Endo 3 Flashcards by Éliane Blondin

What are the steps to the calcium cycle (draw if possible)

Dietary Ca –> feces
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Absorbed in plasma with Vitamin D and PTH
|
Calcitonin helps: 1. bone deposit or 2. Kidney filtration

Can be Reabsorbed with PTH into plasma
When filtered: will be lost in urine or reabsorbed in plasma with PTH

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Where are the parathyroid hormone released from?

One of the four parathyroid hormone behind the thyroid

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What is the general structure of PTH

84 polypeptide, only the 34 terminal are important PTH activity as they are the ones that bind to the receptors to be activated

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What is the half-life of PTH

3-18 minutes depending on the individual, meaning it is a tightly regulated hormone

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What is the main function of PTH? how does it do so?

Increase the concentration of plasma calcium
1. Bone resorption: increase demineralisation
2. Kidney:
…….2.1 increase reabsorption
…….2.2 stimulate the synthesis of 1.25D3 (active vit D)
3. Facilitate the reabsorption of Ca in the gut

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How is PTH release controlled?

The circulating concentration of Calcium is the stimuli of the parathyroid receptors to adapt the amount of PTH released

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Explain the calcium cycle (PTH actions) in LOW calcium situations

LOW Ca in blood
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Parathyroid gland stimulation
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Increased PTH (1.bone 2.kidney)

More Ca reabsorbed with PTH into plasma (bone breakdown)
More Ca is reabsorbed and low Ca in urine

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Explain the calcium cycle (PTH actions) in HIGH calcium situations

HIGH Ca in blood
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Parathyroid gland receives negative feedback
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Decreased PTH (1.bone 2.kidney)

More Ca is deposited with calcitonin, less is reabsorbed
Less Ca is reabsorbed and high Ca in urine (calcitonin)

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What is hypoparathyroidism and what are the associated symptoms?

What is an example of life-threatening symptom?

Low levels of PTH in the blood

-Hypocalcemia
-Decreased production of active vitamin D
-Tetany (convulsion due to neural over excitability, muscle spasms)

Ex: tetany in the laryngeal muscles can lead to death by asphyxiation

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What is the treatment for hypoparathyroidism?

PTH CONTROLS…

Administration of 1.25 vitamin D and calcium supplements

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What is hyperparathyroidism and what are the associated symptoms?

High levels of PTH in circulation, often caused by parathyroid adenoma (benign growth)

-High production of Vit D
-Elevated blood Ca
-Formation of kidney stones (irregular deposit)
(severe cases can effect arteries and bones)

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What is the treatment for hyperparathyroidism?

replacement of what

Removal of the parathyroids and replacement therapy of 1.25 D3 and Ca

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Where can vitamin D be found?

dietary sources: cod liver oil, fatty fish
synthesized from a cholesterol metabolite
- UVB light in skin (not during winter)
  -reaction in liver and kidneys

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What are the functions of vitamin D?

Increase Ca absorption in the intestines
Regulate the immune system (anti-inflammatory)
Anticancer

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How is vitamin D regulated?

Vitamin D synthesis is increased when there is low circulating Ca and high PTH

Synthesis is decreased in the presence of high circulating Ca

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What can the absence of UVB lead to? how is it different in growing individuals vs adults?

a lack of UVB will inhibit vitamin D synthesis and cause a deficiency, as well as deficient bone growth

Growing: causes rickets
Adults: Osteomalacia (soft bones from lack of mineralised Ca)

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What are both ways a vitamin D deficiency can seen in the physiology (genetic defects)?

lack of vitamin D receptors (can’t have replacement therapy, recognizable by lack of hair)
No enzyme for the production of 1.25D3

What is the role of calcitonin? How is it done?

Lower plasma calcium:
1. Promotes Ca transfer from blood to bone
2. Increase urinary excretion of Ca

Of the three calcium controlling hormones (PTH, calcitonin and 1.25D3), which one is of lesser importance?

Calcitonin

What are the two distinct tissues of the adrenal gland?

The cortex and the medulla

Name the histologic appearance, origin and function of the cortex of the adrenal gland

Histology: large lipid-containing epithelial cells
Origin: derived from the mesoderm
Function: Produces steroid hormones (glucocorticoids, mineralocorticoids and progestin)

Name the histologic appearance and origin of the medulla of the adrenal gland

Histology: Chromaffin cells (fine brown granules when fixed with potassium)
Origin: derived from the neural crest

Forms catecholamines (NE and E)

There are three morphologically and functionally different layers to the adrenal cortex. Why is that? WHat do they do?

The different layers have different enzymes. A layer can only produce what it has the hormones for:

Aldosterone
Cortisol
Glucocorticoids, progestin, androgens and estrogen

What is the synthesis if adrenal steroids controlled by?

ACTH (adrenocorticotropin) a pituitary hormones

What is the function of the steroid hormones released from the adrenal gland?

Regulate the transcription of receptors specific to the steroid hormone (remember intra cellular receptor)

What two things vary a target tissue response to a steroid hormone?

1. Each hormone brings on its specific hormone transcription 2. A same hormone will have different reactions on different target tissue (overlap)

What is the primary function of aldosterone?

[Sodium metabolism] Increase the reabsorption of Na+ in the kidney (and plasma concentration of K+ and H+ to balance Na+)

Even with aldosterone, Na+ can't be uptaken on its own since the exchange has to be done in a _______. How is that done?

Electrochemically neutral manner: 1. NaCl 2. Na in // K or proton out

What are the 5 functions of glucocorticoids?

1. Salt retention 2. Effects the protein and carbohydrate metabolism 3. Effects the lipid mechanism 4. Anti-inflammatory 5. Effects on bones

How do glucocorticoid hormones affect salt retention?

Some action, but less effective than aldosterone

How do glucocorticoid hormones affect the protein and carbohydrate metabolisms?

-Stimulates the synthesis of enzymes that break down muscle proteins -Amino acids enter the liver and are converted to glucose and glycogen. -Decrease glucose uptake, which INCREASES BLOOD GLUCOSE LEVELS, and increased insulin production

How do glucocorticoid hormones affect the lipid metabolism?

-Maintain or increase lipid breakdown (lipolytic) in adipose tissue cells resulting in more lipid accessible to muscle as fuel or causing hyperlipidemia

How do glucocorticoid hormones affect inflammation reactions?

-Inflammation can have fundamental changes in the metabolism, glucocorticoids help repress that change by acting as anti-inflammatories

How do glucocorticoid hormones affect bones?

The protein catabolic effects of the hormone also decreased the protein matrix of bones. There can be an increased loss of Ca+ leading to osteoporosis

How is glucocorticoid secretion controlled?

ACTH and a negative feedback loop to the hypothalamus and the pituitary gland

What can happen in cases of enzyme deficiency for cortisol production? | think ffedback

Low cortisol stimulates ACTH production. Because cortisol is not produced, ACTH production will be unchecked and can cause congenital adrenal hyperplasia (acts like a non-toxic groiter)

What is the treatment for an enzyme deficiency for cortisol production?

Administration of cortisol to (i) correct the deficiency (ii) normalize ACTH production

What is the rhythm of plasma cortisol and ACTH release? When will that rhythm be abolished?

a DIURNAL rhythm: minimum at midnight and maximum in the morning Under stress or Cushing's disease

When is CRH, ACTH and cortisol release increased? What does it affect?

Released during stress (ex., running) It provides energy via the protein metabolism, but also prevents wound healing

What are the effects of constant high levels of stress?

Glucocorticoids will lead to increased blood glucose (diabetes), decreased immune system, loss of bone, etc..