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Lecture 14 Anatomy فاضل د. احمد
Triangles of the neck
ANTERIOR TRIANGLE
Borders of the anterior triangle: ●Posteriorly: Anterior border of the sternocleidomastoid ●Superiorly: Inferior border of the mandible ●Anteriorly: Midline of the neck Using the hyoid as a keystone, the omohyoid and digastric muscles subdivide the anterior triangle into: ● Submental triangle ● Submandibular triangle ● Carotid triangle ● Muscular triangle All of the triangles within the anterior triangle are paired except for the submental triangle, which spans the right and the left sides of the neck
1. SUBMENTAL TRIANGLE
Borders of the submental triangle: ●inferiorly: Body of hyoid ● laterally: Anterior digastric on right and left ● anteriorly: midline of the neck
Floor of the triangle is composed of the: ● Mylohyoid
Roof is made of the: ● Skin ● Superficial fascia with platysma ● Deep cervical fascia
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2. SUBMANDIBULAR TRIANGLE
Often called the digastric triangle
Borders of the submandibular triangle: ● superiorly: Inferior border of the mandible ●posteriorly: Posterior belly of digastric and stylohioyd muscle ● anteriorly: Anterior belly of digastric
Floor of the triangle is composed of the: ● Hyoglossus ● Mylohyoid ● Middle constrictor
Roof is made of the: ● Skin ● Superficial fascia with platysma ● Deep cervical fascia
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4. MUSCULAR TRIANGLE
Borders of the muscular triangle: ● Inferiorly: Anterior border of the sternocleidomastoid ● Superiorly: Superior belly of omohyoid ● Anteriorly: Midline
Floor of the triangle is composed of the: ● Sternohyoid ● Sternothyroid Roof is made of the: ● Skin ● Superficial fascia with platysma ● Deep cervical fascia
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Thyroid Gland Location and Description The thyroid gland consists of right and left lobes connected by a narrow isthmus. It is a vascular organ surrounded by a sheath derived from the pretracheal layer of deep fascia. The sheath attaches the gland to the larynx and the trachea. Each lobe is pear shaped, with its apex being directed upward as far as the oblique line on the lamina of the thyroid cartilage; its base lies below at the level of the fourth or fifth tracheal ring. The isthmus extends across the midline in front of the second, third, and fourth tracheal rings. A pyramidal lobe is often present, and it projects upward from the isthmus, usually to the left of the midline. A fibrous or muscular band frequently connects the pyramidal lobe to the hyoid bone; if it is muscular, it is referred to as the levator glandulae thyroideae.
Relations of the Lobes Anterolaterally: The sternothyroid, the superior belly of the omohyoid, the sternohyoid, and the anterior border of the sternocleidomastoid
Posterolaterally: The carotid sheath with the common carotid artery, the internal jugular vein, and the vagus nerve
Medially: The larynx, the trachea, the pharynx, and the esophagus. Associated with these structures are the cricothyroid muscle and its nerve supply, the external laryngeal nerve. In the groove between the esophagus and the trachea is the recurrent laryngeal nerve. The rounded posterior border of each lobe is related posteriorly to the superior and inferior parathyroid glands and the anastomosis between the superior and inferior thyroid arteries.
Relations of the Isthmus Anteriorly: The sternothyroids, sternohyoids, anterior jugular veins, fascia, and skin Posteriorly: The second, third, and fourth rings of the trachea The terminal branches of the superior thyroid arteries anastomose along its upper border.
Blood Supply The arteries to the thyroid gland are the superior thyroid artery, the inferior thyroid artery, and sometimes the thyroidea ima. The arteries anastomose profusely with one another over the surface of the gland.
- The superior thyroid artery, a branch of the external carotid artery, descends to the upper pole of each lobe, accompanied by the external laryngeal nerve
- The inferior thyroid artery, a branch of the thyrocervical trunk, ascends behind the gland to the level of the cricoid cartilage. It then turns medially and
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Functions of the Thyroid Gland The thyroid hormones, thyroxine and triiodothyronine, increase the metabolic activity of most cells in the body. The parafollicular cells produce the hormone thyrocalcitonin, which lowers the level of blood calcium.
Parathyroid Glands Location and Description The parathyroid glands are ovoid bodies measuring about 6 mm long in their greatest diameter. They are four in number and are closely related to the posterior border of the thyroid gland, lying within its fascial capsule.
The two superior parathyroid glands are the more constant in position and lie at the level of the middle of the posterior border of the thyroid gland.
The two inferior parathyroid glands usually lie close to the inferior poles of the thyroid gland. They may lie within the fascial sheath, embedded in the thyroid substance, or outside the fascial sheath. Sometimes, they are found some distance caudal to the thyroid gland, in association with the inferior thyroid veins, or they may even reside in the superior mediastinum in the thorax.
Blood Supply The arterial supply to the parathyroid glands is from the superior and inferior thyroid arteries. The venous drainage is into the superior, middle, and inferior thyroid veins.
Lymph Drainage Deep cervical and paratracheal lymph nodes.
Nerve Supply Superior or middle cervical sympathetic ganglia.
Functions of the Parathyroid Glands The chief cells produce the parathyroid hormone, which stimulates osteoclastic activity in bones, thus mobilizing the bone calcium and increasing the calcium levels in the blood. The parathyroid hormone also stimulates the absorption of dietary calcium from the small intestine and the reabsorption of calcium in the proximal convoluted tubules of the kidney. It also strongly diminishes the reabsorption of phosphate in the proximal convoluted tubules of the kidney. The secretion of the parathyroid hormone is controlled by the calcium levels in the blood.
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