Thyroid and Parathyroid Histology

Question 1

Describe the formation of the thryoid gland.

Answer 1

Endodermal mass of cells invaginates into the underlying mesoderm, creating the thyroid diverticulum that is positioned between anterior 2/3 and posterior 1/3 of the developing tongue.

Question 2

What pharyngeal arches do the thyroid diverticulum grow in between?

Answer 2

2nd and 3rd

Question 3

During what week of embryonic development does thyroid gland respond to TSH?

Answer 3

week 22.

Question 4

What’s Cretinism

Answer 4

Congenital absence of thyroid gland causing irreversible neurologic damage in the infant

Question 5

Describe the steps in synthesis of thyroid hormone.

Answer 5

1. TSH binds, and the cell actively transport aa and iodide ions across the cell membrane. Iodide ions concentration inside the cell increase = Iodide trap
2. Oxidation (organification) takes places in the lumen of colloid
3. Iodine is added to tyrosine residues on TGB
4. MIT and DIT binds. if two DIT binds = T4. if a MIT and a DIT binds = T3
5. The TGB bound T3 and T4 is stored until stimulation.
6. Upon TSH stimulation the complex is endocytosed and via lysosomes TGB is broken down releasing T4 and T3 and Iodide. T4 and T3 are relased into the blood, and the rest are reccyled.

Question 6

What enzyme is responsible for the addition of iodine to tyrosine residues of TGB

Answer 6

Tyrosine peroxidase

Question 7

Thyroid peroxidase activity and the iodination process can be inhibited by what drugs?

Answer 7

Propylthiouracil and methyl mercaptoimidazole

Question 8

What is the MOA of mercaptoimidazole and PTU?

Answer 8

Inhibits the binding of I (organizfiaiotn)

Question 9

Thyroxine-binding protein functions to _.

Answer 9

it’s a capillary transport protein that transports T3 and T4 in the blood.

Question 10

What is the ratio of bounnd vs unbound thyroid hormone int he blood?

Answer 10

> 1% is free

99% is bound to Thyroxine binding globulins, to albumins or others

Question 11

What is the basic functions of thyroid hormones?

Answer 11

Stimulates basic metabolic rate, augment thermogenesis, ,augments glucose production, and is required for normal development of the CNS

Question 12

What are some symptoms of hyperthyroidism?

Answer 12

Increased metabolic rate, weight loss, hyperactivity and heat intolerance

Question 13

What are some common causes of hyperthyroidism?

Answer 13

1. excessive stimulation by adenohypophysis
2. loss of feedback control by thyroid gland (graves disease)
3. ingestion of T4 (used for weight loss)

Question 14

What is Grave’s disease caused by?

Answer 14

Autoimmune disorder that produces antibodies to the receptors for TSH on the follicular epithelium . the bound antibody chronically stimulate thyroid gland to release thryoid hormone. Feedback loop doenst work to inhibit it.

Question 15

what are some symptoms of Graves disease?/

Answer 15

1. enlargement of the thyroid gland (goiter), bulding of the eyes (exophthalmos), tachycardia, warm skin, fine finger tremors are typical clinical features

Question 16

How can graves disease be treated?

Answer 16

Surgical removal, radioactive iodine. Post Tx regimen requires supplementation of thyroid hormones.

Question 17

What are some symptoms of low hypothyroidism?

Answer 17

low metabolic rate, feeling of being cold, weight gain (some patients). In adults coarse skin with puffy appearance due to accumulation of proteoglycans and retention of fluid in the dermis of the skin (myxedema) and msucle.

Question 18

What is Hashitomo’s disease?

Answer 18

autoimmune disease associated with hypofunction of the thyroid gland, caused by autoantibodies (antimicrosoaml antibodies) to thyroid peroxidase and thyroglobulin.

Question 19

How can Hashitomo’s disease be treated?

Answer 19

oral thyroid medication

Question 20

Condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones is characteristics of what disorder?

Answer 20

FKA cretinism aka congenital hypotheyroidism

Question 21

Bone maturation and puberty are severely delayed and ovulation is impeded and interility is common, neurological impairment with reduced muscle tone, and cognitive impairment are all characteristics of what type of disorders.

Answer 21

COngential hypothyroidism aka FKA cretinism.

Question 22

Calcitonin are made where?

Answer 22

In parafollicular cells (C cells) in the follicular epithelium of thyroid gland

Question 23

Calcitonin binds to receptors on what types of cells?

Answer 23

Osteoclasts

Question 24

What gland originates from the interaction of the endoderm of the third and fourth pouch?

Answer 24

parathyroid gland

Question 25

The position of the parathyroid gland switches during development such that the pair of glands which is ultimately inferior develops from which pouch?

Answer 25

Third pouch. superior ones are from 4th pouch.

Question 26

What’s responsible for the switching of the parathyoid pouches?

Answer 26

Migration of the thymus

Question 27

Which cell type are more numerous in the parathyroid glands?

Answer 27

Chief or principal cells

Question 28

what are two cell types found in the parathyroud gland?

Answer 28

Chief cells and oxyphil cells.

Question 29

What cell types secrete PTH?

Answer 29

chief (principal) cells.

Question 30

What receptors on the chief cells sense Ca and then riggers the release of intracellular signals suppressing the secretion of parathyroid horone.

Answer 30

Ca-sensing receptor (CaSR)

Question 31

What cells in the bone do PTH act on?

Answer 31

Acts on osteoblast to prmote osteoclast activity –> increase in circulating Cal levels.

Question 32

How does PTH control rate of Ca uptake in the GI tract?

Answer 32

By regulating production of vitamin D in the kidneys.

Question 33

In response to PTH, vitamin D production is stimulated, vit D then acts on the intestinal mucosa to do what two things?

Answer 33

Absorb Ca and synthesize Calbindin (carrier protein)

Question 34

Ca deficiency resulting in spontaneous depolarization of neurons and muscle fibers resulting in tetany is seen what condition that which cannot sense low blood calcium.

Answer 34

Hypoparathyroidism

Question 35

What are the consequences of hyperparathyroidism?

Answer 35

High blood calcium, bone loss leading to osteomalacia and osteitis fibrosis cystica; abnormal calcium deposition in arteries and kidneys.

Question 36

The calcification of the bone matrix osteoid is deficient in rickets and osteomalacia due to _

Answer 36

Deficiency of vitamin D

Question 37

Rachitic rosary at the costochondral junction, poor calcification of the long bones causing bowlegs or knock-knees are associated with which Vitamin D deficient disease?

Answer 37

Rickets