NBME CBSE key terms

The proportion of people who truly have a condition and are correctly identified by a test as positive. A highly sensitive test produces few false negatives, so it is useful for ruling a disease out.

The proportion of people who truly do not have a condition and are correctly identified by a test as negative. A highly specific test produces few false positives, so a positive result tends to confirm the diagnosis.

The probability that a person with a positive test result actually has the disease. Unlike sensitivity, it changes with how common the disease is in the population being tested.

The number of patients who must receive a treatment for one additional good outcome to occur. It equals one divided by the absolute risk reduction, so smaller values indicate greater benefit.

A situation in which a third factor is linked to both the exposure and the outcome, creating a false or exaggerated association. Researchers limit it through randomization, restriction, matching, or statistical adjustment.

The apparent lengthening of survival that occurs only because a disease is detected earlier by screening, even though the date of death is unchanged. It can make screening look effective when it is not.

A learning process in which a behavior becomes more or less frequent depending on the consequences that follow it. Rewards strengthen the behavior, while punishment or absence of reward weakens it.

An acute, fluctuating disturbance of attention and awareness, often with disorientation and perceptual changes, caused by an underlying medical or toxic condition. It develops over hours to days and is distinct from dementia.

A model describing readiness to alter a health behavior in five steps: precontemplation, contemplation, preparation, action, and maintenance. Counseling is matched to the current stage, and relapse is expected rather than treated as failure.

The percentage or absolute number of young red cells recently released from the marrow. A high count suggests the marrow is responding to blood loss or hemolysis; a low count suggests a production problem.

Anemia with enlarged red cell precursors caused by impaired DNA synthesis, most often from vitamin B12 or folate deficiency. The blood smear shows large oval red cells and hypersegmented neutrophils.

A reduction in all three major blood cell lines: red cells, white cells, and platelets. It usually reflects bone marrow failure, infiltration, or destruction and causes anemia, infection risk, and bleeding.

The degree of stretch on ventricular muscle fibers at the end of filling, roughly proportional to ventricular volume and venous return. Within limits, increasing preload raises stroke volume.

The resistance the ventricle must overcome to eject blood, determined largely by arterial pressure and vascular resistance. Higher afterload lowers stroke volume and raises myocardial oxygen demand.

The percentage of blood present in the ventricle at end-diastole that is pumped out with each contraction. It is a key measure of systolic function, with a normal value of roughly 55 to 70 percent.

The principle that greater filling of the heart stretches the muscle and increases the force of the next contraction, so stroke volume rises as venous return rises, up to a point of overstretch.

A control loop in which rising levels of a hormone suppress the signals that stimulate its release. It keeps hormone concentrations stable and explains why a failing gland raises its stimulating pituitary hormone.

A state in which tissues respond poorly to insulin, so more insulin is needed to move glucose into cells. It drives type 2 diabetes, and the pancreas compensates until beta-cell failure develops.

Glycated hemoglobin; it reflects average blood glucose over the lifespan of red cells, about two to three months. It is used to diagnose and monitor diabetes and does not require fasting.

Fatty, bulky, pale, foul-smelling stool caused by fat malabsorption, as in pancreatic enzyme deficiency, bile salt loss, or small bowel disease. Deficiency of fat-soluble vitamins may accompany it.

The recycling of bile acids from the intestine back to the liver. They are reabsorbed mainly in the terminal ileum, carried by the portal vein, and secreted again, conserving the body's bile acid pool.

An apparent volume relating the total amount of drug in the body to its plasma concentration. Large values indicate extensive uptake into tissues; small values indicate the drug remains mostly in blood.

The time required for the plasma concentration of a substance to fall by half. It guides dosing frequency and predicts how long a drug takes to reach steady state, usually four to five half-lives.

The substrate concentration at which an enzyme works at half its maximum rate. It reflects how tightly the enzyme binds substrate, so a low Km indicates high affinity.

A molecule that binds reversibly to the same receptor site as the natural agonist and blocks it. It shifts the dose-response curve rightward, and its effect can be overcome by adding more agonist.

A gene whose normal product restrains cell growth or triggers repair or death of damaged cells. Cancer usually requires loss of function of both copies, as with retinoblastoma or p53.

The continuous, coupled process in which osteoclasts resorb bone and osteoblasts lay down new matrix. It repairs daily damage and adjusts bone strength, and it becomes unbalanced in osteoporosis.

Separation of the upper epidermis when lateral pressure is applied to the skin, producing a blister or erosion. It signals loss of cohesion between skin layers and occurs in pemphigus vulgaris and toxic epidermal necrolysis.

The area of skin supplied by the sensory fibers of a single spinal nerve root. Maps of dermatomes help localize a spinal cord or nerve root lesion from the pattern of sensory loss.

Findings that indicate damage above the anterior horn cell, including spasticity, hyperreflexia, a Babinski response, and loss of fine dexterity, with weakness but little muscle wasting.

Nonfluent speech with effortful, telegraphic output and relatively preserved comprehension, caused by a lesion in the dominant inferior frontal gyrus. Repetition is impaired, and patients are often aware of the deficit.

A selective interface formed by tight junctions between capillary endothelial cells, supported by astrocytes and pericytes, that limits passage of many substances from blood into brain tissue.

The volume of plasma filtered by the kidneys per unit of time. It is the best overall measure of kidney function and falls as functioning nephron mass is lost.

The percentage of filtered sodium that appears in the urine, calculated from urine and plasma sodium and creatinine values. Low values suggest the kidney is appropriately retaining salt, as in prerenal azotemia.

A sharp midcycle rise in luteinizing hormone triggered by high estrogen output from a mature follicle. It induces ovulation and transforms the follicle into the corpus luteum.

A hormone produced by the syncytiotrophoblast soon after implantation. It maintains the corpus luteum and its progesterone output early in pregnancy and is the molecule detected by standard pregnancy tests.

A phospholipid mixture secreted by type II pneumocytes that lowers alveolar surface tension. It prevents alveolar collapse at low lung volumes, and its deficiency causes neonatal respiratory distress syndrome.

A condition in which airflow and blood flow are unequal in regions of the lung, so some blood passes unventilated alveoli while some ventilated alveoli are underperfused. It is the most common cause of hypoxemia.