Introduction to Tissues, Organ Systems, and Homeostasis

Chapter 4

Homeostasis

• Stable operating conditions in the internal environment

• Brought about by coordinated activities of cells, tissues, organs, and organ systems

Tissue

• A group of cells and intercellular

substances that interact in one or more

tasks

• Four types

Epithelial tissue Muscle tissue

Connective tissue Nervous tissue

Organs

• Group of tissues organized to perform a task or tasks

• Heart is an organ that pumps blood through body

• Heart consists of muscle tissue, nervous tissue, connective tissue, and epithelial tissue

Organ Systems

• Organs interact physically, chemically,

or both to perform a common task

• Circulatory system includes the heart,

the arteries, and other vessels that

transport blood through the body

Epithelial Tissue

• Lines the body’s surface, cavities, ducts, and tubes

• One free surface faces a body fluid or the

environment

simplesquamousepithelium

basementmembrane

connective tissue

Simple Epithelium

• Consists of a single layer of cells

• Lines body ducts, cavities, and tubes

• Cell shapes:

Squamous Cuboidal Columnar

Stratified Epithelium

• Two or more layers thick

• Functions in protection, as in skin

• Cells in the layers may be squamous,

columnar, or cuboidal

Glands

• Secretory organs derived from

epithelium

• Exocrine glands have ducts or tubes

• Endocrine glands are ductless

Cell Junctions

• Tight junctions

prevent leaks

• Gap junctions

connect abutting

cytoplasms

• Adhering junctions

cement cells

together

Connective Tissue

• Most abundant tissue in the body

• Cells are scattered in an extracellular

matrix

• Matrix is collagen and/or elastin fibers in a

polysaccharide ground substance

Soft Connective Tissues

Loose connective

tissue

Dense, regular connective

tissue

Dense, irregular connective

tissue

Specialized Connective Tissues

Cartilage Bone Adipose tissue

Blood

• Classified as a connective tissue

because blood cells arise in bone

• Serves as the body’s transport medium

• Red cells, white cells, and platelets are

dispersed in a fluid medium called

plasma

Muscle Tissue

• Composed of cells that contract when

stimulated

• Helps move the body and specific body

parts

Three Types of Muscle

• Skeletal muscle

• Smooth muscle

• Cardiac muscle

Skeletal Muscle

• Located in muscles that

attach to bones

• Long, cylindrical cells are

striated

• Cells are bundled closely

together in parallel arrays

Smooth Muscle

• In walls of many internal

organs and some blood

vessels

• Cells are not striped and

taper at the ends

Cardiac Muscle

• Present only in the heart

• Cells are striated and

branching

• Ends of cells are joined by

communication junctions

Nervous Tissue

• Detects stimuli, integrates information,

and relays commands for response

• Consists of excitable neurons and

supporting neuroglial cells

Neurons

• Excitable cells

• When stimulated, an electrical impulse

travels along the plasma membrane

• Arrival of the impulse at the neuron

endings triggers events that stimulate or

inhibit adjacent neurons or other cells

Neuroglia

• Constitute more than half of the nervous

tissue

• Protect and support the neurons, both

structurally and metabolically

Replacement Tissues

• Artificial skin

• Bioengineered cartilage and bone

• Organoapatites and coral to repair bone

Stem Cells

• Have the potential to develop into

different kinds of mature cells

• Embryonic cells most useful but use of

embryos as source is controversial

• Some adult tissues also may provide

stem cells

Membranes

• Epithelial tissue membranes– Mucous membranes– Serous membranes– Cutaneous membrane

• Connective tissue membranes– Synovial membranes

Major Organ Systems

• Integumentary

• Muscular

• Skeletal

• Nervous

• Endocrine

• Lymphatic

• Respiratory

• Urinary

• Circulatory

• Reproductive

Major Body Cavities

• Cranial cavity

• Spinal cavity

• Thoracic cavity

• Abdominal cavity

• Pelvic cavity

Planes of Symmetry

Frontal plane(aqua)

Transverse plane(yellow)

Midsagittal plane (green)

Primary Tissues

• In vertebrate embryos, cells become

arranged to form three primary tissues

Ectoderm

Mesoderm

Endoderm

• These give rise to all adult tissues

Functions of Human Skin

• Protects the body from injury,

dehydration, UV radiation, and some

pathogens

• Helps control temperature

• Receives some external stimuli

• Produces vitamin D

Structure of Human Skin

• Part of body’s integument

• Two layers– Outer epidermis

– Inner dermis

• Atop a layer of hypodermis

Epidermis

• Stratified epithelium

• Grows from bottom upward

• Most abundant cells are keratin-

producing keratinocytes

• Melanocytes produce the brown

pigment melanin

Dermis

• Dense connective tissue with many

elastin and collagen fibers

• Includes blood vessels, lymph

vessels, and receptor endings of

sensory nerves

Sweat Glands

• Arise from epidermal cells

• Composition of sweat

– 99% water, with dissolved salts, trace of

ammonia (waste product)

• Controlled by sympathetic nerves

Oil Glands

• Also called sebaceous glands

• Derived from epidermal cells

• Secretions lubricate and soften hair and

skin; also kill many surface bacteria

• Acne occurs when bacteria infect oil-

gland ducts

Hair

• Root is embedded in skin

• Cells near the base of root divide, push

cells above them upward

• Hair follicles nourished by the dermis

• Shaft of dead cells extends above the

skin surface

UV Damages Skin

• UV light stimulates melanin production in skin; produces a tan

• Tan is the body’s way of protecting itself against UV

• Prolonged sun exposure causes elastin fibers to clump, skin to age prematurely, increases risk of cancer

Body Fluids

• The human body contains about 15 liters

of fluid

• Fluid outside of cells is extracellular fluid

– Interstitial fluid lies between cells

– Plasma is the fluid portion of the blood

Fluid Balance

• Changes in extracellular fluid cause

changes in cells

• The component parts of every animal

work to maintain a stable fluid

environment for living cells

Homeostasis

• Stable operating conditions in the internal environment

EFFECTOR(a muscleor a gland)

RESPONSE(system’soutput)

Response to the stimulus leads to change. Change is “fed back” to the receptor.

STIMULUS (input into the system)

RECEPTOR(e.g., free

nerve endingin the skin)

INTEGRATOR(such asthe brain)

Negative Feedback

• Some activity alters a condition in the

internal environment

• Alteration triggers a response

• Response reverses the altered condition

Positive Feedback

• Some activity alters the internal

environment

• The alteration triggers a response

• The response intensifies the change in

the internal condition