The blood-type diet designed by Peter D'Adamo contains four sets of eating and lifestyle instructions, one for each of the four blood types: A, B, AB and O.

White blood cells (WBCs) serve as the principal actors of the immune system. The 5 classes of WBCs, or leukocytes, differ in appearance and function. These classes include neutrophils, monocytes, lymphocytes, eosinophils and basophils.

You rely on your morning coffee to help you feel more alert and awake. Caffeine -- the active ingredient in your coffee -- has a number of effects on your body when it first works. The effects may be unpleasant when the caffeine breaks down in your system.

A low red blood cell count can be a sign of anemia, a condition in which the body does not have enough normal red blood cells and the blood is unable to carry enough oxygen to the tissues that need it.

As the Merck Manuals explain, the body is able to control blood pressure by expanding and constricting blood vessels. This allows the body to raise blood pressure when it is low and also allows the body to regulate the amount of blood that gets to tissues at any given time.

Progesterone is a hormone in the body that helps to control the thickness of the uterine tissue lining, according to Dr. Frederick R. Jelovsek, a physician writing on Women’s Health Resource. This means progesterone plays a vital role in menstruation and ceasing menstrual bleeding.

Blood vessels deliver blood from the heart to the tissues, and return oxygen-depleted blood to the heart. The vascular system is made up of three vessel types.

Red blood cells carry oxygen from the lungs to the rest of the body. A high number of red blood cells--more than 5.72 million red blood cells per mcL for men and 5.03 million per mcL for women--requires further evaluation, according to MayoClinic.com.

The majority of iron in the blood is bound to hemoglobin, the oxygen-transporting protein. Blood iron that is not in hemoglobin may be in transit and bound to the protein transferrin. Iron that comes from body stores is in the form of a protein called ferritin.

Dangerously high blood glucose levels--over 300 milligrams per deciliter (mg/dL)--can cause life-threatening complications. Diabetic ketoacidosis (DKA) occurs mostly in type 1 diabetics, but can occur in type 2 diabetics in some cases. In DKA, insulin stores are exhausted and fats are broken down to use as energy.

Stress can be a positive or negative event. Getting married or buying a new home can be just as stressful as financial or health problems. Stress becomes a problem when it occurs on a regular basis with no break and creates feelings of being out of control or overwhelmed.

All blood is not created equal. It all serves the body, it delivers oxygen and nutrients. It polices, attacking what it perceives to be invaders. But what it perceives to be invaders changes from person to person.