cell homeostasis 11

8/7/2019 Cell Homeostasis 11

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Homeostasis and The Cell

Pamela R. Bosch, PT, PhD

PT 531, Applied Human Physiology

A.T. Still University of Health Sciences, Physical

Therapy Program

The copyrighted materials available in this class are for educationaluse only. One copy per student is permitted for educationalpurposes. Redistribution of copyrighted material is not permitted."


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Lecture Objectives1. Describe the structure of a typical cell and the cell membrane.

2. Identify the purpose of the major parts of a typical cell, the nucleus and the cytoplasm.3. Identify the purpose of the organelles of the cytoplasm, including the smooth and rough endoplasmic

reticulum, the golgi complex, lysosomes, peroxisomes, mitochondria, vaults.

4. Understand the purpose of the cytoskeleton found in the cytosol of the cell.

5. Describe how the cell membrane regulates movement (transport) of substances across the membrane based

on physical properties of the solute.

6. State the difference between simple diffusion, facilitated diffusion and active transport, and provideexamples of each.

7. Describe the membrane potential and why it exists.

8. Describe the distribution of body fluids between intracellular and extracellular fluid, interstitial fluid, and

plasma.

9. State how the balance of fluid is determined between intra- and extracellular fluid spaces.

10. Define osmosis and osmotic pressure. Provide a practical example of this in the human system.

11. Explain how the relative volumes of plasma and interstitial fluids are balanced, and cite factors causing

plasma volume to be lost to interstitial volume.

12. Define edema and ascites.

13. Contrast the composition of plasma, interstitial fluid, and intracellular fluid in terms of concentrations of

sodium, potassium, chlorine ions, and protein.

14. Describe cystic fibrosis and what causes it.

15. Describe stem cells and their significance.


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Homeostasis

Defined as maintenance of arelatively stable internal

environment

Does not mean thatcomposition, temperature, and

other characteristics are

absolutely unchanging

Homeostasis is essential forsurvival and function of all cells

Each cell contributes tomaintenance of a relatively stable

internal environment


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Homeostasis


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Homeostasis

Body cells are contained in watery internalenvironment through which life-sustaining

exchanges are made

Extracellular fluid (ECF)Fluid environment in which the cells live (fluid

outside the cells)

Two componentsPlasma, interstitial fluid

Intracellular fluid (ICF)Fluid contained within all body cells


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Homeostasis

Factors homeostatically regulated include

Concentration of nutrient molecules Concentration of O2 and CO2 Concentration of waste products pH Concentration of water, salt, and other

electrolytes

Fluid volume and pressure Temperature


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Disruptions in Homeostasis

Can lead to illness and death Pathophysiology

Abnormal functioning of the bodyassociated with disease


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Cells & Tissues!

> 200 types of cells! 4 primary!tissue types:!

Nervous !Epithelial !Muscle !Connective !

Blood is !also a tissue!


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Nervous Tissue!

Voltage-sensitive channels! Integrate incoming signals! Conduct signals rapidly to target organs! Connect complex networks! Initiate, integrate and transmit signals!


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Epithelial Tissue!

Lines cavities and free surfaces of body!

Membranes with protein pumps & receptors! Microvilli increase surface area! Endothelium is a type of epithelium that lines

circulatory system!

Glands are specialized epithelial tissue withexocrine or endocrine function!

Serves as boundary with selective permeability!


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3 types: skeletal, cardiac, smooth! Sarcoplasmic reticulum for calcium storage & release! Contractile proteins & regulatory proteins! Sarcomeres (in cardiac & skeletal muscle)! Function: force generation!


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Tendons, cartilage, ligaments, bone, blood! Connects and supports various parts of the body! Blood transports materials throughout the body!


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Typical Cell


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Nucleus!

Contains cells geneticmaterial, DNA , which:!

Directs proteinsynthesis!

Is the genetic blueprintduring cell replication!

Contains theNucleolus, which:! contains RNA !

Translates &transcribes geneticcode!


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Cytoplasm

Portion of cell interior not occupied by thenucleus

Consists of bothOrganelles

little organsDistinct, highly organized, membrane-enclosed

structures

Cytosol Complex, gel-like mass in which the cytoskeleton is

found


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Cellular Organelles!

Endoplasmic reticulum! Golgi complex! Lysosomes! Peroxisomes! Mitochondria!


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Endoplasmic Reticulum!

Smooth ER synthesizes lipids forsteroid hormone synthesis ! Packages and dischargesboth

proteins and lipids! ER increases as needed!

EX: in the liver for dischargingdetoxifying enzymes to break downdrugs or foreign compounds!

Rough ER synthesizes proteins!and lipids! Called rough because it has

ribosomes that synthesizeproteinsand lipids! Proteins may be secreted from the cell

as hormones or enzymes! Proteins and Lipids may be

transported within the cell for cellmaintenance!


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Golgi Complex!

Collects proteins synthesized

in ER and packages them

into vesicles that aredelivered to different sites:!

intracellular sites! May replace missing

segments of membrane!

May be incorporated intoother organelles (like

lysosomes)!! !!

Released from the cell by

exocytosis!


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2 functions of transit through the Golgi stack:"1. Modification of raw proteins into final form"2. Sorting proteins by function and destination"


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Lysosomes!

Contain hydrolytic enzymes thatdestroy cellular bacteria engulfedin vesicles by pinocytosis orphagocytosis!

Participate in apoptosis(programmed cell death)!

Material unable to be digested bylysosomes remains as residual

bodies ! Example: asbestos fibers remain in the

lungs once inhaled!


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Tay-Sachs Disease:! a lysosomal enzyme deficiency that

allows gangliosides to accumulate!Gangliosides are molecules found in nerve

cell membranes; important in cell to cell

communication !

Tay-Sachs disease causes progressiveneurodegeneration and death by theage of 4!


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Peroxisomes

Membranous sacs that houseoxidative enzymes that detoxifyvarious waste products!

Oxidative enzymes use oxygen toremove hydrogen from toxicmolecules, producing

hydrogen peroxide! Catalase breaks hydrogen peroxide into water and oxygen, which are harmless to the cell!


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Mitochondria!

Extract energy from

nutrients, and viathe Krebs Cycle &

Electron TransportSystem, transform

energy into a

useable form for

cellular activities!


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Mitochondria!

Site of most ATP production! Contains citric acid (Krebs cycle) enzymes! Mitochondrial DNA codes for severalmitochondrial enzymes needed for aerobic

metabolism!

Mitochondrial DNA mutates easily!

Thought to be partially responsible for manyneurodegenerative diseases (PD, HD, ALS), SIDS,and cardiomyopathy!


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Cytoskeleton

Complex protein network of cytosol that actsas bone and muscle of cell

Three distinct elementsMicrotubules: transport of other components within cells

Microfilaments: actin, solid fibersIntermediate filaments: structuralstability in cell


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Element Function

Microtubules Transport secretory vesiclesMovement of specialized cellprojections

Form mitotic spindle during cell divisionMicrofilaments Contractile systems

Mechanical stiffenersIntermediatefilaments

Help resist mechanical stress


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Plasma Membrane Structure

Fluid phospholipid bilayer embedded with proteins Also has small amount of carbohydrates

On outer surface onlyCholesterol

Contributes to fluidity and stability of cell membrane


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Plasma Membrane Structure


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CYSTIC FIBROSIS!

Membrane proteins form channels across the lipid bilayer!Channels are selective for specific particles (Na+, K+, forexample)!In CF, a gene mutation impedes or prevents formation ofchloride channels (called CFTR, cystic fibrosis

transmembrane regulator ) in epithelial cell membranes !


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CYSTIC FIBROSIS!

CFTR is made in the endoplasmic reticulum of epithelial cells, !in CF, CFTR is degraded due to a lack of a necessary aminoacid. !

CFTR never gets packaged and sent out of the ER to thecell membrane to form channels!No CFTR means that Cl- cannot be transported across epithelialcells!Cl- moves with Na+ (NaCl), so Na+ transport is also decreased!

Reduced Na+ movement decreases water movement, resultingin thicker mucus in airways!


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Membrane Transport

Unassisted membrane transport (passive)Diffusion Osmosis (refers to diffusion of water)

Assisted membrane transportCarrier-mediated transport

Facilitated transportActive transport

Vesicular transport


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Membrane Transport

Cell membrane is selectively permeable Properties of particles influence whether theycan permeate cell membrane without

assistance, such as:

Relative solubility of particle in lipidSize of the particlepolarity (charge) of the particle


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Diffusion & Osmosis!

Diffusion: passive movement of molecules fromhigh to low concentration!

Osmosis: passive movement of water (across amembrane) down its concentration gradient (that

is, from high concentration to low concentration)!


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Membrane Transport

DiffusionUnassisted membrane transportUniform spreading out of molecules due to theirrandom intermingling

Molecules move from area of high concentrationto area of low transport

Process is crucial to survival of every cellPlays important role in

Exchange of oxygen and carbon dioxide between blood andair in lungs

Movement of substances across kidney tubules


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Membrane Transport

Diffusion

Particles (solutes) and solvents (water) will naturally

disperse to spread evenly if they can"


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Membrane Transport

Factors affecting rate of diffusion collectively

make up Ficks law of diffusion:

Magnitude (or steepness) of the concentrationgradient

Permeability of the membrane to the substance Surface area of the membrane across which diffusion

is taking place

Molecular weight of the substance Distance through which diffusion takes place


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Ficks Law of Diffusion

Q (rate of diffusion) = C P A MW X

C = concentration gradient P = permeability A = surface area MW = molecular weight of the substance X = distance traveled


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Membrane Transport

Osmosis Net diffusion of water down its

own concentration

gradient

Water doesnt want to be crowded! Thus, it will move from

where there is more water to where there is less water!"


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Osmotic Pressure and

Hydrostatic Pressure

The net movement of water increases pressure onthe side the water moves to

Pressure builds until equilibrium is reached This pressure is hydrostatic pressure

The weight of water pushing against a surface Osmotic pressure a measure of the tendency for

osmotic flow of water

Results from differences in relative concentrations ofsolutes and water in cell and ECF


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Fluid dynamics at the capillary!

CHP = capillary hydrostatic pressure!

COP = capillary osmotic pressure!

IFHP = interstitial fluid hydrostatic pressure!

IFOP = interstitial fluid osmotic pressure!


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Fluid Exchange!


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Edema

The presence ofexcess fluid in the

body tissues!Usually, theexcess fluid is inthe extracellularcompartments!


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Intracellular EdemaSwelling of cells!


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Extracellular Edema!


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Extracellular Edema

Increased capillary pressureRetention of salt and water in kidney failureHigh venous pressure, as with heart failure,

venous obstruction (pregnancy), or failure of

venous pumps

Decreased arteriolar resistance


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Extracellular Edema!

Increased Capillary Permeability!

Immune response!Toxins!Bacterial infections!Burns!


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Extracellular edema from decreased plasma proteins

(causes decreased colloid osmotic pressure)!


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Extracellular Edema

Chronic lymphatic obstruction cancer radiation therapy radical mastectomy


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Extracellular

Edema!

Chronic lymphedema fromradical mastectomy!

Lymphedema from

filarial nematode

infection of thelymph system!


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Assisted Membrane TransportCarrier Mediated, and includes

Facilitated Diffusion and ActiveTransport!

A mechanism for transporting large, polar, poorly solublesubstances across membrane!A means of transporting some small ions across themembrane!


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Assisted Membrane Transport

Accomplished by membrane carrier flipping itsshape

Can be active (active transport) or passive(facilitated diffusion)Characteristics that determine the kind and

amount of material that can be transferred

across the membraneSpecificitySaturationCompetition


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Facilitated diffusion Substances move from a

higher concentration to a

lower concentration

Requires carrier moleculeBut no energy required!

Means by which glucoseis transported into cells


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Carrier Mediated


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Active Transport

Moves a substance against its concentrationgradient

Requires a carrier molecule Primary active transport

Requires direct use of ATP Secondary active transport

Driven by an ion concentration gradientestablished by a primary active transport system


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A good example of active transport is the sodium-potassium

pump! It transports sodium (3) from inside to outside thecell; while transporting 2 potassium ions from outside to

inside!!


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Membrane Potential

Plasma membrane of all living cells hasa membrane potential (polarized

electrically)

Separation of opposite charges acrossplasma membrane

Due to differences in concentration andpermeability of key ions


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Na+"Na+"

K+"K+"

- - - - - - - - - - -

+++++++++++

-70 to -90 mV!

Typical Cell at Rest!


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Membrane Potential

Nerve and muscle cellsExcitable cells can do work!Have ability to produce rapid, transientchanges in their membrane potential when

excited

Resting membrane potentialConstant membrane potential present in cells

of nonexcitable tissues and those of excitable

tissues when they are at rest


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Ion Concentration


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Resting Potential

Proteins!


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Membrane Potential

Effect of sodium-potassium pump onmaintaining membrane potential

Makes only a small direct contribution tomembrane potential (20%) through its

unequal transport of positive ions (3 Na+

out/2 K+ in)

This is a good example of active transport,which requires energy (ATP)!


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Hyperkalemia

Abnormal elevation of K+ in bloodNormal ranges: 3.5 5 mEq/LCauses:Kidney dysfunction

Adrenal Gland dysfunctionMedications (ACE inhibitors, NSAIDs)


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Hyperkalemia

Destruction of the concentration gradientfor K+ across muscle cell membranes

interferes with muscle contraction, and ifexcessive (> 7 mEq/L) is associated with:

ArrhythmiasCardiac arrest

Death


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Iontophoresis

A modality used in PT Promotes healing Works because charged particles move

down an electrical gradient

Medication is driven into the skin with astimulator carrying a low electrical current


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Stem Cells

Undifferentiated cells that can become almostany type of cell.

Two types:Embryonic stem cells (ESC): from early divisions

of fertilized eggs; totipotent

Tissue-specific stem cells: generate specialized celltypes of specific tissues; pluripotent

For more information, go to:http://stemcells.nih.gov/info/basics/


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cell homeostasis 11

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