B3

Central nervous system (CNS)

The brain and spinal cord.

Sensory neurone

Carries impulses from receptors to the CNS.

Motor neurone

Carries impulses from the CNS to effectors.

Relay neurone

Connects sensory and motor neurones within the CNS.

Reflex action

A fast, automatic response that protects the body from harm.

Synapse

The gap between neurones where neurotransmitters pass impulses.

Hormone

A chemical messenger carried in the bloodstream.

Endocrine system

A system of glands that release hormones into the blood.

Pituitary gland

The master gland controlling other glands.

Pancreas

Produces insulin and glucagon to regulate blood glucose levels.

Insulin

Lowers blood glucose by causing cells to absorb glucose.

Glucagon

Raises blood glucose by causing the liver to release stored glucose.

Type 1 diabetes

The pancreas produces little or no insulin.

Type 2 diabetes

Body cells become resistant to insulin.

ADH

Hormone that controls water balance by increasing kidney water reabsorption.

Thyroxine

Hormone that controls metabolic rate.

Homeostasis

The maintenance of a stable internal environment.

Negative feedback

A process that reverses a change to restore normal conditions.

Vasodilation

Widening of blood vessels near the skin to increase heat loss.

Vasoconstriction

Narrowing of blood vessels near the skin to reduce heat loss.

FSH

Hormone that stimulates an egg to mature and triggers oestrogen release.

LH

Hormone that triggers ovulation.

Oestrogen

Thickens the uterine lining and inhibits FSH.

Progesterone

Maintains the uterine lining.

Hypothalamus

Part of the brain that controls body temperature.

Sweating

Cools the body by evaporation removing heat from the skin.