Abdomen
The region of the trunk between the diaphragm and the pelvis. It houses most of the digestive organs along with the spleen, kidneys, and major blood vessels.
Medical Glossary
Comprehensive A-Z dictionary of anatomical and medical terms.
A
Abduction
A movement that draws a body part away from the midline of the body, such as raising the arm sideways.
Actin
A thin contractile protein in muscle fibers that slides against myosin during contraction, forming the basis of the sliding filament mechanism.
Adduction
A movement that brings a body part back toward the midline of the body, the opposite of abduction.
Alveolus
A tiny air sac at the end of the smallest bronchioles in the lungs where gas exchange between air and blood takes place.
Anatomical Position
The standard reference posture in anatomy: standing upright, facing forward, arms at the sides with palms turned forward. All directional terms assume this position.
Anterior
A directional term meaning toward the front of the body. Also called ventral in humans.
Aorta
The largest artery in the body. It leaves the left ventricle and distributes oxygen-rich blood to the entire systemic circulation.
Artery
A blood vessel that carries blood away from the heart. Most arteries carry oxygenated blood, the pulmonary artery being the main exception.
Atrium
One of the two upper chambers of the heart that receive blood returning from the body (right atrium) or the lungs (left atrium).
Axon
The long, single projection of a neuron that conducts electrical impulses away from the cell body toward other cells.
B
Biceps Brachii
A two-headed muscle on the front of the upper arm that flexes the elbow and supinates the forearm.
Bronchi
The two main airways branching from the trachea, each leading into a lung and dividing further into smaller bronchioles.
C
Capillary
The smallest blood vessels, forming networks between arterioles and venules where the exchange of oxygen, nutrients, and waste occurs.
Cardiac Muscle
The involuntary, striated muscle tissue found only in the heart wall, capable of rhythmic, self-generated contraction.
Cartilage
A firm yet flexible connective tissue that cushions joints, shapes structures like the ear and nose, and serves as a template for bone growth.
Cerebellum
The part of the brain at the back of the skull that coordinates voluntary movement, balance, and motor learning.
Cerebrum
The largest part of the brain, divided into two hemispheres and responsible for higher functions such as thought, memory, and voluntary action.
Coronal Plane
A vertical plane that divides the body into anterior (front) and posterior (back) portions. Also called the frontal plane.
Coronary Arteries
The arteries that branch from the aorta to supply the heart muscle itself with oxygenated blood.
Cranium
The portion of the skull that encloses and protects the brain, formed by several fused flat bones.
D
Dendrite
A branching extension of a neuron that receives incoming signals and carries them toward the cell body.
Dermis
The thick inner layer of skin beneath the epidermis, containing blood vessels, nerves, hair follicles, and glands.
Diaphragm
A dome-shaped sheet of muscle separating the thoracic and abdominal cavities; its contraction is the main driver of inhalation.
Diaphysis
The long, central shaft of a long bone, composed mainly of compact bone surrounding the marrow cavity.
Diastole
The phase of the heartbeat during which the heart muscle relaxes and the chambers fill with blood.
Distal
A directional term meaning farther from the trunk or point of origin of a limb, such as the wrist relative to the elbow.
E
Endocardium
The thin inner lining of the heart chambers and valves that is in direct contact with the blood.
Endocrine System
The network of glands that release hormones directly into the bloodstream to regulate metabolism, growth, and other body processes.
Epidermis
The outermost layer of the skin, providing a waterproof barrier and producing the pigment melanin.
Epiphysis
The rounded end of a long bone, separated from the shaft by the growth plate during development.
Extension
A movement that increases the angle at a joint, such as straightening the elbow or knee.
F
Femur
The thigh bone, the longest and strongest bone in the body, articulating at the hip and the knee.
Flexion
A movement that decreases the angle at a joint, such as bending the elbow to bring the forearm toward the upper arm.
G
Ganglion
A cluster of nerve cell bodies located outside the central nervous system, serving as a relay point for nerve signals.
Glomerulus
A tuft of tiny capillaries within each nephron of the kidney where blood is first filtered to begin urine formation.
H
Hemoglobin
The iron-containing protein in red blood cells that binds oxygen in the lungs and releases it to the tissues.
Hormone
A chemical messenger secreted by an endocrine gland that travels through the blood to influence the activity of distant target cells.
Humerus
The single bone of the upper arm, forming the shoulder joint above and the elbow joint below.
Hypothalamus
A small region beneath the thalamus that links the nervous and endocrine systems and regulates temperature, hunger, and hormone release.
I
Inferior
A directional term meaning toward the lower part of the body or below another structure.
Integumentary System
The organ system consisting of the skin and its appendages (hair, nails, and glands) that protects the body and regulates temperature.
Intestine
The long tubular portion of the digestive tract, divided into the small intestine (digestion and absorption) and large intestine (water absorption).
J
Jugular Veins
The major veins of the neck that drain deoxygenated blood from the head and brain back toward the heart.
K
Kidney
One of a pair of bean-shaped organs that filter waste from the blood, balance fluids and electrolytes, and produce urine.
L
Larynx
The voice box, a cartilaginous structure in the neck that houses the vocal cords and guards the entrance to the lower airway.
Lateral
A directional term meaning farther from the midline of the body, toward the side.
Ligament
A band of tough fibrous connective tissue that connects bone to bone and stabilizes joints.
Liver
The largest internal organ, located in the upper right abdomen, responsible for metabolism, detoxification, and bile production.
M
Mandible
The lower jawbone, the only movable bone of the skull, which anchors the lower teeth.
Medial
A directional term meaning closer to the midline of the body.
Median Plane
The midline sagittal plane that divides the body into equal right and left halves.
Mediastinum
The central compartment of the thoracic cavity between the lungs, containing the heart, great vessels, trachea, and esophagus.
Mitral Valve
The two-leaflet valve between the left atrium and left ventricle that prevents backflow of blood into the atrium. Also called the bicuspid valve.
Myocardium
The thick, muscular middle layer of the heart wall that generates the force of each contraction.
Myosin
A thick contractile protein in muscle whose heads pull on actin filaments to shorten the sarcomere during contraction.
N
Nephron
The functional filtering unit of the kidney; each kidney contains about a million nephrons that produce urine.
Nerve
A bundle of axons wrapped in connective tissue that transmits electrical impulses between the central nervous system and the rest of the body.
Neuron
The basic signaling cell of the nervous system, consisting of a cell body, dendrites, and an axon.
O
Occipital Bone
The bone forming the back and base of the skull, containing the opening through which the spinal cord passes.
Osteoblast
A bone-forming cell that produces and deposits new bone matrix during growth and repair.
Osteoclast
A large cell that breaks down and reabsorbs bone tissue, allowing bone to be remodeled and reshaped.
P
Pancreas
A gland behind the stomach with dual roles: secreting digestive enzymes into the intestine and releasing insulin and glucagon into the blood.
Parasympathetic Nervous System
The division of the autonomic nervous system that promotes rest, digestion, and energy conservation.
Pericardium
The double-layered sac surrounding the heart that protects it and reduces friction during beating.
Periosteum
The tough membrane covering the outer surface of bones, carrying blood vessels and nerves and supporting bone growth and repair.
Peristalsis
The wave-like muscular contractions that move food and other contents through the digestive tract.
Posterior
A directional term meaning toward the back of the body. Also called dorsal.
Proximal
A directional term meaning closer to the trunk or point of origin of a limb, such as the elbow relative to the wrist.
Pulmonary Artery
The artery that carries deoxygenated blood from the right ventricle to the lungs; the only artery that carries oxygen-poor blood.
Pulmonary Veins
The veins that return oxygen-rich blood from the lungs to the left atrium; the only veins that carry oxygenated blood.
Q
Quadriceps
The four-part muscle group at the front of the thigh that extends the knee and stabilizes the kneecap.
R
Retina
The light-sensitive inner layer at the back of the eye that converts light into nerve signals sent to the brain.
Rotation
A movement in which a body part turns around its own axis, such as turning the head from side to side.
S
Sagittal Plane
A vertical plane that divides the body into right and left portions.
Sarcomere
The repeating contractile unit of skeletal and cardiac muscle, bounded by Z-lines and containing actin and myosin filaments.
Skeletal Muscle
Voluntary, striated muscle attached to bones by tendons that produces movement of the skeleton.
Smooth Muscle
Involuntary, non-striated muscle found in the walls of internal organs and blood vessels.
Spinal Cord
The cylindrical bundle of nerve tissue running through the vertebral column that relays signals between the brain and the body.
Sternum
The flat breastbone in the center of the chest to which the ribs and collarbones attach.
Superior
A directional term meaning toward the upper part of the body or above another structure.
Sympathetic Nervous System
The division of the autonomic nervous system that prepares the body for stress, the so-called fight-or-flight response.
Synapse
The junction between two neurons, or between a neuron and a target cell, across which signals are transmitted by neurotransmitters.
Systole
The phase of the heartbeat during which the heart muscle contracts and pumps blood out of the chambers.
T
Tendon
A strong band of fibrous connective tissue that attaches muscle to bone and transmits the force of muscle contraction.
Thalamus
A central brain structure that acts as a relay station, directing most sensory information to the appropriate areas of the cerebral cortex.
Thorax
The chest region between the neck and abdomen, enclosed by the rib cage and containing the heart and lungs.
Thyroid Gland
A butterfly-shaped endocrine gland in the neck that produces hormones regulating metabolism, growth, and energy use.
Trachea
The windpipe; the cartilage-reinforced tube carrying air between the larynx and the bronchi.
Transverse Plane
A horizontal plane that divides the body into upper and lower portions. Also called the axial plane.
Tricuspid Valve
The three-leaflet valve between the right atrium and right ventricle that prevents backflow into the atrium.
U
Ulna
One of the two forearm bones, located on the little-finger side and forming the prominent point of the elbow.
V
Vein
A blood vessel that carries blood toward the heart. Most veins carry deoxygenated blood, the pulmonary veins being the exception.
Ventricle
One of the two lower chambers of the heart that pump blood to the lungs (right ventricle) or to the rest of the body (left ventricle).
Vertebra
One of the individual bones that stack to form the spinal column and protect the spinal cord.
Villus
One of the tiny finger-like projections lining the small intestine that vastly increase the surface area for nutrient absorption.
Z
Zygomatic Bone
The cheekbone, which forms the prominence of the cheek and part of the eye socket.