Chapter 20 Unifying Concepts of Animal

Structure and Function

Overview:

Hierarchy of Structural Organization

Exchanges with the environment

• 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

• 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 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

• Structure and function are correlated at each level in the structural hierarchy of an animal’s body

Animal structure has a hierarchy

• 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

• 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

• 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

• 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

• 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

• 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 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

• Skeletal muscle is responsible for voluntary body movements

• Cardiac muscle pumps blood

• Smooth muscle moves the walls of internal organs such as the stomach

– 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

• Smooth muscle is named for its lack of obvious striations

– It is found in the walls of various organs– It is involuntary

• 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

• The branching neurons of nervous tissue transmit nerve signals that help control body activities

Nervous tissue forms a communication network

• 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

• 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

• 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

• New technologies enable us to see body organs without surgery– Computed tomography (CT)

Connection: New imaging technology reveals the inner body

– Magnetic resonance imaging (MRI)

– Positron-emission tomography (PET)

• 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

• Animals are not closed systems– An animal must exchange materials and heat with its

environment– This exchange must extend to the cellular level

• 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)

• 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

• 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

• Homeostasis is the body’s tendency to maintain relatively constant conditions in the internal environment even when the external environment changes

Homeostasis

• 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

• 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