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Endocrine > 2-3-16-Thyroid And Parathyroid Histology (Cole) > Flashcards

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

1
Q

Where are the parathyroid glands located?

A

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

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2
Q

The thyroid follicle consists of this epithelial cell type:

A

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

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3
Q

T4=____

T3=____

A

T4= Tetraiodothyronine (thyroxine)

T3=Triiodothyronine

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4
Q

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

What type of feedback loop begins with the pituitary gland?

A

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

Short –> from the pituitary feeding back to the hypothalamus

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5
Q

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

A

AA’s and Iodide ions

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6
Q

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?

A

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

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7
Q

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

A

Tyrosine peroxidase

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8
Q

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

A

Propylthiouracil and Methyl Mercaptoimidazole (MMI)

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9
Q

Thyroid hormones are stored extracellularly as ___

A

TGB

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10
Q

Describe secretion of T3 and T4

A

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)

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11
Q

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

A

T4

T3

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12
Q

___ 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

A

T3

T4

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13
Q

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

A

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

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14
Q

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

A

Hypothalamus stops TRH release, anterior pituitary stops TSH release

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15
Q

What are some functions of thyroid hormone?

A

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

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16
Q

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

A

Hyperthyroidism

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

17
Q

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

A

2nd and 3rd pharyngeal

Anterior

18
Q

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?

A

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

19
Q

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

A

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

20
Q

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

A

Hashimotos disease

21
Q

An __ goiter is caused by iodine deficiency

A

Endemic

22
Q

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

A

Congenital hypothyroidism (AKA Cretinism)

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

23
Q

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

A

Parafollicular cells (AKA C cells)

24
Q

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

A

Calcitonin

25
Q

Calcitonin binds to receptors on ___

A

Osteoclasts

26
Q

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

A

Calcitonin

27
Q

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

A

3rd and 4th

28
Q

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

A

Inferior

29
Q

___ cells secrete parathyroid hormone

A

Chief (principal) cells

30
Q

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.

A

Ca2+-sensing receptor (CaSR)

31
Q

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

A

PTH

32
Q

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

A

Osteoclast

33
Q

List functions of PTH

A
  • 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)
34
Q

___ 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

A

Hypoparathyroidism

35
Q

___ 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

A

Hyperparathyroidism

36
Q

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)

A

Rickets

37
Q

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

A

Osteomalacia

38
Q

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

A

1-alpha-hydroxylase

Endocrine (14 decks)

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