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Physiology > HPA Axis and Adrenal Gland > Flashcards

HPA Axis and Adrenal Gland Flashcards

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1
Q

What are the components of the HPA axis?

A

Hypothalamus
Pituitary
Adrenal Gland

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2
Q

What are the main functions of the HPA axis?

A
  • Adaptive response to stress

- Regulation of immune function

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3
Q

What are the hormones of the HPA axis?

A

Catecholamines – epinephrine and norepinephrine

Glucocorticoids – cortisol

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4
Q

What enacts short loop inhibition on CRH?

A

ACTH

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5
Q

What enacts long loop inhibition on CRH?

A

Cortisol

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6
Q

Where is CRH made?

A

Parvocellular Neurons of the PVN

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7
Q

What is the release pattern of CRH?

A

Pulsatile so it results in periodic release of ACTH

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8
Q

What receptor does CRH use for the release of ACTH?

A

GPCR

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9
Q

What are the main receptors that bind CRH and what is the binding affinity?

A

CRH R1 - Binds with highest affinity to CRH R1 in anterior pituitary.

CRH R2 - Binds with higher affinity to urocortin.

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10
Q

What is the synergistic effect of CRH and AVP?

A

ACTH release is amplified in the presence of AVP and CRH together

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11
Q

What is POMC?

A

Pro-opiomelanocortin and it is the precursor of ACTH

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12
Q

Where is ACTH made?

A

Anterior PItuitary

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13
Q

What receptors does ACTH bind to and with what affinity?

A

Binds with high affinity to MC2R

Binds with low affinity to MC1R (skin)

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14
Q

How do high levels of ACTH causes hyper pigmentation of the skin?

A

It will increase MC1R binding in the skin

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15
Q

What are the 3 layers of the adrenal gland?

A

Capsule
Cortex
Medulla

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16
Q

What hormones does the cortex secrete??

A

Steroids

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17
Q

What hormones does the medulla secrete?

A

Catecholamines

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18
Q

What is the cell type of cortex and the medulla?

A

Cortex - glandular

Medulla - neural

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19
Q

What are the 3 layers of the adrenal cortex and the hormones that they produce?

A

Zona Glomerulosa - Mineralcorticoids
Zona Fascilculata - Glucocorticoids
Zona Reticularis - Weak Androgens (DHEA)

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20
Q

What is the blood supply of the adrenal cortex?

A

Suprarenal arteries break into subcapsular plexus of capillaries (fenestrated).

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21
Q

What is the blood supply of the adrenal medulla?

A

It has a dual blood supply.

  • Bathes the medullary cells with blood carrying corticosteriods from the cortex – important for conversion of NE to E.
  • Arterioles break into fenestrated capillaries.
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22
Q

What is cortisol released in response to?

A

Acute/chronic stress

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23
Q

Where is cortisol released from?

A

Zona Fasciculata

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24
Q

How is cortisol transported in the blood?

A

90% is bound to corticosteroid binding globulin (CBG)

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25
What converts cortisone into cortisol?
11beta-HSD1
26
What is pleiotropy in cortisol?
It has different effects on different tissues.
27
What is the effect of cortisol on bone?
Increases bone resorption and decreases bone formation by decreasing IGF-I receptors.
28
What is the effect of cortisol on muscle?
Decreases muscle mass
29
What is the effect of cortisol on the immune system?
Suppresses immune and inflammatory responses
30
What are the metabolic actions of cortisol?
It is a potent counter-regulatory hormone to insulin. - Increase gluconeogenesis and plasma glucose levels - Increase lipolysis - Increases proteolysis - Redistributes fat to the abdominal area
31
What is the metabolic effect of cortisol in the muscle?
Prevents the insertion of GLUT4 on the membrane
32
How does cortisol inhibit the immune system?
It binds to glucocorticoid receptors (GR) which increases IkB transcription. IkB prevents NFkB from going to the nucleus and the inflammatory response is thus inhibited.
33
What are the CV effects of cortisol?
Increases RBC production
34
What is Cushing Disease?
Pituitary adenoma results in excess cortisol that will result in increased abdominal fat, moon face, osteoporosis, hypertension and glucose intolerance.
35
What is Cushing Syndrome?
It has the same symptoms as Cushing Disease, but is caused by something other than a pituitary adenoma.
36
What is Addison's Disease?
It is a primary failure of the adrenal glands due to autoimmune destruction of the adrenals.
37
What causes secondary/tertiary adrenal insufficiency?
Most common cause = sudden cessation of glucocorticoid therapy with patient failure to secrete CRH or ACTH due to down regulation after chronically being on the glucocorticoid drugs.
38
What is the function of mineralocorticoids?
Steroid hormones that regulate sodium/water balance
39
What is the primary mineralocorticoid and where is it made?
Aldosterone. Zona Glomerulosa.
40
Where are the main sites of mineralocorticoid receptor (MR) expression?
Distal tubule in kidney Colon Salivary ducts Sweat ducts
41
What is the main target of aldosterone?
Kidney
42
What is the effect of aldosterone on the kidney?
Aldosterone stimulates sodium and water reabsorption in the kidney; increases potassium secretion
43
What triggers renin release from the kidney?
Decrease in BP
44
What is the function of renin and its relation to aldosterone?
Renin cleaves angiotensinogen into AT I AT I is cleaved by ACE into AT II AT II is a vasoconstrictor and it stimulates aldosterone release
45
What is the effect of aldosterone?
It is the primary regulator of extracellular volume. - Stimulates sodium and water reabsorption in kidney - Stimulates potassium excretion
46
What is the effect of AVP?
It is the primary regulator of free water balance. - Stimulates distal nephron water permeability which increases water retention - Decreases plasma osmolality which secondarily affects sodium concentration in the blood
47
What is the main difference in the effects of aldosterone/AVP?
ADH has no direct effect on Na -> Aldosterone does
48
What happens to cortisol as it enters an MR targeted cell?
It is converted to cortisone.
49
What converts cortisol to cortisone?
11beta-HSD2
50
What is the function of cortisone?
It is the deactivated form of cortisol
51
What is the main function of the zona reticularis?
DHEA - androstendione (weak androgen) synthesis
52
What delivers free cholesterol to the cell for the synthesis of steroid hormones?
HDL and LDL
53
What transports the free cholesterol from the cytoplasm into the mitochondria?
StAR
54
What is the function of CYP11A1 (desmolase)?
Converts free cholesterol into pregnenlone, the precursor of all steroid hormones
55
Where is 17alpha-hydroxylase found?
Zona Fasciculata and Reticularis | Sites of cortisol and DHEAS production
56
What is the defect in congenital adrenal hyperplasia?
21alpha-hydroxylase deficiency
57
What is the effect of CAH (21alpha-hydroxylase deficiency)?
It results in excess DHEA, with no mineralocorticoids or glucocorticoids It is needed in the zona glomerulosa and fasciculata.
58
What are some clinical presentations of 21alpha-hydroxylase deficiency?
``` Hypotension Hyperkalemia High plasma renin Masculinization High ACTH ```
59
What is the effect of 11alpha-hydroxylase deficiency (CYP11B1)?
It results in no cortisol with increased androgens (DHEAS) and low aldosterone It is needed in the zona fasciculata
60
What are the clinical presentations of 11alpha-hydroxylase deficiency?
Hypertension* due to excess 11-deoxycorticosterone exerting mineralocorticoid effects Hypokalemia Masculinization High ACTH
61
Where is 11alpha-hydroxylase found (CYP11B1)?
Zona Fasciculata
62
What is the effect of 17alpha-hydroxylase deficiency?
No cortisol Decreased DHEAS High MR activity
63
What are the clinical presentations of 17alpha-hydroxylase?
Hypertension Hypokalemia Feminization/ pseudohermaphroditism High ACTH
64
What is CYP11B2 also known as?
11beta-hydroxylase OR aldosterone synthase
65
What is the effect of ACTH on cholesterol?
It stimulates the conversion of cholesterol to pregnenolone by activating StAR
66
What are the effects of ACTH in the adrenal cortex (four)?
Stimulates cellular hypertrophy Stimulates biosynthesis of cortisol Stimulates biosynthesis of DHEA (CYP17) Stimulates 11beta-hydroxylase (CYP11B1)
67
What is the effect of ACTH in the adrenal medulla?
It stimulates the conversion of dopamine to norepinephrine
68
What is the effect of cortisol in the adrenal medulla?
Stimulates the conversion of norepineprhine into epinephrine
69
What is the function of epinephrine?
Response to acute stress and it occurs rapidly
70
What are the 3 main targets of E?
Muscle Liver Fat
71
What is the effect of E in muscle?
Glycogenolysis to generate ATP for local energy
72
What is the effect of E in liver?
Releases glucose into the blood
73
What is the effect of E in fat?
Increases release of FFAs
74
What are the arousal effects of E?
Pupil dilation | Sweating
75
What are the CV effects of E?
Vasoconstriction | Tachycardia
76
What is the main enzyme in the metabolism of catecholamines?
MAO
77
What can be assessed in the urine for excess NE or E production?
VMA - it is a product of MAO metabolism of the catecholamines
78
What is the main cause of catecholamine overproduction?
Pheochromocytomas – tumors originating from chromaffin cells.
79
What are some of the symptoms of pheochromocytomas?
Hypertension with no response to medication Tachycardia Headaches
80
What are pheochromocytomas also known as?
The 10% Tumor

Physiology (81 decks)

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