Endocrine 2 Flashcards by Sereen Feroz

Describe the characteristics of water-soluble hormones

Transported unbound
Short half-life
Cleared fast
Bind to surface receptors on cells

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Give some examples of water-soluble hormones
Where are these stored?

Peptides
Monoamines
Both stored in vesicles before secretion

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Describe the characteristics of fat-soluble hormones

Transported bound to protein
Diffuse into cells
Long half-life
Cleared slowly

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Give examples of fat-soluble hormones
When are they secreted?

Thyroid hormones
Steroids
Secreted upon demand

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What does the endocrine system comprise of?

Pituitary gland
Thyroid
Parathyroid
Adrenal glands
Pancreas
Ovary
Testes

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first lecture of endo

skipped to regulation of appetitie

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How do you calculate BMI?

Weight (kg) / height squared (m2)

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What are the ranges for BMI ?

< 18.5 underweight
18.5 - 24.9 normal
25 - 29.9 overweight
30 - 39.9 obese
> morbidly obese

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Risks of obesity

Type II diabetes
HTN
Coronary artery disease
Stroke
Osteoarthritis
Obstructive sleep apnoea
Carcinoma - breast, endometrium, prostate, colon

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What plays a central role in appetite regulation?

Hypothalamus

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Why is the anatomy of the anterior pituitary unusual?

No arterial blood supply

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Describe the HPA axis

Hypothalamus -> CRH
Pituitary -> ACTH
Adrenal cortex -> cortisol

Cortisol decreases the activity of Hypothalamus & Pituitary
∴ less CRH + ACTH produced

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Describe the HPT axis

Hypothalamus -> ↑ TRH
Pituitary -> ↑ TSH
Thyroid gland -> ↑ T3 + T4

T3 + T4 decreases activity of Hypothalamus and Pituitary
∴ ↓ TRH + TSH produced

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Describe the GH/IGF-I axis with the result of increasing GH

Hypothalamus -> ↑ GHRH
Pituitary -> ↑ GH
Liver -> ↑ IGF-I

IGF-I decreases activity of hypothalamus
∴ ↓ GHRH

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Describe the GH/IGF-I axis with the result of decreasing GH

Hypothalamus -> ↑ SMS (inhibits GH production)
Pituitary -> ↓ GH
Liver -> ↓ IGF-I

IGF-I decreases production of GH
∴ ↓ IGF-I = ↑ GH

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What is the mean age and mean duration of symptom presentation of Acromegaly?

mean age = 44 years
mean duration = 7 years

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What are some co-morbidities of Acromegaly?

HTN and heart disease
Sleep apnoea
Arthritis
Insulin-resistant diabetes (type 2)
Cerebrovascular events & headaches

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What are some questions you could ask to find out the clinical features of acromegaly?

Are rings still fitting you?
Is shoe size changing?
Teeth more separate?

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When is acromegaly excluded?
(Clinical findings)

Random GH < 0.4 ng/ml
Normal IGF-I

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Gold standard for Acromegaly

75gm Oral glucose tolerance test

Acromegaly excluded if :
IGF-I normal
and
OGTT nadir GH <1ng/ml

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What are the aims of treatment in acromegaly?

Restoration of basal GH and IGF-I to normal
Symptom relief
Reverse of visual/soft tissue changes
Stop further skeletal deformity
Normalise pituitary function

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Why can’t you rely on random GH to diagnose acromegaly?

Because GH has pulsatile secretion

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What are some issues that make transsphenoidal pituitary surgery harder?

Large tumour
Invasiveness - if in cavernous sinus

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How does the size of an adenoma (specifically when treating acromegaly) affect the surgical cure rate?

If < 1cm, cure rate ~90%
If > 1cm, cure rate ~ <50%

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What are problems of radiotherapy when treating acromegaly?

Delayed response Hypopituitarism Rare 2ndary tumours Bc close to eyes, could cause damage

What medication can be used to block GH and ∴ treat acromegaly?

Somatostatin analogues Dopamine agonists GH receptor antagonist

What are some advantages of dopamine agonists when treating acromegaly?

No hypopituitarism Oral administration Rapid onset

What are some disadvantages of dopamine agonists when treating acromegaly?

Relatively ineffective Side effects

What are the advantages of using Cabergoline vs bromocriptine (both dopamine agonists used to treat acromegaly)?

Cabergoline is more potent, fewer side effects Twice weekly

When are dopamine agonists especially useful in treating acromegaly?

When tumour is co-secreting GH and prolactin

What are some disadvantages of somatostatin analogues?

Injectable Side effects

What are some determinants of efficacy of somatostatin analogues?

GH levels Tumour size SMS receptor expression

Describe the onset of acromegaly

Insidious

What are some effects of prolactin?

Menstrual irregularity Infertility Galactorrhoea Low libido Low testosterone in men

What type of visual defect can you get with a pituitary tumour?

Bi-temporal hemianopia

Describe the location of the pituitary

Sits within the sella turcica at the base of brain

Name some examples of hormones that are secreted from the anterior pituitary

Thyroid stimulating hormone (TSH) Adrenocorticotrophic hormone (ACTH) Prolactin Growth hormone (GH) Gonadotrophic hormones

Name some examples of hormones that are secreted from the posterior pituitary

Oxytocin Anti-diuretic hormone (ADH)

Describe the blood supply of the anterior pituitary

No direct arterial blood supply Receives blood through portal venous circulation from hypothalamus

Describe how prolactinoma may come about

Ant. pituitary enlarges Impinges on hypothalamus Hypothalamus produces less dopamine ∴ prolactin secreted is NOT suppressed

What can pituitary tumours cause?

1. Pressure on local structures - optic nerve ∴ bitemporal hemianopia 2. Pressure on normal pituitary ∴ hypopituitarism 3. Could be a functioning tumour e.g. prolactinoma, acromegaly, cushing's

Describe symptoms if a pituitary tumour puts pressure on local structures

Could go up and stretch the dura, causing headaches Visual field defects (bitemporal hemianopia) Could go sideways into medial temporal lobe, cause cranial nerve palsies and seizures If goes down through bone, CSF fluid leakage

Describe hypopituitary signs

Pale No body hair Central obesity

Why is a benign adenoma NOT a differential for diabetes insipidus?

Bc diabetes insipidus is caused by dysfunctional posterior pituitary and benign adenomas only are found anteriorly!

What is a carcinoid tumour?

Type of neuroendocrine tumour that grows from neuroendocrine cells

What are the 3 layers of the adrenal cortex and what do they produce?

**GFR makes good SEX*** Zona **g**lomerulosa - **m**ineralcorticoids - aldosterone (AM) Zona **f**asciculata - **g**lucocorticoids - cortisol (GC) Zona **r**eticularis - androgens - **sex** hormones

What is the difference between Acromegaly and Gigantism?

Gigantism- XS GH production in children BEFORE fusion of the epiphyses of the long bones Acromegaly- XS GH in adults

Describe a bitemporal hemianopia

Loss of vision on outer half of both eyes

What inhibits the release of GH?

Somatostatin ! Dopamine High levels of glucose

Where is prolactin secreted from?

Anterior Pituitary

What inhibits the release of of prolactin?

Dopamine

Where is dopamine produced?

Hypothalamus

What is prolactin?

Hormone produced by lactotrophs in ant. pituitary gland

Define prolactinoma

Lactroph cell tumour of the pituitary

Define microadenoma

Tumour < 1cm

Define macroadenoma

Tumour > 1cm

What is a circadian rhythm?

Physical, mental and behavioural changes that follow a daily cycle

What is 1° adrenal insufficiency also called?

Addison's disease

What is 2° adrenal insufficiency also called?

Hypopituiritarism

What is the most common cause of primary adrenal insufficiency worldwide?

What is the most common cause of primary adrenal insufficiency in the UK?

Addison's (autoimmune adrenalitis)

Aldosterone acts on the kidney to :

Increase sodium reabsorption from distal tubule & increase potassium excretion from distal tubule

What is the fun key phrase to remember for Addison's?

Tanned, Toned (fit and ready), Tired, Tearful

If Hypothalamus releases **TRH**, What does the pituitary release? What is the target organ? What does the target organ release? What is the effect of the hormones?

TSH Thyroid T3 + T4 Metabolism

If Hypothalamus releases **CRH**, What does the pituitary release? What is the target organ? What does the target organ release? What is the effect of the hormones?

ACTH Adrenal cortex Cortisol Fat metabolism

If Hypothalamus releases **GnRH**, What does the pituitary release? What is the target organ? What does the target organ release? What is the effect of the hormones?

FSH/LH Gonads Oestrogen/Testosterone Menstrual cycle, Sex

If Hypothalamus releases **GHRH**, What does the pituitary release? What is the target organ? What does the target organ release? What is the effect of the hormones?

GH Liver IGF-I Growth & development

If Hypothalamus releases **Dopamine**, What does the pituitary release? What is the target organ? What does the target organ release? What is the effect of the hormones?

Inhibits prolactin Breast / Milk production

What inhibits TSH?

Somatostatin

When treating adrenal insufficiency, what must you remember?

Double dose of steroids if infection, trauma, surgery or nightshift work

What is the cause of Goitre?

Iodine deficiency

If a patient presents with weight loss, heat intolerance, palpitations, sweating, anxiety etc, what should you be thinking? and ∴ what should you do?

Problem with thyroid ∴ order a TSH test (cheap, doesn't take long and can quickly determine the problem)

What are T3/T4 necessry for?

**3 M's :** **M**ovement, **M**entation & **M**etabolism

Where and when is Parathyroid hormone secreted?

By Chief cells in response to hypocalcaemia

Describe the action of Parathyroid hormone

↑ Osteoclast activity (∴ release Ca2+ & phosphate from bone) -> RAPID! ↑ Intestinal calcium absorption -> slow & indirect ! ↑ Ca2+ & ↓ phosphate reabsorption in kidney ↑ Vitamin D production **Overall, ↑ Ca2+ & ↓ Phosphate**

What is calcitriol release stimulated by?

↓ Plasma Ca2+ ↓ Plasma phosphate Parathyroid hormone (PTH)

What is the role of Vitamin D / Calcitriol / 1, 25-dehydroxycholecalciferol ?

↑ Ca2+ & Phosphate absorption in gut Enhanced bone turnover by ↑ osteoclasts ↑ Ca2+ and phosphate reabsorption in kidneys Inhibits PTH release - neg feedback

What is calcitriol?

The active form of Vitamin D

Where is calcitonin made?

In C-cells of thyroid

What effect does calcitonin have on plasma Ca2+ and phosphate?

↓ Ca2+ and phosphate

What does HYPOcalcaemia cause?

Paraesthesia Muscle spasms Seizures Basal ganglia calcification Cataracts ECG abnormalities (Long QT) Osteomalacia - vit D def CHVOSTEK'S SIGN

How do you look for Chvostek's sign?

Tap facial nerve and look for facial spasm

What are paraganglia cells?

Chromaffin cells that secrete adrenaline