THE NECK: Parathyroid Gland and Vagus Nerve

What shape, size, and total count characterize the Parathyroid Glands?

Ovoid bodies measuring about 6mm long in diameter, four (4) in number, closely related to the posterior border of the Thyroid gland lying within its fascial capsule

Where are the Superior Parathyroid Glands located?

Constant in position, lying at the level of the middle of the posterior border of the Thyroid gland

Where are the Inferior Parathyroid Glands located?

Lie close to the inferior poles of the Thyroid gland within the fascial sheath, embedded in the Thyroid substance or outside the fascial sheath

Which arteries provide blood supply to the Parathyroid Glands?

Superior and Inferior Thyroid arteries

Into which veins do the Parathyroid Glands drain?

Superior, Middle, and Inferior Thyroid Veins

Which lymph nodes receive drainage from the Parathyroid Glands?

Deep Cervical and Paratracheal lymph nodes

What physiological trigger causes the release of Parathyroid Hormone (PTH)?

Low concentration of calcium in blood

What three target organ actions of Parathyroid Hormone (PTH) result in an increased blood calcium concentration?

Efflux of calcium from bone, decreased loss of calcium in urine, and enhanced absorption of calcium from intestine via Vitamin D

How is the Parathyroid Gland organized histologically by its capsule?

Covered by a thin outer capsule extending septa, which divide the parenchyma into lobules

From which embryological structure are the Parathyroid Glands derived?

Pharyngeal pouches (endoderm)

Which embryological structure gives rise to the Superior Parathyroid Glands?

4th pharyngeal pouch

Which embryological structure gives rise to the Inferior Parathyroid Glands?

3rd pharyngeal pouch

What embryological relationship causes ectopic inferior parathyroid glands, and where are they frequently found?

Close relationship between inferior parathyroid and thymus; frequently seen in the SUPERIOR MEDIASTINUM

What is the morphology and function of Principal (Chief) Cells in the parathyroid gland?

Small, polygonal cells with pale, slightly-acidophilic cytoplasm; synthesize and secrete parathyroid hormone (PTH)

What is the morphology and function of Oxyphil Cells in the parathyroid gland?

Large cells with very acidophilic cytoplasm occurring in clusters; degenerated principal cells that accumulate with age

What change occurs in the parenchyma of the parathyroid gland with increasing age?

Adipocytes replace secretory cells with increasing age

Which hormone secreted by Thyroid Follicular Cells controls metabolic rate?

T3, T4

Which hormone is secreted by Thyroid Parafollicular Cells (C cells)?

Calcitonin

Which cells of the Parathyroid Gland secrete Parathyroid Hormone (PTH)?

Chief cells

What role do Oxyphil Cells in the parathyroid gland serve according to secretory review?

Supportive role

Which secretory cells in the stomach secrete Pepsinogen?

Chief cells

Which secretory cells in the stomach secrete HCl and Intrinsic Factor?

Oxyntic cells (Parietal cells)

The activity of osteoclasts in releasing calcium from bones is a result of stimulation of which hormone?

PTH (Parathyroid Hormone)

How does the Right Vagus nerve travel relative to major vessels in the root of the neck and thorax?

Crosses anterior to the right subclavian artery, runs posterior to the SVC, descends at the right surface of the trachea, and then runs posterior to the right main bronchus

Where does the Right Recurrent Laryngeal Nerve originate and hook?

Gives rise from the right vagus nerve, hooks around the right subclavian artery, and ascends between the trachea and esophagus

Where does the Left Vagus nerve enter the thorax and how does it descend?

Enters thorax between left common carotid and subclavian arteries, behind left brachiocephalic vein, and descends on the arch of the aorta

Where does the Left Recurrent Laryngeal Nerve originate and hook?

Gives rise from the left vagus nerve, hooks around the arch of aorta, and ascends through superior mediastinum in a groove between trachea and esophagus

What functional supply is provided by the Internal Branch of the Superior Laryngeal Nerve?

Sensory above vocal cord area

What functional supply is provided by the External Branch of the Superior Laryngeal Nerve?

Supplies cricothyroid muscle

What functional supply is provided by the Inferior / Recurrent Laryngeal Nerve?

Motor to muscles of phonation except cricothyroid; sensory below vocal cord area

Which nerve branch accompanies the Superior Thyroid Artery during its distal course?

External Laryngeal Nerve

Which nerve branch accompanies the Superior Laryngeal Artery (from Superior Thyroid artery)?

Internal Laryngeal Nerve

Which nerve accompanies the Inferior Thyroid Artery?

Inferior / Recurrent Laryngeal Nerve

What clinical deficits occur from an External Laryngeal Nerve lesion?

Paralysis of cricothyroid muscle resulting in inability to lengthen and loss of tension of vocal cord, mild hoarseness, and monotonous speech

What clinical deficits occur from an Internal Laryngeal Nerve lesion?

Loss of sensation ABOVE the vocal cords and loss of taste on the epiglottis

What clinical deficits occur from a Recurrent Laryngeal Nerve lesion?

Respiratory obstruction, hoarseness, inability to speak, and loss of sensation BELOW the vocal cords

In Thyroidectomy, which nerve may be injured during ligation of the superior thyroid artery?

External laryngeal nerve

Paralysis of the Cricothyroid muscle following partial surgical resection of the Thyroid gland results from severing which nerve?

Superior Laryngeal nerve