G-20
Glossary
Seminiferous tubules
(sem
0
ĭ-nif
9
er-us) Highly convoluted tubes within
the testes; form sperm.
Sense organs
Localized collections of many types of cells working to-
gether to accomplish a specific receptive process.
Sensory (afferent) nerves
Nerves that contain processes of sensory neu-
rons and carry impulses to the central nervous system.
Sensory areas
Functional areas of the cerebral cortex that provide for
conscious awareness of sensation.
Sensory receptor
A cell or part of a cell (e.g., receptive endings of sen-
sory neurons) specialized to respond to a stimulus.
Serosa (serous membrane)
(se-ro
9
sah) Te moist membrane found in
closed ventral body cavities.
Serous fluid
(sēr
9
us) Clear, watery fluid secreted by cells of a serous
membrane.
Serum
(sēr
9
um) Amber-colored fluid that exudes from clotted blood as
the clot shrinks; plasma without clotting factors.
Sesamoid bones
(ses
9
ah-moid) Short bones embedded in tendons, vari-
able in size and number, many of which influence the action of muscles;
largest is the patella (kneecap).
Severe combined immunodeficiency syndromes (SCIDs)
Congenital
conditions resulting in little or no protection against disease-causing or-
ganisms of any type.
Sex chromosomes
Te chromosomes, X and Y, that determine genetic
sex (XX
5
female; XY
5
male); the 23rd pair of chromosomes.
Sex-linked inheritance
Inherited traits determined by genes on the sex
chromosomes, e.g., X-linked genes are passed from mother to son, Y-
linked genes are passed from father to son.
Sexually transmitted infection (STI)
Any infectious disease spread
through sexual contact.
Signal sequence
A short peptide segment present in a protein being syn-
thesized that causes the associated ribosome to attach to the membrane
of rough ER.
Simple diffusion
Te unassisted transport across a plasma membrane of
a lipid-soluble or very small particle.
Sinoatrial (SA) node
(si
0
no-a
9
tre-al) Specialized myocardial cells in the
wall of the right atrium; pacemaker of the heart.
Sinus
(si
9
nus) (1) Mucous-membrane-lined, air-filled cavity in certain
cranial bones; (2) dilated channel for the passage of blood or lymph.
Skeletal muscle
Muscle composed of cylindrical multinucleate cells with
obvious striations; the muscle(s) attached to the body’s skeleton; volun-
tary muscle.
Skeletal system
System of protection and support composed primarily
of bone and cartilage.
Skull
Bony protective encasement of the brain and the organs of hearing
and equilibrium; includes cranial and facial bones.
Small intestine
Convoluted tube extending from the pyloric sphincter to
the ileocecal valve where it joins the large intestine; the site where diges-
tion is completed and virtually all absorption occurs.
Smooth muscle
Spindle-shaped cells with one centrally located nucleus
and no externally visible striations (bands). Found mainly in the walls of
hollow organs.
Sodium-potassium (Na
1
-K
1
) pump
A primary active transport system
that simultaneously drives Na
1
out of the cell against a steep gradient
and pumps K
1
back in. Also called Na
1
-K
1
A±Pase.
Sol-gel transformation
Reversible change of a colloid from a fluid (sol)
to a more solid (gel) state.
RNA (ribonucleic acid)
(ri
9
bo-nu-kle
9
ik) Nucleic acid that contains
ribose and the bases A, G, C, and U. Carries out DNA’s instructions for
protein synthesis.
Rods
One of the two types of photosensitive cells in the retina.
Rotation
Te turning of a bone around its own long axis.
Rugae
(ru
9
ge) Elevations or ridges, as in stomach mucosa.
Rule of nines
Method of computing the extent of burns by dividing
the body into a number of areas, each accounting for 9% (or a multiple
thereof) of the total body area.
S (synthetic) phase
Te part of the interphase period of the cell cycle in
which DNA replicates itself, ensuring that the two future cells will receive
identical copies of genetic material.
Sagittal plane
(saj
9
ĭ-tal) A longitudinal (vertical) plane that divides the
body or any of its parts into right and le² portions.
Saliva
Secretion of the salivary glands; cleanses and moistens the mouth
and begins chemical digestion of starchy foods.
Saltatory conduction
±ransmission of an action potential along a my-
elinated fiber in which the nerve impulse appears to leap from gap to gap.
Sarcolemma
Te plasma membrane of a muscle fiber.
Sarcomere
(sar
9
ko-mēr) Te smallest contractile unit of muscle; extends
from one Z disc to the next.
Sarcoplasm
Te nonfibrillar cytoplasm of a muscle fiber.
Sarcoplasmic reticulum (SR)
(sar
0
ko-plaz
9
mik rĕ-tik
9
u-lum) Special-
ized endoplasmic reticulum of muscle cells.
Schwann cell
A type of supporting cell in the PNS; forms myelin sheaths
and is vital to peripheral nerve fiber regeneration.
Sclera
(skle
9
rah) White opaque portion of the fibrous layer of the eyeball.
Scrotum
(skro
9
tum) External sac enclosing the testes.
Sebaceous glands (oil glands)
(se-ba
9
shus) Epidermal glands that pro-
duce an oily secretion called sebum.
Sebum
(se
9
bum) Oily secretion of sebaceous glands.
Second-degree burn
A burn in which the epidermis and the upper re-
gion of the dermis are damaged.
Second messenger
Intracellular molecule generated by the binding of a
chemical (hormone or neurotransmitter) to a receptor protein; mediates
intracellular responses to the chemical messenger.
Secondary sex characteristics
Anatomical features, not directly in-
volved in the reproductive process, that develop under the influence of
sex hormones, e.g., male or female pattern of muscle development, bone
growth, body hair distribution.
Secretion
(se-kre
9
shun) (1) Te passage of material formed by a cell to
its exterior; (2) cell product that is transported to the exterior of a cell.
Secretory vesicles (granules)
Vesicles that migrate to the plasma mem-
brane of a cell and discharge their contents from the cell by exocytosis.
Section
A cut through the body (or an organ) that is made along a par-
ticular plane; a thin slice of tissue prepared for microscopic study.
Segregation
During meiosis, the distribution of the members of the al-
lele pair to different gametes.
Selectively permeable membrane
A membrane that allows certain
substances to pass while restricting the movement of others; also called
differentially permeable membrane.
Semen
(se
9
men) Fluid mixture containing sperm and secretions of the
male accessory reproductive glands.
Semilunar valves
(sĕ
0
me-loo
9
ner) Valves that prevent blood return to
the ventricles a²er contraction; aortic and pulmonary valves.
previous page 1196 Human Anatomy and Physiology (9th ed ) 2012 read online next page 1198 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off