yolk membrane

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mem·bra·na vit·el·li·na

1. the membrane enveloping the yolk; specifically, the thickened cell membrane of large-yolked oocytes; Synonym(s): ovular membrane, vitelline membrane
2. sometimes used to designate the zona pellucida of a mammalian oocyte.
Synonym(s): yolk membrane

yolk membrane

mem·bra·na vit·el·li·na

(mem-brā'nă vi-tĕ-lī'-nă)
1. The membrane enveloping the yolk; specifically, the thickened cell membrane of large-yolked oocyte.
Synonym(s): ovular membrane.
2. Sometimes used to designate the zona pellucida of a mammalian oocyte.
Synonym(s): yolk membrane.


(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.
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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.


a thin layer of tissue that covers a surface, lines a cavity, or divides a space or organ.

alveolocapillary membrane
a thin tissue barrier through which gases are exchanged between the alveolar air and the blood in the pulmonary capillaries.
membrane-attack complex
complement components C5-C9 which form in terminal stage of either of the complement pathways and lead to cell lysis.
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.
membrane carrier
a mechanism in the cell membrane of epithelial cells in the intestinal mucosa which facilitates the rapid transport of for example glucose, into the cell and thus into the bloodstream.
cell membrane
plasma membrane (below).
membrane channels
see channel.
continuous membrane
the middle of the three membranes on the outside of the yolk of the hen egg.
cricothyroid membrane
the membrane connecting the thyroid cartilage to the cricoid cartilage. It is extensive in the horse and surgical incision through it allows access to the interior of the larynx.
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.
drum membrane
tympanic membrane (below).
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.
extravitelline membrane
the outermost of the three membranes on the outside of the yolk of the hen egg.
false membrane
a membrane similar to the pseudomembrane; fibrinous exudates readily loosened from underlying tissue, as in croupous or pseudomembranous inflammation.
fenestrated membrane
one of the perforated elastic sheets of the tunica intima and tunica media of arteries.
fetal m's
see fetal membranes. See also extraembryonic membranes (above).
fibrous membrane
the strong, fibrous support layer in a joint capsule.
Henle's membrane
see henle's membrane.
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 necropsy in premature human infants. See also hyaline membrane disease.
hyoglossal membrane
a fibrous lamina connecting the under-surface of the tongue with the hyoid bone.
interosseous membrane
the membrane connecting the shaft of the fibula to the tibia.
limiting membrane
one that constitutes the border of some tissue or structure.
mucous membrane
the membrane covered with epithelium that lines many tubular organs of the body.
nictitating membrane
see membrana nictitans.
nuclear membrane
1. either of the membranes, inner and outer, comprising the nuclear envelope.
2. nuclear envelope.
olfactory membrane
the olfactory portion of the mucous membrane lining the nasal fossa.
periodontal membrane
perivitelline membrane
the innermost of the three layers on the outside of the yolk in the hen egg.
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.
membrane potential
of a cell is the voltage difference across the cell membrane resulting from the differential concentrations of sodium and potassium on either side of the membrane. The resting potential, for example in a nerve cell, is altered by the temporary opening of the sodium channels in the membrane during an action potential, allowing a redistribution of the ions.
membrane proteins
the large number of proteins attached to a cell membrane. They include integral proteins, called also intrinsic, which are embedded in the phospholipid bi-layer of the cell membrane, and peripheral proteins, called also extrinsic, because they are loosely bound and can readily be extracted without damage to the cell membrane.
pupillary membrane
a vascular membrane which occupies the pupil in the embryo stage, completely covering the anterior surface of the lens but subsequently disappears. See also persistent pupillary membrane.
Reissner's membrane
the thin anterior wall of the cochlear duct, separating it from the scala vestibuli.
Scarpa's membrane
tympanic membrane, secondary.
semipermeable membrane
one permitting passage through it of some but not all substances.
serosal membrane
see serous membrane (below).
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.
shell membrane
the membrane on the outside of the soft contents of the hen egg and just inside the shell. It consists of two membranes close together, with an air cell in between.
synovial membrane
see synovial membrane.
membrane transport
transport of electrolytes across semipermeable membranes with the aid of a transporter.
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.
wing membrane
the membrane comprising the wing of the bat.
yolk membrane
the membrane investing the yolk of the hen egg; it includes (from the inside out) the perivitelline, the continuous and the extravitelline membranes.