chapter 20 unifying concepts of animal structure and function overview: hierarchy of structural...
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Chapter 20 Unifying Concepts of Animal
Structure and Function
Overview:
Hierarchy of Structural Organization
Exchanges with the environment
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• The function of any part of an animal results from its unique structure
• Consider the gecko, a small lizard commonly found in the tropics– A gecko can walk up a wall
and across ceilings– How does it do that?
Climbing the Walls
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• The explanation relates to hairs, called setae, on the gecko’s toes– They are arranged in
rows– Each seta ends in
many split ends called spatulae, which have rounded tips
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– The ability to “stick” to surfaces results from attractions between molecules on the spatulae and molecules on the surface
– The structure of the gecko’s feet leads to a unique function
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• The correlation between structure and function is one of biology’s most fundamental concepts
Structure fits function in the animal body
THE HIERARCHY OF STRUCTURAL ORGANIZATION IN AN ANIMAL
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• Structure and function are correlated at each level in the structural hierarchy of an animal’s body
Animal structure has a hierarchy
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• Life is characterized by hierarchical levels of organization
• In animals– Individual cells are grouped into tissues– Tissues combine to form organs– Organs are organized into organ systems– Organ systems make up the entire organism
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• Biologists distinguish anatomy from physiology
– Anatomy is the study of the structure of an organism– Physiology is the study of the function of an
organism’s structural equipment
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• In most multicellular animals, cells are grouped into tissues
Tissues
– A tissue is a collection of many structurally similar cells that act cooperatively to perform a specific function
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• A tissue is a cooperative of many similar cells that perform a specific function
• Animals have four major categories of tissue– Epithelial tissue– Connective tissue– Muscle tissue– Nervous tissue
Tissues are groups of cells with a common structure and function
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• Epithelial tissue occurs as sheets of closely packed cells – It covers surfaces and lines internal organs and
cavities– Examples: epidermis, stomach lining
• The structure of each type of epithelium fits its function
Epithelial tissue covers and lines the body and its parts
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• Connective tissue is characterized by sparse cells– The cells manufacture and secrete an extracellular
matrix– The matrix is composed of fibers embedded in a
liquid, solid, or gel
Connective tissue binds and supports other tissues
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• Connective tissues have a sparse population of cells scattered through an extracellular matrix
– The matrix consists of a web of protein fibers embedded in a uniform foundation
• The structure of connective tissue correlates with its function– It binds and supports other tissues
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• Loose connective tissue is the most widespread connective tissue
– It binds epithelia to underlying tissues – It holds organs in place
• Adipose tissue stores fat
– It stockpiles energy – It pads and insulates the body
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• Blood is a connective tissue with a matrix of liquid– Red and white blood cells are suspended in plasma
• Fibrous connective tissue has a dense matrix of collagen
– It forms tendons and ligaments
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• The matrix of cartilage is strong but rubbery
– It functions as a flexible, boneless skeleton– It forms the shock absorbing pads that cushion the
vertebrae of the spinal column
• Bone is a rigid connective tissue with a matrix of rubbery fibers hardened with deposits of calcium
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• Muscle tissue consists of bundles of long, thin, cylindrical cells called muscle fibers
Muscle Tissue
• Each cell has specialized proteins that contract when the cell is stimulated by a nerve
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• Skeletal muscle is responsible for voluntary body movements
• Cardiac muscle pumps blood
• Smooth muscle moves the walls of internal organs such as the stomach
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– It is responsible for voluntary movements– The contractile apparatus forms a banded pattern in
each cell or fiber– It is said to be striated, or striped
• Skeletal muscle is attached to bones by tendons
– Its contraction accounts for the heartbeat– Cardiac muscle cells are branched and joined to one
another
• Cardiac muscle is found only in heart tissue
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• Smooth muscle is named for its lack of obvious striations
– It is found in the walls of various organs– It is involuntary
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• Nervous tissues makes communication of sensory information possible
Nervous Tissue
– Sensory input is received and processed– Motor output is then relayed to make body parts
respond
• Nervous tissue is found in the brain and spinal cord
• The basic unit of nervous tissue is the neuron, or nerve cell
– Neurons can transmit electrical signals rapidly over long distances
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• The branching neurons of nervous tissue transmit nerve signals that help control body activities
Nervous tissue forms a communication network
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• The next level in the structural hierarchy after tissue is the organ
Organs and Organ Systems
– An organ consists of two or more tissues packaged into one working unit that performs a specific function
– Examples: heart, liver, stomach, brain, and lungs
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• The level of organization higher than an organ is an organ system
• Each organ system has one or more functions
The body is a cooperative of organ systems
• The organs of humans and most other animals are organized into organ systems
– Organ systems are teams of organs that work together to perform a vital bodily function
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• The digestive system gathers food
• The respiratory system gathers oxygen
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• The circulatory system, aided by the lymphatic system, transports the food and oxygen
• The immune system protects the body from infection and cancer
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• The excretory system disposes of certain wastes
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• The endocrine and nervous systems control and coordinate body functions
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• The integumentary system covers and protects the body
• The skeletal system supports and protects the body
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• The muscular system enables movement
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• The reproductive system perpetuates the species
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• New technologies enable us to see body organs without surgery– Computed tomography (CT)
Connection: New imaging technology reveals the inner body
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– Magnetic resonance imaging (MRI)
– Positron-emission tomography (PET)
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• Every organism is an open system
EXCHANGES WITH THE EXTERNAL ENVIRONMENT
– This means that organisms exchange chemicals and energy with their surroundings
– Organisms must do this to survive
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• Animals are not closed systems– An animal must exchange materials and heat with its
environment– This exchange must extend to the cellular level
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• An animal’s size and shape affect how it exchanges energy and materials with its surroundings
Body Size and Shape
– All living cells must be bathed in water so that exchange of materials may occur (e.g. hydra)
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• Small animals with simple body construction have enough surface to meet their cells’ needs
– Hydras can exchange materials with the environment though direct diffusion
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• Exchange with the environment is easy for single-celled organisms
– The entire surface area of an amoeba is in contact with the environment
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• Animals with complex body forms face the same basic problem
– Every living cell must be bathed in fluid – Every cell must have access to essential nutrients
from the outside environment
• Complex animals have extensively folded or branched internal surfaces– These maximize surface area for exchange with the
environment
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• Larger, complex animals have specialized internal structures that increase surface area
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• Lungs exchange oxygen and carbon dioxide with the air– The epithelium of the lungs has a very large total
surface area for this purpose
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• In response to changes in external conditions, animals regulate their internal environment– They must do this to achieve homeostasis, an internal
steady state
Animals regulate their internal environment
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• Homeostasis is the body’s tendency to maintain relatively constant conditions in the internal environment even when the external environment changes
Homeostasis
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• Most mechanisms of homeostasis depend on a common principle called negative feedback
Negative and Positive Feedback
– The results of some process inhibit that very process
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• Negative feedback mechanisms keep fluctuations in internal conditions within the narrow range compatible with life
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• Less common is positive feedback
– The results of a process intensify that same process– Example: uterine contractions during childbirth