ch19 lecture

8/3/2019 Ch19 Lecture

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Copyright 2009 Pearson Education, Inc..

Lectures by

Gregory AhearnUniversity of North Florida

Chapter 19

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 intonumerous different body parts, with adistinctive size, shape, and combination ofspecialized cell types.


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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


connective

muscle

large

intestine

pancreasstomach

mouth

pharynx

epithelialCells:

epithelial cells

liver

small intestineesophagus

gallbladder

Tissues: Organ:

stomach

Organ system:

digestive system


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



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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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



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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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



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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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.




Cartilage is a flexible and resilient connectivetissue that consists of widely spaced cellssurrounded by a thick, nonliving matrix.


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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


centralcanal

bone cells

concentricbone matrix


Bone resembles cartilage but is enhancedby deposits of calcium phosphate.

Fig. 19-4


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Adipose tissue provides long-term energystorage and insulation for animals adaptedto cold environments.

Fig. 19-5




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


Blood has three types of cells: red bloodcells, white blood cells, and plateletssuspended 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 contractwhen stimulated, then relax passively.

Fig. 19-7


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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



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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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.



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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A nerve cell

Fig. 19-8

dendrites

synapticterminals

cell body

axon


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.


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.



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


Maintaining a homes temperature

Fig. 19-10a



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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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



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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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.



Constancy?

AnimationFeedback Loops and HomeostasisPLAY


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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.



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.

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