Glossary Terms



acini- Small sacs terminating the ducts of some exocrine glands and lined with secretory cells.


active transport - energy-requiring translocation of a substance across a membrane, usually against its concentration or electrochemical gradient


air-sac system – a system of air sacs in birds connected to the lungs and extending as pockets of the airways penetrating in adjacent bones and between organs to aid in ventilation and reduction of the density of the bird


alveolar pressure – measured pressure located in the alveoli sacs in the lungs of vertebrates


alveoli – terminal air sacs of the mammalian respiratory system.


aortic body- A nodule on the aortic arch containing chemoreceptors that sense chemical composition of the blood


band III protein – a special anion carrier protein which binds to Cl- and HCO3- ions and transfers them in opposite directions through the erythrocyte membrane


blood plasma – the extracellular component of blood.


bronchus- Either of the two divisions of the trachea which lead respectively into the right and left lung.


buccal cavity – a mouth cavity


buffers – chemical systems that stabilize the concentration of a substance; acid-base systems serve as pH buffers, preventing large changes in hydrogen ion concentration


carotid body- A nodule on the occipital artery just above the carotid sinus, containing chemoreceptors that sense the chemical composition of arterial blood


carbonic anhydrase – an enzyme catalyzing the reversible interconversion of carbonic acid to carbon dioxide and water


chemoreceptor- A sense organ that responds to a chemical signal in the body.


chloride shift – the movement of chloride ions across the red blood cell membrane to compensate for the movement of bicarbonate ions


diaphragm – the dome-shaped muscle that separates the thoracic and abdominal cavities and serves as the chief muscle of respiration in mammals.



diffusion gradient – when there is an inequality in the amount of substance across a barrier (membrane) and the natural tendency is for particles to move (diffuse) from high concentrations to low concentrations (gradient).


epithelial surface of the gill – the thin, outermost lining of the gill that are exposed to the external environment (water) in order to pick up the oxygen from the water by diffusion.


exoskeleton – the hard, outer shell of many terrestrial and aquatic invertebrates made of chitin.


external and internal intercostal muscles – types of muscles in vertebrates that are located between the ribs and aid in lung ventilation


facilitated diffusion – the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients


flanks – the fleshy parts between the ribs and the hip on either side of the body of an animal; the lateral part of something


gills- Organs used by aquatic animals for obtaining oxygen from water.


glottis – an elongated space between the mouth cavity and the lung in frogs


heme groups – the active site on hemoglobin that contains iron, the oxygen carrier.


hemoglobin- Iron-containing respiratory pigment of the erythrocytes which carry oxygen; formed by the developing erythrocyte in bone marrow.


larynx- In air breathing vertebrates, the modified upper part of the trachea.


lipoprotein – lipid-protein complex within the plasma membrane of cells.


lungs- Organs that constitute the basic respiratory organs of air breathing vertebrates.


mechanoreceptor- A sensory receptor that responds to a mechanical stimulus or pressure.


medulla oblongata- A neural end organ that responds to a mechanical stimulus and which is found in vertebrates between the spinal cord and the pons.


mesobronchus – a large tube which joins the trachea anteriorly and is connected to the air sacs and parabronchi in birds


mitochondria – membrane enclosed cell organelle where ATP is produced during aerobic metabolism.


myoglobin- A red iron-containing protein pigment in the muscles, similar to hemoglobin.


nares - nostrils


O2 gradient – a situation that occurs across a membrane where one side has a higher concentration of oxygen than the other, forcing a diffusion of O2 across the membrane from the high concentration side to the low concentration side.


passive diffusion – the transport of molecules and ions down their concentatration gradient without expending energy for the process to occur.  This may occur across a biological membrane.


pharynx- Part of the vertebrate alimentary canal between the mouth cavity and the esophagus


phrenic nerve- A nerve related to the diaphragm


pleural cavity – the cavity between the lungs and the wall of the thorax


polypeptide chains – proteins having more than one peptide joined together.


pons- Mass consisting of mainly transverse nerve fibers on the ventral surface of the brain of a human, and at the anterior end of the medulla oblongata in lower animals.


pores of Kohn- Small holes between adjacent regions of the lung and which allow for the collateral movement of air.


red blood cell – a body cell that functions to carry oxygen and carbon dioxide throughout the body.


reducing potential- a measurement of the tendency of a reducer to yield electrons in a redox reaction, expressed in volts


respiratory acidosis – a decrease in blood pH associated with an increase in blood PCO2 as a result of lung hypoventilation


respiratory alkalosis – an increase in blood pH associated with a decrease in blood PCO2 as a result of lung hyperventilation


spiracles- Series of small apertures located along each side of the thorax and abdomen used by invertebrates for respiration.


stretch receptor- Sensory receptors that respond to stretch, typically associated with lung or muscle tissue


surface tension – the elasticity of the surface of a substance (particularly a fluid), which tends to reduce the surface area.


thoracic cage – the chest compartment formed by the ribs and diaphragm containing the lungs and heart


trachea- Main trunk of the tube system by which air passes to and from the lungs in vertebrates.


tracheoles – the terminal ends of the tracheal system in insects that deliver oxygen to and carry carbon dioxide away from the body tissues.


ventilationin respiratory physiology, circulation or the process of exchange of gases in the lungs or gills in the ambient air or water, respectively


viscousa measure of how easily a substance moves over itself, its "thickness."