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Glossary of Physiology Terms – T
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T wave
Definition:
The component of the electrocardiogram (ECG) that corresponds to the repolarization of the ventricles. Therefore, the T wave also corresponds to relaxation of the ventricles.

Related glossary terms/phrases:
P wave
QRS complex



Tachyphylaxis
Definition:
Tachyphylaxis describes a condition where a person (or animal subject) develops rapid tolerance to a drug following a single or repeated administration of the drug. Therefore, higher doses of the drug may be needed to achieve the same response.



Tastant
Definition:
Tastants are taste-provoking chemical molecules that are dissolved in ingested liquids or saliva.

Tastants stimulate the sense of taste. It can also be said that tastants elicit gustatory excitation.

A tastant is the appropriate ligand for receptor proteins located on the plasma membrane of taste receptor cells.



Taste buds
Definition:
In humans, taste buds are the sensory receptor areas primarily on the tongue, but also in the throat, where taste receptor cells are located. In humans, there are approximately 10,000 taste buds in the oral cavity (tongue) and throat. A typical human taste bud contains about 50 taste receptor cells. Stimulation of taste receptor cells by tastants elicits the sense of taste (also referred to as gustation).



Tertiary hypothyroidism
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



Tetraethyl ammonium
Abbreviation:
TEA

Definition:
An inhibitor of voltage-gated potassium (K+) channels.

TEA is a quaternary ammonium cation (positively charged ion). It is also commonly used as a cation replacement for sodium (Na+) in physiological buffers used in ion replacement experiments.

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



Tetrodotoxin
Abbreviation:
TTX

Definition:
Inhibitor of fast voltage-gated sodium (Na+) channels of neurons and muscle cells. It is an extremely potent and toxic neurotoxin.

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

Other resources:
Tetrodotoxin (Wikipedia)



Thelarche
Definition:
Development of breasts as an early event during female puberty.

Related glossary terms/phrases:
Adrenarche
Menarche
Pubarche



Thirst
Definition:
A basic and intrinsic craving for drinking fluids.



Threshold
Definition:
The membrane voltage that must be reached in an excitable cell (e.g., neuron or muscle cell) during a depolarization in order to generate an action potential. At the threshold voltage, voltage-gated channels become activated. Threshold is approximately −50 to −40 mV in most excitable cells.

Related glossary terms/phrases:
Sub-threshold
Supra-threshold

See also:
Neuronal Action Potential - Introduction



Thyrocyte
Definition:
Thyroid follicular cell

See:
Thyroid follicular cell



Thyroglobulin
Abbreviation:
Tg

Definition:
The major glycoprotein found within the colloid of thyroid follicles. The thyroid hormones (T3 and T4) are synthesized on the backbone of thyroglobulin.



Thyroid follicular cell
Definition:
Thyroid follicular cells are epithelial cells that form the lining of thyroid follicles. Each thyroid follicle is surrounded by a single layer of follicular cells. Follicular cells play the key role in thyroid hormone synthesis and release.

Thyroid follicular cells are also referred to as thyrocytes.



Thyrotroph
Definition:
Endocrine cell of the anterior pituitary gland responsible for synthesizing and releasing thyroid stimulating hormone (TSH).



Tinnitus
Definition:
The condition of hearing a sound in the absence of an external sound stimulus. The sound may be ringing, buzzing, whistling, or hissing. The sound may be soft, loud, low-pitched, or high-pitched. It may be heard in one ear or both ears (simultaneously or independent of one another).

Other resources:
Tinnitus (Wikipedia)



Tricuspid valve
Definition:
The one-way valve between the right atrium and right ventricle of the heart. It is also known as the right atrioventricular valve.

The direction of blood flow through the tricuspid valve is from the right atrium to the right ventricle.

Related glossary terms/phrases:
Tricuspid valve









Posted: Wednesday, March 6, 2013
Last updated: Thursday, February 11, 2016