STANDARD 2Organization & Development of

Living Systems

Unit 6 – Homeostasis & Health

Objectives

• B2.3B: Describe how the maintenance of a relatively stable internal environment is required for the continuation of life.

• B2.3C: Explain how stability is challenged by changing physical, chemical, and environmental conditions, as well as the presence of disease agents.

• B2.3f: Explain how human organ systems help maintain human health.

• The balance between the amount of calories a person takes in (eats) and the amount of calories burned (physical activity).– Calorie

• The amount of heat required to raise the temperature of one gram of water one degree Celsius, heat-producing or energy-producing value in food

What is Human Nutrition?

Essential Nutritional Processes

• Diffusion = movement of a substance from an area of greater concentration to an area of lesser concentration

Example – spray Windex

• Osmosis = diffusion through a semi-permeable membrane

• Hypotonic Solution = solute concentration is greater in the environment than in the cell, so water enters the cell

• Isotonic Solution = solute concentration is equal

in the environment and in the cell

• Hypertonic Solution = solute concentration is

lower in the environment than in the cell, so water

exits the cell – it dehydrates and dies

Internal Environment

Physical Conditions• Cell function in a narrow range of physical conditions, such as temperature

and pH (acidity), to perform life functions. When these physical conditions are not maintained, the cell will die.

• pH - Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally occurring proteins that speed up biochemical processes.

• All of these enzymes work best at a low pH, reducing the risk that these enzymes will digest their own cell should they somehow escape from the lysosome. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system.

• The term pH derives from a combination of "p" for the word power and "H" for the symbol of the element hydrogen. pH is the negative log of the activity of hydrogen ions and represents the "activity" of hydrogen ions in a solution at a given temperature. The term activity is used because pH reflects the amount of available hydrogen ions, not the concentration of hydrogen ions. The pH scale for aqueous solutions ranges from 0 to 14 pH units, with pH 7 being neutral. A pH of less than 7 means that the solution is acidic, whereas a pH of more than 7 means that the solution is basic.

Physical Conditions• Temperature also affects how a cell can perform and function.

If the appropriate temperature is not maintained, the cell will die.

• For example – Sperm cells are made in the testes; it takes about 72 days to produce a sperm cell. The temperature in the testes is about four degrees below body temperature; that's why they hang outside the body. The scrotum containing the testes helps maintain this temperature by raising or lowering the testicles (in and out of the body cavity) depending on the outside temperature.

• In order to stay alive and functioning, cells must interact with their environment to obtain nutrients, water, ions, etc., and to get rid of wastes and to export materials.

• This is accomplished by the processes of diffusion, and osmosis, which are passive mechanisms. Other passive mechanisms which allow materials to pass in and out of cells such as facilitated transport.

• There are also active transport mechanisms, which require the expenditure of ATP energy. They include ion "pumps", endocytosis, and exocytosis.

Internal Environment

• Endocytosis = the uptake of external materials by a cell; The process by which materials enter a cell without passing through the cell membrane. The membrane folds around material outside the cell, resulting in the formation of a saclike vesicle into which the material is incorporated. This vesicle is then pinched off from the cell surface so that it lies within the cell. See phagocytosis; pinocytosis.

• Exocytosis = the release of materials by the cell. It is when the cell releases vesicular materials to the outside of a cell. The opposite of endocytosis.

• Active Transport = the pumping of a substance across a cellular membrane from a point of lower concentration to one of higher concentration; requires energy.

Maintaining Internal Environments

•←

•←

•Active Transport (05:33)

Internal Environment• It is necessary for the cell to maintain a relatively stable internal

environment for the continuation of life.• The internal environment of cells is challenged by physical,

chemical, and environmental conditions as well as the presence of disease agents.

• The metabolic activities of organisms produce highly reactive chemicals, including strong oxidizing agents. The internal structure of the cell, however, minimizes the harmful effects of such agents; the critical reactions take place within enclosed structures such as ribosomes, membranes, or mitochondria, and counteractive enzymes such as peroxidases and lysosomes enzymes.

• How is this balance achieved and maintained? Putting filtration by the kidney aside, for small molecules such as sugars and amino acids, transport equilibria—spontaneous, reversible processes of equalization between opposing forces—across the membranes of the cells of perfused tissues are responsible. The movement of water-soluble molecules through pores embedded in cell membranes or by means of membrane carrier proteins exemplify these processes.

• The stable concentrations that result are the consequence of the equilibrium process itself.

Diffusion vs Osmosis vs Active Transport• DIFFUSION → The spontaneous movement of particles from an

area of higher concentration to an area of lower concentration. The movement of molecules occurs along a concentration gradient, i.e. from areas of high concentration to a low concentration until their is an equilibrium.

• OSMOSIS → The movement of water through a selectively permeable membrane across a concentration gradient (from a high concentration to a low concentration).

• ACTIVE TRANSPORT → Molecules and ions can be moved against their concentration gradient, but this process requires the expenditure of energy (usually from ATP).

•Cell Membrane: Diffusion

(00:53)

•Diffusion and Osmosis

(02:04)

• What would happen to the stability of a cell if a disease agent was present?

Internal Environment

• Molecules move back and forth, from and into each cellular source compartment and from and into each destination compartment, in response to the concentration gradient between them and blood, until movement in both directions, entry and exit, across each affected membrane, becomes equal though opposite.

• When this occurs, the concentration of the substance in blood becomes unchanging as a matter of course. This holds true whether the substance is passively distributed across the membrane, as in simple equilibria, or whether special transport processes maintain a concentration gradient across it at the cost of metabolic energy.

• Similarly, it pertains whether movement is due to nonspecific leakage or the presence of specific receptors, transporters, or pore-forming proteins. Whatever the particular circumstances, fluxes in both directions across the various membranes become equal when the stationary state applies—that is, when the concentration of the substance in blood is constant.

• From our perspective, these processes have two critical features. First, entry and exit commute—each fully affects and determines the other. Second, attaining and sustaining the resultant concentration in blood is an intrinsic property of the physical mechanism by which it is achieved. No additional mechanisms are needed.

Internal Environment

• Hypertonic solutions• Solutions that have more solute dissolved than another one are said to be

hypertonic to the solution they are being compared to. • A solution which contains more dissolved particles than cellular content. • In biology, a hypertonic cell environment has a higher concentration of

solutes than in cytoplasm. In a hypertonic environment, osmosis causes water to flow out of the cell. If enough water is removed in this way, the cytoplasm can become so concentrated that the cell has difficulty functioning.

Maintaining Internal Environments

•Cells in Hypertonic Solution

•Photomicrograph of blood cellsin a hypertonic solution; thepuckered effect comes from theloss of fluid from inside the cell

• Isotonic solutions• If both solutions being compared have equal amount of dissolved solutes

then the solutions are isotonic to each other. • A solution that has the same salt concentration as the normal cells of the

body and the blood. An isotonic beverage (such as Gatorade) may be drunk to replace the fluid and minerals that the body uses during physical activity.

• An isotonic cellular environment occurs when an equal solute concentration exists inside and outside the cell. Molecules flow in and out at an equal rate by osmosis, causing the cell size to stay the same. It will not lose or gain any solutes.

• When red blood cells are placed in a 0.9% salt solution, they neither gain nor lose water by osmosis. Such a solution is said to be isotonic.

Maintaining Internal Environments

•Normal Cells in Isotonic Solution

•Photomicrograph of blood cellsin an isotonic solution

Maintaining Internal Environments• Hypotonic solutions • The solution with the lower solute concentration is hypotonic. • A solution which contains less dissolved salt than cellular content. • In biology, a hypotonic cell environment is one with a lower concentration of

solutes than the cytoplasm. In a hypotonic environment, osmosis causes water to flow into the cell. Plants thrive in hypotonic environments. Their cells have rigid cell walls that prevent bursting. In fact, the pressure of the cytoplasm against the cell wall keeps the plant from wilting and losing its shape.

• A red blood cell placed in a hypotonic solution (e.g., pure water) bursts immediately ("hemolysis") from the influx of water.

• Plant cells and bacterial cells avoid bursting in hypotonic surroundings by their strong cell walls. These allow the buildup of turgor within the cell. When the turgor pressure equals the osmotic pressure, osmosis ceases.

•Cells in Hypotonic Solution

•Photomicrograph of blood cellsin a hypotonic solution; thebloated effect comes from theswelling of the cell.

Plant Cell Internal Balance

•Equilibrium (05:56)

•http://www.tvdsb.on.ca/westmin/science/Sbi3a1/cells/Osmosis.htm

Normal Cells in Isotonic Solution

Cells in Hypertonic Solution

Cells in Hypotonic Solution

                                                                                         

                                    

                      Photomicrograph of

blood cellsin an isotonic solution.

                                  

                        Photomicrograph of

blood cellsin a hypertonic solution; the

puckered effect comes from the

loss of fluid from inside the cell.

                                      

                    Photomicrograph of

blood cellsin a hypotonic solution;

thebloated effect comes

from theswelling of the cell.

• Homeostasis = Equilibrium or balance of internal environment.• In biology, the term homeostasis is used to describe a condition where an

organism maintains a stable structure where in fact a constant flux of molecules occurs. Although many organisms can live for years, all cellular components like proteins, membranes, sugars, and nucleic acids are constantly recycled while never compromising the integrity of the organism as a whole.

• In a living organism just about everything, from Arterial blood pressure to Zymogen granules, is subject to homeostatic regulation. Homeostasis occurs in single cell organisms and at every level of organization in a multicellular organism (such as yourself) from the single cell up to the entire body.

• The most common way of exploring the principles of homeostasis is to look at how hormones regulate the function of different organs and integrate these functions to the best advantage of the organism as a whole.

• A most literal definition of "internal environment" is the actual salts and water that form the basis of both the cytoplasm and the fluid space between the cells.

Internal Balance

•The condition in whichthe internal environment

of the body remains withinphysiological limits.

•Cell Membrane: Homeostasis (01:13)

• Cells must be small – gives them more surface area.• If a cell gets too large – the cells surface area would be too

small and the cell will die because it is unable to remove toxic substances quick enough or receive needed substances quick enough.

WHY MUST CELLS BE SMALL?

•Amoeba, intestinal cells with microvilli - Extending the outer surface of a cell into folds, fingers or indentations can increase the total surface area by a factor of several times

•Bacillus bacteria, red blood cells, a sphere has a low SA/V ratio. Cells that are drawn out (e.g. cylinder), or flattened have much more membrane per unit of cytoplasm