Endocrinology - Lecture 2

Question 1

Where is the thyroid gland located?

Answer 1

Inferior to the larynx

Question 2

T/F - The thyroid gland has more vascular flow per gram of tissue than the kidney.

Answer 2

True - it has an important endocrine function so it needs to be highly vascularized

Question 3

Where does the thyroid develop?

Answer 3

At the base of the tongue and it moves downward during development

Question 4

What does the internal structure of the thyroid gland consist of?

Answer 4

A series of hollow follicles formed by spheres of epithelial cells and filled with colloid

Question 5

What is colloid?

Answer 5

A gel filling the follicle

Question 6

What does the apical surface of follicle (epithelial) face?

Answer 6

Colloid

Question 7

What does the basal surface of the follicle (epithelial) cells face?

Answer 7

Blood supply

Question 8

What is the function of follicle cells?

Answer 8

They dump all of the ingredients needed to make thyroid hormone into the follicle, and thyroid hormone is made extracellularly in the colloid

Question 9

Why is thyroid hormone made in the colloid?

Answer 9

Thyroid hormone is lipid soluble, so it can be stored in the gel of the colloid

Question 10

How is Thyroid hormone synthesized?

Answer 10

1) Iodide is transported from the blood across the basal side of the follicle cells via a Na/I transporter
2) Iodide diffuses down its concentration gradient across the apical membrane into the colloid of the follicle
3) The follicle cells also synthesize a large-tyrosine-rich protein called thyroglobulin (TG), and the enzyme thyroid peroxidase - and both go into the colloid
4) 3 or 4 Iodides are oxidized by thyroid peroxidase and linked to TG

Question 11

Describe the Na/I transporter

Answer 11

A co-transporter from the blood into follicle cells
Na naturally moves down the concentration gradient and I goes along for the ride
This is the rate limiting step for TH synthesis because I is rare in the body

Question 12

How does the I conc. gradient maintain balance?

Answer 12

As soon as I reaches the colloid, it gets integrated

Question 13

What’s the difference between T3 and T4?

Answer 13

T3 is a tri-iodothyronine made from a DIT and an MIT

T4 is a tetra-iodothyronine made from two DITs

Question 14

What stimulates the release of thyroid hormone?

Answer 14

TSH being released from the anterior ptuitary in response to TRH from the hypothalamus

Question 15

What are the steps of secretion of thyroid hormone?

Answer 15

1) In response to TSH, droplets of colloid containing TG+T3/4 are pinocytosed into the follicle cell
2) The droplet fuses with lysozyme with enzymes that cleave off the TG
3) T3 and T4 are released in the cytoplasm by lysosomal hydrolysis
4) T3 and T4 diffuse into the capillaries, and the amino acids from the degraded TG are recycled into new TG

Question 16

Which thyroid hormone is secreted from the thyroid more?

Answer 16

T4 makes up 90% of the TH secreted

But T3 is more biologically active (binds to receptors with greater affinity)

Question 17

What happens to most of the T4? Why?

Answer 17

80% of the T4 that gets secreted is converted to T3 in the liver and kidney
The extra I is sent back to the thyroid to be recycled
This maximizes the concentration gradient for free I in circulation

Question 18

What effect does TH have on the endocrine system?

Answer 18

It has a negative feedback by acting on the anterior pituitary and limits the secretion of TSH and TRH receptors

Question 19

What other effect does TSH have on follicle cells?

Answer 19

It stimulates follicle cell metabolism and replicaiton

Question 20

Where are TH receptors found?

Answer 20

Nuclei in almost all cells in the body

Question 21

What are the 4 isoforms of TH receptors?

Answer 21

a1, a2, B1, B2

Different tissues may express different receptors

Question 22

What happens when TH binds to a receptor?

Answer 22

It dimerizes with another TH receptor and forms a DNA binding protein that regulates gene transcription

Question 23

What does TH regulate?

Answer 23

Many of the proteins that are responsible for effects on cellular metabolism

Question 24

What do unbound TH receptor dimers do?

Answer 24

They can also bind to DNA and typically inhibit transcription
(aka, if there is no TH, transcription is inhibited)

Question 25

What ways can TH increase metabolism?

Answer 25

Increase Na/K ATPase activity
Increase the synthesis of respiratory enzymes
Increase substrate availability
Increase cellular heat produciton
Effect mitochondria growth and replication

Question 26

What effect does TH have on the sympathetic nervous system?

Answer 26

It upregulates B-adrenergic receptors that are critical for responses to the symp-ns
AKA it increases sensitivities to catecholamines

Question 27

What effect does TH have on growth?

Answer 27

Helps synthesize growth hormone (GH)

It also reacts with GH in periphery to have bone growth

Question 28

How does TH effect the central nervous system?

Answer 28

It helps in development and function (especially the myelination of axons)
It also helps in attention and reflexes (maintaining myelination)

Question 29

What is the main cause of hypothyroidism?

Answer 29

Typically a defect to the thyroid itself, or an iodine deficiency
Without iodine, there is insufficient prduction of TH, and there lacks a negative feedback, which increases TRH and TSH, which leads to the growth of a goiter

Question 30

What are some of the minor causes of hypothyroidism?

Answer 30

Autoimmune throiditis - lacks synthesis of TH
Damage or destruction - surgical, radiation, etc
Dysfunction associated with another illness

Question 31

What are the causes of secondary defects associated with hypothyroidism?

Answer 31

Deficits in TRH or TSH synthesis, release, or receptor deficits

Question 32

Chronic symptoms of hypothyroidism

Answer 32

Abnormal circulating concentrations of TH and TSH
Goiter (primary defect only)
Cretinism and mental retardation if condition is during development

Question 33

Symptoms of mild hypothyroidism

Answer 33

Sensitivity to cold

Slight weight gain

Question 34

Symptoms of moderate hypothyroidsm

Answer 34

Fatigue
Reduced bloodflow
Changes in skin tone
Sluggish gastrointestinal activity
Discoloration of skin

Question 35

Symptoms of severe hypothyroidism

Answer 35

Myxedema

Severe bloating

Question 36

What primary defects cause hyperthyroidism?

Answer 36

Thyroid tumors that produce TH without regulation

Inflammation of the gland that leads to production of excess TH

Question 37

How can Grave’s disease cause hyperthyroidism?

Answer 37

Antibodies are produced against TSH, and antibodies are able to activate the TSH receptor, so there is no negative feedback against the synthesis of TH

Question 38

Thyrotoxicosis factitia

Answer 38

Hyperthyroidism that results from consuming excess thyroid hormone either from medication or inappropriately processed meat

Question 39

Symptoms of hyperthyroidims

Answer 39

Abnormal circulating concentrations of TH (high) and TSH (low)
Goiter
Heat intolerance
Weight loss
Increased appetite
Sweating 
CT behind eye swells

Question 40

Treatment for hyperthyroidism

Answer 40

Surgical removal of gland
Destruction of gland using radiactive I
Antithyroid drugs
B-blocks

Question 41

What are some dental issues that can arise due to Hypothyroidism

Answer 41

Delayed dental eruption leading to malocclusion

Anterior open bite

Question 42

What are some dental issues that can arise due to Hyperthyroidism?

Answer 42

Increased susceptibility to caries
Increased susceptibility to periodontal disease
Accelerated dental eruption
Maxillary and mandibular osteoperosis