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Glossary of Physiology Terms – P
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P wave
Definition:
The component of the electrocardiogram (ECG) that corresponds to the depolarization of atrial myocytes. Atrial depolarization precedes atrial contraction.

Related glossary terms/phrases:
QRS complex
T wave



Parietal cells
Definition:
Cells in the fundus of the stomach that secrete hydrochloric acid and intrinsic factor.

Parietal cells are also known as oxyntic cells.



Permeability
Definition:
Permeability refers to the ease with which molecules cross biological membranes. It may also refer to the ease with which ions or molecules pass through the pore of channel proteins.

Related glossary terms/phrases:
Permeable
Impermeable
Permeant
Impermeant

See also:
Lipid Bilayer Permeability



Permeable
Definition:
Permeable refers to a property of a membrane or channel pore in allowing substances to pass through. For example, the lipid bilayer portion of biological membranes is highly permeable to fat-soluble molecules, but is not permeable to ions and large polar molecules.

See also impermeable.

Related glossary terms/phrases:
Impermeable
Permeability
Permeant
Impermeant

See also:
Lipid Bilayer Permeability



Permeant
Definition:
Permeant refers to the ability of a substance (e.g., ion or molecule) to cross (i.e., permeate or penetrate) a biological membrane or channel pore. For example, it can be said that fat-soluble molecules are membrane permeant.

See also impermeant.

Related glossary terms/phrases:
Impermeant
Permeability
Permeable
Impermeable

See also:
Lipid Bilayer Permeability



Phonocardiogram
Abbreviation:
PCG

Definition:
A recording of the sounds produced by the heart during the cardiac cycle. The main sounds recorded are those associated with turbulent blood flow caused by the closure of heart valves.



Physiology
Definition:
Physiology is the study of how living systems function. The scope of physiological studies ranges from the subcellular level (molecules and organelles) all the way to the level of the whole organism and how organisms adapt to vastly different environmental conditions such as hot, cold, dry, humid, or high altitude.

See also:
What is Physiology?



Pituicyte
Definition:
Glial cell found within the posterior pituitary gland. It resembles astrocytes and functions to provide support to unmyelinated axons whose terminals release oxytocin and vasopressin.



Plasma
Definition:
Plasma is the fluid portion of whole blood, which makes up about 40% to 60% of the total volume of whole blood. Plasma has a light yellow color and is generally obtained by separating the fluid portion from the blood formed elements through sedimentation or centrifugation. Plasma contains mostly water and, in addition, minerals, nutrients, proteins, hormones, and gases (oxygen and carbon dioxide). Unlike serum, in which fibrinogen and other clotting factors have been removed by coagulation, fibrinogen and other clotting factors remain present in plasma.

Plasma is one the main fluid compartments of the human body, making up nearly 10% of the total volume of body fluids. Plasma makes up the intravascular fluid compartment; itself a subcompartment of the extracellular fluid compartment.



Polyphagia
Definition:
Hyperphagia

See:
Hyperphagia



Polyuria
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)



Postprandial
Definition:
Referring to the period after a meal.



Potassium
Abbreviation:
K+

Definition:
The main cation (positively charged ion) of the intracellular fluid.

Potassium (K+) plays an important role in the action potential of neurons and muscle cells.

The extracellular concentration of K+ is about 4 mM. The intracellular concentration of K+ is about 150 mM.



Presbycusis
Definition:
Gradual hearing loss associated with aging.



Primary hypothyroidism
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



Procaine
Definition:
A local topical anesthetic.

Procaine's mechanism of action is to block fast voltage-gated Na+ channels of neurons.

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

Other resources:
Procaine (Wikipedia)



Prolactin
Definition:
Peptide hormone produced by the anterior pituitary gland. Prolactin is best known for its action in stimulating the mammary glands to produce milk (lactation).

Prolactin is known to be involved in many other physiological processes including enlargement of the mammary glands in preparation for milk production, sexual gratification, metabolism, regulation of the immune system, and others.

Other resources:
Prolactin (Wikipedia)



Proptosis
Definition:
Exophthalmos

See:
Exophthalmos



Pubarche
Definition:
Development of axillary and pubic hair during puberty.

Related glossary terms/phrases:
Adrenarche
Menarche
Thelarche



Puberty
Definition:
A period of rapid physical growth and change, brought about by hormonal changes, that culminates in sexual maturity. In most human girls and boys, it starts between the ages of 10 and 14 and it is complete by the age of 16 in most girls, and by the age of 17 in most boys.

Related glossary terms/phrases:
Adrenarche
Menarche
Pubarche
Thelarche



Pulse pressure
Definition:
Pulse pressure is defined as the arithmetic difference between the systolic pressure (the highest blood pressure) and the diastolic pressure (the lowest blood pressure) recorded at any point along the vascular bed. Therefore:

Pulse pressure = Systolic pressure - Diastolic pressure

Pulse pressure values can be reported at any point along the vasculature starting from the left ventricle and aorta all the way to the vena cava and the right atrium. As with systolic and diastolic pressure values, pulse pressure is typically reported in mm Hg (millimeters of mercury). A typical arterial pulse pressure is 40 mm Hg (120 - 80 = 40 mm Hg). This value decreases as one proceeds along the vascular bed from arteries to arterioles, capillaries, venules, and veins. The most significant drop occurs along the arterioles.

See also:
Mean Arterial Pressure Calculator









Posted: Sunday, October 17, 2010
Last updated: Thursday, February 11, 2016