Chemical Pathology Flashcards
What is the homeostasis of Calcium?
If run out of calcium, body takes it from bone which can cause fractures
Key hormones:
- PTH (peptide)
- Vitamin D (steroid hormone – activated to vit D3 from animals not plants) vit D2 is from plants
DECREASE in Ca:
- Hypocalcaemia detected by parathyroid gland
- Parathyroid gland releases PTH
- PTH “obtains” Ca2+ from 3 sources
–Bone – activates osteoclasts to release Ca
–Gut (absorption) – vitamin D (increase in 1,25OH vitD) increases absorption
–Kidney (resorption and renal 1 alpha hydroxylase activation by PTH)
What is the role of circulating calcium?
- Important for normal nerve and muscle function
- Plasma concentration must thus be maintained despite calcium and vitamin D deficiency
- Chronic calcium deficiency thus results in loss of calcium from bone in order to maintain circulating calcium
- Serum Ca2+ in 3 forms
–Free (“ionised”) ~50% - biologically active
–Protein-bound ~40% - albumin
–Complexed ~10% - citrate / phosphate
- Total serum Ca2+ 2.2 – 2.6 mmol/L
- “Corrected” Ca2+ usually reported
–serum Ca2+ + 0.02 * (40 – serum albumin in g/L)
–Calcium levels important in muscle depolarisation and thus in the control of nerve and muscle
•Ionised Ca also measured
Albumin affects free Calcium -> corrected calcium is checked against albumin levels -> low albumin = increase free calcium
- Thus the corrected calcium refers to that
- Albumin=30, total calcium=2.2
- Corrected calcium = 2.2 + (0.02 x 10)
- = 2.2 + 0.2 = 2.4 mM
- (thus the corrected calcium tells you that the problem is the albumin and that the ionised calcium will also be normal)
Blood gas – check the ionised calcium for quick result of free calcium
What is PTH and its role?
- 84 aa protein
- Only released from parathyroids
•
•Roles
–Bone & renal Ca2+ resorption
–Stimulates 1,25 (OH)2 vit D synthesis (1α hydroxylation)
–Also stimulates renal Pi (phosphate) wasting
How is vit D synthesised?
D3 is activated in liver to 25OHD3 (stored in blood and liver and inactive version), then activated in the kidney when needed
- Vitamin D3 is synthesised in the skin (cholecalciferol)
- Vitamin D2 is a plant vitamin (ergocalciferol)
- Both are active
- Next stage in the liver:
- •100% of any absorbed vitamin D is hydroxylated at the 25 position
- •enzyme: 25 hydroxylase
- •25 hydroxy vitamin D is inactive
- •This is the stored and measured form of vitamin D
Activation of Vitamin D:
- •Normally happens in kidney
- •enzyme: 1 alpha hydroxylase
- •RATE LIMITING STEP when Ca is needed to rise
- •Rarely, this enzyme can be expressed in lung cells of sarcoid tissue – sarcoidosis; non-regulated fashion, can cause hypercalcaemia
What is the role of 1,25 (OH)2 vit D?
- Intestinal Ca2+ absorption
- Also intestinal Pi absorption
- Ca+P absorbed together in the gut!
- Critical for bone formation
- •? Other physiological effects
- –Vit D receptor controls many genes eg for cell proliferation, immune system etc
- –Vit D deficiency associated with cancer, autoimmune disease, metabolic syndrome
What is the role of the skeleton?
- Structural framework
- Strong
- Relatively lightweight
- Mobile
- Protects vital organs
- Capable of orderly growth and remodelling
- Metabolic role in calcium homeostasis
- Main reservoir of calcium, phosphate and magnesium
What are the different metabolic bone disease?
- Osteoporosis – take Ca from bone, structure of bone normal but thinner; normal in ageing
- Osteomalacia – not enough vit D so abnormal bones; vit D involved in activation of vitD; bone is decalcified with abnormal structure
- Paget’s disease - ?virus, very active osteoblasts and osteoclasts; pain, tx with bisphosphonates
- Parathyroid bone disease – tumour in PTH gland, pushes up calcium, combined osteoporosis and osteomalacia
- Renal osteodystrophy – renal failure, so don’t activate vit D, so can’t excrete phosphate, bone can’t form properly as not enough OHase
What is vitamin D deficiency?
- Defective bone mineralisation
- Childhood -> Rickets
- Adulthood -> Osteomalacia
- Vitamin D deficiency in the UK
– More than 50% adults have insufficient vitamin D
– 16% have severe deficiency during winter and spring
•Risk factors
- –Lack of sunlight exposure
- –Dark skin
- –Dietary
- –malabsorption
Clinical features:
•Osteomalacia
- –Bone & muscle pain
- –# risk
- –Biochem – low Ca2+ & Pi, raised ALP (alkphos)
- –Looser’s zones (pseudo#s)
•Rickets
- –Bowed legs
- –Costochondral swelling
- –Widened epiphyses at the wrists
- –Myopathy- need ca for normal nerve transmission
What is osteomalacia?
- Bone is demineralised
- Caused by vitamin D deficiency – lack of diet
- Renal failure
- Anticonvulsants induce breakdown of vitamin D (phenytoin)
- Lack of sunlight
- Chappatis (phytic acid)
2nd hyperPTH – low Ca, vit D deficiency, high PTH; push out phosphate in urine and lots of bone is lost, causing rickets and pseudo#
PTHrP – produced by placenta, which maintains Ca in fetus during pregancy
What is osteoporosis?
- •Cause of pathological fracture
- •Occurring more often as people live longer
- •Loss of bone mass
- •Bone slowly lost after age 20
- •Residual bone normal in structure
Causes: Old age, immobilisation, oestrogen, cushing’s; ca + P are normal in this, not metabolic problem, with #s in past; childhood illness; poverty;
- •Lifestyle: sedentary, EtOH, smoking, low BMI/nutritional
- •Endocrine: hyperprolactinaemia, thyrotoxicosis, Cushings
- •Drugs: steroids
- •Others eg genetic, prolonged intercurrent illness
•Reduction in bone density (normal mineralisation)
•Biochemistry NORMAL
- Asymptomatic until # (Fracture is the first symptom). Then it is too late…
- Typical # - neck of femur (NOF), vertebral, wrist (Colle’s)
Diagnosis:
•usually using DEXA scan
- –Dual energy X-ray absorptiometry
- –hip (femoral neck etc) & lumbar spine
- –T-score – sd from mean of young healthy population (useful to determine # risk)
- –Z-score – sd from mean of aged-matched control (useful to identify accelerated bone loss in younger patients)
- Osteoporosis – T-score <-2.5
- Osteopenia – T-score between -1 & -2.5
Treatment for oteoporosis:
•Lifestyle
- –Weight-bearing exercise
- –Stop smoking
- –Reduce EtOH
•Drugs
- •Vitamin D/Ca – safest benefiting drug
- •Bisphosphonates (eg alendronate) –↓ bone resorption
- •Teriparatide (PTH derivative) – anabolic
- •Strontium – anabolic + anti-resorptive
- •(Oestrogens – HRT)
- •SERMs eg raloxifen
Why is ethanol a major point of forensic toxicology concern?
OD
Accidents including RTAs
Additive effects other respiratory depressant drugs
Why is heroin - as morphine - a major point of forensic toxicology concern?
iv injection, mix with tobacco, volatilised
Fatal OD with all routes of ingestion
Additive effects other respiratory depressant drugs
Few rapid deaths
Most respiratory depression or aspiration pneumonitis
tolerance
Why is cocaine a major point of forensic toxicology concern?
Injected with heroin, “speedball”
Tolerance
Acute dangers : cardiac dysrhythmias, acute heart failure, myocardial infarction
Slowly developing damage to the myocardium, ventricular arrhythmias, sudden death
Lethal syndrome of excited delirium, occurs in regular users within 24 hrs of last dose
Body packers
Effects prolonged if used with ethanol, get cocaethylene formed
Why are amphetamines a major point of forensic toxicology concern?
Increasing number of deaths
Large OD causes direct toxic effect on heart
Can cause hyperthermia, leads to rhabdomyolysis, leads to muscle necrosis and renal failure
Why is methadone a major point of forensic toxicology concern?
Tolerance
After ingestion fatal amount takes 4-6 hours to die
Additive effects other respiratory depressant drugs
5 mL can kill a child, 60 mL can kill healthy adult male
Maintenance dose can vary from 5 to 200 mL
Why are benzodiazepines a major point of forensic toxicology concern?
Additive effects other respiratory depressant drugs
Extremely rare to cause death alon
Why is cannabis a major point of forensic toxicology concern?
Never fatal alone
Find in RTAs
Driving after alcohol + cannabis, lethal combination
Why is pregabalin/gabapentin a major point of forensic toxicology concern?
Present in 9% of Coroners’ cases
Widely used for euphoria they produce
Why are legal highs a major point of forensic toxicology concern?
Stimulants (mostly cathinones)
Synthetic cannabinoids or “Spice”
Synthetic Opioids (e.g. acetylfentanyl)
Hallucinogenic compounds (e.g. 1P-LSD)
What are the problems associated with interpretation of the toxicology report PM?
Tolerance
Site dependence
PM redistribution of drugs (NB PM blood concentration cannot be used to calculate the dose)
Individual variation in response
Stability of drugs
Why do we use hair for the analysis of toxicology?
- Blood/serum, drugs typically can be detected for no more than 12 hours
- Urine, drugs typically detected for 2-3 days
- Hair is the only specimen can give information about long term drug use
- Drugs are incorporated into hair from the blood stream during the growth phase
- Hair growth approx 1cm/month – “tape-recording of drug use”
Where can we apply hair analysis?
Child custody cases
Investigating spiked drinks defences
Drug naïve deaths
Monitoring drug use prior to return of driving license – Germany, Italy
Investigation of drug use in exhumed/putrefied bodies
Employment, pre-employment screening – USA
What is chemsex?
Sex under influence of drugs (mephedrone/crystal meth/GHB/GBL)
Associated with men who have sex with men
Harms associated include Increased risk overdose & increased risk HIV
What is the hormone that controls water balance?
ADH
Released from post pit – acts on aq-2 to insert them, via V2 receptors in collecting duct and acts on water retention
V1- causes vasoconstriction of the vessels, receptors present in vascular smooth muscle
Two main stimuli for ADH secretion?
– Serum osmolality (mediated by hypothalamic osmoreceptors). Decreased due to lack of drinking – so ADH is released which means water is retained. Stimulates thirst, so we make more ADH
–Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta) if decreased then water is retained to keep bp high
–ALL are APPROPRIATE responses
ON serum sodium -> increased ADH = hyponatraemia
How do we assess, diagnose and treat hyponatraemia?
Need to differentiate between hypovolaemic, euvolaemic and hypervolaemic
The clinical signs of hypovolaemia?
- –Tachycardia
- –Postural hypotension
- –Dry mucous membranes
- –Reduced skin turgor
- –Confusion/drowsiness
- –Reduced urine output
- –Low urine Na+ (<20)
- •MOST IMPORTANT TEST is URINE SODIUM TEST to check for hypovolaemia as kidneys hold on to salt if hypovolaemia, so low urine Na = hypovolaemia (unless on a diuretic)
- Causes:
- –Renal: diuretics (only if it has been recent – not if it has been a long time on diuretics, needs to be another insult)
- –Extra-renal: diarrhoea, vomiting
- Management:
- –Volume replacement with 0.9% saline
- –Give saline as a diagnosis – if sodium goes up then hypovolaemic, if euvolaemic sodium goes down a bit
The clinical signs hypervolaemia?
- –Raised JVP
- –Bibasal crackles (on chest examination)
- –Peripheral oedema(!!)
- Causes:
- –Cardiac failure – increase dilation of the heart, releasing ANP(?)
- –Cirrhosis – drop in BP due to vasodilation and NO, so increased ADH
- –Renal failure – due to lack of removal of water from the kidneys
- Managment
- –Fluid restriction
- –Treat the underlying cause
Euvolaemic pt hyponatraemia causes:
- Hypothyroidism
- Adrenal insufficiency
- Syndrome of inappropriate ADH (SIADH)
- causes:
- –CNS pathology – tumour, bleeds
- –Lung pathology – cancer, PE, pneumothorax
- –Drugs (SSRI, TCA, opiates, PPIs, carbamazepine)
- –Tumours
- –Surgery
- Diagnosis of SIADH:
- rule out hypovol, hypothyroidism, adrenal insufficiency
- reduced plasma osmolality AND increased urine osmolality
- Treatment for SIADH:
- •Demeclocycline
- –Reduces responsiveness of collecting tubule cells to ADH
- –Monitor U&Es (risk of nephrotoxicity)
- •Tolvaptan
- V2 receptor antagonist
- •Demeclocycline
Treatment for hypervolaemic pts:
- Fluid restriction
- treat underlying cause
Plasma and urine osmolality test:
- Osmolality would still be low as sodium would be low; pseudohyponatraemia caused by hyperlipidaemia or excess proteins, with a normal osmolality
- Urine osmolality is high as the urine is more concentrated as there is less water present
Severe hyponatraemia:
- •Reduced GCS
- •Seizures
- •Seek expert help (Treat with Hypertonic 3% saline)
–Serum Na must NOT be corrected > 8-10 mmol/L in the first 24 hours
–Risk of osmotic demyelination (central pontine myelionlysis)
•quadriplegia, dysarthria, dysphagia, seizures, coma, death
How are potassium levels regulated in the blood?
–Angiotensin II
–Aldosterone
- •Aldosterone increases number of open Na+ channels in the luminal membrane
- increased Sodium reabsorption
- •makes the lumen electronegative & creates an electrical gradient
- •Potassium is secreted into the lumen
- Angiotensin II and potassium levels are the stimuli for aldosterone secretion
RAAS – foundation of K mx in kidney; renin is released from JGA which cleaves angiotensinogen to angI (released from liver); ang I to Ang II via ACE in lung; AngII acts on adrenal, to release aldosterone to retain Na and water and secrete K. Aldosterone reduces K and increases Na
Triggers for release of aldosterone is due to high circulating levels of K in the blood -> acts to produce more K secretion from release of aldosterone
Principal cells in cortical collecting tubule:
Main site of effect of aldosterone -> brings sodium out of urine to absorb it -> K leaves the cell when Na is resorbed as the lumen becomes more negative (Na transporter and K transporter on lumen side, with Na/K ATPase on the other side)
Within the principal cells itself:
Na reabsorption through ENaC (epithelial sodium channels) leads to tubular lumen negative electrical potential, driving potassium secretion
Aldosterone acts on IC mineralocorticoid receptor, which upregulates ENaC, so sodium moves in making lumen negative and K leaves that way
main action is sgk-1 which phosphorylates nedd4-2, adding enac to the wall to increase Na reabsorption
What are the main causes of hyperkalaemia?
- –Renal impairment: reduced renal excretion; reduced renal function, which impedes the whole mechanism, resulting in hyperK
- –Drugs:
- ACE inhibitors block conversion of AngI -> AngII; reduces retention of Na and water, so reduces BP
- ARBs which are used as antihypertensives, which also block effect of aldosterone
- Spirinolactone – competitive inhibitor of aldosterone on mineralocorticoid receptor
- –Low Aldosterone
- •Addison’s disease/adrenocorticoid insufficiency which reduces amount of aldosterone release
- •Type 4 renal tubular acidosis (low renin, low aldosterone); if renin is reduced – chronic NSAID use which reduces aldosterone; t4 renal tubular acidosis, reduces renin/aldosterone
- –Release from cells: rhabdomyolysis (massive tissue injury, so K released) or large tissue death; acidosis causes H+ to enter cells and K+ is released from cells to reduce the acidosis; ALL to maintain electroneutrality
What are the causes of hypokalaemia?
- •GI loss – D (worse loss)+V
- •Renal loss –
- –Hyperaldosteronism, (Excess cortisol), increased aldosterone Conn’s syndrome
- –Increased sodium delivery to distal nephron
- –Osmotic diuresis
- •Redistribution into the cells
- –Insulin, beta-agonists, alkalosis
- •Rare causes: Renal tubular acidosis type 1& 2, hypomagnesaemia
- Low K and low Mg need to replace Mg first to bring potassium up to normal range
How do we know the cause of an acidosis/alkalosis?
HCO3- + H+ = CO2 + H20
Low CO2 = low bicarbonate (which with low pH = acidosis)
Osmolality = charged molecules + uncharged =cations+anions+urea+glucose
Since cations = anions, this can be reduced to:
Osmolality = 2(Na+K) + U + G
Cations (Na/K) = Anions (Cl, Bicarb, others)
“Others” known as “anion gap”.
Anion gap = Na + K – Cl – bicarb
If high – other anion in the gap, like ketones or lactate; if low then normal
Calcium is partly bound to albumin -> in high pH/alkalosis ionised Ca falls as is bound more, which then means they get carpopedal spasm
Metformin in overdose can cause a lactic acidosis – either due to renal failure or deliberate suicide attempt; the Cori cycle = glucose in the muscle -> lactate -> lactate in liver -(inhibited by metformin)> glucose
What are the different types of alkalosis/acidosis?
Kidneys retain bicarb in acute resp acidosis -> reduce pH by increasing CO2; need to ventilate a person, but can’t intubate them as they will have no drive to breathe
Metabolic acidosis – compensate with over breathing
Resp alkalosis – compensation by breathing less
Adrenal micronantomy need to be able to identify this
Adrenal gland – 1 central vein but many arteries -> outer zone makes aldosterone; fasciculata makes cortisol, reticularis makes sex steroids
What are the different studies involved in control of diabetes?
- DCCT: type 1 diabetes, good control improves outcome
- UKPDS: New type 2 diabetes put onto good control
- Low mortality in both groups for 15 years, but then good control improved outcome, LEGACY EFFECT
- ACCORD: take older people who had poor control for a long time, and suddenly massively tighten control (A1c=6%): they already had coronary artery disease, so increased unexpected death
- ADVANCE: (A1c=6.5%, reduced death)
What are the hormones released from the anterior pituitary?
Test for pit failure:
galactorrhoea - PL above 6000 = prolactinoma
amenorrhoea
check for bitemporal hemianopia using a visual field assessment
MRI/CT
- •To ensure that the pituitary gland responds adequately to a metabolic stress (ACTH and GH)
- induce hypoglycaemia with insulin and fasting
- •Ensure no cardiac risk factors, angina and that ECG is normal
- •As you could cause a stroke or a seizure
- •NO history of epilepsy
- •Ensure good IV access
- •When glucose low, first sympathetic activation occur
- •When very low (<1.5mM), neuroglycopenia may occur -> brain doesn’t have enough glucose and becomes confused, aggressive and can go into a coma
- •Put a line in and make sure you can give IV dextrose or give them something to eat
- •Check blood glucose regularly
- •Need to have adequate hypoglycaemia (<2.2 mM)
- •If severe hypoglycaemia occurs (or unconsciousness), rescue patient with 50 ml of 20% dextrose
- •(some books still say 50%, but this is dangerous).
- •This can be difficult to give to an aggressive patient, so line must already be in place
- •If severe hypoglycaemia occurs (or unconsciousness), rescue patient with 50 ml of 20% dextrose
- Guidelines:
- •Fast patient overnight
- •ensure good IV access
- •Weigh patient and calculate dose of insulin required (0.15 units /kg)
- •70 kg woman will need 10.5 units
- •Mix the following in 5 ml syringe:
- •Insulin 0.15 units / kg
- •TRH 200 mcg
- •LHRH 100 mcg
- Give IV patient will have a warm flush and may vomit
- TAKE BLOOD for glucose, coritsol, GH, LH, FSH, TSH and PL every 30min up to 60min plus basal thyroxine
- Check glucose, cortisol and GH up to 120 minutes
- Results:
- •glucose <2.2
- •(if not give more insulin)
- •cortisol reaches 550 nM
- •GH reaches 10 IU/l
- •To ensure the gonadotrophs and thyrotophs are functional
- Administer TRH/LHRH/Stress
What is the zona fasciculata histology?
