Download Tissues & Homeostasis, chap. 31

Homeostasis and the
Organization of the
Animal Body
Chapter 31
pages 604 - 618
Hierarchy of Structures
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Tissues are composed of similar cells that perform a
specific function
Organs perform complex functions and include two or
more interacting tissue types
Organ systems consist of two or more interacting
organs that function in a coordinated manner
Cells, Tissues, Organs, Organ Systems
How Is the Animal Body
Organized?

Animal tissues are composed of similar cells
that perform a specific function

There are four categories of animal tissues
 Epithelial tissue
 Connective tissue
 Muscle tissue
 Nerve tissue
Epithelial Tissue

Covers the body, lines cavities, and forms glands

All body surfaces — skin, digestive, respiratory, and
urinary tracts, and circulatory system

Epithelial tissue is sheets of cells firmly attached to
one another by connections such as desmosomes
and tight junctions

Attached to an underlying layer of fibrous proteins
or basement membrane - provides support,
flexibility, and strength

Cells are continuously lost and replaced
Types of Epithelium

Simple epithelium is one cell thick and lines the
respiratory, urinary, reproductive, and circulatory
systems

Stratified epithelium is found in the skin and just inside
body openings that are continuous with the skin (mouth
and anus) and are continuously lost and replaced

Several cells thick and can withstand considerable wear and tear
Epithelial Tissue
flattened
cells
basement
membrane
(a) Lining of the lungs (simple epithelium)
cilia
mucus
basement
membrane
mucusproducing
cells
(b) Lining of the trachea (simple epithelium)
Skin - Epithelial Tissue
dead
cells
flattened
dying
cells
differentiating
cells
dividing
cells
basement
membrane
(c) Skin epidermis (stratified epithelium)
Glands

Glands are cells or groups of cells specialized to
secrete large quantities of substances outside the cell

Two categories
 Exocrine glands secrete substances into a body
cavity or onto the body surface, usually through a duct
 Sweat glands, mammary glands, salivary glands,
and glands that secrete digestive enzymes

Endocrine glands lack ducts, and release hormones
into the extracellular fluid, diffuses into capillaries
 Hormones are chemicals produced in small quantities
and transported thru the bloodstream to regulate the
activity of other cells
Connective Tissues

Diverse structures and functions



Support and strengthen other tissues, binding the
cells of other tissues into coherent structures, such as
skin or muscle
They consist of fluid containing proteins, especially
collagen
Three categories of connective tissue
 Loose connective tissue
 Dense connective tissue
 Specialized connective tissue
Loose Connective Tissue

The most abundant form
of connective tissue,
consisting of a thick fluid
containing scattered cells
that secrete protein

Flexible tissue connects,
supports, and surrounds
other tissue types,
forming a framework for
organs such as the liver
Dense Connective Tissue

Packed with collagen
fibers that provide
flexibility and strength,
but only in the direction in
which the collagen fibers
are arranged


Tendons, which connect
bones to muscles
Ligaments, which connect
bones to bones
Specialized connective tissues

Diverse functions and structures

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Cartilage
Bone
Fat (adipose tissue)
Blood
Lymph
Cartilage

Widely spaced cells
surrounded by thick,
nonliving matrix composed of
collagen

It covers the ends of bones at
joints, provides the supporting
framework for the respiratory
passages, supports the ear and
nose, and forms shock-absorbing
pads between the vertebrae

Flexible, but can break if bent too
far
Bone

Bone resembles
cartilage, but its matrix is
hardened by deposits of
calcium phosphate

It forms in concentric
rings around a central
canal, which contain
blood vessels
Adipose

Adipose tissue is
made up of fat cells
that are modified for
long-term energy
storage

Can serve as
insulation for animals
living in a cold
environment
Blood and Lymph

Blood and lymph are specialized forms
of connective tissue because they are
composed largely of extracellular fluids
in which proteins are suspended

The cellular portion of blood 



Red blood cells transport oxygen
White blood cells fight infection
Platelets are cell fragments that aid in
blood clotting
The blood cells are suspended in a fluid
called plasma
Lymph

Lymph is fluid that has leaked out of blood capillaries,
it enters the lymph vessels and is carried back to the
circulatory system
Muscle Tissue

Have the ability to contract

The long, thin cells of muscle tissue contract when
stimulated and then relax when the stimulation stops

There are three types of muscle tissue
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Skeletal Muscle

Skeletal muscle is
stimulated by the
nervous system and is
under voluntary, or
conscious, control

Its main function is to
move the skeleton
Cardiac Muscle

Cardiac muscle
spontaneously active, not
under conscious control

Interconnected by gap
junctions, through which
electrical signals spread,
stimulating cardiac muscles
cells to contract in a
coordinated fashion
Smooth Muscle

Found throughout the body, in
the walls of the digestive and
respiratory tracts, uterus,
bladder, and larger blood
vessels

Produces slow, sustained,
involuntary contractions that are
stimulated by the nervous
system, by stretch, or by
hormones or other chemicals
Nervous Tissue

Specialized to produce
and conduct electrical
signals

Brain, spinal cord, and
nerve cells (neurons)


Neurons are specialized to
generate electrical signals and
conduct signals to other
neurons, muscles, or glands
Glial cells surround, support,
insulate, and protect neurons
How Is the Animal Body
Organized?

Organs are formed from at least two types of
tissues that function together; most consist of
all four tissue types

Function as part of an organ system

The skin illustrates the properties of organs

Outer layer of epithelial cells underlain by connective
tissue that contains a blood, nerve supply, muscle,
and glandular structures derived from the epithelium
Structural Components of Skin
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Epidermis, or outer layer, is specialized
stratified epithelial tissue
Immediately beneath the epidermis lies a layer
of loose connective tissue, the dermis, which
contains blood vessels
Specialized epithelial cells dip down from the
epidermis into the dermis, forming hair follicles
Below the dermis is a layer of adipose tissue
Skin is an Organ
hair shaft
pore
sebaceous gland
capillary bed
epidermis
dead cell layer
living epidermal
cells
dermis
sensory nerve
endings
subdermal
connective
and adipose
tissue
hair follicle
arterioles
venules
lymph
vessels
muscle
(pulls hair upright)
sweat gland
Organ Systems

Two or more interacting organs, located in
different regions of the body, that work
together to perform a common function

Digestive system - in which the mouth, esophagus,
stomach, intestines, liver and pancreas, all function
together to convert food into nutrient molecules that
can be absorbed into the bloodstream
Homeostasis

Animal cells need a narrow range of
conditions to survive

Homeostasis is the process by which an
organism maintains its internal environment,
within that narrow range
How does it work?

The internal environment is maintained in a
state of dynamic constancy

The internal environment is in a state of dynamic
constancy

The body adjusts to ongoing internal and external
changes to maintain constant conditions
Examples of Regulated
Conditions

Temperature

Water and salt concentrations
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Glucose concentrations
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pH (acid-base balance)
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Oxygen and carbon dioxide concentrations
Why is this Important?

Animal cells are constantly generating and
using large quantities of ATP to sustain life
processes

Continuous supplies of high-energy
molecules and O2 are required to carry out
the reactions that generate ATP

Energy production helps explain the
importance of glucose and oxygen levels

Each of the reactions for producing ATP is catalyzed
by a protein whose ability to function depends on its
three-dimensional structure

This structure is maintained by hydrogen bonds,
which can be disrupted if the environment is too hot,
salty, acidic, or basic

The need to maintain these bonds helps explain the
requirement for a narrow range of temperature, pH,
and salt
Animals vary in their homeostatic
abilities

Birds and mammals are efficient at maintaining
homeostasis for all the internal conditions listed above

Other animals have reduced or absent homeostasis
for one or more aspects of their internal environment
 For example, many marine invertebrates, including
snails, crabs, and worms, cannot regulate the overall
concentration of their bodily fluids
Classification

Scientists classify animals according to their
major source of body warmth

Endotherms generate heat through metabolic
reactions - birds and mammals
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Warm blooded
Ectotherms derive body heat from the
environment, and maintain it by occupying a
constant environment or by behavioral activities reptiles, amphibians, fishes, and invertebrates

Cold blooded
Warm-Blooded or Cold-Blooded?
Regulation

Feedback systems regulate internal
conditions

Homeostatic mechanisms that maintain internal
constancy are called feedback systems

Two types
 Negative feedback - counteracts the effects of
changes in the internal environment to maintain
homeostasis
 Positive feedback, - drives rapid, self-limiting changes,
such as those that occur when a mother gives birth
Negative Feedback

Works by reversing the effect of a change
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The most important feedback mechanism
A change in the environment causes responses that “feed back”
to counteract the change
The overall result of negative feedback is a return to the original
condition
Three components
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A sensor detects the current condition
A control center compares that condition to the desired state,
called the set point
An effector produces an output that restores the desired
condition
Animation: Elements of a Feedback
System
Home temperature is regulated
by negative feedback

Negative feedback systems that control body temperature are
similar to those used to heat a home

The sensor is a thermometer, the control center is a thermostat, and the
effector is the heater

The thermometer detects the room temperature and sends that
information to the thermostat, where it is compared to the set point of the
desired temperature

If the temperature is below the set point, the thermostat signals the
heater to turn on and generate heat

The heater warms the room, restoring the temperature to the set point,
causing the thermostat to turn off the heater
Animation: Temperature Control in
Your House
Negative feedback maintains
body temperature

The temperature control center is located in the
hypothalamus, a part of the brain

Set point is between 97º- 99º F

Nerve endings act as temperature sensors and transmit
information to the hypothalamus

If the body temperature falls below the set point, the
hypothalamus activates effector mechanisms that raise
body temperature
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Shivering, blood vessel constriction, increased metabolic rate
When body temperature is restored, the sensors signal the
hypothalamus to switch off these actions
Negative Feedback Maintains
Homeostasis

The body’s temperature controls system can
also act to reduce body temperature if rises
above set point
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Blood vessels leading to the skin to dilate, allowing
warm blood to flow to the skin, where heat can be
radiated into the air
Sweat glands secrete fluid, cooling the body as it
evaporates from the skin
Fatigue and discomfort cause the body to slow down,
so the body generates less heat
Animation: The Control of Body
Temperature
Positive Feedback

Positive feedback enhances the effects of
changes

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A change produces a response that intensifies the
initial change
Positive feedback is relatively rare in biological
systems, but occurs during childbirth and blood
clotting
Childbirth
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Labor contractions force the baby’s head against the
cervix at the base of the uterus, causing it to stretch
and open
Stretch-receptor neurons in the cervix signal the
hypothalamus
The hypothalamus releases oxytocin, a hormone
which stimulates more and stronger contractions
Stronger contractions cause the baby’s head to
stretch the cervix even more, causing the release of
more oxytocin
Delivery of the baby relieves the pressure on the
cervix, halting the positive feedback cycle
Animation: The Control of Labor