Body Systems

Body system

A group of organs that work together to perform a specific function.

Homeostasis

The maintenance of a stable internal environment inside the body.

Digestive system

Breaks food into small molecules that can be absorbed and used by cells.

Physical digestion

Breaks food into smaller pieces without changing its chemical composition.

Chemical digestion

Uses enzymes to break large food molecules into smaller molecules.

Enzyme

A protein that speeds up chemical reactions.

Amylase

An enzyme that breaks down starch.

Protease

An enzyme that breaks down proteins.

Lipase

An enzyme that breaks down fats.

Mouth

Teeth chew food, the tongue mixes food, and saliva begins starch digestion.

Saliva

Moistens food and contains amylase, which begins starch digestion.

Oesophagus

A muscular tube that moves food to the stomach using peristalsis.

Peristalsis

Wave-like muscle contractions that push food through the digestive system.

Stomach

Stores food, churns it, produces acid, starts protein digestion and kills many microorganisms.

Liver

Produces bile, processes nutrients, stores glucose and removes toxins from the blood.

Bile

Breaks large fat droplets into smaller droplets to help digest fats.

Small intestine

The main site of chemical digestion and nutrient absorption.

Villi

Tiny finger-like projections in the small intestine that increase surface area for absorption.

Large intestine

Absorbs water and minerals and forms faeces.

Rectum

Stores faeces before they leave the body.

Digestive system and endocrine system

The endocrine system releases hormones that regulate hunger, digestion and blood sugar.

Digestive system and excretory system

The excretory system removes wastes and excess water after nutrients have been absorbed.

Excretory system

Removes wastes, excess water and salts to maintain homeostasis.

Kidneys

Filter blood, remove wastes, control water and salt levels, and produce urine.

Bladder

Stores urine until it is released.

Urethra

Carries urine from the bladder out of the body.

Endocrine system

Controls body activities using hormones.

Hormone

A chemical messenger carried through the bloodstream to target organs.

Nervous system vs endocrine system

Nervous system uses electrical impulses and is fast with short-term effects. Endocrine system uses hormones and is slower with longer-lasting effects.

Hypothalamus

Links the nervous and endocrine systems, controls the pituitary gland and helps maintain homeostasis.

Pituitary gland

The "master gland" that controls growth, reproduction and water balance.

Thyroid gland

Controls metabolism, growth and energy use.

Pancreas

Regulates blood glucose by releasing insulin and glucagon.

Adrenal glands

Produce adrenaline and other hormones involved in the stress response.

Ovaries

Produce oestrogen and progesterone.

Testes

Produce testosterone.

Adrenaline

A hormone that prepares the body for action during stress.

Nervous system

Controls and coordinates body activities using electrical impulses.

Central nervous system (CNS)

The brain and spinal cord.

Peripheral nervous system (PNS)

All nerves outside the brain and spinal cord that carry messages between the body and the CNS.

Brain

Processes information, controls movement, stores memories, regulates emotions and controls body functions.

Spinal cord

Carries messages between the brain and body and controls some reflexes.

Vertebral column

Protects the spinal cord.

Neuron

A specialised nerve cell that carries electrical impulses.

Dendrites

Receive messages from other neurons.

Cell body

Contains the nucleus and controls the neuron.

Axon

A long fibre that carries impulses away from the cell body.

Axon terminals

Pass impulses to the next neuron, muscle or gland.

Sensory neuron

Carries messages from receptors to the central nervous system.

Interneuron

Connects sensory neurons to motor neurons within the central nervous system.

Motor neuron

Carries messages from the central nervous system to muscles or glands.

Stimulus

A change in the environment that causes a response.

Receptor

A specialised cell that detects a stimulus.

Response

The body's reaction to a stimulus.

Pathway of a nerve impulse

Stimulus → Receptor → Sensory neuron → CNS → Motor neuron → Response.

Homeostasis example

If body temperature rises, receptors detect the change, the brain processes it, and sweat glands produce sweat.