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Glossary of Physiology Terms – C
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Calcium
Abbreviation:
Ca2+

Definition:
Calcium (Ca2+) is a divalent cation. It plays an important role in physiological processes such as muscle contraction and synaptic transmission. Calcium is also an intracellular messenger.

The extracellular concentration of Ca2+ is about 2 mM. The intracellular concentration of Ca2+ is about 70 nM.



Cardiac output
Abbreviation:
CO

Definition:
Cardiac output is defined as the volume of blood pumped every minute by each (left or right) ventricle of the heart. It is generally reported in L/min or mL/min.

Cardiac output (CO) is the product of heart rate (HR) and stroke volume (SV). Thus,

CO = HR × SV

Heart rate is defined as the number of heart contractions per minute. Stroke volume is the volume of blood pumped per ventricular contraction.

For a typical resting adult human being at rest, CO is approximately 5 L/min.

CO = 70 contractions/min × 70 mL/contraction = 4,900 mL/min



Cardiac skeleton
Definition:
Thick connective tissue that separates the atria and the ventricles. It is also referred to as fibrous skeleton of the heart. Despite its name, it is important to note that there is no bone in this tissue.



Cation
Definition:
A positively charged ion.

Related glossary terms/phrases:
Anion



Cerumen
Definition:
Earwax



Cervix
Definition:
The lowest part of the female uterus facing the vaginal canal. It is cylindrical in shape and 2-3 cm long. A cervical canal runs the entire length of the cervix and connects the lumen of the vaginal canal to the lumen of the uterus. The opening of cervical canal into the uterus is called the internal os, and the opening into the vagina is called the external os.



Chalone
Definition:
An endogenous, tissue-specific molecule that functions to inhibit mitosis (cell division) in the very tissue releasing the molecule.



Channel inactivation
Definition:
Refers to a conformational change of a channel protein by which the channel goes from the open state to the inactive state. The inactive state refers to a conformational state in which ions are not allowed to permeate the channel pore. Thus, with respect to ion permeability, the inactive state is similar to the close state of the channel. Ions cannot permeate the channel pore either in the closed or inactive state. However, the channel assumes very distinct and different conformations in the inactive state and closed state.

See also:
Neuronal Action Potential - Important Features of the Neuronal Action Potential



Channel
Definition:
An integral membrane protein which contains a pore through which ions, water, or polar molecules permeate. For any given channel, the pore is usually very selective for the particular ion or molecule. For example, sodium (Na+) channels are very selective for Na+ over other cations.

The channel pore may be constitutively open, or it may be gated to the open state by various stimuli such as chemical ligands, voltage, temperature, or mechanical stimulation of the membrane.



Chemical gradient
Definition:
Refers to the concentration gradient of an ion or molecule. The concentration gradient may exist across a biological membrane, where the concentration is higher on one side of the membrane compared to the other side. Concentration gradient may also exist in a solution without an apparent barrier separating the area of higher concentration from the area of lower concentration. In both cases, the free energy that results from the concentration difference drives the movement of the ion/molcule from the area of higher concentration to the area of lower concentration. In free solution, the ion/molecule simply diffuses down its gradient. Movement across a biological membrane is more complicated and is a function of lipid solubility of the ion/molecule as well as the presence of channels or transport proteins that can allow the ion/molecule to cross the membrane (see Lipid Bilayer Permeability and Summary of Membrane Transport Processes).

Related glossary terms/phrases:
Electrical gradient
Electrochemical gradient



Chloride
Abbreviation:
CI

Definition:
The main anion (negatively charged ion) of the extracellular fluid.

Cloride (Cl) plays an important role in several physiological processes such as the action potential of skeletal muscle cells, CO2 transport in blood (via Cl/bicarbonate exchange across the plasma membrane of red blood cells), and many other processes.

The extracellular concentration of Cl is about 110 mM. The intracellular concentration of Cl is about 10 mM.



Cholinergic
Definition:
Refers to neurons, synapses, or receptors where acetylcholine is used as the neurotransmitter.

For example, cholinergic neurons release acetylcholine as their neurotransmitter.

In cholinergic synapses, acetylcholine is released from the presynaptic neuron, and it acts on acetylcholine receptors in the plasma membrane of the postsynaptic cell.

Cholinergic receptors are those that respond to acetylcholine as the physiological ligand. The two major types are nicotinic and muscarinic cholinergic receptors (may also be referred to as nicotinic and muscarinic acetylcholine receptors).

Cholinergic drugs are compounds that mimic the action of acetylcholine by binding to and activating cholinergic receptors.



Chyme
Definition:
The semi-solid, partially-digested contents of the stomach that exit via the pyloric valve to enter the duodenum (initial region) of the small intestine.



Cochlea
Definition:
Coiled, fluid-filled cavity within the bony labyrinth of the inner ear, where the hearing (auditory) structures of the inner ear are located. The cochlea contains the Organ of Corti.

Related glossary terms/phrases:
Organ of Corti



Colloid
Definition:
Specifically, thyroid colloid. Refers to the protein-rich fluid within the lumen of thyroid follicles. The major protein component of the thyroid colloid is thyroglobulin.



Colon
Definition:
The colon is part of the large intestine within the digestive tract that is located between the cecum and the rectum. The colon is subdivided into the ascending colon, transverse colon, descending colon, and sigmoid colon.



Corticotroph
Definition:
Endocrine cell of the anterior pituitary gland responsible for synthesizing and releasing adrenocorticotropic hormone (ACTH).



Cotransport
Definition:
A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In cotransport, the direction of transport is the same for both the driving ion and driven ion/molecule (into the cell or out of the cell).

An example is the Na+/glucose cotransporter (SGLT), which couples the movement of Na+ into the cell down its electrochemical gradient to the movement of glucose into the cell against its concentration gradient.

Cotransport is also commonly referred to as symport.

Transport proteins that are involved in this type of transport are referred to as cotransporters or symporters.

See:
Symport

Related glossary terms/phrases:
Secondary active transport
Exchange

See also:
Lecture notes on Secondary Active Transport



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



Curare
Definition:
A potent blocker of nicotinic cholinergic receptors (nicotinic acetylcholine receptor, nAChR) found at the neuromuscular junction. At small doses, curare can lead to muscle weakness. At high doses, curare can lead to paralysis of skeletal muscles, which would also result in asphyxiation (and ultimately death) due to paralysis of the diaphragm. Curare was commonly the active agent of poison arrow.

Other resources:
See Wikipedia



Current clamp
Definition:
An electrophysiological technique in which the current passing across the cell membrane is controlled experimentally, and the membrane voltage is measured.

Related glossary terms/phrases:
Voltage clamp

See also:
Neuronal Action Potential - Pharmacological Inhibition of Na+ and K+ Channels



Current
Definition:
The flow of charge. In electrical wires and electronic circuits, current is carried by electrons. In physiological solutions, current is carried by ions in solutions.

Related glossary terms/phrases:
Voltage









Posted: Wednesday, February 13, 2013
Last updated: Saturday, November 21, 2015