Iran Medical Basic Sciences Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Brachial plexus cords

The three cords are named lateral, posterior, and medial by their position relative to the second part of the axillary artery; they give rise to the terminal branches of the plexus.

Erb palsy

Traction injury to the upper trunk of the brachial plexus (C5–C6) produces a waiter's tip posture with the arm adducted, internally rotated, elbow extended, and wrist flexed.

Neural tube closure timing

The anterior neuropore closes around day 25 and the posterior neuropore around day 27; failure of posterior closure results in spina bifida.

Frank-Starling relationship

Increasing ventricular end-diastolic volume stretches cardiac muscle and increases stroke volume, up to the point where excessive sarcomere stretch reduces contractile efficiency.

Glomerular filtration rate

GFR equals the filtration coefficient times net filtration pressure, calculated as glomerular capillary pressure minus the sum of Bowman's space pressure and plasma oncotic pressure.

Oxygen-hemoglobin dissociation

The curve shifts right, reducing hemoglobin affinity, when carbon dioxide, hydrogen ions, temperature, or 2,3-BPG rise, improving oxygen unloading in active tissues.

Rate-limiting glycolysis enzyme

Phosphofructokinase-1 catalyzes the committed step of glycolysis; it is activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

Competitive enzyme inhibition

A competitive inhibitor binds the active site, raising apparent Km while leaving Vmax unchanged; increasing substrate concentration can overcome the inhibition.

Urea cycle location

Carbamoyl phosphate synthetase I catalyzes the rate-limiting mitochondrial step; the remaining enzymes are cytosolic, and defects cause hyperammonemia with low blood urea nitrogen.

Staphylococcus aureus identification

Gram-positive cocci arranged in clusters that are catalase-positive and coagulase-positive are identified as Staphylococcus aureus, commonly causing skin and systemic infections.

Hepatitis B serologic markers

HBsAg indicates current infection, anti-HBs indicates immunity, HBeAg indicates high infectivity, and anti-HBc IgM indicates acute infection or the serologic window period.

Dimorphic fungi

Dimorphic fungi grow as molds with hyphae at 25 degrees Celsius but as yeasts with budding at 37 degrees Celsius, reflecting temperature-dependent adaptation to host tissue.

MHC class I presentation

MHC class I molecules present endogenous peptides of about eight to ten amino acids to CD8-positive cytotoxic T cells and are expressed on all nucleated cells.

Complement membrane attack complex

The terminal complement components C5b through C9 assemble into a pore in the microbial membrane; all three activation pathways converge on this common terminal sequence.

Type IV hypersensitivity

Delayed hypersensitivity is T-cell mediated, peaks after 48 to 72 hours, and is exemplified by the tuberculin skin test and contact dermatitis; antibodies play no role.

Coagulative necrosis

Ischemic injury in most solid organs produces coagulative necrosis, in which cell architecture is preserved for a time while nuclei undergo pyknosis, karyorrhexis, and karyolysis.

Granuloma formation

Granulomas are collections of activated epithelioid macrophages with multinucleated giant cells and lymphocytes, seen in tuberculosis, sarcoidosis, and Crohn disease.

Virchow triad

Thrombosis is favored by three factors: endothelial injury, abnormal blood flow such as stasis or turbulence, and hypercoagulability of the blood.

Volume of distribution

Volume of distribution equals the administered dose divided by plasma concentration; a large value indicates extensive tissue uptake rather than plasma binding.

Zero-order elimination

In zero-order kinetics a constant amount of drug is eliminated per unit time because metabolic enzymes are saturated; half-life lengthens as concentration rises.

Warfarin mechanism

Warfarin inhibits vitamin K epoxide reductase, reducing synthesis of functional clotting factors II, VII, IX, and X; vitamin K is the antidote for reversal.

Hardy-Weinberg carrier frequency

For an autosomal recessive disease with mutant allele frequency q, the carrier frequency is 2pq, approximately 2q when q is small.

Turner syndrome features

Monosomy 45,X causes short stature, webbed neck, streak ovaries with primary amenorrhea, and coarctation of the aorta; no Barr body is present.

Mitochondrial inheritance

Mitochondrial DNA is inherited only from the mother; heteroplasmy means mutant and normal genomes coexist, producing variable severity in high-energy tissues.

Positive predictive value

Positive predictive value is true positives divided by all positive test results; unlike sensitivity, it changes markedly with disease prevalence in the tested population.

Case-control study

A case-control study compares past exposure between people with a disease and matched controls, estimating odds ratios efficiently for rare diseases but risking recall bias.

Standard error of the mean

The standard error equals the sample standard deviation divided by the square root of sample size; it quantifies variability of sample means around the true mean.

Informed consent elements

Valid informed consent requires patient capacity, adequate disclosure of risks and alternatives, comprehension of the information, and voluntary freedom from coercion.

Confidentiality exceptions

Confidentiality may be overridden only with patient consent or a legal duty, such as reporting certain communicable diseases, suspected child abuse, or complying with a court order.

Marasmus versus kwashiorkor

Marasmus is severe protein-energy wasting without edema, whereas kwashiorkor shows edema, hypoalbuminemia, and fatty liver despite adequate calorie intake.

Herd immunity threshold

The herd immunity threshold approximates one minus one divided by the basic reproduction number, so highly transmissible infections like measles require very high coverage.

Levels of prevention

Primary prevention reduces exposure before disease occurs, secondary prevention detects disease early, and tertiary prevention limits disability through treatment and rehabilitation.