Final answer:
The parathyroid glands are mainly supplied by the inferior thyroid arteries, with the superior thyroid arteries providing additional circulation. The glands have a dense capillary network that aids in hormone secretion.
Step-by-step explanation:
The vascular supply of the parathyroid glands primarily involves the inferior thyroid arteries, with additional contributions from the superior thyroid arteries. These arteries provide blood flow to the parathyroid glands which are located on the posterior surface of the thyroid gland. A rich network of capillaries within each gland facilitates the distribution of nutrients and the secretion of the parathyroid hormone (PTH), essential for regulating blood calcium levels.
The inferior thyroid artery, branching from the thyrocervical trunk, is the main source of arterial blood to the parathyroid glands and the nearby structures of the neck. However, the superior thyroid artery, a branch of the external carotid artery, also supplies a portion of the superior parathyroids. The venous blood from the parathyroid glands generally drains into the thyroid venous plexus, which in turn drains into the internal jugular vein. The capillary network surrounding the secretory cells of the parathyroid glands is essential for the diffusion of parathyroid hormone into the bloodstream.