Lecture 30 - Chapter 16 - Endocrinology Flashcards
Thyroid Gland
What is the function of follicles?
- Produce a glycoprotein called thyroglobulin
- Produce colloid
- Parafollicular cells: produce hormone calcitonin
As previously mentioned, the thyroid gland produces thyroid hormone (TH). What are the two thyroid hormones?
- T4 (thyroxine): major form that consists of two tyrosine molecules with four bound iodine atoms
- T3 (triiodothyronine): form that has two tyrosines with three bound iodine atoms
What is the function of Thyroid Hormone (TH)?
- 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
Image of Thyroid Hormone (TH) feedback loops
Transportation and Regulation of thyroid hormones (T3 & T4)
How do thyroid hormones travel throughout the circulatory system and how are they regulated?
- 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
Normally Thyroid hormones are regulated by a negative feedback on TSH. What hormone can override TSH to keep stimulating the release of thyroid hormones?
- Thyrotropin-releasing hormone (TRH)
- TRH is released during pregnancy, exposure to cold (especially in infants)
Hyposecretion of TH in adults can lead to **myxedema **. What are the symptoms?
Hyposecretion = less secretion
- Low metabolic rate
- Thick/dry skin
- Puffy eyes
- Feeling chilled
- Thyroid enlarges
Where are the parathyroid glands located in the body?
The parathyroid glands are located on the posterior aspect of the thyroid gland.
What is the function of the parathyroid cells?
Parathyroid cells secrete parathyroid hormone (PTH), which is the single most important hormone controlling calcium balance in the blood.
How does parathyroid hormone (PTH) regulate calcium levels in the blood?
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.
What is the antagonist to the parathyroid hormone?
Calcitonin
* It is produced by parafollicular cells and is the response of high Ca2+ levels
Where are the adrenal glands located in the body?
The adrenal glands are pyramid-shaped organs located on top of each kidney.
How many layers are present in the adrenal glands, and what are they called?
The adrenal glands have two major layers: the outer adrenal cortex and the inner adrenal medulla.
What hormones are secreted by the adrenal cortex?
The adrenal cortex synthesizes over two dozen steroid hormones known as corticosteroids. These include:
* mineralocorticoids
* glucocorticoids
* small amounts of adrenal sex hormones or gonadocorticoids.
What is the function of mineralocorticoids?
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.
What is the primary job of aldosterone?
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.
How does aldosterone affect blood volume and blood pressure?
Aldosterone’s stimulation of sodium reabsorption in the kidney tubules leads to increased blood volume and blood pressure since water follows sodium.
What regulates the secretion of aldosterone?
- **renin-angiotensin-aldosterone mechanism **
- plasma concentrations of potassium
- ACTH
- ANP
What are the three layers or zones of the adrenal cortex?
- Zona glomerulosa: Produces mineralocorticoids, including aldosterone.
- Zona fasciculata: Produces glucocorticoids, such as cortisol.
- Zona reticularis: Produces small amounts of adrenal sex hormones or gonadocorticoids.
What is the structure and function of the adrenal medulla?
The adrenal medulla is the inner region of the adrenal gland. It secretes epinephrine and norepinephrine, helping the body cope with stress.
How does aldosterone affect acid-base balance?
Aldosterone can alter acid-base balance by increasing hydrogen ion (H+) excretion and enhancing bicarbonate (HCO3-) reabsorption.
What are the steps involved in the regulation of aldosterone secretion?
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.
What is the role of glucocorticoids, specifically cortisol?
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.
How is glucocorticoid secretion regulated?
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.
What are the actions of cortisol during stress?
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.
What are gonadocorticoids and which hormones are included in this group?
- 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.
How is the secretion of gonadocorticoids controlled?
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.
Adrenal Medulla
What catecholamines are synthesized by the medullary chromaffin cells?
Epinephrine and norepinephrine (NE), produced via molecular sequence from tyrosine to dopamine to NE to epinephrine.
How does the release of catecholamines affect the body during a short-term stress response?
- Mobilizes the sympathetic nervous system.
- Increases blood pressure, heart rate, and blood flow to essential organs.
- Raises blood glucose levels.
Approximatley 80% BLANK and 20% BLANK are released by the adrenal medulla during short-term stress.
epinephrine; norepinephrine
What effects do epinephrine and norepinephrine have?
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.
How do catecholamines differ from adrenal cortex hormones in terms of stress response?
Catecholamines cause brief responses, while adrenal cortex hormones promote long-lasting responses.
