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Renal and Endocrine Biology > REB 11. Biochemical Synthesis of Steroid Hormones > Flashcards

REB 11. Biochemical Synthesis of Steroid Hormones Flashcards

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1
Q

What type of disorder are Congenital Adrenal Hyperplasia (CAH)? How does it arise? What does it present as? What is the result of it?

A
  • a group of inherited autosomal recessive disorders
  • mutations in genes encoding enzymes in mineralcorticoids, glucocorticoids or sex steroids synthesis
  • enlarged adrenal glands (hyperplastic adrenomegaly)
  • results in reduced levels of cortisol + aldosterone with overproduction of androgen
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2
Q

What is the clinical presentation of classic CAH in infants?

A
  • ambiguous genitalia in females
  • enlarged genitalia in males
  • poor weight gain
  • adrenal crisis (dehydration, vomiting, hypoglycaemia and circulatory collapse)
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3
Q

What is the clinical presentation of classic CAH in children and adults?

A
  • early onset of puberty
  • rapid growth during childhood
  • premature completion of growth (short stature)
  • irregular menstrual cycles
  • infertility in both sexes
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4
Q

What are glucorticoids?

A

regulates metabolism, mood, blood pressure, immunity, pain sensation
e.g. cortisol

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5
Q

What are mineralcorticoids?

A

electrolyte and fluid balance, blood volume

e.g. aldosterone

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6
Q

What are androgens?

A

male reproductive development

e.g. testosterone

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7
Q

What are estrogens?

A

female secondary sex characteristics; regulation of menstrual cycle

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8
Q

What are progestogens?

A

regulation of ovulation; maintains pregnancy

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9
Q

What are the 2 MAIN layers of the adrenal gland?

A

[1] Outer Cortex

[2] Medulla

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10
Q

What are the 3 sublayers of the cortex?

A 
[1] Zona Glomerulosa
- aldosterone
[2] Zona Fasciculata
- cortisol
[3] Zona Reticularis
- sex steroids (androgens)
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11
Q

Which layer of the cortex are mineralcorticoids made in?

A

Zona Glomerulosa

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12
Q

Which layer of the cortex are glucocorticoids made in?

A

Zona Fasciculata

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13
Q

Which layer of the cortex are the sex steroids (androgens) made in?

A

Zona Reticularis

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14
Q

Where are the catecholamines made?

A

Medulla

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15
Q

Which hormones are made in the adrenal glands?

A
  • corticosteroids (mineralocorticoids + glucocorticoids)

- androgens

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16
Q

Which hormones are made in the ovaries?

A
  • estrogens

- progesterone

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17
Q

Which hormones are made in the testis?

A
  • androgen
18
Q

What is the precursor for all steroid hormones?

A

Cholesterol (27 carbon structure)

19
Q

Where is cholesterol synthesized? What is its structure and what type of molecule is it?

A
  • synthesized in the liver

Structure:

  • 4-linked hydrocarbon (steroid nucleus)
  • hydroxyl group (OH)
  • hydrocarbon side chain (hydrocarbon tail)
  • Amphipathic Molecule: both hydrophilic and hydrophobic parts
20
Q

What is the first step in steroid synthesis?

A

Cholesterol to Pregnenolone

21
Q

Explain the steps and enzymes involved in converting Cholesterol to Pregnenolone. What type of step is this?

A

[1] Cholesterol taken up into mitochondria - mediated by StAR enzyme (steroidogenic acute regulatory protein)

[2] Cholesterol converted to Pregnenolone through side-chain cleavage (catalyzed by enzyme Cytochrome P450)

It is a rate-limiting step - NADPH and Oxygen are required

22
Q

What is another name for the enzyme cytochrome P450?

A
  • desmolase

- CYP11A1

23
Q

What are the 3 possible locations that cholesterol may be converted to pregnenolone?

A

[1] Adrenal
[2] Ovary
[3] Testis

24
Q

Explain the process by which Pregnenolone is converted into Progesterone. What enzymes are involved?

A

[1] 3-hydroxyl group (OH) is oxidized to 3-keto group via the enzyme:
- 3beta-OH Dehydrogenase

[2] 5th carbon double bond is isomerized to a 4th carbon double bond via the enzyme:
- Delta5,4 Isomerase

25
Q

What are the enzymes involved in the synthesis of cortisol from progesterone? (in order!)

A

[1] 17 alpha-hydroxylase
[2] 21 alpha-hydroxylase
[3] 11 beta-hydroxylase

26
Q

What are the enzymes involved in the synthesis of aldosterone from progesterone? (in order!)

A

[1] 21 alpha-hydroxylase
[2] 11 beta-hydroxylase
[3] aldosterone synthase
- this is made up of 2 enzymes

27
Q

What are the metabolic functions of glucocorticoids?

A

[1] CARBOHYDRATE METABOLISM

  • stimulates hepatic gluconeogenesis
  • increases deposition of glycogen in the liver
  • antagonizes the peripheral action of insulin on glucose uptake

[2] PROTEIN METABOLISM

  • inhibits amino acid uptake and protein synthesis in extrahepatic tissues
  • potent protein catabolic agent in peripheral tissues such as muscle, skin and bone
  • stimulates amino acid uptake of the liver which are gluconeogenesis precursors

[3] FAT METABOLISM

  • increases mobilisation of fatty acids
  • stimulates the lipolysis in adipose tissue
  • increases the deposition of fat in facial and truncal areas
28
Q

What is the primary function of mineralocorticoids?

A

mineral and fluid balance

29
Q

What is the primary function of gonadal steroids?

A

reproductive functions

30
Q

What are some other roles that steroid hormones play a role in?

A
  • carbohydrate regulation (glucocorticoids)
  • mineral and fluid balance (mineralocorticoids)
  • reproductive functions (gonodal steroids)
  • inflammation
  • stress responses
  • bone metabolism
  • cardiovascular function
  • behaviour and mood
31
Q

What is mineralocorticoids and what is it secreted in response to?

A

[1] Increase ECF

[2] High K+ Concentration

32
Q

What is the actions of mineralocorticoids?

A

[1] stimulates transcription of the sodium-potassium ATPase

[2] increased numbers of sodium pumps in the basolateral membranes of tubular epithelial cells

[3] facilitates uptake of sodium (and with it, water) from the tubular lumen

[4] reabsorbs sodium in the kidney at the expense of potassium and H+ !!

33
Q

What are the 4 main types of Congenital Adrenal Hyperplasia (CAH)?

A

[1] 3beta-Dehydrogenase Deficiency
[2] 17-alpha-Hydroxylase
[3] 21-Hydroxylase Deficiency
[4] 11beta-Hydroxylase Deficiency

34
Q

When there is a deficiency of the 3beta-OH Dehydrogenase enzyme what happens?

A
  • no glucocorticoids
  • no mineralocorticoids
  • no active androgens
  • salt excretion in urine
  • patients have female-like genitalia
  • autosomal recessive with incidence (1:10 000)
35
Q

When there is a deficiency of the 17-alpha-hydroxylase (CYP17) enzyme what happens?

A
  • no androgens or cortisol
  • increase in aldosterone (causes sodium and fluid retention and therefore, hypertension)
  • patients have female-like genitalia
36
Q

When there is a deficiency of the 21 alpha-hydroxylase enzyme what happens?

A

most common!

  • no cortisol
  • no aldosterone
  • increase in androgen (leads to masculinization of external genitalis in females and early virilization in males)
  • there are partially and virtually complete deficiencies are known
  • mineralocorticoids and glucocorticoids are virtually absent (salt-wasting form) or completely deficient (non-classical form)
37
Q

What is the most common type of Congenital Adrenal Hyperplasia (CAH)?

A

Deficiency in 21 alpha-hydroxylase

38
Q

When there is a deficiency of the 11-beta-hydroxylase (CYP11B1) enzyme what happens?

A
  • no cortisol
  • no aldosterone
  • overproduction of deoxycorticosterone (causes fluid retention due to its ability to supress the renin/angiotensin system – hypertension)
  • overproduction of androgens (leads to masculinization of external genitalis in females and early virilization in males)
39
Q

Cortisol deficiency leads to….?

A
  • poor response to stress (both emotional and physical)
  • hypoglycaemia
  • hyperpigmentation (cortisol can directly affect the activity of melanin producing cells)
40
Q

Aldosterone deficiency leads to….?

A
  • hyperkalemia
  • hyponatremia
  • disturbs cardiac rhythm
  • hypotension
41
Q

A combined deficiency of both cortisol and aldosterone can lead to?

A

Vascular Collapse, Shock and Death

42
Q

What is the treatment for CAH?

A

[1] daily glucocorticoid and mineralocorticoid replacement

[2] restore volume, electrolyte and glucose imbalances
- large volumes of 0.9% saline or 5% dextrose in saline

Renal and Endocrine Biology (25 decks)

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