[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.

alveolocapillary membrane

The membrane 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.
SYN: SEE: respiratory membrane

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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 is adherent to the inner surface of the dura by dural border cells. It is connected to the pia mater by a spiderweb of thin connections, owing to their common embryological origin as the leptomeninges. The space between the arachnoid and pia (the subdural space) is filled with cerebrospinal fluid.
SYN: SEE: arachnoid; SEE: arachnoid mater

atlanto-occipital membrane

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

basement membrane

A two-part extracellular membrane 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 (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.
illus. under SEE: 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.
SYN: SEE: oral membrane; SEE: 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.
SYN: SEE: plasma membrane

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choroid membrane

SEE: choroid

costocoracoid membrane

The dense membrane between the pectoralis minor and subclavius muscles.

cricothyroid membrane

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

croupous membrane

SEE: False membrane.

Debove membrane

SEE: Debove membrane

decidual membrane

Any 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

SEE: 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

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

epiretinal membrane

A membrane formed from 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 over 50. Marked visual blurring caused by epiretinal membranes occurs in macular pucker.
SEE: macular pucker

external limiting membrane

1. The outer membrane 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

A membrane of fibrinous exudate on a mucous surface of a membrane, as in croup or diphtheria.
SYN: SEE: croupous membrane

fenestrated membrane

A membrane 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 membranes that protect and support the embryo and provide its nutrition, respiration, and excretion. The structures are the 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 membrane that separates membrana granulosa from the theca of the graafian follicle.
2. The internal membrane 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 membrane 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 forearm connecting ulna to radius.
2. A fibrous membrane in the leg connecting tibia to fibula.

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laryngeal mucous membrane

The mucous membrane, glands, and cilia that line 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

SEE: Endosteum.

mucous membrane

Any of the membranes that line passages and cavities communicating with the atmosphere outside the body. They consist 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. Mucous membranes and the skin prevent the entry of pathogens. 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. Others are normally colonized with commensal organisms that discourage the growth of pathogens.

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

SEE: Buccopharyngeal membrane.

oronasal membrane

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

otolithic membrane

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

palatal mucous membrane

The membrane 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

SEE: Periodontal ligament.

periodontal membrane

SEE: Periodontal ligament.

permeable membrane

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

persistent pupillary membrane

SEE: pupillary membrane

pharyngeal membrane

SEE: Buccopharyngeal membrane.

pharyngeal mucous membrane

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

pial membrane

SEE: Pia mater.

placental membrane

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

plasma membrane

SEE: 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 a persistent pupillary membrane.

pyogenic membrane

The granular membrane lining an abscess or fistula.

pyophylactic membrane

The membrane lining 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

SEE: 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

schneiderian membrane

SEE: 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 of 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.
SYN: SEE: synovium

tectorial membrane

The jelly-like membrane projecting from the vestibular lip of the osseous spiral lamina and overlying the spiral organ of Corti of the inner 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.
SYN: SEE: drum; SEE: eardrum
SEE: ear thermometry; SEE: 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.
SYN: SEE: yolk membrane; SEE: 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

SEE: Vitelline membrane.