Chapter 3

Organization of the Body

Applied Learning Objectives Use the terminology associated with cell structure and function Learn about: body hierarchy cell organization and physiology cell life cycle the chemical environment tissue organization tissue form and function Understand the cellular basis of aging and pathology

Introduction The body’s levels of organization, or hierarchies, are a series of ordered groupings within a system. Each category in a hierarchy relies on the properties of the levels below it.

Hierarchy of Human Structure Humans are multicellular, meaning they are composed of many cells. The cells of most multicellular organisms cooperate with one another to carry out specific jobs. Cells compose tissues, tissues form organs, organs are combined into organ systems, the organ systems make up the organism. Simple organisms, such as bacteria, have fewer levels of organization than complex organisms like humans. A figure of the tissue level of organization is available for instructors in the Visual Aids asset of the Internet Resource Center (IRC).

Hierarchy of Human Structure Organisms are not considered the highest level of organization. Societies, or groups of organisms that interact with one another, are a step above organisms in the hierarchy. Human society is defined as a group of individuals living and working together in a particular region. Scientists have determined that the outcome of human interactions in a society can greatly impact the homeostasis of the human body.

The Human Physiological Environment A suitable physiological environment around the body’s cells is required for the body’s levels of organization to maintain homeostasis. The physiological environment includes internal conditions that optimize cell function and body organization. Water is an essential component of both the internal and external environments of cells. Physiological Environment: All the internal conditions that optimize individual cell function and body organization Internal environment: conditions within the cell External environment: conditions outside the cell

The Human Physiological Environment This watery, or aqueous, environment must have precise conditions that ensure homeostasis. These conditions are determined by: pH ions chemical reactions the transport of molecules between internal and external environments

Ions Ions are electrically charged particles that disperse in water. Some ions are minerals, which are nutrients needed by the body in small amounts. Ions called metals are any of several elements that can form shiny solids that conduct heat and electricity. All ions are water soluble and are therefore easily lost by the body whenever fluids are eliminated. Most ions are composed of a positively or negatively charged element. Some are electrically charged molecules. Ions having a positive charge are called cations while those with a negative charge are called anions.

Ions

Enzymatic Reactions and Energy Enzymes facilitate most of the chemical reactions that permit cells, tissues, organs, and organ systems to carry out their jobs. Most chemical reactions involve some form of energy transfer. Energy is usually defined as the capacity for doing work. This can be measured as the ability to do work (potential energy), or the conversion of this ability into some type of action (kinetic energy). Endergonic chemical reactions require energy to set off and carry out the reaction. In contrast, exergonic chemical reactions release energy. Both endergonic and exergonic chemical reactions generate energy that can be used to build cell structures or carry out physiological functions

Enzymatic Reactions and Energy Enzymes promote the exergonic reactions needed to obtain cell energy. In addition, they carry out endergonic reactions that build body structures and are used in cell work. Enzymes do this by modifying molecules in patterns that release or store energy.

Enzymatic Reactions and Energy Enzymes have an active site, which provides the attachment area and energy needed to modify a molecule. Each active site fits a particular molecule in the way a lock fits a specific key. Substrate is the name given to a chemical that an enzyme modifies in the active site. The substrate in turn is converted into the enzyme product.

Enzymatic Reactions

Molecular Transport A cell’s internal environment is separated from the external environment by a membrane. A selectively permeable membrane allows certain molecules to pass through it, in what is called molecular transport. There are five methods: diffusion passive transport active transport osmosis bulk active transport Diffusion The mixing of liquid or gas molecules as a result of random thermal stirring Passive Transport Diffusion across a membrane that requires no cell energy Active Transport Diffusion across a membrane that requires cell energy Osmosis Diffusion of water across a selectively permeable membrane Bulk Active Transport The movement of large amounts of particles across a membrane due to membrane movement

Discussion Question How well can you describe each type of molecular transport? Describe each type in small groups and then present your best descriptions to the rest of the class. Students should be able to describe each type of molecular transport. Discussing these as a class will help illustrate each type in ways that each student may not have considered.

Cell Structure All cells have three components: Cell membrane Cytoplasm Genome Membrane A sheet-like structure that surrounds a cell or its organelles and keeps the internal environment contained Cytoplasm The cell contents with the cell membrane Genome The genetic material within the cell passed from generation to generation

Cell Structure Human cells are eukaryotic.

Cell Function Cellular activities include metabolism, genetics, and the cell cycle. Metabolism: The sum of all chemical reactions in the body that maintain homeostasis Genetics: The study of heredity and the ways genetic information is converted into cell and body characteristics Cell Cycle: The events a cell goes through to carry out daily functions and the steps it takes to reproduce

Tissues The human body is composed of four types of tissue. Epithelial Tissue Tissue that covers external and internal body surfaces Connective Tissue Tissue that forms the supporting framework of the organs and the body Muscle Tissue Tissue that provides the body with movement and support Nervous Tissue Tissue that conducts and coordinates body information

Organs and Systems Organ systems of the human body include: cardiovascular digestive integumentary lymphatic muscular skeletal endocrine reproductive respiratory urinary Cardiovascular  regulates blood flow Digestive  regulates nutrition Integumentary  provides protection Lymphatic  regulates body fluids, helps fight disease Muscular  provides structure and movement Skeletal  provides support and movement Endocrine  regulates body function and development Reproductive  regulates sexual function Respiratory  regulates atmospheric gasses and certain body wastes Urinary  regulates production, storage, and removal of urine

Wellness and Illness over the Life Span Cell pathology is the basis of understanding dysfunction of the body’s hierarchy. Almost all gross diseases are due to dysfunction of one or more tissues in an organ system. Cellular aging is due to accumulated molecular decay. Dysfunction: Abnormal, impaired, or incomplete functioning of an organism, organ system, organ, tissue, or cell

Summary Each level of complexity is dependent on the proper functioning of the levels below them. Components of each level must work in unison to maintain the overall homeostasis of the body.