Empty fat cells – Fat cells are amongst the largest cells in the human body. They form a thick insulating layer under the skin which serves to cushion us as well as store energy. In this image the normal lipid (fat) deposits of the cells (their major component) have been removed, revealing the honeycomb structure of the cell membranes. When we put on weight, the cells swell with additional fat, and eventually extra cells are added too.
Human skin – The outer layer of the skin, the epidermis (top half of this image) consists of dead cells that are constantly sloughed off and replaced from
below. These tightly packed cells contain high levels of a protein called keratin (yellow) which makes the skin waterproof and strong, to protect the organs inside. In this cross-section, you can also see hair follicles (black).
Influenza A H1N1 virus particles – Influenza A viruses can infect humans,pigs, birds and horses. The H1N1 strain caused the Swine flu outbreak of 2009. At the center of each virus is its genetic fingerprint (the ribonucleic acid, pink), surrounded by a protective protein shell (the nucleocapsid, yellow). The enclosing fatty envelope (green) contains two types of protein, haemagglutinin and neuraminidase (the 'H' and 'N' in the strain's codename), the levels of which determine the strain of virus.
Gallstone crystals – Gallstones mostly consist of cholesterol, but can also contain calcium and bilirubin (a product of old red blood cells). They form in the gallbladder (from which bile is released into the small intestine) when there is an imbalance in the chemical composition of the bile.
Gallstones are usually symptomless, unless one obstructs the bile duct. In that case they cause acute pain, jaundice and infection.
Balancing stone from inner ear – Our sense of balance is derived from a tiny stone in each ear, called an otolith (from Greek, literally "ear-stone"). The stones are built up in the inner ear from deposits of calcium carbonate crystals, seen here on the surface of an otolith.
Blood clot – Red blood cells have been trapped by a web of thin yellow-white strands of fibrin. Fibrin is an insoluble protein produced by platelets (fragments of white blood cells) from a soluble protein called fibrinogen normally present in blood.
Blood clots may occur on the surface of skin in case of injuries or inside blood vessels. These internal clots, known as thrombi, may be caused by having too many platelets. They can lead to heart attacks.
Adrenaline crystals – Adrenaline, also called epinephrine, is normally present in blood in small quantities. It is a hormone produced in the adrenal glands above the kidneys. The glands are controlled by the hypothalamus, the part of the brain responsible for instinct and emotion.
In times of stress more adrenaline is secreted into the bloodstream. It widens the airways of the lungs and constricts small blood vessels. This makes the muscles work harder and produces a "fight or flight" response.
Insulin crystals – These hexagonal crystals are of the hormone insulin. Insulin is produced in the pancreas, and its function is to regulate blood sugar levels. Insufficient production of insulin leads to an accumulation of glucose in the blood, and can cause Type 1 diabetes.
Type 2 diabetes can occur when there is plenty of insulin, but the body's cells do not respond properly to it. A third type, gestational diabetes, occurs in pregnant women who produce high levels of blood glucose.
Brain cells in culture – This image shows two important support cells (glial cells) of the human brain. The green splash is a microglial cell, which responds to immune reactions in the central nervous system.
Microglial cells recognize areas of damage and inflammation and swallow cellular debris. The larger orange shape is an oligodendrocyte. The ragged extensions of an oligodendrocyte can supply many neurons (nerve cells) with myelin, an insulating material which allows each neuron's communicating axon to transmit electrical impulses efficiently.