Thyroid
gland -- secretes a hormone regulating the basal metabolic rate
and a hormone regulating blood calcium levels.
Examine a section of thyroid gland. Identify
thyroid follicles, composed
of follicle cells in a simple cuboidal epithelium, which are
organized into lobes by supporting tissue septa continuous with the
thin capsule.
Clinical note: Increased
height of thyroid follicular cells and infoldings of the follicle
wall are indications of hyperthyroidism or Grave’s disease, a
disorder characterized by restlessness, sleeplessness, tremor, and a
noticeable exophthalmos. Treatment is by subtotal thyroidectomy or
use of radioactive iodine to destroy or inactivate thyroid
follicles.
Identify the calcitonin-secreting,
pale parafollicular cells (or clear cells, which are
closely associated with the thyroid follicles but are not usually in
contact with their lumens. With the light microscope, parafollicular
cells can be very difficult to distinguish from follicle cells.
In what sense can thyroid
follicles be considered both exocrine and endocrine?
Parathyroids
are next. |