American Medical Association Family Medical Guide - American Medical Association [85]
Circulatory system
The circulatory system consists of the heart, lungs, and blood vessels. Your veins (blue in illustration) carry used, oxygen-depleted blood to the right side of your heart, which pumps it to the lungs for a fresh supply of oxygen. The newly oxygenated blood returns to the left side of the heart and is pumped through the aorta, a large blood vessel that directs blood to a system of arteries (red in illustration) that deliver the blood to tissues throughout the body. The veins return the used blood to the heart and the process starts again, about 10,000 times every day.
Brain and Nervous System
The nervous system has two major parts—the central nervous system and the peripheral nervous system. The brain and spinal cord make up the central nervous system, which coordinates all the body’s interactions with the environment. The brain, which is the most complex organ of the body, regulates most of your body’s functions. Each area of the brain is responsible for different functions, such as language, vision, movement, or emotions. The peripheral nervous system consists of nerves that radiate from the brain and spinal cord to all parts of the body. The peripheral nerves transmit information from different parts of the body to the brain and carry messages back to those parts of the body from the brain. The brain is always working, even during sleep.
Nervous system
The central nervous system is made up of the brain and spinal cord. The nerves that radiate from the spinal cord to the rest of the body make up the peripheral nervous system.
Brain
The brain lies inside a rigid, bony container called the skull. The two cerebral hemispheres, the cerebellum, and the brain stem are the major components of the brain. The cerebral hemispheres make up nearly 90 percent of brain tissue. Each hemisphere is about 6 inches from front to back, and together they measure about 4½ inches across. The hemispheres consist of intricate folds of nerve tissue that have a total surface area equal to that of a large newspaper spread.
The cerebellum, which lies beneath the back of the cerebral hemispheres, is concerned with muscle coordination. Like the cerebral hemispheres, the cerebellum consists of nerve cells and is divided into two hemispheres.
The brain stem contains tracts of nerve fibers that connect the brain to the rest of the body by way of the spinal cord. The brain stem also controls breathing and heart rate.
Spinal cord
The spinal cord is covered by three layers of protective membranes called the meninges. The spinal cord has a central canal that contains cerebrospinal fluid. Spinal nerves send and receive messages about body sensation and move to and from the brain by way of the spinal cord. A column of bones called vertebrae surrounds and protects the spinal cord. The vertebral column enables you to stand upright and maintain your balance.
Urinary Tract
The urinary tract filters waste products and excess fluid from the bloodstream and eliminates them from the body in urine. The kidneys filter out excess water, salts, and waste products from the blood, and the remaining substances are reabsorbed into the blood in the exact amounts the body needs. The kidneys then expel the excess water, salts, and waste products as urine (through tubes called ureters) into the bladder, where it is stored until you feel the urge to urinate. Urine is expelled from the body through a narrow tube called the urethra.
Male and female urinary tracts
The urinary tracts differ somewhat in males and females. A male’s urethra is much longer than a female’s, and the male bladder sits higher in the pelvis.
How the kidneys work
The kidneys play a role in regulating blood pressure, producing red blood