2-3-16-Thyroid And Parathyroid Histology (Cole) Flashcards
Where are the parathyroid glands located?
On the posterior surface of the thyroid gland, between or outside the 2 capsules
The thyroid follicle consists of this epithelial cell type:
Single layer of epithelium, varies from cuboidal to columnar with activity
T4=____
T3=____
T4= Tetraiodothyronine (thyroxine)
T3=Triiodothyronine
What type of feedback loop begins with the peripheral endocrine gland?
What type of feedback loop begins with the pituitary gland?
Long –> from the peripheral endocrine gland feeding back to pituitary or hypothalamus
Short –> from the pituitary feeding back to the hypothalamus
In the synthesis of thyroid hormones, binding of TSH to its receptors in the follicle cells of the thyroid gland causes the cells to actively transport __ and __ across their cell membrane from the bloodstream into the cytosol
AA’s and Iodide ions
In the synthesis of thyroid hormones, iodide ions move to the lumen of the follicle cells that border the colloid where they undergo oxidation. The oxidation of 2 iodide ions results in what?
Oxidation of 2 iodide ions (2 I-) results in iodine (I2) which passes through the follicle cell membrane into the colloid
In the synthesis of thyroid hormones, addition of iodine to tyrosine residues of TGB is carried out by this enzyme ___
Tyrosine peroxidase
Thyroid peroxidase activity and the iodination process can be inhibited by __ and __
Propylthiouracil and Methyl Mercaptoimidazole (MMI)
Thyroid hormones are stored extracellularly as ___
TGB
Describe secretion of T3 and T4
Endocytosis and digestion of colloid as a result of TSH stimulus –> colloid droplets fuse with lysosomes –> digestive enzymes breakdown TGB, releasing T3, T4, and iodine –> T3 and T4 diffuse through membrane into capillary (capillary transport is facilitated by thyroxine-binding protein)
More ___ is secreted by the thyroid but ___ is 3-4x more potent
T4
T3
___ has a shorter 1/2 life (18 hrs), and is more potent than its other thyroid hormone counterpart
___ has a 1/2 life of about 5-7 days and represents about 90% of secreted thyroid hormones
T3
T4
What happens when blood [T3/T4] is low?
Hypothalmus releases TRH –> TSH released by anterior pituitary –> TSH triggers release of T3 and T4 by thyroid follicle cells –> T3 and T4 act to increase basal metabolic rate of cells, increase body temperature (calorigenic effect) –> negative feedback –> elevated T3 and T4 levels inhibit release of TRH and TSH
What happens when blood [T3/T4] is high?
Hypothalamus stops TRH release, anterior pituitary stops TSH release
What are some functions of thyroid hormone?
Stimulate basic metabolic rate
Augment thermogenesis
Augment glucose production
Required for normal development of CNS
This disorder is characterized by excessive production of TSH and symptoms include increase metabolic rate, weight loss, hyperactivity and heat intolerance
Hyperthyroidism
Common causes: excessive stimulation by adenohypophysis, loss of feedback control by thyroid gland (Grave’s), and ingestion of T4 (used for weight loss)
The thyroid diverticulum grows inferiorly, often between the skeletal elements of the ___ arches. It then migrates to a position ___ to the upper portion of the developing trachea
2nd and 3rd pharyngeal
Anterior
You are observing a pt whose eyes appear to be bulging out, is tachycardic, and has an enlargement of the anteromedial portion of her neck. You run a test specific for Graves disease. What result would you expect if the test came back positive?
The pt has antibodies to TSH receptors on the follicular epithelium.
Graves–> Abs bind to receptor and chronically stimulate thyroid. Autoimmune; Too much circulating thyroid hormone; Enlargment of the thyroid gland (goiter), bulging of eyes (exopthalmos), tachycardia, warm skin, and fine finger tremors
___ is caused by insufficient production of thyroid hormone. Pts present with low metabolic rate, feeling of being cold, weight gain (some)
Hypothyroidism –> in the adult, it is manifested by coarse skin with a puffy appearance due to accumulation of proteoglycans and retention of fluid in the dermis of skin (myxedema) and muscle
Caused by decrease I2 intake, loss of pituitary stimulation, post-therapeutic or destruction of thyroid by the IS
___ is an autoimmune disease associated with hypofunction of the thyroid gland and is caused by autoantibodies (antimicrosomal abs.) to thyroid peroxidase and thyroglobulin
Hashimotos disease
An __ goiter is caused by iodine deficiency
Endemic
___ is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones
Congenital hypothyroidism (AKA Cretinism)
Bone maturation and puberty severly delayed, ovulation impeded and infertility common, neurological and cognitive impairment may be mild
___ cells are derived from neural crest, contain small cytoplasmic granules representing the stored hormone Calcitonin
Parafollicular cells (AKA C cells)
___ acts to decrease [Ca2+] by inhibiting bone resorption
Calcitonin
Calcitonin binds to receptors on ___
Osteoclasts
In states of hypercalcemia, blood levels of Ca2+ stimulates ___ secretion
Calcitonin
The parathyroid glands originate from the interaction of the endoderm of the ___ pouch
3rd and 4th
During the migration of the thymus (pouch 3), the 3rd pouch of the parathyroid glands ends up being ___ to the 4th pouch
Inferior
___ cells secrete parathyroid hormone
Chief (principal) cells
The ___ is associated with G protein in the plasma membrane of the chief cells. Serum Ca2+ binding to the EC region of this triggers the release of IC signals suppressing the secretion of the paraythyroid hormone, with the consequent decrease in the serum Ca2+ concen.
Ca2+-sensing receptor (CaSR)
When the serum Ca2+ concen decreases, the secretion of ___ is stimulated, resulting in an increase in serum Ca2+
PTH
PTH acts on osteoblasts to promote ___ activity which results in increase in circulating Ca levels
Osteoclast
List functions of PTH
- Acts on osteoblasts to promote osteoclast activity –> increase circulating Ca levels
- Act on renal tubules to stimulate resorption of Ca
- COntrol rates of Ca uptake in GI tract by regulating production of Vit D (kidneys)
- Vit D stimulates cells of intestinal mucosa to absorb Ca and synthesize Calbindin (carrier protein)
___ is characterized by a deficiency in PTH secretion, low blood Ca levels but bone Ca is not released. The Ca deficiency results in spontaneous depolarization of neurons and muscle fibers resulting in tetany
Hypoparathyroidism
___ is characterized by high blood Ca levels, results in bone loss (Can result in osteomalacia and osteitis fibrosa cytica), and can cause abnormal Ca deposition in arteries and kidneys
Hyperparathyroidism
In ___, bone remodeling is defective. The ends of the bones bulge (rachitic rosary at the costochondral junctions), and poor calcification of the long bones causes bending (bowlegs or knock-knees)
Rickets
In ___, pain, partial bone fractures, and muscular weaknesses are typical in the adult.
Osteomalacia
Chronic renal failure or a congenital disorder-resulting in the lack of ___ enzyme-can cause rickets or osteomalacia
1-alpha-hydroxylase
