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PHGY 210 > Endo III > Flashcards

Endo III Flashcards

1
Q

What are the main functions of calcium?

A
  • Essential structural component of the skeleton
  • Important in blood clotting
  • Helps maintain transmembrane potential of cells
  • Important in excitability of nervous tissue
  • Important in contraction of muscles
  • Important in release of hormones and neurotransmitters
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2
Q

Calcium is found in what concentration and form in the circulation?

A

10 mg/100 ml (10%)
In circulation it is 50% free and 50% bound to albumin.

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3
Q

Where is most of the calcium in the body found?

A

About 99% of the body’s calcium is in bone. Bone thus serves as a calcium reservoir.

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4
Q

How does calcium enter the body and then plasma?

A

It is consumed in the diet; milk, cheese, eggs, butter, etc. It is then absorbed from the digestive tract primarily in the duodenum and upper jejunum.

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5
Q

Once calcium is in the plasma, what happens to it?

A
  • Some will be deposited in bone or cells of other tissues
  • Some will go through the kidney and into the urine
  • If plasma Ca2+ concentration is low, it can be reabsorbed into the plasma from the kidney or removed from bone (resorption).
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6
Q

Draw the calcium cycle, including the main areas of influence of Vitamin D, PTH, and calcitonin.

A

Vitamin D: increases absorption of calcium from intestine
PTH: increases absorption of calcium from intestine, increases resorption of Ca2+ from bone and reabsorption from kidney back into plasma
Calcitonin: increases absorption of Ca2+ into kidney from plasma, increases deposition of Ca2+ into bone from plasma

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7
Q

Where is PTH secreted from?

A

Secreted from parathyroid chief cells embedded in surface of thyroid. There are 4 parathyroid glands, located on the back side of the thyroid gland.

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8
Q

What happens if the parathyroids are removed?

A

Severe drop in plasma calcium levels causing tetanic convulsions and death.

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9
Q

How many amino acids does PTH have?

A

84 amino acid polypeptide, but only the 34 terminal amino acids bind to the receptor.

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10
Q

Describe the formation and half life of PTH.

A

Synthesized as part of a larger protein, preproparathyroid hormone, which undergoes proteolytic cleavage to produce the PTH.

It has a very short half life of 3-18 minutes depending on the individual.

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11
Q

What is the main function of PTH? Name the 4 ways in which it accomplishes this function.

A

It increases the concentration of plasma calcium:
1. Bone resorption: increases bone demineralization, increasing Ca2+ in body fluids
2. Kidney: increases the reabsorption of Ca2+ in proximal convoluted tubule
3. Vitamin D synthesis: stimulates conversion of 25-hydroxyvitamin D3 to 1,25D3, the biologically active form of vitamin D, in the kidney.
4. Gut: PTH and 1,25D3 facilitate the absorption of Ca2+ from the gut.

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12
Q

What controls PTH release?

A

It is controlled directly by the circulating concentration of calcium.

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13
Q

What is the mechanism of PTH activity?

A

It is controlled directly by the circulating concentration of calcium.

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14
Q

How does PTH enter the cell?

A

It binds to cognate receptors on target cells.

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15
Q

Describe the actions of PTH when Ca2+ levels in the blood are low.

A
  • More PTH secreted from parathyroid
  • Resorption from bone increases
  • Reabsorption from kidney increases
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16
Q

Describe the actions of PTH when calcium levels in the blood are high.

A
  • Less PTH is secreted from parathyroid
  • Resorption decreases and more Ca2+ deposited on bone/other organs
  • Reabsorption decreases from kidney. More Ca2+ therefore comes out in the urine.
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17
Q

What is the difference between hypoparathyroidism and hyperparathyroidism?

A

Hypoparathyroidism = too little action of parathyroids, low levels of PTH in circulation

Hyperparathyroidism = too much PTH produced due to parathyroid adenoma (benign growth)

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18
Q

What are the 3 symptoms of hypoparathyroidism?

A
  1. Hypocalcemia (low plasma calcium)
  2. Low levels of biologically active vitamin D
  3. Tetany, convulsions that can lead to death by asphyxiation (spasms of laryngeal muscles)
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19
Q

At what blood Ca2+ concentrations do convulsions occur as a result of hypoparathyroidism?

A

<7 mg/100 ml - causes increased neural overexcitability that produces muscle spasms

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20
Q

What are the 2 major symptoms of hyperparathyroidism in non-severe cases?

A
  1. Hypercalcemia (elevated calcium in circulation) because more PTH = more bone resorption and calcium reabsorption from kidney and = more 1,25D3 that (along with PTH) increases absorption of Ca2+ from intestine.
  2. Formation of kidney stones due to excess calcium depositing inappropriately on organs.
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21
Q

What are the 3 main symptoms of severe hyperparathyroidism?

A

Cardiac arrythmias, depressed neuromuscular excitability, calcium deposition on walls of blood vessels and cartilaginous regions of bones.

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22
Q

What is the treatment for hypoparathyroidism?

A

Administration of 1,25D3 and calcium supplements

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23
Q

What is the treatment for hyperparathyroidism?

A

Removal of malfunctioning parathyroids and replacement therapy of 1,25D3 and Ca2+

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24
Q

How do we obtain vitamin D? Include the relevant steps and where they take place in the body.

A

Available from limited dietary sources (cod liver oil, fatty fish). Can be synthesized from a cholesterol metabolite (so strictly speaking, it is not a vitamin!)

Steps of synthesis:
1. UVB light + 7-dehydrocholesterol in skin
2. 25-hydroxylation in liver
3. 1-hydroxylation in kidney and several peripheral tissues -> 1,25D3

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25
Q

What are the 3 main functions of vitamin D?

A
  1. Primary function: increase calcium absorption from the intestine.
  2. Also regulates the immune system -> protects against infection, anti-inflammatory
  3. Anticancer properties
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26
Q

What is the main regulation of vitamin D synthesis? Where does this take place?

A
  • Increased in conditions of low calcium, when PTH is also increased
  • Depressed by high calcium
    The conversion into 1,25D3 takes place in the kidney.
27
Q

What are the main two diseases caused by low vitamin D? Describe the difference between them in terms of:
a) Cause
b) Population impacted
c) Main symptom

A

Rickets vs osteomalacia
a) R: caused by absence of sunlight (UVB), can be hereditary if lacking Vitamin D receptors.
O: caused by kidney failure, which causes less vitamin D to be formed and less absorption from the gut -> more calcium removal from bone

b) R: growing individuals
O: adults

c) R: Deficient bone mineralization
O: Soft bones

28
Q

What type of hormone is calcitonin? How long is it?

A

32-amino acid calcium-lowering peptide hormone (32 a.a. all necessary)

29
Q

Where is calcitonin manufactured?

A

Manufactured in parafollicular or C cells or the thyroid gland.

30
Q

What is the function of calcitonin?

A

It lowers plasma calcium by promoting the transfer of calcium from blood to bone and increasing urinary excretion of calcium.

31
Q

What stimulates the release of calcitonin?

A

A rise in plasma calcium. Similarly, a decrease in plasma calcium wll decrease the release of calcitonin.

32
Q

Out of PTH, 1,25D3, and calcitonin, which hormone is the least important? Explain why.

A

Calcitonin is the least important. Its absence does not compromise calcium homeostasis in man, suggesting that its biological importance is limited.

33
Q

Where are the adrenal glands located?

A

They are adjacent to the upper surface of the kidneys.

34
Q

How do adrenal glands compare between males and females?

A

They are heavier in the male than in the female.

35
Q

What are the two tissue types in the adrenal glands? How do they compare in terms of appearance and origin?

A

Cortex:
Appearance - large lipid-containing epithelial cells
Origin - derived from mesoderm (on the outside)

Medulla:
Appearance - chromaffin cells; fine brown granules when fixed with potassium bichromate
Origin - derived from neural crest

36
Q

What is the function of the adrenal cortex?

A

It produces steroid hormones, glucocorticoids (cortisol in humans, corticosterone in rodents) and mineralocorticoids (e.g. aldosterone), and progestins.

37
Q

What is the function of the adrenal medulla?

A

It produces catecholamines epinephrine and norepinephrine and some peptide hormones.

38
Q

What are the 3 layers of the adrenal cortex from outside to inside? What do they produce?

A

Zona glomerulosa: mineralocorticoids (aldosterone)
Zona fasciculata: glucocorticoids (cortisol)
Zona reticularis: glucocorticoids, progestins, androgens, and estrogens

39
Q

The synthesis of adrenal steroids by the adrenal […] is controlled by the hormone […] produced by the […]

A

Cortex, ACTH, pituitary

40
Q

The enzyme […], which is necessary for the synthesis of mineralocorticoids such as […], is only present in the […]

A

18-hydroxylase, aldosterone, zona glomerulosa

41
Q

The enzyme […], which is necessary for the synthesis of glucocorticoids such as […], is present only in the […].

A

17a-hydroxylase, cortisol, zona faciculata and zona reticularis

42
Q

Describe the molecular mechanism of action of steroid hormones.

A

It enters the cell membrane and binds to a receptor that translocates into the nucleus, where it alters the transcription of specific target genes.

43
Q

What is the main physiological function of aldosterone? Expain how it does this.

A

It increases the reabsorption of Na+ by the kidney (from plasma). To balance out the change in charge, it increases K+ or H+ in the plasma or removes Cl- from plasma.

44
Q

What is the main glucocorticoid in humans vs rodents?

A

Humans: cortisol
Rodents: corticosterone

45
Q

Name the 5 major functions of glucocorticoids.

A
  1. Salt retention
  2. Effects on protein and carbohydrate metabolism
  3. Lipid metabolism
  4. Anti-inflammatory and immunosuppressive actions
  5. Effects on bone
46
Q

Describe the salt retention function of glucocorticoids.

A

Some activity but less effective than aldosterone. Can be important under pathological conditions when plasma cortisol remains elevated.

47
Q

Describe the effects of glucocorticoids on protein and carbohydrate metabolism.

A

They stimulate the synthesis of gluconeogenic enzymes in hepatocytes as well as enzymes that break down proteins in muscle and other tissues. The released amino acids enter the liver and are converted to glucose and glycogen. They also decrease glucose uptake by muscle and fat to conserve glucose for other tissues.

Overall, the result is increased blood glucose levels, leading to increased insulin secretion.

48
Q

What is adrenal diabetes?

A

It is an increase in blood glucose due to excess glucocorticoid activity.

49
Q

What is diabetes mellitus?

A

It is when adrenal diabetes, caused by excess blood glucose due to excess glucocorticoid activity, is prolonged and leads to the destruction of beta-cells of the pancreas.

50
Q

Describe the effects of glucocorticoids on lipid metabolism.

A

Glucocorticoids maintain or increase levels of lipolytic enzymes in the adipose tissue cells and augments lipolytic action of other hormones, e.g. epinephrine. Lipids used by muscle as fuel. Thus, excess glucocorticoids leads to hyperlipidemia and hypercholesterolemia.

51
Q

The action of glucocorticoids on lipid metabolism can lead to the conditions […] and […]

A

hyperlipidemia and hypercholesterolemia

52
Q

Explain the anti-inflammatory and immunosuppressive actions of glucocorticoids.

A

They reduce inflammatory response at the site of injury by causing the atrophy of the lymphatic system (lymph nodes, thymus, spleen). They also decrease histamine formation and thus decrease allergic reactions.

53
Q

What type of hormone is often used in organ transplantation? Explain why.

A

Glucocorticoids, because they reduce inflammatory responses and reduce antibody formation.

54
Q

Describe the effects of glucocorticoids on bone. What condition can this lead to?

A

Decrease the protein matrix of the bone through their protein catabolic effect. As a result, increased loss of Ca2+ from the bone, leading to osteoporosis.

55
Q

What hormone controls glucocorticoid secretion?

A

Controlled by ACTH

56
Q

Draw and describe the feedback control mechanism of glucocorticoid secretion.

A
  • Stress in cerebral cortex
  • Hypothalamus releases CRH
  • Pituitary releases ACTH
  • Adrenal cortex (zona fasciculata and reticularis) release ACTH receptor, which activates cAMP and cellular kinases that cause steroidogenesis.
  • Leads to increased glucocorticoid secretion and increased plasma cortisol levels.
  • Cortisol has a negative feedback on CRH and ACTH release.
57
Q

What condition occurs when cortisol is not produced? Explain what happens.

A

Congenital adrenal hyperplasia. Since cortisol is not produced, the negative feedback loop that downregulates ACTH from the pituitary can’t function. All that ACTH will cause the adrenals to get big to compensate.

58
Q

What is the treatment for congetinal adrenal hyperplasia?

A

Administration of cortisol, which (a) corrects the deficiency and (b) normalizes the ACTH secretion.

59
Q

What is the specific mechanism of action of ACTH?

A
  • Binds to specific ACTH receptor on membranes of zona fasciculata and zone reticularis cells
  • Stimulation of adenylyl cyclase leading to increased production of cAMP
  • Activates steroidogenic enzymes leading to increases synthesis and release of steroid hormones.
60
Q

How do plasma cortisol and ACTH fluctuate throughout the day?

A

They follow a diurnal rhythm (the same rhythm, with ACTH always slightly higher than cortisol). They reach a minimum at midnight, reach a maximum in the morning, and then fall again until midnight.

61
Q

Name two ways in which the daily rhythm of plasma cortisol and ACTH can be disrupted.

A

By stress or by Cushing’s disease.

62
Q

Name an advantage and a disadvantage of glucocorticoid release in stress responses.

A

Advantage: provides energy and amino acids through the breakdown of tissue proteins, especially under conditions where normal feeding is not feasible.

Disadvantage: cortisol inhibits wound healing

63
Q

What is the effect of prolonged stress on the endocrine system? Explain the possible conditions/issues that can arise.

A

Prolonged stress would maintain constantly high levels of glucocorticoids which could lead to increased blood glucose (true diabetes mellitus), decreased immune responses (individual will become susceptible to infections), loss of bone, etc.

PHGY 210 (36 decks)

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