Key Terms

Key Terms

A-C

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

Bowman’s 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 body’s 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

D-F

Deamination: removal of an amino group from an organic compound.

Dendrites: projections of cytoplasm that carry impulses toward the cell body

Depolarization: diffusion of sodium ions into the nerve cell resulting in a charge reversal

Distal tubule: conducts urine from the loop of Henle to the collecting duct.

Dynamic equilibrium: condition that remains stable within fluctuating limits.

Efferent arterioles: small branches that carry blood away from the glomerulus to a capillary net.

Endocrine hormones: chemicals secreted by endocrine glands directly into the blood

Endorphins: natural painkillers belonging to a group of chemicals called neuropeptides; contain between 16 to 31 amino acids

Enkephalins: natural painkillers belonging to a group of chemicals called neuropeptides; contain 5 amino acids and are produced by the splitting of larger endorphin chains

Estrogen: female sex hormone that activates the development of female secondary sex characteristics, including development of the breasts and body hair, and increased thickening of the endometrium

Filtration: process by which blood or body fluids pass through a selectively permeable membrane

Flow phase: phase of the menstrual cycle marked by shedding of the endometrium

Follicles: structures in the ovary that contain the egg and secrete estrogen

Follicle-stimulating hormone (FSH): in females, a gonadotropin that promotes the development of the follicles in the ovary; in males, hormone that increases sperm production

Follicular phase: phase marked by development of ovarian follicles before ovulation

G-I

Ganglia: collections of nerve cell bodies located outside of the central nervous system

Glial cells: non-conducting cells important for structural support and metabolism of the nerve cells

Glomerulus: high-pressure capillary bed that is the site of filtration.

Glucagon: hormone produced by the pancreas; when blood sugar levels are low, glucagons promotes conversion of glycogen to glucose

Glucocorticoids: various hormones, produced by the adrenal cortex, designed to help the body meet the demands of stress

Goiter: disorder that causes an enlargement of the thyroid gland

Gonadotropic hormones: hormones produced by the pituitary gland that regulates the functions of the testes in males and the ovaries in females

Gonadotropin-releasing hormone (GnRH): chemical messenger from the hypothalamus that stimulates secretions of FSH and LH from the pituitary

Homeostasis: process by which a constant internal environment is maintained despite changes in the external environment.

Hormones: chemicals released by cells that affect cells in other parts of the body

Hyperpolarized: condition in which the inside of the nerve cell membrane becomes more negative than the resting potential

Hypothalamus: region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions.

Interstitial fluid: fluid that surrounds the body cells

J-L

Loop of Henle: carries filtrate from the proximal tubule to the distal tubule.

Luteal phase: phase of the menstrual cycle characterized by the formation of the corpus luteum following ovulation

Luteinizing hormone (LH): in females, a gonadotropin that promotes ovulation and the formation of the corpus luteum; in males, hormone that regulates the production of testosterone

M-O

Medulla oblongata: region of the hindbrain that joins the spinal cord to the cerebellum; one of the most important sites of autonomic nerve control

Medulla: area inside the cortex.

Meninges: protective membranes that surround the brain and spinal cord

Mineralocorticoids: hormones of the adrenal cortex important for regulation of salt-water balance

Motor neurons: neurons that carry impulses from the central nervous system to effectors; also known as efferent neurons

Myelin sheath: insulated covering over the axon of a nerve cell

Negative feedback: process by which a mechanism is activated to restore conditions to their original state.

Nephrons: functional units of the kidneys.

Neurilemma: delicate membrane that surrounds the axon of some nerve cells

Neurons: nerve cells that conduct nerve impulses

Neurotransmitters: chemicals released from vesicles into synapses

Nodes of Ranvier: regularly occurring gaps between sections of myelin sheath along the axon

Norepinephrine: also known as noradrenaline, it initiates the fight-or-flight response by increasing heart rate and blood sugar

Olfactory lobes: areas of the brain that process information about smell

Osmoreceptors: specialized nerve cells in the hypothalamus that detect changes in the osmotic pressure of the blood and surrounding extracellular fluids (ECF)

Ovulation: release of the egg from the follicle held within the ovary

P-R

Parasympathetic nervous system: nerve cells of the autonomic nervous system that return the body to normal resting levels after adjustments to stress

Parathyroid glands: four pea-sized glands in the thyroid gland that produces parathyroid hormone to regulate blood calcium and phosphate levels

Parathyroid hormone (PTH): hormone produced by the parathyroid glands, which will increase calcium levels in the blood and lower the levels of phosphate

Peripheral nervous system (PNS): all parts of the nervous system, excluding the brain and spinal cord, that relay information between the central nervous system and other parts of the body

Peritubular capillaries: network of small blood vessels that surround the nephron.

Pituitary gland: gland at the base of the brain that, together with the hypothalamus, functions as a control center, coordinating the endocrine and nervous system

Polarized membrane: membrane charged by unequal distribution of positively charged ions inside and outside the nerve cell

Pons: region of the brain that acts as a relay station by sending nerve messages between the cerebellum and the medulla

Positive feedback: process by which a small effect is amplified.

Postsynaptic neuron: neuron that carries impulses away from the synapse

Presynaptic neuron: neuron that carries impulses to the synapse

Progesterone: female sex hormone produced by the ovaries that maintain uterine lining during pregnancy

Prostaglandins: hormones that have a pronounced effect in a small localized area

Protein hormones: group of hormones composed of chains of amino acids, that include insulin and growth hormone

Proximal tubule: section of the nephron joining the Bowman’s capsule with the loop of Henle.

Reabsorption: transfer of glomerular filtrate from the nephron back into the capillaries

Reflex arc: neural circuit through the spinal cord that provides a framework for a reflex action

Refractory period: recovery time required before a neuron can produce another action potential

Renal pelvis: area where the kidney joins the ureter.

Repolarization: process of restoring the original polarity of the nerve membrane

Resting potential: voltage difference across a nerve cell membrane during the resting stage (usually negative)

S-U

Secretion: movement of materials, such as ammonia and some drugs, from the blood back into the distal tubule

Sensory neurons: neurons that carry impulses from sensory receptors to the central nervous system; also known as afferent neurons

Sodium-potassium pump: an active transport mechanism that moves sodium ions out of and potassium ions into a cell against their concentration gradients

Spermatogenesis: process by which spermatogonia divide and differentiate into mature sperm cells

Steroid hormone: group of hormones, made from cholesterol, that includes male and female sex hormones and cortisol

Summation: effect produced by the accumulation of neurotransmitters from two or more neurons

Sympathetic nervous system: nerve cells of the autonomic nervous system that prepare the body for stress

Synapses: regions between neurons, or between neurons and effectors

Testosterone: male sex hormone produced by the interstitial cells of the testes

Thalamus: area of brain that coordinates and interprets sensory information and directs it to the cerebrum

Thermoregulation: maintenance of body temperature within a range that enables cells to function efficiently.

Threshold level: maximum amount of material that can be moved across the nephron

Threshold level: minimum level of a stimulus required to produce a response

Thyroid gland: a tow-lobed gland at the base of the neck that regulates metabolic processes

Thyroxine: iodine-containing hormone, produced by the thyroid gland, that increases the rate of body metabolism and regulates growth

Urea: nitrogen waste from two molecules of ammonia and one molecule of carbon dioxide.

Ureters: tubes that conduct urine from the kidneys to the bladder.

Urethra: tube that carries urine from the bladder to the exterior of the body.

Uric acid: waste product formed from the breakdown of nucleic acids.

V-Z

Vagus nerve: major cranial nerve that is part of the parasympathetic nervous system

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