Chapter 27: Human Body Organization

Organization of the Human Body

• Human body is composed of cells, tissues, organs, and organ systems
• Cells are the basic units of structure and function, and they tend to be specialized in multicellular organisms
• Tissues are groups of cells that perform a single function
  • Epithelial tissue lines interior and exterior body surfaces
  • Connective tissue provides support for the body and connects its parts
  • Nervous tissue transmits nerve impulses throughout the body
  • Muscle tissue makes movements of the body possible
• Organs are groups of different types of tissues that work together to perform a single function or several related functions
• Organ systems are groups of organs that perform closely related functions

Homeostasis

• Homeostasis is the process of maintaining a controlled, stable internal environment
• Feedback inhibition is a process in which a stimulus produces a response that opposes the original stimulus
• Organ systems keep internal conditions within a certain range
• Example: hypothalamus monitors body temperature and responds to changes by sending signals to cells to speed up or slow down their activities

Liver and Homeostasis

• Liver regulates the level of glucose in the blood
• After a meal, glucose in the blood rises, and the liver takes glucose out of the blood to keep it from rising too much
• As the body uses glucose for energy, the liver releases stored glucose to keep the level of sugar from dropping too low

Human Systems

Digestive System

• Converts food into small molecules that can be used by cells of the body
• Digestion is the breakdown of food into smaller molecules
  • Mechanical digestion: physical breakdown of large food pieces into smaller pieces
  • Chemical digestion: enzymes break down food molecules
• Absorption: nutrients are absorbed into the bloodstream
• Elimination: waste products are eliminated from the body

Excretory System

• Excretes metabolic wastes from the body
• Skin: removes excess water, salts, and small amounts of urea in sweat
• Lungs: removes carbon dioxide from the body
• Liver: converts nitrogen-based wastes into less toxic compounds
• Kidneys: remove excess water, urea, and metabolic wastes from the blood
• Urine: produces and excretes urine

Circulatory System

• Transports oxygen, nutrients, and other substances throughout the body, and removes wastes from tissues
• Heart: pumps blood throughout the body
• Blood: carries oxygen, nutrients, and other substances throughout the body
• Circulation: heart functions as two pumps, one pushing blood to the lungs and the other pushing blood to the rest of the body

Blood

• Human body contains approximately 4-6 liters of blood
• Plasma: 55% of blood, 90% water, and 10% dissolved gases, salts, nutrients, enzymes, and proteins
• Red blood cells: transport oxygen
• White blood cells: fight viral and bacterial infections
• Platelets: necessary for blood to clot

Lymphatic System

• Network of vessels, nodes, and organs that collects lymph that leaves capillaries, "screens" it for microorganisms, and returns it to the circulatory system
• Role in circulation: collects lymph from capillaries and returns it to the bloodstream
• Role in immunity: traps microorganisms, stray cancer cells, and debris
• Thymus and spleen play roles in immune functions

Respiratory System

• Picks up oxygen from the air and releases carbon dioxide
• Air flow: air enters the respiratory system through the nose, mouth, and sinuses
• Gas exchange: oxygen diffuses into the bloodstream, and carbon dioxide diffuses out of the bloodstream
• Breathing: diaphragm and chest muscles contract and relax to bring air into and out of the lungs

Immunity and Disease

• Infectious diseases: caused by viruses, bacteria, fungi, and other pathogens
• Spread of infectious diseases: through coughing, sneezing, physical contact, and contaminated water and food
• Nonspecific defenses: skin, tears, and other secretions; inflammatory response, and fever### First Line of Defense
• Tears contain lysozyme, an enzyme that breaks down bacterial cell walls.
• Stomach secretions destroy many pathogens in food and water.

Second Line of Defense

• Inflammatory response causes infected areas to become red, painful, or inflamed.
• Mast cells release histamines, increasing blood flow to affected areas.
• White blood cells move into infected tissues, engulfing and destroying bacteria.
• The immune system releases chemicals that increase body temperature, producing fever.
• Increased body temperature may slow down or stop the growth of some pathogens.
• Higher temperature helps speed up the immune response.

Specific Defenses

• The immune system distinguishes between "self" and "other," inactivating or killing foreign substances or cells.
• "Self" cells carry chemical markers that act as passwords.
• When the immune system recognizes a bacterium or virus as "other," it uses cellular and chemical weapons to attack.
• The immune system "remembers" invaders, enabling a more rapid and effective response if the same pathogen attacks again.

Antigens and Vaccines

• Antigens are foreign substances that can stimulate an immune response.
• Antigens are molecules on the outer surfaces of bacteria, viruses, and parasites.
• The immune system responds to antigens by producing cells that attack invaders directly or that produce proteins called antibodies that tag them for destruction.
• Vaccines work by taking advantage of antigens and immunological memory.
• Vaccines contain antigens of pathogens that cause diseases, such as smallpox, diphtheria, and polio.

Fighting Infections

• The main working cells of the immune response are B lymphocytes (B cells) and T lymphocytes (T cells).
• B cells are produced in the bone marrow, while T cells are produced in the bone marrow but mature in the thymus.
• Each B and T cell is capable of recognizing one specific antigen.
• The specific immune response has two main styles of action: humoral immunity and cell-mediated immunity.
• Humoral immunity depends on the action of antibodies that circulate in the blood and lymph.
• Cell-mediated immunity defends the body against some viruses, fungi, and single-celled pathogens.

Immune System Disorders

• Problems with immune system functions can result in allergies, asthma, autoimmune disease, and AIDS.
• Allergies occur when antigens trigger inflammatory responses, such as sneezing, watery eyes, and runny nose.
• Allergens can trigger allergic reactions, and antihistamines can relieve symptoms.
• Asthma is characterized by narrow air passages, causing wheezing and difficulty breathing.
• Inhaled medications can relax smooth muscles around airways and relieve asthma symptoms.
• Autoimmune diseases occur when the immune system attacks the body's own cells.
• Type I diabetes is an autoimmune disease in which the immune system attacks insulin-producing cells in the pancreas.
• HIV and AIDS are caused by HIV, which attacks key cells within the immune system, leaving the body with inadequate protection against pathogens.
• HIV is a retrovirus that carries its genetic information in RNA, rather than DNA.
• Over time, HIV destroys T cells, crippling the immune system's ability to fight HIV itself and other pathogens, leading to AIDS.

HIV Transmission and Prevention

• HIV is transmitted through: sexual intercourse with an infected person, sharing needles with an infected person, contact with infected blood or blood products, and transmission from an infected mother to a child during pregnancy, birth, or breastfeeding.
• The best way to avoid HIV infection is through abstinence from sexual activity and avoidance of illegal intravenous drug use.
• There is no cure or reliable vaccine against AIDS.