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Lectures by
Gregory AhearnUniversity of North Florida
Chapter 19
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 intonumerous different body parts, with adistinctive size, shape, and combination ofspecialized cell types.
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How Is The Animal Body Organized?
Body structure and organization can bedescribed at different levels of organization.
Tissues: the basic building blocks of bodieswhose cells perform specific functions
Organs: a combination of tissues, such as thestomach, small intestine, and urinary bladder
Organ systems: the arrangement of organssuch as occurs in the digestive system, which
includes the stomach, small intestine, largeintestine, and other organs
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connective
muscle
large
intestine
pancreasstomach
mouth
pharynx
epithelialCells:
epithelial cells
liver
small intestineesophagus
gallbladder
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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19.2 How Do Tissues Differ?
There are four types of animal tissue: Epithelial tissue
Connective tissue
Muscle tissue
Nerve tissue
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19.2 How Do Tissues Differ?
Epithelial tissue forms sheets that cover thebody 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 itsfunction.
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19.2 How Do Tissues Differ?
Lung epitheliumconsists of flattenedcells in a single layerthat gas moleculescan easily cross.
Another type of lungepithelium consistsof elongated cells,with cilia that
secrete mucus totrap dust particles.
Fig. 19-2
(a ) Thin epithelial tissue
(b ) Ciliated epithelial tissue
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19.2 How Do Tissues Differ?
Epithelial tissues are continuously lost andreplaced by mitotic cell division.
The lining of our mouths, our stomachs, andour skins outer surface are continuouslyreplaced.
Some epithelial tissues form glands, which areclusters of cells that are specialized to secrete
substances.
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19.2 How Do Tissues Differ?
There are two types of glands: Exocrine glands: remain connected to the
epithelium by a passageway, such as withsweat glands and salivary glands
Endocrine glands: are not connected to anepithelium by a duct, and secrete hormonesinto the extracellular fluid and blood
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19.2 How Do Tissues Differ?
Connective tissues have diverse structuresand functions.
Connective tissue serve mainly to support andbind other tissues.
Connective tissues include large quantities of
extracellular substances that are secreted bythe connective tissues themselves.
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19.2 How Do Tissues Differ?
Connective tissues have diverse structuresand functions (continued).
A connective tissue, called the dermis, liesbeneath the epithelial tissue of the skin andcontains capillaries that nourish theepithelium.
Other fibrous connective tissues, known astendons and ligaments, attach muscles tobones and bones to bones; these structuresare held together by strands of an extracellularprotein called collagen.
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19.2 How Do Tissues Differ?
Connective tissues have diverse structuresand functions (continued).
Cartilage is a flexible and resilient connectivetissue that consists of widely spaced cellssurrounded by a thick, nonliving matrix.
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19.2 How Do Tissues Differ?
Cartilage covers the ends of bones at joints,provides the supporting framework for ourair passages, supports the ear and nose,and forms shock-absorbing pads betweenthe vertebrae.
Fig. 19-3
cartilage cells
collagen
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centralcanal
bone cells
concentricbone matrix
19.2 How Do Tissues Differ?
Bone resembles cartilage but is enhancedby deposits of calcium phosphate.
Fig. 19-4
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19.2 How Do Tissues Differ?
Adipose tissue provides long-term energystorage and insulation for animals adaptedto cold environments.
Fig. 19-5
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19.2 How Do Tissues Differ?
Connective tissues have diverse structuresand functions (continued).
Blood and lymph are considered connectivetissues even though they are liquids.
Lymph is a fluid that has leaked out of blood
vessels and is returned to the blood throughthe lymphatic system.
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platelets
white blood cell
red blood cells
19.2 How Do Tissues Differ?
Blood has three types of cells: red bloodcells, white blood cells, and plateletssuspended in a fluid called plasma.
Fig. 19-6
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striations
muscle fiber
19.2 How Do Tissues Differ?
Muscle tissue has the ability to contract.
The long, thin cells of muscle tissue contractwhen stimulated, then relax passively.
Fig. 19-7
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19.2 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 areelectrically connected so that they contract asa unit
Smooth: lacks stripes and is embedded in thewalls of the digestive tract, the uterus, thebladder, and large blood vessels; it producesslow, involuntary contractions
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19.2 How Do Tissues Differ?
Nerve tissue transmits electrical signals.
Nerve tissue allows the body to sense andrespond to the world around it.
Transmission of electrical signals from thebrain and spinal cord occurs from them tonerves that travel to all parts of the body.
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19.2 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 protectneurons and regulate the extracellular fluid,allowing neurons to function optimally.
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19.2 How Do Tissues Differ?
A neuron has four parts, each with aspecialized function.
The dendrites receive information from otherneurons 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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19.2 How Do Tissues Differ?
A nerve cell
Fig. 19-8
dendrites
synapticterminals
cell body
axon
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19.3 How Are Tissues Combined Into
Organs?
Skin is an organ that contains all four tissuetypes.
The epidermis, or outer skin layer, is aspecialized epithelial tissue.
Immediately below the epidermis lies thedermis, a layer of connective tissue.
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19.3 How Are Tissues Combined IntoOrgans?
Skin is an organ that contains all four tissuetypes (continued).
Blood vessels spread through the dermis andcarry the blood that nourishes both the dermaland epidermal tissues.
The dermis contains hair follicle glands thatproduce hair; sweat glands that secrete sweatto cool the body; and sebaceous glands that
secrete oil for lubrication.
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19.3 How Are Tissues Combined Into
Organs?
Skin
Fig. 19-9
sensorynerve ending
livingepidermalcells
dead cell layer
sebaceous gland
capillaries
arteriole
venule
hair folliclemuscle(pulls hair upright)
sweat gland
hair shaft
epidermis
dermis
subdermal
connectiveand adiposetissue
capillarybed
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19.3 How Are Tissues Combined IntoOrgans?
Organ systems consist of two or moreinteracting organs.
The skin is part of the integumentary system,which includes the hair and the nails, andwhich serves as a barrier between theenvironment 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, andall function together to convert food intonutrient molecules.
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19.4 How Do Animals Maintain Internal
Constancy? To function properly, an organ system must be
situated in stable environmental surroundings ofjust the right moisture level, temperature, andchemical composition.
However, the external environment is highly variable;to survive, an animals body must be able to maintainconstant internal conditions regardless of the externalconditions.
Constancy of the internal environment is calledhomeostasis.
Internal homeostasis is maintained in animal bodiesby a host of mechanisms called feedback systems.
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19.4 How Do Animals Maintain InternalConstancy?
Negative feedback reverses the effects ofchanges.
The most important mechanism governinghomeostasis is negative feedback, in whichthe response to a change is to counteract thechange.
In other words, an input causes an outputresponse that feeds back to the initial input
and decreases its effects.
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19.4 How Do Animals Maintain Internal
Constancy? A home thermostat is a familiar example of
negative feedback.
An input, temperature, dropping below a set point, thethermostat setting, is detected by the thermometer.
The thermometer responds with an outputswitchingon the heater.
The heater restores the temperature to the set pointand the heater switches off.
The thermostats negative feedback mechanismrequires a control center with a set point, a sensor(thermometer), and an effector (the furnace), whichaccomplishes the change.
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on off
control
center
below
above
setpoint
thermometer
(sensor)
heater(effector)
(a ) Maintaining a homes temperature
19.4 How Do Animals Maintain InternalConstancy?
Maintaining a homes temperature
Fig. 19-10a
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19.4 How Do Animals Maintain Internal
Constancy? Negative feedback keeps a persons body
temperature close to 98.6F (37C).
The center of the temperature control system is in thehypothalamus, a region of the brain.
Nerve endings throughout the body act astemperature sensors and transmit this information tothe hypothalamus.
When body temperature drops, the hypothalamus
activates effector mechanisms that raise your bodytemperature.
When normal body temperature is restored, thehypothalamus switches off these control mechanisms.
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19.4 How Do Animals Maintain InternalConstancy?
Maintaining a bodys temperature
Fig. 19-10b
nerve endings(sensor)
skeletalmuscles(effector)
hypothalamus(control center)
heat output(shivering)decreases
heat output(shivering)
increases
setpoint
(b ) Maintaining a bodys temperature
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19.4 How Do Animals Maintain Internal
Constancy?
Positive feedback drives an event to itsconclusion.
A change in a positive feedback systemproduces a response that intensifies theoriginal change.
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19.4 How Do Animals Maintain InternalConstancy?
An example of positive feedback in animalphysiology are the events that controlchildbirth.
Early contractions of labor force the babyshead against the cervix, dilating the cervix.
Stretch receptors in the cervix signal thehypothalamus, which releases the hormoneoxytocin that stimulates more uterinecontractions.
The feedback cycle is terminated by theexpulsion of the baby and its placenta.
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19.4 How Do Animals Maintain Internal
Constancy?
AnimationFeedback Loops and HomeostasisPLAY
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19.4 How Do Animals Maintain InternalConstancy?
The bodys organ systems act in concert. Numerous feedback mechanisms are
constantly at work, responding to inputs thatcontinuously change as an animals activitiesand external environment change.
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19.4 How Do Animals Maintain Internal
Constancy? The bodys organ systems act in concert(continued).
For example, the digestive system works inconcert with the systems responsible fortransporting substances within the body, suchas the circulatory system and the systems thatremove waste substances from the body,including the excretory system.
This coordinated action is possible becausethe body continually sends messages fromsensors to effectors, which allow feedbackmechanisms to maintain homeostasis.