Download Chapter 20 Unifying Concepts of Animal Structure and Function

Chapter 20
Unifying Concepts of Animal
Structure and Function
Overview:
Hierarchy of Structural Organization
Exchanges with the environment
Climbing the Walls
• 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?
• 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
– 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
THE HIERARCHY OF STRUCTURAL
ORGANIZATION IN AN ANIMAL
Structure fits function in the animal body
• The correlation between structure and function is
one of biology’s most fundamental concepts
Animal structure has a hierarchy
• Structure and
function are
correlated at
each level in
the structural
hierarchy of an
animal’s body
• 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
• 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
Tissues
• In most multicellular animals, cells are grouped
into tissues
– A tissue is a collection of many structurally similar
cells that act cooperatively to perform a specific
function
Tissues are groups of cells with a common structure and
function
• 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
Epithelial tissue covers and lines the body and its parts
• 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
Connective tissue binds and supports other tissues
• 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 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
• 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
• 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
• 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
Muscle Tissue
• Muscle tissue consists of bundles of long, thin,
cylindrical cells called muscle fibers
• Each cell has specialized proteins that contract
when the cell is stimulated by a nerve
• Skeletal muscle is responsible for voluntary body
movements
• Cardiac muscle pumps blood
• Smooth muscle moves the walls of internal
organs such as the stomach
• Skeletal muscle is attached to bones by tendons
– 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
• Cardiac muscle is found only in heart tissue
– Its contraction accounts for the heartbeat
– Cardiac muscle cells are branched and joined to one
another
• Smooth muscle is named for its lack of obvious
striations
– It is found in the walls of various organs
– It is involuntary
Nervous Tissue
• Nervous tissues makes communication of
sensory information possible
– 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
Nervous tissue forms a communication network
• The branching neurons of nervous tissue transmit
nerve signals that help control body activities
Organs and Organ Systems
• The next level in the structural hierarchy after
tissue is the organ
– 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
The body is a cooperative of organ systems
• The level of organization higher than an organ is
an organ system
• Each organ system has one or more functions
• 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
• The digestive system
gathers food
• The respiratory system
gathers oxygen
• The circulatory system,
aided by the lymphatic
system, transports the
food and oxygen
• The immune system
protects the body from
infection and cancer
• The excretory system disposes of certain wastes
• The endocrine and nervous systems control and
coordinate body functions
• The integumentary
system covers and
protects the body
• The skeletal system
supports and protects
the body
• The muscular system enables movement
• The reproductive system perpetuates the species
Connection: New imaging technology
reveals the inner body
• New technologies enable us to see body organs
without surgery
– Computed tomography (CT)
– Magnetic resonance
imaging (MRI)
– Positron-emission
tomography (PET)
EXCHANGES WITH THE EXTERNAL
ENVIRONMENT
• Every organism is an open system
– This means that organisms exchange chemicals and
energy with their surroundings
– Organisms must do this to survive
• Animals are not closed systems
– An animal must exchange materials and heat with its
environment
– This exchange must extend to the cellular level
Body Size and Shape
• An animal’s size and shape affect how it
exchanges energy and materials with its
surroundings
– All living cells must be bathed in water so that
exchange of materials may occur (e.g. hydra)
• Small animals with simple body construction
have enough surface to meet their cells’ needs
– Hydras can exchange materials with the environment
though direct diffusion
• Exchange with the environment is easy for
single-celled organisms
– The entire surface area of an amoeba is in contact
with the environment
• 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
• Larger, complex
animals have
specialized
internal
structures that
increase surface
area
• Lungs exchange oxygen and carbon dioxide with
the air
– The epithelium of the lungs has a very large total
surface area for this purpose
Animals regulate their internal environment
• In response to changes in external conditions,
animals regulate their internal environment
– They must do this to achieve homeostasis, an internal
steady state
Homeostasis
• Homeostasis is the body’s tendency to
maintain relatively constant conditions in
the internal environment even when the
external environment changes
Negative and Positive Feedback
• Most mechanisms of homeostasis depend on a
common principle called negative feedback
– The results of some process inhibit that very process
• Negative feedback
mechanisms keep
fluctuations in
internal conditions
within the narrow
range compatible
with life
• Less common is positive feedback
– The results of a process intensify that same process
– Example: uterine contractions during childbirth