ITEC Anatomy & Physiology key terms

The thin, selectively permeable outer boundary of a cell, made of a phospholipid bilayer with embedded proteins, that controls which substances enter and leave and helps hold the cell together.

A membrane-bound organelle in which aerobic respiration takes place, converting glucose and oxygen into ATP, the energy currency used for cellular work such as muscle contraction.

The passive movement of particles from an area of higher concentration to an area of lower concentration, driven by random molecular motion and requiring no energy input from the cell.

The passive movement of water across a selectively permeable membrane from a dilute solution toward a more concentrated one, until concentrations on both sides become more equal.

A sheet-like tissue of closely packed cells that covers body surfaces, lines cavities and ducts, and forms glands, functioning in protection, absorption, secretion and filtration.

A group of tissues in which cells are widely spaced within an abundant extracellular matrix, binding, supporting and protecting other structures; examples include bone, cartilage, blood and adipose tissue.

A mature bone cell that sits in a small cavity called a lacuna within the hard matrix and maintains the surrounding bone tissue, communicating with neighbouring cells through tiny channels.

A bone-forming cell that secretes the organic components of bone matrix and later becomes trapped as an osteocyte, playing a central role in growth and repair.

The process by which new bone tissue is laid down, either replacing a cartilage model during growth or forming directly within membrane, and continuing in some form throughout life.

A layer of cartilage near the end of a long bone in a growing child where new cartilage is produced and then converted to bone, allowing the bone to lengthen until growth stops.

A bone that is longer than it is wide, with a shaft called the diaphysis and two expanded ends called epiphyses, such as the femur, humerus and tibia; it acts as a lever for movement.

A freely movable joint in which the bone ends are separated by a fluid-filled cavity lined by a capsule and lubricated by synovial fluid, as found at the knee, elbow and shoulder.

A tough band of dense fibrous connective tissue that joins one bone to another across a joint, limiting excessive movement and helping to stabilise the joint.

A strong cord of dense fibrous connective tissue that attaches a muscle to a bone, transmitting the pull generated by the muscle so that a joint moves.

The smallest contractile unit of a muscle fibre, extending between two Z lines and containing overlapping actin and myosin filaments whose sliding produces shortening of the muscle.

The two main contractile proteins of muscle: thin actin filaments are pulled past thicker myosin filaments, which form cross-bridges, so that the sarcomere shortens during contraction.

A muscle that produces the opposite movement to a given prime mover and relaxes as that muscle contracts, allowing controlled movement and returning the joint to its starting position.

Adenosine triphosphate, a molecule that stores chemical energy in its phosphate bonds and releases it when broken down, powering processes such as muscle contraction, active transport and synthesis.

A blood vessel that carries blood away from the heart under relatively high pressure; most arteries carry oxygenated blood, the pulmonary artery being the main exception.

A blood vessel that returns blood toward the heart at low pressure, usually carrying deoxygenated blood, and containing valves that help prevent backflow in the limbs.

The smallest blood vessel, a thin-walled tube only one cell thick in places, where exchange of oxygen, nutrients and waste between blood and tissue fluid takes place.

The sequence of events in one complete heartbeat, in which the atria and then the ventricles contract and relax, moving blood into the arteries and refilling the chambers.

The volume of blood pumped out by one ventricle in a minute, calculated by multiplying heart rate by stroke volume and used as a measure of how well the heart is working.

A small bean-shaped organ along lymphatic vessels that filters lymph and contains lymphocytes and macrophages, helping to remove pathogens and debris and to mount immune responses.

A network of vessels, nodes and organs that returns excess tissue fluid to the blood, transports absorbed fats from the gut, and supports immune defence against infection.

A tiny air sac at the end of the respiratory passages whose wall is one cell thick and surrounded by capillaries, providing a large moist surface for gas exchange.

A dome-shaped sheet of skeletal muscle separating the chest from the abdomen; when it contracts and flattens during inspiration it increases thoracic volume and draws air into the lungs.

The volume of air moved into or out of the lungs during one normal quiet breath, typically around half a litre in a resting adult.

The maximum volume of air that a person can breathe out after taking the deepest possible breath in, reflecting the combined working capacity of the lungs and chest wall.

A finger-like projection of the small intestinal lining that greatly increases surface area for absorption and contains blood capillaries plus a central lymph vessel called a lacteal.

A protein that speeds up a specific chemical reaction without being used up itself, for example a digestive enzyme that breaks a particular nutrient into smaller absorbable molecules.

Rhythmic waves of contraction by smooth muscle in the wall of a tube such as the oesophagus or intestine, which push contents forward along the digestive tract.

A specialised nerve cell that receives, conducts and transmits electrical impulses, consisting of a cell body, dendrites and usually a single axon with its terminals.

The junction between two neurons, or between a neuron and a muscle or gland, across which a signal passes by release of a chemical messenger rather than by direct electrical contact.

A chemical released from the end of a neuron into a synapse that carries the signal to the next cell by binding to receptors on its membrane, exciting or inhibiting it.

A chemical messenger secreted by an endocrine gland into the blood, which travels to distant target cells bearing matching receptors and alters their activity.

A control mechanism in which a change in a body variable triggers a response that opposes and reverses that change, keeping the variable close to a set point.

The maintenance of a relatively stable internal environment, such as steady temperature, blood glucose and pH, through coordinated detection of change and corrective responses by body systems.

The outer, avascular layer of the skin, made of stratified epithelium whose deepest cells divide and whose surface cells become filled with waterproof keratin before being shed.

A tough, waterproof protein produced by skin cells as they move toward the surface, giving the epidermis, hair and nails their strength and resistance to wear and water loss.

The visible hard part of a nail, formed from tightly packed keratinised cells produced by the nail matrix and resting on the nail bed, protecting the tip of the finger or toe.

The microscopic functional unit of the kidney, consisting of a filtering glomerulus and a tubule, which together remove wastes from blood and adjust water and salt balance.

The first stage of urine formation, in which blood pressure forces water and small dissolved substances out of the glomerular capillaries into the kidney tubule, while cells and large proteins stay behind.

The recurring series of hormonal changes in a female that thickens the lining of the uterus, releases an egg at ovulation, and sheds the lining as menstruation if pregnancy does not occur.