Systems and organs

Blood carries oxygen and nutrients to the cells of our body and helps us fight infection. Veins, arteries and capillaries are blood vessels that combine with the heart to make up the circulatory system.

Bones, muscles and joints hold our body together and support freedom of movement. They are part of the musculoskeletal system (also known as the locomotor system). Fractures, back pain and muscle strain are common conditions.

The brain, nerves and spinal cord form part of the nervous system. Nerve cells and chemicals called neurotransmitters help different parts of the body communicate. Tumours, seizures, headaches and brain disorders can affect the brain.

The digestive system turns food into nutrients that are absorbed by the body and removes waste. The mouth, oesophagus, stomach, small and large intestine, rectum and anus are involved.

The ear, nose and throat are part of the upper respiratory tract. They help us breathe, smell, hear, keep our balance, swallow and speak. Infections and conditions of the sinus, tonsils and adenoids affect these organs.

Our eyes allow us to see. The optic nerve carries images from the retina to the brain. Other eye parts include the cornea, iris, pupil, lens and sclera. Damage can cause vision loss or blindness.

The female reproductive system is involved in sexuality and fertility. It includes the vagina, womb (uterus), fallopian tubes and ovaries. Menstrual periods, ovulation, pregnancy, birth and menopause are part of the female reproductive cycle.

Genes are inherited and contain information that our cells use to control growth, development and health. Genetic changes disrupt these messages and can cause health problems. These may be present at birth or may appear later in life.

Hair and nails work with the skin to protect our body tissues from injury and help regulate temperature. They may be affected by nutritional deficiency, ageing, injury or infection.

Hormones are like chemical messages that control our body's growth, repair and reproduction. Organs of the hormonal or endocrine system include the pituitary, adrenal, thyroid and parathyroid glands and the ovaries, pancreas and testes.

The immune system helps our body fight infection. White blood cells, lymphocytes and antibodies form part of the defence.

The kidneys clean the blood and remove waste through urine, which is stored and passed by the bladder. Genetic disorders, lifestyle, diet and infections can affect the kidneys and bladder.

The lungs are part of our respiratory system. Along with the trachea, alveoli, bronchi and diaphragm, they help us breathe in oxygen and exhale carbon dioxide. Lungs can be affected by infection or allergy or may puncture or collapse.

The male reproductive system is involved in sexuality and fertility. It includes the penis, testicles, epididymis, vas deferens and prostrate gland. These body parts have a role in semen production and ejaculation.

The mouth is made up of the lips, tongue, jaw, teeth and gums. It plays a key role in the digestive system and is also essential for speech.

The neuromuscular system involves our nervous system and muscles working together to control, direct and allow movement of the body. Movement-related disorders include motor neuron disease, Parkinson's disease, multiple sclerosis, Huntington's disease, muscular dystrophy and polio.

The skin protects our body against injury and infection, regulates temperature and controls the loss of body fluids. Its two main layers are the dermis and epidermis. Skin can be affected by sun, ageing, injury and infection.

Teeth help process our food for digestion and play an important role in speech. They are protected by a coating of enamel and their roots are covered by gums.