SYSTEMS OF THE HUMAN BODY

Transcription

1 reflect Think about all of the things you do in a single day. You eat, travel to school, study for tests, communicate with your family members and classmates, and more. All of these activities are possible thanks to the amazing human body! The human body is made of many parts working together to perform important life functions. What are these different parts? What role do they play in your body, and how do they work together to maintain life? Organization in the Human Body The smallest unit of life is the cell. The human body is made of up trillions of cells. There are one million millions in just one trillion! Each cell performs certain functions necessary for keeping the body healthy. Together, cells form tissues, which are groups of cells that perform the same function. The human body is composed of muscle tissue, nervous tissue, and skin tissue. The different kinds of tissues group together to form an organ. The heart and brain are examples of organs. Finally, organs function together to form an organ system. Organ systems are groups of organs that work together to perform all the major functions the body needs to stay alive. Different organ systems serve different functions. From moving blood around the body to deliver nutrients and remove wastes to providing support, protection, and movement, the systems of the body keep us alive. That s why it s important to keep the body systems healthy and strong. Organ Systems The duties of maintaining life are divided among the organ systems. Let s look closer at the systems and the important roles they play in a human body. 1

2 Circulatory System: The circulatory system includes the heart, blood vessels, and blood. The heart is an organ made up of four different chambers (left and right atria and ventricles) that work together to pump blood throughout the body. Blood circulates to all the different parts of the body, delivering oxygen and important nutrients to cells. The circulatory system also picks up carbon dioxide from the cells and carries it to the lungs where it is exhaled. Oxygen-rich blood (blood that carries oxygen molecules) leaves the heart through blood vessels called arteries. Oxygen is delivered to the body through vessels called capillaries that are so thin, the oxygen molecules pass right through their walls and into cells. Oxygen-poor blood (blood that contains a lot of carbon dioxide waste) returns to the heart through veins. Blood also contains white blood cells important for fi ghting infections. Respiratory System: When blood returns to the heart from the cells, it is pumped to the lungs. The lungs are part of the respiratory system, which serves the main purpose of supplying the blood with oxygen. The lungs include two branches called bronchi, narrower tubes called bronchioles, and tiny air sacs called alveoli. The respiratory system also includes the nose, pharynx (throat), and trachea. When a person inhales, oxygen and other gases enter the mouth and nose and pass through the pharynx and trachea. The gases then branch into the left and right bronchi of the lungs. At the end of the bronchioles, alveoli are the sites of gas exchange in the lungs. Oxygen moves across the membranes of the alveoli and into the capillaries of the body. The respiratory system also removes carbon dioxide from the body, which is waste produced by cells. Carbon dioxide passes through capillary walls of the body and into the alveoli. It then moves out of the body through the nose and mouth when a person exhales. trachea: tube connecting the nose and mouth to the entrance to the lungs; also called the windpipe 2

3 Skeletal System: The skeletal system includes bones and joints. (A joint is an area in which two or more bones make contact.) Bones provide the human body with structure and support. They also protect important organs. The skull is like a helmet that protects the brain. Ribs keep the heart and other nearby organs safe. Bones also store important minerals such as calcium and produce new blood cells. Muscular System: The muscular system, as you might have guessed, includes muscles! It also includes tendons and ligaments. Tendons are tissues that attach bones to muscles. Ligaments are tissues that attach bones to other bones. Tendons and ligaments help the body move. There are three types of muscles in the muscular system: skeletal, smooth, and cardiac. Skeletal muscles are voluntary people have the ability to consciously control them and work with bones to provide movement such as walking, jumping, or even just raising a hand to answer a question in class. Smooth muscle is involuntary it moves or contracts without conscious control and lines the inside of many organs such as the stomach and blood vessels. One important function of smooth muscle is to help move food through the body via muscle contractions in various organs like the stomach. Smooth muscle also moves blood through veins. Cardiac muscle is also involuntary and is found in the walls of the heart and aids in the contraction of the heart in order to pump blood. Digestive System: Food provides energy for all of the organ systems, but it must be broken down before it can be used. This is the function of the digestive system. This system includes the mouth, esophagus, stomach, intestines, and anus. Digestion begins in the mouth where it is broken down into smaller pieces by the teeth and saliva. The physical breaking down of food by teeth is called mechanical digestion. Saliva contains substances that also break down the food. This is the start of chemical digestion. Food then travels down a tube called the esophagus and enters the stomach where further chemical digestion occurs. Strong chemicals and churning by stomach muscles break the smaller food particles down into even smaller molecules. The liver and pancreas are organs that also contribute chemicals that help break down food. From the stomach, food moves into the small intestine where nutrients are absorbed into the bloodstream. Materials that are not absorbed travel to the large intestine where any remaining water is absorbed. The rest of the material leaves the body as waste through the anus. 3

4 Excretory System: Removing waste from the body is important to maintaining health. The kidneys, bladder, and liver are the parts of the excretory system that collect and dispose of waste produced by cells. As already stated in the lesson, the lungs remove carbon dioxide waste. The liver and kidneys fi lter the blood and remove toxins, excess water, and other waste. The wastes are then stored in the bladder as urine until they are released from the body during urination. Getting Technical: Waste Removal in Space Astronauts who live in space for long periods of time do not have access to clean, fresh water piped into their faucets every day. Transporting water to space is heavy and expensive. The best option is to recycle the water they have every bit of it! NASA developed a machine that fi lters water produced by the astronauts, including water produced in their urine. The machine uses three steps to fi lter out toxins from the urine. The fi rst step removes particles and debris. The second step fi lters out impurities, and the third step kills bacteria and viruses. NASA scientist Layne Carter says the water purifi ed through the machine in space is cleaner than water from a faucet on Earth. This is because their process of water treatment is more aggressive than the processes used by water treatment facilities on Earth. How would you feel about drinking a glass of water that came from your own urine? Reproductive System: The continuation of the human species depends on reproduction, or producing offspring. Humans reproduce sexually. A sperm from a male fertilizes an ovum, or egg, from a female. In males, the reproductive organs that produce sperm are the testes. The sperm are delivered to the female through the penis. The female reproductive system is much more complex than the male s. sperm: male sex cell ovum: female sex cell; also called egg Ovaries produce and store eggs. Each month, the ovaries release one egg. The egg travels to one of two fallopian tubes. Under normal circumstances, the sperm fertilizes the egg in the fallopian tube. The fertilized egg then travels to, and implants in, the uterus. The uterus is an organ that protects and nurtures the egg as it grows into a baby. If an egg is not fertilized, it is released from the body at the end of the menstrual cycle. 4

5 Integumentary System: The integumentary system contains the largest organ in the human body the skin. Along with hair, nails, and glands, the skin protects the body s internal organs from exposure to the outside environment. Skin is the body s first line of defense against illness and injury. This system also glands: organs that release hormones excretes waste through sweat, helps maintain body temperature, and produces vitamin D. The integumentary system plays an important role in the body s interactions with its surroundings. Special nerves in the skin pick up stimuli from the environment and send messages to the brain. For example, when skin touches something cold, nerves in the skin send a message to the brain that the item is cold. Nervous System: All of the organ systems are controlled by the nervous system because it contains the brain, spinal cord, and nerves. Stimuli from both outside and inside the body travel over the system of nerves as electrical impulses to the brain in fractions of a second. The brain sends messages back to parts of the body just as quickly, directing the body parts on how to react. The lightening fast communication system allows the nervous system to control all parts of the human body at once. Endocrine System: The endocrine system works with the nervous system. Together, they are the body s two systems for control and communication. The main function of the endocrine system is to maintain a stable internal environment, or homeostasis. This system is made up of glands that send messages through hormones instead of electrical signals. Hormones are chemical messengers that regulate processes such as growth, reproduction, development, and energy production. For example, testosterone is a hormone that is largely responsible for the development of male reproductive organs. Estrogen is a hormone that regulates the growth and development of female reproductive characteristics. 5

6 look out! It is important to remember that body systems rarely function independent of one another. Two or more body systems usually work together. For example, the digestive system breaks down food, but the circulatory system moves the nutrients to different parts of the body through the blood. The skeletal and muscular systems work together for movement. The excretory system removes waste that the digestive and respiratory systems produce. All of the organ systems communicate with the nervous system, and the nervous system controls other systems through electrical impulses. Just like groups of cells make up tissues and tissues make up organs, the organ systems together make up an organism. cells tissues organs organ systems organisms what do you think? Which body systems work together to move your hand when you touch something hot? Explain your reasoning. What do you know? Use what you have learned about the human body systems to complete the chart on the next page. Fill in either the missing name of the system, the main parts of the body that make up the system, or the system s functions. 6

7 System Main Parts of System Functions Circulatory Breaks down food into small molecules, absorbs nutrients into blood, removes food waste Endocrine Glands, hormones Kidneys, bladder, liver Protects inner organs from illness and injury, regulates body temperature, detects stimuli from surroundings Muscles, ligaments, tendons Nervous Male: testes, penis Female: ovaries, uterus, fallopian tubes Breathes in oxygen, breathes out waste such as carbon dioxide Skeletal 7

8 connecting with your child Human Body Systems at Home To help students learn more about human body systems, perform a simple dissection at home. Buy a package of bone-in chicken wings from a grocery store and have students analyze the different structures of the chicken that they can observe. Carefully use a knife to cut away the skin and help students identify the muscular system (meat), the skeletal system (bones), and the tendons that hold the bones and muscles together. The tendons look like thick silvery bands at the ends of bones and are connected to the meat. Have students manipulate the muscles to demonstrate how they move the bones by shortening and lengthening the muscles. The bones should move up and down in response. Encourage students to look for structures from other body systems including the circulatory system (blood vessels can often be found in raw meat) and the nervous system (nerves look yellow and stringy). Have them analyze the skin and identify places where feathers were once attached. If a hand lens is available, have students look at the structures more closely to see if they can observe more about the body system parts. Discuss how all of the structures you observe in the chicken wing are similar to structures in the human body systems. Once the dissection is complete, be sure students WASH THEIR HANDS THOROUGHLY. Raw chicken may contain food-borne illnesses such as Salmonella. While eating their next meal, encourage students to describe which of their body systems are in action as they eat. Have them describe which structures are functioning and what tasks they perform. For example, after a bite of food is swallowed, students should explain that food has moved into the stomach. The stomach uses smooth muscle to churn the food. Chemicals from the liver and pancreas help break the food down into small molecules. Soon the small intestine will absorb the food s nutrients into the bloodstream where the nutrients will circulate to the cells. Here are some questions to discuss with students: What were some similarities between the structures you observed in the chicken wings and those found in the different human body systems? What were some differences? What are three main processes the body systems do to keep a human healthy? What body system is working hard when you do your homework? Play sports? Lay out in the sun? Why is it necessary for body systems to work together? 8