Brainscape's Knowledge GenomeTM

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


See full index

PHGY 216 mod 1 > Section 3 > Flashcards

Section 3 Flashcards

1
Q

Where is the thyroid gland located in the body?

A

The thyroid gland is located over the trachea just below the larynx.

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

How many lobes does the thyroid gland consist of, and how are they connected?

A

The thyroid gland consists of two lobes connected by a thinner section of the gland known as the isthmus.

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

Is there any functional difference between the lobes of the thyroid gland?

A

No, there is no difference between the lobes of the thyroid gland. The entire gland serves the same function, which is to produce and secrete thyroid hormones.

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

What is the thin section connecting the lobes of the thyroid gland called?

A

The thin section connecting the lobes of the thyroid gland is known as the isthmus.

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

What is the primary function of the thyroid gland?

A

The primary function of the thyroid gland is to produce and secrete thyroid hormones.

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

What is the arrangement of follicular cells in the thyroid gland?

A

Follicular cells are arranged to form hollow spheres throughout the thyroid gland.

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

How do follicles appear in a microscopic section of the thyroid gland?

A

When looking at a microscopic section of the gland, follicles, which are formed by the arrangement of follicular cells, appear as ring-like structures

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

Besides follicular cells, what is another cell type present in the thyroid gland, and what hormone do they secrete?

A

Another cell type in the thyroid gland is C cells, and they secrete calcitonin.

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

What is the colloid primarily made up of in the thyroid gland?

A

The colloid is primarily made up of a large protein molecule called thyroglobulin, where the thyroid hormones are synthesized and stored.

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

Define Follicular Cells.

A

Follicular cells are the secretory cells of the thyroid gland.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the substance that fills the inside or lumen of the follicles in the thyroid gland called?

A

Colloid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What amino acid is the thyroid gland hormones produced from?

A

The thyroid gland produces hormones from the amino acid tyrosine.

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

What is the unique feature of both thyroid hormones in terms of their composition?

A

Both thyroid hormones contain iodine as a unique feature.

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

What is the collective term for both thyroid hormones, and why are they referred to as such?

A

Both thyroid hormones are collectively referred to as thyroid hormone because they exert the same physiological effects, with differences in their speed and intensity of action.

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

Which thyroid hormone is considered more active, and why?

A

T3 (Triiodothyronine) is considered the more active thyroid hormone, as T4 (Tetraiodothyronine or thyroxine) is converted to T3 in target tissues.

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

ow many iodine molecules does Tetraiodothyronine (T4 or thyroxine) contain, and what percentage does it represent of the thyroid hormones secreted?

A

T4 (Tetraiodothyronine or thyroxine) contains four iodine molecules and represents about 90% of the thyroid hormones secreted.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How many iodine molecules does Triiodothyronine (T3) contain, and what percentage does it represent of the thyroid hormones secreted?

A

T3 (Triiodothyronine) contains three iodine molecules and represents the remaining 10% of secreted hormone.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

From where do follicular cells obtain the basic building blocks of tyrosine and iodine?

A

Follicular cells obtain the basic building blocks of tyrosine and iodine from the blood.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How much iodine does the body require per week for sufficient levels of thyroid hormone?

A

The body requires about 1 mg of iodine per week for sufficient levels of thyroid hormone.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What form does iodine circulate as once ingested, and how efficient is the thyroid gland in extracting it from the blood?

A

Once ingested, iodine circulates as iodide (I)*, and the thyroid gland is very efficient in extracting iodide from the blood, taking up essentially all iodide into the gland.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does the thyroid gland store enough thyroid hormone to endure periods when dietary iodine is not available?

A

The thyroid gland stores enough thyroid hormone by protecting the fully formed hormones from secretion while they are bound to thyroglobulin in the colloid of the thyroid gland.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Why are thyroid hormones considered an exception among lipophilic hormones regarding storage?

A

Thyroid hormones are considered an exception among lipophilic hormones because the fully formed hormones can be protected from secretion while they are stored bound to thyroglobulin in the colloid of the thyroid gland.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How do Canadians generally meet their dietary iodine needs?

A

Canadians generally meet their dietary iodine needs through consuming common table salt, which is supplemented with iodine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the first step in the synthesis of thyroid hormones?

A

The first step in the synthesis of thyroid hormones is the production of tyrosine-containing thyroglobulin within the follicular cells by the endoplasmic reticulum-Golgi complex. It is then transported to the colloid by exocytosis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How is iodide taken up by follicular cells in the process of iodide trapping?

A

Iodide is taken up by follicular cells through a process called iodide trapping, where iodide is driven against its concentration gradient by using a Na+-cotransporter that moves Na+ down its concentration gradient.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the next step after iodide is taken up by follicular cells in the synthesis of thyroid hormones?

A

Iodide is transferred into the colloid of the follicular lumen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What enzyme converts iodide into a highly reactive state (iodine) in the colloid, and what is this process called?

A

The enzyme thyroperoxidase converts iodide into a highly reactive state, iodine (I0), in the colloid. This process is called iodide organification.

28
Q

What are the products of the iodide organification process?

A

The attachment of one iodine to a tyrosine produces monoiodotyrosine (MIT), while the attachment of a second iodine produces diiodotyrosine (DIT).

29
Q

What is the final step in the synthesis of thyroid hormones?

A

The final step involves a coupling process that combines MITs and DITs to form the thyroid hormones. The coupling of one MIT and one DIT forms triiodothyronine (T3), while the coupling of two DITs forms tetraiodothyronine (T4).

30
Q

What is important to note about the chemical reactions in the synthesis of thyroid hormones?

A

It is important to note that both T3 and T4 remain bound to the thyroglobulin molecule after the chemical reactions.

31
Q

Describe the synthesis of thyroid hormones (step-by-step process)

A
  1. Tyrosine-containing thyroglobulin is produced within the follicular cells by the endoplasmic reticulum-Golgi complex and is transported to the colloid by exocytosis.
  2. Iodide is taken up by follicular cells through a process called iodide trapping. Iodide is driven against its concentration gradient by using a Na+-cotransporter that moves Na+ down its concentration gradient.
  3. Iodide is then transferred into the colloid of the follicular lumen.
  4. Almost simultaneous to the iodide moving into the colloid, the enzyme thyroperoxidase
    converts iodide into a highly reactive state, iodine (I0), which immediately attaches to a tyrosine residue on a thyroglobulin molecule. This process is called iodide organification. The attachment of one iodine to a tyrosine produces monoiodotyrosine (MIT), while the
    attachment of a second iodine produces diiodotyrosine (DIT).
  5. A coupling process occurs that combines MITs and DITs to form the thyroid hormones. The coupling of one MIT and one DIT forms triiodothyronine (T3) while the coupling of two DITs forms tetraiodothyronine (T4)
32
Q

What is the first step in the process of releasing thyroid hormones from the thyroid gland?

A

The first step is that follicular cells engulf a portion of the thyroglobulin-containing colloid by phagocytosis and create hormone-filled vesicles.

33
Q

What happens once the hormone-filled vesicles are inside the follicular cell in the process of releasing thyroid hormones?

A

Once inside the follicular cell, lysosomes fuse with the vesicles, and digestive enzymes release all of the MIT, DIT, T3, and T4 from the thyroglobulin.

34
Q

What happens to T3 and T4 once released from the thyroglobulin inside the follicular cell?

A

Because T3 and T4 are very lipophilic, they immediately cross the plasma membrane to the blood.

35
Q

What do T3 and T4 bind to in the blood after crossing the plasma membrane in the process of releasing thyroid hormones?

A

T3 and T4 bind to plasma proteins, mainly thyroid-binding globulin, in the blood.

36
Q

How do the actions of thyroid hormones compare to other hormones in terms of speed?

A

Compared to other hormones, the actions of thyroid hormones are slow.

37
Q

How long can it take before the effects of thyroid hormones are observed, and how long can the duration of the response last?

A

It can take hours before the effects of thyroid hormones are observed, and the duration of the response can last for days, even after plasma concentrations of thyroid hormone have returned to normal.

38
Q

What is one major effect of thyroid hormone on metabolic rate and heat production?

A

Thyroid hormone increases the overall basal metabolic rate by increasing oxygen consumption and energy expenditure, leading to increased heat production.

39
Q

How does thyroid hormone influence intermediary metabolism, and what are the effects at low and high concentrations?

A

Thyroid hormone influences the enzymes involved in fuel metabolism. At low concentrations, it favors the conversion of glucose to glycogen and protein synthesis, while at higher concentrations, it causes the breakdown of glycogen to glucose and the degradation of proteins.

40
Q

How does thyroid hormone affect a target cell’s response to catecholamines?

A

Thyroid hormone increases a target cell’s response to catecholamines by increasing the number of catecholamine receptors.

41
Q

What cardiovascular effects does thyroid hormone have on the heart?

A

Thyroid hormone, due to its sympathomimetic effect, increases both heart rate and the strength of contraction to increase cardiac output.

42
Q

What are the cardiovascular effects of thyroid hormone on blood volume, flow, and blood pressure?

A

Thyroid hormone increases blood volume and flow but does not impact blood pressure.

43
Q

How does thyroid hormone influence growth, and what are its effects on the synthesis of new structural proteins and skeletal growth?

A

Thyroid hormone is essential for normal growth. It stimulates the release of both growth hormone and insulin-like growth factor, promoting their actions to stimulate the synthesis of new structural proteins and skeletal growth.

44
Q

What does the hypothalamus secrete relevant to the thyroid gland, and what is its action on the anterior pituitary?

A

The hypothalamus secretes thyrotropin-releasing hormone (TRH), which acts on the anterior pituitary to secrete thyroid-stimulating hormone (TSH).

45
Q

What is the most important regulator of thyroid hormone secretion, and what are its influences on the stages of thyroid hormone synthesis and release?

A

Thyroid-stimulating hormone (TSH) is the most important regulator of thyroid hormone secretion, and it influences most of the stages of thyroid hormone synthesis and release.

46
Q

How does TSH directly affect the thyroid gland in terms of size?

A

In the absence of TSH, the thyroid gland shrinks in size. Conversely, with excess TSH, thyroid gland follicles get larger and increase in number.

47
Q

What type of control is the release of both TSH and TRH under?

A

The release of both TSH and TRH is under negative feedback control.

48
Q

What is hypothyroidism, and what system does it affect?

A

Hypothyroidism, also called low thyroid or underactive thyroid, is a disorder of the endocrine system.

49
Q

What are the three main causes of hypothyroidism?

A
  1. Primary failure of the thyroid gland: One example is Hashimoto’s thyroiditis, an autoimmune disorder where antibodies target the thyroid gland and impair its ability to produce thyroid hormones.
  2. Secondary failure of the thyroid gland: This occurs when the hypothalamus and/or the pituitary fail to secrete adequate TRH and/or TSH, respectively.
  3. Inadequate dietary supply of iodine: The most common cause of hypothyroidism.
50
Q

What is an example of primary failure of the thyroid gland, and what characterizes it?

A

An example is Hashimoto’s thyroiditis, characterized by low levels of T3 and T4 but elevated levels of TSH due to antibodies targeting the thyroid gland and impairing hormone production.

51
Q

What characterizes secondary failure of the thyroid gland, and what are its causes?

A

Secondary failure occurs when the hypothalamus and/or the pituitary fail to secrete adequate TRH and/or TSH. It is characterized by low levels of T3 or T4 (or both), depending on the location of dysfunction.

52
Q

What is the most common cause of hypothyroidism, and how is it characterized?

A

The most common cause is an inadequate dietary supply of iodine, characterized by low T3 and T4 and elevated TSH.

53
Q

Define primary failure.

A

Primary failure is a dysfunction originating in the endocrine gland itself.

54
Q

Define secondary failure.

A

Secondary failure of an endocrine organ is caused by over- or under-stimulation by the pituitary gland.

55
Q

What are the common symptoms of hypothyroidism?

A
  • Cold intolerance
  • Slower reflexes
  • Reduced mental alertness
  • Easy to fatigue
  • Slow, weak heart rate
  • Weight gain due to decreased basal metabolic rate
56
Q

What is congenital hypothyroidism, and what is it characterized by?

A

Congenital hypothyroidism is thyroid hormone deficiency acquired from birth, and it is called cretinism. Cretinism is characterized by dwarfism and intellectual disability due to the requirement of thyroid hormone for growth and development.

57
Q

What characterizes hyperthyroidism, and what is its primary characteristic in terms of thyroid hormone levels?

A

Hyperthyroidism is characterized by increased levels of thyroid hormone, specifically elevated T3 and T4.

58
Q

What is a cause of secondary hyperthyroidism, and what are the potential tumor locations?

A

Secondary hyperthyroidism can occur due to a tumor in either the hypothalamus (secreting excess TRH) or the anterior pituitary (secreting excess TSH).

59
Q

: How does a thyroid tumor contribute to hyperthyroidism, and what are the expected hormone levels?

A

A tumor in the thyroid gland itself results in increased secretion of thyroid hormones, leading to elevated T3 and T4 and decreased TSH.

60
Q

What is Graves’ disease, and what characterizes its effect on thyroid hormones?

A

Graves’ disease is the most common cause of hyperthyroidism. It is an autoimmune disease where the body produces long-acting thyroid stimulator (LATS), an antibody that targets and activates TSH receptors on follicular cells. This leads to elevated T3 and T4 levels and decreased TSH levels because LATS is not under negative feedback control.

61
Q

What are some signs and symptoms you might expect to find in a patient with hyperthyroidism?

A
  • Increased heart rate
  • Excessive heat production
  • Muscle weakness due to skeletal muscle protein degradation
  • Mood swings due to increased CNS mental alertness
  • Elevated basal metabolic rate that causes weight loss even with increased caloric intake

Graves’ disease is the most common cause of exophthalmos, which is characterized by the bulging of the eyes. This is caused by a buildup of water-retaining carbohydrates behind the eyes that retain fluid and push
the eyeballs forward.

62
Q

What is a goiter, and what causes it?

A

A goiter is an enlarged thyroid gland that is usually visible and results from any condition that leads to increased TSH. TSH stimulation of the thyroid gland increases the number and size of follicles.

63
Q

Under what conditions is a goiter likely to be present?

A

A goiter is likely to be present under conditions that lead to increased TSH, such as both hypothyroidism and hyperthyroidism.

64
Q

In which causes of hypothyroidism would you expect a goiter to be present?

a) primary failure of thyroid
b) secondary failure of the thyroid gland
c) lack of dietary iodine

A

a) and c)

Explanation:
1. Primary failure of the thyroid is associated with impairment of thyroid hormone production but elevated levels of TSH as the negative feedback pathways are still in tact.
2. Dysfunction of either the hypothalamus to secrete TRH or the anterior pituitary to secrete TSH will cause low levels of either TRH or TSH, or both.
3. Lack of dietary iodine, which is required for thyroid hormone production, results in low T3 and T4 and elevated TSH

65
Q

In which causes of HYPERthyroidism would you expect a goiter to be present?

a) secondary to hypothalamus or anterior pituitary tumour
b) hypersecreting thyroid tumour
c) Graves disease

A

a) and c)

  1. When a TRH-secreting tumour in the hypothalamus or a TSH-secreting tumour in the anterior pituitary is present, the tumour usually ignores negative feedback resulting in elevated T3 and T4 with elevated TRH and/or TSH.
  2. A tumour in the thyroid gland itself will result in increased secretion of thyroid hormones, T3 and T4, resulting in decreased TSH through negative feedback.
  3. In Grave’s disease, an antibody known as LATS targets and activates TSH receptors on follicular cells, thereby having the same effect as excessive TSH stimulation.

PHGY 216 mod 1 (7 decks)

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