Diseases

Diseases An Infectious disease is clinically evident disease in humans and animals which damages or injures the host function, and results from an activity of pathogenic agent including viruses, bacteria, fungi, protozoa and multicellular parasites. Transmission can occur through several pathways; including through contact with infected individuals, by water, food, and airborne inhalation. A Non-infectious disease is something that has been caused by the environment or from what we eat and don’t eat. Non-infectious diseases are also caused by genetic factors. Some non-infectious diseases include diabetes, anaemia (nutritional), heart disease, and cancer from radiation (environment) sickle cell anaemia and cerebral palsy (genetic). An antigen is a molecule that stimulates an immune response. • Tolerogen - An antigen that invokes a specific immune non-responsiveness due to its molecular form. If its molecular form is changed, a tolerogen can become an immunogen. • Allergen - An allergen is a substance that causes the allergic reaction. The reaction may result after exposure via ingestion, inhalation, injection or contact with skin. An antibody or immunoglobulin is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. A vaccine is an antigenic preparation used to establish immunity to a disease. Vaccines can be prophylactic (e.g. to prevent or ameliorate the effects of a future infection by any natural or "wild" pathogen), or therapeutic (e.g. vaccines against cancer). Vaccines may be living, weakened strains of viruses or bacteria that intentionally give rise to unapparent-to-trivial infections. Vaccines may also be killed or inactivated organisms or purified products derived from them.

Reproductive System Human reproduction employs internal fertilization, and depends on the integrated action of hormones, the nervous system, and the reproductive system. Gonads are sex organs that produce gametes. Male gonads are the testes, which produce sperm and male sex hormones. Female gonads are the ovaries, which produce eggs (ova) and female sex hormones. Testes are suspended outside the abdominal cavity by the scrotum, a pouch of skin that keeps the testes close or far from the body at an optimal temperature for sperm development. Seminiferous tubules are inside each testis, and are where sperm are

produced by meiosis. About 250 meters (850 feet) of tubules are packed into each testis. Spermatocytes inside the tubules divide by meiosis to produce spermatids that in turn develop into mature sperm. The female gonads, ovaries, are located within the lower abdominal cavity. The ovary contains many follicles composed of a developing egg surrounded by an outer layer of follicle cells. Each egg begins oogenesis as a primary oocyte. At birth each female carries a lifetime supply of developing oocytes, each of which is in Prophase I. A developing egg (secondary oocyte) is released each month from puberty until menopause, a total of 400-500 eggs. Fertilisation or fertilization (also known as conception), is union of gametes to form a new organism of the same species. In animals, the method involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Ovulation occurs when a mature egg is released from the ovary, pushed down the fallopian tube, and is available to be fertilized. Menstruation is a woman's monthly bleeding. It is also called menses, menstrual period, or period. When a woman has her period, she is menstruating. The menstrual blood is partly blood and partly tissue from the inside of the uterus (womb). It flows from the uterus through the small opening in the cervix, and passes out of the body through the vagina. Most menstrual periods last from three to five days. Menopause is the time in a woman's life when her period stops. It is a normal change in a woman's body. A woman has reached menopause when she has not had a period for 12 months in a row (and there are no other causes, such as pregnancy or illness, for this change).