Biomed Flashcards
Accuracy vs precision
Accuracy is the measure of a how close the mean of a set of results is to the expected value. Due to other factors, like precision, the standard deviation may be high.
Precision is a measure of the reproducibility of an assay. When an assay is precise, the standard deviation is low. However, the repeated results may not be close to the expected result.
Abnormal white blood cell counts
White blood cells may be high in cases of acute or chronic infection, autoimmune disease, tissue necrosis, and B and T cell leukymias.
White blood cells may be low in cases of malaria, ionising radiation, and AIDS.
Mean, standard deviation, and coefficient of variation
The mean is the average of a set of values.
The standard deviation is a measure of the spread of data around the mean.
The coefficient of variation is a measure of relative variability and is a ratio between the standard deviation and the mean.
What is the main cause of hyperthyroidism?
The main cause of hyperthyroidism is Graves disease. This is where the body produces antibodies that bind to thyroid stimulating hormone receptor, activating them, and causing the synthesis and secretion of T3 and T4 thyroid hormones. There is a negative feedback control of these hormones on the pituatory gland preventing the production of TSH. In normal cases, this would stop the production of T3 and T4, however the antibodies continue the synthesis leading to excess hormone production.
What are the main symptoms and treatment method of hyperthyroidism?
Symptoms include weight loss, angina, palpitations, tremors, and anemia.
Graves disease is treated by radio therapy treatment to destroy part of the thyroid in order to prevent excess thyroid hormone production. The progress is monitored by testing TSH levels in the blood plasma.
Hashimoto’s antibody and tissue typing tests
Tissue typing can be useful in the diagnosis of hashimoto’s disease due to it being linked with HLA allele DR5. Hashimoto’s is an autoimmune disease which causes immunodeficiency and is the main cause of hypothyroidism. Antibodies are produced against the thyroid tissue called thyroglobulins. The test can detect the anti-thyroid peroxidase antibodies in serum. The antibodies can be detected using an indirect method where a microscope slide is coated in antigen to the measured antibody. The serum is added and the slide is washed to removed any unwound binding. A fluorescently labelled antibody is then added.
How does the thyroid work?
The pituitary gland produces thyroid stimulating hormone (TSH) that travels to the thyroid gland, binds to receptors, activating them. There is synthesis and secretion of T3 and T4 thyroid hormone. When enough of the hormone is produced, there is negative feedback inhibition where the presence of enough thyroid hormone prevents further synthesis of TSH, therefore preventing further thyroid hormone production. In hypothyroidism, there is a decrease in thyroid hormone production leading to continual TSH production by the pituitary gland in an attempt to stimulate the gland. In hyperthyroidism, there is an excess in thyroid hormone production and a reduced production of TSH from negative feedback control.
Total vs differential white blood cell counts
Total white blood count is a measure of the total of all the white blood cells present in the sample. The differential count compares the relative proportions of each of the different white blood cells in a sample in comparison to the total count.
Stages of a tissue biopsy
- Fixation – fixation is a necessary in order to minimise the decay of tissues by enzymes or bacteria, and preserve the morphological and molecular structure of the tissues. Common fixatives are 10% buffered formalin solution (used mainly in light microscopy) and 2-6% buffered glutaraldehyde solution.
- Embedding – the sample must be dehydrated in 70-100% alcohol and then the alcohol is switched for a solvent solution. Then the sample is embedded in paraffin wax or hard epoxy plastic resin in the cases of tissues like bone.
- Slicing – the samples are sliced with a microtome.
- Staining – the samples often need to be stained in order for the tissues to be seen. Common stains are haematoxylin which stains nuclei a blue purple, and eosin which stains cytoplasm and extracellular connective tissue pink.
Different blood tests
Venous blood – iron levels, enzyme levels, hormone levels, total blood count.
Arterial blood – blood gases like oxygen and carbon dioxide.
Capillary blood – blood glucose levels, Guthrie test
How do x-rays work?
X-rays are penetrating short wavelength electromagnetic waves that pass through tissues. Dense tissues, like bone, absorb a lot of the photons and so appear white on the x-ray film. Less dense tissues like fat, water, or skin, absorb less of the photons and appear grey. Areas where no photons are absorbed appear black.
Contrast x-rays
There are two common types of contrast x-ray. Barium meals are used to visualise the gastrointestinal tract as the barium absorbs the photons of the x-ray. Angiograms are another method where radio-opaque dye like iodine is inserted into a catheter on a peripheral artery to assess whether or not there is any damage to blood vessels.
How do ultrasounds work?
Ultrasounds are short wavelength high frequency sound waves released from a transducer over the body. Dense tissue like bone will reflect the sound waves, the reflections (echoes) being detected and translated onto electrical impulses recorded on an oscilloscope. The sound waves pass through less dense tissues like fat and liquids. They have an advantage over x-rays as they are faster and safer due to a lack of radiation.
Thyroid function test examples
TSH levels – low TSH levels indicates hyperthyroidism as there is an overproduction of thyroid hormone preventing the pituitary gland from producing TSH. High TSH levels indicate hypothyroidism as the body attempts to stimulate the thyroid gland into producing more hormone.
T3 and T4 levels – high levels indicate hyperthyroidism as they are in excess production by the thyroid gland. Low levels indicate a lacking production of TSH in hypothyroidism.
General sampling rules
- The sample size must be adequate for analysis.
- Avoid contamination by using sterile equipment and aseptic technique.
- Take the sample before giving any drugs/treatment.
- The sample must be representative of the entire infectious process.
- Specimen should be examined properly.
