Lecture 30 - Chapter 16 - Endocrinology

Question 1

Thyroid Gland

What is the function of follicles?

Answer 1

• Produce a glycoprotein called thyroglobulin
• Produce colloid
• Parafollicular cells: produce hormone calcitonin

Question 2

As previously mentioned, the thyroid gland produces thyroid hormone (TH). What are the two thyroid hormones?

Answer 2

1. T4 (thyroxine): major form that consists of two tyrosine molecules with four bound iodine atoms
2. T3 (triiodothyronine): form that has two tyrosines with three bound iodine atoms

Question 3

What is the function of Thyroid Hormone (TH)?

Answer 3

• Virtually affects every cell in the body
• Enters target cell and binds to intracellular receptors within nucleus
• Triggers transcription of various metabolic genes
• TH increases metabolic rate and heat production
• Regulates tissue growth and development
• Maintains blood pressure

Question 4

Image of Thyroid Hormone (TH) feedback loops

Answer 4

Question 5

Transportation and Regulation of thyroid hormones (T3 & T4)

How do thyroid hormones travel throughout the circulatory system and how are they regulated?

Answer 5

• T3 & T4 are transported by throxine-binding globulins (TBGs) where they then both bind to target receptors.
• T3 is 10 times more active than T4 because peripheral tissues have enzymes that convert T4 to T3
• Thyroid hormones are regulated by negative feedback. TSH decrease so that it doesn’t stimulate the thyroid to release T3 & T4

Question 6

Normally Thyroid hormones are regulated by a negative feedback on TSH. What hormone can override TSH to keep stimulating the release of thyroid hormones?

Answer 6

• Thyrotropin-releasing hormone (TRH)
• TRH is released during pregnancy, exposure to cold (especially in infants)

Question 7

Hyposecretion of TH in adults can lead to **myxedema **. What are the symptoms?

Hyposecretion = less secretion

Answer 7

• Low metabolic rate
• Thick/dry skin
• Puffy eyes
• Feeling chilled
• Thyroid enlarges

Question 8

Where are the parathyroid glands located in the body?

Answer 8

The parathyroid glands are located on the posterior aspect of the thyroid gland.

Question 9

What is the function of the parathyroid cells?

Answer 9

Parathyroid cells secrete parathyroid hormone (PTH), which is the single most important hormone controlling calcium balance in the blood.

Question 10

How does parathyroid hormone (PTH) regulate calcium levels in the blood?

Answer 10

PTH release is triggered by falling blood calcium levels and inhibited by rising blood calcium levels. PTH increases calcium levels in the blood by stimulating three target organs: the skeleton, the kidneys, and the intestine.

Question 11

What is the antagonist to the parathyroid hormone?

Answer 11

Calcitonin
* It is produced by parafollicular cells and is the response of high Ca2+ levels

Question 12

Where are the adrenal glands located in the body?

Answer 12

The adrenal glands are pyramid-shaped organs located on top of each kidney.

Question 13

How many layers are present in the adrenal glands, and what are they called?

Answer 13

The adrenal glands have two major layers: the outer adrenal cortex and the inner adrenal medulla.

Question 14

What hormones are secreted by the adrenal cortex?

Answer 14

The adrenal cortex synthesizes over two dozen steroid hormones known as corticosteroids. These include:
* mineralocorticoids
* glucocorticoids
* small amounts of adrenal sex hormones or gonadocorticoids.

Question 15

What is the function of mineralocorticoids?

Answer 15

Mineralocorticoids, such as aldosterone, regulate sodium (Na+) and potassium (K+). They play a crucial role in maintaining blood volume, blood pressure, and overall body homeostasis.

Question 16

What is the primary job of aldosterone?

Answer 16

Aldosterone, the most common mineralocorticoid, reduces the excretion of sodium from the body. Its main targets are the kidney tubules, where it promotes sodium reabsorption and potassium secretion.

Question 17

How does aldosterone affect blood volume and blood pressure?

Answer 17

Aldosterone’s stimulation of sodium reabsorption in the kidney tubules leads to increased blood volume and blood pressure since water follows sodium.

Question 18

What regulates the secretion of aldosterone?

Answer 18

1. **renin-angiotensin-aldosterone mechanism **
2. plasma concentrations of potassium
3. ACTH
4. ANP

Question 19

What are the three layers or zones of the adrenal cortex?

Answer 19

1. Zona glomerulosa: Produces mineralocorticoids, including aldosterone.
2. Zona fasciculata: Produces glucocorticoids, such as cortisol.
3. Zona reticularis: Produces small amounts of adrenal sex hormones or gonadocorticoids.

Question 20

What is the structure and function of the adrenal medulla?

Answer 20

The adrenal medulla is the inner region of the adrenal gland. It secretes epinephrine and norepinephrine, helping the body cope with stress.

Question 21

How does aldosterone affect acid-base balance?

Answer 21

Aldosterone can alter acid-base balance by increasing hydrogen ion (H+) excretion and enhancing bicarbonate (HCO3-) reabsorption.

Question 22

What are the steps involved in the regulation of aldosterone secretion?

Answer 22

1.) The renin-angiotensin-aldosterone mechanism is activated when blood pressure falls. Renin triggers the formation of angiotensin II, which stimulates aldosterone release.
2.) Fluctuations in plasma potassium levels directly influence aldosterone secretion. Increased potassium stimulates aldosterone release, while decreased potassium inhibits it.
3.) ACTH released during severe stress slightly increases aldosterone secretion.
4.) Atrial natriuretic peptide (ANP), secreted when blood pressure rises, inhibits the renin-angiotensin-aldosterone mechanism, reducing aldosterone secretion.

Question 23

What is the role of glucocorticoids, specifically cortisol?

Answer 23

Glucocorticoids, such as cortisol, influence energy metabolism, help the body adapt to intermittent food intake, and maintain blood pressure. They are involved in stress response and act on target cells by modifying gene activity.

Question 24

How is glucocorticoid secretion regulated?

Answer 24

Glucocorticoid secretion is regulated by negative feedback. Rising cortisol levels inhibit the release of corticotropin-releasing hormone (CRH) from the hypothalamus and adrenocorticotropic hormone (ACTH) from the anterior pituitary, thus decreasing cortisol secretion.

Question 25

What are the actions of cortisol during stress?

Answer 25

During stress, cortisol promotes gluconeogenesis (glucose formation), mobilizes fatty acids for energy, breaks down proteins for repair or metabolic processes, and enhances vasoconstriction to maintain blood pressure. Excessive levels of cortisol can have anti-inflammatory and anti-immune effects and disrupt normal bodily functions.

Question 26

What are gonadocorticoids and which hormones are included in this group?

Answer 26

• Gonadocorticoids are weak androgens (male sex hormones) produced by the adrenal cortex, including androstenedione and DHEA.
• The exact role of adrenal sex hormones is still unclear, but they contribute to secondary sex characteristics.

Question 27

How is the secretion of gonadocorticoids controlled?

Answer 27

The control of gonadocorticoid secretion is not fully understood. ACTH (adrenocorticotropic hormone) stimulates their release, but the gonadocorticoids do not seem to exert feedback inhibition on ACTH release.

Question 28

Adrenal Medulla

What catecholamines are synthesized by the medullary chromaffin cells?

Answer 28

Epinephrine and norepinephrine (NE), produced via molecular sequence from tyrosine to dopamine to NE to epinephrine.

Question 29

How does the release of catecholamines affect the body during a short-term stress response?

Answer 29

• Mobilizes the sympathetic nervous system.
• Increases blood pressure, heart rate, and blood flow to essential organs.
• Raises blood glucose levels.

Question 30

Approximatley 80% BLANK and 20% BLANK are released by the adrenal medulla during short-term stress.

Answer 30

epinephrine; norepinephrine

Question 31

What effects do epinephrine and norepinephrine have?

Answer 31

Both hormones have similar effects.
* Epinephrine is more potent in stimulating metabolic activities and dilating bronchioles.
* Norepinephrine has a greater influence on peripheral vasoconstriction and blood pressure.

Question 32

How do catecholamines differ from adrenal cortex hormones in terms of stress response?

Answer 32

Catecholamines cause brief responses, while adrenal cortex hormones promote long-lasting responses.