Ch 31 lecture

Copyright © 2009 Pearson Education, Inc..
Lectures by
Gregory Ahearn
University of North Florida
Chapter 31
Homeostasis and the
Organization of the
Animal Body

Copyright © 2009 Pearson Education Inc.
How Is The Animal Body Organized?
 The cells of a body are arranged into
numerous different body parts, with a
distinctive size, shape, and combination of
specialized cell types.

 Body structure and organization can be
described at different levels of organization.
• Tissues: the basic building blocks of bodies
whose cells perform specific functions
• Organs: a combination of tissues, such as the
stomach, small intestine, and urinary bladder
• Organ systems: the arrangement of organs
such as occurs in the digestive system, which
includes the stomach, small intestine, large
intestine, and other organs

connective
muscle
large
intestine
pancreas
stomach
mouth
pharynx
epithelial
Cells:
epithelial cells
liver
small intestine
esophagus
gallbladder
Tissues: Organ:
stomach
Organ system:
digestive system
 Cells, tissues, organs, and organ systems
Fig. 19-1

How Do Tissues Differ?
 There are four types of animal tissue:
• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nerve tissue

 Epithelial tissue forms sheets that cover the
body and line cavities, such as the mouth,
the stomach, and the bladder.
• There are many types of epithelial tissues,
and the structure of each type is related to its
function.

 Lung epithelium
consists of flattened
cells in a single
layer that gas
molecules can
easily cross.
 Another type of lung
epithelium consists
of elongated cells,
with cilia that
secrete mucus to
trap dust particles.
Fig. 19-2
(a) Thin epithelial tissue
(b) Ciliated epithelial tissue

 Epithelial tissues are continuously lost and
replaced by mitotic cell division.
• The lining of our mouths, our stomachs, and
our skin’s outer surface are continuously
replaced.
• Some epithelial tissues form glands, which are
clusters of cells that are specialized to secrete
substances.

 There are two types of glands:
• Exocrine glands: remain connected to the
epithelium by a passageway, such as with
sweat glands and salivary glands
• Endocrine glands: are not connected to an
epithelium by a duct, and secrete hormones
into the extracellular fluid and blood

 Connective tissues have diverse structures
and functions.
• Connective tissue serve mainly to support and
bind other tissues.
• Connective tissues include large quantities of
extracellular substances that are secreted by
the connective tissues themselves.

and functions (continued).
• A connective tissue, called the dermis, lies
beneath the epithelial tissue of the skin and
contains capillaries that nourish the
epithelium.
• Other fibrous connective tissues, known as
tendons and ligaments, attach muscles to
bones and bones to bones; these structures
are held together by strands of an
extracellular protein called collagen.

• Cartilage is a flexible and resilient connective
tissue that consists of widely spaced cells
surrounded by a thick, nonliving matrix.

 Cartilage covers the ends of bones at joints,
provides the supporting framework for our
air passages, supports the ear and nose,
and forms shock-absorbing pads between
the vertebrae.
Fig. 19-3
cartilage cells
collagen

central
canal
bone cells
concentric
bone matrix
 Bone resembles cartilage but is enhanced
by deposits of calcium phosphate.
Fig. 19-4

 Adipose tissue provides long-term energy
storage and insulation for animals adapted
to cold environments.
Fig. 19-5

• Blood and lymph are considered connective
tissues even though they are liquids.
• Lymph is a fluid that has leaked out of
blood vessels and is returned to the blood
through the lymphatic system.

platelets
white blood cell
red blood cells
 Blood has three types of cells: red blood
cells, white blood cells, and platelets
suspended in a fluid called plasma.
Fig. 19-6

striations
muscle fiber
 Muscle tissue has the ability to contract.
• The long, thin cells of muscle tissue contract
when stimulated, then relax passively.
Fig. 19-7

 There are three types of muscle tissue:
• Skeletal: under voluntary control, it has a
striped appearance and moves the skeleton
• Cardiac: located only in the heart, its cells are
electrically connected so that they contract as
a unit
• Smooth: lacks stripes and is embedded in the
walls of the digestive tract, the uterus, the
bladder, and large blood vessels; it produces
slow, involuntary contractions

 Nerve tissue transmits electrical signals.
• Nerve tissue allows the body to sense and
respond to the world around it.
• Transmission of electrical signals from the
brain and spinal cord occurs from them to
nerves that travel to all parts of the body.

 There are two types of nerve tissue cells:
• Neurons generate electrical signals and
conduct these signals to other neurons,
muscles, or glands.
• Glial cells surround, support, and protect
neurons and regulate the extracellular fluid,
allowing neurons to function optimally.

 A neuron has four parts, each with a
specialized function.
• The dendrites receive information from other
neurons or from the external environment.
• The cell body directs the maintenance and
repair of the cell.
• The axon conducts the electrical signal to its
target cell.
• The synaptic terminals transmit the signal to
the target cell.

 A nerve cell
Fig. 19-8
dendrites
synaptic
terminals
cell body
axon

How Are Tissues Combined Into Organs?
 Skin is an organ that contains all four tissue
types.
• The epidermis, or outer skin layer, is a
specialized epithelial tissue.
• Immediately below the epidermis lies the
dermis, a layer of connective tissue.

 Skin is an organ that contains all four tissue
types (continued).
• Blood vessels spread through the dermis and
carry the blood that nourishes both the dermal
and epidermal tissues.
• The dermis contains hair follicle glands that
produce hair; sweat glands that secrete sweat
to cool the body; and sebaceous glands that
secrete oil for lubrication.

 Skin
Fig. 19-9
sensory
nerve ending
living
epidermal
cells
dead cell layer
sebaceous gland
capillaries
arteriole
venule
hair follicle
muscle
(pulls hair upright)
sweat gland
hair shaft
epidermis
dermis
subdermal
connective
and adipose
tissue
capillary
bed

 Organ systems consist of two or more
interacting organs.
• The skin is part of the integumentary system,
which includes the hair and the nails, and
which serves as a barrier between the
environment and the inside of the body.
• In the digestive system, the mouth, stomach,
intestines, and other organs, such as the liver
and pancreas, supply digestive enzymes, and
all function together to convert food into
nutrient molecules.

How Do Animals Maintain Internal
Constancy?
 To function properly, an organ system must be
situated in stable environmental surroundings of
just the right moisture level, temperature, and
chemical composition.
• However, the external environment is highly variable;
to survive, an animal’s body must be able to maintain
constant internal conditions regardless of the external
conditions.
• Constancy of the internal environment is called
homeostasis.
• Internal homeostasis is maintained in animal bodies
by a host of mechanisms called feedback systems.

Constancy?
 Negative feedback reverses the effects of
changes.
• The most important mechanism governing
homeostasis is negative feedback, in which
the response to a change is to counteract the
change.
• In other words, an input causes an output
response that “feeds back” to the initial input
and decreases its effects.

Constancy?
 A home thermostat is a familiar example of
negative feedback.
• An input, temperature, dropping below a set point, the
thermostat setting, is detected by the thermometer.
• The thermometer responds with an output—switching
on the heater.
• The heater restores the temperature to the set point
and the heater switches off.
• The thermostat’s negative feedback mechanism
requires a control center with a set point, a sensor
(thermometer), and an effector (the furnace), which
accomplishes the change.

on off
control
center
below
above
set
point
thermometer
(sensor)
heater
(effector)
(a) Maintaining a home’s temperature
Constancy?
 Maintaining a home’s temperature
Fig. 19-10a

Constancy?
 Negative feedback keeps a person’s body
temperature close to 98.6°F (37°C).
• The center of the temperature control system is in the
hypothalamus, a region of the brain.
• Nerve endings throughout the body act as
temperature sensors and transmit this information to
the hypothalamus.
• When body temperature drops, the hypothalamus
activates effector mechanisms that raise your body
temperature.
• When normal body temperature is restored, the
hypothalamus switches off these control mechanisms.

Constancy?
 Maintaining a body’s temperature
Fig. 19-10b
nerve endings
(sensor)
skeletal
muscles
(effector)
hypothalamus
(control center)
heat output
(shivering)
decreases
heat output
(shivering)
increases
set
point
(b) Maintaining a body’s temperature

Constancy?
 Positive feedback drives an event to its
conclusion.
• A change in a positive feedback system
produces a response that intensifies the
original change.

Constancy?
 An example of positive feedback in animal
physiology are the events that control
childbirth.
• Early contractions of labor force the baby’s
head against the cervix, dilating the cervix.
• Stretch receptors in the cervix signal the
hypothalamus, which releases the hormone
oxytocin that stimulates more uterine
contractions.
• The feedback cycle is terminated by the
expulsion of the baby and its placenta.

Constancy?
Animation—Feedback Loops and HomeostasisPLAYPLAY

Constancy?
 The body’s organ systems act in concert.
• Numerous feedback mechanisms are
constantly at work, responding to inputs that
continuously change as an animal’s activities
and external environment change.

Constancy?
 The body’s organ systems act in concert
(continued).
• For example, the digestive system works in
concert with the systems responsible for
transporting substances within the body, such
as the circulatory system and the systems that
remove waste substances from the body,
including the excretory system.
• This coordinated action is possible because
the body continually sends messages from
sensors to effectors, which allow feedback
mechanisms to maintain homeostasis.

Ch 31 lecture

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