Acetylcholine: neurotransmitter released from vesicles in the end plates of neurons, which makes the postsynaptic membranes more permeable to Na⁺ ions

Action potential: the voltage difference across a nerve cell membrane when the nerve is excited

Adrenal cortex: outer region of the adrenal gland that produces glucocorticoids and mineralocorticoids

Adrenal medulla: found at the core of the adrenal gland, the adrenal medulla produces epinephrine and norepinephrine

Afferent arterioles: small branches that carry blood to the glomerulus.

Aldesterone: hormone that increases Na⁺ reabsorption from the distal tubule and collecting duct

Anabolic steroids: substances that are designed to mimic many of the muscle-building traits of the sex hormone testosterone

Antidiuretic hormone (ADH): causes the kidney to increase water reabsorption

Axon: extension of cytoplasm that carries nerve impulses away from the cell body

Bowmans capsule: cuplike structure that surrounds the glomerulus.

Calcitonin: hormone produced by the thyroid gland that lowers calcium levels in the blood

Central nervous system (CNS): the bodys coordinating center for mechanical and chemical actions; made up of the brain and spinal cord

Cerebellum: part of the hindbrain that controls limb movements, balance, and muscle tone

Cerebral cortex: outer lining of the cerebral hemispheres

Cerebrospinal fluid: cushioning fluid that circulates between the innermost and middle membranes of the brain and spinal cord; it provides a connection between neural and endocrine systems

Cerebrum: largest and most highly developed part of the human brain, which stores sensory information and initiates voluntary motor activities

Cholinesterase: enzyme, which breaks down acetylcholine that is released from postsynaptic membranes in the end plates of neurons shortly after acetylcholine

Collecting duct: tube that carries urine from nephrons to the pelvis of a kidney.

Contractile vacuole: a structure in unicellular organisms that maintains osmotic equilibrium by pumping fluid out from the cell.

Corpus callosum: nerve tract that joins the two cerebral hemispheres

Corpus luteum: a mass of follicle cells that forms within the ovary after ovulation; secretes estrogen and progesterone

Cortex: outer layer of the kidney.

Cortisol: hormone that stimulates the conversion of amino acids to glucose by the liver