The Endocrine System
The endocrine system is an organ system which releases molecules into the blood to activate its effects. It is specialized for slow, nonspecific, and long-lasting effects on the body, which is the opposite of the goal of the nervous system. The endocrine system achieves these effects with hormones. The two types of hormones are steroid and nonsteroid hormones. The hormones of the endocrine system are all released by organs called glands. The hypothalamus of the brain controls the pituitary gland, which releases hormones to control all of the other endocrine glands. The thyroid gland regulates metabolism. The parathyroid gland regulates calcium levels in the blood. The adrenal glands are responsible for fight-or-flight responses. The pancreas regulates the level of sugar in the blood. The gonads produce sex hormones that give gender characteristics.
The Reproductive System
The reproductive system is responsible for producing and storing sex cells, known as gametes. The male sex cell is known as the sperm and the female sex cell is known as the egg. The DNA is haploid in gametes because of meiosis. The male reproductive system produces sperm in the testes, where it matures before it can travel through the vas deferens to be delivered through the penis. The female reproductive system produces eggs in the ovaries, where it matures before the egg travels through the Fallopian Tubes. While traveling through the Fallopian Tubes, the female egg can be fertilized by sperm that enters through the vagina and cervix. Fertilization occurs when a sperm and an egg fuse, producing a new diploid organism. This first cell of a new life is known as a zygote.
All living things perform homeostasis, which is a process of maintaining a stable, internal environment. Homeostasis occurs when a sense system notices a change in the stable status, and an effector is signaled to bring the change back to normal. The effectors can be any organ of any organ system, depending on the change needed. Homeostasis often stops its own actions via negative feedback.