The main function of human red blood cells or erythrocytes is usually to carry oxygen to several areas of the body. Their natural beautiful red colors comes from a biomolecule called hemoglobin which binds oxygen and occupies the cytoplasm of the cell. Unlike most human cells, red blood cells don't have nuclei or other organelles (the components or subunits of many cells). Their biconcave appearance can clearly be seen with this image which was captured using a scanning electron microscope (SEM). Looking like doughnuts without holes, they're flat and depressed inside center and also have a dumbbell-shaped cross-section. This unusual form is very important for his or her function because it is great for their smooth passage through minor and major veins. A progesterone blood test is conducted to ascertain how much of the progesterone hormone is within a sample of blood. This female hormone is produced whenever a mature egg is released from an ovary within a process generally known as ovulation. This hormone helps to prepare the endometrium (uterine lining) to just accept the egg if sperm fertilizes it. If the egg goes without getting fertilized, menstrual bleeding occurs and progesterone levels drop. 2. Drink probiotic supplements or drink which can help boosts your energy and improve your immune system. This also makes you younger-looking. This is also an excellent source of natural sodium and potassium.