Download - PowerLecture: Chapter 4 Tissues, Organs, and Organ Systems

PowerLecture:PowerLecture:Chapter 4Chapter 4

Tissues, Organs, and Tissues, Organs, and Organ SystemsOrgan Systems

Learning ObjectivesLearning Objectives

Understand the various levels of animal Understand the various levels of animal organization (cells, tissues, organs, and organization (cells, tissues, organs, and organ systems).organ systems).

Know the characteristics of the various Know the characteristics of the various types of tissues. Know the types of cells types of tissues. Know the types of cells that compose each tissue type and cite that compose each tissue type and cite some examples of organs that contain some examples of organs that contain significant amounts of each tissue type.significant amounts of each tissue type.

Describe how the four principal tissue types Describe how the four principal tissue types are organized into an organ such as the are organized into an organ such as the skin.skin.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Explain how the human body maintains a Explain how the human body maintains a rather constant internal environment despite rather constant internal environment despite changing external conditions.changing external conditions.

Impacts/IssuesImpacts/Issues

Stem CellsStem Cells


Stem cellsStem cells are the first to form when a are the first to form when a fertilized egg starts dividing.fertilized egg starts dividing.

Adults have stem cells in some tissues such as Adults have stem cells in some tissues such as bone marrow and fat; these cells have shown bone marrow and fat; these cells have shown some promise as therapy.some promise as therapy.

Embryonic stem cells can be coaxed Embryonic stem cells can be coaxed to differentiate into many different to differentiate into many different types of cells, which can replace types of cells, which can replace damaged or worn out body cells damaged or worn out body cells perhaps to an extent greater than perhaps to an extent greater than adult stem cells.adult stem cells.


The human body is an orderly assembly of The human body is an orderly assembly of parts (anatomy).parts (anatomy).

A A tissuetissue is an aggregation of cells and is an aggregation of cells and intracellular substances functioning for a intracellular substances functioning for a special ized activity.special ized activity.

Various types of tissues can combine to form Various types of tissues can combine to form organs, such as the heart.organs, such as the heart.

Organs may interact to form organ systems Organs may interact to form organ systems such as the digestive system.such as the digestive system.

Homeostasis allows for the stable functioning Homeostasis allows for the stable functioning (physiology) of all our combined parts.(physiology) of all our combined parts.

Video: New NervesVideo: New Nerves

From ABC News, Biology in the Headlines, 2005 DVD.From ABC News, Biology in the Headlines, 2005 DVD.

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How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

Should researchers be allowed to start Should researchers be allowed to start embryonic stem cell lines from human embryonic stem cell lines from human embryos that are not used for in vitro embryos that are not used for in vitro fertilization?fertilization? a. Yes, most unimplanted embryos are destroyed a. Yes, most unimplanted embryos are destroyed

anyway; the potential of stem cells is too great to anyway; the potential of stem cells is too great to ignore.ignore.

b. No, any human embryo has the potential to b. No, any human embryo has the potential to become a human and so deserves protection become a human and so deserves protection from destruction. from destruction.

Section 1Section 1

Epithelium: The Body’s Epithelium: The Body’s Covering and LiningsCovering and Linings

EpitheliumEpithelium

Epithelial tissue covers the surface of the Epithelial tissue covers the surface of the body and lines its cavities and tubes.body and lines its cavities and tubes.

One surface is free and faces either the One surface is free and faces either the environment or a body fluid; the other adheres environment or a body fluid; the other adheres to a basement membrane, a densely packed to a basement membrane, a densely packed layer of proteins and polysaccharides.layer of proteins and polysaccharides.

Cells are linked tightly Cells are linked tightly together; there may be together; there may be one or more layers.one or more layers.

Fig. 4.1a, p. 69

free surfaceof epithelium

connectivetissue

simplesquamousepithelium

basementmembrane

Animation: Structure of EpitheliumAnimation: Structure of Epithelium

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There are two basic types of epithelia.There are two basic types of epithelia. Simple epitheliumSimple epithelium is a single layer of cells is a single layer of cells

functioning as a lining for body cavities, ducts, functioning as a lining for body cavities, ducts, and tubes.and tubes.

• Simple epithelium functions in diffusion, secretion, Simple epithelium functions in diffusion, secretion, absorption, or filtering of substances across the cell absorption, or filtering of substances across the cell layer.layer.

• PseudostratifiedPseudostratified epithelium is a single layer of cells epithelium is a single layer of cells that looks like a double layer; most of the cells are that looks like a double layer; most of the cells are ciliated; examples are found in the respiratory ciliated; examples are found in the respiratory passages and reproductive tracts.passages and reproductive tracts.

StratifiedStratified epitheliumepithelium has many layers—as in has many layers—as in human skin.human skin.

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Table 4.1, p. 68


Both simple and stratified epithelium can be Both simple and stratified epithelium can be subdivided into groups based on shape at the subdivided into groups based on shape at the tissue surface:tissue surface:• SquamousSquamous epithelium consists of flattened cells; epithelium consists of flattened cells;

examples are found in the lining of the blood vessels.examples are found in the lining of the blood vessels.• CuboidalCuboidal epithelium has cube-shaped cells; examples epithelium has cube-shaped cells; examples

are found in glands.are found in glands.• ColumnarColumnar epithelium has elongated cells; examples epithelium has elongated cells; examples

are found in the intestine.are found in the intestine.

Fig. 4.2b-d, p. 70

basementmembrane

cilia

columnarcells

TYPE: Simple squamous

DESCRIPTION: Friction-reducing slick, single layer of flattened cells

COMMON LOCATIONS: Lining of blood and lymph vessels, heart; air sacs of lungs; peritoneum

FUNCTION: Diffusion; filtration; secretion of lubricants

TYPE: Simple cuboidal

DESCRIPTION: Single layer of squarish cells

COMMON LOCATIONS: Ducts, secretory part of small glands; retina; kidney tubules; ovaries, testes; bronchioles

FUNCTION: Secretion; absorption

TYPE: Simple columnar

DESCRIPTION: Single layer of tall cells; free surface may have cilia, mucus-secreting glandular cells, microvilli

COMMON LOCATIONS: Glands, ducts; gut; parts of uterus; small bronchi

FUNCTION: Secretion; absorption;ciliated types move substances


Glands develop from epithelium.Glands develop from epithelium. GlandsGlands are secretory structures derived from are secretory structures derived from

epithelium that make and release specific epithelium that make and release specific substances, such as mucus.substances, such as mucus.

Glands are classified according to how their Glands are classified according to how their products reach the site where they are used.products reach the site where they are used.

• ExocrineExocrine glands often secrete through ducts to free glands often secrete through ducts to free surfaces; they secrete mucus, saliva, earwax, milk, surfaces; they secrete mucus, saliva, earwax, milk, oil, and digestive enzymes for example.oil, and digestive enzymes for example.

• EndocrineEndocrine glands have no ducts but distribute their glands have no ducts but distribute their hormones via the blood.hormones via the blood.

Section 2Section 2

Connective Tissue: Connective Tissue: Binding, Support, and Binding, Support, and

Other Roles Other Roles

Connective TissueConnective Tissue

Connective tissueConnective tissue binds together, binds together, supports, and anchors body parts; it is the supports, and anchors body parts; it is the most abundant tissue in the body.most abundant tissue in the body.

Fibrous connective tissues and specialized Fibrous connective tissues and specialized connective tissues are both found in the body.connective tissues are both found in the body.

Fiber-like structural proteins and Fiber-like structural proteins and polysaccharides secreted by the cells make up polysaccharides secreted by the cells make up a a matrixmatrix (ground substance) around the cells (ground substance) around the cells that can range from hard to liquid.that can range from hard to liquid.


Fibrous connective tissues are strong and Fibrous connective tissues are strong and stretchy.stretchy.

Fibrous connective tissueFibrous connective tissue takes different takes different forms depending on cell type and the forms depending on cell type and the fibers/matrix produced.fibers/matrix produced.

collagenous fiber

fibroblast

elastic fiber

Loose connective tissue

cartilage cell(chondrocyte)

Cartilage

collagenous fibers

collagenous fibers

fibroblast

ground substance with collagen fibers

Dense, regular connective tissue

Fig. 4.2a-d, p. 70

Dense, irregular connective tissue


Types and examples of fibrous connective tissue:Types and examples of fibrous connective tissue:• Loose connective tissueLoose connective tissue supports epithelia and supports epithelia and

organsorgans,, and surrounds blood vessels and nerves; it and surrounds blood vessels and nerves; it contains few cells and loosely arrayed thin fibers. contains few cells and loosely arrayed thin fibers.

• Dense, irregular connective tissueDense, irregular connective tissue has fewer cells has fewer cells and more fibers, which are thick; it forms protective and more fibers, which are thick; it forms protective capsules around organs.capsules around organs.

• Dense, regular connective tissueDense, regular connective tissue has bundled has bundled collagen fibers lying in parallel; such arrangements are collagen fibers lying in parallel; such arrangements are found in ligaments (binding bone to bone) and tendons found in ligaments (binding bone to bone) and tendons (binding muscle to bone).(binding muscle to bone).

• Elastic connective tissueElastic connective tissue contains fibers of elastin; contains fibers of elastin; this tissue is found in organs that must stretch, like the this tissue is found in organs that must stretch, like the lungs.lungs.

Animation: Soft Connective TissuesAnimation: Soft Connective Tissues

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Cartilage, bone, adipose tissue, and blood Cartilage, bone, adipose tissue, and blood are specialized connective tissues.are specialized connective tissues.

CartilageCartilage contains a dense array of fibers in a contains a dense array of fibers in a rubbery ground substance; cartilage can rubbery ground substance; cartilage can withstand great stress but heals slowly when withstand great stress but heals slowly when damaged.damaged.

• Hyaline cartilageHyaline cartilage has many small fibers; it is found has many small fibers; it is found at the ends of bones, in the nose, ribs, and windpipe.at the ends of bones, in the nose, ribs, and windpipe.

• Elastic cartilageElastic cartilage, because of its elastin component, , because of its elastin component, is able to bend yet maintain its shape, such as in the is able to bend yet maintain its shape, such as in the external ear.external ear.

• FibrocartilageFibrocartilage is a sturdy and resilient form that can is a sturdy and resilient form that can withstand tremendous pressure such as in the disks withstand tremendous pressure such as in the disks that separate the vertebrae. that separate the vertebrae.


Bone tissueBone tissue is composed of collagen, ground is composed of collagen, ground substance, and calcium salts; minerals harden substance, and calcium salts; minerals harden bone so it is capable of supporting and protecting bone so it is capable of supporting and protecting body tissues and organs.body tissues and organs.

Adipose tissueAdipose tissue cells are specialized for the cells are specialized for the storage of fat; most adipose tissue lies just storage of fat; most adipose tissue lies just beneath the skin.beneath the skin.

Fig. 4.2ef, p. 71

compactbone tissue

bone cell(osteocyte)

blood vesselcell bulgingwith fatdroplet

nucleus

TYPE: Bone tissue

DESCRIPTION: Collagen fibers, matrix hardened with calcium

COMMON LOCATIONS: Bones of skeleton

FUNCTION: Movement, support, protection

TYPE: Adipose tissue

DESCRIPTION: Large, tightly packed fat cells occupying most of matrix

COMMON LOCATIONS: Under skin, around heart, kidneys

FUNCTION: Energy reserves, insulation, padding

Animation: Specialized Animation: Specialized Connective TissuesConnective Tissues

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BloodBlood is a fluid connective tissue involved in is a fluid connective tissue involved in transport; plasma forms the fluid “matrix” and transport; plasma forms the fluid “matrix” and blood proteins, blood cells, and platelets blood proteins, blood cells, and platelets compose the “fiber” portion of the tissue.compose the “fiber” portion of the tissue.

Figure 4.3Figure 4.3

Table 4.2, p. 71

Section 3Section 3

Muscle Tissue: Muscle Tissue: MovementMovement


Muscle Tissue: MovementMuscle Tissue: Movement

Muscle tissueMuscle tissue contracts in response to contracts in response to stimulation, then passively lengthens; stimulation, then passively lengthens; movement is a highly coordinated action. movement is a highly coordinated action.

There are three types of muscle:There are three types of muscle: Skeletal muscleSkeletal muscle tissue tissue

attaches to bones for attaches to bones for voluntary movement; long voluntary movement; long muscle cells are bundled muscle cells are bundled together in parallel arrays, together in parallel arrays, which are enclosed in a which are enclosed in a sheath of dense connective tissue. sheath of dense connective tissue.

Figure 4.4aFigure 4.4a

skeletal muscle

Muscle Tissue: MovementMuscle Tissue: Movement

Smooth muscleSmooth muscle tissue contains tissue contains

tapered, bundled cells that function tapered, bundled cells that function

in involuntary movement; it lines in involuntary movement; it lines

the gut, blood vessels, and glands.the gut, blood vessels, and glands. Cardiac muscleCardiac muscle is composed of is composed of

short cells that can function in units short cells that can function in units

due to the signals that pass through due to the signals that pass through

special junctions that fuse the cells special junctions that fuse the cells

together; cardiac muscle is only together; cardiac muscle is only

found in the wall of the heart.found in the wall of the heart.Figure 4.4b-cFigure 4.4b-c

cardiac muscle

smooth muscle

Animation: Muscle TissuesAnimation: Muscle Tissues

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Section 4Section 4

Nervous Tissue: Nervous Tissue: CommunicationCommunication

Nervous Tissue: CommunicationNervous Tissue: Communication

Nervous tissueNervous tissue consists mainly of cells, consists mainly of cells, including neurons (nerve cells) and support including neurons (nerve cells) and support cells; nervous tissue forms the body’s cells; nervous tissue forms the body’s communication network.communication network.

Neurons carry messages.Neurons carry messages. NeuronsNeurons have two types have two types

of cell processes (extensions): of cell processes (extensions):

branched dendrites pick up branched dendrites pick up

chemical messages and pass chemical messages and pass

them to an outgoing axon.them to an outgoing axon.Figure 4.5aFigure 4.5a

Nervous Tissue: CommunicationNervous Tissue: Communication

A cluster of processes from different neurons is A cluster of processes from different neurons is called a called a nervenerve..

Nerves move messages throughout the body.Nerves move messages throughout the body. Neuroglia are support cells.Neuroglia are support cells.

Glial cellsGlial cells ( (neuroglianeuroglia)) make make up 90 percent of the nervous up 90 percent of the nervous system. Neuroglia provide system. Neuroglia provide physical support for neurons.physical support for neurons.

Other glial cells provide Other glial cells provide nutrition (astrocytes), clean-up, nutrition (astrocytes), clean-up, and insulation services (Schwann cells).and insulation services (Schwann cells).

Figure 4.5bFigure 4.5b

Table 4.4, p. 85

Section 5Section 5

Cell Junctions: Holding Cell Junctions: Holding Tissues TogetherTissues Together

Cell JunctionsCell Junctions

Epithelial cells tend to adhere to one Epithelial cells tend to adhere to one another by means of specialized another by means of specialized attachment sites.attachment sites.

Tight junctionsTight junctions link cells of epithelial tissues to link cells of epithelial tissues to form seals that keep molecules from freely form seals that keep molecules from freely crossing the epithelium.crossing the epithelium.

Adhering junctionsAdhering junctions are like spot welds in are like spot welds in tissues subject to stretching.tissues subject to stretching.

Gap junctionsGap junctions link the cytoplasm of adjacent link the cytoplasm of adjacent cells; they form communication channels.cells; they form communication channels.

Cell JunctionsCell Junctions

Sites of cell-to-cell contact are especially Sites of cell-to-cell contact are especially profuse when substances must not leak profuse when substances must not leak from one body compartment to another. from one body compartment to another.

TIGHT JUNCTION ADHERING JUNCTION GAP JUNCTION Fig. 4.6, p. 74

cell

basement membrane

intermediate filaments

plaques

protein channel

Animation: Cell JunctionsAnimation: Cell Junctions

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Section 6Section 6

Tissue Membranes: Tissue Membranes: Thin, Sheetlike CoversThin, Sheetlike Covers

Tissue MembranesTissue Membranes

Epithelium membranes pair with connective Epithelium membranes pair with connective tissue.tissue.

Mucous membranesMucous membranes line the tubes and line the tubes and cavities of the digestive, respiratory, and cavities of the digestive, respiratory, and reproductive systems where embedded glands reproductive systems where embedded glands secrete mucus.secrete mucus.

Serous membranesSerous membranes such as those that line the such as those that line the thoracic cavity occur in paired sheets and do thoracic cavity occur in paired sheets and do not contain glands.not contain glands.

Cutaneous membranesCutaneous membranes are hardy and dry— are hardy and dry—and better known as skin.and better known as skin.

Tissue MembranesTissue Membranes

Membranes in joints consist only of Membranes in joints consist only of connective tissue.connective tissue.

Synovial membranesSynovial membranes line the sheaths of line the sheaths of tendons and the capsule-like cavities around tendons and the capsule-like cavities around certain joints.certain joints.

Their cells secrete fluid that lubricates the ends Their cells secrete fluid that lubricates the ends of the moving bones.of the moving bones.

mucous membrane

serous membrane

synovial membrane

Fig. 4.7, p. 75

cutaneous membrane

(skin)

Section 7Section 7

Organs and Organ Organs and Organ SystemsSystems

Organs and Organ SystemsOrgans and Organ Systems

An An organorgan is a composite of two or more is a composite of two or more tissue types that act together to perform tissue types that act together to perform one or more functions; two or more organs one or more functions; two or more organs that work in concert form an that work in concert form an organ systemorgan system..

The major cavities of the human body are: The major cavities of the human body are: cranial, spinal, thoracic, abdominal, and cranial, spinal, thoracic, abdominal, and pelvic.pelvic.

cranial cavity

spinal cavity

thoracic cavity

pelvic cavity

abdominal cavity

Fig. 4.8a, p. 76

Animation: Major Body CavitiesAnimation: Major Body Cavities

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Animation: Directional Terms Animation: Directional Terms and Planes of Symmetryand Planes of Symmetry

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SUPERIOR (of two body parts, the one closer to head)

INFERIOR(of two body parts,

the one farthest from head)

frontal plane (aqua)

midsagittal plane (green)

ANTERIOR(at or near front of body)

distal (farthest from trunk or from point of origin of a body part)

proximal (closest to trunk or to point of origin of a body part)

POSTERIOR (at or near back of body)

transverse plane (yellow)

Fig. 4.8b, p. 76

Organs and Organ SystemsOrgans and Organ Systems

Eleven organ systems (integumentary, Eleven organ systems (integumentary, nervous, muscular, skeletal, circulatory, nervous, muscular, skeletal, circulatory, endocrine, lymphatic, respiratory, digestive, endocrine, lymphatic, respiratory, digestive, urinary, and reproductive) contribute to the urinary, and reproductive) contribute to the survival of the living cells of the body.survival of the living cells of the body.

Animation: Organ Systems Animation: Organ Systems of the Human Bodyof the Human Body

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Section 8Section 8

The Integument – The Integument – Example of an Organ Example of an Organ

SystemSystem

The IntegumentThe Integument

Humans have an outer covering called the Humans have an outer covering called the integumentintegument, which includes the skin and , which includes the skin and the structures derived from epidermal cells the structures derived from epidermal cells including oil and sweat glands, hair, and including oil and sweat glands, hair, and nails.nails.

The skin performs several functions:The skin performs several functions: The skin covers and protects the body from The skin covers and protects the body from

abrasion, bacterial attack, ultraviolet radia tion, abrasion, bacterial attack, ultraviolet radia tion, and dehydration.and dehydration.


It helps control internal temperature.It helps control internal temperature. Its receptors are essential in detecting Its receptors are essential in detecting

environmental stimuli.environmental stimuli. The skin produces vitamin D.The skin produces vitamin D.

Epidermis and dermis—the two layers of Epidermis and dermis—the two layers of skin.skin.

Fig. 4.10b, p. 79

rapidlydividingcells ofepidermis

outerepidermallayer (alldead cells)

keratinizedcells beingflattened

dermis


EpidermisEpidermis refers to the thin, outermost layers refers to the thin, outermost layers of cells consisting of stratified, squamous of cells consisting of stratified, squamous epithelium.epithelium.

• KeratinocytesKeratinocytes produce keratin; when the cells are produce keratin; when the cells are finally pushed to the skin surface, they have died, but finally pushed to the skin surface, they have died, but the keratin fibers remain to make the outermost layer the keratin fibers remain to make the outermost layer of skin (the stratum corneum) tough and waterproof.of skin (the stratum corneum) tough and waterproof.

• Deep in the epidermis are melanin-producing cells Deep in the epidermis are melanin-producing cells ((melanocytesmelanocytes); melanin, along with carotene and ); melanin, along with carotene and hemoglobin, contribute to the natural coloration of hemoglobin, contribute to the natural coloration of skin.skin.

• Langerhans cells and Granstein cells are two Langerhans cells and Granstein cells are two important cells in skin that contribute to immune important cells in skin that contribute to immune function.function.


The The dermisdermis is the thicker portion of the skin is the thicker portion of the skin that underlies the epidermis.that underlies the epidermis.

• The dermis is mostly dense connective tissue, The dermis is mostly dense connective tissue, consisting of elastin and collagen fibers.consisting of elastin and collagen fibers.

• Blood vessels, hair follicles, nerve endings, and Blood vessels, hair follicles, nerve endings, and glands are located here.glands are located here.

The The hypodermishypodermis is a subcutaneous layer that is a subcutaneous layer that anchors the skin; fat is also stored here.anchors the skin; fat is also stored here.

Fig. 4.10a, p. 78

melanocyte

sweat pore

Langerhans cell

hair shaft

keratinocyteGranstein cell

adipose cells

sweat glandpressure receptor

hair follicle

nerve fiber

living layer

keratinized layer

sebaceous gland

smooth muscle

EPIDERMIS

DERMIS

HYPODERMIS

Animation: Structure of Human SkinAnimation: Structure of Human Skin

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Sweat glands and other structures are Sweat glands and other structures are derived from epidermis.derived from epidermis.

Sweat glands secrete a fluid (mostly water with Sweat glands secrete a fluid (mostly water with a little dissolved salt) that is useful in regulating a little dissolved salt) that is useful in regulating the temperature of the body.the temperature of the body.

Oil (Oil (sebaceoussebaceous) glands function to soften and ) glands function to soften and lubricate the hair and skin; acne is a condition lubricate the hair and skin; acne is a condition in which the ducts become infected by bacteria.in which the ducts become infected by bacteria.


Hairs are flexible, keratinized structures rooted in Hairs are flexible, keratinized structures rooted in the skin and projecting above the surface; growth the skin and projecting above the surface; growth is influenced by genes, nutrition, and hormones.is influenced by genes, nutrition, and hormones.


Sunlight permanently damages the skin.Sunlight permanently damages the skin. Ultraviolet (UV) radiation and the light from Ultraviolet (UV) radiation and the light from

tanning beds stimulate melanin production in tanning beds stimulate melanin production in skin, resulting in a tan; too much UV exposure, skin, resulting in a tan; too much UV exposure, however, can damage the skin.however, can damage the skin.

UV light can activate proto-UV light can activate proto-oncogenes in skin cells, leading oncogenes in skin cells, leading to cancer.to cancer.

Rates of skin cancer are on the Rates of skin cancer are on the rise due to continued destruction rise due to continued destruction of the atmospheric ozone layer that normally of the atmospheric ozone layer that normally protects the Earth from too much UV light.protects the Earth from too much UV light.


Section 9Section 9

Homeostasis: The Body Homeostasis: The Body in Balancein Balance

Homeostasis: The Body in BalanceHomeostasis: The Body in Balance

The internal environment: A pool of The internal environment: A pool of extracellular fluid. extracellular fluid.

The trillions of cells in our bodies are The trillions of cells in our bodies are continuously bathed in an extracellular fluid that continuously bathed in an extracellular fluid that supplies nutrients and carries away metabolic supplies nutrients and carries away metabolic wastes.wastes.

The extracellular fluid consists of The extracellular fluid consists of interstitialinterstitial fluid (between the cells and tissues) and fluid (between the cells and tissues) and plasma (blood fluid).plasma (blood fluid).

In-text Fig., p. 80

Bloodvessel

CellInterstitial(tissue) fluid Blood

Extracellular fluid


The component parts of an animal work The component parts of an animal work together to maintain the stable fluid together to maintain the stable fluid environment (homeostasis) required for life.environment (homeostasis) required for life.

Homeostasis requires the interaction of Homeostasis requires the interaction of sensors, integrators, and effectors.sensors, integrators, and effectors.

Homeostatic mechanisms operate to maintain Homeostatic mechanisms operate to maintain chemical and physical environments within chemical and physical environments within tolerable limits and to keep the body close to tolerable limits and to keep the body close to specific specific set pointsset points of function.of function.


Homeostatic control mechanisms require three Homeostatic control mechanisms require three components:components:

• Sensory receptorSensory receptor cells detect specific changes cells detect specific changes (stimuli) in the environment.(stimuli) in the environment.

• IntegratorsIntegrators (brain and spinal cord) act to direct (brain and spinal cord) act to direct impulses to the place where a response can be impulses to the place where a response can be made.made.

• EffectorsEffectors (muscles and glands) perform the (muscles and glands) perform the appropriate response.appropriate response.

STIMULUS (input into the system)

RESPONSE to stimulus causes change. The change is “fed back” to receptor. In negative feedback, the system’s response cancels or counters the effect of the original stimulus.

Fig. 4.12, p. 80

receptor

(such as anerve ending

in the skin)

integrator

(such as the brain or spinal cord)

effector

(a muscle or gland)


Feedback mechanisms are important Feedback mechanisms are important homeostatic controls.homeostatic controls.

A common homeostatic mechanism is A common homeostatic mechanism is negative negative feedbackfeedback..

• It works by detecting a change in the internal It works by detecting a change in the internal environment that brings about a response that tends environment that brings about a response that tends to return conditions to the original state.to return conditions to the original state.

• It is similar to the functioning of a thermostat in a It is similar to the functioning of a thermostat in a heating/cooling system.heating/cooling system.

Positive feedbackPositive feedback mechanisms may intensify mechanisms may intensify the original signal; childbirth is an example.the original signal; childbirth is an example.

Animation: Negative Feedback at the Animation: Negative Feedback at the Organ LevelOrgan Level

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Animation: Homeostatic Control of Animation: Homeostatic Control of TemperatureTemperature

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Fig. 4.13a, p. 81sweat gland poredead, flattened skin cells

receptorsIn skin and elsewhere; detect the

temperature change.

integratorThe hypothalamus,

a brain region, compares input

from the receptors against the set

point for the body.

effectorsPituitary gland& thyroid gland

trigger widespread

adjustments in many body

organs.

Skeletal muscles in chest wall work to get additionaloxygen into lungs.

Smooth muscle in blood vessels dilates; blood transporting metabolic heat shunted to skin; some heat lost to surroundings.

Sweat glandssecrete more,with coolingeffect onthe brainespecially.

EffectorsThese carry out specific responses, including:

Overall slowing of activity results in less metabolically generated heat.

RESPONSEBody temperature falls,receptors initiate shiftsin effector output.

Fig. 4.13b, p. 81

STIMULUSAfter overexertion on a hot, dry day, surface temperature of body rises.

Section 10Section 10

How Homeostatic How Homeostatic Feedback Maintains the Feedback Maintains the

Body’s Core Body’s Core Temperature Temperature

How Homeostatic Feedback Maintains the How Homeostatic Feedback Maintains the Body’s Core TemperatureBody’s Core Temperature

Humans are Humans are endothermsendotherms, heated from , heated from within by metabolic processes.within by metabolic processes.

Core temperatureCore temperature of the head and torso is of the head and torso is roughly 37roughly 37C (98.6C (98.6F).F).

Above this temperature (~41Above this temperature (~41C) proteins begin C) proteins begin to denature; below this temperature (35to denature; below this temperature (35C and C and below) the body stops functioning.below) the body stops functioning.

Animation: Human ThermoregulationAnimation: Human Thermoregulation

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Fig. 4.14a, p. 82

Fig. 4.14b, p. 82

Animation: Heat Denaturation of EnzymesAnimation: Heat Denaturation of Enzymes

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Responses to cold stress.Responses to cold stress. Cold responses are controlled by an area of the Cold responses are controlled by an area of the

brain called the brain called the hypothalamushypothalamus.. Several things happen when the outdoor Several things happen when the outdoor

temperature drops:temperature drops:• Peripheral vasoconstrictionPeripheral vasoconstriction occurs when the occurs when the

hypothalamus commands the muscles around blood hypothalamus commands the muscles around blood vessels to contract; this diverts blood flow away from vessels to contract; this diverts blood flow away from the body surface.the body surface.

• The The pilomotor responsepilomotor response causes your body hair to causes your body hair to stand on end to trap air around the body to prevent stand on end to trap air around the body to prevent heat loss.heat loss.


• Skeletal muscle contractions cause you to Skeletal muscle contractions cause you to shivershiver in in an attempt to generate heat.an attempt to generate heat.

• In babies, who can’t shiver, hormones raise the rate In babies, who can’t shiver, hormones raise the rate of metabolism in a of metabolism in a nonshivering heat productionnonshivering heat production response; this response occurs in a special type of response; this response occurs in a special type of adipose tissue called brown fat.adipose tissue called brown fat.

If body temperature cannot be maintained, If body temperature cannot be maintained, damage to the body occurs.damage to the body occurs.

• HypothermiaHypothermia is characterized by mental confusion, is characterized by mental confusion, coma, and possibly death.coma, and possibly death.

• Physical freezing can lead to frostbite and death of Physical freezing can lead to frostbite and death of the affected tissues.the affected tissues.


Responses to heat stress.Responses to heat stress. Heat responses are also controlled by the Heat responses are also controlled by the

hypothalamus.hypothalamus.• Peripheral vasodilationPeripheral vasodilation causes blood vessels to causes blood vessels to

expand in the skin, allowing excess body heat to expand in the skin, allowing excess body heat to dissipate.dissipate.

• Heat is also dissipated in sweat from sweat glands; Heat is also dissipated in sweat from sweat glands; water and salts both are lost to cool the body.water and salts both are lost to cool the body.


Various levels of heat stress (Various levels of heat stress (hyperthermiahyperthermia) ) can be experienced:can be experienced:

• Heat exhaustionHeat exhaustion occurs under mild heat stress; occurs under mild heat stress; blood pressure drops as fluid is lost and the person blood pressure drops as fluid is lost and the person can collapse.can collapse.

• Heat strokeHeat stroke occurs when the body ceases to be able occurs when the body ceases to be able to control temperature; death is one possible to control temperature; death is one possible outcome.outcome.

A A feverfever is a natural rise in core temperature is a natural rise in core temperature used to fight off disease; severe fevers, used to fight off disease; severe fevers, however, should be controlled to avoid serious however, should be controlled to avoid serious damage to the body.damage to the body.

Table 4.3, p. 83

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