Basic Anatomy of the human Endocrine System in the Head and Neck

1. TheEndocrineSysteminthe
HeadandNeck
Dr. Hadi Munib
Oral and Maxillofacial Surgery Resident

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PituitaryGland(HypophysisCerebri)
• The pituitary gland is a small, oval structure attached to the undersurface of the brain
by the infundibulum.
• The gland is well protected by virtue of its location in the sella turcica of the sphenoid
bone.
• Because the hormones produced by the gland influence the activities of many other
endocrine glands, the hypophysis cerebri is often referred to as the master endocrine
gland; it is vital to life.
• The pituitary gland is divided into an anterior lobe, or adenohypophysis, and a
posterior lobe, or neurohypophysis.
• The anterior lobe is subdivided into the pars anterior (sometimes called the pars
distalis) and the pars intermedia, which may be separated by a cleft that is a remnant
of an embryonic pouch.
• A projection from the pars anterior, the pars tuberalis, extends up along the anterior
and lateral surfaces of the pituitary stalk.
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• Relations
• Anteriorly: The sphenoid sinus
• Posteriorly: The dorsum sellae, the basilar artery, and the pons
• Superiorly: The diaphragma sellae, which has a central aperture that allows the
passage of the infundibulum.
• The diaphragma sellae separates the anterior lobe from the optic chiasma.
• Inferiorly: The body of the sphenoid, with its sphenoid air sinuses
• Laterally: The cavernous sinus and its contents
• Blood Supply; The arteries are derived from the superior and inferior hypophyseal
arteries, branches of the internal carotid artery.
• The veins drain into the intercavernous sinuses.
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PituitaryGland(HypophysisCerebri)

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• Functions of the Pituitary Gland
• Influences the activities of many other endocrine glands.
• The pituitary gland is itself controlled by the hypothalamus
• The activities of the hypothalamus are modified by information received along
numerous nervous afferent pathways from different parts of the central nervous
system and by the plasma levels of the circulating electrolytes and hormones.
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PituitaryGland(HypophysisCerebri)

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PinealGland
• A small cone-shaped body that projects posteriorly from the posterior end of the roof
of the third ventricle of the brain.
• The pineal consists essentially of groups of cells, the pinealocytes, supported by glial
cells.
• The gland has a rich blood supply and is innervated by postganglionic sympathetic
nerve fibers.
• Functions of the Pineal Gland; can influence the activities of the pituitary gland, the
islets of Langerhans of the pancreas, the parathyroids, the adrenals, and the gonads.
• The pineal secretions, produced by the pinealocytes, reach their target organs via the
bloodstream or through the cerebrospinal fluid.
• Their actions are mainly inhibitory and either directly inhibit the production of
hormones or indirectly inhibit the secretion of releasing factors by the hypothalamus
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ThyroidGland
• 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.
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ThyroidGland
• 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.
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ThyroidGland
• 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 downward to reach the posterior border of the gland.
• The recurrent laryngeal nerve crosses either in front of or behind the artery, or it may
pass between its branches.
• The thyroidea ima, if present, may arise from the brachiocephalic artery or the arch of
the aorta.
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ThyroidGland
• It ascends in front of the trachea to the isthmus.
• The veins from the thyroid gland are the superior thyroid, which drains into the internal jugular
vein; the middle thyroid, which drains into the internal jugular vein; and the inferior thyroid.
• The inferior thyroid veins of the two sides anastomose with one another as they descend in
front of the trachea.
• They drain into the left brachiocephalic vein in the thorax.
• Lymph Drainage; drains mainly laterally into the deep cervical lymph nodes. A few lymph
vessels descend to the paratracheal nodes.
• Nerve Supply; Superior, middle, and inferior cervical sympathetic ganglia
• 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.
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ThyroglossalCyst
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ParathyroidGlands
• 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.
• 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.
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ParathyroidGland
• 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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TheRootoftheNeck
• Defined as the area of the neck immediately above the inlet into the thorax.
• Muscles of the Root of the Neck
• Scalenus Anterior; is a key muscle to the understanding of the root of the neck.
• It is deeply placed and descends almost vertically from the vertebral column to the 1st
rib.
• Because the muscle is an important landmark in the neck, its relations should be
understood.
• Scalenus Medius; lies behind the scalenus anterior and extends from the transverse
process of the atlas and the transverse processes of the next five cervical vertebrae
downward and laterally to be inserted into the upper surface of the 1st rib behind the
groove for the subclavian artery.
• The muscle lies behind the roots of the brachial plexus and the subclavian artery.
• Subclavian Artery; The right subclavian artery arises from the brachiocephalic artery,
behind the right sternoclavicular joint.
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• It passes upward and laterally as a gentle curve behind the scalenus anterior muscle,
and at the outer border of the 1st rib it becomes the axillary artery.
• The left subclavian artery arises from the arch of the aorta in the thorax.
• It ascends to the root of the neck and then arches laterally in a manner similar to that
of the right subclavian artery
• Subclavian Vein; begins at the outer border of the first rib as a continuation of the
axillary vein.
• At the medial border of the scalenus anterior, it joins the internal jugular vein to form
the brachiocephalic vein.
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TheRootoftheNeck

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TheThoracicDuct
• Begins in the abdomen at the upper end of the cisterna chyli.
• It enters the thorax through the aortic opening in the diaphragm and ascends
through the posterior mediastinum, inclining gradually to the left.
• On reaching the superior mediastinum, it is found passing upward along the left
margin of the esophagus.
• At the root of the neck, it continues to ascend along the left margin of the esophagus
until it reaches the level of the transverse process of the seventh cervical vertebra.
• Here, it bends laterally behind the carotid sheath.
• On reaching the medial border of the scalenus anterior, it turns downward and drains
into the beginning of the left brachiocephalic vein.
• It may, however, end in the terminal part of the subclavian or internal jugular veins.
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References
• Chapter 11: The Head and Neck
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