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The propulsion of semen out of the urethra during sexual orgasm in the male.
A microscope which uses an electron beam to illuminate the specimen, and magnetic lenses to focus the beam. There are two main types of electron microscope: the transmission electron microscope which enables the examination of very thin sections of material, and the scanning electron microscope, which allows the visualisation of three-dimensional surfaces. The electron microscope provides considerably higher magnifications than the light microscope.
Atoms of different types from which all matter is made. The different elements have different numbers of protons and neutrons in their nuclei, and different numbers of electrons orbiting around the nuclei. Each element is given a different atomic number. It is possible for some elements to exist in more than one form - the variants have more or less neutrons in their nuclei, even though they have identical numbers of protons and neutrons. These variants are called isotopes.
A gland without a duct that puts its secretion directly into the bloodstream. The secretions of endocrine glands are called hormones. Example of endocrine glands are the pituitary gland, the thyroid gland, and the adrenal glands.
The specialized lining of the uterus. The endometrium is sensitive to the hormones produced by the ovaries, and undergoes changes in thickness and vascularization during menstrual cycles. The endometrium is capable of accepting a conceptus at the time of implantation and supporting its development up until birth.
A protein that helps a chemical reaction to take place and which emerges unchanged itself at the end of the reaction: a biological catalyst. Each enzyme is specific to a particular reaction. Most enzymes are found within cells and are important regulators of cellular metabolism. However, some enzymes are found in extracellular fluids such as the blood plasma and tissue fluid, put there by organs such as the liver.
A gland with a duct which carries the secretion of the gland to an internal or external surface of the body. For example, sweat glands are exocrine glands and pour their secretions onto the surface of the skin. Salivary glands - also exocrine - empty their secretions into the mouth.