Saltatory Conduction
/ˈsæltəˌtɔːri kənˈdʌkʃən/
The propagation of action potentials along myelinated axons from one node of Ranvier to the next, increasing conduction velocity.
Sarcomere
/ˈsɑːrkoʊˌmɪər/
The fundamental unit of muscle contraction, composed of actin and myosin filaments.
Sarcoplasmic Reticulum
/ˌsɑːrkoʊˈplæzmɪk rɪˈtɪkjʊləm/
A specialized type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells.
Schwann Cell
/ʃwɒn sɛl/
Cells in the peripheral nervous system that produce the myelin sheath around neuronal axons.
Sebaceous Gland
/sɪˈbeɪʃəs ɡlænd/
A small gland in the skin which secretes a lubricating oily matter (sebum) into the hair follicles.
Secretin
/sɪˈkriːtɪn/
A hormone released into the bloodstream by the duodenum to stimulate secretion by the liver and pancreas.
Semen
/ˈsiːmən/
The male reproductive fluid, containing spermatozoa in suspension.
Semicircular Canals
/ˌsɛmiˈsɜːrkjʊlər kəˈnælz/
Three fluid-filled bony channels in the inner ear situated at right angles to each other, providing information about orientation.
Semilunar Valve
/ˌsɛmiˈluːnər vælv/
Heart valves (pulmonary and aortic) at the base of the large vessels leaving the ventricles.
Serosa
/sɪˈroʊsə/
The outermost coat or serous layer of a visceral organ.
Serum
/ˈsɪərəm/
An amber-colored, protein-rich liquid that separates out when blood coagulates; blood plasma without the clotting factors.
Sinoatrial Node
/ˌsaɪnoʊˈeɪtriəl noʊd/
A small body of specialized muscle tissue in the wall of the right atrium of the heart that acts as a pacemaker.
Sinusoid
/ˈsaɪnəˌsɔɪd/
A small irregularly shaped blood vessel found in certain organs, especially the liver and spleen.
Smooth Muscle
/smuːð ˈmʌsəl/
Muscle tissue in which the contractile fibrils are not highly ordered, occurring in the gut and other internal organs and not under voluntary control.
Solute
/ˈsɒljuːt/
The minor component in a solution, dissolved in the solvent.
Somatic Nervous System
/soʊˈmætɪk ˈnɜːrvəs ˈsɪstəm/
The part of the peripheral nervous system associated with the voluntary control of body movements.
Spermatogenesis
/ˌspɜːrmətoʊˈdʒɛnɪsɪs/
The production or development of mature spermatozoa.
Sphincter
/ˈsfɪŋktər/
A ring of muscle surrounding and serving to guard or close an opening or tube, such as the anus or the openings of the stomach.
Spleen
/spliːn/
An abdominal organ involved in the production and removal of blood cells and forming part of the immune system.
Squamous Epithelium
/ˈskweɪməs ˌɛpɪˈθiːliəm/
A single layer of flat cells in contact with the basal lamina of the epithelium.
Steroid
/ˈstɪərɔɪd/
Any of a large class of organic compounds with a characteristic molecular structure containing four rings of carbon atoms, including many hormones.
Stimulus
/ˈstɪmjʊləs/
A thing or event that evokes a specific functional reaction in an organ or tissue.
Stroke Volume
/stroʊk ˈvɒljuːm/
The amount of blood pumped out of the ventricle of the heart with each individual contraction.
Sympathetic Nervous System
/ˌsɪmpəˈθɛtɪk ˈnɜːrvəs ˈsɪstəm/
The part of the autonomic nervous system that contains chiefly adrenergic fibers and tends to depress secretion, decrease the tone and contractility of smooth muscle, and increase heart rate.
Synapse
/ˈsaɪnæps/
A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.
Synovial Fluid
/saɪˈnoʊviəl ˈfluːɪd/
A transparent, viscid lubricating fluid which is secreted by a membrane of an articulation or joint.
Systemic Circulation
/sɪˈstɛmɪk ˌsɜːrkjʊˈleɪʃən/
The part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart.
Systole
/ˈsɪstəli/
The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries.