ch 31 lecture
TRANSCRIPT
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Lectures by
Gregory AhearnUniversity of North Florida
Chapter 31
Homeostasis and the Organization
of the Animal Body
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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.
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How Is The Animal Body Organized?
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
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connective
muscle
largeintestine
pancreasstomach
mouth
pharynx
epithelialCells:epithelial cells
liversmall intestine
esophagusgallbladder
Tissues: Organ:stomach
Organ system:digestive system
How Is The Animal Body Organized?
Cells, tissues, organs, and organ systems
Fig. 19-1
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How Do Tissues Differ?
There are four types of animal tissue:• Epithelial tissue• Connective tissue• Muscle tissue • Nerve tissue
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
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
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
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
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
Connective tissues have diverse structures 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.
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How Do Tissues Differ?
Connective tissues have diverse structures and functions (continued).• Cartilage is a flexible and resilient connective
tissue that consists of widely spaced cells surrounded by a thick, nonliving matrix.
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How Do Tissues Differ?
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
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centralcanal
bone cells
concentricbone matrix
How Do Tissues Differ?
Bone resembles cartilage but is enhanced by deposits of calcium phosphate.
Fig. 19-4
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How Do Tissues Differ?
Adipose tissue provides long-term energy storage and insulation for animals adapted to cold environments.
Fig. 19-5
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How Do Tissues Differ?
Connective tissues have diverse structures and functions (continued).• 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.
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platelets
white blood cell
red blood cells
How Do Tissues Differ?
Blood has three types of cells: red blood cells, white blood cells, and platelets suspended in a fluid called plasma.
Fig. 19-6
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striations
muscle fiber
How Do Tissues Differ?
Muscle tissue has the ability to contract.• The long, thin cells of muscle tissue contract
when stimulated, then relax passively.
Fig. 19-7
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How Do Tissues Differ?
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
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
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.
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How Do Tissues Differ?
A nerve cell
Fig. 19-8
dendrites
synapticterminals
cell body
axon
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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.
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How Are Tissues Combined Into Organs?
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.
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How Are Tissues Combined Into Organs?
Skin
Fig. 19-9
sensorynerve ending
livingepidermalcells
dead cell layer
sebaceous gland
capillaries
arteriolevenule
hair folliclemuscle(pulls hair upright)
sweat gland
hair shaft
epidermis
dermis
subdermalconnectiveand adiposetissue
capillarybed
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How Are Tissues Combined Into Organs?
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.
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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.
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How Do Animals Maintain Internal 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.
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How Do Animals Maintain Internal 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.
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on off
controlcenter
below
aboveset
point
thermometer(sensor)
heater(effector)
(a) Maintaining a home’s temperature
How Do Animals Maintain Internal Constancy? Maintaining a home’s temperature
Fig. 19-10a
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How Do Animals Maintain Internal 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.
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How Do Animals Maintain Internal Constancy? Maintaining a body’s temperature
Fig. 19-10b
nerve endings(sensor)
skeletalmuscles(effector)
hypothalamus(control center)
heat output(shivering)decreases
heat output(shivering)increases
setpoint
(b) Maintaining a body’s temperature
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How Do Animals Maintain Internal Constancy? Positive feedback drives an event to its
conclusion.• A change in a positive feedback system
produces a response that intensifies the original change.
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How Do Animals Maintain Internal 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.
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How Do Animals Maintain Internal Constancy?
Animation—Feedback Loops and HomeostasisPLAYPLAY
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How Do Animals Maintain Internal 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.
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How Do Animals Maintain Internal 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.