Parathyroid gland Flashcards
The parathyroid glands play an important role in calcium homeostasis and bone health, predominantly through involvement in calcium and phosphate metabolism.
What is the main hormone of the parathyroid, and what does it do? What other chemicals are important in this process?
The main hormone that mediates the effects of calcium regulation is parathyroid hormone, which acts on the kidneys and bone. PTH increases serum calcium while decreasing serum phosphate concentration.
Vitamin D and calcitonin also play an important role in calcium homeostasis (we’ll get to this later)
Discuss the anatomy of the parathyroid gland as far as where they are, and what arteries and veins supply them
Four small pea-sized structures attached to the posterior aspect of the thyroid gland, external to the fibrous thyroid capsule. The glands are anatomically separated into two superior and two inferior parathyroids. Both sets are supplied by the inferior thyroid artery and the thyroid plexus of veins drain them.
Discuss DiGeorge Syndrome. What causes it and how does it present?
DiGeorge syndrome is a consequence of abnormal development of pharyngeal pouches 3 and 4 due to chromosome 22q11.2 deletion.
Clinical manifestations include hypocalcemia secondary to absence of the parahyroid glands, immune deficiency secondary to absence of thymic tissue leading to abnormal T-Cell maturation, and congenital cardiac malformations.
What are pharyngeal pouches and how do they relate to the parathyroid?
The parathyroid glands are derived from pharyngeal pouch endoderm. Four pharyngeal pouches exist during development, each contributing to the formation of important structures in the head and neck. Each pouch represents an invagination of endodermal tissue within the foregut
Derivatives of the first branchial/pharyngeal pouch
Middle ear cavity, mastoid air cells
Derivatives of the second branchial/pharyngeal pouch
Epithelial lining of palatine tonsil
Derivatives of the third branchial/pharyngeal pouch, dorsal wing vs. ventral wing
dorsal wing - Inferior parathyroids
Ventral wing - Thymus
Derivatives of the fourth branchial/pharyngeal pouch
Superior parathyroids, thyroid gland c-cells
Branchial cysts vs. thyroglossal cysts
Branchial cysts are lesions found lateral to the midline of the neck. They result from failed obliteration of the temporary cervical sinuses.
Thyroglossal duct cysts, found medially, result from failed obliteration of the thyroglossal duct as the thyroid gland migrates inferiorly during development.
When does the third pouch differentiate into two wings?
5 - 6 weeks gestation
What occurs at the seventh week of gestation for the pharyngeal/branchial pouches?
By the 7th week of gestation, the third branchial pouch diverticulum elongates, ultimately allowing the developing thymus and inferior parathyroids to separate from the pharynx
Discuss the derivatives of the 4 branchial clefts and the 4 branchial membranes
First cleft - External auditory meatus
Second, third, fourth clefts - Temporary cervical sinuses (normally obliterated)
First membrane - Tympanic membrane
Second, third, fourth membranes - Temporary structures (normally obliterated)
What is ectopic parathyroid tissue?
Results from abnormal migration. Ectopic parathyroids can be found in the anterior/posterior mediastinum, retroesophageal space, or even within the thyroid or thymus.
Despite abnormal migration, the parathyroids typically remain symmetrical from side to side
What two cell types make up the parathyroid? What are their characteristics and what do they secrete?
Chief cells - Most predominant. They are small, polygonal cells with secretory granules containing PTH, arranged into curvilinear cords separated by capillaries.
Oxyphil cells - Unknown function, are large cells containing abundant acidophilic mitochondria
Where is most of our calcium? In what form is that calcium in?
99% stored in bone, 0.1% found in ECF (extracellular fluid)
40% serum calcium is bound to plasma protein
10% serum calcium is complexed with anions such as phosphate and citrate
50% of serum calcium is in free ionized form
Only free calcium is biologically active