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Homeostasis Key Words


A protein that interacts with myosin to generate tension during muscle contraction

Action Potential

A brief reversal of membrane potential that occurs during the passage of a nerve impulse


Hormone that promotes the release of glucose into the blood in emergencies.


Hormone produced by the adrenal medulla.

Afferent (sensory) Neurone

A neuron carrying impulses from a receptor to the CNS

Ambient Conditions

Environmental conditions.

Amino Acids

Sub-units of proteins, which after deamination, can be converted into glucose.

Anterior Pituitary

Secretes hormones such as growth hormone; TSH; the gonadotrophins; prolactin; ATCH etc.


A threadlike extension of a neuron that transmits impulses

Basal Metabolic Rate

The rate of metabolism needed to support functions essential to life, such as protein synthesis and active transport.

Central Nervous System (CNS)

The brain and spinal chord


Heat transferred by collision between molecules or atoms.


A threadlike part of a neuron that receives information


The inner layer of the skin, containing tissues important in temperature regulation.

Diabetes Melitus

Disease in which the blood glucose level is abnormally high because most of the cells cannot use it.


Able to raise body temperature above that of the environment only by absorbing solar heat.


A cell or organ that produces a physiological response when stimulated by a nerve impulse; usually a muscle or gland.

Efferent (motor) Neurone

Neuron carrying impulses from the CNS to an effector

Endocrine Gland

A gland that secretes its product into the blood rather than into a duct

Endocrine System

Communication system concerned with long-lasting responses


Able to use metabolic heat to raise body temperature above that of the environment.


The outer layer of skin, chief function is protection.


The process by which water turns into steam.

Extracellular Fluid

The liquid outside the cell, in vertebrates this is blood plus tissue fluid


A hormone that promotes the release of glucose into the blood by the liver.

Glucose Transporter

Membrane protein that carries out facilitated diffusion of glucose into cells.


Polysaccharide stored in liver and muscle, can be hydrolysed to glucose.


Swelling of the thyroid gland, usually brought on by a deficiency of iodine in the diet.


The maintenance of near-constant conditions inside an organism


Able to regulate body temperature.


A chemical secreted into the blood, changing the activity of cells in other parts of the body, a chemical messenger


State in which blood glucose level is abnormally high.


Abnormally high body temperature.


State in which blood glucose level is abnormally low.


Part of the vertebrate brain responsible for monitoring hormone levels and indirectly regulating many functions, including food and fluid intake, body temperature and sleep.


Abnormally low body temperature.

Infrared Radiation

Electromagnetic radiation that is felt as heat.


Hormone that promotes the utilisation of glucose and hence the reduction of its blood concentration.

Internal Environment

In multicellular animals, the liquid bathing the cells (tissue fluid in vertebrates).


A neuron connecting the afferent and efferent neurons

Islets of Langerhans

Groups of cells in the pancreas; secrete insulin and glucagon.


Fat storage cells under the skin (also known as adipocytes).


The protective membrane around the brain and spinal chord


The insulating material surrounding larger axons, formed by layers of plasma membrane of Schwann cells


One of the many contractile units in a skeletal muscle fibre


A protein that interacts with actin to generate tension during muscle  contraction


Under-activity of the thyroid gland.

Negative Feedback

Process in which the greater the change, the stronger the tendency to correct it. The output is used to reduce the input.

Nervous System

A communication system concerned with rapid responses in animals

Neuromuscular Junction

The point at which a motor nerve axon comes into near contact with a muscle fibre


A nerve cell


A chemical by which information is carried from one neuron to another across a synapse

Node of Ranvier

The gap between Schwann cells, and the point at which action potentials occur

Peripheral Nervous System

The cranial and spinal nerves

Pituitary Gland

A pea-sized endocrine gland attached by a thin stalk to the hypothalamus at the base of the brain. Consists of the anterior and the posterior.


Body temperature varies with that of the environment.

Positive Feedback

Rare in physiological systems, leads to a response escalating in the same direction. E.g. labour, lactation, fever and blood slotting.

Posterior Pituitary

Secretes the hormones oxytocin and antidiuretic hormone.


Energy travelling in the form of electromagnetic waves.


Structures that detect change.

Reflex Action

An automatic response to a stimulus

Refractory Period

Brief period after an action potential during which an axon cannot undergo another action potential

Resting Potential

The potential difference across the plasma membrane of an inactive neuron or muscle cell


The plasma membrane of a muscle fibre

Sarcoplasmic Reticulum

The endoplasmic reticulum of a muscle fibre, releases Ca2+ ions to trigger contractions

Set Point

The point at which a particular variable is regulated.


The gap between two neurons across which a neurotransmitter diffuses

Target Cell

Cell whose activity is changed by a hormone because it contains a specific receptor molecule for that hormone.


A steady contraction produced in response to a volley of impulses


Receptor sensitive to changes in temperature.


The process of controlling the body’s temperature.


The minimum strength of a stimulus needed to develop an action potential


Hormone secreted by the thyroid gland; stimulates metabolism, and thus heat production.


Thyroid Stimulating Hormone (thyrotropin), secreted by the anterior pituitary gland.


Transverse tubule. Intuckings of sarcolemma carrying action potentials into the interior of a muscle fibre


A short contraction produced in response to a single nerve impulse


The reduction in the internal diameter of blood vessels.


The increase in the internal diameter of blood vessels.

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Neurotransmitter produced by an enzyme in the body that stimulates muscle tissue.


hormone produced by the adrenal medulla that causes vasodilation of the small arteries in muscle and increases cardiac output.


substance that has an effect similar to that of adrenaline.


substance that cancels or counteracts the action of another.


the smallest vessels of the body.

Central nervous system (CNS)

one of two major divisions of the nervous system. The CNS consists of the brain, the cranial nerves and the spinal cord.


substance that has an effect similar to that of acetylcholine.


heat transfer by means of molecular agitation within a material without any motion of the material as a whole. If one end of a metal piece is at a higher temperature, then heat will be transferred down the piece toward the colder end.


heat transfer by motion of a fluid when the heated fluid is caused to move away from the source of heat, carrying energy with it.


layer of connective tissue underlying the skin. Contains smooth muscle tissue, nervous tissue and blood vessels.

Endocrine glands

glands that secrete substances which are released directly into the bloodstream and that regulate metabolism and other body functions.

Endocrine system

the system of glands in the body that secrete their hormones directly into the circulatory system.


 type of protein produced by the body that speeds up chemical reactions. Some enzymes regulate certain functions due to their ability to change their activity by modifying their structure.

Extracellular fluid (ECF)

the fluid found outside of the cells and between the cells in body tissues.

Feedback system 

feedback system uses as input the total or partial output of the system. Feedback systems are used to control and regulate processes. They use the consequences of the process (for example, too much or too little produced) to regulate the rate at which the process occurs (decrease or increase the rate of the process).


stability of the body's internal environment, achieved by a system of integrated control systems activated by feedback systems. Homeostasis is thus the maintenance of a constant internal environment (the immediate surroundings of cells) in response to changes occurring in the conditions of the external environment and the conditions of the internal body environment.


naturally occurring substance secreted by specialized cells that affects the metabolism or behavior of other cells possessing receptors for the hormone.


the hypothalamus is a tiny cluster of brain cells just above the pituitary gland, that is involved in the regulation of body temperature.

Metabolic effectors

substances, such as hormones, that can increase the metabolism of the body or of a target organ.


the sum of all the physical and biochemical processes occurring in the body to produce what is required to maintain life. This includes the transformation of nutrients into energy and the use of energy by the body.

Nervous system

the entire system of nerve tissue in the body. It includes the brain, the brainstem, the spinal cord, the nerves and the ganglia and is divided into the peripheral nervous system (PNS) and the central nervous system (CNS).

Peripheral nervous system (PNS)ne of the two major divisions of the nervous system. The PNS consists of the somatic nervous system (SNS), that controls voluntary activities and of the autonomic nervous system (ANS), that controls regulatory activities. The ANS is further divided into sympathetic and parasympathetic systems.


heat transfer that occurs by the emission of electromagnetic waves which carry energy away from the emitting object.


production of heat.


regulation of body temperature so as to maintain it nearly constant at 98.6°F (37°C).

Thyroid gland 

butterfly-shaped endocrine gland located in the neck on both sides of the windpipe. It controls the rate at which the body produces energy from nutrients. It secretes the hormones triiodothyronine (T3) and thyroxine (T4) which increase the rate of metabolism and cardiac output.


the decrease in the internal diameter of a blood vessel resulting from tightening the smooth muscle located in the walls of the vessel. Vasoconstriction decreases the blood flow.


the increase in the internal diameter of a blood vessel resulting from relaxation of the smooth muscle located in the walls of the vessel. Vasodilation increases the blood flow.

Vasomotor system

the neural systems which act on vascular smooth muscle to control blood vessel diameter.