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Glossary of Physiology Terms
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Definition:
Absence of menstruation in sexually mature female individuals.



Definition:
An enzyme found in the synaptic cleft at cholinergic synapses. It degrades acetylcholine to choline and acetate and, thus, terminates the action of acetylcholine at the synapse. Neither choline nor acetate can bind to acetylcholine receptors (nicotinic or muscarinic).



Abbreviation:
BMI

Definition:
The body mass index is measured by dividing body weight (in kilograms) by body height (in meters) squared (kg / m2). It is highly correlated with body composition, and higher BMI values are correlated with higher body fat content. The BMI value is used to classify one's weight in several categories including underweight, normal, overweight, and obese. The range of BMI values considered to be normal is 18.5 to 24.9. Higher BMI values are associated with an increased risk for diseases such as diabetes mellitus type II, hypertension, and cardiovascular disease.

See also:
Body Mass Index Calculator

Other resources:
Body mass index (Wikipedia)



Definition:
Mental retardation, dwarfism, and abnormal bone formation caused by thyroid hormone deficiency during fetal development.



Definition:
Normal thyroid gland function.

Related glossary terms/phrases:
Hypothyroidism
Hyperthyroidism



Definition:
Excretion of glucose in urine. This is indicative of an abnormal condition such as hyperglycemia caused by diabetes mellitus.



Definition:
Goiter is an enlargement of the thyroid gland caused most commonly by iodine deficiency in the diet. Iodine deficiency leads to low levels of thyroid hormone production, and a reduction in thyroid hormone negative feedback on the hypothalamus and the anterior pituitary leads to a compensatory rise in the thyroid stimulating hormone (TSH). Enlargement of the thyroid gland is, therefore, caused by abnormally high circulating levels of TSH, which has a strong trophic effect on the thyroid gland.



Definition:
Abnormal, unwanted, and excessive hair growth on the face and body. Particularly used to refer to women with such a condition.

Related glossary terms/phrases:
Hirsute



Definition:
A total plasma calcium level that is greater than the normal range of 2.2 - 2.6 mM (9 - 10.5 mg/dL). The free calcium concentration in the plasma is approximately 1.5 mM (6 mg/dL), and the remaining amount is bound to plasma proteins.

Related glossary terms/phrases:
Hypocalcemia



Definition:
Condition in which the plasma glucose concentration is abnormally high. In general, a fasting plasma glucose concentration higher than 110 mg/dL, or a postprandial plasma glucose concentration higher than 180 mg/dL is considered abnormally high.

Normal, fasting glucose concentrations range from 70 to 110 mg/dL.

Related glossary terms/phrases:
Hyperglycemic
Hypoglycemia
Hypoglycemic



Definition:
Hyperthyroidism refers to a pathophysiological condition in which the thyroid gland produces and releases abnormally high levels of the thyroid hormones (T3 and T4).

The symptoms of hyperthyroidism may include high metabolic rate, weight loss, nervousness, excess heat production, tachycardia, and tremor.

Two main forms of hyperthyroidism exist: (1) Primary hyperthyroidism, and (2) Secondary hyperthyroidism.

In primary hyperthyroidism, the thyroid gland produces high levels of the thyroid hormones, either as a result of a secretory tumor of the thyroid gland, or under the control of thyroid stimulating immunoglobulins (such as in Graves' disease).

Secondary hypothyroidism is caused by high levels of thyroid stimulating hormone (TSH) produced by the anterior pituitary gland. TSH then stimulates the thyroid gland to produce excessive amounts of the thyroid hormones.

Related glossary terms/phrases:
Hypothyroidism
Euthyroidism



Definition:
A total plasma calcium level that is less than the normal range of 2.2 - 2.6 mM (9 - 10.5 mg/dL). The free calcium concentration in the plasma is approximately 1.5 mM (6 mg/dL), and the remaining amount is bound to plasma proteins.

Related glossary terms/phrases:
Hypercalcemia



Definition:
Condition in which the plasma glucose concentration is abnormally low. In general, a plasma glucose concentration lower than 70 mg/dL is considered abnormally low.

Normal, fasting glucose concentrations range from 70 to 110 mg/dL.

Related glossary terms/phrases:
Hypoglycemic
Hyperglycemia
Hyperglycemic



Definition:
Hypothyroidism refers to a pathophysiological condition in which the thyroid gland does not produce sufficient amounts of the thyroid hormones (underactive thyroid), leading to abnormally low levels of the thyroid hormones (T3 and T4).

The symptoms of hypothyroidism may include reduced metabolic rate, chronic fatigue, weight gain, myxedema, and depression.

Three main forms of hypothyroidism exist: (1) Primary hypothyroidism, (2) Secondary hypothyroidism, and (3) Tertiary hypothyroidism.

In primary hypothyroidism, the thyroid gland itself is incapable of producing normal levels of the thyroid hormones.

Secondary hypothyroidism is caused by low levels of thyroid stimulating hormone (TSH). TSH, produced by the anterior pituitary gland, is required to stimulate the thyroid gland to produce the thyroid hormones.

Tertiary hypothyroidism is caused by low levels of thyrotropin releasing hormone (TRH). TRH, produced by the hypothalamus, is required to stimulate the anterior pituitary gland to produce TSH which, in turn, is required to stimulate the thyroid gland to produce the thyroid hormones.

Related glossary terms/phrases:
Primary hypothyroidism
Secondary hypothyroidism
Tertiary hypothyroidism

Hyperthyroidism
Euthyroidism



Definition:
The tapping sounds heard through a stethoscope placed over a partially compressed peripheral artery.

For the purpose of non-invasive blood pressure measurements, the stethoscope is usually placed on the skin overlying the brachial artery just distal to an inflated pressure cuff wrapped around the upper arm. As the pressure cuff is gradually deflated, the Korotkoff sounds result from the pulsations of the blood through the partially constricted brachial artery. With each ventricular systole, blood is forced to flow through the partially constricted brachial artery, and the turbulence in blood flow leads to the generation of the Korotkoff sounds. When the pressure cuff is fully deflated, flow through the artery resumes its normal laminar flow and, at that time, the Korotkoff sounds disappear.



Definition:
Lidocaine is a local anesthetic and an antiarrhythmic drug. It is a commonly used local anesthetic for minor surgery and in dental procedures. Lidocaine is also used topically to relieve itching, burning, and pain from skin inflammations.

Lidocaine's mechanism of action is to block fast voltage-gated Na+ channels of neurons and cardiac myocytes.

Other names used for lidocaine are xylocaine and lignocaine.

See also:
Pharmacological Inhibition of Na+ and K+ Channels

Other resources:
Lidocaine (Wikipedia)



Definition:
Neurotoxins are chemical molecules that have an adverse effect on neuron function and, thus, disrupt the normal function of the nervous system. Neurotoxins could be small molecules or peptides and can be derived from a variety of invertebrate and vertebrate animals, as well as plant species.

The following is a short list of some examples of neurotoxins:

α-Bungarotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

Chlorotoxin: A peptide neurotoxin that inhibits chloride channels.

α-Conotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

δ-Conotoxin: A peptide neurotoxin that inhibits voltage-gated sodium channels.

w-Conotoxin: A peptide neurotoxin that inhibits N-type voltage-gated calcium channels.

Picrotoxin: Inhibits GABAA receptor chloride channels.

Tetrodotoxin: Inhibitor of neuronal voltage-gated sodium channels.



Definition:
Chemical messenger molecules released by neurons into the synaptic cleft.

Neurotransmitter molecules may be small molecules such as glutamate, γ-aminobutyric acid (GABA), acetylcholine, dopamine, norepinephrine, serotonin (5-hydroxytryptamine), and glycine. These are referred to as classic neurotransmitters. A neuron generally releases only one type of small classic neurotransmitter.

Neurotransmitters may also be peptide molecules, such as substance P, opioids, and somatostatin. These are referred to as neuropeptides.

Gas molecules, such as nitric oxide (NO), may also act as neurotransmitters.



Definition:
Refers to an abnormally low volume of urine production. Generally, a urine production rate of less than 400 mL/day is referred to as oliguria.

Related glossary terms/phrases:
Polyuria

Other resources:
Oliguria (Wikipedia)



Definition:
Body weight that exceeds the normal or standard weight range. The standard range is generally determined based on height and frame size.

Related glossary terms/phrases:
Body Mass Index

See also:
Body Mass Index Calculator



Definition:
Refers to an abnormally large volume of urine production. Generally, a urine production rate of higher than 2.5 L/day is referred to as polyuria.

Related glossary terms/phrases:
Oliguria
Hypouresis

Other resources:
Polyuria (Wikipedia)



Definition:
Primary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T3 and T4) production, where the defect is at the level of the thyroid gland itself.

In primary hypothyroidism, the circulating levels of the thyroid hormones are low, however, the levels of the thyroid stimulating hormone (TSH) are high due a lack of thyroid hormone negative feedback on the anterior pituitary.

Common causes of primary hypothyroidism include iodine deficiency (which leads to goiter), and Hashimoto's disease, in which autoimmune antibodies destroy the ability of the thyroid gland to produce the thyroid hormones.

Related glossary terms/phrases:
Hypothyroidism
Secondary hypothyroidism
Tertiary hypothyroidism



Definition:
The relative refractory period refers to a period during the action potential. This is the time during which a stronger than normal stimulus is needed in order to elicit an action potential. The relative refractory period immediately follows the absolute refractory period.

Related glossary terms/phrases:
Absolute refractory period

See also:
Neuronal Action Potential - Refractory Periods



Definition:
Refers to the return of the membrane potential toward the normal resting value after a membrane depolarization.

Related glossary terms/phrases:
Depolarization
Hyperpolarization

See also:
Resting Membrane Potential - Introduction
Figure showing depolarization, repolarization, and hyperpolarization



Definition:
Secondary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T3 and T4) production, where the defect is at the level of the anterior pituitary gland.

In secondary hypothyroidism, the anterior pituitary gland is unable to produce sufficient levels of the thyroid stimulating hormone (TSH) which, in turn, leads to insufficient stimulation of the thyroid gland to produce the thyroid hormones (T3 and T4).

Thus, in secondary hypothyroidism, the circulating levels of both TSH and the thyroid hormones (T3, and T4) are abnormally low

Related glossary terms/phrases:
Hypothyroidism
Primary hypothyroidism
Tertiary hypothyroidism



Definition:
Synaptic pathology. Any pathophysiological condition that leads to abnormal function of synapses within the nervous system. The pathology may be due to pre-synaptic and/or post-synaptic mechanisms, or may involve glial cells surrounding synapses.



Definition:
Tertiary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T3 and T4) production, where the defect is at the level of the hypothalamus.

In tertiary hypothyroidism, the hypothalamus is unable to produce sufficient levels of thyrotropin release hormone (TRH). Low TRH levels lead to low production of the thyroid stimulating hormone (TSH) by the anterior pituitary gland which, in turn, leads to insufficient stimulation of the thyroid gland to produce the thyroid hormones (T3 and T4).

Thus, in tertiary hypothyroidism, the circulating levels of TRH, TSH, T3, and T4 are all abnormally low.

Related glossary terms/phrases:
Hypothyroidism
Primary hypothyroidism
Secondary hypothyroidism



Definition:
Dry mouth. Dryness in the mouth resulting from abnormally low levels of saliva production.









Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015