Endocrine Flashcards
Addison’s
Chronic Primary Adrenal Insufficency
Hormone abnormality: Cortisol & Aldosterone Deficiency
Key Clinical Features: Hypotension, hyponatraemia & hyperkalaemia
(Also Hypoglycemia, Eosinophilia and lymphocytosis
Metabolic acidosis)
Testing: 9am Cortisol & Synacthen test
Cushing’s
Hormone abnormality: Cortisol Excess
Key Clinical Features: Hypertension, weight gain & diabetes
Testing: Dexamethasone suppression test or 24-hour urinary cortisol
Conn’s
Hormone abnormality: Aldosterone Excess
Key Clinical Features: Hypertension & hypokalaemia
Testing:
1. Renin/aldosterone ratio,
2. saline (salt) suppression
3. fludrocortisone suppression test
Causes: primary hyperaldosteronism –> adrenal hyperplasia (65%) and adrenal adenoma (30-35%). ((Strictly speaking Conn’s is primary aldosteronism due to adrenal adenoma))
Mineralocorticoid
Class of steroid hormones characterized by their influence on salt and water balance
The primary endogenous mineralocorticoid is Aldosterone
Progesterone is another important example
Synethetic example: fludrocortisone
Mineralocorticoid inhibitors: Spironolactone and Eplerenone
Beta and Delta Thalassemia are associated with abnormalities to which chromosome?
Chromosome 11.
Alpha Thalassemia is associated with abnormalities to which chromosome?
The alpha globulin chain is coded for by genes on Chromosome 16.
From what molecule is DHEA synthesised and when does synthesis occur?
Dehydroepiandrosterone (DHEA) is a steroid hormone synthesised from cholesterol (via Pregnenolone) by the adrenal glands.
The fetus manufactures DHEA, which stimulates the placenta to form estrogen, thus keeping a pregnancy going.
Production of DHEA stops at birth, then begins again around age seven and peaks when a person is in their mid-20s
Aromatase is key to Estradiol production in the ovaries. How is it made?
The theca cells produce androgen in the form of androstenedione.The theca cells are not able to convert androgen to estradiol themselves. The produced androgen is therefore taken up by granulosa cells.
The neighbouring granulosa cells then convert the androgen into estradiol under the enzymatic action of aromatase.
FSH induces the granulosa cells to produce aromatase for this purpose.
Ovarian Endocrine Function: Theca Cells (follicular structure), Thecal Lutein Cells (small luteal) (luteal structure)
Androgen (Androstenedione) production
Thecal Lutein cells produce progesterone
Ovarian Endocrine Function: Granulosa Cells, Granulosal Lutein Cells (large luteal) (luteal structure)
Convert androgen to estradiol via aromatase
Granulosa Lutein cells produce progesterone
Role of LH
LH stimulates Androgen production in the theca (interna) cells
LH also stimulates the contraction of the smooth muscle cells of the theca externa. This increases intrafollicular pressure which results in rupture of the mature oocyte.
Role of FSH
FSH stimulates Aromatase production in the granulosa cells
Glucagon
where is it produced
when is it produced
what does it stimulate/ inhibit
stimulants
inhibitors
Produced by alpha cells
when there is LOW plasma glucose (increases it)
stimulates glycogenolysis and gluconeogen
inhibits glycolysis
stimulants:
Hypoglycemia
Epinephrine
Arginine
Alanine
Acetylcholine
Cholecystokinin
inhibitors:
Somatostatin
Insulin
Uraemia
Increased free fatty acids and keto acids into the blood
Which major hormone of pregnancy is produced by the placenta from 16-hydroxydehydroepiandrosterone sulfate (16-OH DHEAS)?
The placenta produces Estriol from 16-OH DHEAS. Estriol is the major oestrogen (estrogen) of pregnancy and the placenta is the primary site of production.
Pregnenolone is synthesised by the placenta from cholesterol and this is converted to dehydroepiandrosterone (DHEA) in the fetal adrenal gland
Definition: precocious puberty
The development of secondary sexual characteristics at <8 years of age.
Delayed puberty definition
The absence of testicular development (or a testicular volume lower than 4 ml) in boys beyond 14 years old or
by the absence of breast development in girls beyond 13 years old
Testosterone Binding
70% testosterone bound to SHBG
25-30% testosterone bound to albumin
Typical laboratory reference ranges are Male 1.5-3% and female approx 1%.
Causes of Low Sex Hormone Binding Globulin
As a general rule conditions leading to weight gain will lead to a drop in SHBG.
Androgens (inc anabolic steroids)
PCOS
Hypothyroidism
Obesity
Cushing’s syndrome
Acromegaly
Causes of High Sex Hormone Binding Globulin
Oestrogens e.g. oral contraceptives
Pregnancy
Hyperthyroidism
Liver cirrhosis
Anorexia nervosa
Drugs e.g. clomid, anticonvulsants
At ovulation the surge in LH causes rupture of the mature oocyte via action on what?
The luteinizing hormone (LH) surge during ovulation causes:
(1) Increases cAMP resulting in increased progesterone and PGF2 production
(2) PGF2 causes contraction of theca externa smooth muscle cells resulting in rupture of the mature oocyte
Autosomal Dominant Conditions
FAP
MEN
Neurofibromatosis
Noonans
Von Willebrand
Von Hippel Lendea
Autosomal Recessive Conditions
Congenital Adrenal Hyperplasia
Tay Sachs
Cystic Fibrosis
Glycogen Storage Disease
Thalassemia
Haemochromatosis
Sickle Cell
X-Linked Dominant
Fragile X
Rett Syndrome
Vitamin D resistant Ricketts
X-Linked Recessive
Alport Syndrome
G6PD deficiency
Haemophilia
Drugs that cause raised prolactin
Opiates,
H2 antagonists e.g. Ranitidine,
SSRI’s e.g. Fluoxetine,
Verapamil,
Atenolol,
Some antipsychotics e.g risperidone and haloperidol,
Amitriptyline,
Methyldopa
Oestragen conatining
causes of raised prolactin (hyperprolactinaemia):
Hypothyroidism
Chronic renal failure
Liver disease
Pregnancy
Stress
Lactation
Chest wall stimulation & surgery
Drugs
Hypothalamus tumours
Prolactinoma
Acromegaly
PCOS
When do hormones peak in the menstrual cycle
LH, FSH and Oestrogen just before ovulation on day 14
Progesterone peaks around day 21.
What do Chromaffin cells in the Medulla produce?
Epinephrine
Dopamine
Norepinephrine
Tanner stages: female breast
A to E
(1) Pre / nothing (Absent)
(2) Breast bud palpable under the areola (Bud)
(3) Tissue palpable outside areola (Contour)
(4) Areola elevates - “double scoop” / mound (Double mound)
(5) Areolar mound recedes - single breast contour with areolar hyperpigmentation, papillae development, and nipple protrusion (End stage)
Tanner stages: males
(1) Pre / nothing
(2) 4-8 ml (/2.5- 3.3 cm long)
(3) 9-12 ml (/3.3-4cm long)
(4) 15-20ml (/4.1-4.5 cm long)
(5) > 20 ml (> 4.5 cm long)
A-E
Stage1: Absent
Stage2: Bulky testes scrotum
Stage3: Cock lengthens
Stage4: Darkening scrotum
Stage5: End stage(Adult type)
Tanner stages: hair/ both
A small CAT
Stage 1 – Absent
Stage 2 – Straight and sparse
Stage 3 – Curling, darker
Stage 4 – Adult coarse curly
Stage 5 – Thighs
WHO types of ovulation disorder
Anovulation and oligo-ovulation = 21% of infertility
WHO type I
hypothalamic-pituitary failure (10%)
WHO type II
dysfunctions of the hypothalamic-pituitary-ovarian axis (80%)
WHO type III
ovarian failure (5%)
WHO type I ovulation disorders
hypothalamic-pituitary failure (10%)
(1) hypothalamic amenorrhea (low bmi / high exercise)
(2) hypogonadotropic hypogonadism (cause is unknown in most cases but may be congenital)
- Kallmann syndrome
-
Presentation:
Amenorrhoea (primary or secondary)
Low FSH/LH
Low oestrogen
WHO type 2 ovulation disorders
dysfunctions of the hypothalamic-pituitary-ovarian axis (80%)
hyperprolactinaemic amenorrhoea
PCOS
Oligo/Amenorrhoea (primary or secondary)
N FSH
N oestrogen
HIGH LH and androgens
WHO type 3 ovulation disorders
Ovarian failure (5%)
primary ovarian insufficiency
AI
Iatrogenic
high FSH/LH
low oestrogen level
hypogonadism
In relation to ovulation when does the LH surge occur?
24-36hr before
Calcium storage where in the body
99% skeleton hydoxyapatite
1% intracellular
0.1% extracellular (serum conc 2.2-2.6)
Calcium
diet - 1000mg/day (700 is rec)
1250 for lactating women
only 20-30% is absorbed, majority in small intestine.
Vitamin D
10–20% = vitamin D2 (diet)
80–90% = vitamin D3 (skin)
Final activation in PCT
Active metabolite = 1α,25- dihydroxyvitamin D3 (calcitriol)
Major circulating form = 25- hydroxyvitamin D3 (calcidiol)
Regulation of vit D
1α-hydroxylase is
increased by PTH, calcitonin, low Ca2+ levels, low PO43– levels.
Is inhibited by calcitriol.
Megalin
Large glycoprotein
Membrane transporter for calcidiol and calcitriol.
Synthesis of vit D
Keratinocytes
UV SUNLIGHT: 7-dehydrocholesterol–>vitamin D3 (cholecalciferol)
GI tract
DIET: Vit D2
Liver
25-hydroxylase: Vit D2 / D3 –> Calcidiol
PCT
1α-hydroxylase: Calcidiol –> Cancitriol
Organs and hormones involved in homeostasis of calc
Vit D
PTH
Calcitonin
Intestine
PT glands
Kidneys
Bones - Trabecular bone
types of bone cells
osteoblasts
mesenchymal stem cells
mineralise
osteoclasts
multinucleated cells from the bone marrow lineage
reabsorb bone
osteocytes
terminally differentiated osteoblasts trapped in the bone
respond to mechanical strain and release calcium via the canaliculi.
Low serum Calc
Detected by the Ca2+- sensing receptor on the PT glands.
PT released
Action of PTH
Hormone type
Receptor
Site of Synthesis
Physiological actions
Responds to LOW serum calcium - increases
Hormone type: peptide
Receptor: Gprotein coupled receptor (PTHR1)
Site of Synthesis: Chief cells in PT glands
Physiological actions
(1) Bone- increases osteoclastic bone resorption and Ca2+ release
(2) Kidney - reabsorption of Ca2+ (DCT - even through most resorbed in PCT) // excretion of phosphate (PO43–) (PCT and DCT).
(3) Kidney - Increases activity of the 25-hydroxyvitamin D3 1α-hydroxylase, which catalyses the conversion of calcidiol to its active metabolite calcitriol (active vit D)
PT cells
Oxyphil
Cheif - syntheses and secrete PTH
Contain sufficient PTH to maintain secretion for approx 60 minutes.
Action of calcitriol / vit D
Hormone type
Receptor
Site of Synthesis
Physiological actions
Responds to
-LOW serum calcium - increases
- LOW serum phos - increases
- PTH - neg feedback
Hormone type: Secosteroid
Receptor: Nuclear (VDR) - member of steroid/ thyroid receptor superfam
Site of Synthesis: Hydroxylated in PCT mostly
Physiological actions:
(1)Bone - increases bone remodelling - both osteoclasts (bone resorption and Ca2+ release) and osteoblasts (increases mass and calcification)
(2)Gut - increases Ca2+ absorption by increasing TRPV6 MAIN*
(3) Kidney - increases Ca2+ and PO43– reabsorption (and inhibits activation of vitamin D)
Calcitriol increases PO43– - what mechanism controls this
FGF-23
Released from osteocytes in response to calcitriol/ vit D
Action of calcitonin
Hormone type
Receptor
Site of Synthesis
Physiological actions
Responds to HIGH serum calcium - reduces
Hormone type: Peptide
Receptor: G protein coupled
Site of Synthesis: thyroid, C cells (parafollicular cells)
Physiological actions
(1) Bones - inhibits osteoclasts
(2) Kidney - inhibits resorption of Ca2+ and PO43– (PCT)
Calcium balance in PM women
negative Ca2+ balance –>
Calcium absorption from intestine - RECEPTORS. Transport receptors involved
TRPV 6 - transcellular (active)
» TRPV5 = epithelial Ca2+ channel 1 kidneys
» TRPV6 = epithelial Ca2+ channel 2 intestine
Ca2+–CaBP - paracellular (passive)
Where in the kidney is most of calcium absorbed
PROXIMAL CT
Passive paracellular (80%)
Active transcellular (20%)
Hyperparathyroidism
Excess PTH
Increased osteoclastic bone resorption
Primary - tumour in PT gland (usually benign, malig assoc with MEN)
HIGH PTH/calcitriol/calc
LOW PO43-
Secondary - defective feedback - CKD
(the bone is the only place where PTH can act to increase serum Ca2+ levels –> high turnover –> osteomalacia)
HIGH PTH
LOW calcitriol/calc
VARIABLE phos
Tertiary
Follows from secondary when PT gland becomes insensitive
HIGH PTH/calc/phos
LOW/N calcitriol
Calc, PTH, Vit D, and Calcitonin levels in preg
Calc increased
PTH decreased/normal
Vit D increased
Calcitonin increased
Oestrogen and bone development
Inhibits osteoclast function and osteoclastogenesis
May promote osteoblast survival.
Loss at menopause -> osteoporosis
Testosterone and bone health
Hypogonadism accounts for approximately 20% of osteoporosis in men
RANKL
Produced by osteoblast
Acts on osteoclasts - increases formation, function and survival.
