2-3-16-Thyroid And Parathyroid Histology (Cole)

Question 1

Where are the parathyroid glands located?

Answer 1

On the posterior surface of the thyroid gland, between or outside the 2 capsules

Question 2

The thyroid follicle consists of this epithelial cell type:

Answer 2

Single layer of epithelium, varies from cuboidal to columnar with activity

Question 3

T4=____

T3=____

Answer 3

T4= Tetraiodothyronine (thyroxine)

T3=Triiodothyronine

Question 4

What type of feedback loop begins with the peripheral endocrine gland?

What type of feedback loop begins with the pituitary gland?

Answer 4

Long –> from the peripheral endocrine gland feeding back to pituitary or hypothalamus

Short –> from the pituitary feeding back to the hypothalamus

Question 5

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

Answer 5

AA’s and Iodide ions

Question 6

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?

Answer 6

Oxidation of 2 iodide ions (2 I-) results in iodine (I2) which passes through the follicle cell membrane into the colloid

Question 7

In the synthesis of thyroid hormones, addition of iodine to tyrosine residues of TGB is carried out by this enzyme ___

Answer 7

Tyrosine peroxidase

Question 8

Thyroid peroxidase activity and the iodination process can be inhibited by __ and __

Answer 8

Propylthiouracil and Methyl Mercaptoimidazole (MMI)

Question 9

Thyroid hormones are stored extracellularly as ___

Answer 9

TGB

Question 10

Describe secretion of T3 and T4

Answer 10

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)

Question 11

More ___ is secreted by the thyroid but ___ is 3-4x more potent

Answer 11

T4

T3

Question 12

___ 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

Answer 12

T3

T4

Question 13

What happens when blood [T3/T4] is low?

Answer 13

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

Question 14

What happens when blood [T3/T4] is high?

Answer 14

Hypothalamus stops TRH release, anterior pituitary stops TSH release

Question 15

What are some functions of thyroid hormone?

Answer 15

Stimulate basic metabolic rate
Augment thermogenesis
Augment glucose production
Required for normal development of CNS

Question 16

This disorder is characterized by excessive production of TSH and symptoms include increase metabolic rate, weight loss, hyperactivity and heat intolerance

Answer 16

Hyperthyroidism

Common causes: excessive stimulation by adenohypophysis, loss of feedback control by thyroid gland (Grave’s), and ingestion of T4 (used for weight loss)

Question 17

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

Answer 17

2nd and 3rd pharyngeal

Anterior

Question 18

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?

Answer 18

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

Question 19

___ is caused by insufficient production of thyroid hormone. Pts present with low metabolic rate, feeling of being cold, weight gain (some)

Answer 19

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

Question 20

___ is an autoimmune disease associated with hypofunction of the thyroid gland and is caused by autoantibodies (antimicrosomal abs.) to thyroid peroxidase and thyroglobulin

Answer 20

Hashimotos disease

Question 21

An __ goiter is caused by iodine deficiency

Answer 21

Endemic

Question 22

___ is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones

Answer 22

Congenital hypothyroidism (AKA Cretinism)

Bone maturation and puberty severly delayed, ovulation impeded and infertility common, neurological and cognitive impairment may be mild

Question 23

___ cells are derived from neural crest, contain small cytoplasmic granules representing the stored hormone Calcitonin

Answer 23

Parafollicular cells (AKA C cells)

Question 24

___ acts to decrease [Ca2+] by inhibiting bone resorption

Answer 24

Calcitonin

Question 25

Calcitonin binds to receptors on ___

Answer 25

Osteoclasts

Question 26

In states of hypercalcemia, blood levels of Ca2+ stimulates ___ secretion

Answer 26

Calcitonin

Question 27

The parathyroid glands originate from the interaction of the endoderm of the ___ pouch

Answer 27

3rd and 4th

Question 28

During the migration of the thymus (pouch 3), the 3rd pouch of the parathyroid glands ends up being ___ to the 4th pouch

Answer 28

Inferior

Question 29

___ cells secrete parathyroid hormone

Answer 29

Chief (principal) cells

Question 30

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.

Answer 30

Ca2+-sensing receptor (CaSR)

Question 31

When the serum Ca2+ concen decreases, the secretion of ___ is stimulated, resulting in an increase in serum Ca2+

Answer 31

PTH

Question 32

PTH acts on osteoblasts to promote ___ activity which results in increase in circulating Ca levels

Answer 32

Osteoclast

Question 33

List functions of PTH

Answer 33

- 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)

Question 34

___ 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

Answer 34

Hypoparathyroidism

Question 35

___ 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

Answer 35

Hyperparathyroidism

Question 36

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)

Answer 36

Rickets

Question 37

In ___, pain, partial bone fractures, and muscular weaknesses are typical in the adult.

Answer 37

Osteomalacia

Question 38

Chronic renal failure or a congenital disorder-resulting in the lack of ___ enzyme-can cause rickets or osteomalacia

Answer 38

1-alpha-hydroxylase