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KHI > Cushings/Pituitary/Adrenal > Flashcards

Cushings/Pituitary/Adrenal Flashcards

1
Q

Single chain of 191 amino acids? What cell type of ant pituitary releases?

A

Growth hormone
Somatotrophs (acidophilic)

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2
Q

Single chain of 39 amino acids? What cell type releases?

A

ACTH
Corticotrope (basophilic)

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3
Q

Single chain of 198 amino acids? What cell type releases?

A

Prolactin
Lactotroph (acidophilic)

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4
Q

3 glycoprotein hormones released by ant pituitary and the cells producing them?

A

TSH (Thyrotropes)
FSH (Gonadotropes)
LH (Gonadotropes)

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5
Q

2 hormones produced in hypothalamus/stored in post pituitary? How do they differ in chemistry?

A

Oxytocin
Anti-diuretic hormone

Both are polypeptides with 9 amino acids.

Oxytocin contains isoleucine + Leucine
ADH contains phenylalanine + arginine

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6
Q

What are the 3 components of the anterior pituitary gland and what cell types are found in each?

A

Pars distalis
-All types

Pars intermedia
-Corticotrophs -> ACTH + MSH

Pars tuberalis
-Gonadotrophs + Thyrotropes -> FSH LH TSH

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7
Q

In what structures of neurons are hypothalamic hormones stored before release from posterior pituitary?

A

Herring bodies within neurosecretory granules.

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8
Q

How do releasing/inhibitory hormones get from the hypothalamus to the anterior pituitary?

How do anterior pituitary hormones get to the systemic circulation?

A

Hormones from hypothalamus are released from axon terminals at the median eminence.

They enter a primary capillary network which is derived from the superior hypophyseal artery (from int carotid)

They enter the primary capillary plexus and travel via the hypophyseal portal system to the secondary capillary plexus to reach the anterior pituitary cells.

Hormones released from the anterior pituitary exit into the system circulation via:
-Hypophyseal veins -> cavernous sinus -> petrosal sinus -> internal jugular vein.

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9
Q

Two functions of Anti-diuretic hormone?

A

Increases water reabsorption from kidneys back into blood

Regulates blood pressure/blood volume

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10
Q

Two physiological changes related to blood that results in ADH secretion?

A

Low blood pressure
- less stretch of atria stretch receptors / baroreceptors of aortic arch + carotid sinus
-Less inhibitory signals sent to medulla (and subsequently to hypothalamus) via vagus + glossopharyngeal
-increase in ADH secretion

Increased osmolarity of blood (not enough water)
-results in depolarisation of osmoreceptors in hypothalamus
-ADH release.

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11
Q

MOA of ADH on water reabsorption?

A

Collecting ducts/tubules

-Binds to its GPCR on tubular epithelial cells
-Activates Adenylyl cyclase
-Increases cAMP
-phosphorylation of aquaporin vesicles
-Insertions of aquaporins onto luminal surface of epithelial cells

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12
Q

Two functions of oxytocin?

A

Uterine contractions
-Binds to GPCR of uterine smooth muscle cells.
-Downstream cascade of intracellular signalling
-Influx of calcium
-Myosin-cross bridge formation
-Contraction
-Positive feedback for continued contractions.

Milk ejection through contraction of myoepithelial cells

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13
Q

From what layer of the adrenal cortex is cortisol secreted?

What hormone from the pituitary stimulates its release? What is its structure? What type of cell does this originate from? What hormone from hypothalamus stimulates this cell?

A

Zona fasciculata

ACTH
Single chain 39 amino acid
Corticotrope
CRH

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14
Q

MOA of glucocorticoids

A

-Travel in blood bound to steroid binding globulin- active.
-Some travels in plasma, unbound - active
-It is lipophilic and so diffuses into cell.
-Binds the intracellular receptor which is bound by a
heat shock protein
-Binding the receptor results in dissociation of HSP
-Translocates to nucleus
-Alters gene expression

  1. Upregulates anti-inflammatory genes (trans-activation):

(i)Anexin-1 activation
—> Activation of anexin 1 leads to inhibition of phospholipase A2-alpha.
—>This blocks release of arachidonic acid from cell membranes
—> This inhibits production of ecosanoids i.e. prostaglandins + leukotrienes.

(ii) MAPK phosphatase 1 activation
—> leads to dephosphorylation and inhibition of MAPK family of proteins
—> decreased intracellular signalling
—> inhibition of phospholipase A2-alpha
—> blocks release of arachidonic acid

  1. Downregulates pro-inflammatory genes (transrepression): NFkB, Activator protein 1

(i) NFkB: normally binds DNA to promote transcription of inflammatory mediators + COX-2 enzymes

(ii) Activator Protein 1: Normally acts in the transcription of inflammatory mediators.

  1. Increases anti-inflammatory cytokines IL-10, IL-1ra
  2. Also causes non-genomic changes
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15
Q

How does glucocorticoid use cause immunosuppression?

A
  1. Effect on T + B cells
    -reduces T lymphocyte count
    -reduces activation of Th2 cells
    -reduces clonal expansion
    -decreases cytokine release
    -reduces antibody production
  2. Reduces expression of adhesion molecules for leukocytes to adhere to.
  3. Decreases vascular permeability -> more difficult for leukocytes to exit into tissue.
  4. Reduces complement concentration in plasma
  5. Reduces circulating eosinophils.
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16
Q

How do glucocorticoids cause osteoporosis?

A

Can increase the RANK-L : OPG ratio therefore rate of bone resorption > bone formation (osteoclasts more active than osteoblasts).

Can also reduce calcium absorption from small intestine -> stimulates PTH secretion.

17
Q

How do glucocorticoids cause hypertension?

A

Increased activation of alpha-1 adrenergic receptors on vascular smooth muscle -> smooth muscle contraction.

Excess glucocorticoids can also saturate the 11-Beta HSD2 enzyme in renal tubules = less conversion to cortisone -> excess GC can mimic aldosterone by binding to its mineralocorticoid receptor to trigger sodium resorption.

18
Q

What is the embryological origin of the adrenal cortex and medulla?

A

Cortex: Mesenchymal cells (mesoderm)

Medulla: neuroectoderm( neural crest cells from ectoderm)

19
Q

outline the histological and functional characteristics of

Zona Glomerulosa

A
  1. Zona Glomerulosa
    - outer layer
    - overlayed by capsule of the gland
    - Cells organised into rounded column groups.
    - Cells are smaller than other zones
    - Nuclei are dark and round.
    - cytoplasm is basophilic
    - Capillaries run between groups

Function: production of aldosterone using aldosterone synthase in response to angiotensin II and potassium levels.

20
Q

outline the histological and functional characteristics of

Zona Fasciculata

A

-Cells organised into cords/fascicles
-Cords separated by fenestrated, sinusoidal capillaries.
-Nuclei are light and centrally located
-cytoplasm is light, foamy/spongey due to lipid droplets within vesicles (spongiocytes)

Function:
Cortisol + Corticosterone release in response to ACTH.

21
Q

outline the histological and functional characteristics of

Zona Reticularis

A
  • Cells organised into wavy cords which are separated by sinusoidal capillaries.
    -Cytoplasm is eosinophilic.
    -Nucleus is large and light
  • Lipofuscin; produced following oxidation of intracellular lipids; gives browny tinge.

Function:
Produces Dehydroepiandosterone (DHEA)- a precursor for androgen + estrogen- in response of to ACTH

22
Q

What class of hormones are produced in the adrenal cortex vs medulla? from what are they derived? How are these synthesied?

A

Adrenal cortex: Steroid hormones, derived from cholesterol

Synthesis:
-80% of the steroid hormones are made using LDL’s circulating within the plasma.
-The LDLs diffuse into the intersitial space and are endocytosed by adrenocorticol cell membrane receptors contained within coated pits.
- The receptors + LDL contained within vesicle which fuses with lysosome and the cholesterol is then released for use.
-The cholesterol is cleaved at the mitochondra by cholesterol desmolase to form pregenalone (rate limiting step)

Adrenal medulla: Tyrosine derived hormone

Synthesis:
-Tyrosine -> L DOPA by Tyrosine hydroxylase
- L-DOPA -> Dopamine by DOPA decarboxylase
- Dopamine-> noradrenalin by Beta-hydroxylase (within chromaffin cell vesicles)
- Noradrenalin -> Adrenalin by P-N-Methyltransferase

23
Q

Outline histological and functional characteristics of Zona reticularis

A

Zona reticularis

  • Cell cords anastomozing with eachother separated by sinusoidal capillaries
  • Eosinophilic cytoplasm
  • Light and large nucleus
  • Lipofuscin: produced following lipid oxidation; gives browny tinge.

Function: produces Dehydroepiandosterone (DHEA) - a precursor of androgens + estrogren- in response to ACTH.

24
Q

What are the 3 classes of hormones under the heading “steroid hormones” - all of which are produced in adrenal cortex?

A
  1. Mineralocorticoids
    - Aldosterone
    - Deoxycorticosterone
    -> Zona Glomerulosa
  2. Glucocorticoids
    - Cortisol
    - Corticosterone
    - Cortisone
    -> Zona Fasciculata
  3. Sex hormones
    - Dehydroepiandosterone
    -> Zona reticularis
25
Q

What is the function and MOA of aldosterone? From where is it released? What type of hormone is it?

A

Aldosterone is produced in and secreted from the Zona Glomerulosa of the adrenal cortex in response to Angiotensin II and high potassium levels.

It is a steroid hormone - a mineralocorticoid (corticosteroid)

Function:
->increases sodium resorption and potassium secretion in kidneys (principle cells of collecting tubules) -> therefore influences water resorption also.

-> increases sodium resorption by the salivary and sweat glands.

Its release is stimulated by:
1. Increase Angiotensin II
2. Increase potassium in ECF

MOA:
-Diffuses into renal tubule epithelial cells.
-Binds to mineralocorticoid receptor in cytoplasm, which is bound by heat shock protein.
-diffuses into nucleus
- increases gene expression of those pertaining to membrane transport proteins for sodium, potassium and hydrogen.
-increases synthesis of Na+ K+ ATPase

26
Q

Describe the difference between the low dose and high dose dexamethasone test

A

(1) Low dose - 1mg dexamethasone given at night
-> If cortisol levels are normal then no cushings syndrome
-> If cortisol levels are high then cushings syndrome.

(2) High dose- 3mg
-> Low cortisol - ACTH dependant cushing’s - cushing’s disease
-> High cortisol + high ACTH = ectopic ACTH-dependant cushings.
-> High cortisol + low ACTH = ACTH independant cushings i.e. Adrenal cushing’s.

The low dose test is to determine if cushing’s syndrome is present

The high dose test better pinpoints the cause by comparing cortisol levels + ACTH levels.

High dose dex will only inhibit pituitary ACTH; it will not suppress ectopic tumours producing ACTH

27
Q

State whether you would expect the changes to be up or down for each of the following: Red blood cells; platelets; neutrophils; eosinophils

A

RBC: raised due to secondary polycythaemia

Neutrophils: High (but unable to leave blood into tissue)

Eosinophils: Low

Platelets: High (hypercoagulable state)

28
Q

list 5 effects of excess glucocorticoids

A
  1. Osteoporosis
  2. Reduced immunity - opportunistic infections
  3. Increased proteolysis - proximal muscle weakness and cardiomyopathies.
  4. Hyperglycemia and insulin resistance
  5. Hypertension and polycythenia.
  6. Skin hyperpigmentation and easy bruising
  7. Cataract/glaucoma
29
Q

Outline the consequences of suddenly stopping long term glucocorticoids

A

Secondary or tertiary adrenal insufficiency

Secondary - failure of pituitary gland to secrete ACTH. Caused by stopping of GC’s or pituitary resection. Results in low ACTH, low cortisol, normal aldosterone (angiotensin II/potassium driven)

Tertiary - failure of hypothalamus to secrete CRH. Results in low CRH, low ACTH, low cortisol. Due to stopping of GCs or hypothalamtic tumour.

Consequences of low cortisol
- Postural hypotension
- Hypoglycemia
- Weakness and fatigue
- Weight loss

Loss of aldosterone (secondary)
- Hyponatremia due to reduced sodium resorption
- Hyperkalemia due to reduced potassium excretion
- Acidosis due to H+ retension.

30
Q

What factors dictate the size and speed of dose reduction of glucocorticoids?

Outline the 3 scenarios when GC’s can be stopped abruptly

A
  1. The likelihood of relapse of condition/disease
  2. The extent of adrenal atrophy/adrenocorticol hypofunction - will the body be able to return to endogenous cortisol production

Stop abruptly in those who:
(1) are unlikely to relapse
(2) have been on a course for < 3 weeks.
(3) who do not fall into any of the following
- have been on repeated evening doses
- Have been on a course > 3 weeks
- Has recently been on repeated doses
- Has been on a daily dose of >40mg of prednisolone or equivalent for > 1 week
- Has another cause for adrenal insufficiency.

KHI (20 decks)

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