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Section 2: Human Body Systems Preview Bellringer Key Ideas Skeletal and Muscular Systems Integumentary System Nervous and Endocrine Systems Digestive and Excretory Systems Respiratory and Circulatory Systems Summary Bellringer Alternately bend and straighten your arms or legs while feeling the muscles in the front and the back. Write down what you feel when the limb is straightened and what you feel when the limb is bent. Key Ideas How do the skeletal and muscular systems help the body maintain homeostasis? How does the integumentary system help the body maintain homeostasis? How do the nervous and endocrine systems help the body maintain homeostasis? Key Ideas, continued How do the digestive and excretory systems help the body maintain homeostasis? How do the circulatory and respiratory systems help the body maintain homeostasis? Skeletal and Muscular Systems The skeletal and muscular systems enable movement and provide support for tissues and organs. Bones and muscles work together to make movement possible. The ability to move increases the chance of survival by allowing a person to gather food, seek shelter, and escape from danger. Skeletal and Muscular Systems, continued The skeleton provides an anchor for the muscles that move the body. Tendons attach muscles to bones. When muscles contract, tendons pull on bones to cause movement. Opposing Muscles in the Arms Skeletal and Muscular Systems, continued Other types of muscle, known as involuntary muscle, move material within the body. This type of muscle surrounds the inner walls of some blood vessels and makes up some organs, such as the stomach and heart. A heartbeat occurs when this type of muscle contracts rhythmically. Integumentary System Skin is the largest organ of the human body. Skin makes up about 7% of your total body weight. The skin, hair, and nails form the integumentary system. Integumentary System The integumentary system does the following: protects the body from injury and UV radiation defends against disease helps regulate body temperature prevents the body from drying out Visual Concept: Human Skin Click the button below to watch the Visual Concept. Integumentary System, continued Waterproofing The epidermis is the outermost layer of skin. It is made of flattened, dead cells composed of a protein called keratin. Keratin is also found in nails and hair. Integumentary System, continued Keratin makes the skin tough and waterproof. Glands in the dermis, the layer of skin under the epidermis, secrete oil that lubricates the skin. Without the protection of keratin and oil, our bodies would lose water through evaporation or absorb water from the environment. Integumentary System, continued Disease Prevention The epidermis forms a tight barrier that keeps bacteria out and protects the body from disease. Damage to large areas of skin allows bacteria to enter the body freely. This lack of protection is one reason why severe burns are so dangerous. Integumentary System, continued UV Prevention The lower layers of the epidermis contain cells that make melanin, a pigment that absorbs UV light. This absorption prevents DNA damage, which can cause skin cancer. Integumentary System, continued Temperature Regulation A network of blood vessels and nerves in the dermis help regulate body temperatures. Sweat glands also help remove excess body heat through the evaporation of sweat. Nervous and Endocrine Systems The nervous system is composed of signaling cells that collect and respond to information about the body’s internal and external environment. The central nervous system (CNS) includes the brain and spinal cord. The brain is the body’s main processing center. It coordinates the body’s efforts to maintain homeostasis. Nervous and Endocrine Systems, continued Sensory information from all parts of the body converge on the brain’s thalamus. The thalamus relays the information to the cerebrum for processing. At the base of the brain is the brainstem, which regulates heart rate, breathing rate, and blood pressure. Structure of the Human Brain Nervous and Endocrine Systems, continued The spinal cord is a column of nerves that links the brain to most of the peripheral nervous system (PNS). The PNS contains sensory and motor nerves. Sensory nerves carry information to the central nervous system from sense organs such as the skin. Nervous and Endocrine Systems, continued Motor nerves carry commands from the central nervous system to muscles and other organs, such as glands. Motor nerves are grouped into two independent systems: autonomic nervous system somatic nervous system Nervous and Endocrine Systems, continued Motor nerves that are not under conscious control are part of the autonomic nervous system Some ways that the autonomic nervous system maintains homeostasis include: stimulating digestion after a meal slowing down the heart rate after exercise preparing the body for stressful situations Nervous and Endocrine Systems, continued Motor nerves that are under conscious control are part of the somatic nervous system. The nerves we use to signal our legs or arms to move are part of the somatic nervous system. The somatic system also operates without conscious control, to help us maintain balance. the Somatic and Autonomic Nervous Systems Click the button below to watch the Visual Concept. Nervous and Endocrine Systems, continued Endocrine System Like the nervous system, the endocrine system sends messages to the body’s cells. When the body needs an immediate reaction, those messages are sent along the nervous system. When the body needs to bring about a long-term change, those messages are sent through the endocrine system. Nervous and Endocrine Systems, continued The endocrine system does the following: regulates metabolism maintains salt, water, and nutrient balance in the blood controls the body’s response to stress regulates growth, development, and reproduction Nervous and Endocrine Systems, continued The endocrine system uses chemical messengers called hormones. Hormones are made in one part of the body and cause change in another part of the body. Hormones cause cells to change their activities. Nervous and Endocrine Systems, continued For example, as people sweat, they lose water and salts. A hormone signals the kidneys to make less urine and conserve water. Another hormone signals the kidneys to reabsorb salt from urine and the sweat glands to decrease the amount of salt in sweat. Nervous and Endocrine Systems, continued Hormones are produced in special cells. Often, these cells are part of an endocrine gland. An endocrine gland is an organ that produces and releases hormones directly into the bloodstream or into the fluid around cells. The Endocrine System Digestive and Excretory Systems Digestive System The digestive system converts food into nutrients that a body’s cells can use. Some nutrients are used in metabolic reactions. Other nutrients are used to build new cells. Digestive and Excretory Systems, continued Digestion is the breaking down of large food molecules into smaller, more-usable ones. Large food molecules must be broken down both physically and chemically. The physical breakdown of food is called mechanical digestion. Digestive and Excretory Systems, continued Mechanical digestion begins in the mouth, when food is chewed into small pieces. As food is chewed, it mixes with saliva. Saliva adds digestive enzymes to food, starting the process of chemical digestion. Saliva also makes food particles easier to swallow. Digestive and Excretory Systems, continued When food is swallowed, it enters the esophagus, a muscular tube that pushes food along with wavelike contractions. Food is pushed into the stomach, where the digestion of protein begins. Acid produced in the stomach kills bacteria and turns on enzymes that aid in chemical digestion. Digestive and Excretory Systems, continued From the stomach, food is pushed into the small intestine. Bile from the liver and enzymes made by the small intestine and pancreas complete digestion. Proteins are reduced to amino acids. Digestive and Excretory Systems, continued Complex carbohydrates are changed into simple sugars. Lipids are changed to fatty acids and glycerol. Nutrients can then be absorbed into the blood and lymph from the small intestine. Digestive and Excretory Systems, continued Millions of tiny, fingerlike projections, called villi, line the small intestine. The villi increase the small intestine’s surface area so most nutrients are absorbed by the time they reach the large intestine. Cross Section of the Small Intestine Digestive and Excretory Systems, continued Undigested material enters the large intestine. Water, some vitamins, and minerals are absorbed into the bloodstream. The remaining materials exit the body through the anus. Digestive System in theSection 2 Human Body Homeostasis and Human Body Systems Digestive and Excretory Systems, continued Excretory System The human body must remove wastes that are produced by metabolism in a process known as excretion. Excretion enables the body to maintain its osmotic and pH balance. Sweat, exhaled carbon dioxide, and urine are all eliminated through excretion. Digestive and Excretory Systems, continued The kidneys are the primary organs of excretion. Each kidney is composed of nearly one million microscopic filtration units called nephrons. At the end of the nephron is the Bowman’s capsule, a cup-shaped structure. Digestive and Excretory Systems, continued As blood flows through capillaries in the capsule, blood pressure forces fluid out of the capillaries into the capsule. This fluid contains water, salt, glucose, amino acids, urea, and other substances. Urea is a nitrogen-containing waste product that is released into the blood by the liver. Digestive and Excretory Systems, continued The fluid passes into a narrow tubule, which is surrounded by capillaries. There, glucose and some other useful molecules in the fluid reenter the bloodstream. The remaining fluid passes out of the nephron through collecting ducts, where much of the water is removed. Human Kidney Structure Digestive and Excretory Systems, continued Waste solution from the kidneys is called urine. Urine flows from the kidneys through a ureter to the urinary bladder. Urine is collected and stored in the bladder. When the bladder’s muscular walls contract, urine exits through the urethra. Excretory System in the Human Body Respiratory and Circulatory Systems Respiratory System The respiratory system brings oxygen, O2, into the body. It also carries carbon dioxide, CO2, a waste product of cellular respiration, out of the body. Air enters the respiratory system when you inhale through your nose or mouth. Respiratory and Circulatory Systems, continued Inhalation occurs when muscles around the chest area contract and expand the rib cage. Inhaled air passes through a series of tubes to reach the lungs. Within each lung, the tubes carrying the air split into smaller and smaller tubes, called bronchioles. Respiratory and Circulatory Systems, continued The smallest bronchioles end in groups of tiny air sacs called alveoli (singular, alveolus), which are surrounded by blood vessels. Exchange of gases takes place across the thin, moist membranes of the alveoli. Oxygen leaves the alveoli and enters the blood, while CO2 leaves the blood and enters the alveoli. Visual Concept: Parts of the Human Respiratory System Click the button below to watch the Visual Concept. Respiratory and Circulatory Systems, continued Circulatory System The circulatory system carries nutrients, oxygen, hormones, and wastes through the body and distributes heat to maintain homeostasis. The cardiovascular system and the lymphatic system make up the body’s circulatory system. Blood, blood vessels and the heart make up the cardiovascular system. Respiratory and Circulatory Systems, continued This system acts like a network of highways that transports materials to and from the body’s cells. The network is made up of three kinds of vessels: arteries, capillaries, and veins. Arteries have thick, muscular walls to withstand the force of the blood pumped out of the heart. Respiratory and Circulatory Systems, continued Arteries carry blood to capillaries. A capillary has an extremely thin wall that allows gases and nutrients in the blood to pass across it into fluid around body cells. From the capillaries, blood enters the veins, which return blood to the heart. Circulation Pathway in the Human Body Respiratory and Circulatory Systems, continued Blood moves through blood vessels and interacts with every body system. Blood brings materials that the body system needs and carries away the products that the system makes. Blood also carries waste away from the system. Respiratory and Circulatory Systems, continued About 45% of blood is cells and cell fragments. The remaining 55% is plasma, the liquid portion of blood. Plasma is a solution made of about 90% water and 10% solutes. The solutes include nutrients, wastes, and salts. Salts have many functions, including maintaining osmotic balance with the fluids inside of cells and regulating blood pH. Respiratory and Circulatory Systems, continued Besides carrying materials, blood distributes body heat to help the body maintain a steady temperature. When the body is warm, blood vessels in the skin widen, allowing heat to leave the body. Blood vessels narrow when the body is cold. This helps the body to divert blood to deeper tissues and conserve heat. Respiratory and Circulatory Systems, continued Every time the heart pumps, some fluid from the blood is forced out of the capillaries. The escaped fluid collects in spaces around body cells. This fluid, called lymph, is picked up by the lymphatic system and returned to the blood. Respiratory and Circulatory Systems, continued The lymphatic system is made up of a network of vessels, tiny bean-shaped structures called lymph nodes, and lymph tissue. Lymph vessels collect lymph and return it to two large veins in the neck. As lymph moves through lymph vessels, the fluid passes through lymph nodes, where white blood cells collect. Respiratory and Circulatory Systems, continued The white blood cells destroy bacteria and other dangerous material in the lymph. In this way, the lymphatic system helps the body fight infection. Visual Concept: Movement of Lymph Click the button below to watch the Visual Concept. Summary The skeletal and muscular systems enable movement and provide support and protection for tissues and organs. The integumentary system protects the body from injury and UV radiation, defends against disease, helps regulate body temperature, and prevents the body from drying out. Summary, continued The nervous system collects and responds to information about the body’s internal and external environment. The endocrine system regulates metabolism; maintains salt, water, and nutrient balance in the blood; and regulates growth, development, and reproduction. The digestive system converts nutrients that a body’s cells can use. Excretion enables the body to maintain its osmotic and pH balance. Summary, continued The respiratory system brings oxygen, O2, into the body and carries carbon dioxide, CO2, out of the body. The circulatory system carries nutrients, oxygen, hormones, and wastes through the body and distributes heat to maintain homeostasis.
