Learning Objectives
In this Module, you will learn about the general organization and functions of the human body. Specifically, you will learn about:
- The organization of the systems of the body.
- How organ systems work together to carry out the functions of life.
- How organ systems communicate and interact in body processes such as cellular respiration, digestion, the fight-or-flight response to stressors, and physical activities such as sports.
- How homeostasis is maintained to keep the body in a relatively steady, and the problems that can be caused by loss of homeostasis, such as diabetes.
You have probably heard this Billy Ray Cyrus song. Heartache, heartbreak…it all has to do with love. Did you ever wonder why the heart is associated with love? The heart was once thought to be the center of all thought processes, as well as the site of all emotions. This notion may have stemmed from very early anatomical dissections that found many nerves can be traced to the region of the heart. The fact that the heart may start racing when one is excited or otherwise emotionally aroused may have contributed to this idea as well. In fact, the heart is not the organ that controls thoughts or emotions. The organ that controls those functions is the brain. In this concept, you’ll be introduced to the heart, brain, and other major organs of the human body.
Human Organ Systems
Functionally related organs often cooperate to form whole organ systems. The 12 diagrams in the figures below show 11 human organ systems, including separate diagrams for the male and female reproductive systems. Some of the organs and functions of the organ systems are identified in the figure. Each system is also described in more detail in the text that follows. Most of these human organ systems are also the subject of separate chapters in this Flexbook.
Integumentary System
Organs of the integumentary system include the skin, hair, and nails. The skin is the largest organ in the body. It encloses and protects the body and is the site of many sensory receptors. The skin is the body’s first defense against pathogens, and it also helps regulate body temperature and eliminate wastes in sweat.
Skeletal System
The skeletal system consists of bones, joints, teeth. The bones of the skeletal system are connected by tendons, ligaments, and cartilage. Functions of the skeletal system include supporting the body and giving it shape. Along with the muscular system, the skeletal system enables the body to move. The bones of the skeletal system also protect internal organs, store calcium, and produce red and white blood cells.
Muscular System
The muscular system consists of three different types of muscles, including skeletal muscles, which are attached to bones by tendons and allow for voluntary movements of the body. Smooth muscle tissues control the involuntary movements of internal organs, such as the organs of the digestive system, allowing food to move through the system. Smooth muscles in blood vessels allow vasoconstriction and vasodilation and thereby help regulate body temperature. Cardiac muscle tissues control the involuntary beating of the heart, allowing it to pump blood through the blood vessels of the cardiovascular system.
Nervous System
The nervous system includes the brain and spinal cord, which make up the central nervous system, and nerves that run throughout the rest of the body, which make up the peripheral nervous system. The nervous system controls both voluntary and involuntary responses of the human organism and also detects and processes sensory information.
Figure 10.4.310.4.3: Six organ systems (CC BY-SA 4.0; Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon via open.oregonstate.education)
Endocrine System
The endocrine system is made up of glands that secrete hormones into the blood, which carries the hormones throughout the body. Endocrine hormones are chemical messengers that control many body functions, including metabolism, growth, and sexual development. The master gland of the endocrine system is the pituitary gland, which produces hormones that control other endocrine glands. Some of the other endocrine glands include the pancreas, thyroid gland, and adrenal glands.
Cardiovascular System
The cardiovascular system (also called the circulatory system) includes the heart, blood, and three types of blood vessels: arteries, veins, and capillaries. The heart pumps blood, which travels through the blood vessels. The main function of the cardiovascular system is transport. Oxygen from the lungs and nutrients from the digestive system are transported to cells throughout the body. Carbon dioxide and other waste materials are picked up from the cells and transported to organs such as the lungs and kidneys for elimination from the body. The cardiovascular system also equalizes body temperature and transports endocrine hormones to cells in the body where they are needed.
Urinary System
The urinary system includes the pair of kidneys, which filter excess water and a waste product called urea from the blood and form urine. Two tubes called ureters carry the urine from the kidneys to the urinary bladder, which stores the urine until it is excreted from the body through another tube named the urethra. The kidneys also produce an enzyme called renin and a variety of hormones. These substances help regulate blood pressure, the production of red blood cells, and the balance of calcium and phosphorus in the body.
Respiratory System
Organs and other structures of the respiratory system include the nasal passages, lungs, and a long tube called the trachea, which carries air between the nasal passages and lungs. The main function of the respiratory system is to deliver oxygen to the blood and remove carbon dioxide from the body. Gases are exchanged between the lungs and blood across the walls of capillaries lining tiny air sacs (alveoli) in the lungs.
Lymphatic System
The lymphatic system is sometimes considered to be part of the immune system. It consists of a network of lymph vessels and ducts that collect excess fluid (called lymph) from extracellular spaces in tissues and transport the fluid to the bloodstream. The lymphatic system also includes many small collections of tissue, called lymph nodes, and an organ called the spleen, both of which remove pathogens and cellular debris from the lymph or blood. In addition, the thymus gland in the lymphatic system produces some types of white blood cells (lymphocytes) that fight infections.
Digestive System
The digestive system consists of several main organs — including the mouth, esophagus, stomach, and small and large intestines — that form a long tube called the gastrointestinal (GI) tract. Food moves through this tract where it is digested, its nutrients absorbed, and its waste products excreted. The digestive system also includes accessory organs (such as the pancreas and liver) that produce enzymes and other substances needed for digestion but through which food does not actually pass.
Male and Female Reproductive Systems
The reproductive system is the only body system that differs substantially between individuals. There is a range of Biological sex, but most books divide them into male and female. We will discuss the Biology of sex in detail in the reproductive and development chapters.
Figure 10.4.410.4.4: The diagrams 10.4.3 and 10.4.4 represent 11 human organ systems and show some of their organs and functions. The male and female reproductive systems are shown separately because of their significant differences. (CC BY-SA 4.0; Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon via open.oregonstate.education)
