Thyroid

Question 1

Where is the Thyroid located?

Answer 1

Located below the larynx, two lateral lobes w/ a connecting isthmus on anterior surface of the trachea

Question 2

What is the mass of the thyroid?

Answer 2

Largest endocrine gland, 20-30 grams (because it’s purely endocrine)
Has a rich blood supply, one of the body’s highest

Question 3

How many cells make up the thyroid? What are they called?

Answer 3

In a healthy adult, there are over 3,000,0000 follicular cells

Question 4

How much product does the thyroid store? Why is this unique?

Answer 4

2 weeks worth

Thyroid is the only endocrine gland that stores product

Question 5

What is a thyroid follicle?

Answer 5

A microscopic spherical sac (think of a tennis ball)

Follicle is lined by cuboidal follicular cells filled with a protein-rich colloid

Question 6

What is a thyroid follicle filled with?

Answer 6

Thyroglobulin (TGB), a very large glycoprotein

Question 7

How are thyroid hormones formed?

Answer 7

Thyroid hormones are formed by attaching iodine to the aa tyrosine

Question 8

Physically describe TGB

Answer 8

TGB: An amber colored, sticky material

TGB is 5,000 aa long; about 100 are tyrosine

Question 9

What two hormones are produced by follicular cells?

Answer 9

1-T3 or triiodothyronine: 10% of product, most potent

2-T4 or thyroxine: 90% of product, less potent

Question 10

What is TH (Thyroid hormone)?

Answer 10

TH indicates thyroid hormone- the combination of T3 and T4

Question 11

TH is the primary effector of the ________.

Answer 11

Thyroid

Question 12

What are the effects of TH?

Answer 12

↑RR ↑HR ↑Contraction strength

Promotes alertness, bone growth, and development of skin, hair, nails, and teeth

Question 13

How does TH travel?

Answer 13

Attached to a transport protein

Question 14

TH is ____-soluble?

Answer 14

Lipid

Question 15

The transport protein for TH is called?

Answer 15

TBG: thyroxine-binding globulin

B for binding

Question 16

What happens to TH at the target cell?

Answer 16

It’s released from carrier, both enter the cell, then T4 is changed to T3 and then T3 enters the nucleus to affect the cell

Question 17

What are the two cells produced by the thyroid?

Answer 17

Follicular cells
Parafollicular cells (c-cells)

Question 18

What does a C-cell produce?

Answer 18

Calcitonin

Question 19

What is the effect of calcitonin?

Answer 19

“Calcitonin down”
Lower blood Ca++ levels
Promotes calcium deposition
Stimulates osteoblast activity
Decreases osteoclast activity

Question 20

In a child, what is hypothyroidism called?

Answer 20

Cretinism

Question 21

What are the sx of cretinism?

Answer 21

Abnormal bone development: thickened facial features

Lower body temperature, short, mentally retarded

Question 22

What is hypothyroidism in an adult called?

Answer 22

Myxedema

Question 23

What are the sx of myxedema?

Answer 23

Low metabolic rate, dry skin and hair, sluggishness, edema, mental sluggishness, weight gain

Question 24

What are two diseases of hyperthyroidism?

Answer 24

Grave’s disease

Goiter

Question 25

What are the sx of Grave’s disease?

Answer 25

Elevated metabolic rate, elevated heart rate, nervousness, weight loss, abnormal sweating, bulging of eyes, intolerance of heat

Question 26

What is Goiter?

Answer 26

A pathological enlargement of the thyroid gland

Question 27

By what mechanism does goiter occur?

Answer 27

Without iodine the thyroid cannot produce T3 and T4
Without T3 and T4 (TH) in the blood, the pituitary gland does not receive feedback, so it keeps producing TSH (thyroid stimulating hormone)
TSH stimulates the thyroid to produce more TGB, but it’s unusable

Question 28

Increasing TGB amounts leads to ______ of the neck and ________ of the gland.

Answer 28

Swelling

Hypertrophy

Question 29

What is the parathyroid?

Answer 29

Most people have 4, pea-sized glands

Attached to the posterior surface of the thyroid

Question 30

What two kinds of cells compose the parathyroid?

Answer 30

Chief Cells

Oxyphil cells

Question 31

Parathyroid cells are densely packed together, with no ______.

Answer 31

Lumen

Question 32

What does a Chief cell produce?

Answer 32

Produce PTH (parathyroid hormone)
Smaller, but more numerous

Question 33

What do oxyphil cells do?

Answer 33

Unknown what they do

More cytoplasm, fewer of these cells present however

Question 34

What are the effects of PTH?

Answer 34

↑ blood Ca++ levels
So ↑ the number and activity of osteoclasts
Also, induces Ca++ reabsorption in the kidney
↑ rate of vitamin D synthesis and then ↑ rate of Ca++ absorption in the small intestine

Question 35

What is Hypoparathyroidism?

Answer 35

Also, hypocalcemia.

Causes Na channels to open, to ↑ cell permeability to Na+

Question 36

What are the sx of hypoparathyroidism?

Answer 36

Causes depolarizations- muscle spasm, cardiac arrhythmias

Question 37

What is hyperparathyroidism?

Answer 37

Also, hypercalcemia.

Raises blood levels of calcium and phosphate ions

Question 38

What are the sx of hyperparathyroidism?

Answer 38

Bones become soft, deformed, and fragile (because of decreased Ca++)
Promotes formation of kidney stones- which are composed of calcium phosphate
Metastatic calcification: Can also get Ca++ deposits in the soft tissues
Rare

Question 39

What is...?
TH
TSH
TBG
TGB
PTH

Answer 39

TH= Thyroid Hormone
TSH= Thyroid stimulating hormone (goiter)
TBG= Thyroxine-bonding globulin (Txp molecule)
TGB= Thyroglobulin (inside of follicle)
PTH: Pituitary hormone