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R

(also, eupnea) mode of breathing that occurs at rest and does not require the cognitive thought of the individual

radial artery

formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region

radial collateral ligament

intrinsic ligament on the lateral side of the elbow joint; runs from the lateral epicondyle of humerus to merge with the annular ligament

radial fossa

small depression located on the anterior humerus above the capitulum; this space receives the head of the radius when the elbow is maximally flexed

radial nerve

systemic nerve of the arm, the distal component of which is located near the radial bone

radial notch of the ulna

small, smooth area on the lateral side of the proximal ulna; articulates with the head of the radius as part of the proximal radioulnar joint

radial tuberosity

oval-shaped, roughened protuberance located on the medial side of the proximal radius

radial vein

parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein

radiation

transfer of heat via infrared waves

radioactive isotope

unstable, heavy isotope that gives off subatomic particles, or electromagnetic energy, as it decays; also called radioisotopes

radiocarpal joint

wrist joint, located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones

radius

bone located on the lateral side of the forearm

ramus of the mandible

vertical portion of the mandible

reabsorption

in the cardiovascular system, the movement of material from the interstitial fluid into the capillaries

reactant

one or more substances that enter into the reaction

reactive oxygen species (ROS)

a group of extremely reactive peroxides and oxygen-containing radicals that may contribute to cellular damage

receptive aphasia

loss of the ability to understand received language, such as what is spoken to the subject or given in written form

receptor

protein molecule that contains a binding site for another specific molecule (called a ligand)

receptor cell

cell that transduces environmental stimuli into neural signals

receptor potential

graded potential in a specialized sensory cell that directly causes the release of neurotransmitter without an intervening action potential

receptor-mediated endocytosis

endocytosis of ligands attached to membrane-bound receptors

recessive

describes a trait that is only expressed in homozygous form and is masked in heterozygous form

recessive lethal

inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span

reciprocal activation

when the primary response of a reflex inhibits a muscle, reciprocal activation refers to activation of the antagonist muscle which occurs synchronously to the primary inhibition

reciprocal inhibition

when the primary response of a reflex activates a muscle, reciprocal inhibition refers to inhibition of the antagonist muscle which occurs synchronously to the primary activation

recruitment

increase in the number of motor units involved in contraction

rectal valve

one of three transverse folds in the rectum where feces is separated from flatus

rectum

part of the large intestine between the sigmoid colon and anal canal

rectus

straight

rectus abdominis

long, linear muscle that extends along the middle of the trunk

rectus femoris

quadricep muscle on the anterior aspect of the thigh

rectus sheaths

tissue that makes up the linea alba

red blood cells (RBCs)

(also, erythrocytes) one of the formed elements of blood that transports oxygen

red bone marrow

connective tissue in the interior cavity of a bone where blood cell formation (hematopoiesis) takes place

red nucleus

midbrain nucleus that sends corrective commands to the spinal cord along the rubrospinal tract, based on disparity between an original command and the sensory feedback from movement

reduction

gaining of an electron

referred pain

the conscious perception of visceral sensation projected to a different region of the body, such as the left shoulder and arm pain as a sign for a heart attack

reflex

fast, automatic responses to stimuli that send information over a specific neural pathway

reflex arc

circuit of a reflex that involves a sensory input and motor output, or an afferent branch and an efferent branch, and an integrating center to connect the two branches

refractory period

time after the initiation of an action potential when another action potential cannot be generated

regional anatomy

study of the structures that contribute to specific body regions

Regulatory T cells (Treg)

(also, suppressor T cells) class of CD4 T cells that regulates other T cell responses

relative refractory period

time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K+ channels are not closed

relaxation phase

period after twitch contraction when tension decreases

remodeling

process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed

renal artery

branch of the abdominal aorta; supplies each kidney

renal columns

extensions of the renal cortex into the renal medulla; separates the renal pyramids; contains blood vessels and connective tissues

renal corpuscle

consists of the glomerulus and Bowman’s capsule

renal cortex

outer part of kidney containing all of the nephrons; some nephrons have loops of Henle extending into the medulla

renal fat pad

adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidney

renal hilum

recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass

renal medulla

inner region of kidney containing the renal pyramids

renal papillae

medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces

renal pyramids

six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons

renal vein

largest vein entering the inferior vena cava; drains the kidneys and leads to the inferior vena cava

renin

enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyzes the conversion of angiotensinogen into angiotensin I

repolarization

return of the membrane potential to its normally negative voltage at the end of the action potential

reposition

movement of the thumb from opposition back to the anatomical position (next to index finger)

reserve zone

region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis

residual volume (RV)

amount of air that remains in the lungs after maximum exhalation

resistance (axons)

property of an axon that relates to the ability of particles to diffuse through the cytoplasm; this is inversely proportional to the fiber diameter

resistance (blood flow)

any condition or parameter that slows or counteracts the flow of blood

respiratory acidosis

condition wherein an excess of carbonic acid or CO2 causes the blood to be overly acidic

respiratory alkalosis

condition wherein a deficiency of carbonic acid/CO2 levels causes the blood to be overly alkaline

respiratory bronchiole

specific type of bronchiole that leads to alveolar sacs

respiratory cycle

one sequence of inspiration and expiration

respiratory epithelium

ciliated lining of much of the conducting zone that is specialized to remove debris and pathogens, and produce mucus

respiratory membrane

alveolar and capillary wall together, which form an air-blood barrier that facilitates the simple diffusion of gases

respiratory pump

increase in the volume of the thorax during inhalation that decreases air pressure, enabling venous blood to flow into the thoracic region, then exhalation increases pressure, moving blood into the atria

respiratory rate

total number of breaths taken each minute

respiratory volume

varying amounts of air within the lung at a given time

respiratory zone

includes structures of the respiratory system that are directly involved in gas exchange

response

nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli

rest and digest

set of functions associated with the parasympathetic system that lead to restful actions and digestion

resting membrane potential

the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV

reticular fiber

fine fibrous protein, made of collagen subunits, which cross-link to form supporting “nets” within connective tissue

reticular formation

diffuse region of gray matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness

reticular layer

deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibers

reticular tissue

type of loose connective tissue that provides a supportive framework to soft organs, such as lymphatic tissue, spleen, and the liver

reticulocyte

immature erythrocyte that may still contain fragments of organelles

reticuloendothelial cell

(also, Kupffer cell) phagocyte in hepatic sinusoids that filters out material from venous blood from the alimentary canal

reticulospinal tract

extrapyramidal connections between the brain stem and spinal cord that modulate movement, contribute to posture, and regulate muscle tone

retina

nervous tissue of the eye at which phototransduction takes place

retinacula

fibrous bands that sheath the tendons at the wrist

retinal

cofactor in an opsin molecule that undergoes a biochemical change when struck by a photon (pronounced with a stress on the last syllable)

retinal ganglion cell (RGC)

neuron of the retina that projects along the second cranial nerve

retraction

posterior motion of the scapula or mandible

retrograde amnesia

loss of memories before a particular event

retroperitoneal

located outside the peritoneal cavity, between the parietal peritoneum and the abdominal wall

Rh blood group

blood-type classification based on the presence or absence of the antigen Rh on the erythrocyte membrane surface

rhodopsin

photopigment molecule found in the rod photoreceptors

rhombencephalon

primary vesicle of the embryonic brain that develops into the hindbrain, which includes the pons, cerebellum, and medulla

rhomboid major

muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae

rhomboid minor

muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae

ribonuclease

pancreatic enzyme that digests RNA

ribonucleic acid (RNA)

ribose-containing nucleotide that helps manifest the genetic code as protein

ribosomal RNA (rRNA)

RNA that makes up the subunits of a ribosome

ribosome

cellular organelle that functions in protein synthesis

ribs

thin, curved bones of the chest wall

rickets

disease in children caused by vitamin D deficiency, which leads to the weakening of bones

right atrioventricular valve

(also, tricuspid valve) valve located between the right atrium and ventricle; consists of three flaps of tissue

right colic flexure

(also, hepatic flexure) point, at the inferior surface of the liver, where the ascending colon turns abruptly to the left

right gastric artery

branch of the common hepatic artery; supplies blood to the stomach

right lymphatic duct

drains lymph fluid from the upper right side of body into the right subclavian vein

Rinne test

use of a tuning fork to test conductive hearing loss versus sensorineural hearing loss

rod photoreceptor

one of the two types of retinal receptor cell that is specialized for low-light vision

Romberg test

test of equilibrium that requires the patient to maintain a straight, upright posture without visual feedback of position

root of the nose

region of the external nose between the eyebrows

root of the teeth

portion of a tooth embedded in the alveolar processes beneath the gum line

rotation

movement of a bone around a central axis (atlantoaxial joint) or around its long axis (proximal radioulnar joint; shoulder or hip joint); twisting of the vertebral column resulting from the summation of small motions between adjacent vertebrae

rotator cuff

strong connective tissue structure formed by the fusion of four rotator cuff muscle tendons to the articular capsule of the shoulder joint; surrounds and supports superior, anterior, lateral, and posterior sides of the humeral head

round window

membrane that marks the end of the scala tympani

rubrospinal tract

descending motor control pathway, originating in the red nucleus, that mediates control of the limbs on the basis of cerebellar processing

ruga

fold of alimentary canal mucosa and submucosa in the empty stomach and other organs

rugae

(of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth

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