Glossary

absorption:the passage of substances through cells, from one compartment to another. An example is the passage of food nutrients from the intestinal lumen through intestinal epithelial cells and then through capillary endothelial cells into the blood.
acquired patterns:skin patterns that a person develops after birth (such as wrinkles and lines).
actin:a protein component of the thin myofilament involved (along with myosin) in muscle contraction.
adrenal cortex:the outer layer of the adrenal gland which secretes steroid hormones that affect metabolism.
adrenal gland:one of a pair of endocrine glands located on top of each kidney; these glands secrete a variety of hormones that regulate metabolism, chemicals in the blood, certain body characteristics, and the body's response to physical and emotional stresses.
adrenocorticotropic hormone (ACTH):a hormone that stimulates adrenal cortex secretion of hormones, mainly glucocorticoids, such as cortisol.
afferent:describing sensory nerves, which carry information toward the central nervous system.
albinism:a condition in which a person has deficient melanin production. In the most common form of albinism, there is deficient production of the enzyme needed for melanocytes to produce melanin.
allergen:a type of foreign antigen. Most allergens are relatively small, highly soluble proteins that are carried on dry particles such as pollen and mite feces.
alveolus:one of millions of tiny balloon-like structures in the lung located at the termini of the bronchioles, where gas exchange occurs.
amniotic fluid:the fluid in the uterus that surrounds and cushions a developing fetus during pregnancy.
androgen:a sex hormone, such as testosterone, that produces male-like characteristics.
androsterone:a type of weak androgen.
antagonistic effect:when the effect of one hormone on a target organ opposes the effect of another hormone on the same organ.
antagonists:muscles that oppose the action of a prime mover or initiate an opposite movement.
anterior:situated in front of or in the forward part of an organ.
antidiuretic hormone (ADH):a hormone that stimulates the kidneys to absorb water, creating a concentrated urine.
antigen:small proteins; foreign antigens are proteins not normally found in the human body.
anus:the terminal opening of the rectum, through which feces pass to exit the body.
aorta:the major artery leaving the heart, through which oxygenated blood flows to the rest of the body.
appendicular skeleton:bones that make up the upper and lower extremities of the body.
appositional growth:growth accomplished by adding layers to those previously formed, such as that which occurs on the sides of bone.
aqueous humor:the watery fluid that fills the shallow chamber behind the cornea of the eye.
arachnoid mater:the middle of the three meninges covering the brain and spinal cord.
arteriole:minute branches of the arteries, which further branch into capillaries.
articular facet:a smooth bony surface of a joint where bones move upon one another.
articulation:place of union between two bones, usually movable.
atlas:the first cervical vertebra.
auditory ossicles:the three tiny bones (malleus, incus, and stapes) in the inner ear.
auricle:the part of the external ear that protrudes from the side of the head.
autonomic nervous system:the part of the nervous system that controls the viscera of the body automatically, composed of the sympathetic and parasympathetic nervous systems.
Avogadro's Law:all gases at the same temperature and pressure contain the same number of molecules in a given volume.
axial skeleton:bones that form the axis of the body.
axis:the second cervical vertebra.
basophils:white blood cells that contribute to immediate hypersensitivity reactions.
belly (muscle):the thick contractile portion of a muscle.
bicuspid:a tooth with two pointed projections that tears, shreds, and crushes food.
bicuspid (mitral) valve:the valve located between the left atrium and the left ventricle of the heart: the left atrioventricular valve.
bifid:split or in two parts.
bifurcation:a branching of a single structure into two structures, such as the bifurcation of the trachea into the bronchi.
blastocyst:the next stage after the fertilization of a female egg by a sperm to form a zygote; the zygote becomes a blastocyst and develops three distinct germ layers from which all body organs form.
B-lymphocyte (B cell):a lymphocyte that is important in antibody production. “B” stands for “bursa,” which is the source of these cells in birds (the animal model in which they were discovered). B cells arise in the bone marrow in humans.
bolus:food after it has been ingested and mixed with saliva and is ready to swallow.
bone collar:a shell of compact bone laid down by osteoblasts around the shaft of a bone during endochondral bone formation.
borborygmus:the gurgling sound made by the intestines.
Boyle's Law:the pressure of a gas is inversely proportional to its volume.
brain stem:the part of the brain superior to the spinal cord composed of the medulla, pons, and midbrain; responsible for the control of vital functions, such as breathing and blood pressure.
bronchioles:air passageways that branch from the bronchi in the lungs.
calcaneus:the heel bone in the foot.
canaliculus:a small canal or channel, such as that found in bone.
cancellous bone:bone with porous spaces; containing marrow.
capillaries:smallest blood vessels that travel between arterioles and venules. Nutrient and gas exchange between the tissues and the blood occurs through the walls of the capillaries.
cardiac cycle:the repeating pattern of contraction and relaxation of the heart.
carotene:a yellow pigment in the skin.
carotid artery, external:the vessel that supplies blood to the organs of the head and neck outside the cranial cavity.
carotid artery, internal:the vessel that ascends through the carotid foramen into the cranial cavity, supplying the brain with oxygenated blood.
carpal bones:the small bones of the wrist.
carpal tunnel:a narrow, rigid passage formed by the carpal bones of the wrist and the tough, inelastic transverse carpal ligament.
carpal tunnel syndrome:pain, numbness, and weakness of the hand associated with compression of the median nerve against the inelastic transverse carpal ligament, usually caused by the stress of repetitive motion.
cartilage:flexible support connective tissue. There are three types of cartilage found in the body: hyaline, elastic, and fibrocartilage.
cecum:the first part of the colon, joining to the terminal part (ileum) of the small intestine.
cementum:a thin protective tissue layer covering the root of each tooth.
central nervous system:the portion of the nervous system comprised of the brain and spinal cord.
cerebellum:a part of the brain, located at the posterior and inferior aspect, responsible for muscular coordination, balance, and posture.
cerebral aqueduct:the tubular connection between the third and fourth ventricles of the brain, which conveys cerebrospinal fluid through the midbrain.
cerebral cortex:the outer layer of each hemisphere of the brain, which is rich in nerve cells, consists of gray matter, and is involved in conscious thought, movement, and sensation.
cerebrospinal fluid:a fluid that circulates through the ventricles and around the surface of the brain and spinal cord; it cushions it from the bony cavity encasing it and filters and transports waste, hormones, and other substances from the brain to the venous blood.
cerebrum:the largest and most developed part of the human brain, composed of the frontal, parietal, temporal, insular, and occipital lobes and responsible for most conscious and intellectual activities.
cervical vertebrae:the seven neck bones of the spine that support the head.
chondroblasts:cells that produce cartilage.
choroid:the layer of the eye lying between the retina and the sclera, containing a network of branching blood vessels.
choroid plexus:the part of the brain, within the ventricles, that produces cerebrospinal fluid.
chyle:lymph collected from the gut that is rich in fat and appears milky.
chyme:food after it has been broken down by acidic juices in the stomach.
ciliary body:a circular muscle ring in the eye, which contracts to alter the shape of the lens to focus the eye.
circle of Willis:a circle of arteries at the base of the brain, formed by contributions from the internal carotid arteries and basilar artery; this circle gives off cerebral arteries, and it is completed by communicating arteries.
circular muscle:muscle whose fibers encompass an opening.
clavicle:the collar bone.
coccyx:the tail bone located at the inferior part of the vertebral column.
cochlea:the snail-shaped chamber found in the inner ear where the organ of Corti (organ of hearing) is located; it is located in the temporal bone.
cochlear nerve:the nerve through which impulses travel from the hair cells of the cochlea to the brain. This nerve joins with the vestibular nerve to become the vestibulocochlear nerve (cranial nerve VIII).
conducting division:all of the passageways through which air travels to reach the lungs where gas exchange with the blood does not occur.
condyle:a round smooth prominence at the end of bone.
cones:the cells in the retina that detect color.
congenital patterns:feature patterns present in a person when they are born (such as fingerprints).
contraction:an increase in tension (shortening) of muscle tissue.
convergent muscle:fan-shaped muscle whose fibers of origin converge at the insertion point.
cornea:the transparent front part of the eye through which light passes.
coronal section:a plane that splits the body or an organ into front and back halves.
corpus callosum:the thick band of nerve fibers that link the right and left hemispheres of the brain.
corpus luteum:the empty follicle left behind after a mature ovum is released from the ovary; the corpus luteum secretes mainly progesterone and some estrogen and subsequently degenerates.
corpuscle (renal):a body forming the beginning of the nephron, consisting of a tuft of capillaries (the glomerulus) surrounded by Bowman's capsule, the expanded initial portion of the renal tubule.
cranial nerves:12 pairs of nerves that traverse openings in the skull.
cricoid cartilage:a ring-shaped structure of cartilage located at the base of the larynx.
crista:a raised area in the center of the membranous ampulla of a semicircular canal of the inner ear.
cross-bridges:minute protrusions from myosin filaments that attach to actin filaments during muscle contraction.
cuspid:a tooth with a single, very long, sharp cusp, which tears and shreds food.
cutaneous:pertaining to the skin.
cyanosis:a dark blue or purple coloration of the skin due to deficient oxygenation of the blood.
cytokines:cell signaling molecules that are important in a variety of functions including immune reactions.
Dalton's Law:total pressure is equal to the sum of the partial pressures of each gas in a mixture.
daughter cell:a cell resulting from the division of a mother cell.
deciduous teeth:“baby teeth” that fall out and are replaced by permanent teeth.
defecation:the expulsion of feces from the rectum through the anus.
deglutition:swallowing; wave-like contractions of the esophagus that move the bolus to the stomach.
dense bone:densely packed bone, which forms the outer layer of bones.
dentin:the second hardest tissue of the body found in the crown and root of the tooth; the yellow substance under the enamel of the teeth.
dermatome:an area of skin supplied by nerve fibers from a single dorsal (posterior) root and its ganglion.
dermis:the layer of connective tissue located just beneath the surface epidermal layer of the skin (epidermis).
diaphragm:the skeletal muscle partition separating the abdominal and thoracic cavities, serving as a major muscle for inspiration.
diastole:relaxation of the heart.
digestion:the breakdown of food into molecules small enough to be absorbed through the capillaries into the blood and lymph.
diphyodont:having two sets of teeth that develop during a lifetime.
diploid:a cell having two of each chromosome (46 chromosomes total), such as a fertilized ovum (23 from a sperm cell and 23 from an ovum).
distal:remote; farther from a particular point of reference.
dorsal:pertaining to the back.
dorsal (posterior) root:the part of a spinal nerve through which only afferent (sensory) impulses travel toward the spinal cord.
duodenum:the first part of the small intestine, just beyond the pyloric valve of the stomach.
dura mater:the outermost layer of the meninges that covers and protects the brain and spinal cord; the dura mater lines the inside of the skull.
ectoderm:the outer of the three embryonic germ layers that give rise to the specific tissues and organs, such as the skin and nervous system.
efferent:describing nerves through which impulses travel away from the central nervous system.
embryo:the earliest stage of the developing human between fertilization and the fetal stage. Organ development begins in this stage.
enamel:the hardest tissue of the body, covering all exposed surfaces of the teeth and providing protection from food acids, heat, and cold.
endocardium:the inner lining of the heart.
endochondral bone:the long bones of the body that develop when cartilage is first formed and then degenerates and is replaced by bone.
endocrine:relating to the hormonal system of the body.
endocrine glands:glands that secrete into the bloodstream, not into ducts.
endoderm:the inner of the three embryonic germ layers that give rise to the digestive tract lining and other body organs.
endolymph:fluid within the membranous labyrinth (innermost chambers) of the inner ear.
endometrial (uterine, menstrual) cycle:the growing, secreting, and shedding phases of the uterine lining (endometrium) that occur during a woman's reproductive years. Coincides with the ovarian cycle.
endometrium:the highly vascular lining of the uterus that builds during each menstrual cycle in preparation for implantation of a fertilized egg.
endosteum:a layer of cells lining the inner surface of bones.
eosinophil:granulocytic leukocytes that originate in bone marrow. They quell allergic reactions and are important in the body's defense against parasitic infections.
epicardium:the outer layer of heart muscle.
epicondyle:a bony prominence above or on the condyle.
epidermis:the most superficial (outer) layer of the skin.
epididymis:a long, coiled tube connecting the testicles to the vas deferens in the male reproductive tract, where sperm from the testes are stored and mature.
epiglottis:the part of the larynx that permits passage of air and prevents food or solid objects from entering the larynx into the trachea.
epimysium:fibrous tissue enveloping a muscle that is continuous with a tendon.
epinephrine:a hormone that increases heart and respiratory rates, dilates the coronary blood vessels, increases alertness, and elevates metabolic rate.
epiphyseal plate:a region of cartilage found between ossification centers of the epiphysis and diaphysis at which bone growth occurs: it is eventually replaced by bone with age.
erythropoietin:a hormone secreted by the kidneys that stimulates production of hemoglobin and red blood cells.
estradiol (estrogen):a hormone that stimulates female sexual characteristics, helps maintain the endometrium growth, and helps stimulate breast development.
eustachian (pharyngotympanic) tube:an open passageway from the middle ear chamber to the nasopharynx.
exocrine glands:glands that secrete into ducts, not into the bloodstream.
expiration:the passive recoil of the lungs as the diaphragm and intercostal (rib) muscles relax; the release of air.
external acoustic meatus:part of the external ear where sound waves are funneled from the auricle to reach the tympanic membrane.
Fallopian (uterine) tube:one of two structures in the female reproductive system that transports ova from the ovaries to the uterus; also called the oviduct.
farsightedness:a vision imperfection in which light from near objects focuses behind the retina.
fascicle:a group of muscle fibers bound by perimysium.
femur:the thigh bone, which fits into the hip socket.
fertilization:the union of a male sperm cell and a female egg, forming a zygote.
fetus:the stage of pregnancy during which the embryo has developed all of its organs, usually by the eighth week.
fibrous tunic:the outer layer of the eye consisting of the sclera and cornea.
fibula:the smaller of the two bones in the leg, between knee and ankle.
fissure:a narrow slit-like opening.
flexion:the closing and bending of a limb or extremity.
follicle-stimulating hormone (FSH):in females, a hormone that stimulates growth of ovarian follicles; in males, FSH stimulates the production of sperm in the testes.
follicular phase:the period of the ovarian cycle from the first day of menstruation until the day of ovulation.
foramen:a hole or opening through a bone or in an organ.
fossa:a depression in a bone.
fovea:a cup-shaped depression in the retina; the point of sharpest focus in the eye.
gallbladder:a small, pear-shaped organ underneath the liver that stores and concentrates bile and releases it into the small intestine to emulsify fat contained in food.
gamete:a sex cell, either a sperm cell or an ovum, each containing 23 chromosomes.
ganglion:a group of nerve cell bodies located outside the central nervous system (or in the peripheral nervous system).
gas exchange:the diffusion of oxygen and carbon dioxide across the epithelium of the lung alveoli and blood vessel walls. Oxygen passes from inspired air into the blood and carbon dioxide passes from the blood to the air.
gastrin:a hormone that increases gastric motility and stimulates the stomach to secrete hydrochloric acid.
gestation period:the length of time between fertilization and birth.
gingiva:the gums of the mouth.
glomerulus:a filtering unit in the kidney, composed of capillaries through which blood flows; each kidney contains about 1 million glomeruli.
glucagon:a hormone that raises blood levels of glucose by stimulating release of stored glucose from the liver.
glucocorticoids:hormones that regulate the metabolism of blood sugar and other organic compounds.
gonadotropin:anterior pituitary hormones that include follicle-stimulating hormone and luteinizing hormone.
Graafian follicle:the dominant follicle in each ovarian cycle that ruptures in the process of ovulation.
gray matter:the material, rich in nerve cell bodies, that makes up the cerebral cortex and nuclei of the brain and central part of the spinal cord.
growth hormone (GH):a hormone that stimulates growth in all organs, mobilizes fat, and inhibits blood sugar utilization.
gyri:folds in the cerebral cortex of the brain.
haploid:a cell having one of each chromosome (23 chromosomes total), such as a spermatozoon or ovum.
Haversian system (osteon):a central canal and the concentric osseous layers around it; found in compact bone.
hematopoiesis:the formation of red and white blood cells and platelets in the bone marrow.
hemoglobin:the iron-containing pigment found in red blood cells that carries oxygen and other gases.
Henry's Law:the amount of gas dissolved in a fluid depends on the solubility of the gas in the fluid, the temperature of the fluid, and the partial pressure of the gas.
hepatic:referring to the liver.
hepatic triad:the portal vein, hepatic artery, and bile duct, which travel together throughout the liver.
heterodont dentition:the adaptation of teeth into different shapes and sizes to perform various functions.
histamine:a substance released by basophils and mast cells that is derived from the amino acid histidine. It causes an immediate increase in local blood flow and vessel permeability.
homologous chromosomes:a matching pair of chromosomes in a diploid cell.
hormone:a chemical formed in an endocrine gland and transported via the blood throughout the body, where it attaches to specific receptor proteins to alter the function and/or structure of target organs.
humerus:the arm bone that fits into the shoulder socket.
hyaline cartilage:a rubbery tissue found at the ends of bones and in C-shaped rings that hold the trachea open to permit the passage of air.
hyoid bone:a small u-shaped bone that is part of the larynx.
hyperventilation:increased breathing.
hypothalamus:a gland in the brain that regulates body temperature, response to stresses, appetite, sleep, and some emotional responses; also coordinates the functions of the nervous and hormonal systems of the body.
ileum:the terminal portion of the small intestine, which connects with the cecum of the large intestine.
ilium:one of three bones which fuse together to form the mature hip bone, the other two being the ischium and the pubis.
immunoglobulins:antibodies.
incisor:the type of tooth that acts like scissors, grasping and cutting off food pieces.
incus:one of the three small bones in the inner ear, shaped somewhat like an anvil.
ingestion:the process of taking food into the body by way of mouth.
insalivation:mixing of the food within the oral cavity with saliva.
insertion:the distal attachment of a muscle, which moves with the bone during contraction.
inspiration:the contraction of the diaphragm and external intercostal (rib) muscles, causing the thorax to expand laterally, vertically, and anteroposteriorly; the taking in of air.
insulin:a hormone that promotes the cellular uptake of blood glucose, lowering the level of blood glucose.
integumentary system:the system that includes the skin and its associated structures (glands, hair, and nails).
intercalated disks:complex intercellular attachments found between cardiac muscle cells.
interstitial growth:growth from within a structure; cartilage and flat bones grow by interstitial growth.
iris:the colored part of the eye where pupillary muscles are located.
islets of Langerhans:the cells of the pancreas that secrete insulin and glucagon.
jaundice:the yellowish appearance of skin due to an excess of bile in the blood, typically a symptom of liver problems or bile obstruction.
jejunum:the second (middle) part of the small intestine.
jugular veins:the vessels that drain blood from the head and neck toward the heart.
keratin:a protein in the epidermis that waterproofs the skin.
lacrimal glands:the glands that secrete tears.
lactation:the production of milk from the female mammary glands.
lacteal:lymphatic capillaries found in the villus of the small intestine mucosa.
lacuna:a small space, cavity, or depression, such as that found in the osteon.
lanugo:small hairs covering the fetus and newborn.
Laplace's Law:the smaller the alveolar radius, the greater the surface tension and internal pressure.
laryngopharynx:the part of the pharynx from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it becomes continuous with the esophagus.
larynx:the structure located superior to the trachea that functions in producing sound and prevents food from passing into the trachea; contains the epiglottis and vocal cords.
ligament:tissue that typically connects bones with other bones.
limbic system:collectively, the tissues of the brain that play a role in emotion.
lipid mediators:cause smooth muscle contraction, increased vascular permeability, and increased mucus secretion. They also induce the influx and activation of leukocytes, which contribute to the late phase of the allergic response.
liver:the organ that produces bile, detoxifies blood, helps regulate blood glucose levels, and produces plasma proteins.
lumbar vertebrae:the five bones of the spine supporting the lower back.
luteal phase:the period of the ovarian cycle from ovulation to the first day of menstruation, during which the corpus luteum secretes estrogen and progesterone and subsequently degenerates.
luteinizing hormone (LH):a hormone that stimulates ovulation and immediately thereafter converts the ovarian follicle into an endocrine gland called the corpus luteum.
lymph:a transparent and colorless to slightly yellow fluid found only in the lymphatic system. Lymph contains mononucleated cells called lymphocytes.
lymph node:small lymphatic organs that filter lymph and are located along lymphatic vessels.
lymph nodule:accumulation of B-lymphocytes found in lymphoid tissue.
lymphatic capillary:a blind-ending capillary located in the interstitial space that collects extracellular fluid and returns it to the venous system.
lymphatic sinus:lymph-containing spaces within a lymph node where unwanted organisms and material are filtered out of the lymph as it passes through the node.
lymphatic vessel:a thin-walled vessel that conducts lymph. It is similar to a small vein but does not have the muscular wall structure.
macula of the saccule and utricle:the part of the inner ear containing hair cells that are sensitive to movement and help regulate balance.
malleus:one of the three small bones in the inner ear, shaped somewhat like a hammer.
mammary gland:glands responsible for milk production.
mandible:the lower jaw bone that contains the lower dentition (teeth).
manubrium:the upper portion of the breastbone or sternum.
marrow, red:substance located within spongy bone tissue in the center of most bones where blood cells are produced.
marrow, yellow:inactive bone marrow located mainly in the center of long bones, consisting mostly of fat cells.
mast cells:reside in the tissues and release a variety of preformed inflammatory mediators.
mastication:chewing.
maxilla:the upper jaw bone that contains the upper dentition (teeth).
meatus:a tube-like passageway or its opening through bone.
medulla oblongata:the lowest part of the brain stem, situated between the pons and the spinal cord.
meiosis:a specialized cell division that divides a diploid cell (46 chromosomes) into four haploid gametes (23 chromosomes each).
melanin:a pigment in the epidermis that protects the skin by helping to block ultraviolet rays.
melanocyte:cells in the epidermis of the skin that produce melanin.
membrane bone:bone that forms directly from mesenchyme, without preformation in cartilage.
membranous ampulla:a part of a semicircular duct in the inner ear that regulates balance.
membranous labyrinth:the endolymph-filled chambers that lie within the bony labyrinth of the inner ear, which includes the saccule and utricle (in the vestibule), semicircular ducts (in the semicircular canals), and cochlear duct (in the cochlea).
meninges:the three connective tissue layers that cover and protect the brain and the spinal cord.
menopause:the cessation of ovarian activity occurring in women at approximately 50 years of age, if fertilization does not occur. During this phase, a decrease in estrogen and progesterone induces the shedding of the inner endometrial lining of the uterus.
menstrual phase:the period of the menstrual (uterine) cycle at the end of the luteal phase.
mesenchyme:primitive embryonic tissue (loose form of mesoderm) that gives rise to all connective tissues, including cartilage and bone.
mesoderm:the middle of the three embryonic germ layers that give rise to muscle, connective tissue, vascular system, and other body organs.
metacarpal bones:the bones of the hand that lie between the fingers and the wrist.
metastasis:transfer of cancer cells from one organ to another.
metatarsals:bones of the feet that lie between the toes and the ankle.
micturition:urination, or emptying of the urinary bladder.
milium:a whitehead, or small cyst, just below the outer layer of the skin.
mineralocorticoids:hormones that act on the kidney to regulate sodium and potassium balance.
mitosis:a cell division of a mother cell into two identical daughter cells, each having the same number of chromosomes.
molar:the posterior-most teeth that grind food into tiny pieces.
mother cell:a cell that divides and forms two or more daughter cells.
motilin:a hormone that induces powerful contractions in the stomach.
motor (efferent) nerves:nerves through which impulses travel away from the central nervous system to stimulate muscle to contract and glands to secrete.
mucosa:the soft, pink skin-like layer that lines many of the body's cavities and tubes.
muscle fiber, skeletal:long, cylindrical, multinucleated cells with striations that make up a skeletal muscle.
myocardium:cardiac muscle; its contraction results in squeezing of the heart chambers.
myofibrils:bundles of myofilaments within each muscle cell.
myofilaments:small protein strands that make up myofibrils.
myosin:the larger of the two myofilaments (along with actin) responsible for muscle contraction.
nasopharynx:the part of the pharynx posterior to the nasal cavity and superior to the soft palate.
nearsightedness:a vision imperfection in which light from far objects focuses in front of the retina.
nephrons:the functional units of the kidney, composed of the glomerulus and surrounding Bowman's capsule (expanded initial segment of the kidney tubules).
neural tunic:the innermost layer of the eye that includes the retina.
neuron:a nerve cell.
norepinephrine:a hormone that increases heart and respiratory rates, dilates the coronary blood vessels, increases alertness, and elevates metabolic rate.
occipital:relating to the area toward the back of the head and occipital bone.
odontoblast:cells that form dentin in the teeth.
oocyte:another term for the female egg cell; the ovum.
optic chiasm:the juncture of the optic nerves from each eyeball where half of the fibers cross to the opposite side; located at the base of the brain.
optic disc:the site where all of the nerves from the retina join to form the optic nerve.
optic nerves:pair of cranial nerves (cranial nerve II) responsible for sight.
organ of Corti:a structure of the inner ear containing auditory receptor hair cells, innervated by the cochlear nerve.
origin:the proximal attachment of a muscle, which is its most stationary point.
oropharynx:the part of the pharynx posterior to the oral cavity, inferior to the soft palate, and superior to the glottis.
ossification:the development and mineralization of developing bone.
osteoblasts:bone-forming cells.
osteoclasts:cells that break down/remodel bone.
osteocyte:a bone cell.
osteoid:the organic matrix/meshwork of bone that becomes calcified when minerals enter from the blood.
osteon (Haversian system):a central canal and the concentric osseous layers around it found in compact bone.
otolith:microscopic calcium carbonate crystals that rest on a gelatin-like material; movement of the otoliths displaces the gelatin-like material and bends hair cells, sending nerve impulses to the brain to determine the sensation of movement; located in the semicircular canals of the inner ear.
ovarian cycle:cyclic changes in the ovary corresponding to changes in estrogen and progesterone secretion; includes development and release of the ovum followed by corpus luteum development and regression.
ovary:one of two female glands that secrete estrogen and progesterone and are the site of egg production.
ovum:a female sex cell, containing 23 chromosomes.
oxytocin:a hormone that stimulates uterine contractions during labor and simulates the cells surrounding the alveoli and mammary ducts to contract, which causes the milk-ejection reflex during lactation.
pancreas:a gland that secretes hormones regulating digestion and sugar balance in the body.
papule:a small circular elevation of the skin.
parallel muscle:muscle whose fibers run parallel to one another.
parasympathetic nervous system:the part of the autonomic nervous system that decreases heart rate, dilates visceral blood vessels, and increases digestive activity.
parathyroid gland:one of four glands, typically located on the posterior aspect of the thyroid gland, that produce hormones that regulate calcium balance in the body.
parathyroid hormone (PTH):a hormone that helps increase the level of calcium in the blood.
patella:the knee cap.
pepsin:a major digestive enzyme that is produced by chief cells in the stomach mucosa.
pericardium:the layered sac that surrounds the heart.
perichondrium:dense connective tissue membrane around cartilage.
perilymph:fluid located between the bony and membranous labyrinths of the inner ear.
perimysium:fibrous tissue that extends inward from the epimysium, surrounding bundles (fascicles) of muscle.
perineum:body region containing the external genitalia and anus that is located between the pubic symphysis and coccyx; commonly refers to the border of skin and muscle separating the genitalia from the anus.
periodontal ligament:connective tissue fibers that anchor the teeth into the bony alveolar sockets and provide sensory information about the movements of the teeth.
periosteum:a tough, fibrous connective tissue that covers the surface of bones; it is rich in sensory nerves and is responsible for healing fractures.
peripheral nervous system:the portion of the nervous system consisting of nerves (cranial and spinal) and ganglia (sensory and autonomic).
peritoneum:the two-layered membrane that lines the wall of the abdominal cavity and covers the abdominal organs.
permissive effect:the enhancement of a target organ's responsiveness to a hormone from prior or simultaneous exposure to a different hormone.
phalanges:the bones of the fingers and toes.
pharynx:muscular passageway of the throat that conducts air and food.
pia mater:innermost of three layers of meninges covering, and lying directly upon, the brain and spinal cord.
pilosebaceous unit:consists of the hair follicle, sebaceous gland, and arrector pili muscle.
pineal gland:a gland in the brain that secretes melatonin, the hormone that regulates the body's circadian rhythms.
pituitary gland:the gland located at the base of the brain that regulates the activities of other endocrine glands and many body processes.
plasma cell:a tiny “antibody factory” that produces antibodies (immunoglobulins).
pleura:the serous membrane enveloping the lungs and lining the walls of the pleural cavity.
plexus:a network of nerves.
pons:the middle part of the brain stem, situated between the midbrain and the medulla oblongata.
portal venous system:a system of veins in the digestive tract that carry blood to the liver after draining it from the gastrointestinal organs and spleen.
posterior:situated in back of, or in the back part of a structure.
prehormone:a chemical secreted by an endocrine gland that has no potency until converted into an active hormone by the target cells.
primary ossification center:located in the center of the diaphysis of long bones; initial site where endochondral bone formation occurs.
process:a bony projection.
progesterone:a hormone that helps maintain the endometrium during pregnancy, increases sensitivity of the uterus to oxytocin, stimulates breast development, suppresses gonadotropin secretion, and inhibits prolactin secretion.
prohormone:a precursor molecule within an endocrine gland from which a hormone is formed.
prolactin:a hormone that stimulates the mammary glands to produce milk in women after giving birth.
proliferative phase:the period of the endometrial cycle that occurs during the follicular phase of the ovaries; during this time an increase in estrogen stimulates the growth and development of the endometrium.
prostaglandin:lipid compounds produced by most cells in the body; they have multiple hormone-like functions.
prostate gland:the gland at the base of the male bladder that produces secretions that form part of the seminal fluid during ejaculation.
protuberance:a projection.
proximal:nearest; closer to a particular point of reference.
pulp:the innermost part of the tooth, containing tiny nerves and blood vessels.
pupil:the central opening in the eye, which opens and closes in response to light intensity.
pustule:a small circular elevation of the skin, with pus formation.
radius:one of the two bones in the forearm (the other being the ulna).
rami communicantes:two branches of spinal nerves that connect with the sympathetic ganglia of the autonomic nervous system with the ventral (anterior) rami of the spinal nerve.
sacrum:the large triangular bone located between the fifth lumbar vertebra and the coccyx (tail bone).
sagittal section:a plane that splits the body or an organ into right and left parts.
sarcolemma:the membrane encapsulating a muscle cell.
sarcomere:a portion of muscle fibers found between two Z-lines; the functional unit of striated muscle cells.
scapula:the shoulder blade.
sclera:the tough outer coat of the eye; the white of the eye.
sebaceous gland:glands in the skin that secrete an oily, acid-protective film over the skin, which waterproofs the skin and prevents the growth of many microorganisms.
secretin:a hormone that stimulates the pancreas to secrete pancreatic juices.
secretory phase:the period of the endometrial (uterine) cycle that occurs during the luteal phase of the ovarian cycle; during this phase, progesterone stimulates uterine gland mucus secretion and the endometrium becomes very thick and vascularized.
semicircular duct:one of the inner ear structures responsible for regulating balance; contains endolymph.
thyroxine:a hormone that stimulates protein synthesis, promotes maturation of the nervous system, and increases the rate at which energy is utilized in the body.
trimester:a three-month segment during the gestation period.
trochanter:a large bony process found on the femur.
tubercle:a small rounded protuberance.
tuberosity:a large, round, rough protuberance.
tunica adventitia:the outer layer of arteries and veins.
tunica intima:the inner layer of arteries and veins.
tunica media:the middle layer of arteries and veins.
tympanic membrane:the eardrum, which vibrates as sound waves strike it.
ulna:one of the two bones of the forearm (the other being the radius); the elbow bone.
ultrasound:a noninvasive imaging technique that uses high-frequency sound waves to visualize body parts, or a developing fetus within the uterus prior to childbirth.
ureter:the tube through which urine flows from the kidney into the bladder.
urethra:the tube through which urine flows from the bladder to exit the body.
uvula:the small, fleshy dangling process in the back of the soft palate.
vas deferens:a narrow tube that carries sperm from the epididymis; joins with the seminal vesicle duct to form the ejaculatory duct that opens into the urethra.
vasa recta:a network of blood vessels that descend and ascend in the medulla of the kidney; the circulation of salt and water into and out of these blood vessels helps maintain a high concentration of salt in the interstitial tissues of the renal medulla.
vascular tunic:the layer of the eye containing the choroid, ciliary body, and iris.
vena cava:two very large veins (superior and inferior vena cava) into which most circulating deoxygenated blood drains to the heart.
ventilation:the mechanical movement of air into and out of the lungs; breathing.
ventral:anterior part of body.
ventral (anterior) root:the part of a spinal nerve through which only motor (efferent) impulses travel away from the spinal cord.
ventricle:one of two chambers in the heart that pump blood; also one of several fluidfilled spaces deep within the brain containing cerebrospinal fluid.
venules:small vessels that collect blood from capillaries and join to form veins.
villi:millions of microscopic projections on the inner surface of the small intestine that increase the surface area of the intestine and aid in absorption of molecular nutrients from chyme.
viscera:the internal organs of the body.
vitiligo:the occurrence of white spots or white areas of skin that have no color, because of the absence of melanocytes.
vitreous humor:the clear gel that fills the main cavity of the eyeball, behind the lens.
vocal cords:structures within the larynx that vibrate as air passes between them to produce sounds.
white matter:the part of the brain and spinal cord, consisting of tracts of myelinated nerve fibers (axons).
x-rays:high-energy electromagnetic waves capable of penetrating the body to produce images of its various parts.
xiphoid process:the bony projection at the inferior end of the sternum (breastbone).
zygote:a fertilized egg.

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Appendix