HPA + Thyroidal axis Flashcards
Where does the thyroid gland develop from?
Pharyngeal pouches before migrating into the neck to its adult position
Describe the thyroidal axis?
TRH - Hypothalamus
TSH - Anterior pituitary
T3/T4 - Thyroid gland
How are T3 + T4 hormones produced?
Iodine is absorbed from the diet and converted to I-
I- is added to the tyrosine units of thyroglobin to form T3 or T4
T3= mostly and is more potent
What is hypothyroidism, what are the types and what hormones are affected?
hypothyroidism = low levels of thyroid home Primary = defect in thyroid -> normal TSH + low T3/4 central = defect in pituitary/hypothalamus -> LOW EVERYTHING
What are some symptoms of hypothyrodism?
How do we treat hypothyroidism?
dry skin brittle nails menorhagia - heavy periods weight gain cold and fatigue
Treated using levothyroxine = block and replace or dose titration
What is thyrotoxicosis?
What are typical features?
Clinical syndrome when the tissues are exposed to very high levels of thyroid hormone
- weight loss but appetite
- missed/irregular periods
- lack of energy
- mood changes
What is graves disease?
Auto immune disorder which is characterised by hyperthyroidism
Autoantibodies are produced which mimic thyroid stimulating hormone = TSH receptor antibodies
The autoantibodies can bind to thyroid stimulating receptors on the thyroid gland which causes the thyroid gland to synthesis more T3 + T4
This provides negative feedback on the hypothalamus and pituitary gland but the thyroid stimulating receptor is still active
There are other antibodies e.g thyroglobulin antibodies and thyroid peroxidase antibodies
What are some typical features associated with hyper thyroidism and graves?
Thyroid eye disease: Swelling of extra occular muscles and lymphocytic infiltration
dermopathy : skin thickening due to accumulation of amino glycans and lymphocyte infiltration
What can cause hyperthyroidism?
Toxic multi nodular goitre : Independent of the pituitary
Graves disease
Toxic adenoma : Only one area of thyroid produces XS hormones
TSHoma ( pituitary tumour)
How do we investigate thyroid problems?
TSH auto antibodies - Graves
TPO antibodies = hasimotos
Ultrasounds indicate nodules
How do we treat hyper thyroidism?
Propanolol - stop symptoms
Carbimazole
Radio active iodine: Iodine tagged with radioactive tracer and kills the thyroid follicular cells
Surgery
What is a thyroid storm?
What are some signs + symptoms?
Major complication of hyper thyroidism
Life threatening event which is caused by an XS of thyroid hormones
Tachycardia, pyrexia, vomiting, cardiac failure, congestive hepatomegaly, respiratory distress
What is thyroiditis?
What normally triggers it?
- Inflammation of the thyroid gland -> thyrotoxicosis -> hypothyroidism
Triggered by auto immune diseases such De Quervain’s or Ridels
What is the effect of amiodarone?
Drug that can cause severe hypo or hyperthyroidism
1: Increased thyroid hormones
2: Direct toxic effect causing leakage of contents out of the cell
Describe the adrenal axis?
CRH: Hypothalamus
ACTH: Pituitary
Cortisol: Adrenal cortex ( zona fasiculata)
What are the types of adrenal insufficiencies?
Primary = fault in adrenal gland Secondary = HPA axis fault. No mineralocorticoid receptor
What is Addisons disease?
Addison’s disease = auto immune disease causing primary adrenal insufficiency - cortisol and aldosterone deficiencies
Symptoms = lack of energy or motivation,muscle weakness,low mood, loss of appetite and unintentional weight loss, increased thirst
How do we diagnose and treat adrenal deficiencies?
9am cortisol measurements as dirunal variation
ACTH measurements - secondary adrenal insufficiencies
steroids : produces negative feedback on the pituitary to supress CRH + ACTH. Long term use may cause atrophy of the adrenal gland
What are some of the functions of the hypothalamus ?
Homeostasis Sleep Weight and appetite Hormone synthesis HPA axis control
Where does the APG develop from?
Where does the PPG develop from?
Rathkes pouch = protrouding ectodermal tissue from the roof of the mouth
Neuroectodermal tissue from the diencephalon
What is Cushings disease + symptoms?
What is Cushings syndrome?
XS cortisol due to increased ACTH release from the pituitary Plethora Hump back fat thinning of the limbs hair loss abdominal obesity lethary low libido and erectile dysfunction
Cushing syndrome = XS cortisol it may not be due to increased ACTH
How do we diagnose Cushings?
How do we treat Cushings?
9am Cortisol - dirunal variation
ACTH measurements - cushings disease
Dexomethosone supression test: Dexomethosone would cause ACTH + cortisol to decrease, this would not happen in Cushings
- Drugs that inhibit steroidgenesis
- Removing the effector organs of cortisol e.g adrenakl glands
What type of secretion is GnRH?
Describe the gonadol axis ?
How do we treat faults of this axis?
Pulsatile, is at low frequency before puberty and then will increase
- LH = increased frequency pulses
- FSH = low frequency pulses
- e.g increased frequency at ovulation
GnRH
LH/FSH
Oestrogen/progesterone/tesosterone
Hormonal replacement therapy will restore these faults. But exogenous testosterone in males will not restore their fertility.
How is prolactin regulated?
What does high levels of pro lactin cause?
prolactin - lactation + enlargement of mammary glands
Regulated by inhibition via dopamine
Release of dopamine -> no prolactin
Less dopamine -> more prolactin
Dopamine inhibits pro lactin release
Inhibits GnRH release -> hypogonadism
What are prolactinomas?
What are the 2 types of prolactinomas?
They are pituitary tumours which disrupt the inhibitor signals of dopamine leading to hyper prolactinaemia
Micro prolactinoma < 1CM (<2000 micrograms)
Macro prolactinoma> 1CM (>400 micrograms)
What regulates HGH ?
How does HGH exhibit its effects?
Human growth hormone releasing hormone
Human growth hormone inhibiting hormone ( somatostatin)
IGF-1 - affects glucose metabolism
When glucose = high less growth hormone is released
High IGF-1 = less HGH
What is acromegaly?
What are some common symptoms?
How do we diagnose acromegaly?
Disorder that occurs in adult hood when there is an XS of human growth hormone
- enlargement of bones in face, hands and feet
- sweating
- change in ring/shoe size
- lethargy
Diagnosis
- Measure IGF-1 + HGH
- Oral glucose tolerance test: High glucose will not cause HGH to decrease
What is diabetes insipidus?
- Insufficient ADH
- Large volumes of dilute urine
- ## Use desmopressin to treat ( analogue of vasopressin/ADH)
What is SIADH?
Syndrome of inappropriate ADH
- XS ADH produced
- Na+ loss in the urine
- Conc urine is produced
What is pituitary apoplexy?
What is Sheehans syndrome?
Stalk compressed causing infarction
PPH causes infarction of the pituitary gland and it enlarges after birth
