Clinical Conditions Flashcards
What is the nucleotide change, and therefore the amino acid change in sickle cell anaemia? What does this lead to?
A - T
Glu to Val
Leads to hydrophobic pockets when Hb is in the T state (in tissue, when it has given up oxygen). These clump together so the red blood cell is sickle shaped.
What is a sickle cell crisis? What are the precipitating factors?
Blocked capillaries by rbcs clumping together. Ischaemia.
Precipitated by things which promote T state, therefore shift the curve right to release more oxygen at tissue. Eg smoking, infection (increase O2 demand plus increased viscosity) 2,3 bpg, cold, strenuous exercise.
What is sickle cell trait? What is it protective against?
Heterozygous genotype - sickle cell is autosomal recessive
No symptoms but protective against malaria
What gene is implicated in cystic fibrosis? What is the effect of this? Which organs are affected?
Cftr gene (autosomal recessive) Usually the transporter pumps chloride ions back into blood using ATP and Na and water follow In cystic fibrosis this is faulty and mucus becomes thick and salty. Affects sweat glands, lungs, gut, pancreas
What is thalassaemia? What is the difference between A and B?
Unstable haemoglobin due to loss of one type of globin.
A misses alpha
B misses beta
B is only picked up after birth because HbF doesn’t need beta anyway ( 2 alpha, 2 gamma)
What is missing in haemophilia a and b? What is its inheritance pattern?
A - clotting Factor 8
B - clotting factor 9
X linked recessive
What causes scurvy?
Vitamin c required for hydroxyl action of proline.
Deficiency means less hydroxyproline, less cross links in collagen, weakened
What is Down’s syndrome? When can it be screened for?
Trisomy 21
Characteristic facial features, impaired intelligence, heart defects
Screened at 12 week scan unlike most genetic diseases
What is trisomy? What can cause it?
Extra chromosome in one pair.
- Meiosis nondysjunction
- Anaphase lag
Name some important trisomy syndromes other than Down’s.
Edwards - trisomy 18
Patau’s - trisomy 13
Low survival past neonate
What is turners syndrome?
Monosomy X
Short, webbed neck, LD
Ovarian failure - low oestrogen, primary amenorrhoea, infertility
What is klinefelter’s syndrome?
XXY
Reduced testosterone, hypogonadism, gynocomastia, infertility
Increased risk of breast cancer.
What is placenta praevia?
Implantation of the placenta in the lower segment of the uterine wall, blocking the cervix. C section required.
What are the similarities and differences between marfan and Ehlers Danlos syndromes?
Both genetic disorders that cause weak connective tissue. Leads to unstable joints, fragile stretchy skin, weak blood vessel wall - risk of aortic rupture.
But marfan - misfolded fibrillin
Ehlers Danlos - type 3 collagen deficiency (lack of lysyl oxidase which cleaves tropocollagen to collagen)
What is vitiligo?
Autoimmune destruction of melanocytes leading to depigmentation.
What is psoriasis?
Autoimmune overproduction of skin epithelia, leading to excess stratum corneum.
What is the pathogenesis of osteogenesis imperfecta?
Autosomal dominant deficiency of type 1 collagen
Why does vitamin D deficiency lead to rickets?
Less absorption of calcium by the small bowel.
What is the adult version of rickets?
Osteomalacia. Can be vitamin d deficiency or impaired renal function, leading to less reabsorption of calcium
What are the two types of osteoporosis? What are they caused by?
- Menopausal. Due to decrease in oestrogen which downregulates osteoclasts.
- Age related. Due to loss of osteoblast function
Both due to clast>blast function
What is a preclinical decrease in bone density called?
Osteopenia
What is the result of too much growth hormone in adults and children?
Adults - acromegaly. Growth plates are fused so increase in bone width only, large tongue, large hands and feet, prominent facial features.
Children - gigantism. Excessive growth at epiphyseal growth plates so increased height.
What is achondroplasia?
Short limb dwarfism
Caused by mutation to the fibroblast growth factor receptor. Decreased endochondral ossification
What causes myasthenia gravis?
Autoimmune destruction of the nicotinic receptors at the end plate of the neuromuscular junction.
Ach gets broken down and removed from synapse before the intended signal has been transmitted.
Sudden drop in Ach leads to sudden loss of contraction.
What are the key symptoms of myasthenia gravis?
Fatigue, sudden falling, weakness of small muscles: droopy eyelids, difficulties swallowing, chewing and sometimes breathing.
What are the key signs of muscular dystrophy?
Gower’s sign - using hands on knees to push self to standing
Bilateral Winged scapulae
What causes muscular dystrophy? What is the prognosis?
X linked recessive
Absence (Duchenne) or malformed (beckers) dystrophin
Means that muscles tear on contraction.
Degenerative until the chest muscles are destroyed.
How does botulinum toxin causes paralysis?
Cleaves the snare protein, preventing release of Ach.
No Ach, no contraction
What is malignant hyperthermia? How would you treat it?
Autosomal dominant mutation to ryanodine receptor causes reaction to general anaesthesia.
Huge increase in intracellular calcium leads to muscle rigidity, hyperthermia, tachycardia.
Treat with dantrolene
What is diabetes insipidus?
Loss of function in the ADH receptor. Kidneys stop retaining water.
Polyuria and polydipsia
Give five causes of hypotonia.
- Primary degeneration - muscular dystrophy
- Nerve lesion
- Neuropathy
- Lack of use
- Ageing
What causes tetany?
Infection by clostridium tetanii
Toxin prevents release of GABA which normally relaxes skeletal muscle
Leads to muscle spasms and prolonged contraction
What causes whiplash injury?
Sudden jerk of head (damage muscle and ligaments) but also can dislocate C5 and C6. Can damage the spinal cord.
What is the name given to a loss of muscle mass due to aging?
Sarcopenia
Why is hyperkalaemia so dangerous?
Permanent depolarisation of cardiac myocytes, inactivating Na channels. Accommodation occurs and you get bradycardia and eventual heart failure.
Why is hypokalaemia so dangerous?
Permanent hyperpolarisation of the cardiac myocytes.
This excites the funny current HCN channels, leading to tachycardia, ventricular fibrillation and cardiac arrest.