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• coccyx: tail bone, a fusion of the lowest four vertebrae

• femur: thigh bone

• patella: knee cap

• tibia and fibula: lower leg—the tibia is the broader one that runs down toward the big toe; the fibula the narrower one that runs toward the little toe

• tarsus: a collective name for the bones of the ankle and heel, individually known as tarsals

• metatarsus: ditto for the five long bones of the foot

• phalanges: toes

☞ THE CIRCULATORY SYSTEM

Blood is the body’s transportation system—everything from oxygen to hormones is transported around the body in the bloodstream, and its waste products, from carbon dioxide to urea, are carried away for disposal.

In order for blood to do its job, it needs to be pumped around, and that is the primary purpose of the heart. The heart is two pumps, each consisting of two chambers—an auricle and a ventricle—with a valve in between. The left side of the heart receives oxygen-rich blood from the lungs and forces it throughout the body; the right side receives the oxygen-depleted blood and returns it to the lungs to be re-oxygenated. (Oxygen, of course, comes into the lungs in the air that we breathe, and without it the cells in the body would die.)

All this requires a well-organized system of blood vessels. These are divided into arteries, which are strong and muscular and carry fast-flowing blood away from the heart, and veins, which are weaker and more sluggish and bring it back. The principal artery, the aorta, divides into smaller arteries and arterioles. Smaller veins are called venules, and really tiny blood vessels—whether veins or arteries—are called capillaries.

The exception to the useful mnemonia—arteries go away—is the pulmonary artery—the one that goes from the lung to the heart. The pulmonary vein runs from the heart to the lungs. Therefore, the truth is that the arteries simply carry the oxygen-rich blood.

Blood has four major components:

• red blood cells, which carry hemoglobin, made up of heme (an iron-containing pigment) and globin (a protein) (This combines with oxygen to form oxyhemoglobin, the means by which oxygen is transported throughout the body. Oxyhemoglobin also gives the blood its red color, which is why arterial blood is bright red; venous blood, having deposited oxygen in cells all over the body, has a bluish tinge.)

• white blood cells, or leukocytes, which fight infection

• platelets, which are necessary for the clotting process

• plasma, the liquid that makes the blood… well, liquid

☞ THE DIGESTIVE SYSTEM

The digestive process is divided into four parts:

• ingestion: eating food

• digestion: breaking the food down into constituent parts

• absorption: extracting nutrients from the food

• elimination: disposing of waste

Once you swallow food or drink, it enters the esophagus, or gullet, and passes (through a process of muscular contraction called peristalsis) into the stomach. From there it continues into the small intestine (comprising the duodenum, jejunum, and ileum), where digested food is absorbed into the bloodstream. The whole process is helped by the secretion of enzymes. One of the effects of the digestion of protein (which enters the body via meat, fish, eggs, etc.) is the release of amino acids, which are the building blocks of the protein the body needs for all sorts of different purposes.

Anything undigested after this stage passes into the colon (the beginning of the large intestine), where water is extracted from it. What remains are the feces, which pass through the rectum and out of the body via the anus.

Organs encountered along the way include:

• the liver, which in adult life often copes with our alcohol intake, but which has many more functions to do with digestion and keeping the blood healthy

• the gall bladder, which stores bile, needed in the digestion of fats

• the pancreas, which secretes various enzymes and the hormones insulin and glucagon, which regulate levels of blood sugar

• the kidneys, which control the amount of salt and water in the blood. (Excess fluid containing