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