sinus

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1. A depression or cavity formed by a bending or curving.
2. Anatomy.
   1. A dilated channel or receptacle containing chiefly venous blood.
   2. Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils.
3. Pathology. A fistula leading from a pus-filled cavity.
4. Botany. A recess or indentation between lobes of a leaf or corolla.

[Middle English, hollow in the body, from Medieval Latin, from Latin, curve, hollow.]

Any space in an organ, tissue, or bone, but usually referring to the paranasal sinuses of the face. In humans, four such sinuses, lined with ciliated, mucus-producing epithelium, communicate with each nasal passage through small apertures. The ethmoid and sphenoid sinuses are located centrally between and behind the eyes. The frontal sinuses lie above the nasal bridge, and the maxillary sinuses are contained in the upper jaw beneath the orbits. The mastoid portion of the temporal bone contains air cells lined with similar epithelium.

From the Latin, meaning a cavity, channel, or hollow. In the body there are several types of sinus, matching these definitions. The air-containing cavities so-named are within the skull bones, enclosed except for openings into the nasal cavity; these are the frontal sinuses (in each side of the forehead), and the maxillary sinuses (in the cheek bones). Their lining can become acutely or chronically infected (sinusitis), causing pain and muco-purulent nasal discharge (catarrh). The channels known as sinuses are blood-containing spaces such as those in the spleen, liver, and bone marrow; they are not shut off from the circulating blood, but their width allows greater stagnation than in capillary blood vessels, for specific functions such as the addition and the removal of blood cells and other constituents. The venous drainage channels of the brain, inside the skull, and that of the heart muscle, also go by this name; likewise dilated regions of some blood vessels, notably the carotid sinuses in the neck, which have stretch receptors important in the regulation of the arterial blood pressure; also dilated parts of lymphatic channels, and of milk channels behind the nipples. The hollows so named are more often like dead-end channels or pits—abnormal connections to the surface of the skin from deeper areas of infection.

— Stuart Judge

A cavity, recess, or hollow space.

(click to enlarge)
The paranasal sinuses. (credit: © Merriam-Webster Inc.)

Body cavity or hollow. The paranasal sinuses, which are known commonly simply as the sinuses, are any of four sets of cavities in the bones adjoining the nose: maxillary, the largest, between the eye socket and the palate and upper jaw; frontal, just above and between the eye sockets; ethmoid, consisting of 3 – 18 thin-walled cavities between the nasal cavities and the eye sockets; and sphenoid, behind the nasal cavity. All are absent or small at birth, enlarge gradually until puberty, and then grow rapidly. They affect the sound of the voice and may help to warm inhaled air. Their lining produces mucus, which drains into the nasal cavity. Blockage of their outlets by swelling (from allergy or infection; see sinusitis), polyps, or structural problems hampers breathing through the nose and can lead to serious infection. Severe obstruction may require surgery, which must be done with extreme care to avoid harm to nearby brain structures or the eyes.

For more information on sinus, visit Britannica.com.

1. A cavity within a bone filled with air and lined with mucus.

2. A dilated channel allowing the passage of blood, pus, or lymph from deeper tissues to the exterior.

1. a recess, cavity, or channel, as (a) one in bone or (b) a dilated, valveless channel for venous blood.
2. an abnormal channel or fistula, permitting escape of pus. In common, unqualified usage, the word sinus refers to any of the cavities in the skull that are connected with the nasal cavity—the paranasal sinuses.

• anal s's — furrows, with pouchlike recesses at their distal ends, separating the rectal columns; called also anal crypts.
• basilar s. — a dural venous sinus which runs on the floor of the cranial cavity and out through the foramen magnum.
• cavernous s. — an irregularly shaped venous channel between the layers of dura mater of the brain, one on either side of the body of the sphenoid bone and communicating across the midline. Several cranial nerves and, when present, the rete mirabile, course through this sinus.
• cavernous s. syndrome — lesions of the cavernous syndrome, caused by neoplasia or infectious agents, result in a dilated pupil and paralysis of the globe; vision is usually spared.
• cerebral s. — one of the ventricles of the brain.
• cervical s. — a temporary depression in the neck of the embryo containing the branchial arches.
• circular s. — the venous channel encircling the pituitary gland, formed by the two cavernous sinuses and the anterior and posterior intercavernous sinuses.
• conchal s. — cavity of the conchal bone.
• coronary s. — the terminal portion of the great cardiac vein, which lies in the cardiac sulcus between the left atrium and ventricle, and empties into the right atrium.
• dermoid s., dermal s. — see dermoid sinus.
• dorsal sagittal s. — a large dural venous sinus located within the falx cerebri.
• dura mater venous s. — large channels for venous blood forming an anastomosing system between the layers of the dura mater of the brain.
• ethmoidal s. — that paranasal sinus consisting of the ethmoidal cells collectively, and communicating with the nasal meatuses.
• facial s. — see malar abscess.
• frontal s. — one of the paired paranasal sinuses in the frontal bone, each communicating with the middle meatus of the ipsilateral nasal cavity.
• hair s. — see sinus hair.
• infraorbital s. — an air-filled recess in the head of birds which lies lateral to the nasal cavity into which it opens.
• intercavernous s. — channels connecting the two cavernous sinuses, one passing anterior and the other posterior to the stalk of the pituitary gland.
• interdigitalis s. — the cutaneous pouch, which lies between the claws of sheep and some other ruminants and whose wall contains apocrine glands, and whose duct surfaces on the skin just above the coronets; it serves as a trail gland.
• lymphatic s. — irregular, tortuous spaces within lymphoid tissues through which lymph flows.
• maxillary s. — one of the paired paranasal sinuses in the body of the maxilla on either side, opening into the middle meatus of the ipsilateral nasal cavity. In the horse it is divided into two compartments that communicate independently with the nasal chambers. All other sinuses of the horse communicate with the nasal chambers via the caudal maxillary sinus.
• nasal s. — see paranasal sinuses (below).
• s. nerve — a branch of the glossopharyngeal nerve; carries the afferent fibers of the stretch receptors in the wall of the carotid sinus.
• s. node — see sinoatrial node.
• occipital s. — a venous sinus between the layers of dura mater, passing along the midline of the cerebellum.
• paranasal s's — mucosa-lined air cavities in bones of the skull, communicating with the nasal cavity and including ethmoidal, frontal, maxillary and sphenoidal sinuses.
• petrosal s. (inferior) — a venous channel arising from the cavernous sinus and draining into the internal jugular vein.
• petrosal s. (superior) — one arising from the cavernous sinus and draining into the transverse sinus of the dura mater.
• prostatic s. — the dorsolateral recess between the seminal colliculus and the wall of the urethra.
• pulmonary trunk s. — spaces between the wall of the pulmonary trunk and cusps of the pulmonary valve at its opening from the right ventricle.
• red pulp s. — vascular storage in the spleen into which capillaries empty.
• s. reflex arc — afferent fibers are in the sinus nerve; these connect with the cardioinhibitory and vasomotor centers which control blood pressure and heart rate via sympathetic fibers to blood vessels; provides a route for the sinus reflex which relates pressure in the carotid sinus to the performance of the circulatory system.
• renal s. — a recess in the substance of the kidney, occupied by the renal pelvis, calices, vessels, nerves and fat.
• sagittal s. (inferior) — a small venous sinus of the dura mater of large animals found between the cerebral hemispheres and opening into the straight sinus.
• sagittal s. (superior) — a venous sinus of the dura mater that courses between the cerebral hemispheres and ends in the confluence of sinuses.
• scleral venous s. — see schlemm's canal.
• sigmoid s. — a venous sinus of the dura mater on either side, continuous with the straight sinus and draining into the internal jugular vein of the same side.
• sphenoidal s. — one of the paired paranasal sinuses in the body of the sphenoid bone of some species. In the horse it communicates with the nasal cavity via the frontal and caudal maxillary sinuses.
• sphenoparietal s. — one of the venous sinuses of the dura mater, emptying into the cavernous sinus.
• splenic s. — dilated venous channels in the substance of the spleen. See also red pulp sinus (above).
• straight s. — a venous sinus of the dura mater formed by junction of the great cerebral vein and inferior sagittal sinus, and ending in the confluence of sinuses.
• tarsal s. — a space between the calcaneus and talus.
• tentorial s. — straight sinus.
• transverse dura mater s. — a large venous sinus that runs in the attached border of the cerebellar tentorium on either side of the skull.
• transverse pericardial s. — a passage within the pericardial sac, between the aorta and pulmonary trunk cranioventrally, and the left atrium and cranial vena cava dorsally.
• tympanic s. — a deep recess on the medial wall of the middle ear.
• urachal s. — an anomalous closure of the urachal canal in the newborn in which the opening at the umbilicus remains open. The bladder is normal. It is the cause of persistent infection and swelling at the umbilicus in the young animal and may lead to cystitis and pyelonephritis.
• urethral s — a small cavity in the glans penis of the horse, above the urethral process; as a recess of the fossa glandis it is usually filled with a small mass (bean) of inspissated smegma.
• urogenital s. — an elongated sac formed by division of the cloaca in the early embryo, which ultimately forms most of the vestibule, urethra and vagina in the female, and some of the urethra in the male.
• uterine s. — venous channels in the wall of the uterus in pregnancy.
• uteroplacental s. — blood spaces between the placenta and uterine sinuses.
• venae caval s. — the posterior portion of the right atrium into which the inferior and the superior vena cava open.
• s. venarum — a chamber which is the greater part of the right atrium into which the great veins discharge.
• venous s., s. venosus — 1. the common venous receptacle in the heart of the early embryo that receives blood from the umbilical and vitelline veins and from the body via the ducts of Cuvier.
— 2. sinus of venae cavae.
• vertebral s. — a continuation of part of the common occipital vein in birds; it emerges from the foramen magnum and accompanies the vertebral vein.

Sinus may refer to:

Anatomy

In anatomy, where a sinus is a sac or cavity in any organ or tissue:

• Sinus (anatomy), description of the general term
• Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including:
  • the maxillary sinuses, also called the maxillary antra and the largest of the paranasal sinuses, are under the eyes, in the maxillary bones.
  • the frontal sinuses, superior to the eyes, in the frontal bone, which forms the hard part of the forehead.
  • the ethmoid sinuses, which are formed from several discrete air cells within the ethmoid bone between the nose and the eyes.
  • the sphenoid sinuses, in the sphenoid bone at the center of the skull base under the pituitary gland.
• Anal sinuses, the furrows which separate the columns in the rectum
• Dural venous sinuses, venous channels found between layers of dura mater in the brain

In the heart:

• Sinus node, a structure in the superior part of the right atrium
• Sinus rhythm, normal beating on an ECG
• Coronary sinus, a vein collecting blood from the myocardium
• Sinus venosus, a cavity in the heart of embryos
• Sinus venarum, a part of the wall of the right atrium in adults, developed from the sinus venosus

Other:

• Sinus (botany), a space or indentation, usually on a leaf
• Sinus Asperitatis, an area on the Moon

See also

• Hemocoel, a space filled with hemolymph in organisms with open circulatory systems
• Sine a trigonometric math function (Latin sinus)
• Sines, Portugal, a municipality in Alentejo (Latin Sinus)
• Sinusitis, a common ailment resulting in the inflammation of the paranasal sinuses

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Dansk (Danish)
n. - sinus, bihule, hule

Nederlands (Dutch)
holte

Français (French)
n. - sinus

Deutsch (German)
n. - Sinus, Nebenhöhle

Ελληνική (Greek)
n. - κοιλότητα, κοίλωμα, (ανατ.) ιγμόρειο άντρο, κόλπος/-ωμα

Italiano (Italian)
cavità

Português (Portuguese)
n. - cavidade (f) (Anat.), fístula (f) (Med.)

Русский (Russian)
синус, пазуха, свищ

Español (Spanish)
n. - seno

Svenska (Swedish)
n. - sinus, hålighet, håla, bihåla, fistel

中文（简体）(Chinese (Simplified))
窦, 湾, 穴

中文（繁體）(Chinese (Traditional))
n. - 竇, 灣, 穴

한국어 (Korean)
n. - 공동, 구부러짐, (잎의) 결각

日本語 (Japanese)
n. - 洞, 湾曲

العربيه (Arabic)
‏(الاسم) تجويف, جيب, فجوة‏

עברית (Hebrew)
n. - ‮סינוס, גת, חלל בעצם‬

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