alveolar wall, interstitial space (tissue fluid), and cell of the capillary wall. Synonym: respiratory membrane See: illustration

alveolodental membrane


arachnoid membrane

The delicate middle membrane of the three meninges, which enclose the brain and spinal cord. The arachnoid membrane is 5–6 cells thick. It adheres to the inner surface of the dura and is connected to the pia by a spiderweb of thin connections. Thee space between the arachnoid and pia (the subdural space) is filled with cerebrospinal fluid.
Synonym: arachnoid; arachnoid mater

atlanto-occipital membrane

A single midline ligamentous structure that extends from the arch of the atlas to the borders of the foramen magnum.

basement membrane

A two-part extracellular layer found at the interface between some tissues, e.g., skin and dermis. . The basement membrane is made of a basal lamina along the cell surfaces, coated by a stronger collagen-rich layer, the reticular lamina

basilar membrane

The membrane extending from the tympanic lip of the osseous spiral lamina to the crest of the spiral ligament in the cochlea of the ear. It separates the tympanic canal from the cochlear duct and supports the organ of Corti. See: illus. under organ of Corti

black membrane

An artificially constructed membrane made of lipids arranged in a bilayer.

Bowman membrane

See: Bowman, Sir William

Bruch membrane

See: Bruch, Karl

buccopharyngeal membrane

In the embryo, the membrane that separates the oral cavity from the foregut until the fourth week of development. Synonym: pharyngeal membrane

cell membrane

The membrane that forms the outer boundary of a cell; it is made of phospholipids, protein, and cholesterol, with carbohydrates on the outer surface. Synonym: plasma membrane

choroid membrane

See: choroid

costocoracoid membrane

The dense fascia between the pectoralis minor and subclavius muscles.

cricothyroid membrane

The membrane connecting the thyroid and cricoid cartilages of the larynx.

croupous membrane

False membrane.

Debove membrane

See: Debove membrane

decidual membrane

One of the membranes formed in the endometrium of a pregnant uterus.
See: decidua

Demours membrane

See: Demours membrane

Descemet membrane

See: Descemet membrane

diphtheritic membrane

The fibrinous false membrane on the mucous surfaces in diphtheria.

dural membrane

Dura mater.

egg membrane

Any of the protective membranes or envelopes enclosing an ovum. It may be primary (formed by egg itself, as in vitelline membrane), secondary (formed by follicle cells, as in zona pellucida), or tertiary (formed by oviduct or uterus, as in albumin and shell of hen's egg).

elastic membrane

Any of several membranes formed of elastic connective tissue fibers.

enamel membrane

1. Nasmyth membrane.
2. The thin internal layer of cells of the enamel organ.

epiretinal membrane

An excessive proliferation of retinal pigment epithelial cells and extracellular proteins on the retinal surface. This condition, which can distort vision, is typically found in people older than 50. Marked visual blurring caused by epiretinal membranes occurs in macular pucker. See: macular pucker

external limiting membrane

1. The outer layer of cells of the embryonic neural tube.
2. The membrane in the retina of the eye through which the receptor portions of the rods and cones protrude.

false membrane

Fibrinous exudate on a mucous surface of a membrane, as in croup or diphtheria. Synonym: croupous membrane

fenestrated membrane

A layer of elastic connective tissue possessing minute round or oval openings. It is found in the tunica intima and tunica media of medium-sized and large arteries.

fetal membrane

Any of the membranous structures that protect and support the embryo and provide its nutrition, respiration, and excretion. The structures are yolk sac, allantois, amnion, chorion, decidua, and placenta.

fibrous membrane

A membrane composed entirely of fibrous connective tissue. Examples include the fasciae, aponeuroses, perichondrium, periosteum, dura mater, and the capsules of some organs.

glassy membrane

1. The transparent capsule that separates membrana granulosa from the theca of the graafian follicle.
2. The internal layer of a hair follicle separating the epithelial and connective tissues.

glial cell membrane

An extremely delicate membrane, formed of foot plates of astrocytes, that surrounds all the blood vessels in the brain, spinal cord, and the lining of the pia mater, separating these vessels from the nervous tissue proper. This membrane is thought to be one of the components of the blood-brain barrier.

homogeneous membrane

A fine membrane covering villi of the placenta.

Huxley membrane

See: Huxley, Thomas H.

hyaline membrane

The membrane between the outer root sheath of a hair follicle and the inner fibrous layer.

hyaloid membrane

The membrane that envelops the vitreous humor.

hyoglossal membrane

A transverse fibrous membrane uniting tongue to hyoid bone.

internal limiting membrane

1. The inner layer of ependymal cells lining the embryonic neural tube.
2. The glial membrane forming the innermost layer of the retina and the iris.

interosseous membrane

1. A fibrous membrane in the arm connecting ulna to radius.
2. A fibrous membrane in the leg connecting tibia to fibula.

laryngeal mucous membrane

The mucous membrane, glands, and cilia that characterize the lining of the larynx.

lingual mucous membrane

The mucosa covering the tongue.

masticatory mucous membrane

The mucosa of the mouth involved in the masticatory process. It is characterized by a keratinized surface epithelium, and includes the hard palate, gingiva, and dorsum of the tongue.

medullary membrane


mucous membrane

Any of the membranes that line passages and cavities communicating with the air, consisting of epithelium, a basement membrane, and an underlying layer of connective tissue (lamina propria). Mucus-secreting cells or glands are usually present in the epithelium but may be absent. In humans, mucous membranes and the skin prevent the entry of pathogens. Mucous membranes are normally colonized with nonpathogenic organisms that discourage colonization by pathogens because the resident organisms compete for the nutrients essential to their survival. Some mucosal surfaces in the digestive tract have special characteristics that tend to repel or kill organisms, such as the extremely high acid level on the mucosa of the stomach.

Noninvasive examination of membranes should reveal the degree of moisture, cyanosis, pallor, hyperemia, pigmentation, lesions or their absence, and hemorrhage. Pallor is seen in all anemias. If the pallor is temporary, it may indicate shock or vasomotor spasm, or it may occur in severe hemorrhages. Blanching and flushing alternately accompany aortic regurgitation.

Hyperemia of the mucous membranes is indicative of certain pathological changes in particular tissues, e, g., of the buccal mucous membrane, due to decayed teeth, traumatism, or stomatitis; of the nasal mucosa, due to ulceration of the nose, rhinitis, or inflammation; of the eyes (local irritation), due to a foreign body, ulcer, inflammation. Dryness is seen in fevers, chronic gastritis, some liver disturbances, excitement, shock, prostration, fatigue, thirst, and certain drugs.

nasal mucous membrane

The mucosa lining the nasal cavity and characterized by pseudostratified ciliated columnar epithelium with goblet cells.

Nasmyth membrane

See: Nasmyth membrane

nictitating membrane

A third eyelid present in lower vertebrates and represented in humans by a fold of the conjunctiva, the plica semilunaris.

nuclear membrane

The two-layered membrane surrounding the chromosomes of a cell. The membrane has pores and its outer layer is continuous with the endoplasmic reticulum of the cell.
See: nuclear envelope

obturator membrane

A fibrous membrane closing the obturator foramen.

olfactory membrane

The membrane in the upper part of the nasal cavity that contains olfactory receptors.

oral membrane

Buccopharyngeal membrane.

oronasal membrane

A double epithelial layer separating the nasal pits from the embryonic oral cavity.

otolithic membrane

A layer of gelatinous substance containing otoconia or otoliths, found on the surface of maculae in the inner ear.

palatal mucous membrane

The lining of the mouth on the hard and soft palates. The hard palate has heavily keratinized epithelium and copious mucous glands or fat in the submucosa. The mobile soft palate contains muscle in addition to mucous glands, and is much less keratinized on the surface.

peridental membrane

An obsolete term for the periodontal ligament.

periodontal membrane


permeable membrane

A membrane that permits passage of water and certain substances in solution.
See: osmosis; selectively permeable membrane; semipermeable membrane

persistent pupillary membrane

See: pupillary membrane

pharyngeal membrane

Buccopharyngeal membrane.

pharyngeal mucous membrane

The lining of the pharynx. The mucosa of the nasopharynx is pseudostratified ciliated epithelium; the mucosa of the oropharynx and laryngopharynx is stratified squamous epithelium.

pial membrane

Pia mater.

placental membrane

The membrane of the placenta that separates the maternal blood from fetal blood.

plasma membrane

Cell membrane.

pseudoserous membrane

A membrane resembling a serous membrane but differing in structure as the endothelium.

pupillary membrane

The transparent membrane closing the fetal pupil. If it persists after birth, it is called persistent pupillary membrane.

pyogenic membrane

The granular lining of an abscess or fistula.

pyophylactic membrane

The lining membrane of an abscess cavity separating it from healthy tissue.

quadrangular membrane

The upper portion of the elastic membrane of the larynx extending from the aryepiglottic folds to the level of the ventricular folds below.

Reissner membrane

See: Reissner membrane

respiratory membrane

Alveolocapillary membrane.

reticular membrane

The membrane formed by the cuticular plates of the distal ends of supporting cells in the organ of Corti.

Ruysch membrane

See: Ruysch membrane

Scarpa membrane

See: Scarpa membrane

schneiderian membrane

The nasal mucosa.

Schwann membrane

See: Schwann, Theodore

selectively permeable membrane

A membrane that allows one substance, such as water, to pass through more readily than another, such as salt or sugar.

semipermeable membrane

A membrane that allows passage of water but not substances in solution.
See: osmosis

serous membrane

A membrane consisting of mesothelium lying on a thin layer of connective tissue that lines the closed cavities (peritoneal, pleural, and pericardial) of the body and is reflected over the organs in the cavity. Serous fluid, similar to lymph, decreases friction between the two layers.

Shrapnell membrane

See: Shrapnell membrane

submucous membrane

See: submucosa.

synovial membrane

The membrane lining the capsule of a joint and secreting synovial fluid. The synovial membrane is pink, smooth, and shiny and is made of an intima lining a stronger, vascular fibrous membrane. The intima contains synoviocytes (fibroblast- and macrophage-like cells), which remove debris from the synovial fluid and synthesize some of the mucin (specifically, hyaluronic acid) of the synovial fluid. Most of the synovial fluid is filtered from the blood vessels of the outer fibrous layer of the synovial membrane. Synonym: synovium

tectorial membrane

The thin, jelly-like membrane projecting from the vestibular lip of the osseous spiral lamina and overlying the spiral organ of Corti of the ear.

thyrohyoid membrane

The membrane joining the hyoid bone and the thyroid cartilage.

tympanic membrane

The three-layered membrane at the inner (medial) end of the external auditory canal, forming the lateral boundary of the middle ear cavity. The outer layer of the tympanic membrane is keratinized skin, continuous with the skin lining the external ear canal. Synonym: drum; eardrum
See: ear thermometry; tympanum

unit membrane

The phospholipid bilayer first described as the typical cell membrane, then as the membrane of intracellular structures.

vapor-permeable membrane

A membrane, usually transparent, that is permeable to oxygen and water vapor. It may be prepared with an adhesive backing that will stick only to dry skin. This type of membrane has been used in covering wounds. The membrane must be applied properly without wrinkles and changed as often as necessary to prevent excess accumulation of fluid and bacteria under it.

vestibular membrane

The membrane in the cochlea of the inner ear that separates the cochlear duct from the vestibular canal.

vestibular mucous membrane

The mucosa of the oral vestibule with its nonkeratinized stratified squamous epithelium, elastic lamina propria, and seromucous labial glands.

virginal membrane

An obsolete term for the hymen.

vitelline membrane

The membrane that forms the surface layer of an ovum. Synonym: yolk membrane; zona pellucida

vitreous membrane

1. The inner membrane of the choroid.
2. The innermost layer of the connective tissue sheath surrounding a hair follicle.

Wachendorf membrane

See: Wachendorf membrane

yolk membrane

Vitelline membrane.
Medical Dictionary, © 2009 Farlex and Partners


a thin sheet of tissue.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


A thin layer of tissue which covers a surface, separates cellular structures or organs, or connects adjacent structures.
basement membrane of the corneal epithelium A very thin non-cellular layer adjacent to Bowman's layer and upon which the columnar basal cells of the corneal epithelium are bound by hemidesmosomes.
Bowman's membrane See Bowman's layer.
Bruch's membrane Thin (about 1.5 μm), shiny, non-vascular layer of the choroid located on the inner side next to the retinal pigment epithelium. It consists of two contiguous layers; the inner one called the lamina vitrea (or basement membrane of the pigment epithelium) and the outer one called the lamina elastica. See angioid streaks.
Descemet's membrane 
Strong, resistant, thin (about 8 μm) layer of the cornea located between the endothelium (from which it is secreted) and the stroma. It is practically the last corneal structure to succumb to disease processes and it can regenerate after injury. Syn. lamina elastica posterior; posterior limiting layer. See descemetocele; Kayser- Fleischer ring.
Elschnig's inner limiting membrane A thin layer of astrocytes covering the optic disc. It is in continuity with the inner limiting membrane of the retina. In some cases this layer is thickened in the central part of the disc to form the central meniscus of Kuhnt. It is transparent and not usually visible with the ophthalmoscope.
hyaloid membrane This is not really a membrane, but a concentration of cells and fibres enclosing the vitreous body.
intermuscular membrane A thin, elastic membrane originating from the muscle sheath of each rectus muscle and connecting it to the neighbouring rectus muscle. The membrane fuses with the capsule of each muscle, as well as with Tenon's capsule.
nictitating membrane A fold of the conjunctival mucous membrane that can be drawn over part or all of the cornea in a winking-like action to clean and lubricate the cornea. It is present in many birds, reptiles, fishes and some mammals and is normally hidden in the inner canthus. Syn. third eyelid. See plica semilunaris.
membrane of the retina, external limiting This layer has the form of a wire netting through which pass the processes of the rods and cones of the retina. It is located between the latter and the outer nuclear layer. It is believed to be formed by the fibres of Mueller. See Mueller's cell.
membrane of the retina, internal limiting Glass-like membrane lying between the retina and the vitreous body and forming a boundary for both. For that reason it has sometimes also been considered to be the hyaloid membrane of the vitreous. The feet of the fibres of Mueller are attached to this membrane but do not form it. Syn. internal limiting layer of the retina. See Mueller's cell.
preretinal membrane See preretinal macular fibrosis.
pupillary membrane Embryonic mesodermal tissue which is present in the centre of the iris and normally disappears by the eighth fetal month to form the pupil. Some strands of the membrane may remain in adults; this is referred to as a persistent pupillary membrane.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


A thin sheet or layer of pliable tissue, serving as a covering or envelope of a part, as the lining of a cavity, as a partition or septum, or as a connector.
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about membrane

Q. HYALINE MEMBRANE DISEASE in pre-mature infants;what are the causes of it in pregnant women?

A. the cause of Hyaline Membrane disease is pre-mature birth. while the fetus develop, about in the 29th week a substance called surfactant is created in the lungs. this substance's function is to change the surface tension of the fluid in the lungs- therefore decreasing it's force. the surface tension tends to shrink the lungs and can cause the lungs to collapse. so a premature baby wouldn't be able to breath properly.

Q. For those that had an epimacular membrane removed, how long was it before your eye healed? How was your vision afterwards? Do you now require or benefit from glasses?

A. Epimacular membrane removal can be associated with a variety of ocular conditions and therefore the healing process varies tremendously depending on the underlying pathology. Furthermore, this condition may recur.

More discussions about membrane
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