Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

IC1&3 Physiology of Endocrine > Endocrine System (Thyroid) > Flashcards

Endocrine System (Thyroid) Flashcards

1
Q

Describe the differences between endocrine system and nervous system. (response, signaling, what they regulate)

A

Endocrine system: long-term slow response (slow acting hormone messengers travel through bloodstream to act on specific cell receptors)
Regulates: growth, development, reproduction (maintain homeostasis)

Nervous system: short-term quick response (fast acting electrochemical impulses (neurotransmitters) delivered by neurons (nerve cells) to synapses to target cells)
Regulates: muscles, glands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain two differences between endocrine and exocrine glands.

A
  1. Endocrine gland produce hormones, Exocrine gland produce nonhormonal substances
  2. Endocrine glands are ductless, Exocrine glands carry substances to membrane surface via ducts (e.g., sweat and saliva glands)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Endocrine glands are small in size, how many adults required to collect 1kg of endocrine tissues.

A

8-9 adults

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What hormone does the hypothalamus release? (thyroid + reprod lecture series)

A

Thyrotropin-releasing hormones (TRH)
aka TSH releasing hormone

Reprod: Gonadotropin releasing hormones (GnRH)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What hormone does the anterior lobe of the pituitary gland release? (thyroid + reprod lecture series)

A

Thyroid stimulating hormone (TSH)

Reprod: gonadotropins
Follicle stimulating hormones (FSH)
Luteinizing hormones (LH)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What hormones does the thyroid gland release?

A

Tri-iodothyronine (T3)
Tetra-iodothyronine (Thyroxine) (T4)
Calcitonin (decrease calcium levels)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name 2 synthetic estrogens

A
  1. BPA
  2. Paraben

can cause hastening of puberty, incr incidence of breast tumors, falling sperm counts, cryptorchidism)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Protein and peptide hormones are ___
while steroid and amine hormones are ___

List examples

A

Protein and peptide hormones are hydrophilic
while steroid and amine hormones are lipophilic

Protein: FSH, LH, TSH, insulin, glucagon, inhibin
Steroid: testosterone, progesterone, estrogen, Vit D (calcitriol)
Amines (tryptophan or tyrosine AA): T3, T4, melatonin

Exception hydrophilic amines: catecholamines - epinephrine, norepinephrine from adrenal medulla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does the chemical nature of hormones determine?

A

Solubility, transport mechanism, and location of receptor

Hydrophilic: transported free in blood and bind to cell membrane receptor
Hydrophobic: bound to plasma protein, bind to intracellular receptors

*Does not determine specificity of communication - this is determined by presence of specific receptors on target cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the two mechanisms of hormone imbalance?

A
  1. Excess/Deficiency in secretion of hormones
  2. Excess/Deficiency of target-cell responsiveness
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 2 mechanisms of hormone action after binding to receptor?

A
  1. Signal amplification: only low conc. of hormone required as signal gets amplified (therefore slow acting but long-lasting effect)
  2. Alter: functional and structural proteins, enzyme activation, transcription (trigger intracellular events)
    E.g., alter channel permeability, act through second messenger system, activate specific genes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the mechanism in which hormones may inhibit its own release?

A

Negative feedback

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why are hormone levels reported in a range?

A

Secretion rates of hormones rhythmically fluctuate up and down as a function of time

Negative feedback control helps to regulate the fluctuations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where is the thyroid gland located?

A

In neck, anterior to trachea, below the larynx

Two lobes connected by isthmus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe the histology of thyroid gland

A

Follicle Cells - synthesize globular protein, thyroglobulin (Tg) molecule, in endoplasmic reticulum/golgi complex. Tg is secreted it into the colloid

Colloid - extracellular space, where Tg attached with iodine is stored

Thyroid follicles - functional unit of thyroid hormone production (colloid + surrounding follicle cells)

Parafollicular (C) cells - calcitonin (dcr calcium levels)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the 2 basic ingredients in thyroid hormone (T3, T4) synthesis and how are they obtained?

A
  1. Tyrosine (AA synthesized by the body)
  2. Iodine (obtained from dietary intake) - must be reduced to iodide (I-) prior to absorption by SI
17
Q

What are the 5 main steps involved in thyroid hormone synthesis?

A
  1. Iodide trapping
  2. Iodination
  3. Coupling
  4. Colloid resorption
  5. Thyroglobulin proteolysis
18
Q

Where is thyroperoxidase (TPO) found?
What is the function of thyroperoxidase (TPO)?

A

TPO is a membrane-bound enzyme in follicular cells.

TPO oxidizes iodide (I-) to active iodide (I) in the follicular cell, before active iodide exits through a channel into the colloid

TPO is also responsible for attaching iodide to a tyrosine within the Tg molecule, in the colloid.

19
Q

Tyrosine gets incorporated in the Tg molecule in follicular cells. Subsequently, tyrosine-containing Tg is exported in vesicles from follicular cells into the colloid by exocytosis.

How does iodide get transferred through the follicular cell into the colloid to attach to the Tyrosine-containing Tg molecule?

A

Iodide trapping: thyroid captures iodide (I-) from blood and transfers it into follicular cells by an iodide pump (Na+K+ pump)
==> Iodide transport Na+ into follicular cell down its conc. gradient, I- into cell against its conc. gradient

Iodination: Iodide (I-) is oxidised to active iodide (I) by membrane-bound enzyme, thyroperoxidase (TPO). Active iodide exits through a channel to enter the colloid. Within the colloid, TPO attaches iodide to a tyrosine within the Tg molecule ==> MIT, DIT

*1 iodine to tyrosine within Tg molecule: mono-iodotyrosine (MIT)
*2 iodines to tyrosine within Tg molecule: di-iodotyrosine (DIT)

20
Q

Explain the coupling step in thyroid hormone synthesis.
Are these products attached to the Tg?

A

MIT + DIT = Tri-iodothyronine (T3)

DIT + DIT = Tetra-iodothyronine aka Thyroxine (T4)

Yes, these products remain attached to Tg by peptide bonds.

21
Q

How does colloid resorption into follicular cells take place?

A

Follicular cells internalize a portion of the Tg-hormone complex by phagocytosing a piece of colloid (endocytosis of colloid)

22
Q

How are thyroid hormones stored in the colloid (follicular lumen)?

A

Thyroid hormone bound to Tg for storage in the colloid

23
Q

How is Tg removed from the iodinated products?

A

Thyroglobulin proteolysis occurs via lysosomes (lysosomal enzymes) attacking the engulfed colloid vesicle, and cleaving the peptide bond to remove Tg from the iodinated products

24
Q

Where is iodinase found?
What is the function of iodinase?

A

Iodinase (like TPO) is found in the follicular cells

It removes the iodide from MIT and DIT, allowing the freed iodide to be recycled for synthesis of more hormones

25
Q

Describe the chemical nature of thyroid hormones (T3, T4) and explain their solubility, transport mechanism, and location of receptor.

A

Steroid hormones, lipophilic

Diffuse freely out of follicular cells into circulation where it is bound to plasma protein carriers.

TH acts on intracellular receptors (in nucleus).
TH can also be stored in plasma protein in the plasma

26
Q

90% of TH secreted from thyroid glands is T4. However, T3 is the major biologically active form. How is T4 converted to T3?

A

5-deiodinase enzyme removes an iodine from T4 to form T3.

5-deiodinase is found in liver, kidney, pituitary (peripheral tissues)

27
Q

Not all T4 is converted by 5-deiodinase to active T3. Describe the other route that leads to metabolic inactivation of T4.

A

T4 can also be converted by 5-deiodinase in liver and kidney to rT3 (inactive metabolite) as a means for metabolic inactivation or disposal of T4

28
Q

How are T4 (and to a lesser extent T3) metabolized?

A

They are metabolized by conjugation with glucuronic acid in the liver.
The conjugate is then secreted into bile, and eliminated in feces, with a small amount appearing in urine.

29
Q

Explain how T3 and T4 effects can cause increase in BMR

A

Increase size and number of mitochondria and increase in enzymes that regulate oxidative phosphorylation

==> Lead to increase oxygen consumption and energy use under resting conditions. Incr energy consumption at rest leads to incr heat production (sweat to cool off excess heat)

30
Q

What are 6 physiological effects of T3 and T4?
Also explain how the effects come about.

A
  1. Incr basal metabolic rate (BMR), incr O2 consumption, incr heat production [aka consume more energy while at rest]
  2. Sympathomimetic effects (incr proliferation of catecholamine target-cell receptor cause incr target-cell responsiveness to catecholamines)
  3. Cardiovascular effects (due to incr responsiveness to catecholamines)
  4. Bone growth and maturation (TH stimulates GH secretion and incr IGF-1 pdn by liver, it also promotes the effects of GH and IGF-1 on the synthesis of new structural proteins and on skeletal growth)
    - Thyroid-deficient children ==> growth stunted
    - BUT excessive TH dose not cause excessive growth
  5. Development of nervous system
    - Childhood: development of brain, low levels of TH can cause neuronal retardation
    - Adult: maintenance of CNS activity, high levels of TH can cause hyperactivity
  6. Incr synthesis and degradation (metabolism) of proteins, lipids, and carbohydrates, therefore high levels of TH associated with weight loss
31
Q

Name 3 possible causes of hypothyroidism

A
  1. Primary failure of thyroid gland - goiter (-ve feedback)
  2. Secondary to deficiency of TRH, TSH, or both (hypothalamic or anterior pituitary failure)
  3. Inadequate dietary iodine - goiter (-ve feedback)
32
Q

What are some symptoms of hypothyroidism?

A
  • Intolerance to cold
  • Dull blank expression, listlessness, no energy
  • Extreme fatigue, lethargy, sleepiness
  • Weight gain (dcr BMR)
  • Metal sluggishness, slowed reflexes
  • Impaired memory
  • Brittle nails
  • Constipation
  • Cardiac complications
33
Q

Name 3 possible causes of hyperthyroidism

A
  1. Autoimmune (Graves’ disease) Production of Thyroid Stimulating Immunoglobulin (TSI) - goiter
  2. Secondary to excess TRH, TSH, or both (excess hypothalamic or anterior pituitary secretion) - goiter
  3. Hypersecreting thyroid tumor - no goiter (-ve feedback)
34
Q

What are some symptoms of hyperthyroidism?

A
  • Intolerance to heat, sweating
  • Increase systolic BP
  • Increase HR
  • Tremors
  • Restlessness, hyperexcitable
  • Irritability
  • Diarrhea
  • Weight loss
  • Muscle wasting, weakness (break down)
  • Bulging eyes (exophthalmos)
  • Enlarged thyroid
35
Q

Describe TSI action

A

TSI competes with TSH to bind to TSH receptors on thyroid cells. TSI binds to TSH receptor with greater affinity.

TSI mimics the action of TSH and cause unregulated production and secretion of thyroid hormones, since it is not subjected to negative feedback

36
Q

How does graves’ disease cause bulging eyes?

A

Abnormal fluid retention behind eyeballs cause them to bulge

*steroids can be used to reduce

37
Q

What are 3 treatment options for hyperthyroidism?

A
  1. Anti-thyroid drugs that interfere with TH synthesis
  2. Surgical removal of a portion of the over-secreting thyroid gland
  3. Administration of radioactive iodine
38
Q

What causes diffuse goiter? Explain the changes in growth of thyroid tissue.

*Goiter is readily palpable since thyroid glands lie anterior to trachea

A

Goiter (enlarged thyroid gland) develops when there is overstimulation of thyroid glands by incr in TSI/TSH. This can be caused by hyperthyroidism or hypothyroidism.

Increase growth of thyroid tissue:
- incr follicle formation
- incr size and number of cells
- incr DNA, RNA, protein, and phospholipid synthesis

IC1&3 Physiology of Endocrine (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions