Chapter 20

UNIFYING CONCEPTS OF

ANIMAL STRUCTURE AND

FUNCTION

I. Life is based on many structural levels

Levels of animal structure:

Atoms and molecules

Cells

Tissues

Organs

Organ systems

Organism: May consist of a single cell or a

complex multicellular organism.

Levels of Structural Organization in an Animal

TISSUES:

Most animal cells are organized into tissues.

Cooperative unit of very similar cells that perform

a specific function.

Tissue comes from Latin word meaning “weave”.

Cells of tissues may be held together by:

Fibers

Glue-like substance

Plasma membrane structures

Tissue structure is related to its function.

TISSUES:

There are four main types of animal

tissue:

1. Epithelial

2. Connective

3. Muscle

4. Nervous

1. Epithelial Tissue

Cells are tightly fitted together in continuous

layers or sheets.

Cover outside of body (skin), line organs and

internal body cavities (Mucous membranes of

digestive, respiratory, and reproductive systems).

Tight packaging allows tissue to act as a barrier

to protect against mechanical injury, infection,

and fluid loss.

Two surfaces:

Free surface: Exposed to air or fluid.

Bottom surface: Attached to underlying tissues by a

basement membrane, a dense layer of protein and

polysaccharides.

1. Epithelial Tissue

Can be classified based on two criteria:

A. Number of layers:

Simple: One layer.

Stratified: Several layers

B. Shape of cells:

Squamous: Flat cells.

Cuboidal: Cube shaped cells

Columnar: Column shaped cells

Example:

Simple squamous epithelium

Stratified columnar epithelium

Epithelial Tissue Covers and Lines the Body and its Parts

A. Simple squamous

(Lung air sacs)

D. Statified squamous

(Lining esophagus)

B. Simple cuboidal

(Kidney tubes)

C. Statified columnar

(Lining intestine)

1. Epithelial Tissue

Some epithelial tissues, such as mucous membranes,

absorb and secrete chemical solutions.

Mucous membranes:

Digestive tract epithelium (mucous membranes)

secretes mucus and digestive enzymes.

Respiratory tract epithelium secretes mucous that

helps trap dust particles before they reach the lungs.

2. Connective Tissue

Relatively few cells surrounded by large amounts

of nonliving material (matrix).

Cells secrete the matrix, which can be solid,

liquid, or gelatinous.

Diverse functions. Mainly bind, support, and

connect other tissues.

Six types of connective tissue in humans:

1. Loose Connective Tissue: Most widespread connective

tissue in vertebrates. Loose matrix with fibers,

packing material. Attaches skin to muscles, binds and

holds tissues and organs in place.

2. Adipose (fat): Pads and insulates body. Energy

storage.

Connective Tissue Binds and Provides Support

A. Loose Connective Tissue

B. Adipose Tissue

C. Blood

D. Fibrous Connective Tissue

E. Cartilage

F. Bone

Types of connective tissue in humans (Continued):

C. Blood: Fluid matrix (plasma) has water, salts, and

proteins. Red and white blood cells.

D. Fibrous Connective Tissue: Matrix of densely packed

collagen fibers. Strong and nonelastic. Found in:

• Tendons: Attach muscles to bones.

• Ligaments: Attach bone to bone.

E. Cartilage: Rubbery matrix with collagen fibers.

Found on end of bones, nose, ears, and between

vertebra.

F. Bone: Supports the body of most vertebrates. Solid

matrix of collagen fibers and calcium, phosphate, and

magnesium salts. Bone is harder than cartilage, but not

brittle because of collagen.

3. Muscle Tissue

Most abundant type of tissue in most animals.

Accounts for two-thirds (2/3) of human weight.

Specialized for contraction. Made up of long cells

that contract when stimulated by nerve impulses.

Muscle cells have many microfilaments made up

of actin and myosin.

Muscle contraction accounts for much of energy

consuming work in animals.

Adults have a fixed number of muscle cells.

Weight lifting doesn’t increase number of muscle

cells, only their size.

3. Muscle Tissue

There are three types of muscle tissue:

A. Skeletal (striated) muscle : Attached to bones by

tendons.

Responsible for voluntary movements.

B. Cardiac muscle: Forms contractile tissue of heart.

Not under voluntary control.

C. Smooth muscle: Found in walls of digestive tract,

bladder, arteries, uterus, and many internal organs.

Responsible for peristalsis and labor contractions.

Contract more slowly than skeletal muscle, but can

remain contracted longer.

Not under voluntary control.

A. Skeletal muscle

B. Cardiac muscle

C. Smooth muscle

Three Types of Muscle

4. Nervous Tissue

Senses stimuli and transmits signals from one

part of the animal to another.

Controls the activity of muscles and glands, and

allows the animal to respond to its environment.

Neuron: Nerve cell. Structural and functional

unit of nervous tissue. Consists of:

Cell body : Contains cell’s nucleus.

Dendrite: Extension that conveys signals towards the

cell body.

Axon: Extension that transmits signals away from the

cell body.

Supporting cells: Nourish, protect, and insulate

neurons.

Nervous Tissue Forms a Communication Network

Organs are made up of different tissues

Organ: Several tissues that act as a unit

and together perform one or more

biological functions.

Perform functions that component tissues can’t

carry out alone.

Example: The heart is an organ made up of:

• Muscle Tissue: Contraction

• Epithelial Tissue: Lines heart chambers to prevent

leakage and provide a smooth surface.

• Connective Tissue: Makes heart elastic and

strengthens its walls and valves.

• Nervous Tissue: Direct heart contractions.

Organs are Made of Several Different Tissues

Animals Regulate their Internal

Environment

Homeostasis: “Steady state”.

Internal environment of animal remains fairly

constant despite changes in the external

environment.

Control systems maintain internal conditions

within a range in which life’s metabolic

activities can occur.

Homeostasis is a dynamic state resulting from

changes in the outside environment and

internal control mechanisms that oppose such

changes.

Homeostatic Mechanisms Counteract Changes

in External Conditions

Animals Regulate their Internal

Environment

Homeostasis:

Maintained by negative feedback mechanisms.

A change in one condition (e.g.: low body

temperature), results is a response that

counteracts that change (e.g.: shivering, etc.).

Internal conditions regulated by negative

feedback:

• Body temperature (Normal range: 97 - 100oF)

• Salt concentration

• pH

• Blood levels of sugar, calcium, oxygen, etc.

Negative Feedback as Homeostatic Mechanism

Body Temperature is Regulated by Homeostasis

Major Organ Systems in Mammals

Digestive system

Respiratory system

Circulatory system

Cardiovascular

Lymphatic and Immune system

Excretory system

Endocrine system

Reproductive system

Nervous system

Muscular system

Skeletal system

Integumentary

1. Digestive System

Components: Mouth, salivary glands, throat,

esophagus, stomach, intestines, liver, gallbladder,

pancreas, rectum, and anus.

Functions:

Ingest and mechanically break down food.

Digest food: Stomach and small intestine mainly.

Absorb nutrients and water.

Eliminate waste.

Homeostatic Roles:

Supplies energy for life’s activities.

Supplies building blocks for macromolecules

Human Digestive System

2. Respiratory System

Components: Nose, throat, larynx, trachea,

bronchi, and lungs.

Functions:

Exchange gases with the environment:

Supplies blood with oxygen.

Disposes of carbon dioxide (waste product from cellular

respiration).

Homeostatic Roles:

Regulates blood pH.

Regulates blood oxygen and carbon dioxide levels.

Human Respiratory System

3. Cardiovascular System

Components: Blood, heart, arteries, veins, and

capillaries.

Functions:

Exchange gases with the respiratory system.

Supplies tissues with oxygen.

Removes carbon dioxide from tissues.

Transports materials (nutrients, hormones, etc.) inside

body.

Defends against infection.

Homeostatic Roles:

Provides nutrients and removes waste materials from

tissues.

Regulates body temperature, water and ion balance.

Human Cardiovascular System

4. Lymphatic and Immune System

Components: Lymph, lymphatic vessels, bone

marrow, thymus, spleen, and lymph nodes.

Functions:

Defends against infection: bacteria, fungi, viruses, etc.

Destruction of cancer and foreign cells.

Synthesis of antibodies and other immune molecules.

Synthesis of white blood cells.

Homeostatic Role:

Returns fluid and proteins that have leaked from

blood capillaries into tissues.

Up to 4 liters of fluid every day.

Fluid returned near heart/venae cavae.

Lymphatic and Immune Systems

5. Excretory (Urinary) System

Components: Kidneys, bladder, urethra, and

associated ducts.

Functions:

Kidneys remove nitrogen containing waste from blood.

Urine with waste is temporarily stored in bladder.

Excretion of urine.

Homeostatic Role:

Regulates water levels in body.

Removes excess water

Helps conserve water

Human Excretory System

6. Endocrine System

Components: Pituitary, adrenal, thyroid, thymus,

pancreas, ovaries, testes, and other ductless

glands.

Functions:

Produce hormones that regulate:

Blood chemistry: Levels of sugars, minerals, etc.

Reproduction

Growth

Metabolism

Digestion

Homeostatic Role:

With nervous system, regulates metabolism and blood

chemistry.

Human Endocrine System

7. Reproductive System

Components:

Female: Ovaries, oviduct, uterus, vagina, and

associated structures

Male: Testes, seminal vesicles, prostate, urethra,

penis, and associated structures.

Functions:

Only organ system that is not essential for individual

survival.

Continuation of species.

Gamete formation (eggs and sperm cells).

Homeostatic Role:

Maintains secondary sexual characteristics.

Male Reproductive System

Female Reproductive System

Gamete Formation Occurs in Testis

8. Nervous System

Components: Brain, spinal cord, nerves, sense

organs, and associated structures.

Functions:

Works with endocrine system to coordinate body

activities.

Integrates and processes information from sense

organs.

Sends signals (instructions) to muscles and glands.

Responds to internal stimuli.

Homeostatic Role:

Regulates most organ activities along with endocrine

system.

Human Nervous System

Nervous System Allows Us to Respond to Our Environment

9. Muscular System

Components: Skeletal muscles.

Functions:

Skeletal muscle contraction allows for voluntary

movement:

Movement and locomotion.

Mechanical work: Lifting, pulling, pushing objects.

Communication: Body language and facial expression.

Homeostatic Role:

Allows animals to respond to and control their

environment.

Muscular System: Skeletal Muscle Allows

Voluntary Movement

10. Skeletal System

Components: Bones, ligaments, and cartilage.

Functions:

Along with muscular system:

Movement and locomotion.

Mechanical work: Lifting, pulling, pushing objects.

Body support.

Protection of delicate internal organs (brain, heart,

lungs, etc.)

Calcium storage

Homeostatic Role:

Helps maintain constant blood calcium levels.

Skeletal System: Protection, Movement, & Support

11. Integumentary System

Components: Hair, skin, and nails.

Functions:

Protects the body from:

Infection: Barrier to microbes.

Mechanical injury

Excessive heat or cold: Thermoregulation

Water loss

Communication:

Receives stimuli from environment

Gives out subtle signals (blushing, etc.).

Homeostatic Role:

Helps maintain constant body temperature.

Integumentary System: Skin, Nails, & Hair

Organ systems must be coordinated for

animal to survive

Organ systems interact with one another in

order to maintain fairly stable conditions

(homeostasis) that are required for life.

Example: Interactions between:

• Respiratory

• Circulatory

• Digestive

Relationships Between Several Major Organ Systems