Biology Key Terms and Definitions

A comprehensive set of flashcards covering key biological terms and their definitions for exam preparation.

action potential

A momentary change in the electrical potential of a neuron (or muscle) membrane.

adrenal gland

The endocrine gland associated with the kidneys.

alveolus

The terminal structure of the lung passage where gas exchange occurs.

amygdala

A structure within the limbic system that processes fear.

amylase

An enzyme found in saliva and secreted by the pancreas that converts carbohydrates to maltose.

anus

The exit point of the digestive system for waste material.

aorta

The major artery that takes blood away from the heart to the systemic circulatory system.

appendicular skeleton

The skeleton composed of the bones of the upper limbs and lower limbs.

artery

A blood vessel that takes blood away from the heart.

atrium

A chamber of the heart that receives blood from the veins.

auditory ossicles

The bones that transduce sounds from the air into vibrations in the fluid-filled cochlea.

autonomic nervous system

The part of the peripheral nervous system that controls bodily functions.

axial skeleton

Skeleton that forms the central axis of the body.

axon

A tube-like structure that propagates a signal from a neuron’s cell body to axon terminals.

basal ganglia

An interconnected collection of cells in the brain involved in movement and motivation.

bicuspid valve

A one-way opening between the atrium and the ventricle in the left side of the heart.

bile

A digestive juice produced by the liver; important for digestion of lipids.

bolus

A mass of food resulting from the chewing action and wetting by saliva.

brainstem

A portion of the brain that connects with the spinal cord and controls basic functions.

bronchi

Smaller branches of cartilaginous tissue that stem off of the trachea.

bronchiole

An airway that extends from the main bronchus to the alveolar sac.

capillary

The smallest blood vessel that allows the passage of individual blood cells.

cardiac cycle

The filling and emptying of the heart of blood caused by electrical signals.

cardiac muscle tissue

The muscle tissue found only in the heart.

cartilaginous joint

A joint in which the bones are connected by cartilage.

central nervous system (CNS)

The nervous system made up of the brain and spinal cord.

cerebellum

The brain structure involved in posture, motor coordination, and learning new motor actions.

cerebral cortex

The outermost sheet of brain tissue involved in higher-order functions.

cerebrospinal fluid (CSF)

A clear liquid that surrounds the brain and acts as a shock absorber.

chyme

A mixture of partially digested food and stomach juices.

closed circulatory system

A system that keeps blood separated from bodily interstitial fluid.

colon

The largest portion of the large intestine.

corpus callosum

A thick nerve bundle that connects the cerebral hemispheres.

dendrite

A structure that extends from the cell body to receive messages from other neurons.

depolarization

A change in membrane potential to a less negative value.

diaphragm

A skeletal muscle located under the lungs that encloses the lungs in the thorax.

diastole

The relaxation phase of the cardiac cycle.

down-regulation

A decrease in the number of hormone receptors in response to increased hormone levels.

ectotherm

An organism that relies primarily on environmental heat sources.

electrocardiogram (ECG)

A recording of the electrical impulses of the cardiac muscle.

endocrine gland

The gland that secretes hormones into the surrounding interstitial fluid.

endotherm

An organism that relies primarily on internal heat sources to maintain its temperature.

esophagus

A tubular organ connecting the mouth to the stomach.

essential nutrient

A nutrient that cannot be synthesized by the body.

exocrine gland

The gland that secretes chemicals through ducts.

fibrous joint

A joint held together by fibrous connective tissue.

frontal lobe

The part of the cerebral cortex involved in planning and attention.

gallbladder

The organ that stores and concentrates bile.

glia (glial cells)

The cells that provide support functions for neurons.

hippocampus

The brain structure involved in processing memories.

hormone

A chemical released by cells in one area that affects cells in other areas.

hyoid bone

The bone that lies below the mandible in the neck.

hypothalamus

The brain structure that controls hormone release and body homeostasis.

inferior vena cava

The major vein returning blood from the lower body to the right atrium.

interstitial fluid

The fluid found between cells in the body.

intracellular hormone receptor

A hormone receptor in the cytoplasm or nucleus of a cell.

joint

The point at which two or more bones meet.

kidney

The organ performing excretory and osmoregulatory functions.

large intestine

An organ that reabsorbs water and processes waste material.

larynx

The voice box located within the throat.

limbic system

A connected brain area that processes emotion and motivation.

liver

An organ that produces bile for digestion.

membrane potential

A difference in electrical potential between the inside and outside of a cell.

meninges

The membranes covering and protecting the central nervous system.

mineral

An inorganic, elemental molecule that carries out important roles in the body.

myelin sheath

A cellular extension that surrounds and insulates axons.

myofibril

Long cylindrical structures parallel to the muscle fiber.

myofilament

Small structures that make up myofibrils.

nasal cavity

An opening of the respiratory system to the outside environment.

nephron

The functional unit of the kidney.

neuron

A specialized cell that can receive and transmit electrical and chemical signals.

occipital lobe

The part of the cerebral cortex that processes visual stimuli.

open circulatory system

A system where blood is mixed with interstitial fluid.

oral cavity

The point of entry of food into the digestive system.

osmoregulation

The mechanism maintaining water and solute concentrations.

osmotic balance

The appropriate values of water and solute concentrations.

pancreas

An organ that secretes digestive juices.

parasympathetic nervous system

The division regulating visceral functions during relaxation.

parathyroid gland

The gland producing parathyroid hormone.

parietal lobe

The part of the cerebral cortex involved in processing touch.

pectoral girdle

The bones transmitting force from upper limbs to the axial skeleton.

pelvic girdle

The bones transmitting force from lower limbs to the axial skeleton.

pepsin

An enzyme found in the stomach for protein digestion.

peripheral nervous system (PNS)

The nervous system connecting CNS with the rest of the body.

peristalsis

Wave-like movements of muscle tissue.

pharynx

The throat.

pituitary gland

The endocrine gland located at the base of the brain.

primary bronchus

A region of the airway that attaches to the trachea.

pulmonary circulation

The flow of blood through the lungs for oxygenation.

rectum

The area where feces is stored until elimination.

renal artery

The artery delivering blood to the kidney.

renal vein

The vein draining blood from the kidney.

salivary gland

Glands in the mouth secreting saliva.

sarcolemma

The plasma membrane of a skeletal muscle fiber.

sarcomere

The functional unit of skeletal muscle.

sensory-somatic nervous system

The system of sensory and motor nerves.

set point

The target value for a physiological state in homeostasis.

skeletal muscle tissue

Tissue forming skeletal muscles controlling locomotion.

skull

The bone that supports the face and protects the brain.

small intestine

The organ where digestion is completed.